GB2300323A - Seeker head - Google Patents

Seeker head Download PDF

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Publication number
GB2300323A
GB2300323A GB7933009A GB7933009A GB2300323A GB 2300323 A GB2300323 A GB 2300323A GB 7933009 A GB7933009 A GB 7933009A GB 7933009 A GB7933009 A GB 7933009A GB 2300323 A GB2300323 A GB 2300323A
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United Kingdom
Prior art keywords
target
coordinate system
output signal
inertial
seeker head
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Granted
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GB7933009A
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GB7933009D0 (en
GB2300323B (en
Inventor
Reiner Eckhardt
Johann-Friedrich Egger
Wolfgang Gulitz
Alfred Stoll Ing
Hans Tessari
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Bodenseewerk Geratetechnik GmbH
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Bodenseewerk Geratetechnik GmbH
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Priority claimed from DE2841748A external-priority patent/DE2841748C1/en
Application filed by Bodenseewerk Geratetechnik GmbH filed Critical Bodenseewerk Geratetechnik GmbH
Publication of GB7933009D0 publication Critical patent/GB7933009D0/en
Publication of GB2300323A publication Critical patent/GB2300323A/en
Application granted granted Critical
Publication of GB2300323B publication Critical patent/GB2300323B/en
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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41WEAPONS
    • F41GWEAPON SIGHTS; AIMING
    • F41G7/00Direction control systems for self-propelled missiles
    • F41G7/20Direction control systems for self-propelled missiles based on continuous observation of target position
    • F41G7/22Homing guidance systems
    • F41G7/2273Homing guidance systems characterised by the type of waves
    • F41G7/2293Homing guidance systems characterised by the type of waves using electromagnetic waves other than radio waves
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41WEAPONS
    • F41GWEAPON SIGHTS; AIMING
    • F41G7/00Direction control systems for self-propelled missiles
    • F41G7/20Direction control systems for self-propelled missiles based on continuous observation of target position
    • F41G7/22Homing guidance systems
    • F41G7/2213Homing guidance systems maintaining the axis of an orientable seeking head pointed at the target, e.g. target seeking gyro
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41WEAPONS
    • F41GWEAPON SIGHTS; AIMING
    • F41G7/00Direction control systems for self-propelled missiles
    • F41G7/20Direction control systems for self-propelled missiles based on continuous observation of target position
    • F41G7/22Homing guidance systems
    • F41G7/2253Passive homing systems, i.e. comprising a receiver and do not requiring an active illumination of the target

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Aiming, Guidance, Guns With A Light Source, Armor, Camouflage, And Targets (AREA)

Abstract

A seeker head (66) comprising field of view scanning means for cyclically scanning the field of view (46) and for providing picture information referred to a seeker head-fixed co-ordinator system and signal processing means (74) for joint processing of the picture information from at least two consecutive scans, the improvement consistancy of the provision of a gyro assembly (68, 70, 72) in the seeker head (66) providing attitude variation signals (* small Greek omega *N , * small Greek omega *G , * small Greek omega ** small Greek phi *) as a function of attitude variations of the seeker head (66) relative to inertial space, the signal processing means (74) comprising a co-ordinate transformer circuit (100) to which the attitude variation signals (* small Greek omega *N , * small Greek omega *G , * small Greek omega ** small Greek phi *) are applied and which are adapted to transform the picture information from the various scans into a common inertial co-ordinate system.

