A Comparison of Fiducial Shapes for Machine Vision Registration

One way to perform registration and alignment for machine assembly is with respect to precisely located landmarks, called fiducials. that are located by machine vision means. For applications such as elearonics assembly, where densities are high and tolerances must be low. the precision by which the fiducials are located affects everything aligned relative to them. Because of s~a t ia l sam~l ine ffects. differenllv shaoed fiducials . " . . can be measured with different levels of precision. In past work we have determined and mmpared the minimax precision error for simple geometric shapes, and extended the results to pmpose a cmcentric pattem as having desirable qualities of high location precision and rotational invariance. We reiterate this work, and extend it to examine the performance of the concentric fiducial as a function of diameter, number of rings. noise, and ring spacing.