螺纹牙形失真量计算方法研究

Research on Calculation Methods of Thread Profile Distortion

螺纹垂直投影过程中的牙形失真现象会影响螺纹参数的机器视觉测量精度,现有牙形失真量的计算方法繁简程度有差异且未经过统一验证。根据其基本原理,将螺纹牙形失真量计算方法归纳为几何法、代数法和解析法。通过建立螺纹数学模型计算出牙形失真量仿真值并与各方法计算结果进行对比,结果表明:在靠近螺纹牙底95%的牙廓上,各方法计算结果接近;在靠近牙顶5%的牙廓上,几何法和解析法与仿真值趋于一致,而代数法存在明显差异,在大径处误差达到最大失真量的35%。以M20×2.5-6h螺纹塞规牙型角测量为例进行对比实验,实验数据表明:牙形失真现象使垂直投影法与接触式测量结果相对误差达到0.376%,应用各方法补偿后相对误差均低于0.08%,其中解析法效果较好,低至0.032%。

When threads are projected vertically,thread profile distortion can occur.It will affect the accuracy of the machine vision method for measuring thread parameters.There are various algorithms for the value of thread profile distortion,which vary in complexity and have not been uniformly compared.Based on the basic principles of each algorithm,they are summed up into geometric method,algebraic methods and analytical method.After building a mathematical model of the thread,the simulated values of thread profile distortion are calculated and compared with the results of each algorithm.The results show that the values of each algorithm are close on 95%of the thread profile close to the root.The values of the geometric and analytical methods still converge with the simulated values at 5%of the thread profile near the crest.However,the algebraic method is significantly different,with errors reaching 35%of the maximum distortion at the major diameter.A comparison experiment is carried out with the M20×2.5-6h threaded plug gauge thread angle measurement.The experimental data shows that the thread profile distortion causes the relative error between the vertical projection and the contact measurement over 0.376%.The relative error after applying the compensation of each algorithm is less than 0.08%.The analytical method is the more effective,with results as low as 0.032%.