Description

V.f ':' / r, r 1 t 2300323 I- - Z.
1 %" p -1g,,9 The invention relates to a seeker head comprising field of view scanning means for cyclically scanning the field of view and for providing picture informations referenced to a seeker head-fixed coordinate system, and signal processing means for joint processing of the picture informations from at least two consecutive scans.
This might be a seeker head wherein a rectangular or square visual field is scanned in multiple lines by means of a linear array detector, i.e. a linear array of photoelectric detectors, and an oscillating mirror. Subdividing the scanning movement of the oscillating mirror into angular steps results in a raster of the field of view, in which each picture element (called pixel = "Picture element" hereinbelow) has "coordinates" associated therewith, namely the line and column numbers of the respective pixel. The seeker head provides picture informations referenced to this seeker head-fixed coordinate system in such a manner that certain pixels are recognized as "brigh-" and other pixels are recognized as "dark". -110 2 t 1. It is the function of the seeker head to detect targets, which might be only faintly "perceptible", out of white noise, and to select one target out of the recognized targets in accordance with predetermined criteria. One of the criteria may be the movement of the target within the f ield of view.
1 To distinguish a target in the field of view from white noise, it is known to select a threshold value. If the signal from a pixel exceeds this threshold value, it will be observed whether with a predetermined number n (Z 2) of scans the threshold value will be exceeded at least m times (m:..5 n) within the window.
To select a target in accordance with its movement in the field of view. for example in order to discriminate between a tracked aircraft and a mock-target (flare) launched thereby, the displacement of the picture element corresponding to the target in the field of view with consecutive scans has to be detected.
With such and similar applications the picture informations from at least two consecutive scans are processed together. For example the evaluation of a signal exceeding the threshold as a target pulse depends on whether with two consecutive scans such a signal will appear both times within a pixel. The movement of the target can only be derived from the relative positions of the picture informations which are obtained durinq two or more consecutive scans. A prerequisite of the joint evaluation is, however, that the picture informations to be evaluated are referenced to a common coordinate system, which is not additionally affected by the movements of the carrier, for example of a missile carrying the seeker head. This function cannot be complied with by the seeker headfixed coordinate system without additional measures. Due to pitch, yaw or roll movements of the carrier --- /I- 11 ' r_ even a stationary target may be represented by completely different pixels during consecutive scans.
Therefore it is the object of the invention to make the picture informations from consecutive scans, with a seeker head of the type defined in the beginning, jointly processable in spite of the movement of the seeker head itself.
According to the invention this object is achieved in that a gyro assembly is provided in the seeker head and provides attitude variation signals as a function of attitude variations of the seeker head relative to inertial space, and that- the signal processing means comprise a coordinate transformer circuit, to which the attitude variation signals are applied and which are adapted to transform the image informations from the various scans into a common inertial coordinate system.
Further modifications of the invention are subject matter of the subclaims.
Embodiments of the invention are described hereinbelow with reference to the accompanying drawings.
Fig. 1 Fig. 2 shows schematically the opto-electronic part of the seeker head.
shows the reference signals generated by the angle encoder on the mirror axis of the seeker.
Fig. 3 illustrates schematically the scanning of the field of view with the seeker head.
I' it Fig. 4 shows schematically the cooperation of a seeker of the invention with a controller by which the seeker is oriented towards a target.
i is Figs.. 5a to g illustrate in the form of block diagrams in different phases the basic principle of the field of view correction and target selection according to the invention.
Fig. 6 shows an associated flux diagram which illustrates the operation of the program control unit in Figs. Sa to g.
Fig. 7 illustrates in detail the analog-todigital converter for converting the detector signals into digital picture informations.
Fig. 8 illustrates the corrections which have to be applied to the coordinates with displacement and rotation of the field of view.
Fig. 9 shows as block diagram the correction logic for the transformation of the picture element coordinates.
Fig. 10 shows details of the correction logic of Fig. 9.
Fig. 11 shows schematically an analog coordinate transformer and integrator circuit for the generation of signals which represent the position variations of the seeker head-fixed coordinate system in inertial V 1 1 Fig. 12 shows a simplified version of the coordinate transformer and integrator circuit.
p Fig. 13 is a schematic illustration and illustrates the coordinate transformations carried out during two consecutive scans in the.case of a movement of the seeker but of a stationary target.
Fig. 14 is an illustration similar to Fig. 13 but with a moving target.
Fig. 15 is a schematic illustration of the signal processing means during a first scan of the field of view.
Fig. 16 is a schematic illustration of the signal processing means during the dead interval following the first scan.
Fig. 17 is an illustration of the signal processing means similar to Fig. 15 during the subsequent second scan of the field of view.
Fig. 18 is an illustration of the signal processing means during the dead interval following the second scan.
Fig. 19 is an illustration of the signal processing means similar to Fig. 15 during the subsequent third scan of the field of view.
Fig. 20 is an illustration of the signal processing means during a first phase of the dead interval following the third s 1 4 C-7 Fig. 21 is an illustration of the signal processing means during a second phase of this dead interval.
In the following it will be assumed that the seeker head of the invention is provided on a missile (rocket) which is used against intruding air targets (aircraft). The seeker head is to detect the air target in its field of view already at rather large distance, to distinguish it from other detected objects, such as banks of clounds or the horizon, and to guide the migsile into the target.
The optical system 10 of the seeker head comprises a lens 14 and two plane mirrors 16 and 18. Radiation from the object space is focused by lens 14, as indicated in Fig. 1, the path of rays being folded by the two plane mirrors, of which the annular plane mirror 18 is located behind the lens 14 and facing the same, and the plane mirror 18 is affixed centrally to the rear face of the lens 14. Thus the lens 14 forms an image of the field of view as viewed by it in a plane 20. A linear array detector 22 is located in this plane 20. The plane mirror 16 is mounted for tilting movement about an axis 26 and is caused to oscillate about the axis 26 by a drive mechanism, as indicated by the double-arrow 28. Due to these oscillations the image of the visual field is moved back and forth in the plane 20 relative to the linear array detector 22, as indicated by double-arrow 30. The linear array detector 22 consists of a linear array of photoelectric (or infrared sensitive) detectors 32, the linear array of the detectors 32 extending perpendicular to the direction of movement, as indicated by the double-arrow, of the image of the field of view. An angle encoder (not shown) is provided on the mirror axis 26 and provides the following signals as a function of the mirror
A 1 movement (Fig. 2) m 1 t the Inverted column signal, which is applied during the scanning of each column. This signal is supplied also during the dead interval, the picture signal, which during the scan discriminates between the signal interval and the dead interval, and AR the direction-of-scan signal, which characteriizes the direction of scan (left-right).
The scanning of the image of the field of view 46 is schematically illustrated in Fig. 3. In practice the linear array detector 22 is stationary as described and the image of the field of view oscillates due to the oscillating movement of the mirror 16. For the sake of more convenient illustration, however, the image of the field of view 46 has been regarded as stationary and the linear array detector 22 has been regarded as movable in Fig. 3..
The oscillation, which is illustrated by curve 48 in Fig. 3, extends beyond the field of view, whereby the field of view is scanned approximately uniformly. The scanning is effected alternatingly in one or the other direction (direction I and direction II), dead intervals being interposed between the scans. The signal processing takes place during these dead intervals.
The angle encoder generates reference pulses 50 (Fig. 3) by which the individual lines (in direction ZA in Fig. 3) are marked. The linear array detector 22 'comprises fifteen detectors 32, and fifteen reference pulses 50 are generated during each scan, whereby the field of view is subdivided into fifteen times fifteen pixel.
n A g.
1 The seeker 12 is suspended on gimbals, as indicated in Fig. 4, and is adapted to be tilted relative to the gimbal 64 and the seeker head 66 in accordance with controller signal which are provided by a controller 60.
Three rate gyros 68,70 and 72 are mounted on the seeker and respond to the angular speeds w G' W N and wipof the seeker 12 about the pitch, yaw and roll axes, respectively.
Numeral 74 designates signal processing means to which the picture informations of the opto-electronic system 76 of the seeker 12 and, in addition, the angular speed signals w GI W N and wqfrom the rate gyros 68, 70,72 are supplied. The signal processing means 74 apply output signals to the controller 60, to which also signals from the rate gyro are applied, as indicated by the dashed line 72. The controller 60, in turn, controls the torquer 62, as illustrated by line 80.
The field of view 46 is scanned cyclicaly. Picture informations from consecutive scans are processed together by the signal processing means. In order to be able to process picture informations from different scans together, these informations have to be referenced to a common inertial coordinate system. A seeker headfixed coordinate system, as provided by the pixels of the described scanning of the image of the field of view 46 with line addresses and column adresses would not represent such a common inertial coordinate system. A stationary target would be displaced upwards, if the seeker head 66 and thus the seeker 12 made a downward pitch movement. Therefore a picture element might be imaged on a quite different pixel during the second scan of the image of the field of view than during the first scan, so that the seeker head is unable to "know", whether this is the same target or another one, or whether the target moves or the seeker head pitchp-
V- - q For this reason a coordinate correction circuit is provided which transforms the pixels during consecutive scans to a common ineltial coordinate system, whereby consecutive picture informations become comparable. 5 The signal processing means 74 are illustrated in greater detail in figures 5a to g, these figures showing the different phases of the program, the respective active components being drawn in thick solid lines.
