Common aperture multi-sensor boresight mechanism

Abstract: A boresight mechanism 10 incorporating internal boresight target generator 28 to generate a boresight target signal for properly aligning first and second sensors 22, 24. Beam splitter 52 and corner reflector 60 are positioned along optical path 100 such that sensor 22 and sensor 24 can view either the boresight target signal or a target signal without requiring optical elements to be slued into and out of position to provide a clear line of sight.

Description: The present invention relates generally to a multiple sensor, electro-optical fire control system employing a common aperture and, more particularly, to a boresight mechanism having an internal boresight target generator for properly aligning the infrared and visible sensors of the electro-optical fire control system without firing the laser, and which does not require the line of sight to be moved to view externally mounted reflectors or sources. A prior art optical aiming assembly is known from EP-A-0165170. Further, a boresight target generator is known from US-A-5025149. Other optical alignment devices are known from GB-A-2163868 and EP-A-0179186. Current military weaponry employ electro-optical fire control systems to detect, track and deliver weapons to desired targets. These fire control systems often use multiple sensors, such as visible sensors (TV) and forward looking infrared sensors (FLIR), and lasers to perform these functions. These sensors require extremely accurate boresighting in order to satisfy the error limits imposed by the associated weapons, especially precision laser guided weapons. Current fire control system technology employs an external boresight target for aligning and calibrating the TV and FLIR sensors located off-gimbal at which the laser is fired in order to generate a boresight target signal. This shortens the operational life of the laser, increases the time required to appropriately boresight the sensors and creates a potential hazard for the personnel operating the system. Furthermore, most current fire control systems employ multiple apertures to allow each sensor to view targets simultaneously. The use of numerous apertures is not desired since the apertures are vulnerable targets for enemy fire and are difficult to protect or camouflage. A further limitation of current fire control systems is that the optical components of the fire control system must be slued into and out of position to boresight the system. As such, many configurations used today for multiple sensor electro-optical fire control systems lack the ability to be quickly and accurately boresighted while maintaining a common aperture for all of the components of the fire control system. Accordingly, it is an aim of the present invention to solve one or more of the aforementioned problems. In accordance with the aims and advantages of the present invention, there is provided a multi-sensor, electro-optical boresight mechanism comprising: an optical bench; telescope means, mounted on said optical bench, for receiving a target signal; first sensor means, mounted on said optical bench, for sensing a first frequency component of said target signal in pre-expanded space and generating an image therefrom; second sensor means, mounted on said optical bench, for sensing a second frequency component of said target signal in pre-expanded space and generating an image therefrom; boresight target generation means, mounted on said optical bench, for internally generating a boresight target signal along a first optical path; and optical means, affixed to said optical bench, for allowing said first and second sensor means to sense said boresight target signal in pre-expanded space. A preferred embodiment of the present invention also incorporates a laser for generating a rangefinder/designation signal to locate and designate desired targets along the same optical path as the boresight target signal. Higher boresight accuracy is achieved by generating both the boresight target signal and the laser designation signal in pre-expanded (i.e., low magnification) space. In addition, shutter means are employed along the optical paths to block undesired radiation from destroying the sensors or being transmitted out through the telescope. The various features and advantages of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, wherein: FIG. 1 is a perspective of the common aperture multi-sensor boresight mechanism showing the relationship of the various components in accordance with the principles of the present invention; FIG. 2 is a schematic drawing of the boresight mechanism showing the optical components of the present invention in their organizational relationship operating in a boresighting mode; and FIG. 3 is a schematic drawing similar to FIG. 2 showing the present invention operating in a laser rangefinding/designation mode. Referring now to FIG. 1, boresight target generator 28 and laser 46 are attached to optical bench 11 such that a signal generated by either is transmitted along a common optical path. Various optical elements, including 36, 38, 42, 44 and 50, further detailed herein, are employed to allow a target signal, either generated by boresight target generator 28 or received through telescope 12, to be viewed by first and second sensors 22, 24 (not shown). Boresight mechanism 10 can operate in either a boresight mode or a designating mode. In boresight mode