Cutoff-frequency phase-in method to improve tracking error

A cutoff-frequency phase-in method is introduced for iterative learning control (ILC) in this paper. In this proposed method, the cutoff frequency of a filter is a function of time and rolls off, along a predefined profile, from a high value to an estimated learnable bandwidth and, eventually, reduces to a value below the actual learnable bandwidth. Since this method takes advantage of the quick decay of error in the starting time interval and prevents the accumulation of error in the later time interval of the operation, good tracking performance and good learning behavior can be expected simultaneously. Experimental results are presented to show the effect of the proposed method.