Method for measuring location errors using a touch trigger probe on four-axis machine tools

One of the major sources of error affecting the accuracy of multi-axis machine tools is location error. Squareness errors and offset errors affect the locations of tool components. These errors depend on how accurately the machine tool was assembled and are independent of the positions of the affected components inside the machine tool. In this study, we developed a new method to identify all seven possible location errors in four-axis machine tools comprising three linear and rotary axes. A touch trigger probe installed on the tool axis is used to measure the locations of the centers of sphere artifacts as they are rotated through equal angles by the rotary axis. The measured centers are represented as command positions and the seven location errors using the homogeneous transformation matrix in the machine reference coordinate system. With this approach, every location error can be determined from the measured locations of the centers of the sphere artifacts. We validated our proposed method by performing experiments on a four-axis machine tool; additionally, we measured the three squareness errors between the three linear axes using a square master and a capacitive displacement sensor and compared the results with the values calculated using our proposed method.