Aim point correlator
United States Patent 3923273
A system is presented for locking an electro-optical seeker to a desired get without recourse to a television type reproduction of the target scene. A special gunsight is provided in which the axis of an electro-optical scanning system is automatically aligned with the cross-hairs that the operator uses to sight the target. The seeker axis is then varied until signals from the seeker correlate with signals from the scanning system within the gunsight, at which time the seeker axis is in proper alignment with the target sighted with the crosshairs.
US Patent References:
Photoelectric object tracking system using signal delay and multiplying correlators
Bertram - December 1966 - 3290506
Radio controlled missile with television camera
Halton - August 1967 - 3337161
Photoelectric object tracking system using signal delay and multiplying correlators
Bertram - December 1966 - 3290506
Radio controlled missile with television camera
Halton - August 1967 - 3337161
Application Number:
04/614527
Publication Date:
12/02/1975
Filing Date:
01/30/1967
View Patent Images:
Export Citation:
Assignee:
The United States of America as represented by the Secretary of the Navy (Washington, DC)
Primary Class:
Other Classes:
348/169, 250/203.500
International Classes:
F41G7/00; G01S3/786; G01S3/78; F41G7/00
Field of Search:
250/227,23R,23CT 178/6LC,6.8,7.6,DIG.21 350/11 244/3.15,3.16
Primary Examiner:
Farley, Richard A.
Assistant Examiner:
Buczinski S. C.
Attorney, Agent or Firm:
Sciascia St., Richard Amand Joseph Phillips S. M. T. M.
Claims:
What is claimed is
1. For use in an electro-optical guidance system an aim point correlator comprising:
2. For use in an electro-optical guidance system an aim point correlator for correlating the image of a target as viewed by the gun-sight of an aircraft and the image of the target as viewed by the seeker of a missile to be launched against the target from the aircraft, the combination comprising:
1. For use in an electro-optical guidance system an aim point correlator comprising:
2. For use in an electro-optical guidance system an aim point correlator for correlating the image of a target as viewed by the gun-sight of an aircraft and the image of the target as viewed by the seeker of a missile to be launched against the target from the aircraft, the combination comprising:
Description:
BACKGROUND
The present invention relates to electro-optical missile guidance systems and more particularly to electro-optical missile guidance systems wherein the electro-optical seeker is locked to a desired target independent of a television type reproduction of the target scene, imperfections in the mounting alignment of the missile and in-flight flexing of the aircraft structures.
In prior known systems of high-accuracy air-to-surface homing missiles it has been necessary to provide a television display in the launching aircraft cockpit to show precisely the scene being viewed by the missile seeker in order that the seeker tracking circuits may be locked to the desired target. Without this provision to show precisely the scene being viewed by the missile seeker, slight misalignments in mounting the missile to the aircraft, drifts in the electronic circuitry of the missile seeker, flexure of the aircraft structures due to variations in flight conditions, and other sources of error might cause the seeker to be locked to an object other than the desired target. With the television display arrangement, the pilot first maneuvers the launch aircraft to point toward the desired target, and then shifts his attention to his cockpit display and remotely controls the seeker tracking gates (or corrects the aircraft heading) to bring the gates into spatial coincidence with the image of the selected target. For multiple launching of missiles, the pilot would repeat the gate controlling sequence for each seeker. The television display must be sufficiently bright that the pilot does not have to become dark adapted after viewing bright clouds and landscape.
SUMMARY
The present invention provides a missile tracking system which forces the missile seekers to have the same aim point as the aircraft gunsight by correlating what the sensor or each seeker sees with what is seen by a similar sensor that looks through the gunsight. By the use of an array of overlapping circular scans, a simultaneous comparison basis is provided for retaining the alignment or "tracking" once the alignment has been achieved. A simple coded output from each of the parallel match detectors provides the error signal to correct the seeker scan position to counter any drift.
