Field
The present application relates to the field of inductive measurement of
displacement of one mechanical part with respect to another. The term inductive
measurement denotes herein the measurement of alternating electromagnetic fields, by
means of electrical coils. More specifically but not restrictively, the present application
relates to the technical sub-field of eddy-current 5 sensors, wherein an electromagnetic
field generated by an inductor is established differently according to the presence and
the arrangement of movable (with respect to the inductor) conductive parts in the
vicinity of the inductor. Such electromagnetic phenomena become exploitable for
instrumentation purposes when certain electrical frequencies of the electromagnetic
10 field adopt sufficiently large values, this concept of largeness being determined by a
plurality of parameters such as the geometric dimensions of the conductive parts, the
electrical and magnetic properties thereof, the temperature thereof, etc. The term
displacement measurement denotes herein the estimation of information relating to the
position, speed, acceleration or any other characteristic quantity of the displacements of
15 the conductive part with respect to the inductor or to the inductor reference frame. As
displacements, equally well angular (rotation about an axis), linear (translation along an
axis) displacements, or any combination of such displacements with one another or
along separate axes are taken into consideration. More particularly but not restrictively,
the present application relates to the technical sub-fields of inductive position sensors,
20 inductive speed sensors and/or inductive acceleration sensors.
Description of the prior art
2
An inductive displacement sensor typically comprises a transducer (for example
rigidly connected to a measurement reference frame, also known as a frame), and a
target (for example rigidly connected to a movable mechanical part with respect to the
measurement reference frame). The target is placed away from the transducer, and is not
in contact (either mechanically 5 or electrically) with the transducer (contactless
measurement). The transducer includes a primary winding, or inductor, suitable for
producing an alternating electromagnetic field, and at least one secondary winding at
the terminals whereof an alternating voltage is induced, also referred to as electromotive
force or EMF, in the presence of the electromagnetic field produced by the primary
10 winding. The target is a partially or fully conductive element, also referred to as a
coupling armature, the presence and/or movement whereof in front of the transducer
modifies the coupling between the primary winding and the secondary winding. It
should be noted that the effect of the target on the coupling between the primary
winding and the secondary winding is dependent on the position of the target with
15 respect to the transducer, but also on the speed thereof with respect to the transducer.
The electromagnetic field distribution is thus formed spatially according to the
position and the relative displacement of the target with respect to the transducer.
During a displacement of the mechanical part, the spatial distribution of the
electromagnetic field changes, and therefore the EMF induced in the secondary winding
20 also changes. The analysis of the EMF induced, at the terminals of the secondary
winding, by the electromagnetic field produced by the primary winding, makes it
possible to estimate the position and/or the displacement of the target with respect to the
secondary winding of the transducer. More particularly but not restrictively, the
temporal variations of the EMF amplitude at the terminals of the secondary winding
25 make it possible to estimate the position, speed and/or acceleration of the target with
respect to the transducer.
It is specified that, herein and hereinafter in the present application, the term
electromotive force range amplitude at the terminals of the secondary winding refers to
the instantaneous value adopted by a limited frequency content signal, for example in a
30 frequency band between -Δf and +Δf about the excitation frequency (i.e. the frequency
of the alternating voltage applied at the terminals of the primary winding), where Δf
3
could for example adopt a value between 100Hz and 100kHz, carrying the information
or a part of the characteristic information of the mechanical displacement. This signal is
contained in the electromotive force, modulated at the excitation frequency and/or the
harmonics thereof. It can be obtained by means of a frequency transposition and
filtering method, and more 5 specifically by means of base band transposition and
filtering. A preferred example of such a method consists of carrying out synchronous
demodulation of the (modulated) electromotive force using a synchronous excitation
frequency signal, and wherein the electrical phase has been chosen to meet specific
criteria, for example to maximize the signal obtained at the demodulation output. An
10 alternative method consists of computing the modulus of the signal after synchronous
demodulation, which involves the advantage and disadvantage of not setting an
electrical demodulation phase. It is also specified that the amplitude of the
electromagnetic force is a preferred measurement quantity for the implementation of a
displacement measurement with the sensors according to the invention, but that it is in
15 no way exclusive from further electrical measurement quantities such as the phase,
frequency, or the electrical power at the secondary winding when a load of finite value
is connected to the terminals of the secondary winding (load adaptation).
Examples of inductive displacement sensors, and more particularly of eddycurrent
position sensors have been described in the patent EP0182085.
20 However, known inductive displacement sensors involve various drawbacks. In
particular, known sensors are relatively sensitive to assembly inaccuracies
(misalignment, inclination and/or target/transducer distance), as well as the presence of
conductive parts in the vicinity of the measurement zone, which poses problems for
industrial use. Problems associated with the lack of linearity of the sensor response may
25 also arise. Furthermore, the precision and robustness of the estimation of the position
and/or displacement of the target in known sensors would merit being improved.
Moreover, it would be desirable to be able to increase the extent of the measurement
range of some types of known sensors. In addition, one drawback of known sensors is
that they are relatively fragile, which poses problems in some types of application,
30 particularly in an industrial environment.
4
It would be desirable to be able to have inductive displacement sensors
remedying all or some of the drawbacks of known sensors.
Summary
As such, one embodiment e 5 nvisages an inductive displacement sensor,
comprising: a transducer including at least one primary winding suitable for producing a
magnetic excitation, and at least one secondary winding including at least one turn,
suitable for supplying an electromotive force at the terminals thereof in the presence of
said excitation; and a target comprising at least one conductive pattern, this target being
10 suitable for moving parallel with the transducer so as to vary the surface area of said at
least one pattern situated facing said at least one turn, thereby varying the amplitude of
the electromotive force induced in the secondary winding, wherein the target-transducer
distance is between 0.8 and 1.5 times the optimal target-transducer distance, which is
optimal in terms of linearity, i.e. a distance for which the linearity error of the
15 representative curve of said amplitude variation according to said surface area variation
is minimal.
According to one embodiment, the linearity error is the maximum difference
between an amplitude of the electromotive force and a linear approximation of said
amplitude, for a range of displacement of the target with respect to the transducer.
20 According to one embodiment, the sensor further comprises at least one
electromagnetic field confinement part.
According to one embodiment, said part is situated at a distance from the
primary winding of the transducer such that the distance for which the optimal targettransducer
distance in terms of linearity is greater than or equal to 0.3 mm.
25 According to one embodiment, the part has the shape of a solid plate.
According to one embodiment, said part has the shape of a striated plate.
According to one embodiment, the secondary winding comprises N identical
turns in series, regularly distributed along a first strip parallel with a degree of freedom
of displacement of the target with respect to the transducer, and the target comprises N
30 identical conductive patterns regularly distributed along a second strip parallel with a
5
degree of freedom of displacement of the target with respect to the transducer, situated
facing the first strip, where N is an integer greater than or equal to 2.
According to one embodiment, the degree of freedom is a degree of freedom in
rotation, the first and second strips are circular annular strips, and the conductive
5 patterns and turns have the shape of sectors of said annular strips.
According to one embodiment, the ratio between the internal radius and the
external radius of the annular strips is chosen such that the optimal target-transducer
distance dopt is greater than or equal to 0.3 mm.
According to one embodiment, the sectors have an angle equal to 360°/2N + ,
10 and the value  is chosen such that the optimal target-transducer distance (dopt) in
terms of linearity is greater than or equal to 0.3 mm.
According to one embodiment, the degree of freedom is a degree of freedom in
translation, the first and second strips are rectilinear strips, and said conductive patterns
and turns have the shape of portions of said rectilinear strips.
15 According to one embodiment, the ratio between the width of the patterns of the
sensor along the direction parallel with displacement and the width of the patterns of the
sensor along the direction orthogonal to displacement is chosen such that the optimal
target-transducer distance dopt is greater than or equal to 0.3 mm.
According to one embodiment, the width of the patterns of the sensor along the
20 direction parallel with displacement adopts a value different by one electrical halfperiod
of the sensor, this value being chosen such that the optimal target-transducer
distance dopt is greater or equal to 0.3 mm.
According to one embodiment, N is greater than or equal to 4.
25 Brief description of the drawings
These features and advantages, along with others, will be described in detail in
the following description of particular embodiments given non-restrictively with
reference to the attached figures wherein:
figures 1A and 1B are respectively a front view and a profile view schematically
30 representing an example of an inductive angular displacement sensor;
6
figure 2 is a diagram schematically illustrating the operation of the sensor in
figure 1;
figures 3A and 3B are front views schematically representing a transducer and a
target of a further example of an inductive angular displacement sensor;
figure 4 is a diagram schematically 5 illustrating the operation of the sensor in
figures 3A and 3B;
figure 5 is a front view schematically representing a transducer of a further
example of an inductive angular displacement sensor;
figure 6 is a diagram schematically illustrating the operation of the sensor in
10 figure 5;
figure 7 is a front view schematically representing a transducer of a further
example of an inductive angular displacement sensor;
figure 8 is a diagram schematically illustrating the operation of the sensor in
figure 7;
15 figure 9A is a diagram representing the expected theoretical progression of
output signals of an inductive angular displacement sensor;
figure 9B is a diagram representing the actual progression, typically obtained in
practice, of the output signals of an inductive angular displacement sensor;
figure 10 is a diagram representing, for a plurality of distinct target-transducer
20 distances, the progression of an output signal of an inductive angular displacement
sensor;
figure 11 is a diagram representing the progression, according to the targettransducer
distance, of the linearity error of an output signal of an inductive angular
displacement sensor;
25 figures 12A to 12D are cross-sectional views schematically illustrating four
examples of embodiments of an inductive angular displacement sensor;
figure 13A is a diagram representing, for the four examples of sensors in figures
12A to 12D, the progression, according to the target-transducer, of the linearity error of
an output signal of the sensor;
7
figure 13B is a diagram representing the progression of the optimal targettransducer
distance in terms of linearity according to a parameter of an example of an
inductive displacement sensor;
figure 13C is a diagram representing the progression of the optimal targettransducer
distance in terms of lin 5 earity according to a parameter of a further example
of an inductive displacement sensor;
figure 14 is a front view representing an example of a field confinement part of
an example of an embodiment of an inductive angular displacement sensor;
figure 15 is a front view representing a further example of a field confinement
10 part of an example of an embodiment of an inductive angular displacement sensor;
figures 16A and 16B are front views schematically representing two examples of
embodiments of a target of an inductive angular displacement sensor;
figure 17 is a diagram representing the progression, in an inductive angular
displacement sensor, of the optimal target-distances in terms of linearity, according to a
15 shape parameter of a pattern of the target;
figure 18A is a front view schematically and partially representing three
examples of embodiments of a target of an inductive angular displacement sensor;
figure 18B is a front view schematically and partially representing an example of
an embodiment of a secondary winding of a transducer suitable for operating in
20 cooperation with the targets in figure 18A;
figure 19 is a diagram representing the progression, in an inductive angular
displacement sensor, of the optimal target-transducer distance in terms of linearity,
according to a further shape parameter of a pattern of the target;
figure 20A is a front view schematically representing an example of a transducer
25 of an inductive angular displacement sensor;
figure 20B is a front view schematically representing an example of a transducer
of an inductive linear displacement sensor;
figure 20C is a front view schematically representing an example of an
embodiment of a transducer of an inductive angular displacement sensor;
30 figure 20D is a front view schematically representing an example of an
embodiment of a transducer of an inductive linear displacement sensor;
8
figure 20E is a small-signal electrical representation of the behavior of the
transducer in figure 20D;
figures 21A and 21B are front views schematically representing an example of
an embodiment of a transducer of an inductive angular displacement sensor;
figures 22A and 22B 5 are front views schematically representing a further
example of an embodiment of a transducer of an inductive angular displacement sensor;
figure 23 is a front view schematically representing a target of an example of
inductive angular displacement sensor;
figure 24 is a diagram schematically representing the progression of
10 measurement signals of the sensor in figure 23;
figure 25 is a front view schematically representing a target of an example of an
embodiment of an inductive angular displacement sensor;
figure 26 is a front view schematically representing a target of an alternative
embodiment of an inductive angular displacement sensor;
15 figures 27A to 27C are front views schematically representing a further
alternative embodiment of an inductive angular displacement sensor;
figure 28 is a perspective view representing an example of an embodiment of an
inductive angular displacement sensor target; and
figure 29 is a perspective view representing a further example of an embodiment
20 of an inductive angular displacement sensor target.
Detailed description
For the purposes of clarity, the same elements have been denoted with the same
references in the various figures and, furthermore, the various figures are not plotted to
25 scale. Moreover, hereinafter in the description, unless specified otherwise, the terms
"approximately", "substantially", "around", "of the order of", "practically", etc., mean
"within 20% and preferably within 5%", or "within 5° and preferably within 2°" when
they relate to angular distances, and directional references such as "vertical",
"horizontal", "lateral", "below", "above", "top", "bottom", etc., apply to device oriented
30 in the manner illustrated in the corresponding views, it being understood that, in
practice, these devices may be oriented differently.
9
Particular focus is placed on the inductive measurement of displacement of one
mechanical part with respect to another. The term inductive measurement denotes
herein the measurement of alternating electromagnetic fields, by means of electrical
coils. More specifically but not restrictively, the present application relates to the
technical sub-field of eddy-current sensors, wherein an 5 electromagnetic field generated
by an inductor is established differently according to the presence and the arrangement
of movable (with respect to the inductor) conductive parts in the vicinity of the inductor.
Such electromagnetic phenomena become exploitable for instrumentation purposes
when certain electrical frequencies of the electromagnetic field adopt sufficiently large
10 values, this concept of largeness being determined by a plurality of parameters such as
the geometric dimensions of the conductive parts, the electrical and magnetic properties
thereof, the temperature thereof, etc. The term displacement measurement denotes
herein the estimation of information relating to the position, speed, acceleration or any
other characteristic quantity of the displacements of the conductive part with respect to
15 the inductor or to the inductor reference frame. As displacements, equally well angular
(rotation about an axis), linear (translation along an axis) displacements, or any
combination of such displacements with one another or along separate axes are taken
into consideration. More particularly but not restrictively, the present application relates
to the technical sub-fields of inductive position sensors, inductive speed sensors and/or
20 inductive acceleration sensors.
An inductive displacement sensor typically comprises a transducer (for example
rigidly connected to a measurement reference frame, also known as a frame), and a
target (for example rigidly connected to a movable mechanical part with respect to the
measurement reference frame). The target is placed away from the transducer, and is not
25 in contact (either mechanically or electrically) with the transducer (contactless
measurement). The transducer includes a primary winding, or inductor, suitable for
producing an alternating electromagnetic field, and at least one secondary winding at
the terminals whereof an alternating voltage is induced, also referred to as electromotive
force or EMF, in the presence of the electromagnetic field produced by the primary
30 winding. The target is a partially or fully conductive element, also referred to as a
coupling armature, the presence and/or movement whereof in front of the transducer
10
modifies the coupling between the primary winding and the secondary winding. It
should be noted that the effect of the target on the coupling between the primary
winding and the secondary winding is dependent on the position of the target with
respect to the transducer, but also on the speed thereof with respect to the transducer.
The electromagnetic fi 5 eld distribution is thus formed spatially according to the
position and the relative displacement of the target with respect to the transducer.
During a displacement of the mechanical part, the spatial distribution of the
electromagnetic field changes, and therefore the EMF induced in the secondary winding
also changes. The analysis of the EMF induced, at the terminals of the secondary
10 winding, by the electromagnetic field produced by the primary winding, makes it
possible to estimate the position and/or the displacement of the target with respect to the
secondary winding of the transducer. More particularly but not restrictively, the
temporal variations of the EMF amplitude at the terminals of the secondary winding
make it possible to estimate the position, speed and/or acceleration of the target with
15 respect to the transducer.
It is specified that, herein and hereinafter in the present application, the term
electromotive force range amplitude at the terminals of the secondary winding refers to
the instantaneous value adopted by a limited frequency content signal, for example in a
frequency band between -Δf and +Δf about the excitation frequency (i.e. the frequency
20 of the alternating voltage applied at the terminals of the primary winding), where Δf
could for example adopt a value between 100Hz and 100kHz, carrying the information
or a part of the characteristic information of the mechanical displacement. This signal is
contained in the electromotive force, modulated at the excitation frequency and/or the
harmonics thereof. It can be obtained by means of a frequency transposition and
25 filtering method, and more specifically by means of base band transposition and
filtering. A preferred example of such a method consists of carrying out synchronous
demodulation of the (modulated) electromotive force using a synchronous excitation
frequency signal, and wherein the electrical phase has been chosen to meet specific
criteria, for example to maximize the signal obtained at the demodulation output. An
30 alternative method consists of computing the modulus of the signal after synchronous
demodulation, which involves the advantage and disadvantage of not setting an
11
electrical demodulation phase. It is also specified that the amplitude of the
electromagnetic force is a preferred measurement quantity for the implementation of a
displacement measurement with the sensors according to the invention, but that it is in
no way exclusive from further electrical measurement quantities such as the phase,
frequency, or the electrical power 5 at the secondary winding when a load of finite value
is connected to the terminals of the secondary winding (load adaptation).
