Comparison Studies on Anti-Aliasing/Anti-Imaging Filtering and Signal Extension in Multi-Rate ILC

Multirate iterative learning control (ILC) systems have different sampling rates for feedback online loop and feedforward (or ILC) offline loop. The implementation of multirate ILC requires to downsample the signal first and, after processing, upsample the signal again. In the process of downsampling and upsampling, aliasing and imaging may occur and need to be handled properly. In this paper, the multirate ILC with and without anti-aliasing/antiimaging filters are compared with different types of low-pass filter. Furthermore, to satisfy the steady state frequency response, the signals are extended and different extension methods are evaluated. A series of simulation results is provided to demonstrate that anti-aliasing and antiimaging filters significantly improve the tracking performance. However, the extension methods have little influence on the tracking accuracy.