GB2285193A

GB2285193A - Infrared panoramic watching device adjustable in elevation

Info

Publication number: GB2285193A
Application number: GB9425699A
Authority: GB
Inventors: Jacques Rioland; Bertrand Remy; Jean-Francois Boivin
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1993-12-23
Filing date: 1994-12-20
Publication date: 1995-06-28
Anticipated expiration: 2014-12-20
Also published as: FR2714479A1; GB2285193B; GB9425699D0; FR2714479B1

Abstract

The panoramic watching device enables a coverage adjustable in elevation without requiring an electric rotating joint for the transmission of the control signals. The device comprises, on a fixed frame (14), a focusing objective (8) to form an image of the observed zone on a detection array (10) and, on a movable structure (2),a mirror (1) tiltable up and down by a motor (21) and a position sensor (19). According to the invention, the motor (21) and the position sensor (19) are controlled by signals transmitted by light sources (29, 27) associated with optical receivers (28, 30). An electrical accumulator (25) that supplies electricity to the movable structure (2) is recharged by a generator (26) mounted on the movable structure and having a shaft rotationally driven by linkage means (33, 34) positioned between the fixed frame (14) and the movable structure (2). Application to the detection aerial targets. <IMAGE>

Description

INFRARED PANORAMIC WATCHING DEVICE WITH ANGULAR COVERAGE ADJUSTABLE IN ELEVATION The field of the invention is that of infrared panoramic watching designed for the totally passive detection of targets, generally aerial targets. The term "passive detection" is understood to mean a type of detection which, unlike radar type detection, does not use the transmission of electromagnetic waves to detect the targets. Infrared watching enables the detection of the- radiation emitted by the targets in the range of wavelengths of atmospheric transmission, extending conventionally from 3 to 5 micrometers or from 8 to 12 micrometers.

The object of the invention relates to an infrared watching device with a panoramic angular coverage in relative bearing, namely with a 360-degree angular coverage and with angular coverage that is adjustable in elevation.

Known infrared panoramic watching devices associate a focusing objective on an array of photodetectors coupled with a signal reading circuit, this assembly being placed on a rotating plate driven in a rotation that is uniform in relative bearing. The array of photodetectors is placed along a direction close to the vertical.

The angular coverage in elevation of infrared panoramic watching devices is determined by the length of the array of photodetectors placed at the focal point of the focusing objective. Now, an array of infrared photodetectors has a limited length because of technological problems of manufacture. The result thereof is a limitation to about 5% to 10 of the field covered in elevation.

A conventional way of enabling the detection of aerial targets with higher elevation is to place a plane optical mirror, adjustable in elevation, on the plate rotating in elevation so as to obtain a panoramic angular coverage with adjustable elevation. This approach has the drawback of requiring an electric rotating joint to transmit the electrical signals for the excitation of the motor driving the optical mirror in elevation, between the fixed part of the watching device in which there is located the electronic circuitry generating said signals and the part rotating in relative bearing on which the motor is placed.

To overcome this drawback and preserve the possibility of adjustment in elevation, the invention proposes the use, at the rotating part, of an accumulator type device for the storage of electrical energy: this device is constantly recharged during the rotation in relative bearing by means of an electrical generator and provides for the supply of the motor and its electronic circuitry. The transmission of the control signals for the motor and the copying signals between the fixed part and the rotating part may then be done by means of optical sources, for example lightemitting diodes or lasers modulated and associated with adapted optical receivers.

More specifically, the object of the invention relates to an infrared panoramic watching device with angular coverage adjustable in elevation, comprising, on a fixed frame, a focusing objective with an optical axis placed along a relative bearing axis to form, on a photodetector array, an image of a zone observed by the device in the vicinity of a line of sight oriented in elevation and, on a mechanical structure rotationally movable about the relative bearing axis, a reflective element for the orientation, by reflection, of the line of sight, a motor for the orientation in elevation of said reflecting element and a device to encode the position of this element, characterised in that the orientation motor and the encoding device are controlled by signals transmitted by at least one light source associated with at least one optical receiver and wherein a device for the storage of electrical energy, fixedly joined to the movable structure, supplies electricity to the movable structure, the storage device being recharged by means of an electrical generator having a a shaft rotationally driven by means of mechanical linkage between the fixed frame and the movable structure.

