On-machine diameter measurement of a cylindrical workpiece with a reference artefact

Abstract

A system for on-machine diameter measurement of a ceramic cylindrical workpiece on a precision grinding machine is developed by employing a commercial optical micrometer, which can measure the diameter of a workpiece in various sizes. One of the drawbacks of the optical micrometer is its poor thermal stability, which could affect the on-machine diameter measurement in a machine shop where the room temperature is not controlled well. To address the issue, in this paper, a comparative measurement method with a calibrated reference artefact having identical material and nominal diameter with respect to a ceramic workpiece is newly proposed. In the proposed comparative method, the workpiece diameter is evaluated through detecting its deviation from that of the reference artefact calibrated by using a high-precision measuring instrument such as a coordinate measuring machine in advance of the on-machine measurement. Meanwhile, in the comparative measurement method, the uncertainty of the reference artefact should also be taken into consideration as a source of uncertainty. In this paper, measurement uncertainty analysis is carried out for the proposed comparative method based on GUM, while verifying the uncertainty of the reference artefact diameter through numerical calculations by a Monte Carlo method.