Research On Thread Parameter Measurement And Compensation Technology Under Defocus Condition

As one of the most extensive used joint forms in mechanical industry,the manufacturing accuracy of its parameters has great influence on the connection and transmission performance of precision mechanical parts.The machine vision measurement can be used to measure thread parameters efficiently and accurately.Due to the difficulty of focusing thread and the limitation of camera's depth of field,the edge of the thread image is blurred,which reduces the measurement accuracy of thread parameters.Therefore,on the basis of analyzing the cause of defocus imaging and the influence of defocus imaging on the measurement of thread parameters,the compensation algorithms of thread pitch diameter and thread angle under the condition of defocus are given respectively,and the compensation results are verified by comparative experiments.The main contents of this paper can be summarized as follows:(1)By studying the imaging characteristics of screw image edge profile,the causes of defocusing blur phenomenon in screw image are analyzed.(2)A method based on virtual three-needle method is proposed to calculate the thread pitch diameter under defocus condition and the thread profile slope is used to calculate the thread angle,and simulation analysis are carried out.(3)The calculation method of compensation for thread pitch diameter and thread angle under defocus condition are derived,and the corresponding compensation algorithm flow chart is given.(4)According to the compensation algorithm of thread pitch diameter and thread angle under defocus condition,the comparison experiment and repeatability analysis of defocus images of screw plug gauges with different specifications are carried out to verify the feasibility of the proposed thread parameter compensation algorithm based on defocus condition.Based on the GIM-80 A non-contact photoelectric detector developed by the research group and the cylindrical thread plug gauge as the research object,the thread parameter measurement and compensation technology under defocusing condition are studied.The proposed method and compensation algorithm can also be used as a reference for other specifications of thread parameters measurement.It has a good reference value to improve the detection accuracy of thread parameters in machine vision.