Examples of inductive displacement sensors, and more particularly of eddycurrent
position sensors have been described in the patent EP0182085.
However, known inductive displacement sensors involve various drawbacks. In
10 particular, known sensors are relatively sensitive to assembly inaccuracies
(misalignment, inclination and/or target/transducer distance), as well as the presence of
conductive parts in the vicinity of the measurement zone, which poses problems for
industrial use. Problems associated with the lack of linearity of the sensor response may
also arise. Furthermore, the precision and robustness of the estimation of the position
15 and/or displacement of the target in known sensors would merit being improved.
Moreover, it would be desirable to be able to increase the extent of the measurement
range of some types of known sensors. In addition, one drawback of known sensors is
that they are relatively fragile, which poses problems in some types of application,
particularly in an industrial environment.
20 It would be desirable to be able to have inductive displacement sensors
remedying all or some of the drawbacks of known sensors.
Very particular focus is placed herein on angular displacement sensors, and
more specifically on angular displacement sensors having an approximately planar
general shape, for example sensors having a general disk shape, sensors having a
25 circular annular strip shape having an angular aperture less than or equal to 360°. It will
be understood however upon reading the following that all the examples of
embodiments, embodiments and alternative embodiments described in the present
application can be adapted to further types of inductive displacement sensors, for
example inductive linear displacement sensors of the type described in the patent
30 EP0182085 mentioned above. The adaptation of the examples of embodiments
12
described in the present application to further types of inductive displacement sensors is
within the grasp of those skilled in the art and therefore will not be detailed hereinafter.
By way of an illustrative but non-restrictive example, the inductive sensors
described in the present application and illustrated in the figures have characteristic
5 dimensions (diameter for angular sensors and width for linear sensors) between 5 mm
and 200 mm, and preferably between 40 mm and 50 mm.
Figures 1A and 1B are respectively a front view and a profile view schematically
representing an example of a planar type inductive angular position sensor 100, having
a general disk shape.
10 The sensor 100 comprises a transducer 110 including a primary conductive
winding 101 and a secondary conductive winding 103. In figure 1B, the primary and
secondary windings of the transducer 110 have not been detailed. Preferably, the
primary winding 101 comprises two approximately circular, concentric and coplanar
conductive turns or loops 101a and 101b, of opposite winding directions and separate
15 radii. Each turn 101a, 101b of the primary winding 101 comprises at least one
revolution, preferably a plurality of revolutions. The turns 101a and 101b are preferably
connected in series so as to be traversed by currents of the same intensity but in
opposite flow directions, but can optionally be connected in parallel so as to see the
same voltage at the terminals thereof (applied preferably such that the current flow
20 direction in the two turns are opposite). An advantage of the example of primary
winding arrangement in figure 1 is that it makes it possible to produce a substantially
uniform excitation field in the annular strip situated between the two turns, and
substantially zero outside this strip. Alternatively, the primary winding 101 can include
a single turn (with one or a plurality of revolutions). More generally, the primary
25 winding 101 can include one or a plurality of concentric turns (with one or a plurality of
revolutions each) arranged so as to generate an electromagnetic field in the
measurement zone of the transducer. The embodiments described are not restricted to
these particular arrangements of the primary winding.
In the example represented, the secondary winding 103 consists of a conductive
30 turn or loop arranged spatially in the shape of a circular annular strip situated between
13
the turns 101a and 101b. The winding 103 is for example situated approximately in the
same plane as the turns 101a and 101b, or in a substantially parallel plane.
In this example, in a front view, the turn 103 substantially follows the contour of
an angular sector having an angular aperture  of the annular strip defined by the
turns 101a and 101b. The 5 turn 103 particularly comprises radial portions and orthoradial
portions of the contour of the annular strip portion. Such a winding enables an
angular position measurement over a range of °. In the example represented, the
angular aperture  of the turn 103 is approximately equal to 30°. The embodiments
described are however not restricted to this particular case. Alternatively, the angle 
10 can adopt any value between 0 and 180°. The turn 103 preferably comprises a single
revolution but can optionally comprise a plurality of revolutions. The primary 101 and
secondary 103 windings are for example arranged in and on the same dielectric
substrate (not shown) in the form of a wafer of some micrometers to some millimeters
in thickness, for example a PCB ("Printed Circuit Board") type substrate.
15 The sensor 100 further comprises a target 111 comprising a conductive
pattern 107, situated at a distance different to zero from the transducer and suitable for
moving with respect to the transducer. In figure 1A, only the conductive part 107 of the
target has been represented. In this example, the conductive pattern 107 of the
target 111 has substantially the same shape as the annular strip portion defined by the
20 pattern of the turn 103 of the transducer. The target is rotatably mounted about an axis Z
orthogonal to the plane of the transducer passing through the center of the turns 101a
and 101b, such that, when the target rotates by an angle 2 about the axis Z, the
conductive pattern 107 (having the angular aperture ), covers approximately entirely
and then uncovers approximately entirely the surface of the annular strip defined by the
25 turn of the secondary winding 103 of the transducer. By way of non-restrictive example,
the target can consist of a plate made of a dielectric material, for example in the shape
of a disk, wherein one face oriented towards the transducer is partially coated with a
layer of a conductive material, optionally magnetic, for example a metal layer, for
example a layer of iron, steel, aluminum, copper, etc., forming the conductive
30 pattern 107. Alternatively, the target can consist solely of a portion of metal plate cut to
the shape of the conductive pattern 107, mounted by any suitable means so as to be able
14
to move in rotation with respect to the transducer above the portion of annular strip
defined by the turns 101a and 101b.
The operation of the sensor 100 in figures 1A and 1B will now be described with
reference to figure 2 which represents the progression of the amplitude of the
electromotive 5 force V at the terminals of the secondary winding 103 of the sensor
according to the angular position  of the target 111 with respect to the transducer 110.
In operation, the flow of an alternating current IP is applied by electrical means
in the primary winding 101. The flow of the current IP in the winding 101 produces an
electromagnetic field B having, in the absence of a target, a substantially symmetrical
10 distribution by revolution in the circular annular strip traversed by the secondary
winding 103. By way of non-restrictive example, the frequency of the alternative
excitation current IP applied in the primary winding is between 500 kHz and 50 MHz
(for example 4 MHz). The amplitude of the current IP is for example between 0.1 mA
and 100 mA (for example 2 mA). In the absence of a target 111, or, more generally,
15 when the conductive pattern 107 of the target does not cover the secondary winding 103,
the secondary winding 103 supplies between the ends thereof an alternating EMF V,
having a frequency substantially equal to the excitation frequency of the primary
winding, and having an amplitude in principle different to zero. When the conductive
pattern 107 of the target 111 covers all or part of the secondary winding 103, the spatial
20 electromagnetic field distribution in the vicinity of the turn 103 varies according to the
arrangement and the displacement of the surface portion of the conductive pattern 107
situated facing the turn 103. A further formulation consists of considering that, under
the effect of the magnetic excitation generated by the flow of the current IP in the
primary winding, eddy currents appear in the conductive pattern 107, inducing a
25 modification of the spatial distribution of the electromagnetic field according to the
arrangement and the displacement of the surface portion of the pattern 107 situated
facing the turn 103. These changes or variations of the spatial distribution of the
electromagnetic field according to the arrangement and the displacement of the surface
portion of the pattern 107 situated facing the turn 103, are conveyed, by induction, by
30 variations or changes in the amplitude V of the voltage range at the terminals of the
15
secondary winding, according to the arrangement and the displacement of the surface
portion of the pattern 107 situated facing the turn 103.
It is considered by way of non-restrictive illustrative example that the target can
move in rotation about the axis Z with respect to the transducer, in a range of angular
positions from =-° to =5 °. It is considered arbitrarily that the position =-°
corresponds to the arrangement represented in figure 1A, wherein the conductive
pattern 107 does not conceal the turn 103, but has, viewed from above, a radial edge
adjoined to a radial edge of the turn 103. As such, for the angular positions  ranging
from -° to 0°, the surface area of the portion of the conductive pattern 107 situated
10 facing the turn 103 increases when the angular position  increases, and, for the angular
positions  ranging from 0° to °, the surface area of the portion of the conductive
pattern 107 facing the turn 103 decreases when the angular position  increases. Outside
the range of angular positions ranging from =-° to =°, the surface area of the
portion of the conductive pattern 107 facing the turn of the secondary winding 103 is
15 zero, and the position and/or the displacement of the target 111 with respect to the
transducer cannot be measured.
The amplitude V of the range of the voltage measured at the terminals of a
secondary winding of an inductive displacement sensor is theoretically proportional to
the area of the portion of surface area of the conductive pattern of the target situated
20 facing the secondary winding. As such, as seen in figure 2, for the angular positions 
ranging from -° to 0°, the signal V decreases when the angular position  increases,
changing from a high value Vmax for  = -° to a low value Vmin for =0°, and for the
angular positions  ranging from 0° to °, the signal V increases when the angular
position  increases, changing from the low value Vmin for  = 0° to the high value Vmax
25 for =°. The signal V is thus theoretically a triangular signal varying linearly between
Vmin and Vmax over the angular range ranging from -° to °. It will be seen hereinafter
that, in practice, the signal V has non-linearity zones and consequently tends to have a
sinusoidal shape.
As such, in the range of angular positions from =-° to =0°, or in the range of
30 angular positions from =0° to =°, the measurement of the amplitude V of the range
16
of the electromotive force at the terminals of the secondary winding 103 makes it
possible to determine the angular position  of the target with respect to the transducer.
Although the value of the signal V varies according to the angular position  of the
target in the two angular position ranges mentioned above, the measurement of the
signal V does not make it possible to discriminate 5 the position values of the range from
-° to 0° from the position values of the range from 0° to ° (non-surjective
measurement). The extent of the range of angular positions that could actually be
measured by the sensor 100 is thus approximately equal to °, provided that the angle 
does not exceed 180°.
10 Figures 3A and 3B are front views schematically representing a further example
of an inductive angular position sensor having a general disk shape. This sensor
comprises a transducer 112 represented in figure 3A and a target 114 represented in
figure 3B. The target 114 in figure 3B differs from the target 111 in figure 1A
essentially by the conductive pattern thereof. In particular, the target 114 in figure 3B
15 differs from the target 111 in figure 1A in that it no longer comprises a single
conductive pattern 107, but a set of N conductive patterns 117i rigidly connected to the
target, and suitable for moving with respect to the transducer, N being an integer greater
than or equal to 2 and i being an integer ranging from 1 to N. The transducer 112 in
figure 3A differs from the transducer 110 in figure 1A essentially by the shape of the
20 secondary winding 113 thereof. In particular, the secondary winding 113 of the
transducer 112 in figure 3A no longer comprises a single conductive turn, but a set of N
turns 113i. The target 114 in figure 3B is intended to be rotatably mounted with respect
to the transducer 112 in figure 3A, similarly or identically to that described with
reference to figures 1A and 1B.
25 In this example, in a front view, the set of conductive patterns 117i and the set of
turns 113i, consist of the repetition by revolution of N substantially identical patterns,
respectively 117i and 113i. The repetition by revolution of these patterns is performed
with a spatial frequency of 2α, i.e. each pattern having an angular aperture substantially
equal to α° is spaced from the closest neighbor thereof by a portion of empty circular
30 annular strip of ortho-radial range substantially equal to α°.
17
For sensors wherein the general shape is a closed circular annular strip, i.e.
having an angular aperture equal to 360°, the value of the angular aperture α of the
patterns is chosen preferably such that α = 360°/2N, in order to ensure a whole number
of pattern repetitions per revolution (over 360°). In the example in figures 3A and 3B, N
5 = 6 and α = 30°.
In other words, the transducer in figure 3A comprises a secondary winding 113
comprising N loops or turns 113i in series. Each turn 113i has a shape of a circular band
strip sector, of the same type as the turn 103 in figure 1A, and has an angular dimension
approximately equal to =360°/2N (i.e. =30° in this example). The N turns 113i are
10 regularly distributed along the 360° of the circular annular strip approximately defined
by the turns 101a and 101b of the primary winding 101, i.e. two consecutive turns 113i
of the secondary winding are separated by an annular strip portion having an angle
approximately equal to .
The target in figure 3B comprises N conductive patterns 117i. Each pattern 117i
15 has a shape of a circular band strip sector, of the same type as the conductive
pattern 107 in figure 1, and has an angular dimension approximately equal to
=360°/2N. The N conductive patterns 117i are regularly distributed along an annular
strip of the target intended to be positioned facing the annular strip of the transducer
containing the turns 113i.
20 Hereinafter in the present application, the term multi-pole sensor shall refer to
the sensors of the type described with reference to figures 3A and 3B, N denoting the
number of poles of the sensor. In the example in figure 1A, if α adopts the value 180°,
reference is made to a sensor with one pole pair. More particularly, the term multi-pole
sensor shall denote a sensor wherein an elementary conductive pattern is regularly
25 repeated at least twice on the target along a parallel direction with a degree of freedom
of displacement of the target with respect to the transducer (i.e. along an ortho-radial
direction in an angular sensor of the type described above).
By analogy with the electrical period of an electric motor with a plurality of pole
pair, reference shall now be made to the angular aperture between two adjacent
30 patterns 117i, and to the angular aperture between two adjacent patterns 113i, as being
the electrical period of the sensor. In the specific case of the sensor in figures 3A and 3B,
18
for which the conductive patterns have an angular aperture α° and the hollows between
these patterns also have an angular aperture α°, the electrical period is equal to 2α°, and,
conversely, the angular aperture of a conductive pattern is equal to an electrical halfperiod
of the sensor, which is a preferred but not exclusive case. By design, for sensors
wherein the general 5 shape is a closed circular annular strip, an electrical period is
preferably a sub-multiple of 360°, since α = 360°/2N. Under these terms, a multi-pole
inductive sensor has a measurement range of α°, equal to half the electrical period
thereof of 2α°. In the example in figure 1A, if α adopts the value 180°, the electrical
period is equal to 360°, and the measurement range is approximately equal to half the
10 electrical period, i.e. 180°. In the example in figures 3A and 3B for which α = 30°, the
electrical period is 2α = 60°, and the measurement range is approximately equal to half
the electrical period i.e. α = 30°.
Figure 4 is a diagram representing the progression of the amplitude V of the
range of the electromotive force at the terminals of the secondary winding 113 of the
15 sensor in figures 3A and 3B according to the angular position  of the target with
respect to the transducer.
As seen in figure 4, when the angular position  of the target with respect to the
transducer varies from 0° to 360°, the signal V varies periodically between a high
value Vmax and a low value Vmin, with an angular period of variation approximately
20 equal to the electrical period 2 of the sensor.
The amplitude of the range of angular positions  suitable for being measured by
the sensor in figures 3A and 3B is approximately equal to half of the electrical period,
i.e. °.
One advantage of the sensor in figures 3A and 3B with respect to the sensor in
25 figures 1A and 1B is that the greater number of patterns distributed on the target and on
the transducer enables a distributed measurement on an extended measurement zone,
wherein each pattern contributes locally and by design to the generation of an overall
electromotive force, this electromotive force being more immune to positioning errors
of the target with respect to the transducer than in the sensor in figures 1A and 1B,
30 wherein the measurement made is a local measurement made using a single set of
19
patterns 107-103. This robustness of the measurement is especially great as the
number N of pairs of poles of the sensor increases.
Figure 5 illustrates an alternative embodiment of the sensor in figures 3A and 3B.
In figure 5, only the transducer of the sensor has been shown, the target being identical
5 to that in figure 3B.
The transducer of the sensor in figure 5 comprises the same elements as the
transducer in figure 3A, and further comprises a second secondary winding 113'
comprising N loops or turns 113i' in series. For the purposes of clarity, the connections
between the different loops 113i of the winding 113 and the connections between the
10 different loops 113i' of the winding 113' have not been shown in figure 5. The secondary
winding 113' (represented as a dashed line) is substantially identical to the secondary
winding 113 (represented as a solid line), and is arranged in the same annular strip of
the transducer as the secondary winding 113, with an angular offset corresponding to a
quarter of the electrical period of the sensor, i.e. approximately equal to /2, with
15 respect to the secondary winding 113.
