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TECHNICAL BRIEFS

Disk Wobble Control in Optical Disk Drives

[+] Author and Article Information
Jieng-Jang Liu

Department of Mechanical Engineering,  National Taiwan University, No. 1, Roosevelt Road, Sec. 4, Taipei, Taiwan, Republic of Chinajjliu@ntu.edu.tw

Yee-Pien Yang1

Department of Mechanical Engineering,  National Taiwan University, No. 1, Roosevelt Road, Sec. 4, Taipei, Taiwan, Republic of Chinaypyang@ntu.edu.tw

1

Corresponding author.

J. Dyn. Sys., Meas., Control 127(3), 508-514 (Sep 13, 2004) (7 pages) doi:10.1115/1.1988339 History: Received November 18, 2003; Revised September 13, 2004

Focusing errors in optical disk drives comprise significant periodic components and an eventful dc content. The dc component is not explicitly taken into account in many periodic compensation methods. This paper investigates the design of adaptive feedforward cancellation (AFC) and frequency adaptive control technique (FACT) algorithms for periodic components as well as dc disturbance compensation. Both algorithms are applied as a plug-in module to an optical disk drive for demonstrating their facility in the reduction of focusing errors. By making good use of frequency sampling filter (FSF), the real-time harmonic identification can be fulfilled in FACT method for various playing speeds. Analysis and experimental results show that FACT has better properties than AFC in terms of dc cancellation and harmonic independence. It is also shown that AFC fails when both the dc content and harmonics are compensated simultaneously.

Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Optical disk mechanism

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Figure 2

The plug-in wobble cancellation controller

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Figure 3

Frequency response of a designed lead-lag controller Cp(s)

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Figure 4

Generalized adaptive feedforward cancellation

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Figure 5

The values of Eq. 19 with a¯0=1, b̂=0 and various â. The lines indicate as a, b, c, d corresponding to the cases that â has value of 0.5, 1, 1.5, and 2, respectively. For cases a¯0<â, the regions labeled by χ on lines c and d have opposite values to those of lines a and b

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Figure 6

The block representation of FACT

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Figure 7

Experimental setup

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Figure 8

The identified frequency response of W(s)

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Figure 9

The time series and FFT spectrum of FES at 4,500rpm(75Hz) when the controller Gp(s) was shown in Fig. 3

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Figure 10

The dc content in FES can be reduced successfully either by AFC (a) or FACT (b)

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Figure 11

The AFC results when both the fundamental and fractional dc contents are reduced

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Figure 12

100% of dc cancellation followed by an additional first harmonic compensation causes the FES out of control

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Figure 13

By FACT method, both the fundamental frequency and 100% dc contents can be reduced concurrently

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Figure 14

The time series and FFT spectrum of FES at 6,780rpm(113Hz) without the help of AFC or FACT

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Figure 15

With the help of FACT, the dc and the first five harmonics are reduced successfully for CAV 6,780rpm

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