Exploiting Mitigation Capabilities of a Variable-Stiffness Joint to Allow Agile Contact with Surfaces

The motion patterns typically exhibited by a robot manipulator during a pick-and-place task differ from those by a human. Humans often perform that movement in a manner that resembles a collision while still placing the object safely. This research proposes implementing a fast but rough contact motion by utilizing a series elastic actuator (SEA) on the robot’s joints to introduce compliance. Exploiting the impact mitigation of the SEA allows for high contact velocities while keeping safe values of contact force. The proposed method refrains from controlling the link’s actual position and utilizes contact with the environment to actively attenuate oscillations. The contact forces are limited and attenuated by designing the target position of the motor, joint stiffness, and velocity of the link. Simulation and preliminary results verify the capability of the SEA in mitigating impacts and limiting contact forces. In addition, the influence of each variable over the contact force and settling time is analyzed. Improvements over previous work on a variable-stiffness SEA mechanism based on compressed air are implemented. The proposed method is evaluated through simulation and experiments with a one-link arm. Results demonstrated the feasibility of the method, however, parameter settings need to be investigated.