GB2191056A

GB2191056A - Masked direction finder

Info

Publication number: GB2191056A
Application number: GB08711202A
Authority: GB
Inventors: Anton Harasim; Dr Maximilian Koniger
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1986-05-17
Filing date: 1987-05-12
Publication date: 1987-12-02
Anticipated expiration: 2007-05-12
Also published as: FR2598814A1; FR2598814B1; DE3616796C1; GB8711202D0; GB2191056B

Abstract

Optical system (1) images radiation, the direction of which is to be determined, onto an opto-electronic detector (4). A liquid crystal device (2) is placed in the path of radiation between the optical system (1) and the detector (4) for the purpose of masking-out sources of interference or other noise. The liquid crystal mask (2) has horizontal and vertical elements which are controllable by means of electronic row and column drivers (16). The opto- electronic detector (4) is a non- subdivided position detector which is associated with a direction determining system (5), the output signals of which control the row and column drivers (16). To isolate a source of radiation, the raster elements in a region around the position of a detected source of radiation are switched so as to be non- transmissive to radiation. <IMAGE>

Description

SPECIFICATION An Opto-Electronic Position Finding System The invention relates to an opto-electronic position finding system for locating a source of radiation, said system including a reproducing optical system, in the image plane of which an optoelectronic detector is arranged, a liquid crystal element being arranged in the path of radiation between the optical system and the detector, for the purpose of masking-out electro-magnetic interference or noise from various sources of radiation, the liquid crystal element being provided with raster elements which are arranged in a matrixshaped manner and which are controllable by means of electronic row and column drivers. Such an opto-electronic position finding system will hereinafter be referred to as the type described.

Disclosed in German Specification No. 27 22 018 is a so-called liquid crystal diaphragm for optical instruments which has raster elements which are arranged in a matrix-shaped manner and which are controllable by means of an electronic row and column driver. In this respect the raster elements are so controlled that in each case at least one lighttransmissive or light-nontransmissive raster element is surrounded by raster elements of opposite transparency. In this way either an optical window or a limited opaque surface area which is non-transmissive to radiation is produced. With the use of this liquid crystal diaphragm in an observation device, the interference radiation which may surround a target can be masked out.With the use of such a liquid crystal diaphragm in an automatic guidance sight, the diaphragm is arranged in front of the goniometer modulator and can be controlled bywayofthegoniometer modulator which determines the displacements of the rocket from the target.

The present invention relates to the problem of providing an opto-electronic position finding system of the type described in which a diaphragm produced by means of appropriately arranged raster elements is followed-up in a simple way to the image of a source of radiation. The location system is, furthermore, to offer the possibility of detecting and masking-out several sources of interfering radiation which are present in the field of view. It is furthermore, an object of the invention to provide a method of locating one or more sources of radiation with the opto-electronic location system, by means of which the capture and tracking of a specific radiator, secured for example to a missile with the masking-out of other interfering sources of radiation present in the field of view is possible.

According to a first aspect of the present invention there is provided an opto-electronic position finding system of the type described, wherein the optoelectronic detector is a non-subdivided position detector and wherein the system includes a positional electronic system receiving signals from the detector, the output signals from the positional electronic system controlling the row and column drivers, and wherein for the identification of a source of radiation, the raster elements in a region which includes the respective position of a detected source of radiation are switched continuously or in modulating manner either, in positive contrast representation, non-transmissive to radiation or, in negative representation, transmissive to radiation, whilst the remaining raster elements have a respective opposite transparency.

According to a second aspect of the present invention there is provided a method of locating a source of radiation with the aid of the above system including the steps of: a) locating a source of radiation in a scene that is to be observed with a liquid crystal element which is transparent at least in sectors; and b) masking-out of the surroundings around that source of radiation that is to be tracked by controlling the raster elements in negative contrast representation with the position data of the source of radiation that is to be tracked.

The location system in accordance with the invention profits by the use of a so-called nonsubdivided position detector which is manufactured for example by Dr. R. Seitner, Mess-und Regeltechnik GmbH, Herrsching, under the type designation 'PSD S 1200' or 'PSD S 1300'. Such a position detector is in principle constructed in the form of a large-surface PIN-diode, the P- and/or Nlayer of which is designed as a thin layer of very constant surface resistance, which is provided at two or four edges with one or two pairs of electrodes. A light spot striking the surface generates at the electrodes a signal which corresponds to the position of the light spot on the surface and which is processed in a special positioned electronic system and can be tapped.

These output signals are used for the control of the row and column drivers of a liquid crystal diaphragm, in order to identify the source of radiation, the raster elements in a region, including the respective position of the detected source of radiation, are rendered by switch means into a predetermined contrast representation either in a radiation-transmissive or non-transmissive state. In this respect it is particularly advantageous if a choice can be made, in other words a switch-over can be made, between both contrast representations. In this way, either a diaphragm which surrounds the source of radiation is produced which allows the light of the source of radiation through, or masks it out.