The signal processing means 74 comprise a coordinate transformer and integrator circuit 84 to which the angular speed signals N' G and illustrated by an arrow 86 are supplied. This coordinate transformer and integrator circuit 84 provides the translatory and angular variations Y 0 z 0 and 0 of the seeker head-fixed coordinate system referenced to the momentarily defined inertial coordinate system. These signals Y 0 z 0 and 0 are available in digital form at an output 88 of the coordinate transformer and integrator circuit 84.
The analog signals from the linear array detector 22 which are represented by an arrow 89, are converted into digital picture informations by means of an analog-to-digital converter circuit 90, i.e. a digital word is associated with each pixel of the image of the field of view 46 in accordance with the signal amplitude generated in this pixel by the radiation intensity.
These picture informations with their addresses in the seeker head-fixed coordinate system are available at an output 92 of the analog-to-digital converte-r circuit 90.
Numeral 94 designates an end value memory which has a data input 96 and a data output 98 and which serves, in a manner still to be described, to memorize the inertial movement Y E'7JE' v E of the seeker head-fixed coordinate system between consecutive scanning ---mmd 1 times t(n-1) and t(n).
c A coordinate transformer circuit 100 serves to transform the addresses of the pixels at the output 92 from the 5 seeker head-fixed coordinate system into the M. omentarily defined inertial coordinate system.
Two memories 102 and 104 are provided into which, in a manner still to be described, the amplitude values and the addresses of the pixels as transformed by the coordinate transformer circuit 100 are read.
A target selection logic 106 contains signals from the outputs 108-and 110 of the memories 102 and 104, respectively, and recognizes a target in accordance with certain criteria still to be described. The coordinates of this target are stored in a deviation memory 112, which provides a deviation signal representing the target deviation at an output 114.
The program of the signal processing is controlled by a program control unit 116, which receives input signals t S and t B (Fig. 2) from the angle encoder of the seeker 12 at inputs 118,120, and an input'signal TA from the target selection logic 106 at an input 122, when the target selection logic 106 has recognized a target. The program control unit 116 provides control commands for the various components, in a manner still to be described, these control commands at the various control inputs having the following meaning:.
OE = release of data output (output enable) IE = release of data input (input enable) R = reset MUX= parallel-to-series conversion AR = scanning of picture to the right (Fig. 3).
1 9 The output 92 of the analog-to-digital converter circuit 90 is connected to the input 126 of the coordinate transformer circuit 100 through a bus 124.
Furthermore the output 108 of the memory 102 is arranged to be applied to the input 126 through a bus 128, and an output 132 of the target selection logic 106 is arranged to be applied to input 126 through a bus 130.
In addition the output 108 of the memory 102 is applied to an input 136 of the target selection logic through a bus 134.
The output 88 of the coordinate transformer and integrator circuit 84 is arranged to be applied to the input of the end value memory 94 through a bus 138 and to an input 142 of the coordinate transformer circuit 100 through a bus 140..In addition the output 98 of the end value memory 94 can be applied to the input 142 of the coordinate transformer circuit 100 through a bus 144.
The output 146 of the coordinate transformer circuit 100 is arranged to be applied to an input 150 of the first memory 102 through a bus 148, to an input 154 of the second memory 104 through a bus 152, and to an input 158 of the deviation memory 112 through a bus 156.
The output 110 of the second memory 104 is connected to an input 162 of the target selection logic 106 through a bus 160.
Eventually the deviation memory 112 supplies a deviation signal to a bus 164 through its output 114.
The program is determined by the flux diagram of Fig. 6.
During the scanning of the field of view (signal interval) the seeker 12 provides a signal t,3, as mentioned. Furthey-more a square wave signal t is S
X ( k 1 f,' generated during the scanning of each column of the field of view by the mirror 16 and the linear array detector 22, said signal returning to zero, while the mirror 16 is moved from a position, in which the linear array detector 22 scans a column of the field of view, into the next position, in which the adjacent column is scanned. The column signal is generated also during the dead interval. A signal interval flipflop FFS (not shown) is provided in the program control unit
116.
In the initial state of Fig. 5a prior _o the beginning of the n-th picture scan A(n), neither the signal t B nor the column signal t S_ are present. Those coordinate displacements Y EIZE" 'E' which were measured in the time interval between the scan A(n-2) at the moment t(n-2) and the scan A(n-1) at the moment t(n-1) are stored in the end value memory 94. The first memory 102 contains the digital amplitude values from the picture scan A(n-1) with their addresses, i.e. the associated coordinates, transformed into an inertial coordinate system, which coincided with the seeker headfixed coordinate system at the moment t(n-2). The memory 104 contains also the digital amplitude values from the picture scan A(n-1), the addresses, i.e. the associated coordinate values, being referenced by transformation to an inertial coordinate system which coincided with the seeker head-fixed coordinate system at the moment t(n-1), i.e. at the moment when the picture scan A(n-1) was completed.
It be assumed that the target selection logic has not yet recognized a target, so that the signal TA does not appear at the input of the program control unit 116. In this case the program control unit 116 is in the waiting loop W3 in the flux diagram of Fig. 6: The preceding scan did not result in the recognition of a target by the target selection logic 11)6, so that 1 4 the flux diagram of Fig. 6 has to be followed from the rhombus 166 "target recognized" downwards. The test 'It B=?"' which is symbolized by the rhombus 168, is negative, as long as the signal tB does not yet appear, whereby the waiting loop W3 is run through.
When the signal t B appears at the beginning of the scan, thus the test according to rhombus 168 is positive, the waiting loop W3 is left, and the flux diagram is to be followed along the line 170 to the rhombus 172 (cot S =?"), which symbolizes a test for whether the signal t B is present or not.
If this, as assumed, is the case, the path will-extend from the rhombus-174 to the left to a rhombus 176, which symbolizes a test for whether the signal interval flipflop has been set. If this is not the case at the beginning of the scan, the flux diagram will be followed downwards to a rectangle 177, which symbolizes the setting of the signal interval flipflop FFS, and to the rectangle 178. Then the analog-to-digital converter 90 is reset by a signal R. Subsequently a test will be made, whether the column signal t S is present, what is symbolized by the rhombus 180. As long as this signal t S is present, which corresponds to the first pulse 182 in Fig. 4, the waiting loop W2 will be run through. During this time the signals from the linear array detector 22 are converted into corresponding digital amplitude and address signals (coordinates) by the analog-to-digital converter.
When the signal t S has ceased, i.e. on the rear end of the pulse 182 (Fig. 2), the flux diagram is to be followed from the rhombus 180 through line 184 and line 170 to the rhombus 172 aghin. As long as the signal t B is zero, i.e. in the gap between the pulses 182 and 186 in Fig. 2, the waiting loop W 1 wil be run through.
This waiting loop W1 is left upon appearance of the next 1k 1 1 pulse 186 of the signal t B Then the flux diagram is run through as before downwards via rhombus 174 ( tot J-") to the rhombus 176. As meanwhile the signal interval flipflop FFShas been set in accordance with rectangle 177, the test "FFS seC has a positive result, and the flux diagram is run through from the rhombus 176 to the right to the rectangle 188.
Then the commands MUX and OE are applied by the program control unit to the analog-to-digital converter 90 through lines 190 and 192, and the data from the analog-to-digital converter 90 are read serially into the coordinate transformer circuit 100 through the bus 124. Furthermore the command OE is applied to the coordinate transformer and integrator circuit 84 through line 194. Thereby the coordinate transformer and integrator circuit 84 supplies the signals stored at its output through bus 140 to the coordinate transformer circuit 100. Eventually the first memory receives the command IE through line and takes over the output signals of the coordinate transformer circuit through bus 148.
The coordinate transformer and integrator circuit 84 provides the variations Y 0 z 0, 41 0 of the seeker head-fixed coordinate system relative to an inertial coordinate system which, at the moment t(n-1) of the preceding scan, coincided with the seeker head-fixed coordinate system. The coordinate transformer circuit 100 provides the m6asured digital amplitude values of the respective pixels from the data of the coordinate transformer and integrator circuit 84 and the data of the analog-todigital converter, the addresses corresponding to the coordinates in the said inertial coordinate system at the moment t(n-1). Thus the addresses have been transformed by-the coordinate transformer circuit 100. These data are stored in the memory 102.
A 1 T.0- I After this procedure, the flux diagram is again run through to the rectangle 178, i.e. the analog-to-digital converter 80 is reset by a command R through line 198. Subsequently the waiting loop W2 is run through for the duration of the pulse 186 of the signal tS, and the waiting loop W1 is run through during the gap between the pulse 186 and the next- following pulse 120. When the pulse 200 appears, the same operation is carried out with the next column of the field of view in the same manner. This procedure is repeated column-by-column, until the whole field of view has been scanned. At the end of this scan the digital amplitude values of all pixels are stored in the first memory 102 with the coordinates transformed to the moment t(n-1) as addresses, is Now the signal t B ceases, i.e. after the rhombus 174 has been reached, the flux diagram is followed to the right, which again symbolizes a test, whether the signal interval flipflop FFS has been set. This is still the case with the next pulse 204 following the rear end of the signal t B Consequently the flux diagram is run through to the left back to the rectangle 206 and the rectangle 188. In accordance with rectangle 206 the signal interval flipflop FFS is reset. Subsequently the data corresponding to the last column of the field of view are read out and transformed and are stored in the memory 102, wherenpon the analog-to-digital converter 100 is reset.
When the flux diagram is run through the next time through waiting loop W2, waiting loop W1 and rhombus 174.(after the next pulse 208 has appeared) to rhombus 202, the flux diagram is to be followed therefrom further to the right in Fig. 6. This loop represents the signal processing which takes place in the dead interval between the scans of the field of view.
