Error measurement of five-axis CNC machines with 3D probe–ball

Abstract

This paper presents a new measurement device and corresponding method for an accuracy test of five-axis CNC machines. This device is named probe–ball, and consists of a 3D probe, an extension bar and a base plate with a measuring ball on one side. The 3D probe has a standard taper and is capable of three-degrees-of-freedom displacement measurement. The extension bar has a socket at its free end. A permanent magnet is integrated in the socket so that the extension bar and the measuring ball can be connected together with magnetic force. After installing the probe–ball device, the kinematic chain of the five-axis machine tool is closed. To measure the accuracy of five-axis machine tools, curves on a spherical test surface are defined as tool paths. The tool orientation is defined in the surface normal direction. The center of the spherical test surface coincides with the center of the measuring ball. With this path and orientation input to CNC controller, the 3D probe moves relative to the measuring ball on the spherical test surface. The overall positioning errors of the relative motion are measured by the 3D probe and are used to justify the volumetric accuracy of the five-axis machine.