GB2041685A

GB2041685A - Means for automatically controlling a beam of electromagnetic radiation

Info

Publication number: GB2041685A
Application number: GB7941892A
Authority: GB
Original assignee: Diehl GmbH and Co
Current assignee: Diehl Verwaltungs Stiftung
Priority date: 1978-12-13
Filing date: 1979-12-04
Publication date: 1980-09-10
Also published as: FR2444281A1; FR2444281B1; DE2853695C2; DE2853695A1; GB2041685B

Abstract

Automatic beam-controlling means has an aiming device controlled, as a function of a reflected laser signal, so that a laser beam remains constantly directed at a target object 15, said aiming device comprising optically- pervious bodies, 2,3, which are variable in their diffraction behaviour, (preferably acousto-optical defectors), and, in addition to an electronic evaluation circuit 7 for registering the reflected laser signal, a control circuit 9, 10, 11, and a switching unit 8 connecting the aiming device to the control and evaluation circuits. The evaluation of the laser signal is effected preferably by phase- sensitive detectors. The apparatus is suitable for guiding steerable flying bodies. If initially the beam does not detect body 15, the beam is controlled, via a first component 9 of the control circuit so that it scans a predetermined region until it detects body 15. A second component 10,11 generates A.C. voltage signals for modulating the beam. <IMAGE>

Description

SPECIFICATION Means for automatically controlling a beam of electromagnetic radiation This invention relates to means for automatically controlling a beam of electromagnetic radiation.

There is described herein means for automatically readjusting a laser beam to be reflected by a moving target object, more especially for an arrangement for detecting and tracking rapidly-moving objects, of that kind having a receiver which picks up part of the laser light reflected by the target object and which supplies a reception signal, an aiming device which is arranged in a laser beam and which has two separately-controllable deflection units, and an electronic evaluation circuit which acts on the aiming device and which is able to produce, from the reception signal, readjustment signals for adjusting the aiming device, in such a way that a laser beam remains constantly aimed at the target object.

Means of said kind is known from German Offenlegungsschrift No. 27 57585. In the case of this known arrangement, the aiming device consists of a hingedly-mounted mirror which is carried by two piezo columns as supports. The change in length of the piezo columns which is brought about by the readjustment signals leads, in this respect, to swinging motions of the mirror and thus to a change in direction of the laser beam and to its readjustment thereby brought about.

By virtue of the relatively-small achievable change in length of the piezo columns and the accordingly severely-restricted mobility of the mirror, the range of application of this known device is, however, restricted to objects which vary their position with respect to the readjustment means only slightly.

Thus, this known means is, for example, suitable for registering long-term variations on buildings.

In order, nevertheless, to be able to pursue also moving target objects with this known means, the means must additionally be provided with mechanical aids, which ensure a readjustment or following of the laser beam over a larger angular region. For this purpose it is, for example, known to mount readjustment means, of the kind described at the beginning hereof, on a turntable. The readjustment means then serves, in this case, merely additionally to compensate for the aiming errors of the mechanical arrangement.

Readjustment means modified in this way is, for example, suitable for tracking the trajectory of satellites, in other words of target objects which carry out, for the observer, a relatively uniform and constant motion. The readjustment speed of the laser beam is, in this respect, severely restricted on account of the relatively large masses that are to be moved, so that it is not possible to sweep a fairly large solid-angle region in an extremely short time with a laser beam controlled by such an arrangement.

However, this is necessary if it is desired to track rapidly-moving target objects with a means of the kind described at the beginning hereof and more especially also to detect the same with the same laser beam. Mechanical aids for following the laser beam, such as for example a servo drive provided in the case of means known from German Offenlegungsschrift 2533 697, in such cases frequently have too great demands made on them, so that either the target object is not detected or else the contact to it is prematurely lost again.

The task of the present invention is to provide improved means for automatically controlling a beam of electromagnetic radiation, for example a laser beam, such that it makes it possible both to detect rapidly-moving target objects and to pursue the same over a longer period of time, and whereby said means may have a construction which is as simple as possible.

