Guest Editorial Special Issue: “Servo Control for Data Storage and Precision Systems”, from 17th IFAC World Congress 2008

Digital servo control was introduced in mass production hard disk drives (HDD) in 1986. Since then various kinds of digital control technologies have been applied to HDD servo systems, and the performance has been improved dramatically. A 3.5-in. HDD capacity, which was 251 MB in 1988, is 2000,000 MB (2.0 TB) in 2009. Faster access (high quality motion control), more precise positioning (nanometer scale control), and more robustness against disturbances and plant fluctuations are required to meet the increasing demand for larger capacity and higher performance HDDs.The field of HDD servo technology provides an example of techniques for micro or nanometer accuracy. Although the application aspects may be different in other fields requiring high positioning accuracy, the methods used in HDDs are general enough that they can be transferred. This paper is not intended to act as a review paper, but presents several fundamental ideas of precision positioning servo control, especially ones derived from the history of HDD servo control.