Device for optically detecting position and/or orientation of objects and
associated detection methods
The present invention relates to the field of devices for optically
detecting the position and orientation of objects in space. It applies more
particularly to the aeronautical field where, in this case, the object detected is
a pilot's headset.
The detemnination of the positioning of a point in space and the
determination of the attitude of any object are problems that affect many
technical fields.
The various solutions generally provided have to eliminate any
position or attitude ambiguity, respond to a more or less stringent dynamic of
the systems and provide a high accuracy, in particular in the aeronautical
field.
In the systems for detecting position and attitude of objects in
space that provide an accuracy of a few millimeters in position and a degree
in attitude, there are many applications in various fields.
These systems are used in aeronautics, to detect head posture,
notably for the headsets of fighter airplanes, military, civilian or para-civilian
helicopters. In the latter para-civilian application case, it may relate to
offshore rescue missions for example. They are also used for the detection of
simulation headsets, this detection can then be combined with an oculometry
device, also called eyetracker, to detect the position of the look. In the field of
virtual reality and games, there are also many applications for these systems.
More generally, in the field of generic posture detection, there are
also many applications, notably in the medical field for teleoperations and
instrument monitoring, in the field of position monitoring for servo-controlled
machine tools or remote control, and finally for cinema, in order to reproduce
movements in synthesis images.
These various applications have technical solutions that meet
more or less stringent requirements.
Regarding applications with low constraints, notably in terms of
accuracy, there are various systems for detecting position and/or orientation
of objects.
For example, devices with camera-based patch or form
recognition use drawings printed on an object. A number of cameras observe
the scene and detennine the spatial configuration of the observed drawing.
There are also devices with camera-based sphere recognition,
which are used, for example in the cinema, to reconstruct human movement.
The device uses a number of cameras which observe reflecting spheres and
determine their trajectory.
Finally, there are ultrasound positioning devices that rely on the
principle of triangulation between ultrasound emitters and receivers.
Concerning more powerful applications, in particular in the
aeronautical field, the devices for detecting posture of headsets in aircraft
use two main techniques which are electromagnetic posture detection and
electro-optical posture detection.
Electromagnetic posture detection requires devices comprising
means of emitting an electromagnetic field and receiving sensors on the
headset making it possible to determine their position relative to the emitter.
Electro-optical posture detection generally requires motifs of lightemitting
diodes, also called LEDs, positioned on the headset and a number
of camera-type sensors mounted in the cockpit making it possible to
determine the spatial configuration of an LED motif.
To improve perfomiance, it is commonplace to combine other
devices comprising sensors of gyroscopic, accelerometric or magneto-metric
types. This hybridization of sensors makes it possible to improve the dynamic
performance characteristics or eliminate an orientation ambiguity. These
sensors do not modify the static positioning performance characteristics of
the detection devices cited previously.
However, these solutions have a certain number of drawbacks and
limitations, particularly in the aeronautical field.
Regarding the electro-optical devices, the map of the cockpit or
more generally the topology of the area containing the object must be known.
In aeronautics, this topology can be subject to deformations or be difficult to
map.
Moreover, these same devices require a number of cameras and a
number of sensors. The position calculations demand numerous resources
and the real-time analysis is complex to implement.
Furthermore, the diffusion in the detection area of the light from
the LEDs does not make it possible to completely overcome the disturbances
from the light environment of the cockpit due to the sun or to spurious
reflections on the canopy.
Regarding the electromagnetic posture detection devices, robust
solutions are difficult to implement.
In particular, in the aeronautical field, spurious radiations and
electromagnetic disturbances can degrade the performance characteristics of
the existing systems.
The inventive device makes it possible notably to overcome the
abovementioned drawbacks. In practice, the device is of the electro-optical
type. It provides a way of overcoming the drawbacks of the electromagnetic
devices.
Also, it preferably uses image projection means of the holographic
video projector type.
In particular, monochromatic holographic video projectors have the
advantages of emitting, in a very narrow frequency band, a clear image in a
wide field and of making it possible to concentrate a high energy in a very
small area. It is very easy to discriminate the signal originating from the
holographic video projector from the spurious light.
Specifically, the device according to the invention includes electrooptical
sensors positioned on the object and distributed in groups, called
clusters, analysis and computation means making it possible to find the
position and/or the attitude of the object, electronic image generation means
and optical projection means comprising a display and a projection optic.
