METHOD OF AND APPARATUS FOR MEASURING WORKPIECES USING A COORDINATE POSITIONING MACHINE

Velocity dependent measurement errors made by coordinate measuring machines (CMMs) are corrected by deriving a polynomial expression which relates components of the errors to the relative velocity between the probe and the workpiece. A calibration is performed to establish the constant of the polynomial for different stylus configurations of the probe and these constants are stored. During a measuring process the probe produce analogue output signals from which a trigger signal is generated to latch the output signals of the machine measuring devices. The probe and machine output signals are monitored and recorded at clocked intervals over a range of positions within which lies the position at which the machine readings were latched. Actual relative velocity values are calculated at each position and, using these values and the stored constants, the errors in the machine readings at each position can be calculated from the polynomial. Signalling delays introduced to reduce false triggering of the probe can thus be compensated.