Fixturing faceted parts with seven modular struts

Building on results in modular fixturing of 2D parts, this paper describes a new approach to fixturing 3D parts for assembly or inspection using a particularly simple set of modular elements. The approach uses seven modular struts mounted on a regular lattice of sockets embedded in a rectangular frame. Each strut extends normal to a contact surface on the part so that only compressive forces are required to hold the part in form closure: no bending moments are exerted on the struts and the fixture does not rely on contact friction. We give an algorithm for synthesizing such fixtures. Given as input a polygonal part and desired 3D pose, the algorithm enumerates all fixtures that will hold the part in form closure and rank them based on a quality metric. We also describe a fast test for form closure in 3D.