Figure 6 is a diagram representing the progression of the amplitude V (as a solid
line) of the range of the electromotive force at the terminals of the secondary
winding 113 of the sensor in figure 5, and the progression of the amplitude V' (as a
dashed line) of the range of the electromotive force at the terminals of the secondary
20 winding 113' of the sensor in figure 5, according to the angular position  of the target
with respect to the transducer.
As seen in figure 6, when the angular position  of the target with respect to the
transducers varies from 0° to 360°, the signals V and V' vary periodically between a
high value Vmax and a low value Vmin, with a variation period equal to the electrical
25 period of the sensor, i.e. approximately equal to 2° in this example, and with an
angular offset with respect to one another substantially equal to one quarter of the
electrical period of the sensor, i.e. approximately /2° in this example.
One advantage of the transducer in figure 5 with respect to the transducer in
figure 3A is that it makes it possible to extend the range of angular positions  suitable
30 for being measured by the sensors up to approximately an entire electrical period (i.e.
2°), instead of a half-period (i.e. °) in the example in figures 3A and 3B.
20
Figure 7 illustrates a further alternative embodiment of the sensor in figures 3A
and 3B. In figure 7, only the transducer of the sensor has been shown, the target being
identical to that in figure 3B.
The transducer of the sensor in figure 7 differs from the transducer in figure 3A
essentially by the shape 5 of the secondary winding thereof. The transducer of the sensor
in figure 7 comprises a secondary winding 123 comprising 2N loops or turns of
alternating winding directions, interconnected in series. In other words, the secondary
winding 123 comprises 2N patterns of electrical circuits or turns, each being connected
to the closest neighbor thereof in anti-series. More particularly, the winding 123
10 comprises N turns 123i+ of the same winding direction, substantially identical to the N
turns 113i of the transducer in figure 3A, and further comprises N turns 123i- of opposite
winding direction, each turn 123i- being arranged between two consecutive turns 123i+,
and each turn 123i- having a shape of a circular annular strip sector, of the same type as
the turns 123i+. For the purposes of clarity, the connections between the turns 123i+ and
15 123i- of the winding 123 have not been shown in figure 7, and the two winding
directions have been represented schematically by a + sign for the turns 123i+ and by a –
sign for the turns 123i-.
More specifically, in the example in figure 7, the angular aperture α of each
turn 123i+ and 123i- has been chosen strictly less than an electrical half-period so as to
20 enable a more legible graphic representation. In practice, the angular aperture α of each
turn 123i+ and 123i- can approximate an electrical half-period with a lower value, with
an exact value, or with a greater value. In the specific case where the angular aperture
equals exactly one electrical half-period, which is a preferred but non-exclusive
example of an embodiment, the sum of the angular apertures of the N turns 123i+ and of
25 the angular apertures of the N turns 123i- equals 360°, or in other words, the constituent
radial tracks of two adjacent turns 123i+ and 123i- share the same spatial coordinates in a
reference frame {R, θ} (not shown) directed by the axis Z and having as a center the
center of the sensor. This obviously does not mean however that these tracks are merged
and that the turns 123i+ and 123i- are short-circuited, insofar as the tracks can be
30 positioned on two separate planes along the axis Z.
21
The spatial repetition period between two adjacent turns 123i+, and the spatial
repetition period between two adjacent turns 123i-, are kept equal to one electrical
period of the sensor regardless of the angular aperture α of the turns 123i+ and 123i-. A
preferred but non-restrictive example of use of such a set of turns having an angular
aperture 5 different from an electrical half-period of the sensor consists of distributing the
turns 123i+ and 123i- regularly ortho-radially as illustrated in figure 7.
Figure 8 is a diagram representing the progression of the amplitude V of the
range of the electromotive force at the terminals of the secondary winding 123 of the
sensor in figure 7 according to the angular position  of the target with respect to the
10 transducer.
As seen in figure 8, when the angular position  of the target with respect to the
transducer varies from 0° to 360°, the signal V varies periodically between a high
value Vmax and a low value Vmin, with an angular period of variation approximately
equal to one electrical period.
15 One advantage of the transducer in figure 7 with respect to the transducer in
figure 3A is that the amplitude V is approximately centered around 0 volts (Vmin≈-Vmax).
More generally, the use of a spatially differential measurement, such as that which is for
example described with reference to figure 7, makes it possible to a low mean
amplitude V with respect to the values Vmin et Vmax. This simplifies the processing of
20 the measurement for the purposes of estimating the displacement, and in particular
reduces the influence of drift and parasitic disturbances.
Indeed, some variations of the amplitude V associated with parasitic effects, i.e.
not originating from the displacement of the target, are merely conveyed by a gain
variation in the case of the sensor in figure 7, whereas they are conveyed both by a gain
25 variation and an offset variation in the case of the sensor in figure 3A. This is for
example the case when the coupling coefficient between the primary, the target and the
secondary varies due to a parasitic variation of the target-transducer distance. This is
furthermore the case when the amplitude of the excitation current varies, for example in
the case of parasitic fluctuation of the power supply voltage, or in the event of drift of
30 the electrical properties of the primary winding, for example according to the
temperature and the relative distance of the transducer and the target.
22
Moreover, in the example in figure 7, the coupling of the secondary winding
with external fields not carrying information on the displacement of the target, is
considerably reduced due to the spatially differential nature of the measurement. This is
particular the case for the portion of the electromagnetic field generated by the primary
which induces the 5 constant portion (independent of the target position) of the amplitude
of the EMF, but also for any external electromagnetic interference exhibiting a
substantially uniform distribution in the vicinity of the secondary winding 123.
The alternative embodiment in figure 7 can be combined with the alternative
embodiment in figure 5 in order to obtain two signals of amplitude V and V' angularly
10 offset by a quarter of an electrical period and centered on approximately 0 volts.
It should be noted that the fact that the amplitude V of the range of the EMF is
approximately centered on 0 volts does not necessarily mean that the modulated
electromotive force verifies said properties before the implementation of a method of
frequency transposition and filtering. Generally, the electromotive force (modulated)
15 has a mean value different to zero, either due to voluntary referencing of one of the two
terminals of the secondary winding at a defined electric potential (electrical mass for
example), or due to referencing by capacitive coupling of the mean potential thereof to
the potential of the environment (for example the mechanical mass) in the case of a
high-impedance measurement at the secondary winding. This illustrative example
20 applied to the mean value of the electromotive force is also applicable to any frequency
component of the electrical signal, regardless of the origin thereof, which is situated
outside a frequency band of interest -f to +f about the modulation frequency, or, in
other words, which is situated outside a frequency band of interest -f to +f about the
zero frequency following the frequency transposition method.
25
First aspect
Figure 9A is a diagram representing the expected theoretical progression of the
signals of amplitude V and V' according to the angular position , in an inductive sensor
of the type described above combining the embodiment options in figures 5 (two
30 secondaries spatially offset by one quarter of an electrical period) and 7 (each secondary
comprises 2N turns of alternating winding directions). As seen in figure 9A, the
23
expected theoretical amplitudes V and V' are triangular periodic signals having a period
equal to the electrical period of the sensor, varying linearly between the values Vmin and
Vmax, with an angular offset of one quarter of an electrical period with respect to one
another. Indeed, in theory, as indicated in the patent EP0182085 mentioned above
5 (column 12, lines 22 to 57), the amplitude of the range of the voltage measured at the
terminals of secondary winding of an inductive sensor is proportional to the area of the
portion of surface of conductive patterns of the target situated facing this secondary
winding. However, in the examples of embodiments described above, the portion of
conductive surface of the target situated facing the electrical circuit patterns or turns of
10 the secondary winding varies linearly with the angular position , for the patterns 123i+
and for the patterns 123i- in figure 7. Therefore, the signals V and V' should vary
linearly by portions according to the position .
The inventors observed, however, that in practice the variation of the signals V
and V' according to the position  generally has wide non-linear zones in an electrical
15 period of the sensor. More specifically, in practice, the variation of the signals V and V'
according to the position  indeed has two substantially linear zones of reduced range in
an electrical period of the sensor, these zones being approximately centered on the zero
crossings of the amplitudes V and V', but, between these linear zones, saturated and de
facto less linear zones are inserted, these zones being approximately centered on
20 extrema of the amplitudes V and V'.
The low linearity of the amplitudes V and V' according to the position  involves
drawbacks. In particular, by way of non-restrictive example, having ranges of reduced
linearity does not make it possible to benefit fully from the signal processing methods
described in the patents FR2914126 and FR2891362.
25 Figure 9B is a diagram representing the actual progression, typically obtained in
practice, of the signals V and V' according to the angular position  in an inductive
sensor of the type described above. As seen in figure 9B, the signals V and V' only vary
linearly in portions of reduced angular range L of the measurement range of the sensor,
referred to as linearity ranges. By way of example, each linearity range L has a range
30 between 20% and 90% of the electrical half-period of the sensor (equal to ° in the
24
example shown). The linearity range αL is for example defined as being the maximum
angular range, substantially centered on the mean value of the amplitude V, for which it
is possible to find a linear approximation VL to the amplitude V, such that the
difference EL between the linear approximation VL and the amplitude V is less than a
threshold EL0, the threshold EL0 being 5 for example defined as a percentage of the
extrema of the amplitude V, for example in a range of values between 0.01% and 10%
of the extrema of the amplitude V according to the degree of linearity sought for the
sensor. In other words, the linearity range αL is the maximum angular range whereon the
amplitude V varies substantially linearly with the position of the target with respect to
10 the transducer, within one maximum approximation of set value EL0. In practice, it is
generally sought to do the opposite, i.e. evaluate the maximum linearity error ELM over
a given angular range αL, for example but not restrictively the angular range whereon it
is sought to make the measurement. Also, a further manner to assess the linearity of a
sensor is that of assessing the linearity error ELM, defined as the maximum difference
15 between the amplitude V and the linear approximation VL for a given range αL.
Preferably but not restrictively, the linearity range sought for a sensor with two
secondary windings is at least 50% of an electrical half-period, for example between 50%
and 80% of an electrical half-period when the displacements to be measured are rapid
and the observation of a plurality of samples of the amplitude requires going beyond 50%
20 of an electrical half-period. In a further preferred example, the linearity range sought for
a sensor with three secondary windings is at least 33% of an electrical half-period, for
example between 33% and 50% of an electrical half-period when the displacements to
be measured are rapid. Hereinafter, unless specified otherwise and without being
considered to be an exclusive choice, the description will be limited to presenting a
25 sensor with two secondary windings, and the purposes of legibility, the description will
be limited to presenting the linearity error over a sought linearity range of 50% of an
electrical half-period, without explicitly mentioning these terms, and referring to the
linearity error defined under these terms by merely mentioning the linearity error EL.
The inventors particularly observed that, for a given target-transducer distance
30 (and for a given range αL), the linearity error EL generally increases as the number N of
poles of the sensor increases.
25
However, this restriction does not indicate industrial use of an inductive sensor
insofar as such a use generally requires a high number of poles, typically N=6, to ensure
a robust measurement as stated above.
It would be desirable to be able to have inductive displacement sensors, and
particularly 5 multi-pole sensors, having a lower linearity error (or broader linearity
ranges) than existing sensors, in order in particular to facilitate the processing of the
amplitudes supplied by the sensor. By way of non-restrictive example, extending the
linearity ranges can make it possible to benefit from the signal processing methods
described in the patents FR2914126 and FR2891362.
10 According to a first aspect, it is sought, in an inductive displacement sensor, and
particularly (but not only) a multi-pole sensor, for example sensor with two pole pairs or
more and preferably a sensor with six pole pairs or more, to reduce the linearity error EL
over a given angular range αL, for example over a range αL extending over half an
electrical half-period of the sensor for a sensor with two secondary windings, or over a
15 range αL extending over one third of an electrical half-period for a sensor with three
secondary windings. It can also be taken into consideration that it is sought to increase
the extent of the linearity range of the sensor, i.e. the extent of the position range,
included in the measurement range of the sensor, wherein the amplitude of the range of
the electromotive force at the terminals of a secondary winding of the sensor varies
20 approximately linearly according to the angular position  of the target with respect to
the transducer.
The studies conducted by the inventors demonstrated that the extents of the
linearity range of an inductive sensor is dependent on the target-transducer distance d,
sometimes referred to as air gap, i.e. the distance between the median plane of the
25 secondary winding(s) of the transducer, and the conductive patterns of the target. By
way of example, the target-transducer distance d is defined as being the distance
between the median plane of the secondary winding(s) of the transducer and the surface
of the conductive patterns of the target oriented towards the transducer.
Figure 10 is a diagram representing, for a plurality of separate target-transducer
30 distances in an inductive sensor of the type described above (for example of the type
described with reference to figure 7, where N=6 pole pairs), the progression of the
26
amplitude V of the range of the electromotive force measured at the terminals of a
secondary winding of the transducer according to the angular position  of the target.
The curve V1 represents the progression of the amplitude V for a target-transducer
distance d1, the curve V2 represents the progression of the amplitude V for a targettransducer
distance d2 5 less than d1, and the curve V3 represents the progression of the
amplitude V for a target-transducer distance d3 less than d2. The line Vl1, in dotted-line
format, represents the linear approximation of the amplitude V1, the line Vl2, in dottedline
format, represents the linear approximation of the amplitude V2, and the line Vl3,
in dotted-line format, represents the linear approximation of the amplitude V3. As seen
10 in figure 10, the signal V has, at the distance d3, a maximum amplitude greater than the
maximum amplitude obtained at the distances d2 and d1. On the other hand, the
linearity error EL2 of the amplitude V, at the distance d2, is less than the linearity
errors EL1 and EL3 of the amplitude V at the distances d1 and d3 respectively.
Figure 11 is a diagram representing the progression, according to the target15
transducer distance, of the linearity error EL of the amplitude V of the range of the
electromotive force measured at the terminals of a secondary winding of the transducer
of an inductive displacement sensor, for example a sensor of the type described with
reference to figure 7 (where N=6 pole pairs). In this example, the linearity error EL
corresponds, in a given range of angular positions  extending for example over half of
20 the electrical period of the sensor (over a monotone portion of the EMF), at the
maximum difference (in absolute value) between a linear approximation of the response
of the sensor and the actual response measured. As seen in figure 11, there is an optimal
target-transducer distance dopt for which the linearity error EL passes through a
minimum. More generally, the inventors observed that a minimum linearity error can be
25 observed in all the types of inductive displacement sensor, regardless of the number of
pole pairs in particular. This minimum value is achieved for an optimal targettransducer
distance which is dependent on the configuration of the sensor (and
particularly on the number of pole pairs). It is thus theoretically possible to obtain a
linear response regardless of the inductive sensor. The term theoretically denotes that,
30 when the number of pole pairs N is particularly high, the distance dopt becomes
27
extremely small so as no longer to be measurable in practice during the limited
precision and constraints of use of suitable measuring instruments.
According to a first embodiment, an inductive displacement sensor is envisaged
wherein the target-transducer distance d is between 0.8 and 1.5 times the distance dopt
for which the linearity error of the amplitude measured 5 by the sensor is minimal. It
should be noted that this optimal distance can easily be determined using tests, for
example by plotting curves of the type represented in figure 11.
The inventors observed however that, in practice, for some sensors, and
particularly sensors having a high number N of pole pairs, typically greater than or
10 equal to three and more particularly for N greater than or equal to six, the optimal
target-transducer distance in terms of linearity can be relatively small, for example less
than 0.2 mm, which can pose problems for some types of measurement, particularly in
industrial environments wherein such distances are unacceptable, particularly due to
manufacturing, assembly and use tolerances.
15 Moreover, the inventors observed that the optimal target-transducer distance in
terms of linearity is dependent on a plurality of further parameters, including geometric
parameters of the sensor such as the outer diameter of the transducer and/or the target.
More particularly, the inventors observed that when the diameter of the sensors
increases, the optimal target-transducer distance increases and can adopt a relatively
20 high value, for example greater than 1 mm, which can pose problems for some types of
measurements, particularly in industrial environments wherein it is sought to ensure a
somewhat compact design.
In the case where the optimal target-transducer distance in terms of linearity is
incompatible (excessively high or excessively low) with the measurement environment,
25 it is possible to envisage positioning at the closest possible target-transducer distance to
the optimal distance in the environmental constraint limits, and correcting the nonlinearity
by applying mathematical processing (post-processing) of the measurement
signal. The inventors observed however that, in practice, this solution has limitations in
terms of precision and robustness, and is not satisfactory particularly for the
30 implementation of the signal processing methods described in the patents FR2914126
and FR2891362.
28
A first solution proposed by the inventors and illustrated by figures 12A to 12D,
13A to 13C, 14 and 15, is that of adding to the sensor an additional electromagnetic
field confinement part, placed at a specific distance from the primary winding of the
transducer, chosen so as to increase the target-transducer distance significantly in terms
5 of linearity.
