# Position Calibration Software for the form Assessment of Complex Workpieces

## Summary

Many manufactured workpieces are difficult to measure by a coordinate measuring machine (CMM) because for any given orientation of the workpiece some of the important areas cannot be accessed by the CMM’s probe. The use of a measurement strategy and position calibration software developed at NPL can overcome this difficulty. Three or more reference spheres are rigidly attached to the workpiece. Sets of measurements of the workpiece and the spheres are collected with the workpiece at locations and orientations convenient for measurement. The software tracks the changes in position by determining the frame of reference defined by the reference spheres at each stage and then combines the different sets of measurements to yield a composite data set from which an accurate assessment of the complete workpiece can be made. The method, which can be applied to a wide range of artefacts with minimal additional effort, is largely self-calibrating which makes the measurement process straightforward. The software is self-starting which makes it very simple to use.

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