Repetitive control for systems with uncertain period-time, with application to a Compact Disc Drive

Repetitive control is useful if periodic disturbances act on acontrol system. Perfect (asymptotic) disturbance rejection isachieved if the period-time is exactly known. For those caseswhere the period-time changes and can not be measured directly byan auxiliary signal, a robust repetitive controller structure isproposed. It uses multiple memory-loops in a certain feedbackconfiguration, such that small changes in period-time do notdiminish the disturbance rejection properties. The robustrepetitive controller shows good implementation results for atracking control problem of a Compact Disc player