CPG control for assisting human with periodic motion tasks

Abstract

Oscillatory movements play important roles in human life, such as the arm and leg movements during human locomotion. In this paper, we introduce a method for designing a feedback controller for a robotic system to help a human with periodic 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 a mathematical model of reciprocal inhibition oscillator (RIO), a simple-structured and well-studied type of CPG. The RIO controller acts as a nonlinear damping compensator and removes part of the resistive forces in the system, thereby reducing the human effort. It is shown that the resulting human-intended oscillation is a locally stable periodic solution of the closed-loop system. The result is first presented for a single degree-of-freedom (DOF) mechanical system and then extended to a multi-DOF system.