Synthesis Methods for Robust Nonlinear Control

In this paper, we will discuss the application of robust control techniques and especially ¿-synthesis to the Army´s ATB-1000 test fixture. For comparison, two SISO controller designs are also described. The test fixture is pattered after the Apache helicopter´s 30 mm gun and has tunable nonlinearities which may be representative not only of the nonlinearities of the gun, but of other mechanical systems as well. The models of the test fixture which were available at the time of the work are also described. The goal in pointing the gun is to reduce dispersions of fired gun rounds on targets. The resulting ¿-synthesis design, when connected with a nonlinear simulation, exhibited limit-cycle behavior of unacceptable amplitude. The unacceptable performance is due to the nonlinearities and, in future work, would be improved upon by frequency domain trade-offs during the synthesis step. In particular, we will sketch the use of advanced nonlinear H^¿ techniques for such problems.