Precision Positioning of Hard Disk Drives Using Piezoelectric Actuators with Passive Damping

Abstract

Positioning precision is crucial to today's increasingly high-speed, high-capacity, high data density, and miniaturized hard disk drives (HDDs). The demand for higher bandwidth servo systems that can quickly and precisely position the read/write head on a high track density becomes more pressing. Recently, the idea of applying dual-stage actuators to track servo systems has been studied. The push-pull piezoelectrically actuated devices have been developed as micro actuators for fine and fast positioning, while the voice coil motor functions as a large but coarse seeking. However, the current dual-stage actuator design uses piezoelectric patches only without passive damping. In this paper, we propose a dual-stage servo system using enhanced active-passive hybrid piezoelectric actuators. The proposed actuators will improve the existing dualstage actuators for higher precision and shock resistance, due to the incorporation of passive damping in the design. We aim to develop this hybrid servo system not only to increase speed of track seeking but also to improve precision of track following servos in HDDs. New piezoelectrically actuated suspensions with passive damping have been designed and fabricated. In order to evaluate positioning precision for the dual-stage servo systems, simulation and experiments are carried out to implement the active-passive hybrid suspension with enhanced piezoelectric actuators using a composite nonlinear feedback controller.Index Terms -hard disk drive, precision positioning, piezoelectric actuator, dual-stage servo system, active-passive hybrid

Preview Control of Dual-Stage Actuator Systems for Superfast Transition Time

“…where ref i is the i-th reference level and ±r is the range of the secondary actuator, then, whenever y 1 is within the manifold S i , the total output of the system y will be at the i-th reference level with negligible error. Moreover, if the output y must stay at an initial reference level ref 1 (2), and a control saturation levelū 1 , find a controller…”

“…Lemma 3.1: For given parameters τ, p τ , v τ , ref 2 and S 2 determined by (2), the controller (9) with t ∈ [τ, ∞) drives the primary actuator from x 1 (τ) = [p τ v τ ] T into S 2 in the sense of (5). In particular, the transition time t r is called PTOSoptimized w.r.t.…”

“…Due to the redundancy of actuators a significant reduction of t r can be achieved by allowing a pre-actuation, i.e., by allowing action before the output transition instant t = t 0 . This strategy is specially relevant in applications likely to face the successive set point control scenario such as dual-stage Hard-Disk Drives (HDDs) [1], [2]. Other larger scale DSA systems that can benefit from the proposed technique include wafers alignment in microlithography [3], dual-stage machine tools [4] and dual-stage XY positioning tables [5].…”

Guest Editorial Introduction to the Focused Section on Electromagnetic Devices for Precision Engineering

“…High-precision positioning systems are vital to a variety of relevant high-tech applications such as: surface IC-photolithography; multimedia home appliances (VCD/DVD players); electronic storage devices [hard disk drives (HDDs)]; and a multitude of scientific equipment (i.e., scanning probe microscopy). In this context, conventional positioning systems are facing severe challenges to achieve both high-resolution and large traveling range, along with additional requirements such as compact design and low-power consumption [38], [39]. In order to meet these challenges, more advanced positioning systems need to be developed.…”

“…One of the key technological limitations of VCAs is its low bandwidth, which prevents fast positioning of the read-write head thereby limiting its data-access speed. As the track density of an HDD increased dramatically to accommodate more data per unit area than earlier, dual-stage actuators (DSAs) have been introduced since the 1990s [38], [48]- [51]. In these DSAs, piezoelectric actuators or microelectromechanical systems-based actuators are employed to generate highprecision motions, and recently the piezoelectric actuator has become a workhorse in precision engineering with various applications [52]- [55].…”