4 At first the end values Y E'ZEt'PE Of the coordinate displacement which exist, after the scan of the field of view has been completed, are read in into the end value memory 94 through bus 138. To this end the end value memory 94 gets a command IE from the program control unit 116 through a line 210, while the coordinate transformer and integrator circuit 84 gets the command OE through line 194. This is symbolized by the rectangle 214 in,the flux diagram.
Thereafter the integrators in the coordinate transformer and integrator circuit 84 are reset by means of a command R through line 216. Then the coordinate transformer and integrator circuit provides, at its output 88, the further variations of the seeker head-fixed coordinate system relative to that inertial coordinate system which coincided with the seeker head-fixed coordinate system at the moment, when the integrators were reset. This operation is symbolized by the rectangle 218 of the.flux diagram.
In the next step, symbolized by the rectangle 220 of the flux diagram, the store contents of the two memories 102 and 104 are applied to the target selection logic 106 through bus 134 and.bus 160, respectively (Fig. 5d).
To this end a command OE is applied to the first memory 102 through line 222, and the target selection logic 106 gets a command IE through line 224 to take over the data from the second memory 104 through bus 160 and to make a target selection.
The memory 102 contains, as described, the data of the scan A(n), the coordinates of the pixels being transformed into an inertial coordinate system which coindided with the seeker head-fixed coordinate system at the moment t(n-1), namely at the moment, at which the integrators of the coordinate transformer and integrator circuit 84 has been reset (rectangle 21-U. As will be explained aw 1 1M 001 MW V9 hereinbelow, the memory 104 contains the data of the scan A(n-1), the coordinates of the pixels being also transformed into the inertial coordinate system, which coincided with the seeker head-fixed coordinate system at the moment t(n-1). Thus the two memories provide the data resulting from consecutive scans referenced to indentical coordinate systems, whereby the data are comparable with each other.
The target selection logic 106 may, for example, operate in accordance with the method of "m from n selection" for the target recognition. This method is known per se (RCA "Electro-Optics Handbook" (1968) 8-1 to 8-7). With this method.the assumption is made that the target signal is only slightly different from the noise of the opto-electric receiving system. Therefore there is a certain probability of a false target signal being supplied from a pixel from a first scan of the field of view, depending on the level of the lowest threshold of the analog-to-digital converter circuit 90 to which the signal from the receiving system is applied. As the noise is uncorrelated, the probability of false target recognition in the target selection logic 106 can be reduced by observing the same pixel in a number n of consecutive scans. If a predetermined number m of exceedings of the lowest threshold is not achieved thereby, the pixel information may be erased in the target selection logic as false target. In the other case a target is recognized. If a plurality of targets is recognized this way, that target is fixed as the one to be tracked, which is closest to the center of the field of view. The target selection logic 106 supplies a signal TA to the input 122 of the program control unit, when a target has been recognized.
q 1 A )g n 1 After the storage contents of the two memories 102 and 104 have been supplied to the target selection logic 106, an exchange of the storage contents takes place, which is symbolized by the rectangle 226 in the flux diagram. The storage contents of the memory 104 is overwritten by the,torage contents of the memory 102, the addresses of the digital amplitudes corresponding to the individual pixels being, however, transformed into an inertial coordinate system which coincided 10 with the seeker head-fixed coordinate system at the moment t(n), i.e. at the moment of the resetting of the integrators of the coordinate transformer and integrator circuit 84, which is effected after the scan A(n). The transformation parameter Y E'ZE and TE for this transformation are stored in the end value memory 94, as described (rectangle 214). As illustrated in Fig. Se, a command OE is applied by the program control
unit 116 to the end value memory 94 through line 228. Then the end value memory 94 supplies the transformation parameters Y VZE and % to the coordinate transformer circuit 100 through bus 144 and input 142. Furthermore the program control unit 116 applies an order OE through the line 222 to the first memory 102 whereby this memoy supplies its storage contents to the input 126 of the coordinate transformer circuit 100 through the bus 128. An order IE, which is applied by the program control unit to the second memory through a line 232 causes take-over of the digital amplitute values from the memory 102 with the addresses transformed by the coordinate transformer circuit 100.
Now the result of the scan A(n) is stored in memory 104 35 referenced, however, to an inertial coordinate system whic coincided with the seeker head-fixed coordinate system at the moment t(n)l 'I t 1 4 'A i 9 1k -...W The computing operation to be carried out to this end by the coordinate transformer circuit is slightly different from the computing operation for the transformation of the coordinates from the analog-to5 digital converter 90 for reading into the memory 102. These computing operations are:
Y A (n) = (Y K(n-1) - Y E (n)). cos T E (n) + ( z K (n-1) - z E (n) s in TE (n) z = (Z - z) cos v - (Y - Y A (n) K (n- 1) E (n). E (n) K(n-1) E.(n) s in TE (n) wherein Y A(n)' z A(n) Y K(n-1)' z Mn-1) y E(n)" z E(n) 1 q, E (n) are the coordinates of a picture element in the seeker head-fixed coordinate system at the moment t(n), are the coordinates of a picture element in the seeker head-fixed coordinate system at the moment t(n-1), are the attitude variation end value signals of the translatory displacement of the coordinate system from the moment t (n-1) till t (n), and is the end value of the rotation of the seeker head-fixed coordinate system from the moment t(n-1) till t(n).
This change of the transformation equation of the coordinate transformer circuit 100 is caused by-a change-over command U which is supplied by the program control unit 116 through a line 234.
26. in the manner described the result of the scan Mn-1) transformed into an inertial coordinate system associated with the moment t(n-1) had been read into the memory 104 during the preceding cycle.
After the data have thus be supplied to the target selection logic 106 and the data from memory 102 have been exchanged to memory 104, a test is made, as is symbolized by rhombus:166, whether the target selection logic 106 has recognized a target and provides the signal TA. If this is not the case the operation described is repeated through rhombus 168. When a target has been recognized, the flux diagram is run through from the rhombus 166 to the left to the rectangle 236. Thereafter the operations illustrated in Fig. 5f will be carried out.
The target selection logic 106 gets a command OE through line 238 and supplies the data of the recognized target, referenced to the coordinate system.associated with the moment t(n-1), to the coordinate transformer circuit 100 through bus 128. The end value memory 94 gets a command OE through line 228, and the coordinate transformer circuit gets the change over command U through line 234 as in Fig. 7e. Therefore it transforms the target coordinates into the coordinate system associated with the moment t(n) in accordance with the equation given hereinbefore. The deviation memory 112 gets the command IE through line 240, whereby the transformed target coordinates are read into the deviation memory 112 through bus 156, the deviation memory providing a corresponding target deviation signal at its output 114 and the bus 164.
Subsequently the program control unit is operated in the waiting loop W3, until the signal t B initiates a new scan of the field of view.
1 A A 2; 1 At the beginning of this next scan A(n+1) the system is in the state illustrated in Fig. 5g. Memory 102 contains the result of the scan A(n) referenced to the coordinate system, which is associated with the moment t(n-1). This storage contents is overwritten during the scan A(n+ l). Memory 104 contains the result of the scan A(n) referenced to the coordinate system which is associated with the moment t(n). The deviation memory 112 contains the target coordinates also referenced to the coordinate system which is associated with the moment t(n) and provides a corresponding deviation signal.
The analog-to-digital converter circuit 90 is illustrated in detail in Fig. 7, only four detectors of the linear array detector 22 being shown. The signals of the detectors are amplified by pre-amplifiers 242. The output signal of each amplifier 242 is filtered by a filter 244 and is applied to a conventional analog- to-digital converter 246. The resolution of the analog-to-digital converter 246 is selected such that the least significant bit (LSB) defines a relatively low threshold, which is matched to the signal amplitude of remote targets, while the most significant bit (MSB) defines a relatively high threshold which is matched to the signal amplitudes of near targets. The outputs of the analog-to-digital converters are connected to a memory 248 each. The memory 248 takes over the analog-to-digital converted amplitude values during the scanning of a pixel, the memory 248 itself being so designed that during the scanning always the maximum aplitude value remains stored. At the end of the scan, the memories 248 are read out by a multiplexer 250 on the command MUX through line 190, and thereafter the memories are reset by the reset command R for the scanning of the next pixel.
4 ib 1 The output signals of the multiplexer 250 are composed of data (i.e. digital amplitude values) and addresses of the scanned pixels. A line address results from the respective detector of the linear array detector 22. A column address is provided by a column counter 253, to which the reference pulses of the column signal (Fig. 4) t S are supplied. A direction signal AR causes upward or dounward counting of these reference pulses depending on the direction of scan.
On output gate 254, which is arranged to be opened by the OE7command through line 192, controlls the application of the data and addresses to the bus 124.
The coordinate transformer circuit 100 receives the attitude variation signals Y 0 z 0. PO and thereby changes the addresses of the individual picture elements defined by the line and column numbers Y A' z A in the seeker head-fixed coordinate system in accordance 20 with Y Y sin 91 + Y K A Cos ZA 0 0 z K = z A Cos (p + Y A sin T + Z 31 wherein Y K' z K are the coordinates of a picture element in an inertial coordinate system, 30 Y A' z A are the coordinates of the picture element in the seeker head-fixed coordinate system of the image of the field of view 46, 35 y 0 'z 0 are, as attitude variation signals, the translatory displacements of the seeker head-fixed coo ystem in inertial space, and 1 c c 1 ff c) 1 21 is the rotation of the seeker head-fixed coordinate system.
These conditions can be seen from Fig. 8, in which T is a target and YATZAT designate the target coordinates In the seeker head-fixed coordinate system and Y T z T designate the target coordinates in a coordinate system rotated relative to the seeker head-fixed coordinate system through the angle - 9.
