On the Disturbance Rejection Control of Flexible-joint Robot: A GPIO-based Approach

A robust disturbance rejection control scheme is addressed for the trajectory tracking problem of a flexible-joint robot (FJR). The system is always severely affected by various types of unknown disturbances including model errors, couplings, changing working environments as well as unmodeled dynamics. These disturbances on the link and actuator side will deteriorate the control performance of FJR. By considering all the disturbances as an unknown lumped time-varying disturbance, a flatness description of FJR is developed. Then, a new output feedback controller is constructed through the estimates of unmeasurable states and unknown lumped disturbance provided by a generalized proportional integral observer (GPIO). The stability of the closed-loop system with the driven of the proposed control scheme is guaranteed under some mild assumptions. Compared with the conventional linear active disturbance rejection control (LADRC) scheme, test results are presented to demonstrate the feasibility and efficacy of the proposed control approach.