The optical projection means emit, in a projection cone, a clear
image at any point of the travel range in which the object can move. The
analysis of the portions of images received by the sensors of at least one
cluster make it possible to identify the position and/or the attitude of the
object in the frame of reference defined by the projection means, the latter
comprising a plane perpendicular to the projection axis, called image plane,
and the projection axis.
Advantageously, the projection means are a holographic video
projector. The latter comprises a coherent light source, a display making it
possible to produce a phase image, the projection optic then being arranged
so as to create, from the wave emitted by the light source, a first reference
wave and a second wave modulated by the display and comprising means
making it possible to make these two waves interact.
Furthermore, this holographic video projector can project images
in a solid angle of 10 degrees minimum to 120 degrees maximum and can
reach a projection speed of at least 24 images per second.
The light source of such a holographic video projector can be
monochromatic and emit in a frequency band in the infra-red or near-infra-red
band, the sensitivity of the sensors being adapted to the emitted radiation.
Advantageously, the projected images can be polarized.
Moreover, any type of image can be generated by such a holographic video
projector including patterns occupying all or part of the image and comprising
light motifs of constant intensity.
As an example, these patterns consist of light motifs, the form of
which can be horizontal and/or vertical bars or even circle or concentric rings,
each ring being able to alternately consist of dark and bright angular parts,
the number of angular portions varying from one ring to the next ring.
Any type of combination of patterns is possible in the image
generated by the holographic video projector.
The inventive device uses light, matrix or unit length sensors. The
latter can be positioned in groups, also called clusters, having geometric
forms adapted to increase the performance characteristics of the device and
reduce the computation times.
For example, groups of three sensors can be arranged in star fomri
or in parallelogram form in the inventive device
The electro-optical sensors and the analysis means can
advantageous interpret and/or discriminate the polarization of the received
signals.
Advantageously, a first method of optically detecting the position
and the orientation of an object in space by means of the inventive detection
device comprises:
• a first step of generation by the holographic video projector
of a succession of images, all different, each image giving a
different signal on at least one cluster;
• a second step of analysis of the signals received by the
sensors of the cluster making it possible to find the position
and/or the attitude of the sensors in space without a priori
indication.
Advantageously, a second method of optically detecting the
position and the orientation of an object in space by means of the inventive
device comprises:
• a first step of generation of an image comprising light motifs,
said motifs being generated so as to illuminate the clusters;
• a second step of analysis of the signals received by the
sensors making it possible to find the position of the sensors
in space;
• finally, a third servo-control step making it possible to
reposition the motifs of the image generated on the clusters.
Advantageously, a first method combining the two preceding
abovementioned methods comprises an initialization step performed
according to the first method and an operating step corresponding to the
second method.
Other features and advantages of the invention will become
apparent from the following description, given in light of the appended
drawings which represent:
• figure 1, the general device according to the invention in 3D
view;
• figure 2, two position patterns and one roll pattern;
• figure 3, the projection of a position pattern on a cluster;
• figure 4, is an exemplary sequence of patterns projected on a
star-configuration cluster;
• figure 5, is a representation of the combination of patterns
according to figure 4 projected in succession.
In the description that follows, the device described is used for
aeronautical applications where the object is a pilot's headset. Obviously, it is
possible to adapt the device, with no major modification, to the detection of
other objects.
As indicated in figure 1, the inventive device comprises an image
projector 1. Said image projector emits an image 3, in focus in the entire area
4, comprising a set of patterns 7. The patterns are projected onto sets of
electro-optical sensors 6 situated on the object 5. A pattern is a set of
geometrical light motifs on a black background. These patterns can be
circles, rings, bars or a noteworthy geometrical form. The set of sensors is
called a cluster. These sensors can be grouped in such a way that the cluster
has geometrical properties for detection. In order to find the position and the
orientation of the clusters in space, the inventive device comprises means of
analyzing the data obtained from the sensors. The position and the
orientation, of at least one cluster, being determined, the position and the
orientation of the object are then known.
For the device to be able to operate correctly, it is essential for the
motifs of the patterns to be clear at all points of the sensors. There are
various optical means that make it possible to obtain this property.
