Accurate tracking control of a limited angle torque motor

This paper presents a novel control scheme that was developed and implemented to provide accurate tracking control of a limited angle torque motor following a 50 Hz sawtooth reference waveform. The approach could be extended to other limited motion actuators which require high tracking accuracy, but are subject to a single dominant nonlinear element, such as magnetic stiffness, which may be defined experimentally. One example is the variable reluctance linear actuator, used in the aerospace industry for control of aerodynamic surfaces. Despite the significant nonlinearities inherent in the torque motor, a complex nonlinear controller can be designed using simple linear design techniques, and it is demonstrated that the motor is then able to track the reference signal with ct very high accuracy. The hybrid scheme uses a multicompensator, multiloop linear controller to reshape substantially the motor response characteristics, which have both inherent time-lag and oscillatory dynamics and an additional nonlinear gain-scheduled controller which effectively compensates for the nonlinear variations of the motor parameters. The system stability is ensured by the linear controller.