According to a particular embodiment, an accumulator is permanently recharged by a generator rotationally driven by a friction device or gears.

The invention will be understood more clearly from other particular embodiments, and other advantages shall appear from the following description accompanied by the appended drawings, of which: - Figure 1 shows an infrared panoramic watching device according to the prior art; - Figure 2 shows an infrared panoramic watching device with an elevation-steering mirror according to the prior art; - Figure 3 exemplifies a watching device in which the invention is embodied; - Figure 4 is a drawing showing an arrangement of the means for the transmission of signals to control the elevation-steering motor of a particular embodiment of of the watching device of Figure 3; - Figure 5 shows a variant of the arrangement described in Figure 4;; - Figure 6 is a drawing showing a particular arn~W31nt of the means for the transmission of the signals from the elevation position sensors of the watdlng device of Fibre 3; - Figure 7 shows a particular embodiment of the coupling of the tranmrission/reception diodes of the watching device of Figure 3 by nans of semi-reflector plates.

In order to illustrate the technological background, Figure 1 shows a conventional infrared panoramic watching device whose angular coverage is not adjustable in elevation. This device is chiefly constituted by the following elements: - a head mirror 1 placed on a rotating plate 2.

This head mirror bends the incident optical beams F, coming from a scene to be observed, by 90'. The beams are thus directed along the relative bearing axis Z'Z towards the detection array 10; - an optical image erecting prism 3, used to compensate for the rotation of the image induced by the rotation in relative bearing of the head mirror 1 and thus constantly preserve a vertical field of view for the photodetection array 10 during the rotation of the mirror 1. This optical image erecting prism may be formed according-to known methods, for example by means of a so-called Taylor or Pechan optical prism.It is driven in uniform rotation by means of a set of bearings 6 by an annular motor 7 about the vertical axis ZZ' and has a rotation speed equal to half of the rotation speed of the mirror 1; - a focusing objective 8 with a vertical optical axis ZZ', positioned behind the image erecting prism 3 (which may also be placed between two lenses of the objective) that projects an image of the observed scene on the photodetection array 10.The array is associated with a circuit 11 for the multiplexing of the electrical signals given by each of the elementary photodetectors of the array; - a cryostat 13 cooled by means of a "cold finger" 12, the cryostat being closed by an optical window 9 transparent to infrared radiation, this window being positioned on the optical path between the objective 8 and the detector 10; - an electronic pre-processing circuit 15 coupled to the reading circuit 11 to filter, amplify and, as the case may be, digitise the signals that it receives; - an electronic extraction pack 16 enabling the detection and localising of the targets; ; - a fixed mechanical bearing structure forming a frame 14 on which there are fixed the objective 8, the set of constituent elements of the cryostat 13 and the electronic circuits 15 and 16, said frame bearing the external rings associated with the bearings 6 providing for the rotation of the image erecting prism 3 and the stator of the motor 7.

The plate 2 is driven in uniform rotation at about one or two rotations per second about the axis ZZ' by means of a set of bearings 4 by an annular motor 5 whose stator is fixedly joined to the fixed frame 14.

This rotational motion enables the analysis, by the array 10, of a 360" field in relative bearing. An angular position sensor 17 of the plate 2 is used to obtain knowledge at each instant, of the value of the relative bearing observed. In certain embodiments, the image erecting prism 3 will be driven at half-speed by means of a set of gears.

Figure 2 shows a development of the watching device According to the prior art enabling the orientation, along the elevation axis, of the panoramic field under watch. Indeed, especially in the case of aerial targets, it is often necessary to be able to centre the observed field at varying heights above the horizon.

This is not possible with the device described in Figure 1. To this end, there is provision for means for the shifting, in elevation, of the mirror 1 in order to orient the line of sight.

Figure 2 shows a view, along a projection plane perpendicular to Figure 1, of: - the mirror 1 associated in this example with two rotational half-shafts 201 and 202 enabling its rotation in elevation along an axis XX' perpendicular to the axis ZZ' (said axis XX' itself rotating in a horizontal plane with the movable plate 2 that bears it) by means of a set of bearings 181 and 182; - a motor 21 for the rotational driving of the mirror 1; - a sensor 19 of the angular position of the mirror 1 with respect to the mechanical structure 2; - a rotating joint with a fixed internal ring 221 and a movable external ring 222 that is fixedly joined to the structure 2.This rotating joint transmits the electrical power given by an electrical supply unit 24 and the control signals for the motor 21 coming from the control circuit 23 to the motor 21 and the position sensor 19. It also transmits the position signals from the unit 19 to the control circuit 23.

