Disturbance-rejection high-precision motion control of a Stewart platform

A simple robust autodisturbance rejection controller (ADRC) in linkspace is proposed to realize high precision tracking control of a general 6 degrees of freedom (DOF) Stewart platform in this paper. In practice, the performance of the controlled system is limited by how to select the high-quality differential signal in the presence of disturbances and measurement noise. Moreover, unmodeled nonlinear friction provides degradation on the motion precision. So, a nonlinear tracking differentiator in the feedforward path and an extended states observer in the feedback path are designed to obtain high quality differential signal and the real action component of unknown disturbance signals including nonlinear friction without a precise mathematical model. The nonlinear PD (proportional derivative) controller is used to synthesize the control action to give a superior performance. Extensive simulations and experimental results are presented to verify the effectiveness and ease of engineering implementation of the proposed method. The developed ADRC controller is simple and directly intuitive to the practitioners.