JPS6447905A - Method for measuring straightness - Google Patents

Abstract

PURPOSE:To determine the straightness of an object to be measured accurately, by obtaining the quadratic curve component in the shape of the object to be measured, and correcting the component. CONSTITUTION:Before actual measurement, a detector attaching stage 3 is made to face a reference object 4, whose shape is approximately straight. Intervals DA, DB and DC between displacement detectors A, B and C and the object 4 are measured with the displacement detectors A, B and C. A distance d0 between a straight line connecting the detectors A and C and the detector B is obtained by an expression I. When, the detectors A-C are aligned on a straight line, i.e., d0=0, the detectors are made to face an object to be measured 1, which has the shape of the quadratic curve of y0=alpha0.x<2> as shown in Figure (b). Then, intervals dA, dB and dC are measured. The measured values DA, DB and DC, which are obtained by the three detectors A-C, are multiplied by a constant alpha (average value) shown in an expression II, which is obtained from the intervals dA, dB and dC (intervals La and Lb denote the interval between the detectors A-C). The results are added. Thus the true straightness of the object 1 is obtained. Therefore, this method can be simply applied to a practical machine. The measuring work is also simple, and high skill is not required.