According to the invention, there is provided means for automatically controlling a beam of electromagnetic radiation that is to be reflected by a moving target object, more especially for an arrangement for detecting and tracking rapidlymoving objects, having a receiver which picks up part of the electromagnetic radiation reflected by the target object and which supplies a reception signal, an aiming device arranged in a beam of electromagnetic radiation and which has two separatelycontrollable deflection units, and an electronic evaluation circuit which acts on the aiming device and which is able to produce, from the reception signal, control signals for adjusting the aiming device, in such a way that a beam of electromagnetic radiation remains constantly aimed at the target object, characterised in that the deflection units comprise two optically-pervious bodies which are arranged one behind the other and at an angle to one another and by means of which there is achievable a beam of electromagnetic radiation which is diffracted at a variable angle relative to the original beam direction, and the beam direction of which is variable as a function of the kind and magnitude of the control signal which is applied to the aiming device, and in that, in addition to the electronic evaluation circuit, there are provided a further control circuit which also acts on the aiming device and which contains at least two components, and a switching unit which connects the components of the control circuit and the electronic evaluation circuit to the aiming device.

The said means may be provided for automatically controlling a laser beam.

Because the change in direction and therewith the readjustment of the beam is achieved without the use of mechanical aids or component parts, the readjustment speed of the beam can -even over a relatively large solid-angle region - be enlarged almost at will. Thus, it is not only possible to detect even rapidly-moving target objects with the beam within the shortest time, but also to continue tracking them in the case of sudden changes in path.

The control circuit which is provided in addition to the evaluation circuit serving for adjusting of the beam directed at the target object, and which is also connected by way of the switching unit to the aiming device, makes it possible to perform a plurality of functions, e.g. detection and steering of a target object, with a single beam. In this respect, an arrangement constructed in accordance with the invention can allow both a rapid change of the functions and an extremely rapid signal sequence, i.e. the transfer of the greatest possible number of items of information to the target object.

The use of acousto-optical deflectors, such as are for example used in high-speed printers, in respect of the controlled deflection of the beam leads to a particularly simple and compact construction of the beam-control means. From this there results consid .erable advantages with regard to a mobile use of this arrangement, for example for the steering of flying bodies and projectiles from the ground.

The control ccircuit may contain: a first component which serves to control the beam for detection of the target object, with the aiming device being controllable by said first component in such a way that the direction-variable beam scans a predetermined solid-angular region; and a second component comprising two generators for producing A.C.

voltage signals usable for a control, leading to oscillations of the direction-variable beam, of the two bodies which form the aiming device; and the electronic evaluation circuit may have two phasesensitive detectors to inputs of respective ones of which are applied said A.C. voltage signals. Thereby there can ensure a particularly reliable and rapid beam following or readjusting.The control circuit may contain a third component which serves to transmit commands to a steerable flying body which has a receiver and an evaluation logic and which may form the target object, which third component may co-operate with o"i / one of the two bodies forming the aiming dcv'ce, in srich a way that a brief deflection of the direction-variabie beam in one direction is achievable, and whicn third component may be coupled to a computer for acquiring steering commands fo sad flying body. with said computer having an input connected to the evaluation circuit, and there may be connected in advance of said third component an encoder or converting the steering commands transmit.ed oy the computer into control signals for the aiming device. Thereby, the control means can be used in a particularly simple manner at the same time for the transmitting of signals, more es;,ecially steering commands, to the target object.In this respect, the advantage results that a flying body guided by such means can suffice with an extremely slight expenditure on additional con structional means forth transmission of informa ton and can ri erefore at the same time be produced in a cost-favourable manner and be provided with the largest possible useful load.

Control means in accordance with the invention is for example also suitable for measuring the flight path of non-guided projectiles, for example of grenades, and thus be used for fire control. Within the scope of the invention it is, moreover, self a-videniiy also possible to use, instead of laser light, other adequately-monochromatic electromagnetic radiation.

Also, according to the invention, there is provided means for automatically controlling a beam of electromagnetic radiation that is to be reflected by a moving object, said means comprising: electronic control means; a beam-aiming device having optically-pervious means in which, in use, there occurs diffraction or refraction behaviour variable by the electronic control means, whereby to provide, from electromagnetic radiation incident on the beamaiming device, a beam of electromagnetic radiation, leaving the beam-aiming device, variable in direction through a solid angle; and a receiver for picking up electromagnetic radiation reflected by the mov- - ing object and for supplying reception signals to the electronic control means to cause, utilising control by the electronic control means of the diffraction or refraction behaviour in the optically-pervious means, the beam leaving the beam-aiming device to be kept constantly aimed atthe moving object.

