2 Methodology
2. 方法
2.1 Calibration of non-collimated light
2.1 非準直光的定標
The phase-shift fringe projection method [7–12] has been widely used for 3-D measurement in the past but has not been applied to component tilt measurement in PCBAs. 相移條紋投影法7－12在過去已廣泛用於三維測量，但是還沒有被用於印制電路板組件上元件傾角的測量。The technique was adopted in this research due to the following advantages: (i) it allows the use of a single overhead camera, (ii) it enables 3-D whole-field measurement and (iii) it is non-contacting. 這項技術由於以下優點而在本研究中得到了采用：1）它可以采用單壹的架空攝像機；2）它可進行三維的全場測量；3）它是無接觸的。
For precise surface or height measurement, collimated light is commonly employed in the fringe projection method [13]. 對於精密的表面測量或高度測量來說，準直光常被用於條紋投影法中13。The advantage of using collimated light is that it has constant angle of illumination over the surface being inspected.采用準直光的優點是，在被檢驗的表面上有恒定的光照角。 However, size of object that can be measured is limited by the diameter of the collimated beam. 不過，可以測量的物體尺寸受到準直光束直徑的限制。A non-collimated source is a diverging source that illuminates a larger area, thus allowing a larger area to be measured [14]. 非準直光源是壹種能照明較大面積的發散光源，因此可以允許較大的被測面積14。When a non-collimated source is used, the variation of the illumination (projection) angle over the surface of the object must be determined before accurate measurement can be made, referred to as projection angle calibration. 當采用非準直光源時，在物體表面上的照明（投影）角必須先確定，然後才能進行精確測量，這就稱為投影角定標。The calibration involves finding a relationship between the projection angle and distance on a flat surface. 定標涉及到找出投影角和壹個平坦表面上距離之間的關系。Although this relationship can be established mathematically using the geometry of the experimental layout, errors could be introduced in the calculation due the difficulty in defining the coordinates of the illumination source and target location precisely. 雖然這壹關系可以用實驗平面布置的幾何結構在數學上建立，但是在計算中由於難以精確限定照明光源的坐標和目標位置而引入誤差。In this work, glass blocks of known heights were used to determine experimentally the projection angle variation over the surface being measured. 在本文中，采用壹些已知高度的玻璃塊來實驗確定被測表面上投影角的變化。The methodology described in this section consists of four main stages: (a) obtaining a relationship between the angle of projection and the distance on a single block surface, (b) verifying the relationship obtained in the first stage by measuring the tilt angle of a single specimen block, (c) repeating the first step for different block heights, (d) verifying the accuracy for the formulated equations by measuring the absolute height of multiple blocks at different locations in the field of view (FOV). 本小節所描述的方法包括4個主要的階段：a. 得出投影角和單壹玻璃塊上距離的關系；b. 通過測量單壹樣本塊的傾角，驗證第壹階段得出的關系；c. 針對不同的玻璃塊高度重復第壹步；d. 通過測量在觀察範圍（FOV）內不同位置多個玻璃塊的絕對高度，驗證公式化的方程式的精度。