2-STAGE HIGH-PRECISION VISUAL INSPECTION OF SURFACE-MOUNT DEVICES

A two-stage high-precision algorithm for detecting the orientation and position of the surface mount device (SMD) is described. In the prepr ocessing step, a coarse orientation of the SMD is obtained by line fit ting. A high-precision fuzzy Hough transform (FHT) is applied to the c orner points to estimate precisely the orientation of the device, with its position determined by using four detected corner points. The FHT employed has a real-valued accumulator over the limited range of angl es that is determined in the preprocessing step. Computer simulation w ith a number of test images shows that the parameters obtained by the presented algorithm are more accurate than those by conventional metho ds such as the moment method, projection method, and Hough transform m ethods. It can be applied to fast and accurate automatic inspection an d placement systems. (C) 1997 SPIE and IS&T.