An example of the coordinate transformer circuit 100 is illustrated in Figures 9 and 10. It transforms the addresses of the individual pixels with each scan of the field of view and reads the amplitude values into the memory 102 under the transformed addresses. If, for example, a pixel with the seeker head-fixed coordinates Y A'ZA is applied, the amplitude data from the respective pixel are read into that storage location of which corresponds to the transformed coordinates.
Fig. 9 illustrates the coordinate transformer circuit 100 schematically. The value from the coordinate transformer and integrator circuit 84 is applied to a computer 258 through bus 140 and the values Y A and Z A from the analog-to-digital converter circuit 90 are applied to the computer through bus 124. YA and Z A are practically the addresses of a pixel in a seeker head-fixed coordinate system, i.e. the number.of a detector element of the linear array detector and a column number provided by the angle encoder. The computer forms Y cos T - Z A sin 9.
y The output signal of the computer together with Y 0, which is provided by the coordinate transformer and integrator circuit 84, is applied to an adder 260, which provides Y K on the bus 148. In similar manner 1P,Z A and Y A are supplied to a computer 264.. whi-rjl.,úWs 2,Lt.., 1 Y A sin op + ZA cos 'p This output of the computer 264 together with Z 0, which is also applied through bus 140, is applied to an adder 266. The adder provides Z K also on the bus 148.
The set-up of the computer 264 and adder 266 is illustrated in greater detail in Fig. 10. The computer 264 contains a read-only memory (ROM) 268 and a read-only memory 270. YA and are supplied to the read-only memory 268 as address. The read-only memory 268 provides Y Y sin qp. Z A and also T are supplied to the read-only memory 270 as address. Then the read-only memory 178 provides Z A cosIT. The two numerical values provided by the read-only memories 268 and 270 are applied to an adder 272, which forms therefrom Y A sinT + Z A cosIF. The output of the adder 272 together with the representation of Z 0 limited to the two most significant bits are applied to the adder 266, which proves Z K The computer 258 is constructed in similar manner.
Fig. 11 illustrates one embodiment of an analog circuit arrangement for forming the attitude deviation signals Y 0 ' Z 0.
The roll gyro 72 provides as output signal the angular speed"Orpof the seeker head about the roll axis. This angular speedwyis integrated by means of an integrator 274. The integrator is reset to zero by a signal R on line 216 after each scan of the field of view. Therefore it povides the angle(f through which the seeker head 12 has rotated about its roll axis since the last scan of the image of the field of view 42. This angle Tis digitalized by an analog-to-digital converter 276 and is available at-aa__2ut2qt 278, which is part --I Z of the data output 88. The output signal of the integrator 274 is applied to a sine function generator 280 and to a cosine function generator 282, which provide signals representing sinT and cos T, respectively.
The signals sin? and cos T as well as signals analog to the angular speeds w andcO about yaw and pitch G N axes from the yaw and pitch gyro 70 and 68, respectively, are applied to an analog computer circuit 284. The computer circuit 146 forms YO = 0 G cos q - W N sin T This signal is integrated by means of an integrator 286, which is also arranged to be reset to zero by the signal R.on line 216. The output signal of the integrator 148 is then analog to the transversal displacement Y 0 of the coordinate system. This analog output signal is converted into a corresponding digital word at an output 289 by an analog-to-digital converter 288.
In similar manner the signals sin and cos as well as the signals % G and w N are applied to a computer circuit 290. The computer circuit 152 forms zo = W N cos If + W G sin V.
The output signal of the computer circuit 290 is integrated by means of an integrator 292, which is also arranged to be reset to zero by the signal on line 216. Then the output signal of the integrator 292 is analog to the transversal displacement Z 0 of the coordinate system. This analog output signal is converted into a corresponding digital word at an output 296 by an analogtodigital converter 294.
The outputs 278,289 and 296 form the data output 88 of Fig. Sa.
b 2t Thus the circuit of Fig. 11 provides the three attitude deviation signals Y 0 z 0 and 9in digital form.
A simplified circuit is shown in Fig. 12. It is assumed therein that the angle Vis small so that cosrf = 1 and the sine can be replaced by the angle. Corresponding elements are designated by the same reference numerals in Fig. 12 as in Fig. 11. Then the sine and cosine function generators can be omitted, and the computer circuits 298 and 300, respectively, receive directly the output signal of the integrator 274. The computer circuit 298 forms is Y =0 - W - 0 G N V and the computer circuit 300 forms z =W + W 0 N G q) The signal processing according to figs. 1 to 12 is suitable for stationary targets. When the target moves, additional measures are necessary, if the picture informations obtained with consecutive scans are to be compared.
Furthermore it may happen that a moving target cannot be observed temporarily. For example a tracked airplane may fly through a cloud. It is essential that the target will be found again even in this case as soon as it becomes visible again to the seeker.
Eventually it is known that fighter planes launch mocktargets (flares) as soon as they notice that they are tracked by a missile, in order to deceive the seeker head and to deviate the missile away from the aircraft and towards the mock-target. It is desirable for the seeker-head to discriminate between the tracked target, i.e. the aircraft, and the,-mock-tatget.
Z.7 24 1 It is the object of the embodiment as shown in figs. 13 to 21, which otherwisely corresponds closely to the embodiment illustrated in figs. 1 to 12, to modify a seeker head such that it provides the possibility to compare the target signals in consecutive scans even with moving targets, to recover a temporarily lost target and to discriminate between the actual target and a mocktarget.
In principle this object is achieved in that (a) the signal processing means are adapted to provide the inertial sight line rate to the target after a target has been selected and, is (b) after each scanning and signal processing cycle, to determine the location in the field of view in which the target is to the expected according to the sight line rate measured during the preceding cycles.
Thus a location is determined by two or more scans in which location the target is to be expected during the next scan. With the "m-out-of-n"method, for example, it can be checked whether a target signal appears at this location. If a target gets lost temporarily, a location defined by calculation is given with each scan in or near which location the target can be recovered. Eventually the determination of the location at or near which the target is to be expected with straight uniform movement permits discrimination between the actual target, which in first approximation moves this way, and a mocktarget (flare) which naturally follows a trajectory different from that of the target (aircraft).
1 0 n For this reason the signal processing means 74 comprise a coordinate transformer and integrator circuit to which the signals of the rate gyros 68,70 and 72 are supplied and which provide attitude variation signals Y 0 z 0 9therefrom in accordance with the attitude variations of a seekerfixed coordinate system relative to an inertial coordinate system which at a predetermined moment, for example in the dead interval after the completion of the preceding scan, coincided with the seeker-fixed coordinate system. Thus all picture informations are referenced to one single inertial coordinate system. After completion of the scan the picture informations are transformed into an inertial coordinate system which coincided with the seeker-fixed coordinate system at the end of the scan, using the end values Y E' z E'9E of the signals provided by the coordinate transformer and integrator circuit. The picture informations are also transformed into this latter inertial coordinate system during the subsequent scan, whereby at this predetermined moment the picture informations from consecutive scans referenced, however, to the same coordinate system are available.
For better understanding the coordinate transformation is at first explained for a stationary target hereinbelow with reference to Figure 13.
Referring to Figure 13 numeral 302 designates the field of view picked up by the seeker 76 during a first scan which is subdivided into columns of pixels by the individual detectors of the linear array detector 22 and into lines by the reference pulses 50. Eight columns and eight lines are illustrated, the columns being designated A to H, and the lines being designated 1 to 8.
t 9 19 411 1 Each line corresponds to a certain moment on the time axis which is illustrated in the upper part of Figur 13. The columns and lines of this field of view define a seeker-fixed coordinate system, which will be designated "measured coordinate system" M 1 hereinbelow.
The picture informations which have been obtained in the measuring coordinate system M I are transformed into an inertial coordinate system 304 which coincided with the measuring coordinate system M I at a predetermined moment t 01 and which will be designated as "inertial coordinate system" K i hereinbelow. A target signal which is obtained from a pixel 306 is transformed into the inertial coordinate system K i in the course of the signal interval SEij as indicated by the arrow 308 as well as by block 310, arrow 312 and block 314. In the inertial coordinate system K i the target signal will, for example, appear in pixel 316, if a pitch movement of the seeker 76 is assumed.
During the dead interval T i but after the predetermined moment t oj, the stored picture information is transformed into an inertial coordinate system which coincided with the seeker-fixed coordinate system at a predetermined moment t oj and which will be designated inertial coordinate system K j hereinbelow. This is symbolised by the arrow 320 as well as by arrow 322 and block 324.
There is a second scan of the field of view, another seeker-fixed coordinate system 326 being now defined and being designated measuring coordinate system M j During this second scan the target appears in pixel 328 of the measuring coordinate system M.. Also during this scan 3 the picture informations are transformed into the associated inertial coordinate system Kj, as indicated by arrow 330 as well as by block 332, arrow 334 and block 324. After the signal acquisition interval SE j the picture informations from both scans referenced to the same low 9 cl coordinate system K i are available. A stationary target appears in the same pixel 336 of the inertial coordinate system Y% i with both scans.
In Figure 13 and in the remaining Figures K i 4- m i designates, for example, the coordinate transformation from the measuring coordinate system M i into the inertial coordinate system K 1.
This mode of operation has been described in detail with reference to figs. 1 to 12.
is Figure 14 shows in the same mode of illustration as Figure 13 the situation with a moving target. Corresponding elements bear the same reference numerals in Figure 14 as in Figure 13.
