2D Lobbing Characteristics of Touch Trigger Probes with Spring/Magnet Return Mechanism

Touch trigger probes are most widely used on coordinate measuring machines (CMM) and machine tools. Due to the tripod structure, pretravel of the probe varies when it triggers in different directions, which has been acknowledged as a key error source resulting in large measurement uncertainty. Return mechanism is one of the key factors affecting the probes' pretravel variation and repeatability. Currently, spring and magnet are two main return methods employed in trigger probes. Typical products are TP20 from RENISHAW with a spring return mechanism and T2 from TELES with a magnet return mechanism. Lobbing characteristics of those two kinds of touch trigger probes in the XY plane was studied analytically in this paper. Experiments were carried out on a high precision CMM to exam the mathematical model. Results show that theoretical model is in good consistent with the experiments, Both of the two kinds of probes have obvious lobbing characteristics especially when the stylus is relatively short. Long stylus leads to shrinkage PTV. Overall, TP20 (spring return) has a better performance in experiments, but investigation from probe users show that T2 (magnet return) stands longer due to its noncontact return mechanism.