Design of a Novel Compliant Transmission for Secondary Microactuators in Disk Drives

One of the bottlenecks limiting the data density in conventional disk drives is the resonant frequency of the suspension arm connecting the actuator and the read-write elements. In this paper we present a compliant transmission to be integrated with a secondary microactuator to deal with this limitation. The compliant transmission was designed to reduce overall footprint. This paper presents an optimization scheme which maximizes energy efficiency while constraining natural frequency, maximum stress, and axial loading. The final design meets both kinematic and dynamic criteria. INTRODUCTION In the semiconductor industry, the 10-10 rule measures growth of the industry, stating that every ten-year period brings a tenfold increase in the level of technology. One subset of the semiconductor industry that has consistently out-performed this measure is the area of data storage. The last decade has seen a growing need for increased data capacity in smaller spaces. Increased storage of personal digital data and the shrinking size of computing technology both contribute to the need for high density data storage. Figure 1 shows the actuation scheme of a typical disk drive. Data is stored on a rotating disk. The slider contains the read-write head, which houses the elements used to read and write data onto the disk. The slider is suspended above the disk via a suspension connected to a voice-coil motor (VCM). As the VCM rotates, the suspension arm and slider move radially across the disk. There is a direct relationship between the precision of the actuation scheme and the areal density of a hard disk. To achieve high areal density, it is necessary to pack data close together. Actuation precision dictates how closely data can be packed. A servo controlled VCM must operate at relatively high frequencies to achieve precise actuation. The bandwidth of servos using the current actuation scheme, however, is limited by the resonant frequency of the suspension arm. Because the precision of the current actuation scheme is limited by a feature critical to its operation (i.e. the suspension arm), it is necessary to develop a new design that facilitates higher data density. Nearly a decade ago, researchers in the magnetic storage community contemplated the use of a secondary microactuator placed in between the slider and the suspension arm to alleviate effects introduced by the dynamics of conventional designs (Fig. 2). A piggy-back microactuator operates (in translation or rotation) at high frequencies to augment the operating frequency currently limited by resonance of the suspension arm. Several researchers have designed such devices [1, 3, 4]. Figure 1: Conventional actuation scheme Disk Voice Coil Motor