Nick Van Gestel

Influence of feature form deviations on CMM measurement uncertainties

Dimensional quality inspections of high precision parts are often performed by coordinate measuring machines (CMMs) equipped with touch-trigger probes. Features of these parts are then measured with a limited set of points, due to time constraints. This limited sampling has an important influence on the measurement uncertainty because the form deviation of the feature can not be completely assessed. It will not only affect the measurement uncertainty of the form deviation, but also the measurement uncertainties of other feature parameters like size, position and orientation. The quantification of this influence is difficult since the true form deviation is unknown. This paper describes a method, based on Monte Carlo simulations, that allows to determine these measurement uncertainties based on an estimate of the form deviation using a limited set of points. The method is illustrated for circles with theoretical shapes of form deviations, as well as measured shapes.