Reduced-Order Nominal Model Design and Validation for Task Space DOB-Based Motion Control of an Industrial Robot

In conventional robust motion control systems, disturbance observer (DOB) nominal models are designed with same order as the actual plant such that the nominal model directly cancels with the actual plant dynamics. However, for multi-DOF systems such as 6-DOF industrial robots, identifying the higher-order model is laborious. Moreover, there is a high risk of obtaining a nominal model with large deviation from the actual plant due to severe parameter uncertainty. Thus, a reduced-order nominal model is derived from the actual plant model and compared with the one which same order as the actual plant in this paper. The designed model is simple, easy to identify and implement. From the analyses and experiment results, DOB with the proposed nominal model is not affected by severe robot model uncertainty and show significant improvement in motion control performance in terms of transient response and tracking accuracy.