The presence of this electrical rotating joint introduces a major constraint as regards the designing of the watching device and, by the gradual wearing out of the electrical collectors permanently rubbing on the rings during the rotation of the unit 2, greatly reduces the reliability of the device.

The watching device that is an object of the invention can be used to overcome these problems by providing, firstly, for the transmission of the electrical control signals for the mirror used for the aiming and positioning of the line of sight by means of light sources and receivers and, secondly, for the presence in the movable plate 2 of a device for the storage of electrical energy coupled to an electrical generator rotationally driven by the rotating plate to give the energy to the electronic assemblies in rotation (motor, position sensor, light source, etc.).

Figure 3 shows a diagram giving a non-restrictive illustration of an exemplary embodiment of the invention seen in the same projection plane as in Figure 2. The elements described with respect to Figure 2 appear with the same references.

Figure 3 notably shows an electrical generator 26 placed on the rotating plate 2, the shaft of this electrical generator 26 being joined to a friction wheel or a toothed wheel 33 rotationally driven by a pinion 34 fixedly joined to the fixed frame 14. An electrical accumulator 25 is then recharged permanently by. the electrical generator 26 during the rotation of the plate 2, this accumulator giving the necessary energy to the elements carried by the rotating plate (motor, sensor, diode control circuits, etc.).

The control in elevation is achieved by a lightemitting diode 29, fixedly joined to the fixed frame 14 that emits encoded light pulses towards a receiver diode 28 which, for its part, is fixedly joined to the rotating plate 2. The diode 29 is driven by a set of control circuits 23 as a function of the desired angular position in elevation.

An electronic circuit 32 controls the motor 21 as a function of the instruction received by the receiver diode 28, this circuit being carried by the plate.

Another electronic circuit 31 receives the information elements relating to the angular position of the mirror 1, given by the positional sensor 19, and controlsa light-emitting diode 27 that is fixedly joined to the rotating plate 2.

A receiver diode 30, fixedly joined to the fixed frame 14, receives the encoded light pulses sent out by the diode 27 and a decoding circuit 35 prepares the position of the line of sight in elevation as a function of the information elements received by the diode 30.

This position of the line of sight may be used, for example, by the target extraction module 16 to give the co-ordinates, in terms of elevation, of the targets, the co-ordinates in relative bearing being obtained in a conventional way by a position sensor of the rotating plate 2 (such as the sensor 17 of Figure 1).

The position of the line of sight can also be compared to the instructed value given by the control circuits 23 in order to servo-control the position in elevation of the mirror 1 more efficiently.

In a particular embodiment of the invention which has the advantage of simplifying its implementation, the circuits 35, the emitter diode 27, its control circuit 31 and the receiver diode 30 are eliminated: the angular position of the mirror 1, given by the position sensor 19, is then directly compared with the instruction signal in the electronic circuit for the excitation of the motor 32. This approach has the advantage of great simplicity.

Furthermore, in order to obtain sure optical coupling between the emitting and receiving diodes (29 and 28; 27 and 30) during the rotation of the rotating plate 2, several particular embodiments are described here below.

Thus, Figure 4 shows a particular arrangement of the control diodes of the motor in a plane perpendicular to that of Figure 3 and going through the axis Z'Z. As illustrated by Figure 4, the receiver diode 28 is placed at the intersection of the axes XX' and ZZ' in a recess made in the centre of the mirror 1, and is fixed to said mirror. The emitter diode 29 is placed on the structure 14 outside the axis ZZ' and is positioned so the emission lobe Le of the diode 29 is inclined in relation to the axis ZZ', so as to be centred on the receiver diode 28, this centering being then kept by symmetry during the rotation of the plate 2.

Owing to the small size of the receiver diodes, the concealment of the infrared beam by the diode 28 is negligible. Furthermore, there is no disturbance in the infrared detector 10 related to the presence of the emitter diode because the wavelength emitted is very different and is not perceived by the detector 10 (for example about 0.8 micrometers while the detector 10 is conventionally sensitive to the radiation of wavelengths between 8 and 12 micrometers).