To this end, an exemplary embodiment of the invention uses as
projection means a holographic video projector 1. Such holographic video
projectors are produced and marketed, for example, by the company Light
Blue Optics and are known by the brand name PVPro. This holographic
video projector has the advantageous property of emitting a clear image at
any point of the travel range 8.
This holographic video projector comprises a coherent light
source, which is generally a laser diode, a display making it possible to
produce a phase image, optical means arranged so as to create, from the
wave emitted by the light source, a first reference wave and a second wave
modulated by the display and means making it possible to make two waves
interact. The final image obtained is a Fraunhofer hologram of the phase
image generated on the display. It is possible to generate any type of image
by this means. The display can be a liquid crystal display, for example of
LCOS type.
The image 3 generated by the holographic video projector consists
of patterns 7 which can be patterns located on a sensor, called position
patterns or roll patterns, or patterns that can cover all of the field, thus
occupying all of the image or a large part thereof. The patterns can be
emitted sequentially in time, the motifs that make up the pattern being able to
change or remain identical between two successive emissions.
The device of figure 1 shows an example of clusters 6, each
consisting of three sensors, arranged in stars. Each of the clusters is
contained in a plane on the surface of the object 5. The sensors can, for
example, be unit length matrix sensors.
Patterns generated in this way by the holographic video projector
are projected locally on the planes of a sufficient number of clusters of the
object. Each cell of each electro-optical sensor that is a part of a cluster
detects the presence of the light signals obtained from the pattern. These
signals are sent to the computer for analysis.
The size of the patterns and the form and the number of the
sensors are optimized data dependent on the travel space and the form and
the volume of the object as well as the desired accuracy. The number of
clusters and the positioning and the number of patterns can be sufficient for
the projection of the patterns to reach a sufficient number of clusters making
it possible to find the position of the object from the analysis means 2. The
analysis means are generally an electronic computer.
The device has various operating modes. A first operating mode is
a servo-controlled mode. The determination of the position and the
orientation of the clusters or of the object in space depends on a position and
an orientation that are known a priori from a recent past and estimated at the
moment of projection, the generated patterns being emitted in the direction of
said clusters.
In this mode, the computer 2 analyzes the positions and the
orientations of one or more clusters. This computer, based on these data,
servo-controlled the position of the patterns projected by the holographic
video projector. To this end, the estimated position and orientation of the
clusters in space are used to detemriine the next position of the patterns to be
projected in the image plane.
Figure 2 represents an example of patterns used in this first
operating mode. Two position patterns 22 and 23 and one roll pattern 21 are
represented within the area 20 delimited by the part of the object that is
visible from the projector, this area being represented by a circle. These
three patterns are local, in other words, they are centered around a cluster.
The position pattern 22 is an exemplary pattern having a single
light ring. Some cells of a sensor of the cluster 24 receive light and supply the
computer with information with which to easily estimate, by construction, the
position of the cluster in the light ring.
The position pattern 23 is another exemplary pattern having
8
several light rings. In the same way, the computer is capable, based on the
information from each cell of each sensor, of restoring the position of the
cluster in the light rings.
The pattern 21 is an exemplary roll pattern. The latter comprises
various concentric rings, each ring comprising light and dark angular portions
of constant width, positioned in such a way that, over the width of a portion,
the sequence fomned by all of the portions on a radius are unique. The
angular position, that is, the orientation, is deduced by analyzing the
information collected from each sensor of the cluster.
Figure 3 represents an exemplary position pattern and a cluster on
the same plane. The servo-control of the patterns projected by the video
projector makes it possible to situate the pattern 31 locally around the cluster

Each cell of each sensor 30 restores to the computer the
information from the signal received on the computer. From the distribution of
the light on the sensor, the computer can, by construction, estimate the
position of the cluster in the image plane. In practice, the generation of the
patterns, and the estimation of the position and/or attitude parameters, takes
account of the corrections of defonnation linked to the projection.
The projection speed of the images generated by the holographic
projector must be faster than the travel speed of the object.
To this end, the holographic video projector is capable of emitting
a series of images at the speed of 24 images per second. This speed is
sufficient to emit two successive patterns on at least one cluster.
In another operating mode, it is necessary to find the position and
the orientation of the object, that is, without knowing the initial position and
orientation of the object beforehand.
