Solution for monitoring an elevator brake
TECHNICAL FIELD
The invention concerns in general the technical field of elevators. More
particularly, the invention concerns a monitoring solution of a machinery brake
in an elevator.
BACKGROUND
An elevator comprises an elevator hoisting machine into which a machinery
brake is implemented. The machinery brake engages mechanically with a
rotating part of the hoisting machine causing the braking effect. The machinery
brake may e.g. be a shoe brake, a drum brake or a disc brake.
A structure of the machinery brake is typically such that it comprises an
armature part provided with a brake pad and a frame part comprising an
electromagnet. Between the armature part and the frame part is arranged one
or more springs. The operation of the machinery brake is based on a utilization
of the springs that are arranged to push the armature part provided with a
brake pad against the braking surface of a rotating part of the hoisting machine
in order to achieve the braking effect i.e. holding the elevator car stationary in
the shaft when the control of the motor is inactivated. By means of the
electromagnet when provided with an electric current it is possible to pull a
magnetic core of the armature part, and thus the armature part, against the
spring force of the springs so that the brake may be released away from the
braking surface. Hence, the control of the machinery brake between the
activated and inactivated states may be achieved by controlling the current
supply of the electromagnet and, thus, the force of attraction of the
electromagnet may be controlled.
As is clear the machinery brake of an elevator hoisting machine is under heavy
forces when used. Additionally, the elevator is affected by great number of
environmental variables, such as constant change in load, vibration caused by

the hoisting motor among others, thermal expansion due to ambient
temperature and temperature generated by elevator operation. All these have
also effect on elevator brake and the elevator parts in general and in the worst
case may cause displacement of parts even so that the elevator starts to
misoperate or stop operation in full. As regards to elevator brake it is important
to detect that the brake parts have such mutual positions that they do not
prevent the operation of the elevator brake.
In known solutions so called micro switches are used for detecting mutual
positions of at least two objects, and especially a change in positions of the
objects. However, the problem in the use of micro switches is that they cannot
be used in every application areas because there is no possibility to arrange a
space for them and/or the operational environment is such that it prevents the
use of the micro switches. For example, an electromagnetic field of the
electromagnets may cause challenges in using the micro switches, which is
the case in elevator brakes. Moreover, one problem with micro switches is that
they are unreliable by default and their accuracy is inadequate in many
application areas. For example, in elevator brakes the mutual motion of the
armature part and the frame part is in scale of 0.15 mm, but the micro switches
cannot detect such a small motion with acceptable reliability. Further,
manufacturing of the micro switches is challenging.
Hence, there is need to develop solutions by means of which it is at least partly
possible to improve a monitoring of an operational state of elevator brakes.
SUMMARY
The following presents a simplified summary in order to provide basic
understanding of some aspects of various invention embodiments. The
summary is not an extensive overview of the invention. It is neither intended to
identify key or critical elements of the invention nor to delineate the scope of
the invention. The following summary merely presents some concepts of the
invention in a simplified form as a prelude to a more detailed description of
exemplifying embodiments of the invention.

An objective of the invention is to present a solution for monitoring an
operational state of a machinery brake for elevators. Alternatively or
additionally, it is an object of the present invention to provide a solution by
means of which the operational state monitoring is achieved by a sophisticated
sensor arrangement implemented in the machinery brake.
The objectives of the invention are reached by a machinery brake for an
elevator and a method as defined by the respective independent claims.
According to a first aspect, a machinery brake for an elevator is provided,
wherein the machinery brake comprises: a frame part comprising an
electromagnet, an armature part; wherein the machinery brake further
comprising an inductive proximity sensor mounted to one of the following: the
frame part, the armature part and a target mounted to the other of the
following: the frame part, armature part, wherein the inductive proximity sensor
and the target are mounted with respect to each other so that in a normal state
of the machinery brake the target resides within an operational area of the
inductive proximity sensor and in an abnormal state of the machinery brake the
target resides at least partly outside the operational area of the inductive
proximity sensor.
The proximity sensor may be configured to generate a first output signal when
the machinery brake is in the normal state and a second output signal when
the machinery brake is in the abnormal state.
The target may comprise a planar surface facing the proximity sensor wherein
the planar surface is arranged perpendicularly to a center axis of a coil in the
proximity sensor. A boundary defining the planar surface of the target may
comprise rounded shapes. The planar surface may be a circle.
Further, a ratio of an outer diameter of the coil with respect to a shortest
diameter of the target surface may be 1:3.
The inductive proximity sensor and the target may be mounted with the
respective parts so that a direction of a central axis of a coil residing in the