Figures 12A to 12D are cross-sectional views schematically illustrating four
examples of embodiments of an inductive angular displacement sensor.
In the example in figure 12A, the sensor comprises a transducer 201 and a
target 203, arranged at a target-transducer distance d (d being in this example the
10 distance between the median plane of the secondary winding(s) of the transducer and
the plane of the surface of the conductive patterns of the target oriented towards the
transducer), and does not comprise an additional field confinement part.
In the example in figure 12B, the sensor comprises a transducer 201 and a
target 203, arranged at a target-transducer distance d, and further comprises an
15 additional field confinement part 205 made of a conductive material, for example made
of the same material as the conductive patterns of the target, or of any other conductive
material, optionally magnetic, such as iron, steel, aluminum, copper, etc. In this
example, the part 205 is arranged on the side of the target 203 opposite the
transducer 201 (i.e. the target 203 is situated between the transducer 201 and the
20 part 205), the surface of the part 205 oriented towards the target 203 being preferably
approximately parallel with the median plane of the transducer, and therefore also
approximately parallel with the median plane of the target (subject to assembly
imprecision). The field confinement part 205 is preferably periodic along a parallel
direction with a degree of freedom of displacement of the sensor, i.e. periodic by
25 revolution (about an axis which is approximately the axis of symmetry of the target) in
the case of an angular position sensor, the spatial period of the conductive patterns of
the confinement part being preferably separate from that of the conductive patterns of
the target. By way of illustrative but non-restrictive example, the part 205 is symmetric
by revolution. The part 205 is arranged at a part-transducer distance l, defined in this
30 example as being the distance between the median plane of the primary winding(s) of
the transducer, and the plane of the surface of the conductive pattern(s) of the part
29
oriented towards the transducer. The part 205 is preferably rigidly connected to the
target, i.e. movable with respect to the transducer when the position of the target with
respect to the transducer changes.
In the example in figure 12C, the sensor comprises a transducer 201 and a
target 5 203, arranged at a target-transducer distance d, and further comprises an
additional field confinement part 205', for example identical or similar to the part 205 in
figure 12B. The part 205' is preferably periodic by revolution, and for example
symmetric by revolution, about an axis of symmetry which is approximately the axis of
symmetry of the primary winding of the transducer. In this example, the part 205' is
10 placed on the side of the transducer 201 opposite the target 203 (i.e. the transducer 201
is situated between the target 203 and the part 205'). The part 205' is arranged at a parttransducer
distance l'. By way of example, the distance l' is defined as being the distance
between the median plane of the primary winding(s) of the transducer, and the plane of
the surface of the conductive patterns of the part oriented towards the transducer. The
15 part 205' is preferably rigidly connected to the transducer, i.e. fixed with respect to the
transducer when the position of the target with respect to the transducer changes.
In the example in figure 12D, the sensor comprises a transducer 201 and a
target 203, arranged at a target-transducer distance d, a first field confinement part 205
(for example identical or similar to the part 205 in figure 12B) arranged on the side of
20 the transducer 201 opposite the target 203, at a distance l from the transducer, and a
second field confinement part 205' (for example identical or similar to the part 205' in
figure 12C), arranged on the side of the target 203 opposite the transducer 201, at a
distance l' from the transducer (i.e. the transducer 201 and the target 203 are situated
between the parts 205 and 205').
25 The parts 205 and/or 205' can be electrically connected or not, point-wise or in a
spatially distributed manner, to other elements of the sensor. In particular, the part 205
can be electrically connected to one or a plurality of conductive patterns of the target,
and the part 205' can be electrically connected to an electrical potential available on the
transducer, for example at a point of a secondary winding, at a point of the primary
30 winding, or to the ground of the transducer.
30
Figure 13A is a diagram including four curves ELA, ELB, ELC and ELD
representing respectively, for the four examples of a sensor in figures 12A to 12D, the
progression of the linearity error EL of the sensor according to the target-transducer
distance. Each of the curves ELA, ELB, ELC and ELD is of the same type as the curve in
figure 11, i.e. it passes 5 via a linearity error value for a certain optimal target-transducer
distance, doptA, doptB, doptC and doptD, respectively. As seen in figure 13A, the
distance doptA is less than the distance doptB which is in turn less than the distance doptC
which is in turn less than the distance doptD. The tests conducted by the inventors
demonstrated that adding one or a plurality of additional field confinement parts can
10 increase the optimal target-transducer distance in terms of linearity of an inductive
displacement sensor from several tens of millimeters to several millimeters.
The positioning along the axis Z of the additional field confinement part(s), and
more specifically the distance between this or these parts and the primary winding of the
transducer, has an influence on the effectiveness of the increase in the optimal target15
transducer distance in terms of linearity resulting from adding this or these parts. There
is therefore a (some) optimal distance(s) lopt and/or lopt' between the primary winding
and the additional field confinement part(s), such that the optimal target-transducer
distance dopt is increased to attain a value between 0.65 and 1.25 times the distance d at
which it is sought to have the sensor operate, this sought value possibly being but not
20 restrictively between 0.5 and 1.5 mm, which is a range of values compatible with
various industrial applications.
Figure 13B is a diagram representing the progression, for an inductive angular
displacement sensor of the type described above, of the optimal target-transducer
distance dopt in terms of linearity, according to the ratio of the part-primary distance dpipr'
25 over the target-primary distance dcpr, in the case of addition of the additional field
confinement part 205' as represented in figure 12C or 12D. As seen in figure 13B, the
optimal target-transducer distance in terms of linearity increases as the ratio dpipr'/dcpr
decreases.
Figure 13C is a diagram representing the progression, for an inductive angular
30 displacement sensor of the type described above, of the optimal target-transducer
distance dopt in terms of linearity, according to the ratio of the part-primary distance dpipr
31
over the target-primary distance dcpr, in the case of addition of the additional field
confinement part 205 as represented in figure 12B or 12D. As seen in figure 13C, the
optimal target-transducer distance in terms of linearity increases as the ratio dpipr'/dcpr
decreases.
In other words, if the transducer is 5 considered as an assembly wherein the
constituent layers are not differentiated, the optimal target-transducer distance dopt can
be said to increase as the ratio l/d (respectively l'/d) decreases.
Under these conditions, an illustrative but non-restrictive example of positioning
of the additional field confinement parts in figure 12D, is that of placing:
10 - the upper part 205' at a distance from the primary winding approximately
between 0.5 and 2 times the distance separating the primary winding and the surface
area of the conductive patterns of the target;
- the lower part 205 at a distance from the primary winding approximately
between 1.3 and 3 times the distance separating the primary winding and the surface
15 area of the conductive patterns of the target.
As such, for a given sensor configuration, the ratio dpipr/dcpr and/or the
ratio dpipr'/dcpr can be chosen such that the distance dopt is compatible with the constraints
of the application, for example either greater than or equal to 0.3 mm, for example
between 0.3 and 10 mm, and preferably between 0.5 and 1.5 mm, particularly for a
20 sensor including a high number N of pole pairs, for example N4 and preferably N≥6.
It should be noted that the abovementioned choice of distance between the field
confinement part and the transducer is generally not optimal in terms of signal level
supplied by the secondary winding(s) of the transducer. Indeed, at this distance, the
conductive part 205/205' causes a non-negligible reduction in the level of the signals V
25 and V' supplied by the transducer. It should be noted in particular that in the prior art of
inductive angular displacement measurement, it is accepted to separate the conductive
parts liable to modify the spatial distribution of the electromagnetic field which is
established in the presence of only the primary, secondary and target elements as much
as possible. This dimensioning criterion applies in particular in the case of electrostatic
30 screens (or shielding screens), which, when provided, are arranged at distances along
32
the axis Z much greater than the distances envisaged in the embodiments described, so
as not to attenuate the wanted signal level measured at the secondary excessively.
However, the embodiments proposed define a compromise which may be
appropriate in applications for which the linearity is important, and particularly in
applications wherein it 5 is sought to implement signal processing methods of the type
described in the patents FR2914126 and FR2891362 mentioned above.
Figures 14 and 15 are front views representing examples of field confinement
parts 205 liable to be used in an inductive displacement sensor of the type described
above (the parts 205' of the sensors mentioned above can have similar or identical
10 configurations). In the example in figure 14, the part 205 is a mere disk made of a
conductive material (for example metal) having a diameter for example greater than or
equal to the outer diameter of the target. Alternatively (not shown), the disk can be
drilled at the center thereof, for example with a hole less than or equal to the inner
diameters of the conductive patterns of the target. In the example in figure 15, the
15 part 205 is a disk of the same diameter but having cohesive radial striations or slots with
the patterns of the target, suitable for obtaining a Moiré type structure effect with the
target suitable for amplifying the influence of the part 205 on the field distribution at a
secondary winding of the transducer. The embodiments described are, however, not
restricted to these two particular examples.
20 A second solution for modifying the optimal target-transducer distance in terms
of linearity, suitable for use in addition or as an alternative to adding a conductive field
confinement part, is illustrated by figures 16A, 16B and 17.
Figures 16A and 16B illustrate two examples of embodiments of an inductive
angular position sensor. In figures 16A and 16B, only the target of the sensor has been
25 represented. The arrangement of the transducer, and particularly of the primary winding
thereof or the secondary windings thereof, is consistent with the arrangement of the
target, and can easily be deduced from the shape of the target on reading the above. In
this example, the target of the sensor in figure 16A is similar or identical to the target in
figure 3B. The target of the sensor in figure 16B also comprises N conductive
30 patterns 137i in the shape of an annular strip sector of angular aperture  approximately
equal to one electrical half-period (for example 360°/2N), the N patterns 137i being
33
regularly distributed along an annular strip described by the target. The target in
figure 16B differs from the target in figure 16A in that the conductive patterns 137i have
different radial dimensions (less in the example shown) from the radial dimensions of
the conductive patterns 117i of the target in figure 16A. More particularly, in this
example, the annular strip 5 determining the shape of the conductive patterns 137i has an
external radius Rext substantially identical to that of the annular strip determining the
shape of the patterns 117i, but has an internal radius Rint less than that of the annular
strip of the conductive patterns 117i.
The inventors observed, as illustrated by figure 17, that, for a given number of
10 pole pairs, the optimal target-transducer distance dopt in terms of linearity of the
response of the sensor, varies according to the ratio Rint/Rext between the internal radius
and the external radius of the annular strip wherein the conductive patterns of the target
are situated, and consequently wherein the turns of the secondary winding(s) of the
sensor are situated. It should be noted that the embodiment of figure 16B, which
15 consists of varying the ratio Rint/Rext by modifying the internal radius Rint of the
conductive patterns of the target, is in no way exclusive of further embodiments suitable
for varying the ratio Rint/Rext by modifying either the external radius Rext, or both radii
in combination.
Figure 17 is a diagram representing the progression, for an inductive angular
20 displacement sensor of the type described above, of the optimal target-transducer
distance dopt in terms of linearity, according to the ratio Rint/Rext. As seen in figure 17,
the optimal target-transducer in terms of linearity increases as the ratio Rint/Rext
increases. As such, for a given sensor configuration, the ratio Rint/Rext can be chosen
such that the distance dopt is compatible with the constraints of the application, for
25 example either greater than or equal to 0.3 mm, for example between 0.3 and 10 mm,
and preferably between 0.5 and 1.5 mm, particularly for a sensor including a high
number N of pole pairs, for example N4 and preferably N≥6.
In electromagnetic terms, it would appear that the modifications made to the
internal and/or external radii of the target have the effect of modifying the conductive
30 pattern shape ratio, and in particular modifying the contribution of the radial edges with
respect to the contribution of the ortho-radial edges, this ratio of the contributions being
34
a determining factor of the optimal target-transducer distance in terms of linearity dopt.
When the ratio Rint/Rext between the internal radius and the external radius of the target
increases, the annular strip portion constituting a conductive pattern is compressed
along the radial direction, inducing a reduction in the contribution of the radial edges to
the overall field distribution measured 5 by the secondary, conveyed at the secondary
output signal by an increase in the optimal target-transducer distance in terms of
linearity. The solution described therefore consists of modifying the spatial distribution
of the electromagnetic field, and more particularly the ratio of the radial contributions
with respect to the ortho-radial contributions, so as to adjust the optimal target10
transducer distance in terms of linearity dopt so that it is compatible with the constraints
of the application.
In the sensor in figure 16B, when the internal radius Rint and/or the external
radius Rext of the target in figure 16B change, the internal and external radii of the
associated transducer change preferably substantially in the same proportions, so as to
15 maximize the signal level received by the secondary. By maximizing the signal level at
the secondary output, reference is more specifically made to maximizing the slope at the
origin of the signal rather than maximizing the values adopted by the signal extrema for
some positions.
For a given set of internal Rint and external Rext target radii, the signal received
20 by the secondary of the associated transducer is maximum when the annular strip
defining the patterns of the target and the annular strip defining the patterns of the
secondary are substantially overlaid, or in other words, when the external and
respectively internal ortho-radial edges of the target and the external and respectively
internal ortho-radial branches of the secondary are overlaid.
25 It should be noted that for a given sensor size (and particularly for an upper
external radius limit and a lower internal radius limit), increasing the ratio Rint/Rext
amounts to decreasing the surface area of the conductive patterns of the target, which
induces a decrease in the amplitude of the variations of the sensor output signal level
according to the position of the target with respect to the transducer. As such, in the
30 prior art of inductive angular displacement measurement, the internal diameter and the
external diameter of the annular strip wherein the conductive patterns of the target are
35
situated, and consequently wherein the turns of the secondary winding(s) of the sensor
are situated, are designed so as to occupy the maximum surface area available in the
given size, the size being generally restricted by the internal aperture and the external
diameter of the substrate and/or the casing wherein the sensor is integrated, or by the
external diameter of the shaft about 5 which the sensor is fitted and by the internal
diameter of the interface parts between which the sensor is housed.
Nevertheless, the proposed solution consisting of modifying the ratio Rint/Rext
defines a compromise which may be appropriate in applications for which linearity is
important.
10 A third solution for modifying the optimal target-transducer distance in terms of
linearity, suitable for use in addition or as an alternative to adding an additional field
confinement part, and/or to modifying the ratio Rint/Rext, is illustrated by les figures 18A,
18B and 19.
This third solution follows the same logic as the solution that has just been
15 described, in that it consists of modifying the shape factor of the conductive patterns of
the target and/or the corresponding secondary winding turns, and particularly of
modifying the ratio between the radial dimension and the ortho-radial dimension of the
patterns of the target and/or secondary winding turns, so as to adapt the optimal targettransducer
distance in terms of linearity to the constraints of the application.
20 Figure 18A illustrates three examples of embodiments of an angular position
sensor of the type described above. In figure 18A, only one conductive pattern of the
target, designated respectively by the references 117i for the first example (solid line),
117i' for the second example (dashed line), and 117i'' for the third example (dotted line),
has been shown. In each example, the target is obtained by regularly repeating the
25 conductive pattern represented along a circular annular strip. The internal and external
radii of the patterns 117i, 117i', and 117i'' are substantially identical, but the patterns 117i,
117i', and 117i'' differ from one another by the angular dimensions thereof. More
particularly, in this example, the angular aperture of the pattern 117i' is approximately
equal to one electrical half-period (for example 360°/2N), as described above, the
30 angular aperture of the pattern 117i'' is greater than one electrical half-period of a
value 1, for example between 0% and 50% of an electrical half-period, and the
36
angular aperture of the pattern 117i is less than 360°/2N of a value 2, for example
between 0% and 50% of an electrical half-period.
As for the embodiment of the solution in figures 16A, 16B and 17, the
arrangement of the secondary of the transducer is preferentially consistent with the
arrangement of the con 5 ductive patterns of the target, i.e. the angular aperture of the
secondary patterns adapted to the patterns 117i' of the target is substantially equal to one
electrical half-period (for example 360°/2N), the angular aperture of the secondary
patterns adapted to the patterns 117i'' of the target is greater than 360°/2N of a value
substantially equal to 1, and the angular aperture of the secondary patterns adapted to
10 the target 117i is less than 360°/2N of a value substantially equal to 2. In practice,
when the angular aperture of the secondary patterns adopts a value greater than an
electrical half-period of the sensor, it can be envisaged, in order to provide electrical
insulation between adjacent turn tracks, to modify the shape of the tracks in at least one
metallization plane, and/or to increase the number of metallization planes. A further
15 embodiment option can consist of limiting the maximum angular aperture of the
patterns of the secondaries to substantially one electrical half-period, and only varying
the angular aperture of the patterns of the target (of the values 1 or 2). In this case,
the angular aperture of the secondary winding patterns of the transducer is not strictly
consistent with the angular aperture of the patterns of the target.
