Rapid volumetric calibration of coordinate measuring machines using a hole bar artefact

Abstract

The paper reports on the development of a new rapid volumetric accuracy calibration system for multiaxis coordinate measuring machines (CMMs). The system utilizes a calibrated mechanical artefact, in the form of a 540mm long I-beam hole bar. The 21 effective parametric error components for a three-axis machine can be obtained by probing the artefact when it is placed at 17 specified orientations within the measuring volume. The parametric errors are then further transformed into the CMM volumetric error by applying formulae derived from the rigid-body motion for the structural configuration of the CMM. Software has been developed to automate the probing of the artefact, data acquisition and the analysis of the parametric errors. Options for graphical and numerical data output of the volumetric error map is also included. Practical calibration tests and results from a moving bridge CNC (computer numerically controlled) CMM are shown, where the overall time for the calibration process, including equipment set-up time, was found to be less than two hours.