Pretravel compensation for horizontally oriented touch trigger probes with straight styli

Abstract Touch trigger probes are devices through which coordinate measuring machines (CMMs) and machine tools collect dimensional measurement data in modern manufacturing environments. Advances in machine accuracy and tighter part tolerances leave probe error as one of the major error sources in these dimensional measurement processes. Pretravel accounts for the majority of touch trigger probe errors and is caused by bending deflection of the probe stylus shaft. A pretravel model for horizontally oriented touch trigger probes is described in this paper. A trigger force model based on the principle of mechanics is derived and used to develop the pretravel model, and the model accounts for bending deflection of the stylus shaft at the trigger instant. Pretravel is modeled as a function of probe design parameters (such as stylus length, tripod leg length, and stylus material) and probe operating parameters (such as spring force setting and probe approach direction). In applying the model to predict probe pretravel, only one model parameter needs to be calculated from 24 points of experimental probe data. In addition, the influence of probe approach speed on probe pretravel and model applicability has been investigated in this paper. The model is robust and can be implemented by means of a software correction module, which can be incorporated into machine systems.