The present invention makes it possible to eliminate a cockpit television display, permits a free interchange of weapons between guided and unguided types, provides quicker target acquisition, and avoids the pilot diversion associated with viewing a television display.
Many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
FIG. 1 is a schematic diagram of a preferred embodiment of the invention.
FIG. 2 is a graph showing the alignment of reference system of the embodiment of FIG. 1.
FIG. 3 is a graph showing a correlation search of a missile seeker.
FIG. 4 is a graph showing the match detection mode.
FIG. 5 is a graph showing the automatic tracking mode.
FIG. 6 shows one form of a multi-aperture image dissector used in the invention.
Referring now to the drawings there is shown in FIG. 1 a gunsight 10 which receives reflected light energy from a target. A partially silvered mirror 12 reflects a portion of the light received to a multi-aperture image dissector (MAID) 14 and also passes light to the pilot 16 where the image of the target can be viewed. By use of the aircraft control stick 13 the aircraft airframe 15 can be made to maneuver to bring gunsight 10 into line with the target. A master scan oscillator 18 provides the sine and cosine scanning voltages that will produce a circular scan in dissector 14. An automatic gain control circuit 20 has as its input the video from the center aperture of dissector 14 which provides an output voltage to control the gain of dissector 14 in accordance with the average scene brightness encountered in the course of the center circular scan. The sine and cosine outputs of master scan oscillator 18 are also coupled to quadrature pulse generator 22 which for each of scan quadrant generates a pulse that is fed to scan centering circuit 24. The output signals from multi-aperture image dissector 14 are fed to match detectors 26 where they are compared with the video signal received at terminal 28 from the seeker (not shown). The output signals from match detectors 26 are fed to sequence control circuits 30 which produce seeker control signals that are fed to the seeker AGC circuit, scan control circuit and memory circuits at output terminals 32, 34, and 36, respectively. Pulses for triggering sequence control circuits 30 are provided by a search pattern generator 38. Pilot 16 also provides an input to sequence control circuits 30 via seeker lock button 17.
In operation, the correlator accomplishes its function in four steps, which are illustrated in FIGS. 2 through 6. First, the multi-aperture dissector (FIG. 6) associated with the gunsight is caused to perform a circular scan 40 that is electronically aligned by means of scan centering circuit 24 to center on the point defined by the gunsight crosshairs 41; this scan produces a reference video signal 42 whose waveform depends on the scene being viewed at a given instant, except that signals 43 representing the crosshairs are superimposed at the points in the scan where the crosshairs come in front of the scene. Second, a synchronized circular scan of equal diameter (1.0°) is established in each seeker, and these scans are made by electronic deflection to search over their respective images through an angle of ±2° in both pitch and yaw (FIG. 3) about the nominal seeker axis position (±2° is the maximum alignment deviation anticipated between each seeker axis and the point identified by the gunsight crosshairs). Third, the video signal resulting from the scan in each seeker is continuously checked against the reference video from the gunsight dissector by match detectors 26, and when a match throughout a scan cycle is detected (FIG. 4), the searching action for that particular seeker is stopped. Fourth, as the search actions are stopped, each seeker is switched into a condition in which automatic alignment tracking of the seeker axis with that of the center aperture of the gunsight dissector (FIG. 5) is maintained by the correlator. Each seeker is thus accurately and dynamically aligned so that the axis of its circular scan coincides with that of the scan of the gunsight dissector, which in turn is aligned with the axis of the gunsight. False matches which may occur momentarily due to coincidental similarities between different portions of the scene viewed will be quickly discarded and a search for true alignment reinstituted as the scene changes due to forward motion and maneuvering of the aircraft.