inductive proximity sensor deviates from a normal of the surface of the
armature part facing the frame part.
The target may be brought to the operational area of the inductive proximity
sensor through a through hole arranged in the part into which the inductive
proximity sensor is mounted to.
The target may at least partly be made of ferromagnetic material.
The machinery brake may further comprise a control unit that is configured to
generate an alarm signal in response to a detection that the machinery brake
is in the abnormal state.
According to a second aspect, a method for monitoring an operational state of
a machinery brake of an elevator is provided, wherein the machinery brake
comprises a frame part comprising an electromagnet and an armature part, the
method comprising: monitoring an output signal of an inductive proximity
sensor that is mounted to one of the following: the frame part, the armature
part wherein the output signal is dependent on a mutual position of the
inductive proximity sensor and a target mounted to the other of the following:
the frame part, armature part; and in response to detection that the output
signal of the inductive proximity sensor is changed a control unit of the
machinery brake is configured to generate an alarm signal.
Various exemplifying and non-limiting embodiments of the invention both as to
constructions and to methods of operation, together with additional objects and
advantages thereof, will be best understood from the following description of
specific exemplifying and non-limiting embodiments when read in connection
with the accompanying drawings.
The verbs "to comprise" and "to include" are used in this document as open
limitations that neither exclude nor require the existence of unrecited features.
The features recited in dependent claims are mutually freely combinable
unless otherwise explicitly stated. Furthermore, it is to be understood that the
use of "a" or "an", i.e. a singular form, throughout this document does not
exclude a plurality.

BRIEF DESCRIPTION OF FIGURES
The embodiments of the invention are illustrated by way of example, and not
by way of limitation, in the figures of the accompanying drawings.
Figure 1 illustrates schematically a cross-sectional view of a machinery brake
according to an embodiment of the invention.
Figure 2A and 2B illustrate schematically an inductive proximity sensor as well
as the target in different states according to an embodiment of the invention.
Figures 3A and 3B illustrate schematically some aspects of the invention
relating to the fundamental idea behind the invention.
Figure 4 illustrates schematically some aspects of an embodiment of the
invention.
Figures 5A-5D illustrate schematically some examples of a target applicable in
the invention.
Figures 6A and 6B illustrate schematically some embodiments of the invention.
Figure 7 illustrate schematically some aspects of a further embodiment of the
invention.
DESCRIPTION OF THE EXEMPLIFYING EMBODIMENTS
The specific examples provided in the description given below should not be
construed as limiting the scope and/or the applicability of the appended claims.
Lists and groups of examples provided in the description given below are not
exhaustive unless otherwise explicitly stated.
The present invention is at least partly based on a utilization of at least one
proximity sensor in elevator solutions and especially in a machinery brake of
the elevator. The proximity sensor is a type of sensor that is configured to
detect a presence or an absence of a target within an operational area of the
sensor. There are different types of proximity sensors available. For example,
the operation of the proximity sensors may be based on a capacitance

