光碟機內音圈馬達型動態吸振器之研究

Abstract

造成光碟機運轉時的振動主要是來自於光碟片旋轉的不平衡量，目前市售光碟機大多以被動式吸振器抑制某固定轉速所引起的振動，但實際上光碟機會依據不同的光碟片或不同的狀況而改變運轉速度。先進的光碟片儲存密度提高且軌距縮小，光碟機讀寫時對微小的振動就更敏感，所以讓光碟機在各種不同轉速下具有最小振動的狀況，以利資料讀寫是重要的課題。 本文旨在研究應用於多轉速光碟機的主動式吸振器的動態特性，比較被動式吸振器的制振效益。所提出的主動式吸振器主要結構由音圈馬達與被動式吸振器改裝而成，稱為音圈馬達型動態吸振器。本文推導運動方程式以呈現音圈馬達型動態吸振器的特性與效益。實驗方面則利用波形產生器產生弦波電壓，再經功率放大器提供音圈馬達吸振器之致動電源，並利用都卜勒雷射干涉儀量測不同轉速下的振動結果，顯示適當的致動電壓大小及接近於轉速的致動頻率時，其吸振效益最佳。在閉迴路控制方面，本文採用線性二次高斯方法控制動態吸振器，計算與實驗結果均顯示可有效地減少光碟機的運轉振動。在控制實驗方面則是利用資料擷取卡與個人電腦做為其控制器。因為光碟機內部空間有限，本文針對音圈馬達型動態吸振器在外型尺寸、驅動電壓與驅動電流所受限制下，改變不同永磁厚度、線圈有效空間及線徑，從事最佳化設計，利用有限元素方法模擬分析各狀況下的電磁力常數與電感，由克希荷夫電壓定律與音圈馬達型動態吸振器的運動方程式，計算出平均消耗功率，並做分析討論。

Unbalanced disks in rotation will lead to main vibration of an optical disk drive. Passive vibration absorbers are usually used in current optical disk drives to suppress vibration. Generally, optical disk drives have to make a disk spin at multiple speeds by different read/write conditions. However, the passive vibration absorber only suppresses vibration at a specific rotating speed and may excite vibration at other speeds. This study aims to investigate an active vibration absorber to reduce disk drive vibration at multiple rotating speeds using an effective control. In addition to the basic absorber as a passive device, a voice coil motor serves to actively control vibration. In this study, combining passive and active devices is named as a voice coil motor type vibration absorber. The derived mathematical model depicts the advantage of an active vibration absorber. For reducing vibration of the traverse, corresponding to the disk speed, required electrical voltages in a voice coil motor type vibration absorber are calculated as the control system input. Using voice coil motors makes optical disk drives more stable and robust at multiple speeds. A function generator generates sinewave signal, which actuates the active absorber through a power amplifier. The vibration of a disk drive at different rotating speeds is measured by a laser Doppler vibrometer. Experimental results show that a suitable actuating amplitude and a rotating speed nearby actuating frequency lead to effective vibration reduction of a voice coil motor type vibration absorber. This study investigates vibration reduction by the vibration absorber with a linear quadratic Gaussian method in the closed-loop control. Simulation and experimental results show that a voice coil motor type vibration absorber effectively decreases vibration of an optical disk drive at different operating speeds. A data acquisition hardware and a personal computer act as a controller of the vibration absorber in experiments. Moreover, this study proposes a method to design a voice coil motor type vibration absorber. A better voice coil motor type vibration absorber performance, such as low average consumption power, can be achieved by tuning the wire diameter of a coil, the thickness of the permanent magnet, and coil spaces. In design procedure it also needs to consider allowable currents and voltages in this system. The force constant and the coil inductance of the voice coil motor are obtained by the finite element method simulation. Then, the average consumption power is computed from the Kirchhoff’s voltage law and dynamic equations. This study demonstrates the performance of this proposed vibration absorber.