High-accuracy roundness measurement of small cylindrical workpieces by a high-frequency filtering method

In this paper, a ruby ball stylus is employed as hardware filtering for high-frequency data in the stitching linear scan method for the roundness and diameter measurement of small cylinders (diameter less than 3 mm). The conventional rotary scan method is improper for measuring small cylinders due to the crucial alignment. Thus, the stitching linear scan method is proposed, with which the cross-sectional circle of small cylinders is divided into several arcs to be measured and stitched. Although small cylinders can be measured by this method, the final results of roundness and diameter are affected by the low-accuracy stitching due to the high-frequency data. To address this issue, a ruby ball stylus with a tip radius of 150 mu m is used for eliminating the influence of highfrequency data which is obtained by a diamond stylus with a tip radius of 2 mu m in the stitching linear scan method. Since the measuring force of the ruby ball stylus influences the measurement of the small cylinders very much, a series of new alignments are carried out. Two groups of experiments by ruby ball stylus and diamond stylus have been conducted under the same conditions respectively. Results show that the average matching coefficient of adjacent arc profiles is enhanced by 86% and the repeatability of the ruby ball stylus is better than the diamond stylus.