Non-Adjustable Pointer-Tracker Gimbal Used For Directed Infrared Countermeasures Systems

Abstract

In a directed infrared countermeasure system, to assure parallelism between the line-of-sight to a target and the output beam, the input and output mirrors are fixedly attached to a uni-construction arm mounted to a rotatable azimuth platter to which internal mirrors are also fixedly attached. A system is provided for zeroing out alignment errors by developing an aim-point map for the gimbal that records initial alignment errors induced by manufacturing tolerances and uses the aim-point map error values to correct the output mirror orientation. The system also corrects for alignment errors induced by thermal gradients.

Description

RELATED APPLICATIONS[0001]This application is a divisional of U.S. patent application Ser. No. 13 / 506,901 filed May 23, 2012 and is a continuation of co-pending U.S. patent application Ser. No. 13 / 373,775 filed Nov. 30, 2011 which is a continuation of U.S. patent application Ser. No. 12 / 499,584 filed Jul. 8, 2009. This application claims the benefit under 35 USC §119(e) from U.S. Application Ser. No. 61 / 134,277 filed Jul. 8, 2008, the contents of which are incorporated herein by reference.FIELD OF THE INVENTION[0002]This invention relates to directed infrared countermeasures and more particularly to a non-adjustable pointer-tracker gimbal for use in such systems.BACKGROUND OF THE INVENTION[0003]In directed infrared countermeasures (DIRCM) systems there has always been a problem of making the line-of-sight (LOS) to the target and the laser beam that is emitted from the DIRCM head coincident or parallel. While there have been many efforts to reduce the amount of parallax between the t...

AI Technical Summary

Benefits of technology

[0013]Rather than trying to adjust all of the mirrors and affiliated hardware in the DIRCM head or gimbal to compensate for all pointing errors, in the subject case the input and output mirrors are mounted to a rigid uni-construction elevation arm that is part of an elevation stage and are initially fabricated to reasonable tolerances. The subject system does not try to adjust the mirrors for every pointing direction, rather deals with the original unadjusted alignment of the mirrors and provides a system to compensate the aiming direction of the laser by adjusting the azimuth and elevation stages with an offset determined during an initial calibration procedure to bring the outgoing laser beam as close as possible to being parallel to the line-of-sight to the target. With this parallelism, the result is that the laser beam hits the target with maximal energy on target.

[0021]Thus, using these aim-point map values, the azimuth and elevation stages are stimulated to correct the position of the output mirror to make the output beam parallel to the line-of-sight to the target and thus assure 200 or better microradian aiming accuracy.

[0024]This completely eliminates the problem of trying to independently adjust multiple moving mirrors to provide the precision necessary to accomplish the 200 microradian pointing accuracy for the laser beam. Thus the subject system compensates for manufacturing errors in a software look-up table and permits designing the mirrors and affiliated support mechanisms without adjustments. Additional simplicity is added when the first stage input mirror and the laser output mirror are designed and fabricated as a single part called a uni-construction elevation arm.

[0025]Concurrent with the look-up table approach which eliminates or minimizes the effects of manufacturing tolerances, there is also the problem of temperature gradients. As hardware heats and expands or contracts, asymmetrical parts change shape which will affect overall performance, especially pointing accuracy.

[0027]In summary, a system is provided to assure that the laser beam from a DIRCM head or gimbal places laser energy on the target without complicated adjustments, and expensive parts. This is accomplished by providing a uni-constructed elevation arm with both input and output mirrors fixed to it, and an aim-point map that compensates for all manufacturing tolerances to gain the end objective of jamming heat-seeking missiles. In operation, the position of the output mirror is moved in accordance with target image displacement corrected by the error recorded in the aim-point map to correct the angular orientation of the output mirror for assuring that the outgoing beam is parallel to the line-of-sight to the target. Thermal gradient problems are also compensated by using the sensed gradient-induced errors to adjust aim-point map values.

Problems solved by technology

In directed infrared countermeasures (DIRCM) systems there has always been a problem of making the line-of-sight (LOS) to the target and the laser beam that is emitted from the DIRCM head coincident or parallel.

While there have been many efforts to reduce the amount of parallax between the two and therefore reduce the aiming errors of the outgoing laser beam, the difficulty in the past has always been with the multiple mirrors that are utilized both for positioning the received image at the center of a focal plane array and for directing the laser beam out the DIRCM head.

While it is possible for one pointing direction to adjust out the parallax by adjusting all the mirrors, the adjustment does not correct for all pointing directions.

Since these mirrors move independently, the positional errors of the mirrors add up and are not easily compensated for over the entire field of regard.

The situation is even further complicated as to how to lock the adjustment mechanisms without moving the adjustment while at the same time retaining boresight in view of the harsh environment.

Thus, in a cut and try operation one can spend an inordinate amount of time trying to compensate for the positional errors of these mirrors for all pointing directions; but in general these efforts have not met with success.

Moreover, compensating these mirrors for a single direction does not compensate the system for the entire field of regard.

This is where the problem arises.

However, and as described above, it is difficult or impossible to post align the incoming image with the exiting laser beam after the gimbal has been assembled due the accumulation of errors throughout the assembly especially since a high degree of accuracy is required.

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