Disturbance observer based robust control for industrial robots with flexible joints

In this paper, a disturbance observer based control algorithm is proposed for industrial robots having flexible joints. The joint flexibility of the robot is modeled as a two mass system. We study on the practical issues for implementing disturbance observer based control scheme in flexible joint robots. For industrial robots, generally the sensors are located on the motor side. If we construct disturbance observer using motor side dynamics, due to the zero dynamics, disturbance observer cannot directly reject the disturbance at the link side. To solve this problem, we propose a dual observer that estimates disturbance and states simultaneously. Using the proposed dual observer, we construct full state feedback controller. The effectiveness of the proposed control scheme for disturbance rejection and robustness is demonstrated by numerical simulation and experiment using HILS (Hardware In the Loop Simulation) system.