Research On Measurement Method Of External Thread Parameters Based On Machine Vision

Threads are the most common mechanical connection in industrial production,which geometric parameters have a direct impact on the performance of mechanical equipment.With the development of the precision machinery industry in China,there is an urgent need for comprehensive measurement of the parameters of the thread,and the traditional mechanical detection methods cannot be realized.This project has used machine vision inspection technology to measure various parameters of the thread.Through the analysis of the measurement results,it is verified that the machine vision measurement technology has the advantages of high precision and high speed.Firstly,through the analysis of the universal vision measurement system,a set of suitable external thread image acquisition device was designed.With reference to the imaging principle of machine vision,a suitable CMOS industrial camera is used in conjunction with Sunny Optical Lens,and a LED planar light source is used to perform real-time acquisition of the threaded image by means of backlight illumination.Secondly,according to the relevant algorithm of digital image processing,the thread image contour extraction method was studied.The edge information of the thread outline is obtained by performing preprocessing such as noise reduction and contrast enhancement on the collected image,and then the high-precision edge data of the thread image is extracted through the Sobel operator and the improved Gauss subpixel edge fitting.Then,the thread parameter measurement principle and thread image distortion problem are studied.Based on the extraction of the tooth profile corners of the threads,the calculation methods of the thread size,median diameter,pitch,and profile angle are designed according to the definition of the thread parameters;the real curve and the shielding curve equation of the thread profile are deduced.A thread image distortion model is established to compensate for parametric measurement errors caused by distortion.Finally,the parameter measurement experiment was conducted and the errors generated in the measurement process are analyzed.According to the proposed thread measurement program,the measurement system calibration experiment and the thread parameter measurement experiment are performed respectively;the error calculation of the experimental data is compared with the national standard.The results show that the measurement method can realize the measurement of various parameters of the thread and can meet the measurement requirements.