Abstract: On a machine tool, a program 12 receives data from a scanning or analogue probe P, measuring a feature of a workpiece W. This data is combined with assumed machine position data during the scanning movement. This avoids having to break into the servo feedback loop 24 to get actual measured machine position data. The assumed machine position data can be derived from a part program 20 which controls the scanning movement. Several ways are described for compensating for errors between the assumed machine position values and the actual values.

Abstract: A method of calibrating an articulating probe head comprising the steps of measuring an artefact of known dimensions with the workpiece sensing probe mounted on the articulating probe head, in which the articulating probe head is unlocked. An error functional map is generated corresponding to the difference between the measured and known dimensions of the artefact. Subsequent workpieces are measured with the articulating probe head unlocked and the corresponding correction applied. The true dimensions of the artefact may be determined by measuring it with a probe mounted on an articulating probe head in which the axes of the articulating probe head are locked. A mechanical lock is provided to lock the axes of the articulating probe head.