Velocity field control with energy compensation toward therapeutic exercise

Human-machine systems, such as those for rehabilitation, are required to be safe for human use when performing a given operating task. Passivity-based controllers such as passive velocity field control have an advantage to realizing the safe operation of human-machine systems. However, active behavior toward the external environment, including human bodies, is required to realize a given task. Such active behavior is difficult for passivity-based controllers. This study focused on ensuring that a manipulator behaves passively toward an external force when the kinetic energy is greater than or equal to a given threshold and actively otherwise. A velocity field control method with an energy compensation mechanism was developed. Numerical simulations demonstrated that the closed-loop system generally behaved passively toward external forces, and the proposed method inhibited the decrease in the kinetic energy of the closed-loop system from a dissipative external force.