The type of automatic tracking action selected for the aim point correlator depends upon a simultaneous comparison technique that can be most easily implemented by the use of a multiple-aperture type of image dissector in the gunsight. The multi-aperture arrangement of the dissector in the gunsight is illustrated in FIG. 6 and the overlapping circular scans that are obtained with this arrangement are illustrated in FIGS. 4 and 5. The arrangement consists of nine apertures 44 in a 3 × 3 matrix. Channeltron type multiplier channels 45 of the Bendix Research Laboratories may be utilized at the output end of the dissector which will make it possible to space these apertures only one resolution element apart. Thus nine video outputs will be derived: one from a circular scan centered on the crosshair position as discussed above, one from a circular scan displaced one resolution element to the right, one from a scan displaced both one element upward and one element to the right, one from a scan displaced one element upward, etc. In the correlator tracking action, coincidence of the video from a given seeker with that from the center scan of the gunsight dissector will produce no correction of the seeker scan axis, while coincidence of the seeker video with that of the right circle of the gunsight dissector will result in a small leftward correction of the seeker scan axis, coincidence with the up circle will result in a downward correction, etc. The alignment will thus be retained without reverting to the search mode despite possible electronic drifts or flexure of structures between the cockpit and the missile seeker. The multiple aperture arrangement not only makes possible this simultaneous comparison type of tracking but also speeds up the search time since it makes it possible to check the seeker video signal simultaneously against nine different reference video signals.
The first of the four steps of the correlation process described above is implemented by quadrature pulse generator 22 and the scan centering circuit 24. The quadrature pulse generator 22 may be a set of four blocking oscillators arranged to trigger respectively at the four points in the scan cycle when either the sine or cosine voltage becomes zero, and generator 22 therefore generates a pulse 23 for each quadrant of advance of the circular scan. The scan centering circuit 24 may be a set of bistable multivibrator circuits (commonly called "flip flops"), each of which is turned on by a quadrature pulse 23 and turned off by a subsequent crosshair signal 43, followed by differential detector circuits that compare the on cycles of the opposing multivibrators to derive dc outputs that control the position of the dissector scanning and thereby center the scan. Thus the scan positioning is based on the relative timing of the quadrature pulses 23 and the black-level video signals 43 that result as the scan crosses each crosshair, and when the quadrature pulses and the corresponding black-level video signals are respectively in coincidence, the central scan circle is properly centered about the crosshair point. The scan centering circuit 24 should have a very long time constant so that integration will serve to eliminate any false centering effects caused by other black-level signals that appear momentarily due to dark line-like objects (e.g., asphalt roads) in the scene viewed by the gunsight dissector.
The second step in the correlation process (that of causing seeker search) is performed by the search pattern generator 38. This unit includes a back-to-back sawtooth generator for horizontal search and a synchronized staircase waveform generator for vertical search that combine to produce the raster indicated in FIG. 3. The faster circuit scan is treated as an ac signal that is superimposed on the slower search pattern, which is treated as dc, and the two together are fed to the seekers in the missiles.
Both the third and fourth steps of the correlation process are performed basically by the match detectors 26, while the sequence control circuits 30, which can readily be implemented by a suitable connection of relays, regulate the switching of individual seekers from step to step as the correlation progresses. Each match detector may consist of a difference detector, an integrating circuit (to determine that the match is obtained over a complete cycle or more), and a bistable output; each detector will accept two analog video inputs and give a single digital-type "yes-no" output that indicates whether or not the two inputs match each other over a complete scan cycle. An entire "bank" of match detectors will be required--a separate one to compare the video from each seeker with each of the nine videos from the gunsight dissector. For each seeker being correlated, the outputs of the match detectors as a group will give (1) an indication of whether or not a match is present at that instant, and (2) an indication of the position of any existing match with respect to the desired match involving the center aperture of the matrix. The first output from match detectors 26 can be supplied as a voltage to initiate appropriate relay action in the sequence control circuits 30; the second can be supplied in the form of small dc yaw and/or pitch correction signals that can be delivered to the seeker via terminals 36 to center the scan as required. During the correlation search and tracking processes, the sequence control circuits 30 cause the AGC circuit within each seeker to switch to a functioning mode that directly parallels that of the correlator AGC circuit in order that the amplification of the respective dissectors will be equal and the resultant videos will be of comparable voltage levels; and these sequence circuits also cause the seeker's own scanning circuits to be temporarily deactivated and the scan/search signals from the correlator to be substituted.