The reception diode 28 has a high angular field of reception because of the relative motion of rotation of the diode 29 in its field of reception during the deflection in elevation about the axis XX' of the mirror 1 bearing the diode 28.

As for the signals delivered by the diode 28 and intended for the electronic assembly 32 for the excitation of the motor, they may travel through a flexible wire Fs because the angular play of the mirror 1 is limited (in the range of + 20 in the example illustrated).

Another way to position the receiver diode 28 on the optical axis ZZ, shown in Figure 5, consists in the use of a mechanical support 37 fixedly joined to the assembly 2 to simplify the electrical link between the diode 28 and the excitation circuits 32 of the motor 21.

Figure 6 shows an approach that makes it possible to ensure the efficient operation of the position copying diodes, and that may be implemented independently of or simultaneously with the above approaches described with reference to Figures 4 and 5.

This Figure 6 shows the receiver diode 30 placed before the image erecting prism 3 on the optical axis ZZ' and held in relation to the frame 14 by means of a mechanical support 36. This support may be formed in a standard way by three or four radially tensed plates.

The transmission lobe L'e of the diode 27 also is also seen drawn schematically. The angular field of reception of the diode 30 should at least be equal to the half-angle cone at the summit 9 represented in the drawing.

Figure 7 illustrates another embodiment for the positioning of the control and copying diodes. A first semi-reflective plate 38 is fixed to the movable structure 2 in such a way that the normal to its surface forms an angle, for example approximately equal to 450 with the axis ZZ'. This plate is treated optically to reflect the radiation coming from the emitter diodes 27 and 29 and transmit the infrared radiation. A second plate 39 of the same type is placed before the objective 8 and is fixed into the structure 14 at one and the same angle of inclination, equal to about 45" in the exemplary embodiment illustrated.

Diodes 27 and 28 are placed side by side on the structure 2 and are oriented towards the centre of the plate 38. The diodes 29 and 30 are also placed side by side but on the fixed structure 14, and they are oriented towards the centre of the plate 39. Thus, the beam Fe sent out by the diode 27 is reflected in parallel to the axis ZZ' by the plate 38 and then reflected by the plate 39 towards the receiver diode 30. The principle is the same for the flux F'e emitted by the diode 29. The aperture of the beam is chosen so as to be sufficient to illuminate the receiver diodes which are not placed at the centre of the beams.

Furthermore, in order to prevent the reception of the diode 28 from being disturbed by the emission of the diode 27 and, similarly, the diode 30 from being disturbed by the emitter diode 29, the diodes 27 and 29 emit light fluxes at different wavelengths and passband optical filters 40, 41 are placed respectively before the receiver diodes 28 and 30. The filter 40 placed before the diode 28 is chosen so as to let through only the flux sent out by the emitter diode 29 and stop the flux sent out by the diode 27 and then back-reflected parasitically by the elements such as the plate 38.

The filter 41 placed before the receiver diode 30, in the same way, lets through only the flux emitted by the diode 27.

As a variant of this embodiment, the mirror 1 could advantageously be used as a semi-reflective plate instead of the semi-reflective plate 38. In this case, it is treated optically to reflect the infrared radiation towards the objective 8 and transmit the radiation coming from the diodes 27 and 29. The diodes 27 and 28, which are fixedly joined to the movable structure 2, are then placed in the vicinity of the axis ZZ' above the mirror 1 to let through the radiation of the diodes.

It is also possible to replace the two semireflective plates 38 and 39 by two small mirrors whose dimensions are chosen so as to produce a negligible concealment of the infrared beams and whose surface may diverge from a plane in order to ensure a more efficient illumination of the receiver diodes.

The invention is not limited to the means that have just been described for the transmission of information for the control of the motor of the head mirror and of the sensor. Other means are possible for transmitting the radiation emitted respectively by the diodes 27 and 29 to the receiver diodes 30 and 38 such as optical fibers placed axially or in a ring with respect to the fixed and movable structures. Light-scattering devices of the integrating sphere type, well known to those skilled in the art and capable of being arranged in rings so as not to disturb the reception of the infrared radiation by the objective 8, could also be used.