between the sensor and the target or an inductance between the sensor and
the target. Further, photoelectric sensors may also be considered as proximity
sensors as a reflection of a transmitted light may be monitored and analyzed in
order to detect the presence or the absence of the target. Also other types of
proximity sensors are known. A selection of the type of proximity sensor is
typically dependent on an application area in which the proximity sensor is
applied to. More specifically, the selection depends heavily on a material of the
target. As an example, if the target is metal an inductive proximity sensor is
applicable.
The proximity sensor, and especially the inductive proximity sensor, comprises
an inductive coil made of numerous turns of conductive wire, such as copper,
and a capacitor for storing electrical charge. An input current is provided to an
oscillator that generates an alternating current to the coil, which, in turn,
generates a magnetic field in front of the proximity sensor. Now, when a target
made of conductive metal is brought in a zone defined by boundaries of the
magnetic field, some of the energy is transferred into the target causing eddy
currents flowing in the target surface. Thus, the power loss affects to current
flow in the internal LC resonance circuit of the proximity sensor, and when the
target moves away from the zone at some point the state of the sensor
changes. In other words, the sensor may indicate the presence of the target
within the magnetic field for example by outputting a signal and when the
target moves enough away from the boundaries of the magnetic field, the
proximity sensor changes its state and the output signal is not present
anymore.
In order to monitor an operational state of the machinery brake, according to
an embodiment of the invention, an inductive proximity sensor is arranged in
the machinery brake as schematically illustrated in Figure 1 that illustrates a
cross-sectional view of a machinery brake according to an embodiment of the
invention. The machinery brake, as illustrated, comprises an armature part
110, a frame part 120 and a number of springs 130 arranged between the
armature part 110 and the frame part 120. The springs may be mounted either
to the armature part 110 or the frame part 120 or both. The frame part 120

comprises an electromagnet having a coil and by supplying electric current to
the coil of the electromagnet a magnetic field may be generated. As the
armature part 110 comprises a core of magnetic material the armature part is
pulled towards the frame part 120 when the magnetic field is generated. By
dimensioning the springs and the electromagnetic force optimally it is possible
to control the triggering of the machinery brake between an active and an
inactive state with the current supplied to the electromagnet. Furthermore, a
brake pad 112 may be mounted to the armature part 110 which brake pad 112
is arranged to hit against a braking surface of a rotating part of a hoisting
machine 140 in order to hold elevator car stationary if the control of the motor
is inactivated. According to an embodiment of the present invention an
inductive proximity sensor 122 is arranged in an aperture of the frame part
120. The inductive proximity sensor 122 comprises a coil into which an electric
current is supplied in order to generate a magnetic field by means of which it is
possible to monitor a position of a target 124 with respect to the proximity
sensor 122. The target 124 in this embodiment refers to a metal structure that
is mounted, or arranged, to the armature part 110 and that is such in shape
that it may intrude to the aperture arranged in the frame part. Moreover, the
target 124, in this embodiment, is arranged to intrude through an aperture hole
arranged in the frame part 120 so that it reaches an operational distance of the
inductive proximity sensor 122. Naturally the target 124 and the proximity
sensor 122 are dimensioned and arranged so that the proximity sensor
arrangement with the target does not prevent the operation of the machinery
brake. The proximity sensor 122 and the target may be mounted to the frame
part and the armature part with known methods, like using fixing devices like
screws and bolts and/or by welding when applicable. Figure 1 also illustrates a
control unit that is configured to supply current to the proximity sensor, but also
to monitor the output of the proximity sensor in order to monitor changes in
there.
Figure 2A schematically illustrates the inductive proximity sensor 122 in more
detail as well as the target 124. As already mentioned the inductive proximity
sensor 122 comprises a coil 210, preferably having a magnetic core made of
iron or ferrite inside the coil 210. In Figure 2 the core 220 is T shaped ferrite

which is arranged at least partly inside the coil 210 for increasing the magnetic
field generated when an alternating current is supplied in the coil. Figure 2A
does not illustrate the needed wiring and other means for supplying the current
in the coil in order to maintain clarity in the figure. As said the supplied current
to the coil 210 generates a magnetic field that travels to and through the target
124 over an air gap between the proximity sensor 122 and the target (the
magnetic field is schematically illustrated as ellipses in Figure 2A). According
to the present invention a target surface i.e. a planar surface of the target 124
facing the proximity sensor 122, and thus the frame part 120, is preferably
arranged perpendicularly to a center axis of the coil 210 (illustrated as dashed
line in Figure 2A).
At least some aspects of the present invention relate to a utilization of the
arrangement, as illustrated e.g. in Figure 2A, for monitoring a lateral
displacement of the target 124 with respect to the proximity sensor 122, and
especially the coil 210 therein. The lateral displacement refers to a situation in
which the point on the planar surface of the target 124 through which the
imaginary center axis of the coil 210 travels changes due to the lateral
displacement of either the target 124 or the proximity sensor 122 (a changed
situation is schematically illustrated in Figure 2B). Naturally the mutual motion
may comprise a component representing a displacement in the direction of the
center axis of the coil 210. The lateral displacement is important to detect as it
may indicate a misoperation of the machinery brake in the elevator.
For sake of clarity one may consider that in Figure 2A it is illustrated a normal
state of a machinery brake and in Figure 2B it is illustrated a situation in which
the machinery brake is in an abnormal state due to a mutual displacement of
the frame part and the armature part. The mutual displacement may be a result
of displacement of either the frame part or the armature part or both.
Next the at least some aspects of the invention relating to the monitoring the
lateral displacement is described by referring to Figure 3A and Figure 3B.
Figure schematically illustrates the monitoring of lateral displacement with a
help of a coordination system arranged on the target surface wherein the

