Total measurement of geometric errors of a three-axis machine tool by developing a hybrid technique

A hybrid measurement technique using a five-DOF measuring system and laser interferometer is suggested for all geometric errors of a three-axis machine tool. All geometric errors are defined in a single coordinate system, by eliminating the effect of Abbe’s offsets, for accurate measurement. The five-DOF measurement comprises five capacitive sensors and an L-type reference mirror. The system measures three PIGEs (position independent geometric errors) and five PDGEs (position dependent geometric errors) for each axis. The 18 geometric errors of the machine tool are measured using the results from two experiments (XY and YZ-planes), and the homogeneous transform is used to identify the geometric errors in a single coordinate system, eliminating the effects of installation errors such as mirror misalignment. A laser interferometer is used to measure three PDGEs (one linear displacement error and two straightness errors) for each axis. The two straightness errors are used to estimate the optimal Abbe’s offsets (for the X, Y and Zaxes) between the two measuring coordinate systems, and the linear displacement of each axis is calculated, minimizing the effect of Abbe’s offsets. Through this analytical approach, all geometric errors are expressed for a single coordinate system. The suggested measurement technique can therefore be used to investigate all geometric errors of a three-axis machining tool.