Electronic image stabilization

• US 4,637,571 A
• Filed: 09/03/1985
• Issued: 01/20/1987
• Est. Priority Date: 09/03/1985
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Phillips, William R., Holder, Donald W.
• Primary Examiner(s): Jordan, Charles T.
• Application Number:
  US06/771,751
• Time in Patent Office: 504 Days
• Field of Search: 244/3.16, 244/3.15, 244/3.14, 244/3.11
• US Class Current: 244/3.16
• CPC Class Codes: F41G 7/2253 Passive homing systems, i.e. comprising a receiver and do not requiring an active illumination of the target
• CPC Class Codes: F41G 7/2293 using electromagnetic waves other than radio waves

Abstract

In an optical guidance system, body fixed electronic image stabilization of television imaging is used to allow strapdown seeker guidance in a missile. Electronic image stabilization eliminates the need for a stabilized sensor or seeker platform while providing the same line-of-sight information that would have been obtained from the platform. Body fixed electronic image stabilization compensates for routine vibrational and rotational motion experienced by a missile airframe during flight. This compensation is accomplished by deliberately underscanning the camera and driving the camera'"'"'s deflection coils with signals from pitch and yaw body rate sensors on the missile. The image developed on the camera detector raster is thereby moved in an equal and opposite direction to the sensed, experienced, motion during the same instant that the motion is occuring. Compensation thus stabilizes the resultant image, which would otherwise be a blur of motion on the display screen.

Claims

1. In a target tracking system wherein a television image of a target is used for guidance of a missile toward the target, a method of compensating for undesirable missile body motion and providing a stable television image output from the television camera to the missile target tracker, comprising the steps of:

rigidly mounting a video camera to the missile body;

directing the camera lens along a field-of-view that is referred to the missile longitudinal axis;

deriving a television image of a target within the field of view;

sensing missile body disturbances;

providing missile pitch and yaw angular velocity signals in response to said disturbances;

processing said angular velocity signals;

coupling said processed angular velocity signals to a television camera'"'"'s vertical and horizontal deflection coils and;

moving the camera scanning raster of the television camera in the opposite direction of undesirable missile body motion for providing said stable image output to the missile target tracker.

2. A method of compensating for undesirable missile body motion and providing a stable image output from a television camera to a missile target tracker as set forth in claim 1, and further comprising the steps of:

summing a line-of-sight, pitch and yaw, rate output from the tracker with respective of said processed pitch and yaw angular velocity signals; and

integrating the respective summed signals prior to the step of coupling.

3. A method of compensating for undesirable missile body motion and providing a stable image output from a television camera to a missile target tracker as set forth in claim 2, and wherein the step of processing provides error rate damping of the angular velocity signals.

4. In a missile system wherein a missile is directed toward a target and the missile comprises at least a video camera rigidly mounted to the missile body, a rate gyro, a video tracker, and filter compensation circuits;

a method of compensating for undesirable missile body disturbances comprising the steps of;

detecting an optical image of a target within the field-of-view of said video camera;

sensing missile body disturbances in pitch and yaw angular velocity with said rate gyros;

tracking the target with an optical contrast tracker to provide a line-of-sight pitch and yaw rate signal for directing missile guidance;

combining the tracker'"'"'s respective pitch and yaw rates with the rate gyros respective pitch and yaw rates; and

driving the video camera'"'"'s deflection coils to cancel out undesired image motion by moving the camera scanning raster in the opposite direction to the sensed direction of missile body motion.

5. In a target tracking system wherein a television image of a target is sensed by a sensor and used for guidance of a missile in response to the target position within the sensor'"'"'s field-of-view, the improvement of an electronic image stabilization system for providing a stabilized target image output from the sensor, comprising:

an optical sensor for viewing a scene of interest and having an electrical control input and an optical image output;

said sensor being body fixed to said missile;

a video optical contrast tracker coupled to receive the output of said sensor and for providing a line-of-sight rate output that is indicative of the relationship of a target, within the sensor field-of-view, to the sensor;

a missile autopilot responsive to said line-of-sight rate output for directing missile trajectory;

pitch and yaw rate gyros fixed to said missile body for providing pitch and yaw angular velocity outputs in response to motion disturbances affecting the missile;

means coupled to said rate gyros outputs and to said tracker output for providing integrated outputs of the combined sums of tracker and gyro pitch signals and the combined sums of tracker and gyro yaw signals respectively, said integrated outputs being coupled to provide respective pitch and yaw bias inputs on said control input to drive the optical sensor output in the opposite direction of missile body motion disturbances.

6. In a target tracking system the improvement of an electronic image stabilization system as set forth in claim 5 wherein said optical sensor is a television camera having a lens, vertical and horizontal deflection coils and a video detector, said deflection coils having an output coupled to the video detector for driving the raster scanning lines and the sensor control input being the driving input for said coils;

said video detector being a vidicon tube having said optical image output; and

said lens being for directing an optical image to the detector raster; and

said motion disturbances being vibrational and rotational motions.