Accuracy test of five-axis CNC machine tool with 3D probe–ball. Part I: design and modeling

Abstract

The error model of CNC machine tool describes the relationship between the individual error source and its effects on the overall position errors. A practical problem in applying this technique to five-axis machine tool is that the predicted position errors cannot be justified. This paper, the first in a set of two, presents a new measurement device, the probe–ball, which can be used to measure the overall position errors of five-axis machine tools directly. To perform the accuracy test, a three-degree-of-freedom (3D) measuring probe is installed in the main spindle and a base plate is fixed on the turntable. The kinematic chain of the five-axis machine tool is then closed through connecting the central ball on the base plate with the extension bar of the probe. To generate simultaneous axes motion under the condition of closed kinematic chain, the central ball is defined as origin of the workpiece coordinate frame and the probe is driven along a path on a spherical test surface with the central ball as center. The overall position errors are measured with the 3D measuring probe. A theoretical model is derived to explain the nature of the probe–ball error measurements.