Research Papers

Commutational Output Feedback Control for Disk Drive Ramp Loading

[+] Author and Article Information
Ryan T. Ratliff

 The Boeing Company, St. Louis, MO 63166

Prabhakar R. Pagilla

School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078

J. Dyn. Sys., Meas., Control 130(2), 021001 (Jan 18, 2008) (10 pages) doi:10.1115/1.2745853 History: Received May 24, 2005; Revised October 03, 2006; Published January 18, 2008

The feasibility of a ramp load controller using a conventional disk drive actuator is investigated. The controller 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. A disk drive designed with a conventional actuator is outfitted with a ramp and optimized for ramp load operation. While on the ramp, there exists a set in the state space where the actuator dynamics are uncontrollable. An input commutation is required within the uncontrollable region to sustain the direction of actuator motion. Additionally, the motor torque factor, magnetic restoration bias, and friction torque are nonlinear and can be represented by functions that are Lipschitz within the actuator ramp angle. A state trajectory is generated that, when tracked, moves the actuator through the uncontrollable set for a successful load onto the disk at the desired load velocity. Because position and velocity information are not available during a load maneuver, an output feedback controller is necessary. A stable, output feedback tracking controller is designed to track the trajectory and handle the nonlinear effects. A unique disk drive is manufactured and experiments are performed to verify the complete ramp loading design strategy.

Copyright © 2008 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 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

Unique, commutational ramp load disk drive

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Figure 7

Actuator torque profiles along the ramp angle, θr

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Figure 8

Example ramp load trajectory profiles

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Figure 9

Reference trajectory profile

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Figure 10

Simulated trajectory profiles (observer loaded with tolerance limit initial conditions)

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Figure 11

Simulated tracking error performance (observer loaded with tolerance limit initial conditions)

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Figure 12

Simulated observer error (observer loaded with tolerance limit initial conditions)

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Figure 13

Experimental setup for ramp load control

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Figure 14

Open-loop comparison

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Figure 15

Experimental trajectory profiles

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Figure 16

Experimental tracking error performance

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Figure 17

Current observer error




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