高轉速下光學反射鏡之製程與加工研究

Abstract

近年來，對於光學元件的要求越來越高，針對不同的元件選擇合適的加工方法，已成為掌握規格及品質之關鍵。以反射鏡的製作方式為例，製程上需根據規格條件進行基材選擇、成型、精密加工、拋光、鍍膜等流程規劃，才能製作符合要求的成品。 本論文針對適用在高速轉動下光學反射鏡的製作方式和測試結果，進行研究與討論。首先針對高速轉動希望在三萬轉以上的特性，進行反射鏡的設計，選擇使用鋁合金6061作為基材，並制訂其加工規格，其中表面精度P-V要求條件為 。透過各種精密加工法的比較，本研究選擇使用一般機械化學拋光和鑽石切削兩種加工方法，並根據精密加工方法規劃製程。而為了提高反射率，選擇鋁金屬膜，提高針對特定波長的光之反射率，本研究並選擇無電解鎳作為基材與金屬膜之間的過渡層。經過製程加工後，拋光製程後表面精度P-V約為 ，而鑽石切削製程後表面精度P-V可改善至 ，進行綜合性的討論。 反射鏡加工完後進行系統測試，反射鏡轉速可達三萬轉以上，但本研究發現反射後的光有偏移的現象，分析原因為軸心偏擺和基材變形所造成；因此進一步利用模擬軟體進行建模分析，並根據模擬的結果找尋改善精度的方向。 本論文最後發現鑽石切削方式加工出來的反射鏡可達到基本規格需求，但仍有諸多缺陷；本研究最後根據製程分析比較的結果和成品測試結果的討論，提出改善製程規劃的方向和建議事項。

In recent years, specifications of optical elements are getting stringent. It’s crucial to plan an effective fabrication process to ensure their engineering functionalities. Based on the functional requirements and service environment, optical reflectors must go through a series of manufacturing processes including material selection, forming, precision manufacturing, super-finishing and coating. In these processes, precision manufacturing is the key to the accuarcy of reflectors. In this thesis, optical reflectors were designed to be used in high-speed rotating environment. Al 6061 was selected for the reflector to run in high rotation speeds of minimum 30,000 rpm. The specifications require flatness P-V of facets on reflector less than . In order to obtain perfectly flat surface, mechanical chemical polishing (MCP) and single-point diamond turning (SPDT) are used in the fabrication process plan and comparisons are made for the end results. Final measurement gives a result of flatness P-V by polishing of about , while that by diamond turning of . To get more reflectivity, Al layer coated on electroless Nickel as combination material is selected for light of specific wavelength in experiments. Further, testing whole system proves that the reflector rotation speed can reach 30,000 rpm as required. In the testng, the displacement of reflective light is observed and measured. It is found that spindle wobbling and substrate deformation remian as key issues. Further study is made by simulation and the model of deformation is established and analyzed. The present study shows that diamond turning process can best make reflector flatness within specification, but some defects on surface remain. Therefore, fabrication processes shall be further investigated in future work for the improvement of reflectors quality.