With the first scan a target is detected in pixel 338 in the measuring coordinate system M I. The coordinate transformation K i ----M i brings the target into pixel 340 of the inertial coordinate system K 1. When after completion of the first scan the picture informations are transformed from the inertial coordinate system K I into the inertial coordinate system Kjj the target will appear in pixel 342 of this coordinate system K j, During the second scan the target appears in pixel 344. A transformation K 3 '1-M I transforms the pixel 344 of the measuring coordinate system M i into the pixel 346 of the inertial coordinate system K j, This pixel is offset to the bottom by two colums relative to pixel 342. This offset represents the movement of the target itself referenced to the inertial coordinate system K j, The inertial sight line rate; may be derived from the offset and the scanning frequency.
c a 1 32 1 The signal processing means are illustrated in their various phases as block diagrams in Figures 15 to 21, the respective active elements being drawn in thick solid lines.
Numeral 348 designates a coordinate transformer, to which the coordinates of the various pixels are supplied and which carries out a coordinate transformation therewith in accordance with the output signals Yo 'z 0, Tof the coordinate transformer and integrator circuit (Figure 4) or with the end values Y EZE' IP E of these output signals stored in an end value memory at the end of a scan at the moment t oj This has been described in detail in the main patent... (patent application P 28 41 748.3). A first memory 350, a second memory 352, a third memory 354 and a fourth memory 356 are provided. The picture informations contained in the memories may be applied to a target selection logic 358.
Numeral 360 designates a computer which is adapted for floating averaging for forming a mean value of the inertial sight line rate 6. A coordinate transformer 362 causes coordinate transformation of the mean value used during the preceding scan into the inertial coordinate system associated with the respective present scan so that a new averaging may take place with the value of the inertial sight line rate obtained in this inertial coordinate system. On the basis of this mean value of the sight line rate the adresses of the picture informations stored in the third and fourth memories are corrected by a correcting unit.
The target selection logic 358 supplies a signal to a target deviation computer 366.
1 3 2_ 1 The mode of operation of the described arrangement is as follows:
As illustrated in Figure 15, the picture informations obtained in the measuring coordinate system M 1 with the first scan are transformed into the inertial coordinate system K 1 by a coordinate transformation K 1 &M 1 by means of a coordinate transformer 348. The picture informations thus transformed are read into the first memory 350.
By the next step (Figure 16) the picture informations from the first memory 350 are applied to the target selection logic 358 during the dead interval following the first scan. When the target selection logic 358 recognizes a possible target, the target coordinates are transformed by the coordinate transformer 348 into the inertial coordinate system K 2 associated with the next signal acquisition (K,-,3;.K 2). The target signals thus transformed with respect to their addresses are again read into the first memory 350, the picture informations stored therein previously being overwritten. Thus the first memory 350 contains the target picture informations referenced to the inertal coordinate system K 2" Figure 17 shows the next scan which provides the picture information in a seeker-fixed measuring coordinate system m 2 The coordinate transformer transforms the picture informations into the inertial coordinate system K 2 The picture informations thus transformed are read into the second memory 352. After the signal acquisition of this scan the picture informations of the second scan are available in the second memory and the picture informations of the first scan are available in the first memory 350, both informations being referenced to the same inertial coordinate system. The two storage contents are applied to the target selection logic 358, where the pictures are compared.
1 3 113 It is checked, as indicated in Figure 17, whether a new target picture information occurs within a "window" defined around the target recognized first. A target picture information appearing within such a "window" is assumed to originate from the same target. At first the "window" is made rather large for the purpose of target detection so that even a moving target appears within the "window" during the second scan.
The coordinate of the two target picture informations are supplied to the computer 360 during the first part of the following dead interval, the computer calculating therefrom the inertial sight line rate or the average of the sight line rate referenced to the inertial coordinate system.
As illustrated in Figure 18, the target picture informations from the second memory 352, i.e. the picture informations from the second scan referenced to the inertial coordinate system K 2' are transformed by the coordinate transformer 348 into the inertial coordinate system K 3 which is associated with the third scan. These transformed picture informations are read into the first memory 350.
The picture informations obtained with the third scan and obtained in the seeker-fixed measuring coordinate system M 3 are transformed into the coordinate system K 3 by the coordinate transformer. The picture informations thus transformed are read into the second memory 352. At the end of the third scan again the picture informations from the second and the third scan referenced to the same coordinate system K 3 are available. These picture informations are supplied to the target selection logic. The target picture informations obtained from the storage contents of the first and second memories provided by the target selection logic 358 are supplied to the third memory 354 1 3k and the fourth memory 356 through the correction unit 364. The correction unit 364 is controlled bv the computer 360. It Drovides the target picture informations as obtained from the storaqe contents of the first and second memories 350 and 352, respectively, but with a correction of the coordinates with respect to 'the inertial siqht --v line rate 9. This inertial sight line ratecror its average are calculated by the computer 360 from the target picture informations of the first and second scans.
The correction of the coordinates of the target picture informations which are read into the third memory 354 from the first memory 350 throuqh the target selection logic and the correction unit 364 corresponds-to the variation of the sight lineaduring the scanning interval, i.e. the time interval from the end of one scan to the end of the next one. The correction of the coordinates of the target picture informations which are read into the fourth memory 356 from the second memory through the target selection logic and the correction unit 364 correspond to the variation of the sight line 3during the time interval between the end of the preceding scan, the moment when the inertial coordinate system K 3 coincided with the seeker-fixed coordinate system M 3' and the moment when the pixel providing the target picture information was scanned.
This is illustrated in Fig.
At the time t oi the seeker-fixed measuring coordinate system M I coincides with the inertial coordinate system K. At this moment the target image is located in pixel 340. The target image is scanned at the moment a a t t. In the time interval from t oi to t i the target image has moved due to the movement of the target itself.
If the pixel 338 scanned as target image at the moment ta is transformed into the inertial coordinate i a - A m system K i without taking the movement of the target itself into account, the target picture information will appear in pixel 368. Transformed into the inertial coordinate system K i the pixel 368 will change into the pixel 370, while the pixel 340 will change into the pixel 342. The inertial sight line rate is derived from the distance of the pixels 342 and 346.
Because of the rather coarse raster of the seeker the --1.91 measurement of the sight line rate 0 is subject to inaccuracy. Therefore the mean value of the measured sight line rates is formed by the computer 360 by means of a floating averaging in accordance with the relation r-7 (n) cr (n- 1) + c (n) 1+1 v 7 wherein a (n-1) is the mean value of the vectorial sight line rate obtained in cycle n-1, a (n) is the mean value Z-P, obtained in cycle n, 0(n) the momentary value of the sight line rate obtained in cycle n, and n and n+1 are serial numbers of the cycles and 1 represents the weight factor for the averaging. In order to permit combination of the mean value 4'(2) derived in the inertial coordinate system K, in the case of Figure 19, with the momentary .2 value a (3) measured in the inertial coordinate system K 3' the mean value a(2) from the computer 360 is supplied to a coordinate transformer 362, whichreceives the end values Y E'ZE''E Of the coordinate transformer and integrator circuit of Fig. 12 and transforms the 91 mean value -,V (2) into the inertial coordinate system K 3 The target picture information stored in the third memory 354 and corrected for the target speed defines a "window" around the pixel containing the target picture information, as indicated in Fig. 19. It can be expected that the target in the picture information stored in the fourth memory 356 and also corrected for the target speed is represented by the I 9 a 3h same or an adjacent pixel. Thus a target picture information from the fourth memory 356 and falling into the window can be regarded as originating from the same target. The window can be made very small in order to suppress secondary targets, for example flares launched by the aircraft. During the target tiacking phase of Fig. 19 the window is substantially smaller than during the target detection in Fig. 17.
p If no target picture information from the fourth memory 356 appears in the window in Fig. 19, what might be due to the fact that the target is only feebly perceptible in the noise and does not provide a target signal with each scan or that the target is covered temporarily, for example by clouds, the location in which this. target is to be expected and around which the window is defined will be computed continuously by the computer 360 based on the last mean value of the sight line rate, until a target signal will appear again in the window. In order to take uncertainties and variations of the inertial sight line rate into account, the window is continuously increased with the time elapsed since the last target recognition..
As il lustrated in Fig. 20 the inertial sight line 9 rate Q(3) is again derived from the target picture informations contained in the memories 250 and 252, both informations being referenced to the inertial coordinate system K and being supplied to.the computer 3.91 360, this sight line rate 0(3) being used in the floating averaging.
At the same time the target picture informations from the second memory 352 are transformed by the coordinate 35 transformer 348 into the inertial coordinate system K 4 which is associated with the fourth scan (Fig. 12) and is read into the first memory 350.
c 1 34t 1 In accordance with Fig. 21 this transformed target picture information is then applied to the target deviation computer 366 via the target selection logic 358, said computer providing a target deviation signal, this target deviation signal tending to orient the seeker 16 towards the target.
is I 7, 1

