光碟聚焦的伺服控制研究與分析

Analytical study of the focus servo control for optical disc

陳有田(Yu Tien Chen)

指導教授 ： 劉宗平

元智大學/工程學院/電機工程學系/碩士(2002年)

摘要

由於碟片的軸向擺動以及主軸馬達轉速變動等因素的影響，那將會造成光碟機的系統性能不夠穩定。為了維持系統的穩定性，必須針對光碟機的聚焦伺服系統進行補償。因此，本文的研究目的著重在：設計串、並聯式相位落後-領先等化器。
首先，藉由光學系統聚焦之特性，以及控制系統的相關規格，研擬出系統的性能需求。其次，建構、修正受控裝置的模型，使其更趨近於真實的系統，藉以估計數位等化器的延遲時間。同時，針對不同的主軸馬達轉速，引用串、並聯式相位落後-領先等化器之結構，調整等化器相關的參數值，以期分析伺服系統的頻域穩定性。有關數位訊號處理的理論背景、研究方法、實驗裝置、以及量測結果，將會在文中詳加地敘述。
一般市售碟片的軸向擺動約為300 μm，本研究將軸向擺動之範圍提高到500 μm，來設計所需要的等化器。根據量測的結果分析可知，本文中等化器的直流增益可達67 dB、增益邊限> 6 dB、相位邊限> 30 degree。最後，針對等化器性能的優劣，提出未來研究的改進方案。

關鍵字

光碟 ； 聚焦 ； 伺服 ； 控制 ； 軸向擺動 ； 受控裝置 ； 等化器 ； 相位落後-領先

並列摘要

Due to the axial runout of the optical disc and the change of the spindle motor, the performance of the disc system would probably be unstable. In order to improve the stability of the system, the gain of the focus servo needs to be tuned and compensated. In this thesis, we aim to elaborate on the design of the cascade / parallel phase lead-lag equalizer.
Firstly, the system requirement is stipulated based on the focusing properties of the optical system and the related specifications of the control system. Secondly, the model of the plant must be built up and modified such that it can further approach the real system to estimate the time delay of the digital equalizer. At the same time, for different speeds of the spindle motor, the related coefficients of the equalizer used in the system could be adjusted by the structure of the cascade / parallel phase lead-lag equalizer to find the stability of the servo system in the frequency domain. The theoretical background, the experimental setup, and the measured results about those topics would be discussed in the text in detail.
The axial runout of the commercial disc is about 300 μm. The equalizer used in this study was designed for 500 μm. According to the measurements, we know that the DC gain of the equalizer is nearly 67dB, its gain margin and phase margin are greater than 6dB and 30 degree, respectively. Finally, for the strong / weak points of the equalizer performance, the further enhancement approach and future study are also recommended.

並列關鍵字

optical disc ； focus ； servo ； control ； axial runout ； plant ； equalizer ； phase lead-lag

參考文獻

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[1] Heitaro Nakajima and Hiroshi Ogawa, ”Compact Disc Technology”, Japan by Ohmsha Ltd. 1992.

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[24] Benjamin C. Kuo, ”Automatic control systems ”, 7th ed, John Wiley & Sons, Inc. 1995.