Tracking Accuracy Improvement by Sliding Phase-in Iterative Learning Control

The earlier works by Zhang, B. et al, (2004) on cutoff-frequency phase-in ILC show that the scheme can suppress initial state error/position offset properly and improve tracking accuracy. However, since cutoff frequency is set high in initial phase of operation cycles, the improvement of tracking accuracy is mainly in this phase and the tracking error in later phase of operation cycles can still be large. A uniformly good tracking accuracy is favorable in many applications. In this paper, a sliding cutoff-frequency phase-in ILC is proposed to achieve this goal. In this scheme, cutoff frequency profile moves along the time axis after some cycles according to the assessment of tracking performance. Experimental results on an SCARA robot show that this scheme can further improve the tracking accuracy and generate a uniform tracking error over the entire operation interval