Nonlinear Target Impedance Design and Its Use in Robot Compliant Motion Control with Time Delay Estimation

Nonlinear target impedance is proposed for robot compliant motion control. The target impedance is designed by adding a nonlinear damping term to conventional linear target impedance to suppress undesired energy. A robust control method, time delay control, is used to achieve proposed target impedance, and the stability of closed loop dynamics is proved by using Popov´s hyper-stability theory. Through experiments on 1-DOF arm with friction, the proposed target impedance has been compared to linear impedance to confirm its effectiveness. Compared to linear target impedance, nonlinear target impedance is better for tracking discontinuous trajectory, and more robust against Coulomb friction in free space motion control. The nonlinear target impedance intelligently absorbs impact energy when the robot collides with the environment