Dual-Stage Actuated Servo Systems

Abstract

The present demand for large-capacity disk drives is leading to an increase in areal density at a rate of 100% per year. This requires a positioning accuracy of the order of few nanometres. The servo bandwidth of the current disk drive actuators makes it very hard to achieve this. The VCM actuator used in conventional disk drives has hundreds of flexible resonances in high frequencies (see e.g., [1, 29]), which limits the increase of bandwidth and hence the positioning accuracy. In order to develop high bandwidth (track following) servo systems, dual-stage actuation has been proposed as a possible solution. Dual-stage actuator refers to the fact that there is a microactuator mounted on a large conventional VCM actuator. The VCM actuator is used for coarse and relatively slow positioning and the microactuator is used for fine and fast positioning. The two most fundamental choices in a dual-stage system are the actuator configuration and the control algorithm. There have been proposals for electromagnetic, electrostatic, piezoelectric, shape memory and rubber microactuators, etc., each with their own advantages and disadvantages. Many research studies have been done and reported in the literature (see e.g., [20, 114, 120–137] just to name a few). In this chapter, we focus on the design of complete HDD servo systems with a dual-stage actuator with a piezoelectric actuator in its second stage (see Figure 9.1).KeywordsControl SignalOutput ResponsePiezoelectric ActuatorDisk DriveServo SystemThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.