Research on Algorithm of Thread Contour Compensation Based on Image Comparison
To study the influence of tooth shape distortion on the measurement accuracy of thread parame-ters,a compensation amount algorithm based on machine vision of thread tooth angle and median diameter is proposed based on the analysis of existing methods for calculating the amount of thread tooth distortion.A threaded annular groove without a helical lift angle with the same thread parameters was compared with a picture of a threaded plug gauge with a helical lift angle to obtain the compensation amount of thread tooth angle,and then the corresponding compensation amount of the mid-diameter of the threaded tooth was calculated using the geometric relationship.An in-depth study revealed that a series of threads with the same spiral lift angle at the large diameter of the thread produced the same tooth flank angle error,and as the spi-ral lift angle increased,the tooth flank angle error also increased.The data showed that the mean value of 59.999° and the mean value of 18.290 mm were close to the mean value of 60.015° and the mean value of 18.326 mm measured by the contact thread gauge.The compensated variance of 7.76×10-5 and 8.65×10-4 is smaller than the variance of 3.38×10-3 and 8.55×10-3 measured by the comprehensive measuring instrument,and the results show that the proposed compensation algorithm is feasible.
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