Abstract: Checking mechanism design, one of the most complex tasks in the checking fixture design (CFD), for which accurately mate to the surface shape of the checked part, usually contains lots of complicated surface extension operations. However, there are many branching and intersection/overlapping problems at the first-order-discontinuity points of B-rep edges by current surface extension methods. A new automatic surface extension approach was proposed, which can repair the branching and intersection/overlapping problems at the first-order-discontinuity points. By recognizing edges of checking surfaces without manual intervention, it judges the first-order-continuity condition at the co-endpoint, if the endpoint satisfies the convex condition, it will use spherical positive weights rational quartic Bézier curve to bridge the branching offset curves, and if the endpoint satisfies the concave one, it will use cubic Bézier curve to bridge the gap after cutting the intersection/overlapping curves. A car fender CFD as an example illustrates its feasibility and practicability.

Key words: checking fixture, surface extension, branching, intersection, overlapping, reparation