變焦光學讀取頭對精密位移量測性能之影響探討

The Influence of Variable Focal Length of the DVD pick-up head on the Performance of the Displacement Measurement System

錢正清(Cheng-Ching Chien)

指導教授 ： 黃光裕

國立臺灣大學/工學院/機械工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.00540

摘要

DVD讀取頭運用像散原理使光碟片數據軌跡得以被對焦，運用相同原理也可以設計開發出高精度光學位移量測系統。在DVD讀取頭之原始物鏡焦長的限制下，只能作短行程的位移量測，為了擴大量測行程，本研究採取改變物鏡焦長的方式，來改變光束之聚合情形，使雷射成像光點都能投射到光電感測器範圍中。透過光學分析軟體對DVD讀取頭之光學系統進行深入探討分析，其中包括雷射光點之像散變化以及聚焦誤差訊號對位移變化之關係。除此之外，在實驗中並以高精度之雷射干涉儀作為位移校正準據，進行聚焦誤差訊號對位移校正曲線之量測。首先探討系統之量測穩定性以及被測面傾斜之干擾影響，更進一步系統化地探討四種不同焦長之物鏡對位移量測範圍、線性誤差、解析度以及重現性之影響。驗證測試則以精密剪力式壓電步進器作為測試對象，以瞭解長行程位移量測之重現性和誤差。在系統誤差分析上，利用熱像分析儀和熱電偶分別量測DVD讀取頭運轉中的溫度變動，並透過模擬分析光學元件溫升現象對成像光點之影響，再經由成像光點變化推導出對應的聚焦誤差訊號變化，分析數據與實驗數據之比對驗證以提升分析模型之可靠性。

關鍵字

DVD讀取頭 ； 像散現象 ； 位移量測 ； 聚焦誤差訊號 ； 誤差分析

並列摘要

DVD pick-up head applies the astigmatic principle to let the data track on the disc be focused and read out. Furthermore, based on the same principle we can also design and develop a high-precision optical displacement measurement system. However, the original DVD pick-up head is limited to a narrow measuring range by the short focal length of the objective. In order to expand the measuring range, this thesis proposes varying focal length of the objective to modify the beam convergence, which makes the imaging laser spot completely project onto the photodiode-IC. Through the optical analysis software, the optical system of the DVD pick-up head is thoroughly analyzed and studied to find out the relationship between the variation of astigmatic spot and the defocus signal. Besides, a high precision laser interferometer is adopted as displacement reference to experimentally acquire the calibration curve between the defocus signal and the displacement. Firstly, the measuring stability and the inclination interference are investigated; and further, a systematic study on four objectives with different focal length is conducted in terms of measuring range, linearity, resolution and repeatability. For the verification testing of the measuring performance, a precision shear force type piezoelectric stepping actuator is used as the testing subject to comprehend the repeatability and the error driving the measurement of the long-distance motion. For the error analysis, the infrared thermo graph and the thermocouple are utilized to measure the temperature variation inside the operating DVD pick-up head; moreover, the thermal influence on the imaging laser spot is also analytically researched. And from the variation of the imaging laser spot the corresponding defocus signal can be derived. Through the comparative evaluation between the analytical and the experimental data the analytical model can be improved to achieve higher reliability.

並列關鍵字

DVD pickup head ； Astigmatism ； Displacement measurement ； Focus error signal ； Error analysis

參考文獻

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