FDOB-Based Robust Impedance Control of Force Sensor Implemented Force Servo System

Instability which occurs when the robot’s end effector contacts a very stiff environment is a challenge in designing control systems for safe physical interaction and cooperation of robots with environment. One of the reasons for the instability is force disturbances caused by the mechanical factors of the robot system. To this effect, this paper presents the design, analysis, and implementation of a robust impedance controller for a force servo system. To suppress the force disturbances, a force disturbance observer (FDOB) is implemented in the impedance-controlled system. For comparison purposes, impedance control system when the FDOB is not implemented is also designed and analyzed. Further, using the passivity approach, coupled stability conditions of the designed impedance control systems are derived and analyzed to assess the effect of FDOB on passivity and overall control performance. Simulations and experiments are conducted to evaluate performance of the designed impedance control systems and it is found that the FDOB-based control system shows superior performance by improving contact stability compared to direct force sensor feedback control system.