When the pilot has a target sighted in his crosshairs and pushes the "Seeker Lock" button, 17, the sequence control circuits 30 cause the seeker in the selected missile to commence independent scanning through activation of the seeker's own scan circuit, and also cause the seeker to convert to an AGC mode that is optimized for seeker gray-level tracking, as described in copending application Ser. No. 434,740 filed Feb. 18, 1965 entitled "Gray-Level Angle-Gated Electro-Optical Seeker." In the lock-on process, the seeker memory circuits retain the aim point positional information supplied by the correlator at the instant of switchover; the seeker commences its circular scan about this point at essentially zero scan diameter, and gradually increases this diameter until changes in gray level occur which signify that the edges of the target have been reached, whereupon normal seeker tracking and scan size control functions take over. The gray-level memory in the seeker first "memorizes" the target gray level encountered when the scanning circle is at essentially zero diameter, and thereafter tracks the gray level in the manner described in the above-referenced copending application.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
The present invention relates to electro-optical missile guidance systems and more particularly to electro-optical missile guidance systems wherein the electro-optical seeker is locked to a desired target independent of a television type reproduction of the target scene, imperfections in the mounting alignment of the missile and in-flight flexing of the aircraft structures.
In prior known systems of high-accuracy air-to-surface homing missiles it has been necessary to provide a television display in the launching aircraft cockpit to show precisely the scene being viewed by the missile seeker in order that the seeker tracking circuits may be locked to the desired target. Without this provision to show precisely the scene being viewed by the missile seeker, slight misalignments in mounting the missile to the aircraft, drifts in the electronic circuitry of the missile seeker, flexure of the aircraft structures due to variations in flight conditions, and other sources of error might cause the seeker to be locked to an object other than the desired target. With the television display arrangement, the pilot first maneuvers the launch aircraft to point toward the desired target, and then shifts his attention to his cockpit display and remotely controls the seeker tracking gates (or corrects the aircraft heading) to bring the gates into spatial coincidence with the image of the selected target. For multiple launching of missiles, the pilot would repeat the gate controlling sequence for each seeker. The television display must be sufficiently bright that the pilot does not have to become dark adapted after viewing bright clouds and landscape.
SUMMARY
The present invention provides a missile tracking system which forces the missile seekers to have the same aim point as the aircraft gunsight by correlating what the sensor or each seeker sees with what is seen by a similar sensor that looks through the gunsight. By the use of an array of overlapping circular scans, a simultaneous comparison basis is provided for retaining the alignment or "tracking" once the alignment has been achieved. A simple coded output from each of the parallel match detectors provides the error signal to correct the seeker scan position to counter any drift.
The present invention makes it possible to eliminate a cockpit television display, permits a free interchange of weapons between guided and unguided types, provides quicker target acquisition, and avoids the pilot diversion associated with viewing a television display.
Many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
FIG. 1 is a schematic diagram of a preferred embodiment of the invention.
FIG. 2 is a graph showing the alignment of reference system of the embodiment of FIG. 1.
FIG. 3 is a graph showing a correlation search of a missile seeker.
FIG. 4 is a graph showing the match detection mode.
FIG. 5 is a graph showing the automatic tracking mode.
FIG. 6 shows one form of a multi-aperture image dissector used in the invention.
