Research On Measuring Technology For Taper Thread's Dimensions Based On CCD

With the rapid development of our market economy , the require of taper thread is more and more and the demand of the taper thread precision is higher and higher both at home and abroad. The traditional process of measuring the parameters of taper threads is done by professional operator, which takes more time and only gets worse precision. The photoelectric measuring technology has become a new measuring technology which mixes the optics and electrics technology, and the technology of Digital Image Identification with good specialty based on The Charge Coupled Device (CCD) is used widely in measurement, such as high precision and good stability. In this thesis, a new automatic instrument for measuring the parameters of taper threads using the photoelectricity technology has been designed, which has got high precision of measuring the parameters of taper threads automatically.In the thesis, an overall design of the measurement part is discussed firstly, Through comparing the ways for measuring the thread's diameter in common use, the three ball method is used here at last, then research the traditional three ball method and empolder the three ball method in the environment of image. Image filtering, edge detection, subdivision and beeline fitting are all presented in details. An appropriate image processing method is found out with the combination of image information of detected taper thread; Firstly, most noises are filtered by the median filter, secondly the edge of the taper thread is detected by Canny operator; thirdly find the sub pixel position by the operator of spatial moment-based edge detection;then points with bigger variance are filtered by Hough transition, finally the least squares technique is applied to filter extraneous points further more and fit the edge lines. According to the above methods, the program is designed to process thread's images and thus acquire the required parameters. Also the man-machine interactive software interface is developed.Finally, calibration method for the system by adopting standard parts and error analysis is discussed by emphasis, the result of calibration is given.Experiment shows the feasibility of the image processing software developed in this system.