Form tolerance-based measurement points determination with CMM

Abstract

In an intelligent manufacturing environment, computer aided inspection (CAI) provides a critical role in closing the computer aided design (CAD) to computer aided manufacturing (CAM) loop. A coordinate measuring machine (CMM) is often used as a measurement tool in a mechanical part manufacturing environment. Feature-based measurement (FBM) with CMM plays an important role in the concurrent engineering environment (Fig. 1) (Yau and Menq, 1993). It measures a part and feedbacks the results to the concurrent control center to modify related process attributes. Feature-based computer aided inspection (CAI) systems define various measurement attributes for different features (Jacobohn et al., 1990). Part of the system determines the number of measurement points for a feature. In this research, a computer aided feature-based statistical concept is used to calculate sufficient measurement points for a feature. Circular and cylindrical parts are used to demonstrate the proposed methodology for determining the number of measurement points. The results show that the measurement error is significantly lower with the proposed method in determining the number of measurement points as compared to the method commonly used with a CMM. The proposed methodology is also computerized for on-line applications.