Metrological feasibilities of CMM touch trigger probes. Part II: Experimental verification of the 3D theoretical model of probe pretravel

The 3D theoretical model of a touch trigger probes pretravel is experimentally verified. A new method applying a low force high resolution displacement transducer is proposed to measure a probe pretravel in XYZ space. Experiments are carried out for both one and two stage types of probes. 3D surfaces of the probe pretravel are collected. Statistical regression and variance methods are applied for experimental data analysis. Good agreement with theoretical approach presented in part I of the paper is obtained. The investigations reveal that testing probes only in the plane perpendicular to its axis (which is a typical procedure so far) cannot detect the most significant probe functioning errors. Study of the probe hysteresis is performed. It is shown that parameters used so far like instability and repeatability of the pretravel are not sufficient for the full description of the accuracy of touch trigger probes. This applies particularly to two stage devices. Both the theoretical analysis and the experimental studies pointed at the hysteresis of the triggering point being the main source of probe errors. (C) 2003 Elsevier Ltd. All rights reserved.