International Business Machines Corporation

Western Digital Technologies, Inc.

Western Digital Corporation

Jeffrey E Mason

Hal Hjalmar Ottesen

Gerald Daniel Malagrino, Jr

Peter E Brooks

Michael Charles Stich

Daniel L Good

In a disk drive having a dual stage actuator, a method to improve head switching time by aligning a target head with a target track before a head switch occurs by using a second stage actuator attached to the target head to align the target head with the new track. The radial offset required to align the target head with the target track is either calibrated at startup or is measured dynamically during normal disk operations. A dual stage actuator with either a milli-actuator second stage or a micro-actuator second stage, positions a read/write head over a disk surface. The disk drive has a radial offset table for storage of radial offsets for head switches.

Disk drive with dual stage actuator radial offset calibration

A head disk assembly ('HDA') comprises an enclosure including a base and a pivot bearing cartridge having a shaft and a outer shell rotatable about the shaft. The outer shell has a cylindrical surface. The shaft is affixed to the base at a predetermined location. The enclosure has an internal volume with a limited height above the predetermined location. The cartridge has an elongated portion in the volume, the elongated portion having a height approximately equal to the limited height. The HDA further comprises a plurality of rotating disks, each having at least one recording surface. The HDA further comprises an arm stack comprising a plurality of arms, and a plurality of head gimbal assemblies. Each arm has a stacking portion and a cantilever portion. Each head gimbal assembly has one end attached to the cantilever portion of a respective arm and has an opposite end positioned adjacent a recording surface. Each stacking portion includes a first spring element and a second spring element, the spring elements being positioned to define a generally C-shaped bearing surface, the first spring element including a first compression-receiving surface and the second spring element including a second compression-receiving surface, each C-shaped bearing surface contacting a portion of the cylindrical surface. The HDA further comprises an overmolded coil assembly that includes a coil portion and an arcuate wall portion, the coil portion projecting perpendicularly from the wall portion and the wall portion including a first compression-supplying surface and second compression-supplying surface. The arcuate wall portion compressively locks the plurality of arms to the cartridge with each of a plurality of spaced-apart portions of the first compression-supplying surface compressively abutting the first compression-receiving surface of each arm in the arm stack, and each of a plurality of spaced-apart portions of the second compression-supplying surface compressively abutting the second compression-receiving surface of each arm in the arm stack. The arcuate wall portion has a height approximately equal to the height of the elongated portion of the cartridge, and the height of the arm stack is approximately equal to the limited height.

Stacked arms assembled in a head disk assembly

The fly height of read/write heads in multiple disk drives is dynamically adjusted to optimum fly height by a servo loop. The fly height is sensed in real time with a harmonic ratio fly height detector and compared to an optimum or reference fly height. The suspension system of each head is adjusted in accordance with the departure of the fly height of that head from the optimum fly height. The adjustment of the suspension system is accomplished by bonding a piezoelectric film to the flexible suspension arm carrying each head. The fly height is corrected for both radial and circumferential error as the head changes radial and circumferential position relative to the disk surface. The reference fly height, to which each head is moved by the servo loop, may be selectively changed in the fly height servo operation. This can be done to lift the heads away from the disk surface during track seek mode or disk drive sleep mode. The reference fly height can also be changed to lower the heads towards the disk surface during error recovery mode.

Fly height servo control of read/write head suspension

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Rochester, MN, United States of America

Jeffrey E Mason