Adaptive Control of an Alignment System with Nonlinear Plant Characteristics

This paper presents Model Reference Adaptive Control (MRAC) of a precision angular alignment system (small gimbaled mass) with nonlinear friction characteristics. Open loop frequency response tests yield a family of curves for different amplitude sweep generator inputs as seen in Fig. 1 giving the ratio of alignment angle output to amplifier input over frequency. These results are directly traced to nonlinear bearing friction. The goal of the control design is to regulate alignment errors to within 2 arcseconds of a given reference angle in the presence of variable friction parameters and torque disturbances. The adaptive controller is derived by considering a linearized 2nd order Plant, of relative degree 2, with variable parameters. The MRAC design is tested with nonlinear simulation using Boeing Computer Services EASY5/sup TM/.