One means, using the holographic video projector, of estimating
the position of the object in the travel range, is to emit a sequence of patterns
in a sufficiently short time. On each projection, a single pattern entirely
occupies all or a large part of the generated image. Moreover, between two
successive projections, the light motifs of these patterns are different.
The analysis of the signals received from each cell of each sensor
throughout the sequence makes it possible to calculate the position of the
sensors in space.
Figure 4 shows an example of circular patterns 42 and 44, the
motifs of which are light bands alternately separated by dark bands,
respectively vertical and horizontal.
A first row of patterns represents a particular sequence of patterns
with motifs that are straight vertical bands. This sequence of images is
generated in a time 43. The analysis of the sequence of signals received in a
cell makes it possible to calculate the vertical position of each cell in the
pattern.
A second row of patterns represents another sequence of patterns
with motifs that are straight horizontal bands. This sequence of images is
generated in a second time 43. The analysis of the sequence of signals
received in a cell makes it possible to calculate the horizontal position of
each cell in the pattern.
The entire sequence of images consists of the two preceding
sequences. These sequences of images can, for example, be generated in
succession. Each image can alternately comprise a pattern with horizontal
bands and the next with vertical bands.
The cluster 40 is represented in the plane of the pattern, called
image plane, said cluster is exposed to the light signals of the motifs of each
pattern. The principle is to emit, in a time 43, a sequence of patterns 42, each
exposed for a time interval 41. The width of the bands and the pitch between
the bands that make up each pattern are increasingly small. They can
diminish by a factor of two between each projection, for example.
Figure 5 represents an exemplary representation of a compilation
52 of patterns 42 comprising light vertical bands and another representation
of a compilation 54 of patterns 44 comprising light horizontal bands. The
compilation of patterns comprising vertical bands represents the succession
of light or dark signals received by a cell of a sensor when it is located in the
band 55 during the time interval 41. The sequence of signals received in the
time 43 is analyzed. By construction, the horizontal position of the cell in the
pattern is deduced.
In the same way, the cell interprets its vertical position when it is
located in the band 56 of the compilation of patterns 54.
To eliminate any position ambiguity on the projection of the first
image on the sensors, that is, to differentiate the case of a signal received by

the cell from a dark fringe and the case where no signal is received, it is
necessary for the light bands of the first two patterns projected to be of the
same size and alternate.
Advantageously, a binary coding can be used for the analysis of
these signals. In the case of a signal obtained from a light fringe, the cell
interprets a bit of value equal to 1, othenwise it interprets a bit of value equal
too.
Since the bands diminish from one projection to the next in one
and the same sequence, the high-order bits are interpreted at the start of the
sequence. The information concerning the accuracy of the vertical and/or
horizontal position is interpreted at the end of the sequence, by the low-order
bits.
Such sequences of patterns, associated with this type of binary
coding of the receiving signal, make it possible to directly determine the
vertical and, respectively, horizontal position of a cell of a sensor in the
pattern.
The accuracy of the position of a cell of a sensor is determined to
within the error of the width of the light or dark band of the last projected
pattern of the sequence.
Generally, any unambiguous image or series of images can be
used as a means of determining the initial position.
The two operating modes, servo-controlled and absolute, can be
combined. On initializing or reinitializing the detection of the object, that is,
when the position of the object is not known, the position and the orientation
of the object can be detemriined by the second detection mode. Then,
secondly, the position and the orientation being detemnined by the detection
initialization step, a servo-controlled mode detection step begins. The second
step proceeds independently until the detection is deliberately interrupted or
until the position of the object is lost. In the latter case, the first step, that is,
the second operating mode, can be reactivated automatically or manually to
find the position of the object.
The benefit of using the servo-controlled mode is that it makes it
possible to generate a very limited number of patterns between two
measurements. Consequently, very fast measurement rates can be used.

CLAIMS
1. A device for optically detecting position and/or orientation of an object moving in a given travel range, said device comprising electro-optical sensors positioned on said object and distributed in groups, called clusters, analysis and computation means making it possible to identify the position and/or the attitude of said object, electronic image generation means and optical projection means comprising a display and a projection optic, characterized in that the optical projection means emit, in a projection cone, a clear image at any point of the travel range, the analysis of the signals received by the sensors of at least one cluster making it possible to identify the position and/or the attitude of the object in the frame of reference defined by the projection means, the latter comprising a plane perpendicular to the projection axis, called image plane, and the projection axis.
