An Analysis of Parameter Variations of Disturbance Observer for Motion Control

This paper analyzes a disturbance observer with a focus on parameter variations. The parameter variations are the inertia variation and the variation of torque coefficient. Conventionally, their nominal values are designed not as control parameters but the same values as the actual ones. However, disturbance observer is able to include the effect of phase compensation by properly selecting the nominal model parameters. In this paper, these nominal model parameters are actively designed to achieve the phase compensation. This paper proposes the design method of observer to achieve phase compensation based on disturbance observer. Compared with implementing phase compensator, the control system is simple and easy to design. The selection of these parameters has some restriction. When the nominal model parameters are much separated from the actual ones, the stability of the control system deteriorates. This paper focuses on the inertia variation and neglects the variation of torque coefficient. Furthermore, the stability of position and force control systems is analyzed. The validity of the proposed design method and the effect of phase compensation are verified by some experimental results.