投影疊紋法在複合結構量測之研究

Abstract

光學檢測在產業界佔有舉足輕重的角色，具非破壞性、全域且高精密度的良好特性，因此在產品檢測的應用更極為廣泛，本研究運用疊紋干涉術(Moiré interferometry)為基礎架構建立一套用於量測待測表面的相對起伏高度、粗糙度以及極微小位移量的光學量測系統，希望能提供新的想法對產業界有所助益以突破目前的光學檢測限制。 以疊紋干涉術為基礎的光學檢測研究之發展早已行之有年，而在本研究中所採用的投影疊紋法(Projection moiré)之主要精神在於藉由兩道空間頻率相近或相同的光柵相互疊加而成的效應，其中一道為參考光柵(Reference grating)，而本研究中的參考光柵是以程式產生可調整不同空間頻率的虛擬光柵；另一道則為投影至待測物表面的光柵影像，而在起伏高度不一的待測表面上的光柵影像會受到待測物表面起伏狀況不同而在觀測方向產生光柵投影條紋影像的歪曲變形，將電腦產生的參考光柵與由影像擷取裝置所獲取投影於待測物表面的光柵影像作疊合，便會產生所謂的疊紋效應；利用基本的光學干涉理論與疊紋效應結合，本研究中以相移法來改變投影於待測表面的光柵相位，再以相移法的理論反運算出在帶有待測面各點高度資訊之介於(-π,π]相位主幅角，再以離散傅立葉轉換解偏微分方程的相位重建程式還原待測面的相位值，以得知待測面之表面輪廓。 本研究量測樣本為印有字樣的塑膠蓋(樣本一)以及鋁片(樣本二)的熱變形量測，對樣本一的量測為驗證系統之可行性，而樣本二之量測為測試系統的量測解析度範圍。希望本研究能夠將此系統應用於各項材料上的表面檢測，例如：複合材料在製程中因殘留應力而產生的表面微小波紋，諸如此類的材料檢測都可應用。以提供產業界有更好的檢測技術。

Optical measuring plays a very important role in the industry. It has excellent features of non-destructiveness, holographic measurement, and high sensitivity, so it is applied to examine the quality of product extensively. This research based on moiré interferometry constructed a optical measuring system to measure the relative height, roughness, and slight displacement on a surface. We expect it will benefit the industry field to break through the optical measuring limits at present by offering some new ideas. Optical measuring research based on moiré interferometry has developed for several decades. The main idea of this research is to utilize the moiré effect caused by two superimposed gratings of identical or similar spatial frequency. One is the reference grating and it is a virtual grating created by a computer program in this research; The other grating is the image of grating projected on the measured surface by the DLP projector, and this grating will distort because of the different sloped profile of the surface. To superimpose the program-created grating and the captured distorted grating will derive the so-called moiré effect. This research combined the basic theory of optical interferometry and moiré effect to project the different phases of the projected grating fringes by the phase-shifting method and compute the principal value of arguments between (-π,π]. In the end, the phase unwrapping program based on discrete Fourier transform of solving PDEs is used to unwrap the phase of the measured surface, and finally the surface profile is derived by the optical measuring system. These measured samples in the research are a plastic cap with printed words (Sample 1) and a aluminum plate (Sample 2). Measuring Sample 1 is to verify the feasibility of the system, and measuring Sample 2 is to verify the range of measuring resolution of the system. Expect this research can apply to surface measurement of various materials such as the ripple vein on the surface of composite material caused by residual stress produced during the manufacturing procedures. This research can be applied to this kind of material examination.