center axis of the coil 210 is considered to travel through the origin (point 0, 0).
The coordination system provides a tool for understanding the displacement in
predetermined measurement units, such as millimeters.
By combining the coordination system with the switching point consideration in
three dimensional space the advantages of the invention may be explained in
more detail. As already mentioned the switching point in the context of the
inductive proximity sensors refers to a distance between the sensor and the
target at which the sensor changes its state due to the fact that magnetic field
traveling through the target changes over a limit, i.e. sensor's detection circuit
detects a reduced strength in an oscillating magnetic field. The change of the
state in sensor refers to output signal from the proximity sensor. Figure 3B
schematically illustrates, as a non-limiting example, a switching point with
respect to a coordinate system of Figure 3A. In other words, from Figure 3B it
is possible to find a switching point with different mutual positions of the target
124 and the proximity sensor 122 in the coordinate system. As may be seen
from Figure 3B when the arrangement is aligned optimally, i.e. there is no
lateral deviation or it is minimal, the switching point is much larger than in a
situation when the target and the proximity sensor have a larger mutual lateral
displacement. The larger mutual lateral displacement causes the switching
point to be smaller than in the previous situation. As may also be seen from
Figure 3B the larger a gradient of a tangent plane becomes the larger is the
lateral deviation between the mentioned entities and this phenomenon may be
used in an application area of elevator brakes, as will be described.
According to an embodiment of the invention it may be desirable that the
monitoring of the lateral displacement is arranged to be symmetric in every
direction. Such an embodiment is schematically illustrated in Figure 4 wherein
the planar surface (lined surface in Figure 4) of the target 124 facing the
proximity sensor is arranged to be circle in shape and the central axis of the
coil 210 in the proximity sensor is arranged to travel, at least essentially,
through the center of the circular surface. The non-limiting embodiment as
schematically illustrated in Figure 4 enables the monitoring of the lateral
displacement equally to every direction.

The shape of the planar surface facing the proximity sensor may vary from the
circle one as depicted in Figure 4. For example, in application area wherein the
displacement is to be monitored in one direction more closely than in another
direction it is possible to select a target with a shape of ellipse. Figures 5A-5D
schematically illustrates some non-limiting examples of shapes of the planar
surface of the target facing the proximity sensor. The shape may e.g. be ellipse
(Figure 5A), rounded triangle (Figure 5B), rounded cross (Figure 5C) ortoroid
shape (Figure 5D). In order to apply the proximity sensor in the application
area of elevator brakes the switching point surface is advantageously
continuous. For this reason in the selection of planar surface shape of the
target it is essential that a boundary of the planar surface does not comprise
sharp corners, but is implemented with rounded shapes. As already mentioned
the shape may be selected according to the need in the application area. This
may refer, but is not limited to, to a decision that a displacement to some
directions is more acceptable than to some other directions.
Next the operation of the arrangement as disclosed is described in more detail.
Namely, the proximity sensor 122 and the target 124 mounted to the actuating
part i.e. armature part 110 are initially mutually positioned so that the central
axis of the coil 210 in the proximity sensor 122 travels, at least essentially,
through the center of the circular surface of the target 124. The coil generates
the magnetic field when supplied with current which magnetic field travels from
a first end of the coil through the metallic target and the air gap back to the
other end of the coil 210. The volume of the metallic conductive target material
defines, at least partly, the resistance, i.e. reluctance, for the magnetic field. As
at least one aim of the present invention is to monitor the operational state of
the machinery brake, and specifically to detect permanent changes in the
mutual positions of the proximity sensor 122 and the target 124, the target
surface is advantageously symmetric and changes in the magnetic field are to
be monitored. At some point the magnetic field experienced in the sensor may
change due to a change in mutual positions of the mentioned elements. This is
because the magnetic field does not travel anymore in the same manner as
originally due to displacement that causes an increase in the reluctance of the
magnetic circuit. In other words the mutual lateral displacement of the