a boresight target signal is internally generated by boresight target generator 28 and projected through the optical elements of boresight mechanism 10 to precisely align first and second sensors 22, 24 (not shown). In rangefinder/laser designation mode laser 46 produces a designation signal by generating light pulses which are projected through telescope 12 thereby designating target 110 and causing a return signal to be reflected therefrom. During rangefinder/laser designation mode sensors 22, 24 can be employed to view the return signal received through telescope 12. The return signal can be transmitted to rangefinder 23 along optical path 100 to determine the range of target 110. The return signal can also be tracked by a laser homing weapon to guide and deliver the weapon to the desired target. While the present invention, as described, employs laser 46 for generating the designation signal, one skilled in the art would readily recognize that the boresight mechanism of the present invention may be employed in a common aperture multi-sensor fire control system that utilize other types of target designation signals. Referring now to FIGS. 2 and 3, boresight target generator 28 includes source bulb 30 located behind target plate 32 having pinhole aperture 33 located therein for attenuating a broadband, incandescent, boresight target signal produced by source bulb 30. The boresight target signal is projected along optical path 100. Collimating lens 34 and beam splitter 36 located along optical path 100 as shown are adapted to collimate the visible and infrared frequencies generated by boresight target generator 28. Laser 46 is located adjacent to beam splitter 36 such that a laser designation signal generated by laser 46 reflects off beam splitter 36 along first optical path 100 in alignment with the boresight target signal. Rangefinder 23 is interposed between laser 46 and beam splitter 36 to measure the time delay between when a light pulse leaves laser 46 and when it returns after reflecting off target 110. The measured time delay is used to calculate the range of target 110. While various components may be used for boresight target generator 28, collimating lens 34, and beam splitter 36, suitable and presently preferred components are disclosed in U.S. Patent No. 5,025,149 entitled, "Integrated Multi-spectral Boresight Target" to Hatfield, which is assigned to the assignees of the present invention and is incorporated by reference herein. Planar reflector element 38 located along optical path 100 reflects a signal transmitted along optical path 100 into pre-expander 40 which employs concave mirrors 42, 44 to magnify the signal. Planar reflector element 50 located along optical path 100 directs the signal towards beam splitter 52. Beam splitter 52 transmits the visible and infrared components of the boresight target signal along optical path 100. In addition, front surface 54 of beam splitter 52 is adapted to reflect the laser designation signal along optical path 106. Corner reflector 60 located at the end of optical path 100 opposite boresight target generator 28 retro-reflects the boresight target signal back precisely parallel along optical path 100 towards beam splitter 52. The rear surface 56 of beam splitter 52 reflects a portion of the retro-reflected boresight target signal along optical path 102. Beam splitter 58 located along optical path 102 transmits the visible frequency component of the target signal further along optical path 102 and reflects the infrared frequency component of the target signal, either the boresight target signal or the return signal, along optical path 104. Sensor 22, such as a TV sensor, located at the end of optical path 102 opposite beam splitter 52, senses the visible frequency component of the target signal and generates a visible image therefrom. Sensor 24, such as a FLIR, located at the end of third optical path 104 opposite second beam splitter means 58, senses the infrared frequency component of the target signal and generates a visible image therefrom. Telescope 12, located adjacent to beam splitter 52 along optical path 106 enables the laser designation signal generated by laser 46 to be projected out onto target 110 (not shown). Telescope 12 includes concave mirror 14, convex mirror 16, and concave mirror 18 for magnifying and directing the target signal along optical path 106. Sensor shutter 26, located along optical path 102 between beam splitter 52 and corner reflector 60, can be positioned to prevent residual laser energy transmitted through beam splitter 52 from damaging sensors 22, 24. Boresight shutter 20, located along optical path 106 can be positioned to prevent the boresight target signal from being transmitted through telescope 12. Boresight mechanism 10 is shown operating in a boresighting mode in FIG. 2. Boresight target generator 28 is energized causing a boresight target signal measuring approximately 6.34 mn (one-quarter of one inch) in diameter to be transmitted along optical path 100. The visible and infrared frequency component of the boresight target signal are collimated by collimating lens 34, transmitted through beam splitter 36 and reflected by planar reflector element 38 into pre-expander 40. The boresight target signal is expanded fourfold by concave mirrors 42, 44 to approximately 25.4 mm (one inch) in diameter. The expanded boresight target signal is reflected by planar reflector element 50 and