Calibration Technology And Its Application In Machine Vision Measurement And Control

With the rapid development of modern industrial technology, vision measurement technology plays an increasingly important role in industry. It has lost of advantages, such as the fast speed, high precision, non-contact, high automation. In recent years, it plays an increasing role in the field of non-contact measurement. Vision measurement includes not only the general content in the machine vision, such as visual perception, image processing, image analysis and pattern recognition and so on, but also has the particularity of measurement, such as the precise detection of space geometry, location and identification.Camera calibration originated from the mid-20th century, and after decades of development, it has been more and more mature, developed from traditional calibration technique to self-calibration technique. Calibration can been applied in the manufacturing, electronic information, the printing industry, iron and steel metallurgy, national defense and so on. With the rapid development of automation, calibration has great development potential. The paper focused on calibration in machine vision applications.This topic came from the research cooperation project "Research and development of embedded machine vision controller" (contract number: 07398). With engineering thinking, this paper presented a new calibration method based on a single image. First, the calibration needed the optical path adjustment. It was divided into two steps: light intensity adjustment system can effectively prevent the edge of the target information losing, which can lead to sub-pixel corner detection inaccurate. Verticality adjusting system between optical axis and object surface can effectively prevent the angle between the CCD plane and the object surface, which lead to measurement error. Corners detections of this calibration used a modified Harris operator extracted pixel corners. It effectively reduced the algorithm computation. Then it used the space moment method to sub-pixel corner extraction. It had high accuracy and the accuracy of the sub-pixel corner can reach 0.1 pixels. Calibration technique had high precision, good stability, low computation. It has been applied in the embedded machine vision industry. Measurement accuracy can reach 0.05mm.The calibration based a single image had a defect that the measuring plane must be in the same flat with the calibration plane. So the topic proposed a new calibration based on a number of feature points. The plan did not require auxiliary facilities-X target. Although it needed to capture multiple images, it had easy operation and lower costs. In future, I need to further research three-dimensional measurements. We will use structured light as auxiliary facilities to three-dimensional measurement and three-dimensional reconstruction.