CPG Control for Harmonic Motion of Assistive Robot With Human Motor Control Identification

Various movements in human life, such as walking, bicycling, cleaning, chewing, swimming, and so on, are periodic or repetitive. This paper proposes a method for designing a feedback controller for a robotic system to help a human with periodic (harmonic, in particular) motion tasks. The control objective is to stabilize a human-intended oscillatory movement while reducing the required human effort. For the control architecture, we adopt the central pattern generator (CPG), which is a neuronal circuit for rhythmic motor pattern. Animal locomotions under CPG control are capable of complying with various environment dynamics to yield different oscillatory movements. We take advantage of this adaptation property of the CPG controller that acts as a nonlinear damping compensator and removes part of the resistive forces in the system, thereby reducing the human effort without interfering with the human intention. It is shown that the resulting human-intended oscillation is a locally stable harmonic solution of the closed-loop human-robot CPG system, assuming a simple model of the human motor control. The proposed control method is experimentally validated for a simple robotic arm, with a system identification of the human motor control.