20 The inventors observed that the optimal target-transducer distance dopt in terms
of linearity of the response of the sensor, varies according the angular deviation 
between the angular aperture chosen for the patterns of the target and the secondary, and
the nominal angular aperture α equal to one electrical half-period of the sensor.
Figure 19 is a diagram representing the progression, for a given multi-pole
25 angular displacement sensor of the type described above and illustrated in figures 18A
and 18B, of the optimal target-transducer distance dopt in terms of linearity, according to
the value . As seen in figure 19, the optimal target-transducer distance in terms of
linearity decreases as the value  increases for negative values, and conversely
increases as the value  increases for positive values. As such, for a given sensor
30 configuration, the angular aperture of the conductive patterns of the target can be
37
modified by a value  with respect to the nominal value  (equal to one electrical halfperiod,
for example 360°/2N), the value  being chosen such that the distance dopt is
compatible with the constraints of the application, for example either greater than or
equal to 0.3 mm, for example between 0.3 and 10 mm, and preferably between 0.5 and
1.5 mm, particularly for a sensor including 5 a high number N of pole pairs, for example
N≥4 and preferably N≥6.
Solutions have been described for reducing the linearity error (or increasing the
extent of the linearity range) of the response of an inductive displacement sensor, as
well as for modifying, i.e. increasing or reducing according the initial situation, the
10 target-transducer distance for which an inductive displacement sensor has or approaches
optimal characteristics in terms of linearity.
It should be noted that if the linearity error remains nonetheless excessively high
(or if the extent of the linearity range obtained remains insufficient), one or a plurality
of additional secondary windings, spatially offset (by a substantially equal angular
15 offset between one another), may be added, so as to reduce the extent of the minimal
linearity range required for proper reconstruction of the information in respect of
positioning and/or displacement of the target, in combination with the application of the
solutions described above. By way of illustrative example, in the sensor in figure 5,
instead of providing two identical secondary windings spatially offset by a quarter of an
20 electrical period, it is possible to envisage three identical secondary winding spatially
offset by a sixth of the electrical period of the sensor.
Furthermore, it should be noted that the solutions described above can be
adapted to inductive linear displacement sensors, for example by "unwinding" the
patterns in circular strip form described above in order to convert same into patterns in
25 rectilinear strip form.
Moreover, it should be noted that the solutions described above can be adapted
to inductive angular displacement sensors wherein the transducer has an angular
aperture less than 360°, for example less than 180° in order to enable assembly "from
the side" of the transducer about a rotary shaft, rather than a "through" assembly. In this
30 case, the angular aperture of the target can have a value of 360°, independent of the
38
angular aperture of the transducers, or adopt a value less than 360°, corresponding for
example to the angular displacement range of the application.
Second aspect
The inventors further o 5 bserved that, in practice, independently of the issue of
linearity, existing inductive displacement sensors, and particularly multi-pole sensors,
are sensitive to various disturbances induced by coupling effect. Such disturbances
occur for example at the transduction zone, i.e. directly at the secondary of the
transducer, and furthermore at the electrical connection zone between the secondary of
10 the transducer and a functional conditioning block of the electronic means. These
disturbances particularly feature the coupling of electromagnetic disturbances from
outside the sensor (i.e. not generated by the primary winding), direct inductive coupling
of the primary winding with the secondary winding (i.e. the proportion of inductive
coupling remaining constant regardless of the position of the target), and/or capacitive
15 coupling between the primary winding and the secondary winding. These disturbances
can cause undesirable fluctuations of the sensor output signal(s) and sensor output
signal interpretation errors.
It would be desirable to be able to avail of inductive displacement sensors, and
particularly multi-pole sensors, less sensitive to parasitic disturbances and/or less
20 subject to parasitic couplings than existing sensors.
As such, according to a second aspect, it is sought to reduce the sensitivity to
disturbances and parasitic coupling effects of multi-pole inductive displacement sensors,
and more particularly of the sensors of the type described with reference to figure 7, i.e.
wherein the secondary winding(s) each comprise 2N turns of alternating winding
25 directions, N being the number of pole pairs of the sensor. For this, the inventors
propose a particular arrangement of the secondary winding(s) of the sensor, which will
be described hereinafter.
Figures 20A and 20C schematically illustrate two examples of embodiments of
an inductive angular displacement sensor, of angular aperture 360°, consisting of N=6
30 pole pairs, and making a spatially differential measurement (for example as described
with reference to figure 7). In figures 20A and 20C, only one secondary 213 of each
39
sensor has been shown, the embodiment of the primary winding, the target, and,
optionally, one or a plurality of secondary windings spatially offset with respect to the
winding 213, being within the grasp of those skilled in the art on the basis of the
explanations of the present description. In this example, the secondary of the sensor in
figure 20A and the secondary 5 of the sensor in figure 20C are similar or identical to the
secondary in figure 7, except that the electrical connections between the turns are shown.
The secondary in figure 20A shows a first method for interconnecting the turns,
whereby the entire angular aperture of the annular strip whereon the secondary extends
is traversed a first time, for example in the trigonometric direction in the figure, and the
10 entire annular strip is traversed a second time, this time in the clockwise direction, so as
to approach the electrical terminal end E2 towards the electrical starting end E1, and
thereby close the measurement circuit. The secondary in figure 20C shows a second
method for interconnecting the turns, whereby a first half of the angular aperture of the
annular strip whereon the secondary extends is first traversed, for example in the
15 trigonometric direction in the figure, then the return path is traversed in the clockwise
direction so as to approach the input end E1, then the other half of the angular aperture
of the annular strip whereon the secondary extends is traversed, retaining the clockwise
direction of rotation, and then the return path is traversed in the trigonometric direction
so as to approach the electrical terminal end E2 towards the electrical starting end E1,
20 and thereby close the measurement circuit as for the secondary in figure 20A.
Figures 20B and 20D are front views schematically representing an example of
an embodiment of a transducer of an inductive linear displacement transducer. The
sensors in figures 20B and 20D are sensors wherein a target (not shown) comprising N
conductive patterns is suitable for moving in translation along a rectilinear direction x
25 with respect to the transducer. The sensor in figure 20B is for example of the same type
as the sensor in figure 20A, adapted to a linear configuration, which essentially consists
of "unwinding" the circular annular strips of the sensor in figure 20A and replacing the
conductive patterns and turns in the shape of an annular strip sector, by conductive
patterns and turns having a general rectangular or square shape. The sensor in
30 figure 20D is for example of the same type as the sensor in figure 20C, adapted to a
linear configuration. In figures 20B and 20D, only one secondary winding 213 of each
40
sensor has been shown, the embodiment of the target, the primary winding, and,
optionally, one or a plurality of additional secondary windings spatially offset with
respect to the winding 213 being within the grasp of those skilled in the art on the basis
of the explanations in the present description. By way of example and unlike the
primary winding 5 of the angular sensors in figures 20A and 20C, an example of primary
winding obtained when the set of two concentric turns 101a and 101b for example
described for the sensor in figure 1A is "unwound", consists for example of a single turn
for a linear sensor as described in figures 20B and 20D, optionally consisting of a
plurality of revolutions. The turn of the primary winding has for example a general
10 rectangular shape, of dimension along y similar to the dimension along y of the
conductive patterns of the target and/or of the turns of the secondary as described above,
and of dimension along x greater than the dimension along x of the conductive patterns
of the target and/or of the turns of the secondary, so that the contribution to the overall
electromagnetic field distribution, created at the primary branches oriented along y and
15 which are situated at both ends along x of the primary, are relatively attenuated in the
vicinity of the secondary branches oriented along y and which are situated at both ends
along x of the secondary. In particular, for a transducer with a single secondary winding,
the range along x of the primary will be greater than the range along x of the secondary,
and preferably but not exclusively, greater by at least one electrical half-period of the
20 sensor, distributed equally (at one quarter of an electrical period) at each end of the
sensor. As a general rule, a preferred example of embodiment of the primary winding of
an inductive linear displacement sensor is a turn having a rectangular general shape and
a range greater than the overall range of the set of secondaries, for example but not
exclusively, greater by at least one electrical half-period of the sensor, distributed
25 equally (at one quarter of an electrical period) at each end of the sensor.
In the examples in figures 20B and 20D, the sensors comprise N=6 pole pairs.
However, the embodiments described are not restricted to this particular case.
In the example of the sensor in figure 20D, the secondary winding 213 extends
into a zone having a dimension Dtot parallel with the degree of freedom of the sensor, i.e.
30 parallel with the direction x of displacement of the target with respect to the transducer.
The winding 213 comprises 2N loops or turns of alternating winding directions
41
electrically connected in series between the ends E1 and E2 thereof. More particularly,
the winding 213 comprises N loops or turns 213i+ having the same first winding
direction, and N loops or turns 213i- having the same second winding direction opposite
the first direction, each turn 213i+ or 213i- having a dimension along the direction x
approximately equal to an electrical h 5 alf-period of the sensor (i.e. for example
approximately equal to Dtot/2N), and the turns 213i- and 213i+ being juxtaposed in pairs
in alternation along the zone of dimension Dtot of the secondary winding.
According to a second embodiment, the secondary winding consists of:
a first coiled conductive section 213A forming N half-turns of alternating
10 directions, extending between a first end E1 of the winding, situated approximately at
the midpoint of the distance Dtot along which the winding 213 extends parallel with the
direction x, and a first intermediate point A of the winding, situated at a first end of the
distance Dtot;
a second coiled conductive section 213B forming N half-turns of alternating
15 directions, complementary to the N half-turns of the section 213A, extending between
the point A and a second intermediate point M of the winding, approximately at the
midpoint of the distance Dtot;
a third coiled conductive section 213C forming N half-turns of alternating
directions, extending between the point M and a third intermediate point B of the
20 winding, situated at the second end of the distance Dtot; and
a fourth coiled conductive section 213D forming N half-turns of alternating
directions, complementary to the N half-turns of the section 213C, extending between
the point B and a second end E2 of the winding, situated approximately at the midpoint
of the distance Dtot, in the vicinity of the first end E1 of the winding.
25 More particularly, in the example shown, in the left part of the winding (in the
orientation of the figure), the section 213A comprises N U-shaped half-turns wherein
the vertical branches are oriented in opposite directions along a direction y
approximately normal to the direction x, and the section 213B comprises N U-shaped
half-turns wherein the vertical branches are oriented alternately in opposite directions
30 along the direction y. Each U-shaped half-turn of the section 213A has the vertical
branches thereof approximately aligned with the vertical branches of a U-shaped half42
turn of opposite orientation of the section 213B. The sections 213C and 213D are
arranged according to a similar arrangement in the right part of the winding. As such, in
this example, the portions of the winding 213 orthogonal to the direction of
displacement x are traversed twice and twice only by the wire or track of the winding
(except for the two orthogonal 5 end portions of the winding situated at both ends of the
distance Dtot, which, in this example, are traversed a single time - this exception does
not arise however in the case of an angular sensor of angular aperture of 360°, wherein
all the radial portions of the primary winding can be traversed twice and twice only by
the wire or track of the winding), and the portions of the winding 213 parallel with the
10 direction of displacement x are traversed once and once only by the wire or track of the
winding.
In terms of path travelled by the constituent electrical circuit of the patterns of
the secondary winding, the embodiment of the solution in figure 20D corresponds to the
embodiment of a solution of the type described with reference to figure 20B, and by
15 linear-angular transposition also corresponds to the embodiment of the solutions in
figures 20A and 20C. On the other hand, the sequence whereby this path is travelled
differs between the transducer in figure 20D (and by transposition the transducer in
figure 20C), and the transducer in figure 20B (and by transposition the transducer in
figure 20A). In particular, the arrangement described with reference to figures 20D and
20 20A is designed so as to show an intermediate connection point M between the ends E1
and E2.
The winding 213 can be provided, in addition to the connection terminals PE1
and PE2 at the ends E1 and E2 thereof, with a third access terminal PM connected to the
midpoint M of the winding.
25 In the case of multi-pole sensors comprising an even number N of pole pairs,
and as represented in figure 20D, the secondary winding has as many turns 213i+
(referred to as positive) on the right as turns 213i+ on the left (N/2 on each side), and
consequently the secondary winding has as many turns 213i- (referred to as negative) on
the right as turns 213i- on the left (N/2 on each side).
30 One advantage of the secondary winding arrangement in figure 20D when the
number of pole pairs adopts an even value, lies in that the induction is substantially
43
identical, to the nearest sign, regardless of the position of the target with respect to the
transducer, on the two portions E1-M and E2-M on either side of the midpoint, while
enabling the three connections E1, E2 and M to be situated adjacent to one another.
This preferred embodiment wherein the number of pole pairs adopts even values
is in no way 5 exclusive of other embodiments. Alternatively, if the number N of pole
pairs is high, the choice of an odd number N is perfectly acceptable insofar as the error
of signal symmetry between the portion E1-M and the portion E2-M varies as an
inverse function of N.
The inventors observed that when the sensor is embodied according to the
10 second embodiment, if the midpoint M of the winding is referenced at a given electric
potential of the differential measurement means, for example at a constant potential
centered on the voltage measurement range of the measurement means, the common
mode component contained in the electrical signal present at the terminals of the
dipole E1-E2, which does not carry useful information on the position and the
15 displacement of the target with respect to the transducer, is low with respect to the
differential mode component contained in the same electrical signal present at the
terminals of the dipole E1-E2, the differential mode component carrying however, the
useful information on the displacement of the target with respect to the transducer. The
arrangement of the sensor in figures 20C and 20D suitable for positioning the
20 midpoint M in the immediate vicinity of the ends E1 and E2 therefore has a definite
advantage, for example with respect to the arrangement of the sensor in figure 20B
wherein the midpoint M is removed from the ends E1 and E2, and more generally with
respect to the arrangement of the sensors in figures 20A and 20B wherein the values E1-
M and E2-M are dependent on the position of the target with respect to the transducer,
25 or, in other words, with respect to the sensor arrangements wherein the ratio of the
common mode component over the differential mode component at the terminals of a
secondary winding is not low and varies significantly with the position of the target
with respect to the transducer.
In particular, one advantage of the sensors described in figures 20C and 20D
30 when the midpoint M is suitably connected to the measurement means, lies in high
immunity of the two electric potentials at the ends E1 and E2, to the component of the
44
electromagnetic excitation field (primary) which does not vary with the position,
whereas the spatially differential nature of the measurement of the sensor in figure 7
only guarantees immunity on the difference in potential at the ends E1 and E2.
In addition to the immunity to the "direct" field emitted by the primary (internal
source of the system), th 5 e sensors in figures 20C and 20D also offer increased immunity
to electromagnetic and/or electrostatic disturbances emitted by an external source at the
transduction zone and wherein the spatial distribution is relatively homogeneous, or
more generally increased immunity to any form of electromagnetic and/or electrostatic
disturbance with respect to sensors as described in figures 20A and 20B.
10 Examples of practical examples of increased immunity to external disturbances
in the transduction zone are for example the reduction of constraints on electronic
measurement means protections, such as voltage surge protections, and/or the relaxation
of design constraints on electrical signal conditioning systems, such as the common
mode rejection rate of differential amplifiers.
15 It should be noted that adapting an inductive sensor to apply a midpoint
according to the second embodiment can give rise to an increase in the number of
interfaces of the conditioning circuit (for example the number of tabs of an integrated
circuit). It should particularly be noted that according to the prior art of inductive
measurement, it tends to be conventional to minimize the number of physical interfaces
20 by substituting same with electronic or digital processing. However, this second
embodiment makes it possible to achieve a relatively simple electronic solution, of high
immunity and measurement robustness levels than with known solutions.
Figure 20E is a "small signal" electrical representation of the effective induction
phenomena VM1 and VM2, i.e. of the signals carrying the information or a portion of the
25 information on the position and/or displacement of the target with respect to the
transducer, and parasitic induction phenomena VP, VP', et VP'' at the connection wires
between the terminals E1, E2 and M of the transducer, and the terminals PE1, PE2 and
PM for example connected at the external electrical means. In this figure, and inasmuch
as the wires connected from E1, E2 and M follow each other in close succession, the
30 common mode disturbances VP, VP', and VP'' are substantially equal and are
substantially offset in the measurements VPE1 (made at the terminals of the dipole PM45
PE1) and VPE2 (made at the terminals of the dipole PM-PE2) on one hand, and in the
measurement VPE1PE2 made at the terminals of the dipole PE1-PE2 on the other. Once
the potential of the terminal PM set to a known value VREF, the signals measured at the
terminals of the tripole (PE1, PE2, PM) become extremely immunized to external
electromagnetic interference in the connection zone 5 between the terminals of the
transducer (E1, E2, M) and the connection terminals for the external electrical
means (PE1, PE2, PM), firstly by limiting the risks of overvoltage on the inputs of the
electrical means (the signal levels remain within the range of the conditioning means,
and the measurement is unconditionally valid), and secondly by relaxing requirements
10 on the common mode rejection rate of the differential measurement VPE1PE2 (the
measurement error introduced by the disturbances is low). For example, it is possible to
apply to the terminal PM a reference voltage of the conditioning block, or half the
power supply range of the conditioning block, or the electronic ground, without these
embodiments being exclusive of other embodiments such as for example the connection
15 of the terminal PM or M directly to a potential of the transducer such as the ground.