Claims (1)

  1. Patent Claims
    1. Seeker head comprising field of view scanning means for cyclically scanning the field of view and for providing picture informations referenced to a seeker head-fixed coordinate system, and signal processing means for joint processing of the picture informations from at least two consecutive scans characterized in that a gyro assembly is provided in the seeker head and provides attitude variation signals as a function of attitude variations of the seeker head relative to inertial space, and that the signal processing means comprise a coordinate transformer circuit, to which the attitude variation signals are applied and which are adapted to transform the picture informations from the various scans into a common inertial coordinate system.
    1 2. Seeker head as set forth in claim 1, characterized in that the gyro assembly comprises rate gyros, from the signals of which the attitude variation signals are generated by means of a coordinate transformer and integrator circuit, the integrators of the coordinate transformer and integrator circuit being arranged to be reset to zero once during each scan.
    3. Seeker head as set forth in claim 2, characterized in that the gyro assembly comprises pitch, yaw and roll gyros which respond to angular speeds about the pitch, yaw and roll axes, respectively, c 1 59 1 1 that the output signal of the roll gyro is applied to a first integrator the output signal of which is converted by a first analog-to-digital converter into a digital attitude variation signal representing the roll movement of the seeker head, that the analog output signal of the first integrator is applied to a sine function generator and to a cosine function:generator, that the output signals of the sine function generator, of the cosine function generator.. of. the pitch and of the yaw gyros are applied to a first computing circuit which.forms therefrom an output signal 0 G cos ff - W N sin T, wherein w G is the output signal of the yaw gyro W N is the output signal of the pitch gyro, and cosip and sin9lare the output signals from the cosine and sine function generators, respectively, that the output signal from the first computer circuit is applied to a second integrator the output signal of which is converted by a second analog-to-digital converter into a digital attitude deviation signal representing the translatory movement of the seeker head-fixed. coordinate system in a first inertial direction, that the output signals of the sine function generator, of the cosine function generator, of the pitch and of the gaw gyros are applied to a second computer circuit which forms therefrom 6) COS Cf + sin N C 1 h and that the output signal of the second computer circuit is applied to a third integrator, the output signal of which is converted by a third analog-to-digital converter into a digital attitude deviation signal which represents the tranlatory movement of the seeker head-fixed coordinate system in a second direction perpendicular to the first inertial direction.
    Seeker head as set forth in claim 2, characterized in that the gyro assembly comprises pitch, yaw and roll gyros which respond to the angular speeds about the pitch, yaw and roll axes, respectively, that the output signal of the roll gyro is applied to a first integrator the output signal of which is converted by a first analog-to-digital converter into a digital attitude deviation signal representing the roll movement of the seeker head that the analog output signal of the first integrator and the output signals of the pitch and of the yaw gyros are applied to a first computer circuit, which forms an output signal W G - W N T " wherein w G is the output signal of the yaw gyro, w N is the output signal of the pitch gyro, andqis the output signal of the first integrator, A I 1 - %1.1 41 - that the output signal of the first computer circuit is applied to a second integrator the output signal of which is converted by a second analog-to-digital converter into a digital attitude deviation signal representing the translatory movement of the s.eeker head-fixed coordinate system in a first inertial direction, that the analog output signal of the first integrator and the output signals of the pitch and yaw gyros are applied to a second computer circuit, which forms an output signal to N + W G 9' and that the output signal of the second computer circuit is applied to a third integrator the output signal of which is converted by a third analog-to-digital converter into a digital attitude deviation signal representing the translatory movement of the seeker-head fixed coordinate system in a second direction perpendicular to the first inertial direction.
    Seeker head as set forth in claim 3 or 4, characterized in that the coordinate transformer circuit (100) comprises a first digital computer (258) to which the output signal (rp) of the first analog-to-digital converter and coordinates (Y A'ZA) of a picture element in the seeker headfixed coordinate system are applied, and which forms Y A cos If - Z A sin rf, kh a - #gib - 1 is wherein YA and Z A are the coordinates of the picture elements in the seeker head-fixed coordinate system and 9is the output signal of the first analog-to-digital converter, that, furthermore, the coordinate transformer circuit (100) comprises a first adder (260) to which the digital output signal of the first computer and the output signal (Y 0) of the second analogto-digital converter are supplied and which provides a corrected coordinate (Y K) in an inertial coordinate system, that the coordinate transformer circuit (100) comprises a second digital computer (264) to which the output signal ( 9) of the first analog-to- digital converter and the coordinates (Y A' Z A) of the picture element in the seeker head-fixed coordinate system are applied, and which forms Y A sinT + Z A cos 9 91 and that, eventually, the coordinate transformer circuit (100) comprises a second adder (266) to which the digital output signal of the second computer (264) and the output signal (Z 0) of the third analog-todigital converter are applied and which provides the other corrected coordinate (Z) in the inertial K coordinate system.
    6. Seeker head as set forth in claim 5, characterized in that each of the computers (258,264) comprises a pair of read-only memories (268,270), each of which has applied thereto as address a respective one of the coordinates (Y A and Z A) in the seeker head-fixed c:) 'r earh in combination IP m 1 - 43 1 with the output signal ( T) of the first analog-todigital converter, the read-only memories having stored under each address Y A cosTand -Z A sin Tor Y A sinTand ZA cos4p,, respectively, and.that the outputs of the read- only memories (268,270) are appied to an adder (2'72).
    Seeker head as set forth in anyone of the claims 1 to 6, characterized in that, during each signal processing cycle in a first operation during a scan, the picture informations are transformed by the coordinate transformation circuit into an inertial coordinate system which after completion of the preceding scan, coincided with the seeker head-fixed coordinate system, and the picture informations thus transformed with respect to their addresses are written into a first memory, that upon completion of each scan the attitude variation signals from the coordinate transformation and integrator circuit (84) are written into an end value memory (94), that in a second operation the picture informations stored in the first memory (102) are transformed by the coordinate transformer circuit (100), with the end values of the attitude variation signals stored in the end value memory (94), into an inertial coordinate system which, at the end of the scan, coincided with the seeker headfixed coordinate system, and the picture informations thus transformed with respect to their addresses are written into a second memory (104), and 1 A ---M 4 tt 1 8.
    that a target selection logic (106) is provided, to which the data from the first and second memories (102 and 104, respectively) are applied.
    Seeker head as set forth in claim 7, characterized in that, by a signal (TA) provided by the target selection logic (106) upon the target data provided by the target selection logic (106) are transformed by the coordinate transformation circuit (100) with the end values (Y E'ZE' E) of the attitude variation signals provided by the end value memory, into an inertial coordinate system which coincided with the seeker headfixed coordinate system at the end of the last scan, and that the target data thus transformed are written into a deviation memory, which applies deviation signals to the controller (60).
    9. Seeker head as set forth in Claim 8, characterized in that (a) the signal processing means are adapted to provide the inertial sight line rate to the target after a target has been selected and, (b) after each scanning and signal processing cycle, to determine the location in the field of view in which the target is to be expected according to the sight line rate measured during the preceding cycles.
    1 1 10. Seeker head as set forth in claim 9, characterized in that (a) the signal processing means are adapted to form the average of the inertial sight line rate, by means of floating averaging, from the differences of the target coordinates during consecutive scans, and (b) the location in which the target is to be expected is determined, for each scanning and signal processing cycle, by the average of the sight line rate as provided during the preceding cycles.
    11. Seeker head as set forth in claim 10, characterized in that 791 (a) the average (47(n-1)) of the inertial sight line rate resulting from the preceding scanning and signal processing cycle, which is provided in an inertial coordinate system associated with this cycle, is transformed by the coordinate transformer circuit into an inertial coordinate system associated with the new cycle (A(n)), 7P (b) a sight line rate ( a(n)) in this coordinate system is provided from the target coordinates resulting from the preceding and the new scan in the latter coordinate system, and -qw, 4 1 4-ú (c) the signal processing means are adapted to or form the average cv(n) in the latter coordinate system in accordance with the relation ::75.7 7 1 C- (n- + cy (n) @ (n) = 1+1 12. Seeker head as set forth in anyone of the claims 9 to 11, characterized in that, (a) after the signal processing means have recognized a target, only the picture informations of the pixels within a "window" containing the recognized target are taken into account during the subsequent scanning and signal processing cycles, and, (b) during each scanning and signal processing cycle, the "window" is defined around the location which results from the target coordinates of the preceding cycle transformed into the inertial coordinate system associated with the new cycle and from the sight line rate as the target location to be expected.
    13. Seeker head as set forth in anyone of the claims 9 to 12, characterized in that the respective transformed coordinates are corrected for the displacement of the selected target which displacement results from the sight line rate of the target and the time difference between the moment of the scanning of the pixels and said predetermined moment.
    441 1 14. Seeker head as set forth in claim 13, characterized in that the uncorrected target coordinates which are measured in the inertial coordinate system associated with the respective last scan or are transformed into this coordinate system, respectively, serve to measure the sight line rate.
    15. Seeker head as set forth in plaim 12, characterized in that, is (a) if a target recognized by the target selection logic has got lost, a target location to be expected will be computed continuously by the signal processing means during the subsequent scanning and signal processing cycles taking into account the last measured target coordinates and the sight line rate measured prior to the loss of the target, the sight line rate being transformed into the inertial coordinate system of the respective cycle, and (b) a "window" the picture informations of which are processed is defined around this location.
    16. Seeker head as set forth in claim 15, characterized in that the size of the window increases with the time elapsed since the loss of the target.
    7 1 L 41 1 17. Seeker head as set forth in anyone of the claims 9 to 16, characterized in that is (a) a first, a second, a third and a fourth memory (350,352,354,356) are provided, (b) a coordinate transformer (348) is provided which is controlled by a resettable coordinate transformer and integrator circuit (Fig. 4) to which rate gyro signals (w N' (0 G' wT) are applied or by an end value memory in which the end values of the output signals of said coordinate transformer and integrator circuit are stored after each scan, (c) the coordinate transformer (348) is adapted for coordinate transformation of the picture informations obtained in a seeker-fixed measuring coordinate system (M i) during a scan into an inertial coordinate system (K i) associated with the scan and for coordinate transformation from the inertial coordinate system (K i) associated with the scan into the inertial coordinate system (K j) associated with the next scan, (d) a target selection logic (358) is provided to which the picture informations from the memories (350,352,354,356) are applied and which provides target picture informations of recognized targets, (e) the target picture informations, which are derived by the target selection logic (358) from the first and second memories (350,352), are supplied to a computer (360) for floating averaging to provide a mean value of the P inertial sight line rate (C), 2 1 1 - 4R, - 1 r (f) these target picture informations, furthermore, are supplied to a correction unit (364) which is controlled by the computer (360) and corrects the target picture information for the target speed, (g) the target picture informations are read into the third and fourth memories, respectively (354,356), and (h) the target selection logic (358) is adapted to make a picture comparison of the corrected target picture informations stored in the third and fourth memory (354,356) for the purpose of target recognition.
    1 1 Amendments to the claims have been filed as follows Seeker head comprising field of view scanning means for cyclically scanning the field of view and for providing picture informationf refertL4 to a seeker head-fixed coordinate system, and signal processing means for joint processing of the picture informationj from at least two consecutive scans characterized in that a gyro assembly is provided in the seeker head and provides attitude variation signals as a function of attitude variations of the seeker head relative to inertial space, and that the signal processing means comprise a coordinate transformer circuit, to which the attitude variation signals are applied and which dVt-e adap d ansform the picture Ir information from the A atl common inertial coordinate system.