Claims

CLAIMS:

1. An infrared panoramic watching device with angular coverage adjustable in elevation, comprising, on a fixed frame , a focusing objective with an optical axis placed along a relative bearing axis to form, on a photodetector array t an image or a zone observed by the device in the vicinity of a line of sight oriented in elevation and, on a mechanical structure rotationally movable about the relative bearing axis, a reflective element for the orientation, by reflection, of the line of sight, a motor for the orientation in elevation of said reflecting element and a device to encode the position of this element, wherein the orientation motor and the encoding device are controlled by signals transmitted by at least one light source associated with at least one optical receiver and in that a device for the storage of electrical energy , fixedly joined to the movable structure , supplies electricity to the movable structure , the storage device being recharged by means of an electrical generator having a a shaft rotationally driven by means of mechanical linkage between the fixed frame and the movable structure

2. A device according to claim 1, wherein the generator has a shaft fixedly joined to a friction wheel or toothed wheel , rotationally driven by a pinion fixedly joined to the frame and in that the light sources and receivers are emitting diodes and receiving diodes.

3. A device according to any of the claims 1 and 2, wherein an emitter diode fixedly joined to fixed frame controls the adjustment in elevation of the reflective element by the emission of encoded pulses towards a receiver diode fixedly joined to the mobile structure , the emitter diode being controlled by an instruction given by control circuits fixedly joined to the fixed frame as a function of the desired elevation position, and the receiver diode transmitting this instruction to the control circuit of the motor fixedly joined to the movable structure

4.A device according to any of the foregoing claims, wherein an electronic circuit fixedly joined to the movable structure receives information elements pertaining to the angular position of the reflective element given by a position sensor and controls the emission of pulses encoded by a light-emitting diode fixedly joined to the movable structure towards a receiver diode fixedly joined to the fixed frame coupled to a circuit for decoding the position of the line of sight as a function of the information elements received by the diode

5. A device according to any of the claims 1 to 3, wherein the angular position of the reflective element given by a position sensor is compared directly with the instruction signal at the level of the control circuit of the motor

6.A device according to claim 3, wherein the receiver diode is placed substantially at the intersection of the elevation and relative bearing axes in a recess made in the reflective element , in that the emitter diode is positioned on the frame so that the emitted light flux has a lobe that is inclined with respect to the relative bearing axis to be centered on the receiver diode and in that a flexible conductor provides for the coupling between the receiver diode and the excitation circuit of the motor.

7. A device according to claim 3, wherein the receiver diode is positioned on the relative bearing axis by means of a mechanical support fixedly joined to the movable structure and in that the emitter diode is positioned on the frame so that the emitted flux has a lobe inclined so as to be centered on the receiver diode

8. A device according to claim 4, wherein the receiver diode is placed on the relative bearing axis by means of a support and in that the emitter diode is positioned on the movable structure so that the emitted flux has an inclined lobe to be centered on the receiver diode

9.A device according to the claim 3 or claim 4, wherein a first semi-reflective plate fixedly joined to the movable structure is positioned so as to be inclined on the bearing axis and is processed to reflect the luminous flux emitted by the emitter diodes and a second semi-reflective plate is positioned on the relative bearing axis along one and the same angle of inclination, so as to optically conjugate the diodes fixedly joined to the mobile structure and the diodes fixedly joined to the fixed frame by means of plates

10. A device according to claim 9, wherein the diodes fixedly joined to the mobile structure and to the fixed frame are positioned side by side and are oriented approximately towards the center of the corresponding plate and in that the plates are inclined substantially at 45 with respect to the relative bearing axis

11.A device according to claim 10, wherein with the emitter diodes emitting at different wavelengths, the passband optical filters are placed before the receiver diodes to let through only the flux emitted by the respectively associated emitter diode

12. A device according to claim 9, wherein the reflective element is used, after optical processing, as a semi-reflective plate to reflect the infrared flux towards the photodetective array and transmit the flux emitted by the emitter diodes the diodes fixedly joined to the movable structure being placed above the reflective element.

13. A device according to one of claims 3 and II, wherein the emitter diodes and the- receiver diodes are conjugated by means of optical fibers configured axially in the form of rings, facing the fixed and movable structures.

14. An infrared panoramic watching device with angular coverage adjustable in elevation, substantially as described hereinbefore with reference to Figures 3 to 7 of the accompanying drawings and as shown in Figure 3, or in Figure 3 and one of Figures 4, 5 and 7, or in Figures 3 and 6 with one of Figures 4, 5 and 7.