應用偏擺法對鏡射表面三維量測與重建之研究

Abstract

三維形貌量測在自動光學檢測上有著不可取代的地位，而三角量測法則為目前主要使用的量測方法，但此量測方法對具鏡射性質之物件三維形貌量測，仍無法有效達成，而本研究中將提出一套對鏡射面物件進行三維形貌量測之系統與技術，利用偏擺法 (Deflectometry Method)量測鏡面物件，以投影二值碼圖樣並進行空間結構光編碼，其具有絕對偏移量測的優點，並以藉由建立高度校正曲線方式，有效補正高度對量測結果的誤差累積，可以得到校正後之精確光程相位偏移量，配合位移量與梯度關係式，可得到準確相位梯度值。本研究同時提出利用陰影區域為起始點與將邊界之偏移量設定為零點(終止端)，突破以往使用積分方式重建時，存在僅可量測邊緣不具斷面之待測物與遇到陰影時誤差累積等量測方法之缺點，利用此方法可以使用路徑積分方式重建鏡射物件，並進行全域式形貌之量測與重建。 藉由實驗之實際驗證，此方法在深度量測範圍70 mm以內，平均量測誤差可控制在30μm以內，是以往量測鏡射表面物件較難達成的量測精確水準，其量測之殘留誤差來源主要應來自起始高度的不準確與積分上誤差的累積。

3-D profile measurement has an irreplaceable position in automated optical inspection (AOI), especially to precision engineering. Among various techniques, optical triangulation principle is the most commonly used method to detect profiles. Objects having specular free-form surfaces have been regarded as a difficult task due to specular characteristic stopping reflected light to be detected by imaging sensors. The research established a measuring method to measure and reconstruct specular free-form surfaces. The developed method basically employing Deflectometry applies liquid crystal display (LCD) to project scattering binary code patterns (BCP) onto the measured surface. The BCP projection provides a unique advantage in achieving absolute phase measuring capability. To correct potential cumulative errors along the integration paths, a height calibration curve establish accurate relationship between the calibrated height and the detected phase gradient. In the measuring method, an optically shaded area can be used as a starting measurement point and the object’s boundary having a zero height value as an ending point. Employing the path integral method can reconstruct full-field measured surfaces. The experimental results show that the developed method can achieve an average measured error less than 30 μm with a measuring depth up to 70 mm for free-form specular surface measurement and reconstruction.