Long-Sheng Fan

Magnetic recording-head positioning at very high track densities using a microactuator-based, two-stage servo system

The storage capacities and areal densities found in magnetic disk drives are increasing very rapidly. Data is recorded in ever-narrower tracks which must be followed with extreme precision. Also, the advent of portable applications exposes these smaller drives to higher levels of vibration and shock. A description is given of the many factors which contribute to recording track misregistration (TMR) in todays drives. The mechanics of the drive and actuator and the architecture of the servo control system are also described. A projection is made for the TMR sensitivities and control system at an areal density of 10 Gb/in/sup 2/, having roughly 25000 tracks/in. A two-stage servo may be needed to achieve such track densities. This would comprise a high bandwidth microactuator for rapid position corrections of the recording head, coupled with a conventional actuator. The characteristics of such a microactuator are discussed, and operational examples of fabricated electroplated microactuators, driven electrostatically, are shown. The mechanical behavior of the devices and some of the factors which would affect their implementation are also described. >

MEMS milliactuator for hard-disk-drive tracking servo

This paper describes the design, fabrication, and operational characteristics of a MEMS milliactuator designed for servo tracking in a hard-disk drive (HDD). The actuator is designed to increase the bandwidth of an HDD tracking servo and pack more recording tracks on a disk. An Invar (low thermal expansion metal) electrode position process was developed to meet the thermal stability requirement. The electroplated Invars thermal coefficient of expansion is as low as 6.3/spl times/10/sup -6//K, which is almost half of that of pure nickel. For the plating mold pattern definition, a high-aspect-ratio polymer etching technique was developed. A high-aspect-ratio structure line-and-gap definition is required to achieve both a high directional stiffness ratio and electrode efficiency for the actuator. The etching technique described can etch through a thick (<40 /spl mu/m) polymer layer with an aspect ratio of 16:1 at an etch rate of <2 /spl mu/m/min. Low-cost/high-volume manufacturing is achievable by this batch fabrication technique. A milliactuator was fabricated and assembled with a suspension and a slider weighted at around 2 mg. The slider was successfully driven by the milliactuator while the slider was flying on a spinning disk. The operational characteristics (frequency response) of the in-flight milliactuator were measured, and the results indicate that the actuator is suitable for high-bandwidth HDD servo-tracking applications.

Closed Loop Control And Performance Of A Microactuator For Dual Stage Servo

of position bursts used in this work includes two parts: positive burst part and negative burst part. Physically, those two parts are identical and of the same bit length. However, the positive burst will be read with positive bias current and the negative burst will be read with negative bias current. The readout amplitude of positive burst and negative burst is, then, added up with pre-defined weight for each of them to form the positioning signal of that particular burst. Two significant advantages of the new method were confirmed. First, the new positioning signal is much more symmetric comparing with the signal obtained with bias current in one direction only. Second, the profile of the positioning signal is rather independent of the different asymmetry of different MR heads, if the written track is of the same track width and the width deviation of the MR heads is within specification. Detailed experimental results of the new method will be presented in the full paper.