Development of straightness measurement technique using the profile matching method

Abstract

The property of straightness is one of fundamental geometric tolerances to be strictly controlled for guideways of machine tools and measuring machines. Straightness measurement for long guideways is usually difficult to perform, and it requires additional equipment or special treatment with limited applications. In this paper, a new approach is proposed using the profile matching technique for the long guideways, which can be applied to most straightness measurements. An edge of relatively short length is located along a divided section of a long guideway, and the local straightness measurement is performed. The edge is then moved to the next section with several overlap points. After the local straightness profile is measured for every section along the long guideway with overlap, the global straightness profile is constructed using the profile matching technique based on the least-squares method. The proposed technique is numerically tested for two cases of known global straightness profile: arc profile and irregular profile, with and without random error intervention, respectively. The developed technique has been practically applied to a vertical milling machine of the knee type, and demonstrated a good performance. Thus the accuracy and efficiency of the proposed method are demonstrated, and show great potential for a variety of applications for most straightness measurement cases, including straight edges, laser optics and angular measurement equipments.