Elasto-plastic Control for Physical Human-Robot Interaction

This work presents a novel impedance controller for physical human-robot interaction. The controller exhibits two behaviors based on the force applied to the end-effector. Low forces result in temporary (elastic) motion, canceled once the force is removed to accommodate for the temporary need for displacement. In contrast, high forces give rise to permanent (plastic) deformations of the trajectory to deal with permanent path modification. The control method is based on a LuGre friction model, which exhibits a combination of the two behaviors sought. The model has been improved to distinguish clearly between elastic and plastic motion and extended to the 3D Cartesian space. Experiments on a real robot have been performed to validate the proposed method.