transmitted through beam splitter 52 into corner reflector 60. Boresight shutter 20 is positioned along optical path 106 to prevent boresight target signal reflected off the front surface 54 of beam splitter 52 from being transmitted along optical path 106 and out telescope 12. The boresight target signal transmitted through beam splitter 52 is retro-reflected by corner reflector 60 back towards beam splitter 52 such that the boresight target signal entering and exiting corner reflector 60 along optical path 100 are precisely parallel. The rear surface 56 of beam splitter 52 reflects approximately one percent (1%) of the boresight target signal along optical path 102. The balance of the retro-reflected boresight target signal is transmitted through beam splitter 52 back along optical path 100. The boresight target signal reflected along optical path 102 encounters beam splitter 58. The visible frequency component of the boresight target signal is transmitted through beam splitter 52 and received by sensor 22, while the infrared frequency component of the boresight target signal is reflected off beam splitter 52 along optical path 104 and received by second sensor 24. The visual and infrared components of the boresight target signal are used to precisely align first and second sensors 22, 24 with the boresight target signal. Boresight mechanism 10 is shown operating in a rangefinding/laser designation mode in FIG. 3. Laser 46 is energized to generate a laser designation signal, approximately 6.34 mm (one-quarter of one inch) in diameter which is projected onto beam splitter 36 and reflected along first optical path 100 as shown. The laser designation signal is reflected by planar reflector element 38 into pre-expander 40 and magnified by concave mirrors 42, 44 to approximately 25.4 mm (one inch) in diameter. Planar reflector element 50 reflects the expanded laser designation signal onto the front surface 54 of beam splitter 52 where the laser designation signal is reflected along optical path 106. Sensor shutter 26 is positioned along optical path 100 in front of corner reflector 60 so that laser designation signal which may be transmitted through beam splitter 56 will not be transmitted onto sensors 22, 24. Beam splitter 52 reflects the laser designation signal into telescope 12 where concave mirror 14, convex mirror 16 and concave mirror 18 magnifies the laser designation signal to approximately 152 mm (six inches) in diameter and projects it out onto target 110 (not shown). The reflection of the laser designation signal from target 110 generates a return signal which can be used by laser-guided weapons to track the desired target. In this mode of operation, telescope 12 is also employed to receive the target signal, such as the return signal. The return signal is magnified by telescope 12 and directed towards beam splitter 52 along the optical path 106. Beam splitter 52 transmits the visible and infrared frequency components of the target signal along optical path 102. Beam splitter 58 transmits the visible frequency component of the target signal along optical path 102 where it is received by sensor 22. Beam splitter 58 reflects the infrared frequency component of the target signal along optical path 104 where it is received by sensor 24. In the preferred embodiment the laser designation signal is transmitted through rangefinder 23 to initialize a timing function. A portion of the return signal reflected off target 110 and received by telescope 12 as described above is reflected off the front surface 54 of beam splitter 52 along optical path 100. Beam splitter 36 reflects the return signal back into rangefinder 23 to stop the timing function. From this data rangefinder 23 calculates the range of target 110. From the foregoing, those skilled in the art should realize that the present invention provides an improved multi-sensor, electro-optical fire control system which incorporates internal boresight target generator 28 to precisely align sensors 22, 24 without firing laser 46. The present invention greatly reduces the likelihood of a mishit resulting from improper alignment of sensors 22, 24 with the line of sight of the laser designation signal. The present invention significantly improves on the previous state the art which relied on external boresight targets illuminated by a laser, or factor preset mechanical boresight alignments, or a combination of the two. The accuracy of the boresighting procedure is improved by locating boresight target generator 28 and laser 46 on optical bench 11. Substantial safety hazards associated with firing the high powered laser are eliminated by incorporating boresight target generator 28. The present invention further provides a boresight mechanism that utilizes fixed powered optical components and a common aperture telescope to reduce boresight error buildup. Furthermore, the present invention allows sensors 22, 24 to be boresighted during flight with the entire boresighting process requiring less than 10 seconds as compared with several minutes for other boresighting mechanisms. As a result, the present invention provides a more maintainable, smaller, lighter, less expensive, higher performance boresight mechanism for an electro-optical fire control system. Although the invention has been described with particular reference to a preferred embodiment, variations and modifications can be effected within the scope of the following claims.

