Roundness and Absolute Radial Motion Accuracy Measurement by an Improved Reversal Method

Reversal method is a well known method for roundness measurement. Although it is simple, it requires the reversion of the workpiece relative to the rotary mechanism. Such a reversion is impossible in some situations, for example, when the axis of the rotary mechanism itself is to be measured. In order to solve this problem, this paper proposes a new method called Improved Reversal Method (IRM), in which the reversion of the workpiece becomes unnecessary. In the IRM, an auxiliary reference (a cylindrical master) is set on a workpiece. The workpiece and the auxiliary reference are rotated and measured simultaneously. The auxiliary reference is then reversed and the measurement is repeated. By processing results of the first and the second measurements, not only roundness errors of the workpiece and the auxiliary reference, but also radial motion errors of the workpiece axis before and after the reversion can also be obtained. The effectiveness of the IRM is demonstrated by experiments in which a measurement reproducibility better than 17nm and repeatability better than 31nm were achieved.