The Study Of Screw Parameter Measurement Based On Computer Vision

The screw connection has been widely used in mechanical equipment and other devices because of its high reliability and convenient assembly characters. The interchangeability and reliability of the screw are required strictly in engineering application, so it must be measured seriously. Mechanical measurement is incapable of satisfying the actual demand of production because of its low measuring speed and low precision. With the development of computer technology, a new inspection technology based on computer visual has been presented.The paper analyzes the visual inspection system's basic composing, characteristics and superiority; presents main principle of the system hardware selection; and establishes computer visual inspection experimental system. Focused on the interfere factors that affect image quality in the process of image collection, and through the experiments comparison we takes mean filtering operator to preprocess the image. First-order differential edge detection operator, second-order differential edge detection operators are studied and discussed. In the base of the character of screw thread and experiments comparison of the operators, many operators are presented, and gray-histogram threshold method is used to detect edge. In the base of the character of screw thread, a sub-pixel orientation method used to line edge—least-squares fitted regression line is proposed, which has faster speed of running and better orientation precision and is adaptive to line edge's whole orientation. According to practical application character of 2-D image measurement, a calibration method which takes the average of the calibration value from different orientation is used. It can eliminate the aberration and error in calibration at one time. According to measure request of screw thread, four main characters-major diameter, screw pitch, angle of thread and simple pitch diameter are chosen to be measuring objects of computer vision. The experiment takes hex bolt as a sample, and the result shows that it can reach the precision requirement of industry measurement.