机器视觉螺纹测量的误差分析

Error analysis of thread measurement with machine vision

为了提高机器视觉方法测量螺纹的精度,采用理论分析和实验验证的方法,研究了用垂直投影测量和切向投影测量方法进行螺纹测量时发生的延伸螺旋面投影遮挡问题。在介绍垂直投影测量和切向投影测量方法的基础上,解释了垂直投影测量和切向投影测量方法产生原理误差的原因。通过对遮挡误差和不同螺旋升角误差对螺纹牙形角测量影响情况的理论分析和推导,给出了垂直投影测量时延伸螺旋面遮挡和不同螺旋升角影响的误差计算式,并进行了实例验证和分析。结果表明,对导程较大的螺纹按垂直投影法测量时,由延伸螺旋面遮挡造成的牙形角测量误差可达到1°以上。这一结果对牙形角测量而言是不容忽视的。

In order to improve measuring precision of thread based on machine vision, tangential and vertical projection measuring methods were discussed in theory, and verified experimentally, mainly related to the matter of extending helicoidal surface shade error when measuring thread profile with both the methods. After introducing the tangential and vertical projection measurement methods, the error sources were analyzed which cause principle error in measuring thread. The shade error calculating formula was given that caused from measuring thread with vertical projection measurement, and the effect that the shade error and the error caused by different lead angle was studied in measuring thread profile experiments. The result shows that the helix angle measurement error caused by extend helicoids shade error can reached over 1 ° when measuring larger-size helical pitch by vertical projection measurement, it can＇ t be ignored for helix angle measurement.