Uncertainty Management for CMM Probe Sampling of Complex Surfaces

Abstract

Abstract A method is presented to reduce the measurement uncertainty for surface point inspection when using a Coordinate Measuring Machine (CMM) equipped with a mechanical touch trigger probe and rotary probe head. The largest contributor to measurement uncertainty in this situation is the variation in probe deflection before a trigger signal is sent to the CMM. This variation is dependent on the angle between the major axis of the touch trigger probe and the surface normal of the point being probed. When the major axis of the probe body is nearly collinear with the surface normal at the sampled point, the probe deflection variation decreases significantly. Experimental results show that the uncertainty due to repositioning the probe head to achieve this near collinear orientation is considerably less than the uncertainty associated with probe approaches where there is a large angle between the major axis of the probe and the surface normal of the point being probed. This result is particularly applicable to the measurement of complex surfaces.