In the accompanying drawings, which show, by way of the example, embodiments of the invention: Figure 1 shows a block diagram of an exemplary embodiment of control means constructed in accordance with the invention; Figure 2 shows a block diagram of a further exemplary embodiment of control means, constructed in accordance with the invention, for steering flying bodies; and Figure 3 shows a schematic representation of an aiming device of control means constructed in accordance with the invention.

In the Figures, identical parts are provided with the same reference numbers.

Referring to Figure 1 of the drawings, a control means for a laser beam that is to be reflected by a target object has a laser 1, and has an aiming device which as, as deflection units, two optically-pervious bodies 2, 3, controllable from the outside. Said bodies 2,3 are arranged one behind the other and at an angle to one another in the beam path of the laser light. A beam which extends at a variable angle relative to the original beam direction can be produced, from the incident laser beam, in these bodies 2, 3.

The control means has a receiver 4, in this case a photodetector, for registering the laser beam reflected by a target object 5. The target object 5 is in this respect equipped, for the reflection of the laser beam, with one or more reflectors 6, preferably triple min-ors. Connected subsequent to the receiver 4 is an electronic evaluation circuit 7, which is connected to a switching unit 8 which acts on the aiming device.

A further control circuit, consisting of at least two components, is provided, which is also connected by 'uay of the switching unit 8 to the aiming device. In the exemplary embodiment shown here, the control circuit has a first component 9, with which a systematic deflection of the laser beam can be carried out over a predetermined angular region to detect the target object. Furthermore, the control circuit has, as a second component, two generators 10 and 11 for generating a respective A.C. voltage signal of predetermined frequency, which can be modulated upon the laser beam and can be used for signal evaluation.

The following or readjusting of the laser beam is effected, in this respect, in the manner described hereinunder. The beam produced by the laser 1 enters the aiming device, wherein from this there is produced a laser beam which extends at a variable angle relative to the original beam direction. The angle at which this laser beam extends relative to the original beam direction can be varied, as a function of the control signal supplied from the outside, within a solid-angle region of approximately 25 mrad. The laser beam emerging from the aiming device is now so deflected relative to the original beam direction of the laser that it impinges on the target object 5, part of the light being beamed back from the reflector 6 into the receiver 4.The reception signal registered in this receiver 4 is supplied to the electronic evaluation circuit 7, which acquires therefrom the following or readjusting signal for the aiming device. With the aid of this following or readjusting signal, which arrives at the aiming device by way of the switching unit 8, the direction of the laser beam is so corrected that it remains constantly directed at the target object.

If, on the other hand, the laser beam has initially not detected the target object 5, then initially, with the aid of the component 9, contained in the control circuit, for deflection control of the laser beam, the beam is controlled in such a way that it systematically scans a predetermined solid-angle region until it detects the target object. Only when this has taken place does the switching unit 8 separate the component 9 from the aiming device and now connect the aiming device to the electronic evaluation circuit 7, which from now on ensures the following or readjustment of the laser beam in the above-described manner.

At the same time as the electronic evaluation circuit 7, the second component of the control circuit, i.e. the generators 10 and 11, also is connected by way of the switching unit 8 to the aiming device.

In this way, the A.C. voltage signals of different frequency which are produced in these generators are additionally superimposed on the laser beam, whereby the beam performs angle oscillations of small amplitude in two co-ordinates. The superimposed oscillations lead to intensity modulations of the laser beam which is reflected by the target object 5 and which is registered by the receiver 4, which modulations are evaluated in the electronic evaluation circuit 7 to acquire the following or readjustment signal. The evaluation circuit has, for this purpose, two phase-sensitive detectors each having an advance-connected pre-amplifier as well as a subsequent-connected amplifier and low-pass filter.

The phase-sensitive detectors are connected by way of a reference input each to a respective one of the generators 10 and 11.

The receiver signal is demodulated after preamplification in the phase-sensitive detectors, in which respect the generator frequency serves as reference frequency. The following or readjustment signal acquired therefrom is supplied by way of the amplifier and low-pass filter and by way of the switching unit 8 to one of the two deflection units of the aiming device. The two deflection units and the evaluation electronics form in each case a control loop or control system which is balanced when the centre of the laser beam lies over the target object.

