High-power illumination device for a camera

A high-power illumination device (2) integrated with a camera (1) for measuring the direction, distance and/or attitude of two objects relative to each other, one of the objects carrying the device. For obtaining a high-power emission several elementary light sources (10) are arranged in a ring configuration around the input-optical system (7) of the camera. The light beam emitted by each source is focused via a deflecting mirror (12) onto a facet mirror (13) surrounding the input-optical system (7) and comprising as many facets as there are light sources. Each facet is inclined so as to align the direction of the reflected beam with the direction of the field of view of the camera. The beams from these facets are thus quasi-superimposed around the optical axis of the camera.

BACKGROUND OF THE INVENTION 
The invention relates to a high-power illumination device integrated with a 
camera for measuring the direction, distance and/or attitude of two 
objects relative to each other. One of the objects carries the device, and 
the camera images the other object on a detector via an input-optical 
system. The device has a plurality of elementary sources each associated 
with an optical system for adjusting the field of view of each source to 
that of the input-optical system of the camera. 
A device of this type is used, for example, in encounters between two 
objects in space, one of which is referred to as the "hunter" which is to 
make contact with the other object referred to as the "target". 
It is necessary that the coupling between the two objects is established 
with the least possible mechanical shock at the instant of contact so that 
the orbital conditions of the target are not modified too much. 
For this purpose the hunter must take the theoretical orbit of the target 
into account at a sufficiently early moment in order to contact it at the 
right speed and particularly at the right attitude. 
This requires equipment installed in the hunter and measuring the distance 
between the hunter and the target (for the final approach they may take up 
positions at, for example 200 m) the direction of the target with respect 
to the reference mark of the hunter and the attitude of the target with 
respect to this mark. 
This equipment comprises a camera provided with a radiation emitter 
emitting a certain cone of radiation along the same axis and in the same 
field as that of the camera, which cone is projected onto the target on 
which retroreflectors have been disposed, i.e. small mirrors having three 
faces (or corner tubes) which return the reflected beam along itself, 
independent of their position in space. 
A laser diodes commonly used as light emitter necessitate the use of an 
optical system for adapting the angle of the emitted cone to the field of 
view of the camera. 
For spatial encounters between two objects it is necessary to use an 
emitter which is sufficiently powerful so that the luminous flux coming 
from the retroreflectors and impinging upon the camera is stronger than 
that emitted by the sun. 
Consequently, several elementary sources each comprising a laser diode and 
a optical system must be used for enhancing the power of the emitter to a 
considerable extent. It is difficult to arrange these sources in a very 
small space and such that they emit in one and the same cone. 
SUMMARY OF THE INVENTION 
The object of the invention is to mitigate this difficulty and to provide a 
device wherein the fluxes of several elementary sources are coupled 
adequately and the high power of the emission thus realized can be 
modulated, which device moreover has some over-power of emission so that 
breakdown of one or several of the sources is not detrimental. 
The elementary sources are regularly spaced in a ring configuration around 
the pupil of the input-optical system, the light beam from the optical 
system of each source being focused via a deflecting mirror arranged 
opposite each source onto a facet mirror surrounding the pupil of the 
input-optical system. The mirror has as many facets as there are light 
sources, each facet being inclined so as to align the direction of the 
reflected beam with the direction of the field of view of the camera in 
such a way that the light beams from the mirror facets are 
quasi-superimposed all around the optical axis of the camera.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The distance, direction and relative attitude measurements between two 
objects can be realized by means of the device the principle of which is 
shown in FIG. 1. 
One of the objects carries the camera 1 equipped with its illuminator 2 and 
the other object carries three regularly spaced non-coplanar 
retroreflector patterns 3, 4 and 5 in the emission cone 6 of the 
illuminator. 
The parts of the beams reflected along themselves by the retroreflector 
patterns are indicated by lines on which arrows in opposite directions 
have been indicated. 
The retroflectors 3 and 4 are separated by a distance d. 
The retroflectors 5 is shifted by h with respect to the reflectors 3 and 4. 
The camera measures the angular direction of the reflectors 3, 4 and 5. 
The angular information of the central point provided by 
##EQU1## 
provides the direction of the retroreflector, thus the direction of the 
object carrying the retroreflectors. 
The distance between camera and retroreflector patterns is provided by 
measuring the angle at which the distance d from the camera is viewed. 
The relative attitude between the two objects can be determined by the 
angular space between the retroreflector 5 and the virtual central point 
of the distance d separating the patterns 3 and 4. 
A longitudinal section of the illumination device according to the 
invention is shown diagrammatically in FIG. 2 illustrating the optical 
head of a camera for a spatial encounter. 
The input-optical system of the camera 1 comprises the entrance pupil 7 and 
the optical filter 8 which focus the image of the scene on a detector 9 
comprising, for example a charge-coupled device the temperature of which 
is kept for example at 20.degree..+-.3.degree. by means of for example a 
Peltier element. 
The illumination device 2 according to the invention is arranged in front 
of the camera 1 and its principle is to image of emissive surfaces of an 
assembly of laser diodes onto a mirror having facets which are concentric 
with the optical system of the camera. This principle has the advantage 
that all direct light diffusion in the said optical system of the camera 
is avoided. 
The device according to the invention comprises N elementary sources 10 
(continuous wave laser diodes or pulsed laser diodes) spaced in a ring 
configuration around the entrance pupil 7 of the optical system of the 
camera. For each source 10 an optical system 11 operating with an 
elementary source is provided for adapting the emission field to the 
desired field of view. The light beam emitted by the optical system 11 is 
focused by means of a deflecting mirror 12 arranged opposite each source 
onto a mirror 13 having N facets surrounding the entrance pupil 7 of the 
camera. Each facet of this mirror is inclined so as to return the beam of 
the corresponding elementary source in a direction which is aligned with 
the direction of the field of view of the camera. 
The light beams are thus quasi-concentric with the optical axis of the 
camera. 
Moreover, no high-power light beam impinges on the optical components 
(entrance pupil, filter) or traverses them in the path of the field of 
view of the camera, which diminishes the risks of diffusion and thus the 
risks of direct injection of parasitic light. 
Modulation of the emission level becomes possible by using 1 to N 
elementary sources. 
With this illumination device strong luminous fluxes can be generated 
ensuring a correct operation of the camera, even in a very bright 
atmosphere, (such as sun-radiation in the field of view when the camera is 
used for spatial encounters or in very luminous environments in robot 
applications). The illumination device according to the present 
application can also be used in vision systems for robots and generally in 
all applications wherein a combination of a camera and an illumination 
device is used.