Research On Microscopic Vision Measurement Technology Of Triangular External Thread Parameters

Our threaded fastener products can only occupy the low-end market. Domestic fastener manufacturers cost more but reward less. In addition to materials, processing technology, the lack of high-precision automated measuring equipment to control the processing quality is an important reason. Low efficiency, limited measurement range and poor consistency of manual measurement mode can’t meet the production requirements. For these situations, this dissertation studies microscopic vision measurement technology of triangular external thread parameters to improve the measurement efficiency and measurement precision of threaded fastener parameters. The main contributions of this dissertation are as follows.The lack of research on microscopic vision measurement technology of triangular external thread parameters at home and abroad is analyzed. Foreign researchers study machine vision and image processing technology more but lack of papers related on the vision measurement of thread parameters. Domestic researchers ignore the principle error that thread tooth image is blocked in the projection process. And mature image technology that is not applied to measurement and not considering the thread profile features results in poor stability algorithm.The micro-vision system hardware measurement platform is set up. Reforming universal tool microscope, right lens and camera are selected based on measurement range and accuracy. To obtain a sharp image, light source is selected based on spectral response curve of CCD and imaging experiments. Gratings in both directions are installed to measure large thread parameters.Sharp image and accurate edge are obtained based on the analysis of acquisition and processing about thread image. Sharpness functions are studied to guide focus process. The true edges of thread and noise are separated based on the thread profile features. The stability of the measurement algorithm is enhanced.The measurement methods of thread parameters are studied. The compensation formula of blocked thread are analyzed and verified by mathematics experiment mainly. The image is calibrated and the lens distortion is corrected as well. Subpixel precision technology is adjusted to be more suitable for backlight projection measurement method. Image mosaic are proposed to measure large thread parameters.Triangular external thread measuring software is programmed based on these research results and repeatability test is made. Environmental noise, repeat focus, thread skew and source light intensity have little effect on measurement results. The accuracy of measurement is examined. Correctness and necessity of thread form modification is verified.