Self-centering probes with parallel kinematics to verify machine-tools

In this paper, a new type of self-centering probe is presented to verify the performance of machine-tools in an efficient and rapid way using ball artifacts. A self-centering probe is placed in the spindle of the machine-tool and a ball artifact on the work table. The probe is moved to the calibrated center positions of the balls of the reference artifact. The probe touches these balls and, in a single measurement, it provides the X, Y, Z offset of the actual machine position from the desired (programmed) position. A non-conventional probe design has been chosen: three independently movable probe styli form a miniature coordinate measuring machine with parallel kinematics. The development process of two variants of such a self-centering probe is presented in this paper. The results obtained in laboratory tests show a repeatability of less than 0.5 μm and an error range of less than 2 μm throughout the large measurement range (2 mm × 2 mm × 2 mm) of the probe.