Repetitive control is applied here to compensate for roll eccentricity disturbances in thickness control of the cold rolling process. A unique aspect of the process is that the eccentricity disturbance may be from multiple rolls and hence may becomposed of multiple periodic components whose periods may not be commensurate, namely, divisible by a common factor an integral number of times. The paper presents a multiple-period repetitive controller structure that can compensate for such adisturbance. The structure proposed is also applicable to other tracking and regulation applications involving multiple periodic signals. Procedures to analyze and design control systems with such a structure, to ensure stability and performance, arepresented.
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