A Linear Time-Varying Control Strategy for Tracking with Disturbance and Measurement Error Rejection

A robust servomechanism control strategy is proposed for a class of stable discrete-time processes so that the tracking error is asymptotically zero independent of the disturbances. The tracking and the disturbance signals are assumed to be bounded and are solutions of some known difference equation. The controller consists of a tracking error driven servocompensator and a constant gain output feedback stabilizer. Only the frequency response of the process at the tracking and disturbance signal frequency are required to compute the stabilizer gains. In the presence of measurement noise, it is shown that asymptotic tracking is ensured if the tracking error input to the servocompensator is multiplied by a 1/k decay factor, where k is the time index.