With such a position finding system it is then possible to track and to guide for example a missile having a rearward source of radiation, in which respect, already prior to the launching of the missile any unwanted sources of radiation which appear in the field of view and which may interfere can be masked out.

The present invention will now be described in greater detail by way of example with reference to the accompanying drawings, wherein: Fig. 1 is a block circuit diagram showing the construction of a position finding system provided with a liquid crystal diaphragm; Fig. la is a block circuit diagram illustrating the processor shown in Fig. 1 in greater detail; Figs. 2a and 2b are diagrams illustrating the state of the liquid crystal diaphragm in positive and negative contrast representation; Fig. 2c is a diagram illustrating the state of the liquid crystal diaphragm upon inversion ofthe state shown in Fig. 2b; Fig. 2d is a diagram illustrating the state of the liquid crystal diaphragm in the capture phase of a source of radiation;; Fig. 3 is a block circuit diagram of the driver circuit shown in Fig. 1, for the control of a liquid crystal diaphragm with the possibility of switch-over from positive to negative contrast representation and vice versa; Fig. 4 is a cross-section through an integrated unit consisting of position detector and liquid crystal diaphragm; Fig. 5 is a block circuit diagram of a system containing a liquid crystal diaphragm with control electronics for the location and tracking of a source of radiation; and Referring first to Fig. 1, a liquid crystal element 2 is constituted by raster elements arranged in a matrixshaped manner and is located in the intermediate image plane of a receiving optical system 1.The intermediate image arising in the plane of the liquid crystal element 2 is reproduced by way of an optical system 3 on a non-subdivided position detector 4.

Such a position detector is 'per se' only in a position to detect the location of a single source of radiation.

The signals of the position detector 4 pass into a positional electronic circuit 5, which supplies as output signals the co-ordinates x and y as well as the intensity I as analog output signals of a source of radiation reproduced on the position detector 4.

These signals are transformed for the further signal processing in analog-to-digital converters 6 and 7 into digital signals.

In the case of instruments which are followed-up to the target or which are held in the hand, a circuit 8 with two acceleration sensors or two to three magnetic sensors orientating themselves at the earth's magnetic field is provided, the output signals x5 and Ye ofwhich are converted by means of an analog-to-digital converter 9 into digital signals. The movement of the opto-electronic elements 1,2,3 and 4 are measured with the acceleration sensors or the magnetic sensors contained within the circuit 8.

The positional dataxand yofthe positional electronic circuit 5 is corrected with the aid of the signals XB and ye from the acceleration sensors or magnetic sensors in a ROM or EPROM module 10, which is used as a so-called Look-up-Table, in accordance with the measured, movementoccasioned displacement.

The corrected values X and Y then pass by way of a ROM-module 17 into a processor 11. The processor comprises a window size generator 14, a window control circuit 15, a predictor 13, which contains a Kalman filter and a cycle control circuit 12. The control of the liquid crystal element 2 then takes place by way of a driver circuit 16, which is controlled by the processor 11 and which contains a contrast reversal, as described with reference to Fig.

3.

Referring nowto Fig. la,which shows the processor 11 in greater detail, and in particular the cycle control circuit 12, the window control circuit 15 and the window size generator 14. The cycle control circuit 12 consists of a timing generator 12.1, a programme counter 12.2 and a programme ROM 12.3. The programme counter 12.2 controls, byway of the programme ROM 12.3, the functional cycle and gives the necessary control signals C, D, Clock 1,2,3 for the circuit shown in Fig. 3 as well as forthe window circuit 15 and the window size generator 14.

The Kalman filter contained with the predictor 13 compares the displacement-corrected position addresses X and Y as well as the intensity I with precalculated values. If the deviations lie within preset limits, then the Kalman filter supplies a 'True' signal to the programme ROM. The window control circuit 15, which consists substantialiy of analog switches supplies the X- and Y-addresses from the ROM 17 of Fig. 1 to the window size generator 14. The window size generator consists of a data ROM 14.1 and a shift register 14.2. The ROM 14.1 associates with each address X or Y respectively, a data record as a function of the time and/or of the place (i.e. of the address X and Y). The data addresses generated in this way by the data ROM 14.1 are written into the shift register 14.2, the length of which corresponds to the sum of the row and column count.The data signals processed in this way then pass to the driver circuit shown in Fig. 3.

In the event that there is no intensity signal I from the positional electronic circuit 5, the cycle control circuit 12 supplies from the Kalman filter of the predictor 13, a prediction regarding the position of the source of radiation that is to be detected, to the window size generator 14. Either the displacements X and Y or the intensity information I are used for the window size control. If the source of radiation is a missile which comes from the outside into the image field, then the amount of the X- or of the Ysignal is used as multiplierforthe minimum window size.