elements is that large that the target does not anymore provide a path for the
magnetic field to travel so that the reluctance remains within limits defined by
the structure. The change in the magnetic field is detected in the proximity
sensor and the sensor changes it state. One additional inventive aspect of the
arrangement as described is that when the state of the sensor changes it does
not return to the original state at the same displacement point where the
change of the sensor state happened if the elements return towards their
original positions (i.e. when the sensor was at the first state ("normal state")).
This is due to the fact that the coil in the proximity sensor aims to resist the
change in the magnetic field. The phenomenon is known as hysteresis. Due to
hysteresis in the monitoring arrangement the machinery brake may be driven
to a state that it is not allowed to return to operative state without maintenance.
The maintenance may comprise an alignment of the frame part and the
armature part, with respect to each other, so that the operation of the proximity
sensor may be brought to a normal state. Naturally, the alignment may relate
to an alignment of the proximity sensor and the target, especially in case if it is
concluded that the frame part and the armature part has not laterally displaced
with each other. An advantage of the invention is that the monitoring of the
elevator brake operation with the proximity sensor as described reveals
displacement of the armature part with respect to the frame part, but also if
either or both the proximity sensor and the target are displaced. The result is
that a need for service is detected.
The operation of the monitoring arrangement may at least partly be adjusted
by dimensioning sizes of the coil 210 of the proximity sensor 122 and the
target 124 optimally for the application area. According to an embodiment of
the invention the optimal dimensioning in the machinery brake may be such
that a ratio of an outer diameter of the coil 210 with respect to a diameter of
the circular target surface is 1:3. In case the target is not circular, but another
shape with rounded shape, such as any of the ones illustrated in Figures 5A-
5D, the ratio may also advantageously be 1:3 wherein the outer diameter of
the coil 210 may be defined with respect to a shortest diameter of target
surface. The diameter in this context means a straight line dividing the shape
surface into two portions with equal size. The ratio provides flat enough

switching point area for the mutual positions of the coil and the target so that
random displacement due to e.g. manufacturing tolerances and small
mounting errors may be eliminated, but at the same time the monitoring of the
operational state may be performed so that a displacement exceeding a
predetermined limit is detected.
Figures 6A and 6B schematically illustrate some examples of a machinery
brake used in elevators into which the present invention is implemented. As
already described the machinery brake comprises a frame part 120 having an
electromagnet inside and an armature part 110. Between the frame part 120
and the armature part 110 are arranged one or more springs to take the
mentioned parts apart from each other when braking (the springs are not
shown in Figures 6A and 6B). During the braking a brake shoe 112 mounted
together with the armature part 110 is arranged to hit a rotating part of an
elevator hoisting machine. A release of the brake is achieved by providing
current to the electromagnet and by controlling the current it is possible to
control the braking force. The frame part 120 may also comprise a proximity
sensor 122 that comprises a coil in it. A current may be supplied with a cable
610 traveling along the frame part 120. According to an embodiment of the
invention the proximity sensor 122 is mounted in an aperture arranged in the
frame part 120. A target 124, such as a plunger, is, according to an
embodiment, mounted to the armature part 110 and arranged to reach, along
the movement of the armature part 110, an operational area of the proximity
sensor 122 through a through hole arranged in the frame part 120 (see the
embodiment shown in Figure 6A). Alternatively, the target 124 may be
mounted to an outer surface of the armature part 110 and, thus, no through
hole is needed in the frame part 120 (see the embodiment shown in Figure
6B). The operational area of the proximity sensor 122 refers to a positioning of
the sensor 122 with respect to the target so that it is possible to detect the
normal state and an abnormal state of the machinery brake as described. As
mentioned above according to an embodiment of the invention the target 124
may be brought to the operational area of the sensor through an open
aperture, i.e. not through a hole. According to still further embodiment the
proximity sensor and the target may be mounted to outer sides of the frame

