Design and Dynamics of Flying Height Control Slider With Piezoelectric Nanoactuator in Hard Disk Drives

[+] Author and Article Information
Jia-Yang Juang

Department of Mechanical Engineering, Computer Mechanics Laboratory, University of California at Berkeley, Berkeley, CA 94720jiayang@me.berkeley.edu

David B. Bogy

Department of Mechanical Engineering, Computer Mechanics Laboratory, University of California at Berkeley, Berkeley, CA 94720

C. Singh Bhatia

 Hitachi GST, 5600 Cottle Road, San Jose, CA 95193

J. Tribol 129(1), 161-170 (Jun 17, 2006) (10 pages) doi:10.1115/1.2401208 History: Received March 15, 2006; Revised June 17, 2006

To achieve the areal density goal in hard disk drives of 1Tbitin.2 the minimum physical spacing or flying height (FH) between the read/write element and disk must be reduced to 2nm. A brief review of several FH adjustment schemes is first presented and discussed. Previous research showed that the actuation efficiency (defined as the ratio of the FH reduction to the stroke) was low due to the significant air bearing coupling. In this paper, an air bearing surface design, Slider B, for a FH control slider with a piezoelectric nanoactuator is proposed to achieve virtually 100% efficiency and to increase dynamics stability by minimizing the nanoscale adhesion forces. A numerical study was conducted to investigate both the static and dynamic performances of the Slider B, such as uniformity of gap FH with near-zero roll over the entire disk, ultrahigh roll stiffness and damping, low nanoscale adhesion forces, uniform FH track-seeking motion, dynamic load/unload, and FH modulation. Slider B was found to exhibit an overall enhancement in performance, stability, and reliability in ultrahigh density magnetic recording.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Two operational modes of a FH control slider with piezoelectric actuation: (a) passive mode; (b) active mode

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Figure 2

(a) Air bearing surface design, Slider B; and (b) air bearing pressure profile at the MD (radial position 23.88mm, skew: −2.56deg). The scale displayed is normalized to ambient pressure: (p−pa)∕pa.

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Figure 3

(a) A conventional pico-slider ABS, Slider A, used for comparison; and (b) air bearing pressure profile at radial position 23.88mm. The scale displayed is normalized to ambient pressure: (p−pa)∕pa.

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Figure 4

Simulation of gap FH and minimum FH profiles of Slider B at sea level, 0m, and high altitude, 4500m

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Figure 5

Simulated FHs at the read/write transducer and one point on one of the side ABS rails. The radial position is at the MD.

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Figure 6

Air pressure distributions before (a) and after (b) a 8nm actuation stroke

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Figure 7

Frequency responses of the air bearings of Slider B and Slider A

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Figure 8

Comparison of modal frequencies and damping ratios of various ABS designs. The data of Slider B and Slider A were evaluated at the MD. The data of ABS I and ABS II were obtained from Ref. 24.

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Figure 9

The drop of minimum FH caused by the electrostatic potential across the HDI. The actuation stroke of Slider B is 4nm. The pitch of Slider B is 108μrad at zero voltage. The results of the high-pitch slider (245μrad) and low-pitch slider (190μrad) are from Ref. 26.

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Figure 10

Comparison of magnitudes of intermolecular adhesion forces of Slider B and Slider A as a function of minimum FH. The FH of Slider B was reduced by actuating the central trailing pad toward the disk and the obtained flying attitudes (minimum FH, pitch, and roll) were then used to calculate the intermolecular forces of Slider A.

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Figure 11

Track-seeking profiles. The maximum acceleration is 65g.

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Figure 12

Gap FH changes due to the seek motion for (a) Slider A (with a maximum difference of ∼0.75nm near the MD); and (b) Slider B (with a maximum difference of ∼0.2nm near the OD)

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Figure 13

Comparison of the displacement and minimum clearance histories during the unloading processes with two unloading velocities, 50mm∕s and 150mm∕s, at the OD (7.22deg skew) and 15,000rpm

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Figure 14

Air bearing force histories during unloading processes at the OD: (a) unloading velocity: 50mm∕s; and (b)150mm∕s

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Figure 15

Displacement, minimum clearance and force histories during loading at the OD with 50mm∕s loading velocity and 15,000rpm disk velocity

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Figure 16

Measured disk morphology used in the simulation at three radial positions, ID, MD, and OD. The peak-to-peak and standard deviation of the disk roughness are 1.76nm and 0.31nm, respectively

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Figure 17

Comparison of FHMs of Slider B and Slider A at three radial positions, ID, MD, and OD with skews −15.62deg, −2.56deg, and 7.22deg, respectively. The solid and dash curves are the results of Slider B and Slider A, respectively.




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