The above-mentioned possibility of switch-over between positive and negative contrast, in other words the so-called contrast reversal, is integrated in the driver circuit which is shown in greater detail in Fig. 3. As a result of the provision of the driver circuit 16, a change-over of the contrast representation is achieved, as is shown in Fig. 2a (positive contrast representation) and Fig. 2b (negative contrast representation). The change-over of the contrast is achieved with static control, in other words not upon multiplex operation. Thus by inverting the signals X and Y a contrast reversal can - change over for example from a representation in accordance with Fig. 2b into a representation in accordance with Fig. 2c. A representation in accordance with Fig. 2c is, however, not desired for the arrangement described here, since more raster elements than absolutely necessary are darkened. In the case of a substantially punctiform source of radiation, thus for example a flying body which moves from the outside to the centre of the image field, the image surface must without fail be kept free at the edge (see Fig. 2d). This is, however, not achieved by a contrast reversal by inverting the data signals, as described above.In contrast to the above, the driver circuit shown in Fig. 3 makes possible all the representation possibilities illustrated in Figs. 2a, b and d.

An essential feature of the driver circuit shown in Fig. 3 is the change-over of the reference potentials 16.91 or 16.92 of the respective driver-IC 16.1 and 16.2 by the electronic switches 16.3, 16.4 and 16.5.

The output data signals for the drivers are always stored in the shift register of the driver IC 16.1 and 16.2 when the reference potential, in other words earth potential, of the logic circuit 16.6 is applied to the electronic switches 16.4 and 16.5.

The circuit shown in Fig. 3 uses commerciallyavailable LCD drivers (for example Hughes 064), which need 5 volts supplies 16.94 and 16.96 for the internal logic and driver voltage supplies 16.93 and 16.95 of for example -20 volts. In contrast to the otherwise customary circuit wiring, in the circuit in Fig. 3 the voltage supplies 16.93, 16.94 and 16.95, 16.96 have to be present in a potential-free manner, e.g. by way of transformers which are not shown in Fig. 3. Only then is it possible to shift the reference potentials of the drivers by way of the switches 16.4 and 16.8 by the potentials of the voltage supplies 16.91 or 16.92 respectively and, on the other hand, the so-called U/3-control method which is necessary for the control of an LCD matrix is achieved.The U/3 control method is described in detail for example in 'Funkschau 1984, No. 11, page 55to 61'. Upon the change-over of the reference potentials with the timing frequency 'Clock 1', some further driver-logic signals have to be switched over in proper phase relation. This is indicated in Fig. 3 symbolically with the aid of the inverters 16.10 and 16.11. The data pulses for the drivers are written with 'Clock 2' into the shift register integrated in the driver circuit 16.

The contrast switch-over is effected by way of the switch 16.3. In the position of the switch 16.3 shown in Fig. 3, the rows and columns selected with logic 1 at the respective point of intersection are switched bright, whilst the remaining elements of the matrix 16.12 and 16.13 remain dark. If the switch is reversed, the potential of voltage supply 16.91 which is additionally added to potential of voltage supply 16.92 brings about a contrast reversal, i.e.

the matrix elements previously switched so as to be transparent become dark and vice versa.

Some detector arrangements, such as for example photo-conductor detectors, require a modulated source of radiation for operation. This requirement is conventionally taken into account by placing an electro-mechanically driven modulator disc in front of the detector. The disc is driven at a fixed frequency adapted to the sensitivity of the detector. The necessity for this requirement is abolished in the case of the arrangement shown in Fig. 1, since the LCD cell 2 can bring about a modulation of the incident radiation through the switch 16.14 shown in Fig. 3. The switch 16.14 is in this respect actuated continuously with the timing frequency 'Clock 3', which corresponds to an integral multiple of the timing frequency 'Clock 1'.

The timing frequency 'Clock 3' can be generated, for example, in the cycle control circuit 12.

Particularly in the case of position detectors in alternating-current operation, in which the signal processing is isolated from the detector outputs by capacitors, the arrangement in accordance with Fig.

1 can advantageously be used. In this respect, only those raster elements of the liquid crystal cell 2 are modulated which are associated with the source of radiation in the image field, whilst the remaining raster elements remain unmodulated. The modulated raster elements move synchronously with the source of radiation. In this arrangement both the positive and the negative contrast representation can be selected. This method has the advantage that with relatively simple electronic means several sources of radiation can be tracked simultaneously. This is achieved, for example, by means of a RAM module which is associated with the cycle control circuit 12. The displacements X and Y of the sources of radiation are written into the RAM module.The positions of these sources of radiation are interrogated successively and fed to the window size generator 14 as well as to the window control circuit 15, which modulates the corresponding raster elements with a preselected frequency, e.g. with 'Clock 3, 4, 5', which is an integral multiple of the Clock frequency 1 in Fig. 3.