A representative signal of the position of the target with respect to the transducer
is thereby obtained, particularly robust to disturbances and/or to parasitic coupling
effects, whether they occur at the transduction zone or the connection zone between the
transducer and external electrical means, and whether they are inductive in nature as
20 shown in the electrical diagram in figure 20E, or capacitive in nature with the electrical
environment of the transducer and/or the primary winding or in particular the portions
close to the hot spot of the primary (high voltage).
Moreover, in the case where the transducer comprises a plurality of spatially
offset secondary windings (for example as described with reference to figure 5), the
25 various windings can be arranged in and/or on various overlaid support layers each
comprising one a plurality of metallization levels. This configuration, though
satisfactory for many applications, can however pose problems in respect of robustness
and precision. Indeed, as a result, the median planes of the various secondary windings
are situated at slightly different distances from the primary winding and the target. This
30 results in particular, firstly, in a difference in transduction gain, and therefore a
difference in output signal level of the various secondary windings, and secondly in
46
different linearity characteristics between a plurality of secondary windings of the same
transducer.
To solve this problem, it is preferably envisaged, as illustrated by figures 21A,
21B, 22A and 22B by way of non-restrictive example, to distribute the various
secondary windings of the transducer into two metallization lev 5 els, for example in the
same support layer with two metallization levels, such that, for each winding, the length
of track or wire of the winding arranged in the first metallization level is approximately
equal to the length of track or wire of the winding arranged in the second metallization
level. Preferably, a sustained alternation of the changes of metallization plane is
10 envisaged, such that a secondary track cannot travel, on the same plane, a distance (for
example an angular aperture in the case of an angular sensor) greater than an electrical
half-period. In a preferred embodiment, the metallization plane transition zones are
located such that there is a symmetric and/or anti-symmetric relationship between most
of the track portions arranged on the first metallization level, and most of the track
15 portions arranged on the second metallization level, as illustrated in figures 21A, 21B,
22A and 22B.
As such, the median planes of the various secondary windings are merged and
correspond to a virtual intermediate plane situated between the first and second
metallization levels. This gives each electromotive force induced at the terminals of
20 each secondary, a response according to the position of the target substantially identical
in terms of amplitude and linearity, to that of the electromotive forces induced at the
terminals of the other secondaries.
It should be noted that the examples of embodiments shown in figures 21A, 21B,
22A and 22B correspond to sensors of angular range Dtot=360°, i.e. wherein the angular
25 range occupied by each secondary has an angular aperture substantially equal to a
complete revolution. These examples are exclusive of alternative embodiments
involving sensors of angular aperture strictly less than 360°, for example less than 180°
in order to enable assembly "from the side" of the transducer about a rotary shaft, rather
than a "through" assembly of the sensor about said shaft in the case of a sensor of
30 angular aperture 360° as described in figures 21A, 21B, 22A and 22B for example.
Under these conditions, it is reiterated moreover that the angular aperture of the target
47
can alternatively retain a value of 360° independently of the angular aperture adopted by
the secondary/secondaries of the transducer, or adopt a value less than 360° and for
example adapted to the angular displacement range of the application.
Figures 21A and 21B are front views schematically representing an example of
5 an embodiment of a transducer with two secondary windings 223 (hollow line) and 223'
(solid line) spatially offset by a quarter of an electrical period, for an inductive angular
displacement sensor. In the example shown, the number N of pole pairs of the sensor is
equal to 6, and each secondary winding 223, 223' comprises 2N=12 loops or turns. The
embodiments described are not however restricted to this specific case. In this example,
10 the two secondary windings 223 and 223' are formed in and on the same substrate with
two metallization levels M1 and M2 connected by conductive vias (schematically
represented by circles). For each winding, the length of track formed in the level M1 is
approximately equal to the length of track formed in level M2. Figure 21A is a front
view of the metallization level M1, and figure 21B is a front view of the metallization
15 level M2. The patterns of the level M1 are substantially found on the basis of the
patterns of the level M2 by antisymmetry with respect to an intermediate plane between
the median planes of the levels M1 and M2.
The windings 223 and 223' each have, viewed from above, an arrangement of
the type described with reference to figure 20C (i.e. an arrangement of the type
20 described with reference to figure 20D adapted to an angular configuration, the coiling
principle described with reference to figure 20D applying in a similar manner, the
distance Dtot no longer being a linear distance but now being an angular distance, equal
to 360°).
As such, the winding 223 comprises:
25 a first curved coiled conductive section 223A forming N half-turns of alternating
directions, extending along a first circular annular half-strip in the example shown
between a first end E1 of the winding 223, situated approximately at the midpoint of the
distance Dtot (for example in the vicinity – i.e. within 5° and preferably with 2° - of an
angular position to which the value 0° is arbitrarily assigned), and an intermediate
30 point A of the winding, situated at a first end of the distance Dtot (for example in the
vicinity of the angle 180°);
48
a second curved coiled conductive section 223B forming N half-turns of
alternating directions, complementary to the N half-turns of the section 223A, extending
along the first annular half-strip between the point A and a second intermediate point M
of the winding, situated approximately at the midpoint of the distance Dtot (for example
5 in the vicinity of the angle 0°);
a third curved coiled conductive section 223C forming N half-turns of
alternating directions, extending along a second annular half-strip complementary with
the first half-strip between the point M and a third intermediate point B of the winding,
situated at an opposite end of the distance Dtot (for example in the vicinity of the angle -
10 180°); and
a fourth curved coiled conductive section 223D forming N half-turns of
alternating directions, complementary to the N half-turns of the section 223C, extending
along the second annular half-strip between the point B and a second end E2 of the
winding, situated approximately at the midpoint of the distance Dtot (in this example in
15 the vicinity of the angle 0°).
As seen in figures 21A and 21B, in this (non-restrictive) example, the portions of
the winding 223 orthogonal to the direction of displacement of the target with respect to
the sensor, i.e. the radial branches of the winding, are traversed twice and twice only by
the wire or track of the winding, and the portions of the winding 223 parallel with the
20 direction of displacement of the target with respect to the sensor, i.e. the ortho-radial
branches of the winding, are traversed once and once only by the wire or track of the
winding.
More particularly, in this example: the radial portions positioned at angles offset
by 0° modulo an electrical half-period, with respect to the angle characterizing the
25 end E1, are traversed twice and twice only by the wire or track of the winding 223; the
radial portions positioned at angles offset by a quarter of an electrical period modulo an
electrical half-period, with respect to the angle characterizing the end E1, are traversed
twice and twice only by the wire or track of the winding 223'; and the ortho-radial
portions are traversed once and once only by the wire or track of the winding 223, and
30 once and once only by the wire or track of the winding 223'.
49
This embodiment makes it possible to contain over two planes and only two
metallization planes, two secondaries as described in the preceding solutions, i.e.
without making any concession on the overall shape of the patterns of each secondary.
It should be noted that the embodiments shown in figures 21A, 21B, 22A and 22B
implement two secondaries arranged over two metallization planes, 5 but are in no way
exclusive of further embodiments such as an embodiment implementing for example
three secondaries arranged over three metallization planes.
In this example, each of the U-shaped half-turns of each of the sections 223A,
223B, 223C and 223D of the winding 223 (hollowed line) has approximately half of the
10 length thereof in the metallization level M1 and the other half of the length thereof in
the metallization level M2. A change of level occurs approximately every L/2 meters of
conductive track, where L denotes the length of a turn of the winding, consisting of the
connection in series of two complementary U-shaped half-turns. In the example shown,
the level change points of the winding are situated at the midpoints of the ortho-radial
15 branches (or horizontal branches) of the U shapes forming the half-turns. However, the
embodiments described are not restricted to this specific case. In figures 21A and 21B,
the numbers ranging from c1 to c28 denote, in the order of travel between the
terminals E1 and E2, different portions of the winding 223.
The secondary winding 223' (solid line) is arranged in the levels M1 and M2
20 according to an arrangement substantially identical to that of the winding 223, but with
an angular offset of approximately a quarter of an electrical period (i.e. 15° in this
example) with respect to the winding 223.
It should be noted that in the structure in figures 21A and 21B, the connection
tracks to the ends E1 and E2 of the winding 223 can for example be situated
25 respectively in the metallization levels M1 and M2, and be overlaid on one another.
This makes it possible to minimize the parasitic coupling difference on each of these
branches with any source of external induction (connection track to the primary,
external electromagnetic disturbance, etc.). An access track to the midpoint M of the
winding can be situated in a third metallization level (not shown), overlaid on the access
30 tracks to the terminals E1 and E2 which are situated in the metallization levels M1
and/or M2, to be situated in one of the metallization levels M1 and M2, slightly offset
50
with respect to the access tracks to the terminals E1 and E2. A similar arrangement of
the access tracks to the corresponding terminals E1', E2' and M' of the winding can be
envisaged for the winding 223'. More generally, regardless of the arrangement of the
access tracks, so as to increase the immunity to electromagnetic disturbances between
the transduction 5 zone (secondary) and the access and/or connection terminals to the
signal conditioning means, it is preferably sought to keep the paths from the ends E1
and E2 as close as possible (for example overlaid in PCB technology), and to a lesser
degree position the path from the intermediate point M relatively close to the paths from
the ends E1 and E2.
10 It should be noted further that, in the example in figures 21A and 21B, besides
the vias making changes in metallization levels of the windings 223 and 223', and the
conductive tracks travelling in each metallization level for field pickup purposes, vias or
conductive filling chips, with no electrical connection function between field pickup
tracks, have been regularly distributed along the windings 223 and 223'. These
15 conductive filling patterns have the role of symmetrizing the conductive structure of the
transducer, so as to periodize the influence thereof on the spatial distribution of the field,
and more particularly of minimizing the field distribution singularities which would be
conveyed by a variation of the secondary output signal according to the position. The
addition of these conductive filling patterns is however optional. In particular, if the vias
20 making the changes of metallization level have small dimensions with respect to the
skin thickness, the operating frequency, the constituent material thereof, it is possible to
envisage not adding the conductive chips and in particular not performing the drilling
thereof, which can reduce the cost of the device.
Figures 22A and 22B are front views schematically representing an alternative
25 embodiment of a transducer of the type described with reference to figures 21A and 21B.
This alternative embodiment differs from the example in figures 21A and 21B in that, in
the example in figures 22A and 22B, the changes of metallization level are more
numerous than in the example in figures 21A and 21B. As such, in the example in
figures 22A and 22B, instead of a change of metallization level every L/2 meters of
30 conductive track of the secondary winding, where L is the length of a turn of the
winding, it is envisaged to make k changes of metallization level every L/2 meters of
51
track, where k is an integer greater than or equal to 2. The number k can be chosen
accounting for the internal and external radii of the transducer. By way of nonrestrictive
example, for given sensor sizes and when the changes of level are made only
in the ortho-radial portions of the turns, k can be chosen as great as it possible to place
5 adjacent (for example equi-distributed) vias over other-radial portions without these vias
short-circuiting. For the purposes of simplification, figures 22A and 22B show an
example of an embodiment for a sensor with N=2 pole pairs, wherein the transducer
comprises 2 secondary windings 233 (dashed line) and 233' (solid line) angularly offset
by a quarter of the electrical period of the sensor (i.e. 360°/4N = 45° in this example).
10 The alternative embodiment in figures 22A and 22B is however compatible with
sensors comprising a greater number of pole pairs. As in the example in figures 21A
and 21B, conductive filling patterns with no electrical connection function can be
envisaged to symmetries the structure further.
15 Third aspect
In the examples of embodiments of multi-pole sensors hitherto described, for a
given dimension Dtot of a secondary winding of the transducer parallel with the degree
of freedom of the target with respect to the sensor, and for a given number N of pole
pairs, the maximum extent of the range of positions suitable for being detected by the
20 sensor is approximately one electrical half-period (for example Dtot/2N i.e. 360°/2N in
the case of an angular sensor) if the sensor comprises a single secondary winding, and
can increase to approximately one electrical period (for example Dtot/N i.e. 360°/N in
the case of an angular sensor) if the sensor comprises more than one secondary winding,
for example if it comprises two identical secondary windings spatially offset by a
25 quarter of an electrical period (for example Dtot/4N, i.e. 360°/4N in the case of an
angular sensor), or if it comprises three identical secondary windings spatially offset by
a sixth of an electrical period (for example Dtot/6N, i.e. 360°/6N in the case of an
angular sensor). In any case, the multi-pole angular displacement sensors of the type
described above do not make it possible to make displacement measurements over a
30 complete revolution (360°) absolutely, i.e. without using displacement log
memorization methods, and/or methods for referencing the position at start-up and/or
52
during the operation of the sensor. This remark is valid regardless of the number N of
pole pairs greater than or equal to 2, and can be more problematic when the number N is
high, for example N≥4 and preferably N≥6. The inductive linear displacement sensors
described above have the same limitations and do not make it possible to make a
5 measurement over the complete range of Dtot absolutely.
According to a third aspect, it is sought to embody an inductive displacement
sensor such that, for a given number N of pole pairs, for a given dimension Dtot of the
secondary winding(s) of the transducer parallel with the degree of freedom of the sensor,
the sensor is suitable for detecting the position of the target with respect to the
10 transducer substantially over the entire range Dtot of the transducer. In particular, in the
case of an angular position sensor, it is sought to embody a sensor suitable for detecting
the position of the target with respect to the transducer over a complete revolution, i.e.
over an angular range of approximately 360°, even when the number N of the pole pairs
of the sensor is high, for example N≥4 and preferably N≥6.
15 Figure 23 is a front view schematically representing an example of a multi-pole
inductive angular displacement sensor. In figure 23, only the target of the sensor has
been shown.
The target of the sensor in figure 23 comprises, as in the example in figure 3B, N
conductive patterns 117i (N=6 in the example shown) regularly distributed along the
20 360° of a first circular annular strip 118 of the target. Each conductive pattern 117i has
the shape of a portion or of a sector of the first annular strip 118, of angular aperture N
approximately equal to Dtot/2N = 360°/2N, two consecutive patterns 117i being
separated by a sector of the first annular strip 118, substantially of the same angular
aperture N. The target of the sensor in figure 23 further comprises N+1 conductive
25 patterns 119j, where j is an integer ranging from 1 to N+1, regularly distributed along
the 360° of a second circular annular strip 120 of the target, concentric with the first
strip 118 and not overlaid with the first strip 118. In the example shown, the second
annular strip has an internal radius greater than the external radius of the first annular
strip. Each conductive pattern 119j has the shape of a sector of the second annular
30 strip 120, of angular aperture N+1 approximately equal Dtot/2(N+1) = 360°/2(N+1), two
53
consecutive conductive patterns 119j being separated by a sector of the second annular
strip 120, substantially having the same angle N+1.
The transducer (not shown for simplification purposes) of the sensor in figure 23
corresponds with the target shown, i.e. it comprises:
one or a plurality of primary 5 windings suitable for producing a magnetic
excitation in first and second circular annular strips of the transducer substantially
identical to the first and second annular strips 118 and 120 of the target, intended to be
positioned respectively facing the first and second annular strips 118 and 120 of the
target;
10 at least first and second secondary windings of electrical period Dtot/N (for
example 360°/N in the example of an angular sensor), each comprising N turns of the
same winding direction, in the shape of sectors of angular aperture N of the first
annular strip of the transducer, regularly distributed along the first annular strip of the
transducer, or, alternatively, comprising 2N turns of alternating winding directions in
15 the shape of sectors of angular aperture N of the first annular strip of the transducer,
regularly distributed along the first annular strip of the transducer; and
at least third and fourth secondary windings of electrical period Dtot/(N+1) (for
example 360°/(N+1)), each comprising N+1 turns of the same winding direction in the
shape of sectors of angular aperture N+1 of the second annular strip of the transducer,
20 regularly distributed along the second annular strip of the transducer, or, alternatively,
comprising 2(N+1) turns of alternating winding directions in the shape of the sectors of
angular aperture N+1 of the second annular strip of the transducer, regularly distributed
along the second annular strip of the transducer.
