ERROR COMPENSATION FOR CMM TOUCH TRIGGER PROBES

We present the analysis of a simple mechanical model ofa common type o f kinematic seat touch trigger probe widely used on modern coordinate measuring machines (CMMs). The model provides a quantitative descripti on of the pretravel variation or ''probe-lobing'' characteristics that limit the use of such probes for high-accuracy dimensional measuremen ts. We include the effects of stylus bending and the frictional intera ction between the stylus ball and the part surface. The model is restr icted to probes with simple straight styli, and we demonstrate signifi cant error reduction both for vertically and horizontally oriented sty li. In the latter case, gravitational forces are shown to play an impo rtant role in probe triggering and pretravel variation. Extensions to arbitrary orientations are discussed.