Fin Failure Compensation for an Unmanned Underwater Vehicle

A. S.-F. Cheng and N.E. Leonard

Abstract

We study fin failures on a torpedo-shaped unmanned underwater vehicle (UUV) and design control laws to compensate for a fin that gets stuck at an arbitrary deflection angle. Our control strategy combines sliding mode control with modified fin mixing and a method for handling fin deflection saturation. The saturation-compensating control design follows recent work of Teel and Kapoor and has the advantage that it is only active when there is saturation. This allows the nominal controller to be designed independently for desired performance under non-saturation conditions. Our complete controller has been tested on the simulator for the 21UUV, a full-scale, 21-inch diameter, torpedo-shaped UUV. We describe the results of these tests which demonstrate good tolerance to a fin failure. As our objective is the design of failure compensation, we assume in our work that we have available an identification package that provides fin failure information. Our simulator test results suggest, however, that only very little information about the failure is required for effective compensation.

Postscript Version (10 pages postcript)