Referring now to the drawings there is shown in FIG. 1 a gunsight 10 which receives reflected light energy from a target. A partially silvered mirror 12 reflects a portion of the light received to a multi-aperture image dissector (MAID) 14 and also passes light to the pilot 16 where the image of the target can be viewed. By use of the aircraft control stick 13 the aircraft airframe 15 can be made to maneuver to bring gunsight 10 into line with the target. A master scan oscillator 18 provides the sine and cosine scanning voltages that will produce a circular scan in dissector 14. An automatic gain control circuit 20 has as its input the video from the center aperture of dissector 14 which provides an output voltage to control the gain of dissector 14 in accordance with the average scene brightness encountered in the course of the center circular scan. The sine and cosine outputs of master scan oscillator 18 are also coupled to quadrature pulse generator 22 which for each of scan quadrant generates a pulse that is fed to scan centering circuit 24. The output signals from multi-aperture image dissector 14 are fed to match detectors 26 where they are compared with the video signal received at terminal 28 from the seeker (not shown). The output signals from match detectors 26 are fed to sequence control circuits 30 which produce seeker control signals that are fed to the seeker AGC circuit, scan control circuit and memory circuits at output terminals 32, 34, and 36, respectively. Pulses for triggering sequence control circuits 30 are provided by a search pattern generator 38. Pilot 16 also provides an input to sequence control circuits 30 via seeker lock button 17.
In operation, the correlator accomplishes its function in four steps, which are illustrated in FIGS. 2 through 6. First, the multi-aperture dissector (FIG. 6) associated with the gunsight is caused to perform a circular scan 40 that is electronically aligned by means of scan centering circuit 24 to center on the point defined by the gunsight crosshairs 41; this scan produces a reference video signal 42 whose waveform depends on the scene being viewed at a given instant, except that signals 43 representing the crosshairs are superimposed at the points in the scan where the crosshairs come in front of the scene. Second, a synchronized circular scan of equal diameter (1.0°) is established in each seeker, and these scans are made by electronic deflection to search over their respective images through an angle of ±2° in both pitch and yaw (FIG. 3) about the nominal seeker axis position (±2° is the maximum alignment deviation anticipated between each seeker axis and the point identified by the gunsight crosshairs). Third, the video signal resulting from the scan in each seeker is continuously checked against the reference video from the gunsight dissector by match detectors 26, and when a match throughout a scan cycle is detected (FIG. 4), the searching action for that particular seeker is stopped. Fourth, as the search actions are stopped, each seeker is switched into a condition in which automatic alignment tracking of the seeker axis with that of the center aperture of the gunsight dissector (FIG. 5) is maintained by the correlator. Each seeker is thus accurately and dynamically aligned so that the axis of its circular scan coincides with that of the scan of the gunsight dissector, which in turn is aligned with the axis of the gunsight. False matches which may occur momentarily due to coincidental similarities between different portions of the scene viewed will be quickly discarded and a search for true alignment reinstituted as the scene changes due to forward motion and maneuvering of the aircraft.
The type of automatic tracking action selected for the aim point correlator depends upon a simultaneous comparison technique that can be most easily implemented by the use of a multiple-aperture type of image dissector in the gunsight. The multi-aperture arrangement of the dissector in the gunsight is illustrated in FIG. 6 and the overlapping circular scans that are obtained with this arrangement are illustrated in FIGS. 4 and 5. The arrangement consists of nine apertures 44 in a 3 × 3 matrix. Channeltron type multiplier channels 45 of the Bendix Research Laboratories may be utilized at the output end of the dissector which will make it possible to space these apertures only one resolution element apart. Thus nine video outputs will be derived: one from a circular scan centered on the crosshair position as discussed above, one from a circular scan displaced one resolution element to the right, one from a scan displaced both one element upward and one element to the right, one from a scan displaced one element upward, etc. In the correlator tracking action, coincidence of the video from a given seeker with that from the center scan of the gunsight dissector will produce no correction of the seeker scan axis, while coincidence of the seeker video with that of the right circle of the gunsight dissector will result in a small leftward correction of the seeker scan axis, coincidence with the up circle will result in a downward correction, etc. The alignment will thus be retained without reverting to the search mode despite possible electronic drifts or flexure of structures between the cockpit and the missile seeker. The multiple aperture arrangement not only makes possible this simultaneous comparison type of tracking but also speeds up the search time since it makes it possible to check the seeker video signal simultaneously against nine different reference video signals.
