A combined optical and mechanical reference artefact for coordinate measuring machines.

The calibration of CMMs using calibrated ball plates or hole plates is a well established technique In the case of CMMs equipped with optical sensors based upon CCD cameras a series of artefacts based upon chromium-on-glass structures have been proposed. Calibration of these artefacts can not be performed using the reversal method which can be used for ball or hole plates. A new two-dimensional artefact based upon mechanical elements has been developed allowing both optical and mechanical probing and calibration This artefact combines in one piece the possibilities of performance verification of both optical and mechanical CMMs. The mechanical elements have been manufactured with form errors less than 3 μm and using a special surface preparation that makes optical CNC-measurements non-problematic. Reproducibilities better than 0.5 μm have been obtained in optical probing. Calibration of the artefact can be carried out using reversal methods using both optical and mechanical probing.