Preferably, in the first annular strip, the second secondary winding of electrical
25 period Dtot/N is substantially identical to the first winding and spatially offset by a
quarter of an electrical period (Dtot/4N) with respect to the first winding, and, in the
second annular strip, the fourth secondary winding of electrical period Dtot/(N+1) is
substantially identical to the third winding and spatially offset by a quarter of an
electrical period (Dtot/4(N+1)) with respect to the second winding. More generally, the
30 transducer can comprise, in the first annular strip, a plurality of secondary windings of
electrical period Dtot/N, substantially identical to the first winding and spatially offset
54
with respect to one another by a certain electrical period percentage, and, in the second
annular strip, a plurality of secondary windings of electrical period Dtot/(N+1),
substantially identical to the third winding and spatially offset with respect to one
another by a certain electrical period percentage.
The operation of the s 5 ensor in figure 23 will now be described with reference to
figure 24. The (non-restrictive) case is taken into consideration where the transducer of
the sensor comprises, in the first annular strip of the transducer, a first pair of identical
secondary windings of electrical period 360°/2N, spatially offset by a quarter of an
electrical period, and, in the second pair of identical secondary windings of electrical
10 period 360°/2(N+1), spatially offset by a quarter of an electrical period. As described
above, this sensor is suitable for supplying two sets of two separate electromotive forces,
from which it is possible to construct an estimation of position respectively over a
position range equal to 360°/2N and over a position range equal to 360°/2(N+1).
Figure 24 is a diagram representing the progression, according to the position of
15 the target with respect to the transducer, of the estimation N (solid line) of the position
obtained using the electromotive forces measured at the terminals of the first pair of
secondary windings, and of the estimation N+1 (dashed lines) of the position obtained
using the electromotive forces measured at the terminals of the second pair of secondary
windings of the transducer.
20 As seen in figure 24, when the angular position  of the target with respect to the
transducer varies from 0° to 360°, the position estimation signal N varies periodically
between a low value substantially equal to 0 and a high value substantially equal to 1
(the position estimations are standardized herein for the purpose of simplification, the
embodiments described not being restricted to this particular case), with a variation
25 period equal to the electrical period of the first pair of secondary windings, i.e. equal to
360°/N = 60° for N = 6. Furthermore, the position estimation signal N+1 varies
periodically between the low 0 and high values 1, with a variation period equal to the
electrical period of the second pair of secondary windings, i.e. equal to 360°/N+151.4°
for N = 6.
30 By combining the levels of the position estimation signals N and N+1, two
separate measurement scales are obtained over a complete sensor revolution, i.e. two
55
different splits of the same range of 360°. The principle of a vernier applied to these two
angular measurement scale, i.e. the construction of the difference N+1-N between the
two standardized position estimations N+1 and N, is suitable for estimating the position
and/or the displacement of the target relative to the transducer over the entire
5 distance Dtot = 360° (i.e. over a complete revolution).
More particularly, one of the position estimation signals, for example the
signal N, can be used to provide "refined" target displacement information in N angular
ranges restricted to the electrical period 360°/N, and the difference N+1-N between the
other position estimation signal (the signal N+1 in this example) and this signal can be
10 used to provide rough absolute information of the position of the target over a complete
revolution. Under these conditions, the rough absolute information makes it possible to
adapt the refined but angularly restricted information, so as to carry out an absolute and
refined displacement estimation over 360°.
One advantage of the sensor in figure 23 is that it makes it possible to benefit to
15 a certain degree of the advantages of multi-pole sensors, particularly in terms of
robustness to positioning errors, while being suitable for providing measurements over
an extended position range with respect to the multi-pole sensors of the type described
above.
As a general rule, it should be noted that the embodiment described above can be
20 adapted to two signals N1 and N2, N1 and N2 being different integers not necessarily
exhibiting a unitary difference. Under these conditions, a sensor characterized by N1
and N2 = N1+2, exhibiting a similar arrangement to the arrangement of the sensor in
figure 23, is suitable for extending the absolute measurement over a range Dtot/N = 180°.
As a general rule, a sensor characterized by N1 and N2 = N1+r, where r is a positive
25 integer strictly less than N1, makes it possible under certain conditions to extend the
absolute measurement over a range Dtot/k = 360°/r.
In this general case, r is obviously a strictly positive integer, i.e. different to zero
(or greater than or equal to 1), such that N2 is greater than or equal to N1+1. If r was not
strictly positive, N2 could be equal to N1 if r=0, and the two signals N1 and N2 would
30 be identical (not distinct) and would not be suitable for estimating the absolute position
by the difference between the two standardized position estimations, as explained above.
56
Furthermore, r is an integer less than or equal to N1-1, such that N2 is less than
or equal to 2N1-1. If N2 could be equal to 2N1, the difference between the two
standardized position estimations, as described above, would furnish information
similar to that furnished solely by the first set of patterns (corresponding to N1), and
would not be suitable 5 for better estimating the absolute difference by the two
standardized position estimations. As such, once r is less than or equal to N1-1, the
embodiments and advantages of the invention are applicable.
In practice, r has a preferably low value, for example r is equal to 1 as described
above and illustrated in figure 23. This makes it possible to make an absolute
10 measurement over the greatest range, 360°. In some applications, it can be preferable to
choose a value of r equal to 2 (absolute measurement over 180° when Dtot = 360°), or
choose a value of r equal to 3 (absolute measurement over 120° when Dtot = 360°), or
choose a value of r equal to 4 (absolute measurement over 90° when Dtot = 360°), or
choose a value of r equal to 5 (absolute measurement over 72° when Dtot = 360°), etc.
15 The sensor in figure 23 poses a number of problems, however. In particular, the
size of the sensor is increased with respect to a sensor of the type described above.
Indeed, in the example in figure 23, the "effective" transducer surface area for making a
measurement is that of a circular annular strip approximately two times greater in width
than that of the "effective" annular strip of a transducer of the type described with
20 reference to figure 3A. Similarly, the "effective" target surface area for making a
measurement is that of an annular strip approximately two times greater in width than
that of the "effective" annular strip of the type described with reference to figure 3B.
Furthermore, the embodiment of the primary is more complex than in the preceding
embodiments if it is sought to excite in a relatively uniform manner each of the annular
25 strips of scale N and N+1 of the sensor. In practice, it can be necessary to use three sets
of separate turns to embody the primary excitation winding.
Figure 25 is a front view schematically representing an example of an
embodiment of an inductive displacement sensor. The sensor in figure 25 is a multi-pole
sensor with two measurement scales N and N+1, operating according to the principle of
30 a vernier as described with reference to figures 23 and 24. In figure 25, only the target
of the sensor has been shown.
57
The target of the sensor in figure 25 comprises a plurality of separated
conductive patterns 127i, distributed along the 360° of a circular annular strip 130 of the
target. As seen in figure 25, the set of patterns formed by the conductive patterns 127i is
not periodic. The various conductive patterns 127i have the shape of angular sectors, of
5 different angular apertures, of the annular strip 130 of the target, and are in principle
irregularly distributed along the annular strip 130.
The set of patterns formed by the conductive patterns 127i over the annular
strip 130 of the target corresponds to the (virtual) overlay of the first and second sets of
periodic conductive patterns of respective periodicities 360°/N and 360°/(N+1). The
10 first set of patterns comprises N elementary patterns 129j (solid lines) regularly
distributed along the annular strip 130 of the target, each elementary pattern 129j having
the shape of a sector of the annular strip 130, of angular aperture approximately equal to
360°/2N. The second set of patterns comprises N+1 elementary patterns 131k (dashed
lines), regularly distributed along the annular strip 130, each elementary pattern 131k
15 having the shape of a sector of the annular strip 130, of angular aperture approximately
equal to 360°/2(N+1). In other words, the surface areas of conductive patterns of the
target in figure 25 correspond to the total or the combination of the surface areas of the
conductive patterns of a first target of the type described with reference to figure 3B, of
electrical period 360/N, and of a second similar target, having the same internal and
20 external radii as the first target, but having an electrical period 360°/(N+1).
The transducer (not shown for the purpose of simplification) of the sensor in
figure 25 is for example suitable for the conductive patterns of the target in a similar
manner to that described with reference to the example in figure 23. In particular, it
comprises for example:
25 at least one primary winding suitable for producing an approximately uniform
magnetic excitation in a circular annular strip of the transducer substantially identical to
the circular annular strip 130 of the target, intended to be positioned facing the annular
strip 130 of the target;
at least first and second secondary windings of periodicity 360°/N, spatially
30 offset by a fraction of an electrical period, extending along the circular annular strip of
the transducer; and
58
at least third and fourth secondary windings of periodicity 360°/(N+1), spatially
offset by a fraction of an electrical period, extending along the same annular strip of the
transducer.
The inventors observed that, although the conductive patterns of electrical
period 360°/N 5 and 360°/(N+1) of the target overlap and short-circuit one another, and
consequently the target comprises conductive patterns 127i irregularly distributed over a
complete revolution of 360°, these patterns having residual angular apertures which
may be different to the periodic angular apertures of the patterns of the sets of
secondary windings of the transducer, the sensor in figure 25 is suitable for making,
10 with very good performances, displacement measurements over the entire distance Dtot
(i.e. over a complete revolution) using a vernier type reading method similar or identical
to the method described with reference to figures 23 and 24.
One advantage of the sensor in figure 25 is that, due to the overlay of the
patterns of respective electrical periods 360°/N and 360°/(N+1), the size of the sensor
15 can be reduced with respect to a configuration of the type described with reference to
figure 23. Furthermore, a single primary winding, for example of the type described
with reference to figure 3A, suffices to generate a sufficiently uniform magnetic
excitation for proper operation of the sensor.
Figure 26 is a front view schematically representing an alternative embodiment
20 of the sensor in figure 25. In figure 26, only the target of the sensor has been shown.
The target of the sensor in figure 26 comprises a plurality of separated
conductive patterns 137i, distributed along the 360° of a first circular annular strip 138
or wide strip of the target.
The set of patterns formed by the patterns 137i on the annular strip 138 of the
25 target corresponds to the overlay of the first and second sets of periodic patterns of
respective electrical periods 360°/N and 360°/(N+1). The first set of patterns comprises
N elementary conductive patterns 139j (solid lines) regularly distributed along the first
annular strip 138 of the target, each elementary pattern 139j having the shape of a sector
of the first annular strip 138 of the target, of angular aperture approximately equal to
30 one electrical half-period 360°/2N. The second set of patterns comprises N+1
elementary patterns 141k (dashed lines), regularly distributed along the second circular
59
annular strip 142 or narrow strip of the target, concentric with the annular strip 138 and
included in the annular strip 138, i.e. having an internal radius greater than the internal
radius of the first annular strip, and/or an external radius less than the external radius of
the annular strip 138. Each elementary pattern 141k has the shape of an annular sector of
the annular strip 142 of the target, 5 of angular aperture approximately equal to
360°/2(N+1). The width (radial dimension) of the second annular strip 142 of the target
is preferably markedly less than the (radial) width of the first annular strip 138 of the
target, for example two to twenty times less than the width of the first annular strip (the
wide strip).
10 The transducer (not shown for the purpose of simplification) of the sensor in
figure 26 is for example suitable for the conductive patterns of the target in a similar
manner to that described with reference to the examples in figures 23 and 25. In
particular, it comprises for example:
at least one primary winding suitable for producing an approximately uniform
15 magnetic excitation in a first circular annular strip of the transducer (wide strip)
substantially identical to the first annular strip 138 of the target, intended to be
positioned facing the first annular strip of the target;
at least first and second secondary windings of periodicity 360°/N, spatially
offset by a fraction of an electrical period, extending along the first circular annular strip
20 of the transducer (the wide strip); and
at least third and fourth secondary windings of periodicity 360°/(N+1), spatially
offset by a fraction of an electrical period, arranged along a second circular annular strip
of the transducer (narrow strip), substantially identical to the second annular strip 142 of
the target and intended to be positioned facing the annular strip 142 of the target.
25 The operation of the sensor in figure 26 is similar to that of the sensor in figure
25. Preferably, in the sensor in figure 26, the secondary winding(s) making the "refined"
measurement as described above, are windings wherein the turns have the shape of
annular sectors of the widest annular strip of the transducer (substantially identical to
the annular strip 138 of the target). By the concept of refined measurement, it is
30 understood that priority is given to design work to provide the measurement made by
the secondaries of the wide strip with performance and robustness, optionally and to a
60
certain degree, at the expense of the performance and robustness of the measurement
made by the secondaries of the narrow strip.
An additional advantage of the sensor in figure 26 with respect to the sensor in
figure 25 is that it is more robust to positioning errors between the target and the
transducer than the sensor in figure 25. In particular, t 5 he measurement obtained at the
terminals of the secondary windings of the wide strip (preferably associated with the
refined measurement) is more robust to positioning errors between the target and the
transducer than the sensor in figure 25. Indeed, in the sensor in figure 26, reducing the
surface area of one of the measurement scales with respect to the other makes it possible
10 reduce to a certain degree, the coupling created by the patterns of the narrow strip on the
patterns of the wide strip at the target, particularly with respect to the target in figure 25
for which the mutual influence of one set of patterns on the other is substantially
equivalent and very strong. It is thereby possible to increase the robustness of one of the
sets of secondaries to positioning errors.
15 It should be noted that, in the example shown, the mean radius of the second
circular annular strip of the sensor (the narrow strip) is approximately equal to the mean
radius of the first circular annular strip of the target (the wide strip). This configuration
is advantageous as it makes it possible to remove in a substantially equivalent manner
the effects of the internal and external ortho-radial portions of the conductive patterns.
20 The embodiments described are however not restricted to this particular configuration.
Figures 27A to 27C are front views schematically representing a further
alternative embodiment of the sensor in figure 25. More particularly, figure 27A is a
front view of the target, figure 27B is a front view of a portion of the transducer, and
figure 27C is a front view of a further portion of the transducer. In practice, the two
25 portions of the transducer represented separately in figures 27B and 27C for illustration
purposes, are rigidly connected and overlaid concentrically in a single transducer,
without the breakdown of the constituent elements of said transducer in these two
figures foreseeing a particular distribution over a plurality of metallization levels.
The target of the sensor in figures 27A to 27C comprises a plurality of separated
30 conductive patterns 147i, distributed along the 360° of a first circular annular strip 148
or wide strip of the target.
61
The set of patterns formed by the conductive patterns 147i on the first annular
strip 148 corresponds to the overlay of a first set of periodic patterns of electrical
period 360°/N, and of second and third sets of periodic patterns of electrical
periods 360°/(N+1). The first set of patterns comprises N elementary conductive
patterns 149 5 j (solid lines) regularly distributed along the annular strip 148 of the target
(wide strip), each elementary pattern 149j having the shape of a sector of the strip 148,
of angular aperture approximately equal to 360°/2N. The second set of patterns
comprises N+1 elementary conductive patterns 151k (dashed lines), regularly distributed
along a second annular strip 152 of the target (narrow strip), concentric with the first
10 annular strip 148 and included in the strip 148, i.e. having an internal radius greater than
the internal radius of the annular strip 148, and an external radius less than the external
radius of the annular strip 148. In this example, the internal radius of the annular
strip 152 of the target is greater than the mean radius of the first annular strip 148. This
example of an embodiment is in no way restrictive, and in particular the narrow
15 strips 152 and 154 can be arranged differentially in the wide strip 148, without the mean
radius of the wide strip 148 representing an impassable limit for either of the narrow
strips. Each elementary pattern 151k has the shape of a second of the second annular
strip 152 of the target, of angular aperture approximately equal to 360°/2(N+1). The
(radial) width of the annular strip 152 of the target is preferably low with respect to the
20 width of the annular strip 148 of the target, for example three to twenty times less than
the width of the first strip. The third set of patterns comprises N+1 elementary
conductive patterns 153k (dashed lines), regularly distributed along a third annular
strip 154 of the target (narrow strip), concentric with the annular strip 148 and included
in the annular strip 148. In this example, the external radius of the annular strip 154 of
25 the target is less than the mean radius of the annular strip 148. The difference between
the mean radius of the first annular strip 148 and the mean radius of the third annular
strip 154 is for example approximately equal to the difference between the mean radius
of the second annular strip 152 and the mean radius of the first annular strip 148. Each
elementary pattern 153k has the shape of a sector of the third annular strip 154 of the
30 target, of angular aperture approximately equal to 360°/2(N+1). The width of the third
annular strip is for example approximately equal to the width of the second annular strip.
62
Alternatively, the width of the third annular strip 154 is such that the surface area of a
pattern of the annular strip 154 is approximately equal to the surface area of a pattern of
the annular strip 152. These two examples of embodiments are in no way restrictive.