The first of the four steps of the correlation process described above is implemented by quadrature pulse generator 22 and the scan centering circuit 24. The quadrature pulse generator 22 may be a set of four blocking oscillators arranged to trigger respectively at the four points in the scan cycle when either the sine or cosine voltage becomes zero, and generator 22 therefore generates a pulse 23 for each quadrant of advance of the circular scan. The scan centering circuit 24 may be a set of bistable multivibrator circuits (commonly called "flip flops"), each of which is turned on by a quadrature pulse 23 and turned off by a subsequent crosshair signal 43, followed by differential detector circuits that compare the on cycles of the opposing multivibrators to derive dc outputs that control the position of the dissector scanning and thereby center the scan. Thus the scan positioning is based on the relative timing of the quadrature pulses 23 and the black-level video signals 43 that result as the scan crosses each crosshair, and when the quadrature pulses and the corresponding black-level video signals are respectively in coincidence, the central scan circle is properly centered about the crosshair point. The scan centering circuit 24 should have a very long time constant so that integration will serve to eliminate any false centering effects caused by other black-level signals that appear momentarily due to dark line-like objects (e.g., asphalt roads) in the scene viewed by the gunsight dissector.
The second step in the correlation process (that of causing seeker search) is performed by the search pattern generator 38. This unit includes a back-to-back sawtooth generator for horizontal search and a synchronized staircase waveform generator for vertical search that combine to produce the raster indicated in FIG. 3. The faster circuit scan is treated as an ac signal that is superimposed on the slower search pattern, which is treated as dc, and the two together are fed to the seekers in the missiles.
Both the third and fourth steps of the correlation process are performed basically by the match detectors 26, while the sequence control circuits 30, which can readily be implemented by a suitable connection of relays, regulate the switching of individual seekers from step to step as the correlation progresses. Each match detector may consist of a difference detector, an integrating circuit (to determine that the match is obtained over a complete cycle or more), and a bistable output; each detector will accept two analog video inputs and give a single digital-type "yes-no" output that indicates whether or not the two inputs match each other over a complete scan cycle. An entire "bank" of match detectors will be required--a separate one to compare the video from each seeker with each of the nine videos from the gunsight dissector. For each seeker being correlated, the outputs of the match detectors as a group will give (1) an indication of whether or not a match is present at that instant, and (2) an indication of the position of any existing match with respect to the desired match involving the center aperture of the matrix. The first output from match detectors 26 can be supplied as a voltage to initiate appropriate relay action in the sequence control circuits 30; the second can be supplied in the form of small dc yaw and/or pitch correction signals that can be delivered to the seeker via terminals 36 to center the scan as required. During the correlation search and tracking processes, the sequence control circuits 30 cause the AGC circuit within each seeker to switch to a functioning mode that directly parallels that of the correlator AGC circuit in order that the amplification of the respective dissectors will be equal and the resultant videos will be of comparable voltage levels; and these sequence circuits also cause the seeker's own scanning circuits to be temporarily deactivated and the scan/search signals from the correlator to be substituted.
When the pilot has a target sighted in his crosshairs and pushes the "Seeker Lock" button, 17, the sequence control circuits 30 cause the seeker in the selected missile to commence independent scanning through activation of the seeker's own scan circuit, and also cause the seeker to convert to an AGC mode that is optimized for seeker gray-level tracking, as described in copending application Ser. No. 434,740 filed Feb. 18, 1965 entitled "Gray-Level Angle-Gated Electro-Optical Seeker." In the lock-on process, the seeker memory circuits retain the aim point positional information supplied by the correlator at the instant of switchover; the seeker commences its circular scan about this point at essentially zero scan diameter, and gradually increases this diameter until changes in gray level occur which signify that the edges of the target have been reached, whereupon normal seeker tracking and scan size control functions take over. The gray-level memory in the seeker first "memorizes" the target gray level encountered when the scanning circle is at essentially zero diameter, and thereafter tracks the gray level in the manner described in the above-referenced copending application.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.