Defect Detection Of Grating Code Channel Based On Image Processing Technology

Recently, with the rapid development of measurement and control technology, the optical encoder, as an angular and linear displacement sensor, is playing an increasingly important role in such areas as CNC machine tools, servo motor, elevator, aerospace and aviation owing to its high resolution, high accuracy, long service life, high reliability, wide measuring range and small size. As the detecting element of the optical encoder, a grating's quality poses an immediate impact on measuring accuracy and service performance of the encoder. Limitations on workmanship of grating codes disc lead to such defectio ns as star points, chrome points, burr and breakage in code channel. At present, grating code channel defection is mainly detected manually, which hardly meets the demand of accuracy, efficiency and automaticity due to its high labor intensity, subjectivity and cost. Amid such a background, a detection system of grating code channel defection based on digital image processing is developed by our research group, laying foundation for achieving automatic detection on grating code channel defection.Firstly, in terms with detection principles and technical requirements of detection on grating code channel defection, key technology of detection on grating code channel defection is analyzed. With a hardware platform set up, optimization of industrial camera, lens and electric two-dimensional translation stages is completed. Proper combination of light sources and grating jig are also designed to do experimental researches on various image collection modes for high-quality images of grating code channel.Then, based on digital image processing, an image processing algorithm of detection on grating code channel defection is designed according to features of grating code channel images. Image pre-processing algorithms of image denoising, contrast enhancement and restoration of motion blurred images are also designed. After analyzing such traditional image segmentation algorithm as thresholding segmentation and edge detection, a special edge drawing algorithm is utilized to segment grating code channel defection. And s uch geometric characteristics as the perimeter, area, long and short diameters and roundness of the targeted defection area are measured to extract defection characters and identity multiple grating code channel defections.Finally, running on VC++ platform and Open CV computer vision database, a detection system software of grating code channel defection is developed. Experiments on its overall performance, detection results and detection efficiency demonstrate that the developed system is feasible and effective, applicable to multiple detection on grating code channel defection with a defect recognition rate higher than 95%, a false detection rate lower than 4%, a missing detection rate lower than 5%,a detection efficiency reaching one grating of 2000/3P for 43 seconds and a detection accuracy of micron grade.