ONLINE FREE-FORM SURFACE MEASUREMENT VIA A FUZZY-LOGIC CONTROLLED SCANNING PROBE

This paper presents a system and methodology for on-line free form sur face measurement via a scanning contact probe installed on a CNC (comp uter numerical control) machine. The scanning probe provides more samp ling points than any traditional touch trigger type of probes used on CNC machines, and better measuring accuracy than laser displacement se nsing or structured lighting. The presented measuring system's main ad vantage is that the number of measured points can vary with the change of surface curvature. To improve the measuring stability and continui ty, fuzzy logic control, in lieu of traditional PID control, is employ ed. As a result, the system is capable of continuously detecting the b oundaries of a measured object and measuring a relatively large comple x surface. Based on the experimental results, the measuring accuracy i s estimated between 20 and 30 mu m (micrometers). In addition to surfa ce measurement, the reconstructed surface data can be fed to a CAD/CAM system for component making or reproduction, which makes the reverse engineering of models comprised of free form surfaces readily accessib le. (C) 1998 Elsevier Science Ltd. All rights reserved.