Design and Analysis of a Disk Drive Actuator for Commutational Ramp Loading

[+] Author and Article Information
Ryan T. Ratliff

 The Boeing Company, St. Louis, MO 63166

Prabhakar R. Pagilla1

School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK74078pagilla@ceat.okstate.edu


Corresponding author.

J. Mech. Des 129(3), 346-360 (Feb 27, 2006) (15 pages) doi:10.1115/1.2406106 History: Received July 18, 2005; Revised February 27, 2006

A voice-coil motor actuator system is designed to perform a unique disk drive ramp load/unload operation. The design eliminates the necessity of increased material requirements common in ramp load disk drives. Therefore, disk drives with lower cost, higher performance actuators can realize the linear shock protection benefits of ramp loading. This study offers a complete, systematic design procedure together with required analysis for manufacture of a commutational ramp load/unload drive. The actuator is designed and optimized to meet specific move-time performance requirements. When used for ramp load/unload, however, there exists a location where input current has no influence on actuator motion. An input polarity reversal is required within the uncontrollable region to sustain the direction of actuator motion. A magnetic, restorative bias is designed that prevents the actuator from resting in the uncontrollable region while providing resistance to rotational shock effects. A state trajectory is designed that, when tracked, moves the actuator through the uncontrollable set for a successful load onto the disk at the desired load velocity. A ramp load controller is designed to track the trajectory and handle the nonlinear effects from bias and friction torque. The unique disk drive is manufactured and experiments are performed to demonstrate effectiveness of the complete design strategy.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Ramp load concept (courtesy of Fujitsu Corp)

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Figure 2

Disk depression resulting from ramp loading HDI

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Figure 7

Magnetic bias feature

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Figure 8

Actuator torque profiles along the ramp angle, θr

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Figure 9

Rotational shock performance

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Figure 10

Time-optimal move comparison in the data zone

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Figure 11

Actuator ramp dynamic characteristics without commutation

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Figure 12

Actuator dynamic characteristics with commutation. Actuator forced back to OCS.

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Figure 13

Actuator dynamic characteristics with commutation. Actuator rests at θeq+.

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Figure 3

Left of the red line depicts additional magnet material required specifically to provide actuation while maneuvering on the ramp

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Figure 4

Conventional actuator: (a) controllable; and (b) uncontrollable

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Figure 5

Actuator after traveling through MT. Current polarity is reversed.

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Figure 6

Lumped parameter coil

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Figure 14

Actuator dynamic characteristics with commutation. Actuator loads onto disks.

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Figure 15

Example ramp load trajectory profiles

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Figure 16

Unique, commutational ramp load disk drive

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Figure 17

Air gap flux density (Tesla)

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Figure 18

Leakage measurement area at PCB location

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Figure 19

Leakage flux density at PCB location (Gauss)

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Figure 20

Comparisons for torque factor and bias. Torque factor is measured for 1Å of current.

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Figure 21

Experimental setup for ramp load control

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Figure 22

Open-loop comparison

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Figure 23

Experimental commutational ramp load maneuver



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