近場光碟機之類神經控制

Abstract

在資訊爆炸的現代，近場光碟機是一項為了提高儲存容量和密度的重要發明，但是由於近場光碟片的軌距僅有500 nm而且讀寫頭的飛行高度僅50 nm，因此以往只憑藉音圈馬達做為制動器必無法勝任尋軌與循軌，必須發展有效的控制方法。 本研究就是利用二階段控制，粗調仍由音圈馬達擔任，而多加裝壓電材料PZT來擔任微調的工作。控制方法在VCM方面採用PID控制器，而PZT部分由於有遲滯效應，並且為了克服雜訊與非線性而利用類神經控制，且在類神經控制器方面設計了線上倒傳遞學習跟經過時間的倒傳遞，並比較兩種結果，發現無論存在隨機干擾與否，後者表現都較佳。在實驗方面，利用雷射都普勒干涉儀從事PZT動態的量測，並且初步設計能供微調及飛行高度之讀寫頭，預期能利用這種方法達成循軌與讀寫頭高度的控制。

In this era of information explosion, a near-field optical disk drive is an important innovation of higher capacity and higher density. Due to the demand of 500nm track pitch density and 50nm only flying height of the R/W head, previous actuators are not able to conduct track seeking and following well. In this study, dual-stage control is proposed. Coarse control is carried out by a voice coil motor, whereas a piezoelectric material of PZT undertakes fine tuning. A PID controller is used for VCM. Since it is complicated to generate a plant model including an air bearing and structural elasticity, a neural network controller is developed to deal with both fine tuning and flying height control. This work compares both results of backpropagation and backpropagation through time in the neural network control. The latter outperforms the former whether runout disturbance exists or not. The latter proves better due to its capability dealing with time varying system. A laser Doppler vibrometer is used to measure PZT vibration in experiments, and an early design of R/W head is built for the sake of fine tuning and flying height control.