Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1999-08-26
2001-09-11
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C356S138000, C359S401000
Reexamination Certificate
active
06288381
ABSTRACT:
BACKGROUND
The present invention relates generally to electro-optical systems, and more specifically, to a system that provides for line of sight stabilization and auto alignment of off-gimbal passive and active electro-optical sensors.
The assignee of the present invention manufactures electro-optical systems, such as forward looking infrared (IR) receivers and laser designator/range receiver systems, for example, that include passive and active sensors. A typical electro-optical system includes subsystems that are located on a gimbal while other subsystems that are located off of the gimbal.
Some off-gimbal sensor and laser systems have no auto-alignment of the sensor and laser lines of sight nor any compensation for any motion due to vibration, thermal or g-force angular deformation in and between the two optical paths. Large errors between the sensor and laser lines of sight are present that limit the effective laser designation ranges, weapon delivery accuracy, and target geo-location capability, all of which require precise laser and sensor(s) line of sight alignment and stabilization.
The resolution and stabilization requirements for third generation tactical airborne infrared (IR) systems are in the same order of magnitude as those required by space and strategic systems, but with platform dynamics and aerodynamic disturbances that are orders of magnitude higher, even above those encountered by tactical surface systems. The environments of third generation airborne system approach both extremes and can change rapidly during a single mission. However, conformance to the physical dimensions of existing fielded system is a driving constraint in their design.
Ideally, a high resolution imaging and laser designation system in a highly dynamic disturbance environment would typically have, at least, a four gimbal set, with two outer coarse gimbals attenuating most of the platform and aerodynamic loads and the two inner most, flexure suspended gimbals providing fine stabilization, with the inertial measurement unit (IMU), IR and visible imaging sensors, and a designating/ranging laser located on the inner most inertially stabilized gimbal.
To reduce gimbal size, weight and cost, the assignee of the present invention has developed a pseudo inner gimbal set for use on various tactical airborne and airborne surveillance systems. This pseudo inner gimbal set uses miniature two-axis flexure suspended mirrors mounted on the inner gimbal together with the IMU and IR sensor, in a residual inertial position error feedforward scheme. The pseudo inner gimbal set replaces the two innermost fine gimbals, while maintaining equivalent performance. With increasing aperture size and constraints required to maintain the size of existing fielded systems, some tactical airborne IR systems are forced to locate the IR and visible sensors and laser off the gimbals using an optical relay path.
In order to re-establish the ideal configuration, an on-gimbal IR sensor(s) and laser configuration can be implemented with an active auto-alignment scheme employing miniature two-axis mirrors, laser reference source(s) and a photodetector. An active auto-alignment and fine stabilization configuration would in effect be equivalent to having the IR sensor(s) and auxiliary components, such as a laser, all mounted on the stabilized inner gimbal. This configuration may be used with any off gimbal multi-sensor system requiring a coincident and stabilized line of sight (LOS), such as targeting systems, and the like.
A previously developed off-gimbal sensor and laser auto-alignment system developed by the assignee of the present invention that provides for such an auto-alignment scheme is disclosed in U.S. Pat. application Ser. No. 09/152,952, filed Sep. 14, 1998, entitled “System for Pseudo On-Gimbal, Automatic Line-of-sight Alignment and Stabilization of Off-Gimbal Electro-Optical Passive and Active Sensors”. This system has a separate two-axis mirror on an inner gimbal to perform the enhanced line of sight stabilization function to dynamically steer both beams along laser and IR sensor lines of sight. The steering command to the stabilization mirror is the residual position error of inertial rate loops that inertially stabilize the inner gimbal. An on-gimbal auto-alignment photodetector is operated at null.
It is an objective of the present invention to provide for an improved system that provides for line of sight stabilization and auto alignment of off-gimbal passive and active electro-optical sensors, and which improves upon the system disclosed in the above-identified patent application.
SUMMARY OF THE INVENTION
To accomplish the above and other objectives, the present invention comprises an integrated system for providing automatic line of sight alignment and stabilization of off-gimbal electro-optical passive and active sensors. The system dynamically boresights, aligns and stabilizes one or more sensor input beams and a laser output beam with automatic closed loop feedback with an on-gimbal reference light (photo) detector, two off-gimbal, time multiplexed, modulated optical-reference sources and two alignment mirrors. Alternatively, a reference source may be located on the gimbal while individual light detectors are aligned with the sensor and laser beams.
More particularly, the present invention comprises at least one reference source that outputs at least one reference beam that is optically aligned with the line-of-sight of at least one sensor. A laser reference source outputs a laser reference beam that is optically aligned with the line-of-sight of the laser. A laser alignment mirror adjusts the alignment of the line of sight of the laser beam. A sensor alignment mirror adjusts the line of sight of the optical paths of the at least one sensor and the laser. Combining optics couples the plurality of reference beams along a common optical path. A light detector, or photodetector, disposed on gimbal apparatus that detects the plurality of reference beams. A processor is coupled to the light detector, and the alignment mirrors, processes signals detected by the photodetector, and outputs control signals to the respective mirrors to align the line-of-sight optical paths of the at least one sensor and the laser.
The present integrated system eliminates additional processor software loading, and the cost of, volume of, power of, and complexity to drive the stabilization mirror by combining the stabilization function with the auto-alignment function. This is achieved by dynamically steering the null of the alignment light detector with the inertial rate stabilization loop residual position error signal.
The present and previously developed off-gimbal sensor and laser auto-alignment systems have one alignment loop nested within the other, making the alignment capability of the outer alignment loop dependent on the performance inner of the loop. However, the present integral auto-alignment system has a feed across error term, wherein the inner loop error is summed into the outer loop error, to effectively decouple the outer and inner loops to minimize alignment errors between both loops.
Aligning the sensor(s) and laser lines of sight to the on-gimbal reference light detector is equivalent to having both the sensor(s) and laser mounted on a stabilized inner gimbal. Also, dynamic steering of the light detector null point provides a common optical reference path for enhanced stabilization of the sensor(s) and laser lines of sight.
The system provides for automatic boresighting and aligning of the sensor input beam coincident with the dynamic null of the on-gimbal light detector, which is mechanically aligned to the system line of sight, by correcting for initial sensor optical train component misalignments.
The system provides for dynamic maintenance of the sensor boresight by automatically correcting the sensor line of sight angle caused by deformations of the IR/CCD optical bench due to thermal and platform g-forces, nutation due to derotation mechanism wedge angle deviation errors, rotation axis eccentricity a
Alkov Leonard A.
Allen Stephone B.
Lenzen, Jr. Glenn H.
Raytheon Company
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