Biomimetic motor behavior for simultaneous adaptation of force, impedance and trajectory in interaction tasks

Interaction of a robot with dynamic environments would require continuous adaptation of force and impedance, which is generally not available in current robot systems. In contrast, humans learn novel task dynamics with appropriate force and impedance through the concurrent minimization of error and energy, and exhibit the ability to modify movement trajectory to comply with obstacles and minimize forces. This article develops a similar automatic motor behavior for a robot and reports experiments with a one degree-of-freedom system. In a postural control task, the robot automatically adapts torque to counter a slow disturbance and shifts to increasing its stiffness when the disturbance increases in frequency. In the presence of rigid obstacles, it refrains from increasing force excessively, and relaxes gradually to follow the obstacle, but comes back to the desired state when the obstacle is removed. A trajectory tracking task demonstrates that the robot is able to adapt to different loads during motion. On introduction of a new load, it increases its stiffness to adapt to the load quickly, and then relaxes once the adaptation is complete. Furthermore, in the presence of an obstacle, the robot adjusts its trajectory to go around it.