On-machine inspection system: Accuracy improvement using an artifact

A correction methodology for measurement data is proposed for accuracy improvement of an on-machine measurement system. A volumetric error model to synthesize transient thermal and geometric errors is developed. Geometric errors are determined by an off-line calibration procedure. Under the assumption that the on-machine measuring procedure is a pure cooling process, the transient thermal errors are modeled as exponential functions with different thermal time constants and gains. The thermal time constants characterize transient thermal responses of machine elements during the on-machine measurement. The gains are determined by measuring a 3-D artifact twice when the on-machine measurement of a machined part is required. Total time taken for measuring the artifact is less than 5 minutes. Experiments are performed to verify the proposed method. The measuring accuracy of the on-machine inspection system has been improved from 60 mum to 10 mum.