Observer-based adaptive force control of multi-degrees-of-freedom manipulator

The authors describe adaptive force control based on a disturbance observer. In the proposed method, the control gains of the force controller are adjusted according to the environment which the manipulator contacts. First, a disturbance observer, which estimates disturbance torque imposed on the manipulator, is applied to each joint. By the feedback of the estimated disturbance torque the total system becomes robust against the disturbance torque. Then, the dynamics including the environment are cleared up, and the workspace force controller is described as a second-order system. Therefore, it becomes easier to apply the adaptive control algorithm to the force controller in the observer-based system. A least-squares method is introduced to estimate the unknown parameters of the environment. Experimental results are presented to verify the proposed adaptive force controller