2. The detection device as claimed in claim 1, characterized in that the image projection means are a holographic video projector, said holographic video projector comprising a coherent light source, a display making it possible to produce a phase image, the projection optic being arranged to create, from the wave emitted by the light source, a first reference wave and a second wave modulated by the display and comprising means making it possible to cause these two waves to interact.
3. The detection device as claimed in claim 2, characterized in that the projection means project in a solid angle of 10 degrees minimum to 120 degrees maximum.
4. The detection device as claimed in either of claims 2 or 3, characterized in that the projection means generates the images at the speed of at least twenty-four images per second.
5. The detection device as claimed in any one of claims 2, 3 or 4, characterized in that the projection means generates polarized images.
6. The detection device as claimed in any one of claims 5, characterized in that the electro-optical sensors and the analysis means interpret and/or discriminate the polarization of the received signals.
7. The detection device as claimed in any one of claims 2, 3, 4, 5 or 6, characterized in that the images projected in the image plane by the projection means comprise a set of patterns, the patterns consisting of light motifs.
8. The detection device as claimed in claim 7, characterized in that the patterns consist of motifs of constant light intensity.
9. The detection device as claimed in either of claims 7 or 8, characterized in that the light source is monochromatic and emits in a frequency band in the infra-red or near-infra-red band, the sensitivity of the sensors being adapted to the emitted radiation.
10. The detection device as claimed in any one of claims 7, 8 or 9, characterized in that at least one pattern consists of concentric light motifs, said pattern being a position detection pattern.
11. The detection device as claimed in any one of claims 7, 8 or 9, characterized in that at least one pattern consists of concentric rings, each ring alternately consisting of dark and bright angular parts, the number of angular portions varying from one ring to the next ring, said pattern being a roll detection pattern.
12. The detection device as claimed in any one of claims 7, 8, 9, 10 or 11, characterized in that the image comprises two position detection patterns and one roll detection pattern.
13. The detection device as claimed in any one of claims 7, 8 or 9, characterized in that a single projected pattern occupying all or part of the image consists of motifs, the form of which is a series of alternately dark and light parallel bands.
14. The detection device as claimed in claim 13, characterized in that the bands are of identical width, the pitch separating two successive bands being constant.
15. The detection device as claimed in claim 13, characterized in that a series of patterns are projected successively in time with motifs, the pitch and width of which change on each generated image.
16. The detection device as claimed in claim 13, characterized in that the size of the band and of the pitch reduces by a factor of 2 between two successive projections.
17. The detection device as claimed in claim 1, characterized in that the sensors are matrix, unit length or light sensors.
18. The object position detection device as claimed in claim 17, characterized in that the topology of the sensors, on the object, comprises a number of clusters of sensors, each cluster having a flat form consisting of three star-configuration branches.
19. The object position detection device as claimed in claim 17, characterized in that the topology of the sensors, on the object, consists of a number of clusters of sensors, each cluster having a parallelepipedal flat form.
20. The detection device as claimed in any one of the preceding claims, characterized in that the object is a headset and the travel range is a part of the cockpit.
21. A method of optically detecting the position and the orientation of an object in space by means of a detection device as claimed in any one of claims 13, 14, 15 or 16, characterized in that said method comprises a first step of generation by the holographic video projector of a succession of images, all different, each image giving a different signal on at least one cluster and a second step of analysis of the
signals received by the sensors of the cluster making it possible to find the position and/or the attitude of the sensors in space without a priori indication.
22. The method of optically detecting the position and the orientation of
an object in space by means of a device as claimed in any one of
claims 7, 8, 9,10, 11 or 12, characterized in that it comprises:
o a first step of generation of an image comprising light motifs,
said motifs being generated so as to illuminate the clusters; o a second step of analysis of the signals received by the
sensors making it possible to find the position of the sensors
in space; © finally, a third servo-control step making it possible to
reposition the motifs of the image generated on the clusters.
23. The method of optically detecting the position of an object,
characterized in that it comprises an initialization step performed
according to the method of claim 21 and an operating step
corresponding to the method as claimed in claim 22.