Thread Parameter Measuring System Based On Machine Vision

Threaded parts are widely used in mechanical equipment.With the development of precision machinery,the thread is not only required to be reliable and long service life,but also required a higher precision of the screw connection.Therefore,it is of great practical value to realize t he high precision measurement of the screw thread.In recent years,the technology of machine vision has been developed rapidly,which has been widely used in the measurement of the thread.However,the domestic and international devices based on machine vision have some problems.The device measurement range is small,and cannot obtain the overall contour coordinates.What's more,the thread image has the occlusion distortion.Aiming at the problem of measurement of thread parameters,the thread parameter measuring system based on machine vision is established.It takes the CCD camera as the core device,and uses the method of coordinate calculation of the thread contour data which is collected by CCD camera.The system can realize large range,high precision and fast measurement.The main research topics are as follows:(1)According to the measuring principle of projection method,the measuring platform of thread pa rameters is established.The contour data of the thread in the parallel light is collected by the camera,which is rotating on the platform.The method expands the measurement range of the system,and can measure a variety of dimensions of thread.(2)The camera is used to capture the image of the tooth contour.The image is smoothed,and the largest class of variance method is used to segment the image,and the Canny operator is used to extract the contour of the tooth.The two time curve fitting method is used to realize the sub-pixel location of the tooth edge.(3)The formula of coordinate system transformation is derived,and the feature points of the thread are extracted according to the geometrical features of the thread.The measurement method of the major diameter,pitch diameter,minor diameter,pitch and tooth angle is achieved.The thread contour data is obtained by rotating the turntable,and the 3D reconstruction is realized by 3D coordinate transformation.(4)According to the spatial geometry principle,the phenomenon of the occlusion distortion of the screw projection is analyzed.The true tooth type boundary and the curve equation are deduced,and the distortion model is established.The influence of tooth type distortion on the measurement of the parameters of thread is analyzed.The compensation of the errors caused by the distortion is realized.According to the measurement principle and process of the thread,the software and hardware of the system are developed.The experimental results show that the system can accomplish all the parameters of the thread.