Furthermore, a weighting of the various sources of radiation is possible in that it is possible to select the predetermined frequency from 'Clock 3,4, 5'.

If a source of radiation is, for example, a missile which travels from the outside into the image field, then as controlled by the cycle control circuit 12 prior to the firing of the missile, the image field is scanned for interfering sources of radiation and the displacements of these sources of radiation are stored in the RAM 17. In this respect, any movement of the components 1 to 4 defining the optical axis, leads.to a connection of these displacements through the electronic circuit which is equipped with acceleration sensors or magnetic sensors. After termination of this scanning procedure, which is controlled by the cycle control circuit 12, only the raster elements are modulated at the image edge, which elements correspond to the expected position of the missile after the launching thereof. If the missile has been detected, then subsequently a tracking thereof takes place by modulation of the raster element or elements which correspond or respectively correspond to the position of the missile.

Fig. 5 shows a simplified analog circuit corresponding to the digital circuit shown in Fig. 1 without the use of acceleration or magnetic sensors comprised within the circuit 8 and without Kalman filter comprised within the predictor 13. The elements 1 to 5 correspond to those of Fig. 1, likewise the driver circuit 16 corresponds to that shown in Fig. 3. The cycle control circuit 12 generates as in the case of Fig. lathe necessary control signals for the driver circuit 16 and the window generator 19.

Fig. 4 shows the structure of an integrated detector/liquid crystal unit. Layers 21 to 25 are applied onto a glass plate 20 facing a receiving optical system in order to produce a liquid crystal cell with controllable raster elements. The glass plate 20 containing the layers 21 to 25 is separated by means of a transparent insulating layer 26 from the layers 27 to 29 of a position detector. The liquid crystal cell is formed by means of the layers 21 to 25 which comprise transparent column electrodes 21, an orientation layer 22 consisting of long-chain polymers without lateral branching, a liquid crystal 23, a further orientation layer 24 as well as line electrodes 25. The four outer electrodes 27 of the position detector are applied behind the insulating layer 26 consisting, for example, of SlO2 or polyamide. Positioned in contact with the electrodes 27 is a light-transmissive resistance layer 28 of an indium tin oxide e.g. indium stannic oxide, or doped semiconductor material, followed by a lightsensitive layer 29 of lead sulphide or another semiconductor material, and finally base electrodes 30. A plate 31 of glass or silicon is arranged, on the bare electrodes 30, which plate serves as a carrier for the layers 26 to 30 and for the liquid crystal layer.

As a result of this arrangement, an intermediate reproduction, in other words the optical system shown in Fig. 1, is abolished.

Claims

1. An opto-electronic position finding system of the type described, wherein the opto-electronic detector is a non-subdivided position detector and wherein the system includes a positional electronic system receiving signals from the detector, the output signals from the positional electronic system controlling the row and column drivers, and wherein for the identification of a source of radiation, the raster elements in a region which includes the respective position of a detected source of radiation are switched continuously or in modulating manner either, in positive contrast representation, non-transmissive to radiation or, in negative representation, transmissive to radiation, whilst the remaining raster elements have a respective opposite transparency.

2. A system according to claim 1, wherein there is provided an electronic circuit for the change-over between the two contrast representations.

3. A system according to claim 1 or 2, wherein the detector and the liquid crystal elements form an integrated unit.

4. A method of locating a source of radiation with an opto-electronic position finding system as claimed in any one of claims 1 to 3, including the steps of: a) locating a source of radiation in a scene that is to be observed with a liquid crystal element which is transparent at least in sectors; and b) masking-out of the surroundings around that source of radiation that is to be tracked by controlling the raster elements in negative contrast representation with the position data of the source of radiation that is to be tracked.

5. The method according to claim 4, including the following additional steps between the steps (a) and (b): a) masking-out of the disturbing source of radiation by controlling the raster elements in positive contrast representation with the positional data of the disturbing source of radiation; and b) locating the source of radiation that is to be tracked with a liquid crystal element which masks out only the interfering source of radiation and which is for the rest transparent.

6. The method according to claim 4 or 5, wherein the masking-out of several interfering sources of radiation is effected by controlling the raster elements in positive contrast representation with the positional data of the interfering source of radiation in image multiplex operation.

7. The method according to any one of claims 4 to 6, wherein the controlling of the raster elements with the positional data of at least one source of radiation that is to be located is effected in modulated manner with different frequencies which are clearly associated with the source or sources of radiation to be located.

8. The method according to any one of claims 4 to 7, wherein movements of the location system are detected and the positional data of detected sources of radiation are corrected in accordance with the image shift caused by the movement.

9. An opto-electronic position finding system of the type described, constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

10. A method of locating a source of radiation with an opto-electronic position finding system substantially as hereinbefore described with reference to the accompanying drawings.