We propose the measurement method for location errors in a horizontal 4-axis machine tool using a touch trigger probe and a sphere artifact. Location errors (type of geometric errors), are values that do not change with the position of each feed axis because these errors are usually fixed in an assembly procedure. There are seven location errors in a horizontal 4-axis machine tool; three squareness errors in three linear axes and two squareness and two offset errors in a rotary axis. The positions of center point of sphere artifact on a rotary axis are measured by a touch trigger probe mounted on a tool axis. Because measured center points are expressed by seven location errors via the homogeneous transformation matrix, location errors can be separated by analyzing measured data. To validate the proposed method, measurement experiments were performed on a horizontal 4-axis machine tool. Measurement results were verified by comparing before and after compensation.

In this study, effect of the sensor gain error is theoretically analyzed and simulated when mixed sequential two-prove method(MTPM) is applied for the precision measurement of straightness error of a linear motion table. According to the theoretical analysis, difference of the gain errors between two displacement sensors increases measurement error dramatically and alignment error of the straightedge is also amplified by the sensor gain difference. On the other hand, if the gain errors of the two sensors are identical, most of error terms are cancelled out and the alignment error doesn’t give any influence on the measurement error. Also the measurement error of the straightness error is minimized compared with that of the straightedge’s form error owing to close relationship between straightness error and angular motion error of the table in the error terms.