- 學位論文
線型雷射光束成型模組於口內齒模掃描裝置之設計與應用研究
The Application and Design of Line Laser Beam Shaping Module for Intra-Oral Scanner
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摘要
數位齒科膺復的市場需求正在逐年成長之中。電腦輔助設計/電腦支援製造(CAD/CAM)齒雕系統是利用口內光學齒模掃描儀取模，並配合軟體3D牙體設計與調整修復，而後將此掃描與重建之齒列形貌的數位檔案遠端傳送至五軸CNC牙雕加工機台進行自動化加工，變成實體化的膺復成品。不但過程迅速、準確，也能夠消弭傳統手工取模對於病患造成的不舒適感與印模材料的不準確性。而其中口內齒模掃描裝置成為取模之關鍵硬體設備。其功能是以一雷射光源並配合光束整型裝置，投射出一線型或其他型式之結構光於齒列上，並利用馬達配合傳動機構使結構光進行前後往覆地掃描作動，而後由CMOS取像系統擷取反射自齒列且因齒列形貌變化而扭曲之線光束，量測齒模曲面及取得齒模表面點資訊並經由背後演算法之計算，於人機介面中建置和即時顯示掃描之齒模三維輪廓。 為求取得之扭曲線型圖案能精確重建齒列的形貌，該線型光束之品質在線長、線寬、聚焦深度與均勻度等，均須滿足規格要求。而本論文之研究主題即在設計並評估各類雷射線型光束整型系統應用於手持式口內掃描裝置的可行性、實用性與商品性，研究的範疇屬於應用性之設計分析類型。 目前現有之線型結構光束之光學整型系統其相關技術主要有三類型，包括折射式、反射式，和繞射式。本研究所提出之設計方法分別為折射式與繞射式。折射式光束整型是利用光經過透鏡因其折射率和表面曲率所造成之光路偏折，以達到光束整型的效果。在設計上其系統組成皆選用標準光學元件，也因為架構相對簡易，面對不同的規格變化其調整彈性度高；繞射式元件是利用波傳遞特性將入射光場進行相位的調變，藉此改變光場的分佈。本研究採用一純相位調變型的矽基液晶(LCoS)空間光調制器作為動態線型結構光干涉圖像之記錄，將一併整合光束整型系統以及動態掃描機制，未來有機會作為口掃裝置愈加微型化發展之基礎。整型成線型光束圖像所需之相位分佈資訊透過電腦全像技術，以疊代傅立葉演算法(Iterative Fourier Transform Algorithm)計算得出。此外，將針對連續之相位分佈作階梯化結構近似，同時對分階之相位作優化處理以降低階梯化所導致的相位失真，以及實驗量測、分析比較在不同階梯化程度下之光束表現，並可作為未來若將送件製造成浮雕結構之靜態穿透式繞射元件之前的預期結果驗證和先期評估。
並列摘要
Market of digital dentistry is growing fast in recent years. Dental CAD/CAM system uses an intra-oral scanner to acquire the digital surface profile of the teeth, which is also called digital impression, and modify or design a 3D dental model with the simulation software. After the contour of the teeth is scanned, send the digital files to the following CAD/CAM process of making artificial teeth like a 5-axis CNC milling machine for the dental restoration. The digital impression method not only has the advantages of less required scanning time, high scanning accuracy, but also can ease the discomfort or distress of patients who undergo the dental impression. The intra-oral scanner is especially the key hardware for taking the digital impression. A commonly used approach is to project a line laser beam on the teeth and make the laser beam move back and forth with the assembled scanning mechanism. The image sensor detects and reconstructs the real-time 3D teeth profile from the distortion of the reflected line beam image with the algorithm behind. In order to acquire the accurate teeth model detected from the distorted line laser beam pattern, the quality of the line laser beam is supposed to meet the requirement in beam length, beam width, depth of focus, uniformity, etc. The topic of my thesis is to design some different kinds of laser module that generates a line laser beam and evaluate the possibility, applicability and commercialization of the laser module for the application of the intra-oral scanner. Currently there are several kinds of line laser beam shaping systems widely used, including refractive beam shapers, reflective beam shapers, diffractive beam shapers, etc. The research proposed designs containing both the refractive line laser beam shaper and the diffractive line laser beam shaper. A refractive beam shaper utilizes the refraction property, which happens when the light propagates through an optical lens because of the refractive index and the curvature of the lens, so as to have a laser beam shaped into a laser stripe. Each component of the refractive beam shaper is availably selected. Since the embodiment is relatively simple, it is flexible to adjust its configuration for different design requirements. The diffractive optical elements provide the incident light waves with the phase modulation to redistribute the light field. The research utilize a pure phase type liquid crystal on silicon (LCoS) SLM as the holographic recording of the interference pattern of dynamic line laser beam (object beam) and reference beam. The LCOS-SLM projective system is able to combine the function of line laser beam shaping with the one of scanning. Therefore, there will be a potential to minimize much more the volume of the intra-oral scanner. The required phase distribution information for generating a line laser beam pattern, called hologram, can be obtained by computer generated holography technique and calculated by the iterative Fourier transform algorithm. In addition, quantize and optimize the acquired continuous phase distribution into several levels, as well as analyze the performance of the line laser beam in different levels. The results can be treated as an evaluation for manufacturing the diffractive optical elements.
參考文獻
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