Impact control in hydraulic actuators with friction: theory and experiments

Stabilizing manipulators during the transition from free motion to constraint motion is an important issue in contact task control design. A Lyapunov-based control scheme is introduced to regulate the impact of a hydraulic actuator coming in contact with a nonmoving environment. Due to the discontinuous nature of friction model and the proposed control law, existence, continuation and uniqueness of Filippov´s solution to the system are first proven. Next, the extension of LaSalle´s invariance principle to nonsmooth systems is employed to prove that all the solution trajectories converge to the equilibria. The controller is tested experimentally to verify its practicality and effectiveness in collisions with hard and soft environments and with various approach velocities.