Implementation of plug-in type repetitive controller for position-base periodic control systems

Position-based periodic motions have appeared in many industrial processes such as cam-followers. The period of the output motion driven by the cam varies in the time-domain but is fixed in the angular position-domain, which is called time-varying periodic motion. This paper presents a plug-in type repetitive control scheme for reducing tracking errors via position-based periodic reference signals and/or disturbances. Two kinds of control strategies, namely disturbance feed-forward and disturbance rejection control, are proposed to investigate control performance with time-varying periodic disturbances. The implementation technique utilized in this position-based repetitive controller is discussed in detail, and an anti-vibration control system with position-base load disturbances generated by a cam is realized. Experimental results are given to demonstrate that the repetitive control can effectively eliminate the steady-state errors within a few cycles caused by time-varying periodic disturbances. This study offers an alternative method for realizing a repetitive controller to track and/or reject periodic signals under variable periods.