Iterative Learning Control and Repetitive Control in Hard Disk Drive Industry - A Tutorial

This paper presents a tutorial on iterative learning control (ILC) and repetitive control (RC) techniques in hard disk drive (HDD) industry for compensation of repeatable runouts (RRO). After each tutorial, an application example is given. For ILC, a simple filtering-free implementation for written-in RRO compensation is presented. For the RC part, a new application of RC in dual stage HDD servo is presented. Finally, the widely used adaptive feedforward control (AFC) technique is explained from ILC point of view with discussions on challenges and issues in implementation in HDD industry