INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING Int. J. Adapt. Control Signal Process. 2008; 22:325–343 Published online 17 September 2007 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/acs.1003 Iterative learning control and repetitive control in hard disk drive industry—A tutorial YangQuan Chen 1, ∗, † , Kevin L. Moore 2 , Jie Yu 3 and Tao Zhang 4 1 Center for Self-Organizing and Intelligent Systems (CSOIS), Department of Electrical and Computer Engineering, 4160 Old Main Hill, Utah State University, Logan, UT 84322-4160, U.S.A. 2 Division of Engineering, Colorado School of Mines, Golden, CO 80401-1887, U.S.A. 3 Western Digital Technologies 20511 Lake Forest Drive, Lake Forest, CA 92630, U.S.A. 4 Seagate Technology, 1280 Disc Drive, Shakopee, MN 55379, U.S.A. SUMMARY 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. Copyright 2007 John Wiley & Sons, Ltd. Received 30 October 2006; Revised 25 June 2007; Accepted 8 August 2007 KEY WORDS: hard disk drives; repeatable runout; non-repeatable runout; iterative learning control; repetitive; disturbance rejection; comb filter 1. INTRODUCTION Hard disk drives (HDDs) are ubiquitous and pervasive. HDDs are complex intelligent mechatronic systems/devices. Just hook up and plug-in HDDs and they will work for us reliably and efficiently. Just like electrical motors, today, we take HDDs for granted. To enhance our appreciation of the sophisticated HDD servo controls, Messner and Ehrlich [1] presented a nice tutorial on controls for disk drives. The history of HDDs servo controls has been reviewed in [2] and [3] is a textbook dedicated to HDD servo systems. To further motivate the readers, let us indicate the first fact that, as early as the year 2000, HDDs were ‘nanotech products’. For example, if a HDD has TPI (tracks per inch) of 58 000. Then, the track pitch (TP) is 25.4mm/58 000 = 497nm. Assuming that the track following accuracy is ∗ Correspondence to: YangQuan Chen, Center for Self-Organizing and Intelligent Systems (CSOIS), Department of Electrical and Computer Engineering, 4160 Old Main Hill, Utah State University, Logan, UT 84322-4160, U.S.A. † E-mail: yqchen@ece.usu.edu, yqchen@engineering.usu.edu Copyright 2007 John Wiley & Sons, Ltd.