Three-Axis Image Stabilization System

Abstract

An image stabilization system includes an optical assembly configured to receive electromagnetic radiation emitted by a target and produce focused image of the target; a focal plane array, the focal plane array being configured to receive the image and integrate at least a portion of the electromagnetic radiation making up the image to produce an electrical representation of the image; sensors configured to provide kinematic data; a control system receiving the kinematic data and estimating jitter-induced motion of the image on the focal plane and outputting a control signal; and piezo-electric actuators configured to receive the control signal and to translate the focal plane along two orthogonal axes and rotate the focal plane about a third orthogonal axis such that jitter-induced motion of the image on the focal plane is reduced.

1 . A system comprising:
 an optical assembly configured to receive electromagnetic radiation emitted by a target and produce an image of the target;   a focal plane array configured to receive the image and integrate at least a portion of the electromagnetic radiation making up the image to produce an electrical representation of the image;   sensors configured to provide kinematic data;   a control system receiving the kinematic data and estimating jitter-induced motion of the image on the focal plane and outputting a control signal; and   piezo-electric actuators configured to receive the control signal, and to translate the focal plane along two orthogonal axes, and to rotate the focal plane about a third orthogonal axis, such that jitter-induced motion of the image on the focal plane is reduced, wherein the piezo-electric actuators comprise an X-Y stage that has been machined to form flexural joints that are moved by piezo-electric material.   
     
     
         2 . The system of  claim 1 , wherein the third orthogonal axis is substantially parallel to a bore axis of the optical assembly. 
     
     
         3 . The system of  claim 1 , wherein the third orthogonal axis is substantially collinear with a bore axis of the optical assembly. 
     
     
         4 . The system of  claim 1 , wherein the system is configured to reduce jitter-induced motion of the image on the focal plane in a range which includes frequencies of 25 Hz to 500 Hz. 
     
     
         5 . The system of  claim 1 , wherein the piezo-electric actuators further comprise a rotation stage, the X-Y stage producing translations on the order of 100 microns and the rotation stage producing rotations on the order of 10 milliradians. 
     
     
         6 . The system of  claim 5 , wherein the focal plane is directly attached to the rotation stage, the rotation stage being attached to the X-Y stage such that actuation of the X-Y stage moves both the rotation stage and the focal plane. 
     
     
         7 . The system of  claim 6 , in which natural modes of the X-Y stage, when supporting the rotation stage and the focal plane, are greater than 300 Hz. 
     
     
         8 . The system of  claim 6 , in which natural modes of the rotation stage, when supporting the focal plane, are greater than 300 Hz. 
     
     
         9 . The system of  claim 1 , further comprising a multi-axis gimbal, the multi-axis gimbal providing pointing capabilities to the system. 
     
     
         10 . The system of  claim 1 , wherein the sensors measure angular displacement. 
     
     
         11 . The system of  claim 1 , wherein the sensors are angular rate sensors configured to provide angular rates of motion about three orthogonal axes. 
     
     
         12 . The system of  claim 1 , wherein the control system comprises notch filters, the notch filters reducing excitation of resonant frequencies within the system; the control system further comprising a feed-forward transfer function which provides frequency domain response information of the actuator. 
     
     
         13 . The system of  claim 1 , wherein the control system is configured to receive data from the sensors and calculate a measured piezo position; the control system summing the measured piezo position with the jitter-induced motion of the image on the focal plane to find a positional error of the focal plane. 
     
     
         14 . The system of  claim 1 , wherein the piezo-electric actuators comprise a flexure and at least one strain gage position sensor attached to the flexure. 
     
     
         15 . A system for reducing jitter-induced smear on an infrared focal plane comprising:
 an infrared focal plane array configured to receive electromagnetic radiation and integrate at least a portion of the electromagnetic radiation to produce an electrical representation of an image;   a gimbaled optical assembly configured to receive electromagnetic radiation emitted by a target and focus the image of the target on the infrared focal plane array;   gyroscopic sensors configured to provide angular rate data in three orthogonal axes;   a control system receiving the angular rate data and estimating jitter-induced motion of the image on the focal plane and outputting a control signal, the control system comprising notch filters, the notch filters reducing excitation of structural resonant frequencies within the system;   piezo-electric actuators configured to receive the control signal and to translate the infrared focal plane along two orthogonal axes and rotate the infrared focal plane about a bore axis such that jitter-induced motion of the image on the infrared focal plane is reduced; and   a visible camera having a higher frame rate than the infrared focal plane array, in which changes between image frames produced by the visible camera are analyzed to sense angular rotations of the system to supplement angular rate data produced by the gyroscopic sensors.   
     
     
         16 . The system of  claim 15 , wherein the system controls two coarse rotational degrees of freedom provided by a two axis gimbal and three finer degrees of freedom actuated by the piezo-electric actuators. 
     
     
         17 . A method for reducing jitter-induced smear in an imaging system comprising:
 sensing jitter of the imaging system;   calculating jitter-induced motion of electromagnetic energy on a focal plane; and   rotating said focal plane about a bore sight axis of the imaging system using a piezo-electric stabilization system to reduce the jitter-induced smear within the imaging system, wherein the piezo-electric stabilization system comprises piezo-electric actuators comprising an X-Y stage which has been machined to form flexural joints which are moved by piezo-electric material.   
     
     
         18 . The method of  claim 17 , wherein:
 the sensing comprises measuring angular rates of rotation of the imaging system in three orthogonal axes; and   the calculating comprises:
 integrating the angular rates of rotation to determine a short term attitude of the imaging system; 
 mapping the short term attitude of the imaging system to determine the jitter-induced motion; and 
 calculating a demanded position of the focal plane to reduce the jitter-induced motion of the electromagnetic energy on said focal plane.