A machine vision system is proposed to measure the diameter of a mini milling cutter on line, and the measurement uncertainty is analyzed in this paper. The system consists of a back-light source, a rotate stage, a rotary encoder, a camera and corresponding software. While the milling cutter rotates, the camera is triggered by the rotary encoder and a series of images are captured. The sources of uncertainty and their effects are analyzed, including the parallelism of the light source, lens distortion, CCD noise, focusing situation, the geometric properties of tested objects and the algorithm design. According to results of experiments, the uncertainty mainly depends on the geometric property of the tested object when sampling rate is not enough, otherwise, it is mainly relative to the parallelism of the light source. In the experiment performed, the system uncertainty is 4μm with a sampling rate of 33 frame/circle, both accuracy and efficiency meet the requirement of manufacturing.%建立了基于机器视觉的测量系统,实现了微型铣刀外径的在线测量,并对测量不确定度进行了分析.测量系统由背光源、夹头与旋转平台、旋转编码器、摄像机和相应的测量软件组成.系统运行时,铣刀匀速旋转,由旋转编码器触发相机对其进行采样拍照并完成测量.从照明光源平行性、摄像机的镜头畸变与CCD噪声、调焦效果、待测物体表面几何特性、算法设计5个方面分析了测量结果不确定度来源及其影响.实验表明,当系统采样率不足时,对于铣刀外径测量不确定度影响最大的是待测物体表面几何特性；在采样率足够大的情况下,外径测量不确定度主要由光源平行性确定.本文系统采样率为33 frame/circle,系统测量不确定度为4μm,可满足生产要求.
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