In the case of the exemplary embodiment shown in Figure 2, the control circuit has, as a third component 12, means for transmitting command signals to a steerable flying body 15 which forms the target object. The flying body 15 is equipped with a receiver 13, an evaluation logic 14, and steering means, for example in the form of peripherallyarranged, individually-ignitable impulse charges.

The third component 12 co-operates, by way of the switching unit 8, with one of the two deflection units of the aiming device in such a way that a brief deflection of the laser beam in one co-ordinate is achievable.

The means for transmission of command signals is, in this respect, coupled with a computer 16, which is for its part connected to the output of the electronic evaluation circuit 7. Furthermore, in the case of the exemplary embodiment shown here, there is provided a coder 17 which lies between the computer 16 and the third component 12 of the control circuit and serves to convert the computer commands into control signals for the aiming device.

Serving for the acquisition of the steering commands which are necessary for steering the flying body 15 to an intended target point are the regulating signals for the beam following or readjustment, which the electronic evaluation circuit 7 transmits to the two deflection units of the aiming device. These are used as a measure of the deviation of the flying body 15, to be steered, from the desired flightpath, which is predetermined either by the line of sight of a sighting device 24 or by stored flightpath data. The computer 16 then computes, from the thusascertained angular position relative to the desired flightpath and the instantaneous distance of the flying body 15 from the launching and command means, the deviation of the flying body perpendicularly to the desired flightpath and derives therefrom the necessary correction commands.

The transmission of the correction commands to the flying body 15 by the laser beam is effected with a suitable beam deflection frequency which can easily be separated electronically from the frequencies used for the beam following or readjustment.

For the duration of the command transmission - and controlled by the computer 16 - one of the two control loops or control systems for the beam following or readjustment is interrupted by the switching unit 8.

The evaluation of the correction commands in the flying body 15 is effected by way of the receiver 13 and the evaluation logic 14, in this case a decoding unit. To carry out steering corrections, additionally information regarding rolling or rotational position and rolling or rotational speed of the flying body is necessary, for example in orderto determine the instant of ignition of the impulse charges.

Upon the use of partially linearly-polarising reflectors 6 on the flying body and in combination with an acceleration sensor in the flying body, a clear ascertainment of the instantaneous rolling or rotational position, and therewith of the ignition instant for the impulse charges used for the flightpath correction, is possible.

In the case of the aiming device shown in Figure 3, there are provided two acousto-optical deflectors 2, 3 which are arranged perpendicularly to one another. These consist in each case of an opticallypervious crystal, 18 or 19, which is acted upon by a respective sound transmitter, 20 or 21. Each of the two acousto-optical deflectors 2, 3 has a respective follow-on diaphragm arrangement, 22 or 23.

With the aid of the sound transmitter 20 it is possible to produce, in the crystal 18 of the first acousto-optical deflector 2, a diffraction screen. This is brought about by local fluctuations in the diiffraction index which occur in the crystal 18 as a result of the spreading of the sound waves. In this way there can be produced a diffraction screen having a variable screen constant, which the laser beam has to run through. One thus obtains, in addition to the laser beam running undiffracted through the crystal 18, diffraction beams of the first and higher order, which are deflected through a variable angle, which is dependent upon the screen constant, relative to the original direction.As a result of the follow-on diaphragm arrangement 22, all the beams save for a diffraction beam I of first order are diaphragmed-out, which beam I is subsequently supplied to the second acousto-optical deflector 3, where from this beam, in the manner described alcove, in turn there is produced a beam 1 which is diRracted in a direction perpendicular to the first diffraction direction.

By both sound transmitters 20, 21 being connected by way of the switcir!r! unit 8 io the components 9, 10,11 or 12 of the ço,- O! .ircui. and tG the electronic evaluation circuit 7, it is foSs - - to deflect the laser beam in this way in defined mani?sr îer and with neg!igible delay within a predete;n7ined solidangular region.