As seen in figure 27A, the periodic patterns of periodicity 360°/(N+1) of the
annular strip 5 154 of the target are spatially offset by 360°/2(N+1) with respect to the
periodic patterns of periodicity 360°/(N+1) of the annular strip 152 of the target. As
such, in the "empty" angular ranges of angular aperture 360°/(N+1) separating two
adjacent elementary conductive elements 151k, extends approximately an elementary
pattern 153k, and, in the "empty" angular ranges of angular aperture 360°/(N+1)
10 separating two adjacent elementary conductive patterns 153k, extends approximately an
elementary conductive pattern 151k. In other words, substantially all the radial
directions of the target encounter an elementary conductive pattern 151k or an
elementary pattern 153k.
The transducer of the sensor in figures 27A to 27C is for example suitable for
15 the conductive patterns of the target in a similar manner to that described with reference
to the examples in figures 23, 25 et 26. It comprises for example:
at least one primary winding 211 (figure 27B) suitable for producing an
approximately uniform magnetic excitation in a first circular annular strip of the
transducer substantially identical to the first annular strip 148 of the target, intended to
20 be positioned facing the annular strip 148 of the target;
at least first and second secondary windings 243 (only one secondary
winding 243 has been shown in figure 27B) of electrical period 360°/N, each
comprising N turns of the same winding direction or, alternatively, 2N turns of
alternating winding directions, each turn of the first and secondary windings having the
25 shape of a sector of angular aperture 360°/2N of the first annular strip of the transducer,
and the N or 2N turns of each winding being regularly distributed along the 360° of the
first annular strip of the transducer;
at least third and fourth secondary windings 253 (only one secondary
winding 253 has been shown in figure 27C) of periodicity 360/(N+1), each comprising
30 N+1 turns of the same winding direction or, preferably, 2(N+1) turns of alternating
winding direction, each turn of the third and fourth secondary windings having the
63
shape of a sector of angular aperture 360°/2(N+1) of a second annular strip of the
transducer, substantially identical to the second annular strip 152 of the target and
intended to be positioned facing the strip 152 of the target, the N+1 or 2(N+1) turns of
each winding being regularly distributed along the 360° of the second annular strip of
5 the transducer; and
at least fifth and sixth secondary windings 255 (only one secondary winding 255
has been shown in figure 27C) of periodicity 360°/(N+1), each comprising N+1 turns of
the same winding direction or, preferably, 2(N+1) turns of alternating winding
directions, each turn of the fifth and sixth secondary windings having the shape of a
10 sector of angular aperture 360°/2(N+1) of a third annular strip of the transducer,
substantially identical to the third annular strip 154 of the target and intended to be
positioned facing the annular strip 154 of the target, the N+1 or 2(N+1) turns of each
winding being regularly distributed along the 360° of the third annular strip of the
transducer.
15 The third and fifth secondary windings are of opposite polarities, i.e. they are
spatially offset by 360°/2(N+1) according to the polarity convention (represented by a +
or - sign) defined in figure 7 and adopted hereinafter in the description. The fourth and
sixth windings are arranged with respect to one another according to a substantially
identical arrangement to the arrangement between the third and fifth secondary
20 windings.
Preferably, in the first circular annular strip, the first and second secondary
windings are spatially offset by 360°/2N with respect to one another, in the second
circular annular strip, the third and fourth secondary windings are spatially offset by
360°/2(N+1) with respect to one another, and, in the third circular annular strip, the fifth
25 and sixth secondary windings are offset by 360°/2(N+1) with respect to one another.
More generally, the transducer can comprise, in the first annular strip, a plurality
of secondary windings of electrical period Dtot/N, substantially identical to the first
secondary winding and spatially offset with respect to one another by a fraction of an
electrical period; in the second annular strip, a plurality of secondary windings of
30 electrical period Dtot/(N+1), substantially identical to the third secondary winding and
spatially offset with respect to one another by a fraction of an electrical period; and in
64
the third annular strip, a plurality of secondary windings of electrical period Dtot/(N+1),
substantially identical to the fifth secondary winding and spatially offset with respect to
one another by a fraction of an electrical period.
The operation of the sensor in figures 27A to 27C is similar to that of the sensor
5 in figures 25 and 26.
Various reading configurations can be used in the example in figures 27A to 27C.
The inventors particularly observed that:
reading of the set of patterns 147i by a secondary winding 243 generates a
wanted signal suitable for processing, of electrical period 360°/2N;
10 reading of the set of patterns 147i by a secondary winding 253 generates a
wanted signal suitable for processing, of electrical period 360°/2(N+1);
reading of the set of patterns 147i by a secondary winding 255 generates a
wanted signal suitable for processing, of electrical period 360°/2(N+1);
a combination of the simultaneous readings of the set of patterns 147i by a
15 secondary winding 253 and by a secondary winding 255, for example when both
secondaries are of alternating polarities (as illustrated by figure 27C) and electrically
connected in series, generates a wanted signal suitable for processing, of electrical
period 360°/2(N+1) and of amplitude approximately equal to double the wanted signal
read by the secondary winding 253 or of the wanted signal read by the secondary
20 winding 255;
reading of the set of patterns 147i by a secondary winding 243 generates a
relatively weak parasitic signal (particularly of periodicities 360°/(N+1) and 360°) with
respect to the wanted signal detected by this secondary winding;
a combination of the simultaneous readings of the set of patterns 147i by a
25 secondary winding 253 and by a secondary winding 255, for example when two
secondaries are of alternating polarities (as illustrated by figure 27C) and electrically
connected in series, generates a relatively weak parasitic signal (particularly of
periodicities 360°/N and 360°) with respect to the wanted signal detected by this
secondary winding.
65
An additional advantage of the sensor in figures 27A to 27C is that it is even
more robust to positioning errors between the target and the transducer as the sensor in
figure 26.
In particular, the measurement obtained at the terminals of the secondary
windings 243 of the wide 5 strip (preferably associated with the refined measurement) is
more robust to positioning errors between the target and the transducer than in the
sensor in figure 26. Indeed, in the sensor in figures 27A to 27C, substantially all the
radial directions of the target encounter a single elementary conductive pattern of a
narrow strip, arranged on either of the two narrow strips of the target. Furthermore, the
10 two narrow strips of the target are preferably arranged at a sufficient distance from the
two internal and external ortho-radial branches of the secondaries 243 of the wide strip
of the transducer. Under these conditions, the coupling of the conductive patterns of the
two narrow strips of the target on the measurement at the terminals of the
secondaries 243 of the wide strip results from the combination of the induction of the
15 conductive patterns of a narrow strip of the target, these two contributions compensating
each other substantially regardless of the position of the target with respect to the
transducer. The parasitic coupling then adopts a relatively stable value when the
position of the target with respect to the transducer changes. Furthermore, the coupling
adopts a substantially zero value when the secondaries of the wide strip comprise 2N
20 turns of alternating winding directions, as described for the sensor in figure 3 for
example, in order to make a spatially differential measurement. A further formulation
consists of considering that the secondaries of the wide strip of the transducer "see"
roughly the two offset narrow strips as a single narrow median conductive strip and
substantially solid or continuous over Dtot in electromagnetic terms (and not electrically),
25 and that this virtual strip as such induces a substantially position-independent signal at
the terminals of said secondaries.
Moreover, the inventors observed that the measurement obtained at the terminals
of the secondary winding 253 (of a narrow strip) exhibit a behavior according to the
position of the target with respect to the transducer which is similar to the behavior
30 according to the position of the measurement obtained at the terminals of the secondary
winding 255 (of the other narrow strip). The inventors also observed that, in the event of
66
positioning defects of the target with respect to the transducer, the behavior according to
the position of the measurement at the terminals of one of the two windings 253 or 255
of one of the two narrow strips, exhibits deformations relatively complementary with
the deformations obtained on the measurement at the terminals of the other winding. As
such, by combining th 5 e measurements of the two secondaries of the two narrow strips,
and preferentially connecting the two windings in series if they are designed so as to
exhibit a relatively similar behavior in respect of position in terms of amplitude and
linearity in particular, it is possible to obtain a measurement at the terminals of the new
composite winding which is relatively robust to positioning defects. Indeed, in the
10 sensor in figures 27A to 27C, substantially all the radial directions of the transducer
encounter exactly two elementary turns of the composite winding, of opposite polarity
and alternately arranged on each of the two narrow strips of the transducer. Furthermore,
the two narrow strips of the transducer are at a sufficient distance from the two internal
and external ortho-radial branches of the conductive patterns of the wide strip of the
15 target. Under these conditions, the coupling of the conductive patterns 149j of the wide
strip of the target on the measurement at the terminals of the composite winding results
from the combination of the induction of the conductive patterns 149j on the
secondary 253 (one narrow strip) and from the induction of the conductive patterns 149j
on the secondary 255 (the other narrow strip), these two contributions compensating
20 each other substantially regardless of the position of the target with respect to the
transducer. The parasitic coupling then adopts a relatively stable value when the
position of the target with respect to the transducer changes. Furthermore, the coupling
adopts a substantially zero value when the secondaries 253 and 255 (narrow strips)
comprise 2(N+1) turns of alternating winding directions, as described for the sensor in
25 figure 3 for example, in order to make a spatially differential measurement. A further
formulation consists of considering that, when the position of the target with respect to
the transducer changes, the reading made by a secondary of the narrow strip of the
transducer of the set of conductive patterns associated therewith on the target is
substantially "in phase" with the reading made by the secondary of the other narrow
30 strip of the transducer of the set of conductive patterns associated therewith on the target.
Moreover and when the position of the target with respect to the transducer changes, the
67
reading made by a secondary of the narrow strip of the transducer of the set of
conductive patterns 149j of the wide strip is substantially "in phase opposition" with the
reading made by the secondary of the other narrow strip of the transducer of the same
set of conductive patterns of the wide strip of the target. As such, when the two
measurements are added by mathematical or electrical 5 means (for example by a serial
electrical connection), the parasitic coupling adopts a substantially zero value when the
secondaries of each narrow strip are designed for this purpose, whereas the wanted
signal is retained and/or amplified.
It should be noted that, in the case of the serial electrical connection of the
10 secondary winding of a narrow strip with the secondary winding of the other narrow
strip, and so as to obtain the features of the sensors described with reference to figure
2E, it is for example possible to select as the midpoint of the composite winding, the
serial connection point of the two elementary windings.
It should be noted that further methods for combining the measurements of the
15 two secondaries of the narrow strip can be envisaged, such as linear combinations of the
signals conditioned separately, or further methods for electrically interconnecting the
secondaries, with for example the same aim of increasing the robustness of the
measurements at the wide strip and/or the narrow strips of the transducer, to positioning
defects of the target with respect to the transducer.
20 It should be noted that in the examples shown in figures 23, 25, 26 and 27A, one
of the elementary patterns of electrical period 360°/(N+1) is approximately centered on
the same angular position as one of the elementary patterns of electrical period 360°/N.
For example, in figure 25, the pattern 1311 is centered on the same angular position as
the pattern 1291, and in figure 27A, the pattern 1511 is centered on the same angular
25 position as the pattern 1491. This configuration is preferential as it helps increase the
overall level of symmetry of the sensor, which particularly makes it possible to facilitate
the manufacture and visual inspection of the target, or facilitate the design and
manufacture of the sets of secondary windings. The embodiments described are
however not restricted to this particular case.
30 As a general rule, it should be noted that the embodiments described above can
be adapted to two signals N1 and N2, N1 and N2 being different integers but the
68
difference thereof not necessarily being unitary. Under these conditions, a sensor
characterized by N1 and N2 = N1+2 and of a similar arrangement to the arrangement of
the sensors in figures 23, 25, 26 and 27A to 27C, makes it possible to extend the
absolute measurement over a range Dtot/N = 180°. As a more general rule, a sensor
characterized by N1 and N2 = N1+r, 5 where r is a positive integer, different to zero and
strictly less than N1 (in other words, less than or equal to N1-1), makes it possible under
certain conditions to extend the absolute measurement over a range Dtot/r = 360°/r.
Furthermore, alternatively in the examples in figures 26 and 27A to 27C, instead
of reducing the width of the patterns of periodicity 360°/(N+1) with respect to the width
10 of the patterns of periodicity 360°/N, it could be envisaged to reduce the width of the
patterns of periodicity 360°/N with respect to the width of the patterns of
periodicity 360°/2(N+1).
Furthermore, it should be noted that the number of pole pairs is preferably even
for the patterns of the wide strip, so as to benefit from increased symmetry of the
15 transducer on either side of the midpoint (particularly when the transducer is embodied
according to the second aspect).
Moreover, it should be noted that the embodiments described with reference to
figures 23 to 27C do not merely be applied to planar angular displacement sensors, but
can be applied to further types of inductive displacement sensors, and particularly
20 planar linear displacement sensors, or non-planar angular displacement sensors, for
example linear displacement sensors "wound" (for example shaped according to a
cylinder) about and facing a part in rotation whereon on a target also of the linear type
and "wound" (for example shaped according to a cylinder).

CLAIMS
1. Inductive displacement sensor, comprising:
a transducer (201) including at least one primary winding suitable for producing a
magnetic excitation, and at least one secondary winding including at least one turn (113i;
123i), suitable for supplying an electromotive force at the terminals thereof in the
5 presence of said excitation; and
a target (203) comprising at least one conductive pattern (117i; 137i), this target (203)
being suitable for moving parallel with the transducer (201) so as to vary the surface
area of said at least one pattern (117i; 137i) situated facing said at least one turn (113i;
123i), thereby varying the amplitude of the electromotive force induced in the secondary
10 winding,
wherein the target-transducer distance is between 0.8 and 1.5 times the optimal targettransducer
distance (dopt), which is optimal in terms of linearity, i.e. a distance for which
the linearity error (EL) of the representative curve of said amplitude variation according
to said surface area variation is minimal.
15
2. Sensor according to claim 1, wherein the linearity error (EL) is the maximum
difference between an amplitude (V) of the electromotive force and a linear
approximation (VL) of said amplitude, for a range of displacement of the target with
respect to the transducer.
20
3. Sensor according to claim 1 or claim 2, further comprising at least one
electromagnetic field confinement part (205; 205').
4. Sensor according to claim 3, wherein said part (205; 205') is situated at a distance
25 from the primary winding of the transducer (201) such that the distance for which the
optimal target-transducer distance (dopt) in terms of linearity is greater than or equal to
0.3 mm.
75
5. Sensor according to claim 3 or 4, wherein said part (205; 205') has the shape of a
solid plate.
6. Sensor according to claim 3 or 4, wherein part (205; 205') has the shape of a striated
5 plate.
7. Sensor according to any one of claims 1 to 6, wherein said at least one secondary
winding comprises N identical turns (113i; 123i) in series, regularly distributed along a
first strip parallel with a degree of freedom of displacement of the target (203) with
10 respect to the transducer (201), and the target comprises N identical conductive
patterns (117i; 137i) regularly distributed along a second strip parallel with a degree of
freedom of displacement of the target (203) with respect to the transducer (201),
situated facing the first strip, where N is an integer greater than or equal to 2.
15 8. Sensor according to claim 7, wherein said degree of freedom is a degree of freedom
in rotation, the first and second strips are circular annular strips, and said conductive
patterns (117i; 137i) and turns (113i; 123i) have the shape of sectors of said annular
strips.
20 9. Sensor according to claim 8, wherein the ratio between the internal radius (Rint) and
the external radius (Rext) of said annular strips is chosen such that the optimal targettransducer
distance dopt is greater than or equal to 0.3 mm.
10. Sensor according to claim 8, wherein said sectors have an angle equal to 360°/2N +
25 , and the value  is chosen such that the optimal target-transducer distance (dopt) in
terms of linearity is greater than or equal to 0.3 mm.
11. Sensor according to claim 7, wherein said degree of freedom is a degree of freedom
in translation, the first and second strips are rectilinear strips, and said conductive
30 patterns and turns (213i) have the shape of portions of said rectilinear strips.
76
12. Sensor according to claim 11, wherein the ratio between the width of the patterns of
the sensor along the direction parallel with displacement and the width of the patterns of
the sensor along the direction orthogonal to displacement is chosen such that the
optimal target-transducer distance dopt is greater than or equal to 0.3 mm.
5
13. Sensor according to claim 11, wherein the width of the patterns of the sensor along
the direction parallel with displacement adopts a value different by one electrical halfperiod
of the sensor, this value being chosen such that the optimal target-transducer
distance dopt is greater or equal to 0.3 mm.
10
14. Sensor according to any one of claims 7 to 13, wherein N is greater than or equal to
4.