A repetitive process approach to modeling and control for ‘bootstrap’ self‐servowriting in hard disk drives

Abstract

This paper considers modeling and correction signal design for self-servowriting in hard disk drives. Self-servowriting is a process whereby the position and timing burst information are written on the disk surface by using the servo information from a previously written track (i.e. 'bootstrap') as a reference (seed) for writing the burst information on a subsequent track, and repeating the process. An obstacle to this process is radial error propagation, whereby the distortion in the successive written tracks builds up. In this paper, a reference correction signal is designed which when added to the position error signal prevents the radial error propagation. The design of the correction signal is carried out through a repetitive systems analysis and does not require several revolutions of track following in order to compute it. The analysis is verified by means of simulations, which show the containment of radial error propagation.

Improved sliding mode observer based repetitive control for linear systems with time‐varying input and state delays

“…The mechanism of the modification is that the filter makes the high‐frequency poles move towards the left half plane from the imaginary axis as RC originally has infinite poles at imaginary axis. RC has demonstrated efficacy in numerous rotational systems, including hard disk drives, 4,5 robot manipulators, 6 DC servo motors, 7 permanent magnet synchronous motors, 8 robots with rotational joints, 9 gantry robots, 10 and others.…”

Intelligent control and its applications to hard disk drives

“…This special issue aims at providing a forum for control researchers and engineers to report the latest developments and trends in HDD control applications. This special issue contains seven papers 1–7 that cover several HDD control techniques such as iterative learning control (ILC), repetitive control (RC), sliding mode, robust tracking control, H ‐infinity design, and time‐optimal control. The following is a brief summary of each paper.…”

“…Melkote and McNab 6 present a repetitive process approach to modeling and control for self‐servowriting problem in HDDs. A fundamental obstacle in self‐servowriting is due to propagation of errors as successive tracks are written.…”