Control of a Series Elastic Actuator Based on Sigmoid-Proportional-Retarded (SPR) with Online Gravity Compensation.

In this paper, a rotary series elastic actuator (SEA) based on torsion spring is designed. A novel position control law (Sigmoid-proportional-retarded) with online gravity compensation (OGC) is presented in order to reduce the residual vibration of the link and shorten the response time. Moreover, the stability of SPR control law is proved by the Lyapunov method. Some comparative experiments were implemented. It is concluded that SPR control based on OGC can reach the target position accurately and quickly. Meanwhile, the results show that the method is also effective in eliminating residual vibration.