Claims: A multi-sensor, electro-optical boresight mechanism comprising: an optical bench (11); telescope means (12), mounted on said optical bench (11), for receiving a target signal; first sensor means (22), mounted on said optical bench (11), for sensing a first frequency component (102) of said target signal in pre-expanded space and generating an image therefrom; second sensor means (24), mounted on said optical bench (11), for sensing a second frequency component (104) of said target signal in pre-expanded space and generating an image therefrom; boresight target generation means (28), mounted on said optical bench (11), for internally generating a boresight target signal along a first optical path (100); and optical means (52,58,60), affixed to said optical bench (11), for allowing said first and second sensor means (22,24) to sense said boresight target signal in pre-expanded space. A boresight mechanism according to claim 1, wherein: said first sensor means (22) senses a visible frequency component of said target signal; and said second sensor means (24) senses an infrared frequency component of said target signal. A boresight mechanism according to claim 1 or claim 2, wherein said optical means comprises: corner reflector-means (60) disposed at an end of the first optical path (100) opposite the boresight target generation means (28) for retro-reflecting the boresight target signal; first beam splitter means (52) interposed between the boresight target generation means (28) and the corner reflector means (60) along the first optical path (100) for transmitting the boresight target signal towards the corner reflector means (60) along the first optical path (100) and reflecting said boresight target signal retro-reflected by said corner reflector means (60) from a rear surface (56) thereof along a second optical path (102); said first sensor means (22) being disposed along the second optical path (102) opposite the first beam splitter means (52); second beam splitter means (58) interposed between the first beam splitter means (52) and the first sensor means (22) along the second optical path (102) for transmitting the first frequency component of the boresight target signal towards the first sensor means (22) and reflecting the second frequency component of the boresight target signal therefrom along a third optical path (104); and said second sensor means (24) being disposed along the third optical path (104) opposite the second beam splitter means (58). A boresight mechanism according to any preceding claim, wherein said boresight target generator means (28) includes: source bulb means (30) for generating an incandescent boresight target signal; target plate means (32) disposed adjacent to the source bulb means (30), said target plate means (32) having a pinhole aperture (33) sufficiently sized for attenuating the incandescent boresight target signal; and collimating means (34) interposed between the target plate means (32) and the first beam splitter means (52) for collimating the first and second frequency component of the boresight target signal. A boresight mechanism according to any preceding claim, wherein said boresight mechanism further comprises pre-expander means (40) interposed between the boresight target generation means (28) and the telescope means (12) for magnifying a signal transmitted along the first optical path (100). A boresight mechanism according to any preceding claim, wherein said boresight mechanism further comprises sensor shutter means (26) for blocking a signal prior to impingement on the first or second sensor means (22,24). A boresight mechanism according to any preceding claim, wherein said boresight mechanism further comprises boresight shutter means (20) for blocking a signal being transmitted or received through the telescope means (12). A boresight mechanism according to any preceding claim, wherein said boresight mechanism further comprises laser source means (46), mounted on said optical bench (11), for transmitting a laser designation signal through said telescope means (12). A boresight mechanism according to claim 8, wherein said optical means further comprises third beam splitter means (36) disposed adjacent to the laser source means (46) for reflecting the laser designation signal therefrom and transmitting the boresight target signal along the same optical path (100). A boresight mechanism according to claim 8 or claim 9, wherein said first beam splitter means (52) reflects the laser designation signal from a front surface (54) thereof through the telescope means (12) along a fourth optical path (106). A boresight mechanism according to claim 8, claim 9 or claim 10, wherein said boresight mechanism further comprises rangefinding means (23) for measuring a time delay between the laser designation signal transmitted through said telescope means (12) and a return signal received by said telescope means (12). A multi-sensor, electro-optical boresight mechanism comprising: telescope means (12) having an aperture for receiving a target signal; first sensor means (22) for sensing a first frequency component of said target signal in pre-expanded space and generating an image therefrom; second sensor means (24) for sensing a second frequency component of said target signal in pre-expanded space and generating an image therefrom; boresight target generation means (28) for internally generating a boresight target signal along a first optical path (100); corner reflector means (60) disposed along the first optical path (100) for retro-reflecting the boresight target signal; first beam splitter means (52) interposed along the first optical path (100) between the boresight target generation means (28) and the corner reflector means (60) for transmitting the boresight target signal towards the corner reflector means (60) along the first optical path (100) and for reflecting the retro-reflected boresight target signal along a second optical path (102); second beam splitter means (58) disposed along the second optical path (102) between the first beam splitter means (52) and the first sensor means (22) for transmitting the first frequency component of the boresight target signal towards the first sensor means (22) and reflecting the second frequency component of the boresight target signal along a third optical path (104) towards the second sensor means (24).

Inventors: HATFIELD DEAN, KIUNKE PAUL, HATFIELD, DEAN, KIUNKE, PAUL
Applicants: HUGHES AIRCRAFT CO, HUGHES AIRCRAFT COMPANY
Application year: 1993
Main classification: F41G3
IPC codes: F42B15, F41G3, G01C15, F41G1