Claims

1. Means for automatically controlling a beam of electromagnetic radiation that is to be reflected by a moving target object, moe especially for an arrangement for detecting and tracking rapidlymoving objects, having a receiver which picks up part of tre electromagnelic radiation reflection by the target object and which supplies a reception signal, an aiming device arranged in a beam of electromagnetic radiation and which has two sepa rately-controliable deflection units, and an electronic evaluation circuit which acts on the aiming device and which is able to oroduca, from the reception signal, control signals for adjusting the aiming device, in such a way that a beam of electromagnetic radiation remains constantly aimed at the target object, characterised in that the deflection units comprise two opticallv-pervious bodies which are arranged one behind the other and at an angle to one another and by means of which there is achievable a beam of electromagnetic radiation which is diffracted art a variable angle relative to the original beam direction, and the beam direction of which is variable as a function of the kind and magnitude of the control signal which is applied to the aiming device, and in that, in addition to the electronic evaluation circuit, there are provided a further control circuit which also acts on the aiming device and which contains at least two components, and a switching unit which connects the components of the control circuit and the electronic evaluation circuit to the aiming device.

2. Means for automatically controlling a beam of electromagnetic radiation that is to be reflected by a moving object, said means comprising: electronic t control means; a beam-aiming device having optically-pervious means in which, in use, there occurs diffraction or refraction behaviour variable by the electronic control means, whereby to provide, from electromagnetic radiation incident on the beamaiming device, a beam of electromagnetic radiation, leaving the beam-aiming device, variable in direction through a solid angle; and a receiver for picking up electromagnetic radiation reflected by the moving object and for supplying reception signals to the electronic control means to cause, utilising control by the electronic control means of the diffraction or refraction behaviour in the optically-pervious means, the beam leaving the beam-aiming device to be kept constantly aimed at the moving object.

3. Means as claimed in Claim 1, characterised in that the deflection units are acousto-optical deflectors in each of which, as a result of local fluctuations of the index of refraction which are brought about by a sound transmitter in an optically-pervious crystal, there can be produced a diffraction screen of variable screen constant, by means of which the incident beam can be split up into a plurality of diffracted beams, the diffraction angles of which vary with the screen constant, and in which respect, as a result of a subsequent diaphragm arrangement, all of the diffraction beams can be diaphragmed-out except for a beam of first order.

4. Means as claimed in Claim 1 or 3, characterised in that the control circuit contains a first component which serves to control the beam for detecting of the target object and in that the aiming device is controllable by this first component in such a way that the direction-variable beam scans a predeterminable solid-angular region.

5. Means as claimed in Claim 4, characterised in that the control circuit contains, as a second component, two generators for producing A.C. voltage signals and in that these A.C. voltage signals are usable for a control, leading to oscillations of the direction-variable beam, of the two bodies which form the aiming device.

6. Means as claimed in Claim 5, characterised in that the electronic evaluation circuit has two phas6- sensitive detectors.

7. Means as claimed in Claim 6, characterised in that the A.C. voltage signals produced by the generators are at the same time applied each to an input of a respective one of the phase-sensitive detectors.

8. Means as claimed in Claim 7, characterised in that in the receiver is a photodiode and in that second inputs of the phase-sensitive detectors are connected to the said receiver.

9. Means as claimed in any one of Claims 5 to 8, characterised in that the control circuit contains a third component which serves to transmit command signals to a steerable flying body which has a receiver and an evaluation logic and which forms the target object.

10. Means as claimed in Claim 9, characterised in that the third component of the control circuit co-operates with only one of the two bodies forming the aiming device, in such a way that a brief deflection of the direction-variable beam in one direction is achievable.

11. Means as claimed in Claim 9 or 10, characterised in that the third component of the control circuit is coupled to a computer for acquiring steering commands for the flying body, said computer having an input connected to the electronic evaluation circuit.

12. Means as claimed in Claim 11, characterised in that connected in advance of the third component of the control circuit is an encoder for converting the steering commands transmitted by the computer into control signals for the aiming device.

13. Means as claimed in Claim 11 or 12, characterised in that the switching unit is controllable by the computer.

14. Means as claimed in any one of the preceding claims, when provided for automatically controlling a laser beam, the electromagnetic radiation being in such case laser light.

15. Means for automatically controlling a laser beam, substantially as herein described with referpence to Figure 1 or Figure 2, or Figures 1 and 3, or Figures 2 and 3, of the accompanying drawings.