建立即時立體數位影像相關法於三維工程問題的動態量測

Development of Real-Time Stereo Digital Image Correlation Tracking System for Three-Dimensional Dynamic Measurement

黃右年(Yu-Nien Huang)

指導教授 ： 馬劍清

國立臺灣大學/工學院/機械工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802562

摘要

數位影像相關法(DIC)是一種非接觸全場位移量測的影像光學方法，由於其方便性與實用性高，目前在實驗力學領域上是最常被學者開發及應用的量測技術之一。本文主要開發即時數位影像相關法量測系統，整合相機校正、數值運算並即時呈現待測物體追蹤結果，取代傳統實驗繁瑣的流程，更能符合工業界的需求。文中使用標準測試影像搭配內插平移的方試驗證DIC演算法的量測精度為0.01pixel，配合Matlab程式將運算效率提升至30fps。實務量測的部分，本文量測精密對位平台複雜的二維動態行為，並即時呈現完整的位移軌跡，更將平台結合影像追蹤技術將其升級為回授制系統，能夠將待測物體定位在畫面的中央位置。接著將單點的即時量測系統提升為多點的即時量測系統，可以應用於長時間量測工具機主軸運轉時的熱伸長量，這些熱變形大約都是微米等級。有了多點的位移資訊，就可以即時求得應變的量值，搭配熱電偶得到溫升資訊，就可以進一步求得材料的熱膨脹係數。接著本文探討相機校正的問題，透過校正板取得影像扭曲係數，將此校正技術與即時量測系統整合改善鏡頭曲面的問題，使得影像量測將不再受到硬體相關問題的限制。除此之外，鏡頭斜向拍攝也是一個常見的問題，本研究透過已知像素座標對應的尺度因子搭配二次曲線擬合出整張影像的尺度因子，就可以校正斜向拍攝的梯形影像，僅使用單眼視覺量測到具有深度方向變化的運動行為，將二維平面量測精度推至極限。最後本文將單眼視覺的即時量測系統進一步提升成雙眼視覺的立體即時量測系統，除了可以即時追蹤待測物體在空間中的三維動態軌跡，更能夠建構複雜的立體曲面、全域搜尋世界座標、計算待測物體重的心位置。本研究使用此量測系統於市售的三次元量床、機械手臂動態量測，並探討立體量測系統的量測精度。

關鍵字

二維數位影像相關法 ； 立體數位影像相關法 ； 即時量測 ； 相機校正 ； 鏡頭曲面 ； 斜向拍攝 ； 精密對位平台 ； 工具機主軸 ； 三次元量床 ； 機械手臂

並列摘要

Digital image correlation (DIC) is a convenient and practical optical metrology for non-contacting and full-field deformation measurement of structures, which has been commonly accepted and widely used in the field of experimental mechanics. This thesis mainly contributes to develop real-time digital image correlation tracking system, which integrates the calibration of the camera, numerical analysis, and the display of result in real-time. Compared to a traditional DIC experiment, the development of the real-time DIC system improves the efficiency of an experiment, and fits more for the industry. In this thesis, the precision of the DIC algorithm is proved to be 0.01pixel by the interpolation of standard testing image, and the real-time DIC system is able to process 30 images within a second with Matlab program. Practically, the real-time DIC system is capable of measuring the complicated 2D movement of the alignment stage immediately. Also, this thesis combines the real-time DIC system and the alignment stage, and the feedback control system can maintain the target in the center of the image. Furthermore, the single point system is upgraded to a multi points tracking system, which can be used to measure the heat deformation of a spindle for a long period of time. The scale of the deformation is about 10 micro meter, and the system can provide the real-time strain value between points. The thermal expansion coefficient can also be obtained from the information of thermal couple. Afterwards, this thesis discusses camera calibration. With the integration of calibration technique and the real-time DIC system, the lens distortion effect can be solved and image measurement won’t be constrained by the hardware anymore. Besides lens distortion, keystone effect is also a serious problem. This thesis calculates the specified scale factor by the intrinsic and extrinsic camera matrix, and obtained all the scale factor of the image using second time surface fitting. The real-time DIC system then can measure the difference of depth using a single vision. Finally, the single vision system is further developed to binocular vision system, which is the real-time stereo DIC system. The system has the ability to measure the complete process of 3D movement, construct complicated 3D surface, and provide the center of gravity of an object. Additionally, this thesis uses the real-time stereo DIC system to measure the movement of a coordinate measuring machine and a robotic arm.

並列關鍵字

Two-dimensional digital image correlation ； Stereo digital image correlation ； Real-time tracking system ； Camera calibration ； Lens distortion ； Keystone effect ； Alignment stage ； Spindle ； Coordinate measuring machine ； Robotic arm

參考文獻

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