Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Aeronautical vehicle
Reexamination Certificate
1998-04-07
2001-01-30
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Aeronautical vehicle
C244S003160
Reexamination Certificate
active
06181988
ABSTRACT:
BACKGROUND
The present invention relates generally to missile guidance systems, and more particularly, to a missile guidance system employing a fixed missile seeker having an adjustable look angle.
Conventional missile seekers employ a gimbal system that typically includes rate gyros, resolvers, torquers, bearings, and a support structure therefor. Infrared or visible television cameras have heretofore been used on missiles for the purpose of implementing a missile seeker to provide missile guidance.
However, simply fixing the camera to the missile forces a compromise between field of view and resolution because cameras typically have a fixed number of image pixels in azimuth and elevation. Using pursuit guidance against moving targets is usually not satisfactory because of the high lateral acceleration required as the missile closes on the target. Proportional guidance requires an offset look angle relative to the velocity vector of the missile to account for the velocity of the target. Accommodating this look angle requirement by enlarging the field of view usually increases the pixel size to the point where resolution does not define the target adequately for tracking purposes. Consequently, prior art attempts to use fixed television cameras in missile seekers has not been successful.
Accordingly, it is an objective of the present invention to provide for a missile guidance system employing a fixed missile seeker having an adjustable look angle that overcomes the limitations of and improve upon prior art missile seeker designs.
SUMMARY OF THE INVENTION
To meet the above and other objectives, the present invention provides for an improved missile guidance system employing a missile seeker having a fixed body (i.e., a body that is fixed relative to the missile) that has an adjustable look angle. The missile seeker comprises an infrared or visible television camera that is fixed to the body of the missile that has adjustable look or viewing angle, which is changed to keep a target within and generally centered in the field of view of the camera. The video output of the camera is processed by a tracker to generate target angle and line of sight rate signals. The target angle signal is input to pointing angle adjustment apparatus that is used to adjust the look angle of the camera.
In one embodiment, the pointing angle adjustment apparatus comprises a stepper motor which is used to control the angular position of a gimbal on which the camera is mounted to control the pointing angle of the camera. Alternatively, the pointing angle adjustment apparatus may comprise one or more stepper motors that control an adjustable zoom lens or a plurality of optical wedges, respectively, that replace the gimbal. These alternative embodiments are less costly than implementing the gimbaled camera embodiment.
A body angular rate output signal of a body-fixed inertial measurement system having a built-in rate gyro is summed with the line of sight rate signals from the tracker to determine the inertial line of sight rate of the moving target. The inertial line of sight rate is driven to zero or a low value by a control system in order to accurately track a target. The control system and missile dynamics of the missile are employed to generate a body angle signal. The body angle signal is input to a difference circuit along with the camera pointing angle signal output by the pointing angle adjustment apparatus to generate a desired camera pointing angle that is input to the pointing angle adjustment apparatus to point the camera in the desired pointing direction.
The present invention eliminates the use of a gimbal system that is conventionally used as part of the missile seeker, and thus significantly reduces the cost of the missile seeker by eliminating rate gyros, resolvers, torquers, structure, and bearings. The measured line of sight rates are driven to zero or a low fixed value depending on the selected guidance law used by the seeker.
The present invention uses inexpensive and reliable stepper motors to point the camera at approximately the desired angle, while keeping the target within the field of view dictated by resolution requirements. The stepper motor has a number of fixed stopping points within and beyond the field of view, and they are selected to keep the target within the field of view. In general, the line of sight rate of the moving target is measured using the output from the camera and the body-fixed inertial measurement system, and the line of sight rate driven to zero.
When the stepper motor moves from one fixed angle to the next one, the target is temporarily lost. However, a target tracker on the missile is used to reacquire the target. This is not difficult because the step size is known and tracking processes employed in the tracker easily reacquires the target.
The present system reduces the cost of the seeker while keeping the field of view small enough to provide the resolution required by the tracker. However, the present invention is limited in the degree of target acceleration that can be processed. Never the less, the present system may be readily used against tank and helicopter targets, for example, or other targets that have reasonable line of sight rates.
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patent: 4520973 (1985-06-01), Clark et al.
patent: 4690351 (1987-09-01), Beckerleg et al.
patent: 4738412 (1988-04-01), Ozunas
patent: 5125595 (1992-06-01), Helton
patent: 5201895 (1993-04-01), Grosso
patent: 5323987 (1994-06-01), Pinson
Coleman Guy B.
Schneider Arthur J.
Collins David W.
Cuchlinski Jr. William A.
Gibson Eric
Lenzen, Jr. Glenn H.
Raytheon Company
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