Improvement of In-Situ Circularity Measurement Technique Based on Three-Point Method and Development of n-Point Method

The three-point methods such as the summit method and the rider method give convenient way of assessing circularity. Especially, the method by the use of three displacement detectors is a promising technique to separate precisely the circularity profile of a workpiece from apparent runout on a machine tool. Several in-situ circularity measuring systems based on this method have been developed so far. In these systems, however, relative angles between three detectors are not necessarily determined in a reasonable way. In this study, the performance index of the detecting angles has been derived by applying the law of error propagation to the method and the most reasonable angles have been determined by optimizing the performance index. In addition, by utilizing the performance index, generalized n-point method has been developed and its effectiveness in improvement of measuring accuracy has been verified analytically and experimentally.