USDE-Based Cascade Control for Servo Motor Systems with Uncertain Dynamics

In this paper, a cascade control strategy is proposed for servo motor system with uncertaines and nonlinearities. With this method, not only the lumped unknown dynamics can be accommodated but also the armature current and position tracking performance can be guaranteed. To achieve this purpose, a set of filter operations and simple algebraic calculations are employed to design an unknown system dynamics estimator (USDE) with only one tuning parameter. Then, the USED is integrated with a typical PID controller and a feedback controller for current loop and position loop, respectively. The closed-loop system stability is analysed in terms of the Lyapunov theory. Finally, experiment is carried out based on autofocus optical system to validate the reliability and effectiveness of the proposed method.