part and the armature part, correspondingly, so that no apertures are needed.
The inventive idea is not limited to the described embodiments, but e.g. the
positioning of the target 124 and the proximity sensor 122 may vary.
An aspect of the present invention is that the coil in the proximity sensor and a
coil of the electromagnet residing in the frame part preferably does not
interfere each other. The interference may be mitigated by optimal selection of
the proximity sensor so that a frequency of the magnetic field generated by the
coil in the proximity sensor differs from any other magnetic field frequency
existing in the environment of the machinery brake. For example, it is possible
to optimize the operation of the electromagnet in the frame part 120 so that the
operation does not generate frequencies overlapping the operational
frequency of the proximity sensor. For example, the operational frequency of
the proximity sensor 122 may e.g. be > 100 kHz, whereas the frequencies of
the magnetic fields originating from machinery brake, due to disturbances
among other, remain < 50 KHz.
Some further embodiment of the present invention may be implemented so
that the proximity sensor 122 and the target 124 are mounted in a slanted
position with respect to an axis of motion of the armature part 110. More
specifically, the central axis of the coil 210 in the proximity sensor 122 travels
slanted with respect to the axis of a normal motion of the armature part 110 i.e.
wherein the armature part 110 is configured to move essentially along a normal
of the surface of the armature part 110 facing the frame part. Such an
implementation is schematically illustrated in Figure 7. An advantage of this
kind of mounting arrangement is that the operation of the present invention is
enhance when the distance of motion of the armature part 110 with respect to
frame part 120 is small. Then, any un-allowed lateral displacement may be
detected efficiently with the slanted positioning.
The embodiments as described above are implemented so that the proximity
sensor 122 is mounted in the frame part 120 and the target is mounted, or
arranged, in the armature part 110 of the machinery brake. However, the
inventive idea of the present invention may also be applied so that the

proximity sensor 122 is mounted in the armature part.110 and the target 124 is
mounted in the frame part 120. In such an implementation the cable supplying
current to the proximity sensor 122 shall be brought to the sensor so that
arrangement enable the movement of the armature part 110 in such a manner
that the cable does not prevent the motion nor it is possible that the cable, or
any part of it, ends up to any un-allowed location, such as between the frame
part and the armature part, in the machinery brake. Hence, the mounting
arrangement of the cable is important. Alternatively or in addition, the cable
shall be protected so that it may stand the stress caused by the motion.
As already mentioned the target material shall be made of conductive metal.
Advantageously, the target for the proximity sensor is a flat piece of ferrous
metal, but non-ferrous metals may also be used. Generally speaking some
non-limiting examples of the target materials may be: steel (Fe360), stainless
steel, aluminum, brass, copper. Especially, in elevator environment and in the
application area of machinery brakes for elevators, ferromagnetic material is
used as the target material at least partly, such as coated with the
ferromagnetic material. This is due to the fact that as the ferromagnetic
material maintains the magnetic characteristic it has a further effect in the
elevator environment. Namely, they may collect at least part of the dust from
the elevator shaft around the target. That forms a protection layer to the target
against other dirt ending up between the target and the proximity sensor.
Hence, the operation of the present invention is also improved by using the
ferromagnetic material as the target material, such as iron or any other
applicable.
The proximity sensor and the target may be mounted to the entities, such as to
the frame part or to the armature part, with any known method. For example,
any applicable mounting device, such as screw, bolt or similar may be used.
As well, gluing, welding or any similar may be used either both or one of the
mountable parts.
Some aspects of the invention relate to a method for monitoring an operational
state of a machinery brake of an elevator, wherein the machinery brake