    2. Seeker head as set forth in claim 1, characterized in that the gyro assembly comprises rate gyros, from the signals of which the attitude variation signals are generated by means of a coordinate 25 transformer and integrator circuit, the integrators of the coordinate transformer and integrator circuit being arranged to be reset to zero once during each scan.
    3. Seeker head as set forth in claim 2, characterized in that the gyro assembly comprises pitch, yaw and roll gyros which respond to angular speeds about the pitch, yaw and roll axes, respectively, 1 k - 54 that the output signal of the roll gyro is applied to a first integrator the output signal of which is converted by a first analog-to-digital converter into a digital attitude variationsignal representing the roll movement of the seeker head, that the analog output signal of the first integrator is applied to a sine function generator and to a cosine functiongenerator, that the output signals of the sine function generator, of the cosine function generator,. of the pitch and of the yaw gyros are applied to a first computing circuit which forms therefrom an output signal W cos 9 - W sin 9, U Ily wherein w G is the output signal of the yaw gyro W N is the output signal of the pitch gyro, and cosq) and sin T are the output signals from the cosine and sine function generators, respectively, that the output signal from the first computer circuit is applied to a second integrator the output signal of which is converted by a second analog-to'-digital converter into a digital attitude deviation signal representing the translatory movement of the seeker head-fixed. coordinate system in a first inertial direction, that the output signals of the sine function generator, of the cosine function generator, of the pitch and of the gaw gyros are applied to a second computer circuit which forms therefrom 6) N COS ff + to G sin rp, 4 1 9 and that the output signal of the second computer circuit is applied to a third integrator, the output signal of which is converted by a third analog-to-digital converter into a digital attitude deviation signal which represents the tranyatory movement of the seeker headfixed coordinate system in a second direction perpendicular to the first inertial direction.
    4. Seeker head as set forth in claim 2, characterized in that the gyro assembly comprises pitch, yaw and roll gyros which respond to the angular speeds about the pitch, yaw and roll axes, respectively, that the output signal of the roll gyro is applied to a first integrator the output signal of which is converted by a first analog-to-digital converter into a digital attitude deviation signal representing the roll movement of the seeker head that the analog output signal of the first integrator and the output signals of the pitch and of the yaw gyros are applied to a first computer circuit, which forms an output signal W G - W N T wherein w G is the output signal of the yaw gyro, w N is the output signal of the pitch gyro, and? is the output signal of the first integrator, 1 is 111_12 that the output signal of the first computer circuit is applied to a second integrator the output signal of which is converted by a second analog-to-digital converter into a digital attitude deviation signal representing the translatory movement of he'seeker head-fixed coordinate system in a first inertial direction, that the analog output signal of the first integrator and the output signals of the pitch and yaw gyros are applied to a second computer circuit, which forms an output signal W N + W G 'p and that the output signal of the second computer circuit is applied to a third integrator the output signal of which is converted by a third analog-to-digital converter into a digital attitude deviation signal representing the translatory movement of the seeker-head fixed coordinate system in a second direction perpendicular to the first inertial direction.
    Seeker head as set forth in claim 3 or 4, characterized in that the coordinate transformer circuit (I@@)- comprises a first digital computer 4258) to which the output signal IF) of the first analog-todigital converter and coordinates of a picture element in the seeker headfixed coordinate system are applied, and which forms Y A cos IF - Z A sin cp, I 1 - - - q 5A_ wherein Y A and Z A are the coordinates of the picture elements in the seeker head-fixed coordinate system andIfis the output signal of the first analog-to-digital converter, that, furthermore, the coordinate transformer circuit (QQQ) comprises a first adder 4Q68) to which the digital output signal of the first computer and the output signal-(F k of the second analog04 to-digital converter are supplied and which provides a corrected coordinate 4---) in an inertial coordinate system, that the coordinate transformer circuit (I comprises a second digital computer +264) to which the output signal -t-" of the first analog-to-digital converter and the coordinates of the t) picture element in the seeker head-fixed coordinate system are applied, and which forms Y A sinq) + Z A cos 9.
    and that, eventually, the coordinate transformer circuit (498) comprises a second adder 4P66 to which the digital output signal of the second computer (244 and the output signal of the third analog-to digital converter are applied and which provides the other corrected coordinate -L2-1 in the inertial W5R14 coordinate sYstem.
    6. Seeker head as set forth in claim 5, characterized in that each of the computers (4&8,264). comprises a pair of read-only memories 2?0-Y, each of which has applied thereto as address a respective one of the coordinates -E---).in the seeker A head-fixed coordinate svstem. each in combination 59 1 is with the output signal of the first analog-to digital converter, the read-only memories having stored under each address Y A cos(fand -Z A sin q) or Y A sinq)and Z A cosq), respectively, and,that the outputs of the read-only memories 4268-,-21901 are appied to an adder (4?2).
    1 Seeker head as set forth in any 1 one of the claims 1 to 6, characterized in that, during each signal processing cycle in a first operation during a scan, the picture informations are transformed by the coordinate transformation circuit into.an inertial coordinate system which after completion of the preceding scan, coincided with the seeker head-fixed coordinate system, and the picture informations thus transformed with respect to their addresses are written into a first memory, that upon completion of each scan the attitude variation signals from the coordinate transformation and integrator circuit +84)- are written into an end value memory (!M)-, that in a second operation the picture informations stored in the first memory-"2) are transformed by the coordinate transformer circuit 44.094, with the end values of the attitude variation signals stored in the end value memory Jm94), into an inertial coordinate system which, at the end of the scan, coincided with the seeker head-fixed coordinate system, and the picture informations thus transformed with respect to their addresses are written into a second memory 44.04-), and 1 1 that a target selection logic (106)- is provided, to which the data from the first and second memories -4109 and 104, r-ecleett!64&el!y) are applied.
    8. Seeker head as set forth in claim 7, characterized in that, by a signal 4ZA) providedby the target selection logic (106) upnn--the target data provided by the target selection logic-+4.G63 are transformed by the coordinate transformation circuit.(4.@@) with the end values of the attitude variation signals provided by the end value memory, into an inertial coordinate system which coincided with the seeker head fixed coordinate system at the end of the last scan, and that the target data thus transformed are written into a deviation memory, which applies deviation signals to the controller +6.e).
    Seeker head as set forth in Claim 8, characterized in that (a) the signal processing means are adapted to provide the inertial sight line rate to the target after a target has been selected and, (b) after each scanning and signal processing cycle, to determine the location in the field of view in which the target is to be expected according to the sight line rate measured during the preceding cycles.
    v -1 t A 51 10. Seeker head as set forth in claim 9, characterized in that (a) the signal processing means are adapted to form the average of the inertial sight line rate, by means of floating averaging, from the differences of the target coordinates during consecutive scans, and (b) the location in which the target is to be expected is determined, for each scanning and signal processing cycle, by the average of the sight line rate as provided during the preceding cycles.
    11. Seeker head as set forth in claim 10, characterized in that -77 (a) the average ( c(n-l)) of the inertial sight line rate resulting from the preceding scanning and signal processing cycle, which is provided in an inertial coordinate system associated with this cycle, is transformed by the coordinate transformer circuit into an inertial coordinate system associated with the new cycle (A(n)), :-,p, (b) a sight line rate ( a(n)) in this coordinate system is provided from the target coordinates resulting from the preceding and the new scan in the latter coordinate system, and 9 1 1 S-% (c) the signal processing means are adapted to -=F form the average cr(n) in the latter coordinate system in accordance with the relation =:5 77 7 - 7 a (n) (n- + a (n) 1+1 1 12. Seeker head as set forth in anyone of the claims 9 to 11, characterized in that, (a) after the signal processing means have recognized a target, only the picture information$ of the pixels within a "window" containing the recognized target axe taken into account during the subsequent scanning and signal processing cycles, and, (b) during each scanning and signal processing cycle, the "window" is defined around the location which results from the target coordinates of the preceding cycle transformed into the inertial coordinate system associated with the new cycle and from the sight line rate as the target location to be expected.
    1 13. Seeker head.as set forth in anylone of the claims 9 to 12, characterized in that the respective transformed coordinates are corrected for the displacement of the selected target which displacement results from the sight line rate of the target and the time difference between the moment of the scanning of the pixels and said predetermined moment.
    v 1 1 14. Seeker head as set forth in claim 13, characterized in that the uncorrected target coordinates which are measured in the inertial coordinate system associated with the respective last scan or are transformed into this coordinate system, respectively, serve to measure the sight line rate.
    15. Seeker head as set forth in claim 12, characterized 10 in that, (a) if a target recognized by the target selection logic has got lost, a target location to be expected will be computed continuously by the signal processing means during the subsequent scanning and signal processing cycles taking into account the last measured target coordinates and the sight line rate measured prior to the loss of the target, the sight line rate being transformed into the inertial coordinate system of the respective cycle, and (b) a "window" the picture informations of which are processed is defined around this location.
    16. Seeker head as set forth in claim 15, characterized in that the size of the window increases with the time elapsed since the loss of the target.
    of 4 GP j 17. Seeker head as set forth in anyone of the claims 9 1 to 16, characterized in that (a) a first, a second, a third and a fourth memory 4 352,354,3 " are provided, (b) a coordinate transformer -348) is provided which is controlled by a resettable coordinate transformer and integrator circuit (Fig. 4) to which rate gyro signals are applied or by an end value memory in which the end values of the output signals of said.
    coordinate transformer and integrator circuit are stored after each scan, (c) the coordinate transformer (j48 is adapted for coordinate transformation of the picture informations obtained in a seeker-fixed measuring coordinate system top during a scan into an inertial coordinate system Itv associated with the scan and for coordinate transformation from the inertial coordinate system (j!; associated with the scan into the inertial coordinate system _1. associated with the next scan, (d) a target.selection logic +J358 is provided to which the picture information# from the memories ±35e,352-,,-3--T4,35el a=%!2. applied and which provides target picture informations of recognized targets, (e) the target picture information$, which a-r-e derived by the target selection logic (998) from the first and second memories ±3.5e,352, ack-- supplied to a computer -(36e) for floating averaging to provide a mean value of the inertial sight line rate (G, 4 1 is 611 L. (f) th& gsf target picture information, furthermore, supplied to a correction unit-4364) which is controlled by the computer (360)- and corrects the target picture information for the target speed, (g) the target picture informations areread into the third and fourth memories, respectively and (h) the target selection logic is adapted to make a picture comparison of the corrected target picture informationj stored in the third and fourth memory 954,356. for the purpose of target recognition.
GB7933009A 1978-09-26 1979-09-24 Seeker head Expired - Fee Related GB2300323B (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE2841748A DE2841748C1 (en) 1978-09-26 1978-09-26 Search head, especially for automatic target tracking
DE2932468A DE2932468C1 (en) 1978-09-26 1979-08-10 Seeker head

Publications (3)

Publication Number Publication Date
GB7933009D0 GB7933009D0 (en) 1996-07-17
GB2300323A true GB2300323A (en) 1996-10-30
GB2300323B GB2300323B (en) 1997-03-19

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GB7933009A Expired - Fee Related GB2300323B (en) 1978-09-26 1979-09-24 Seeker head

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GB (1) GB2300323B (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106094822B (en) * 2016-06-27 2022-12-16 中国计量大学 Inertial guided vehicle positioning method based on auxiliary positioning device and inertial guided vehicle

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB818494A (en) * 1900-01-01
GB736200A (en) * 1943-02-18 1955-09-07 Sperry Gyroscope Co Inc Improvements in or relating to aiming systems for missile-despatching apparatus
GB900047A (en) * 1959-04-20 1962-07-04 North American Aviation Inc Integrated aircraft fire control autopilot

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB818494A (en) * 1900-01-01
GB736200A (en) * 1943-02-18 1955-09-07 Sperry Gyroscope Co Inc Improvements in or relating to aiming systems for missile-despatching apparatus
GB900047A (en) * 1959-04-20 1962-07-04 North American Aviation Inc Integrated aircraft fire control autopilot

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GB2300323B (en) 1997-03-19

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