COMPARISON OF ERROR MAPPING TECHNIQUES FOR COORDINATE MEASURING MACHINES USING THE PLATE METHOD AND LASER TRACER TECHNIQUE

The accuracy of coordinate measuring machines (CMMs) strongly depends on geometrical errors that effect the measurements. Several methods for mapping these errors have been developed and some have been implemented. Examples are the direct measurement analysis by means of interferometers, straight edges, squareness standards or the analysis by application of artefacts like ball or hole plates or by using the multilateration approach using high accurate tracking laser interferometers. In this paper a comparison between the well established ball or hole plate method against the new multilateration approach will be presented and discussed. The measurements were carried out on a high accurate and commercial CMM at the Physikalisch - Technische Bundesanstalt (PTB) in cooperation with the National Institute for Standards in Egypt (NIS). For error mapping a ceramic hole plate 960 mm x 960 mm with a grid spacing of 60 mm and a commercial Laser Tracer (LT) were used. Both were originally developed at PTB. The result of the comparison shows that the differences between all estimated rotational axis errors are within 1 arc second. The differences of most of the translatorical errors are less than 1 micrometer. Consequently, both error mapping methods can be used alternatively. Moreover, the paper will show that the multilateration approach can cover a long range of the working volume of machines, is easy for handling, and reduces the time of measurements.