comprises a frame part 120 comprising an electromagnet and an armature part
110. In the method an output signal of an inductive proximity sensor 122 is
monitored. The inductive proximity sensor 122 is mounted either to the frame
120 part or the armature part 110. The output signal of the inductive proximity
switch is dependent on a mutual position of the inductive proximity sensor and
a target 124 that is mounted to the other of the frame part 120 or armature part
(110) i.e. to the other of the one into which the sensor 122 is mounted to.
According to the method, in response to detection that the output signal of the
inductive proximity sensor 122 is changed a control unit of the machinery
brake is configured to generate an alarm signal.
As described the proximity sensor generates an output signal having typically
two states. The solution according to the invention is based on an idea that
when the machinery brake operates normally, i.e. the parts of the machinery
brake are mutually positioned in an acceptable way, the proximity sensor is
configured to generate a first output signal. In case the proximity sensor
changes its state due to a change in mutual positions of the parts exceeding
the limit defined by the arrangement according to the invention the proximity
sensor is configured to generate a second output signal. A control unit may be
configured to monitor the output signal and in response to a detection of a
change from the first output signal to a second output signal the control unit
may be configured to perform predetermined tasks. The predetermined tasks
may e.g. comprise, but are not limited to, one or more of the following:
controlling of operation of the elevator, controlling of a maximum travel speed
of the elevator, controlling of access to the elevator.
The monitoring of an operational state of the machinery brake comprises at
least to detecting with sensor arrangement if the machinery brake is operating
normally or if it is misoperating. The misoperation may e.g. be due to
misalignment, or un-allowed displacement, of parts of the machinery brake
with respect to each other.
The specific examples provided in the description given above should not be
construed as limiting the applicability and/or the interpretation of the appended

claims. Lists and groups of examples provided in the description given above
are not exhaustive unless otherwise explicitly stated.

WHAT IS CLAIMED IS:
1. A machinery brake for an elevator, wherein the machinery brake
comprises:
a frame part (120) comprising an electromagnet,
an armature part (110),
wherein the machinery brake further comprising an inductive proximity sensor
(122) mounted to one of the following: the frame (120) part, the armature part
(110) and a target (124) mounted to the other of the following: the frame part
(120), armature part (110), wherein the inductive proximity sensor.(122) and
the target (124) are mounted with respect to each other so that in a normal
state of the machinery brake the target (124) resides within an operational
area of the inductive proximity sensor (122) and in an abnormal state of the
machinery brake the target (124) resides at least partly outside the operational
area of the inductive proximity sensor (122).
2. The machinery brake as claimed in the claim 1, wherein the proximity
sensor (122) is configured to generate a first output signal when the machinery
brake is in the normal state and a second output signal when the machinery
brake is in the abnormal state.
3. The machinery brake as claimed in any of the preceding claims, wherein
the target (124) comprises a planar surface facing the proximity sensor
wherein the planar surface is arranged perpendicularly to a center axis of a coil
(210) in the proximity sensor (122).
4. The machinery brake as claimed in the claim 3, wherein a boundary
defining the planar surface of the target (124) comprises rounded shapes.
5. The machinery brake as claimed in the claim 4, wherein the planar
surface is a circle.

6. The machinery brake as claimed in any of the preceding claims, wherein
a ratio of an outer diameter of the coil (210) with respect to a shortest diameter
of the target surface is 1 ;3.
7. The machinery brake as claimed in any of the preceding claims, wherein
the inductive proximity sensor (122) and the target (124) are mounted with the
respective parts so that a direction of a central axis of a coil (210) residing in
the inductive proximity sensor (122) deviates from a normal of the surface of
the armature part (110) facing the frame part (120).
8. The machinery brake as claimed in any of the preceding claims, wherein
the target (124) is brought to the operational area of the inductive proximity
sensor (122) through a through hole arranged in the part into which the
inductive proximity sensor (122) is mounted to.
9. The machinery brake as claimed in any of the preceding claims, wherein
the target (124) is at least partly made of ferromagnetic material.
10. The machinery brake as claimed in any of the preceding claims, wherein
the machinery brake further comprising a control unit that is configured to
generate an alarm signal in response to a detection that the machinery brake
is in the abnormal state.
11. A method for monitoring an operational state of a machinery brake of an
elevator, wherein the machinery brake comprises a frame part (120)
comprising an electromagnet and an armature part (110), the method
comprising:
- monitoring an output signal of an inductive proximity sensor that is mounted
to one of the following: the frame part (120), the armature part (110) wherein
the output signal is dependent on a mutual position of the inductive proximity
sensor and a target (124) mounted to the other of the following: the frame part
(120), armature part (110), and

- in response to detection that the output signal of the inductive proximity
sensor (122) is changed a control unit of the machinery brake is configured to
generate an alarm signal.