A novel 6R metamorphic mechanism with eight motion branches and multiple furcation points

Abstract The furcation point in a mechanism is a salient feature of reconfigurable mechanisms and change of a joint from an unconstrained condition to a geometrically constrained condition resulting in naturally link annexing with this geometrical constraint is a typical feature of metamorphic mechanisms. This paper presents a novel 6R metamorphic mechanism by inserting two revolute joints to a Bennett mechanism. From parameters of this novel 6R metamorphic mechanism, the source mechanism before changing is a special case of the Bricard 6R line-symmetric mechanism while the closure equation gives constraint conditions of joints. The geometrically constrained conditions result in variable motion branches of the mechanism. When all joints are unconstrained geometrically, two 6R motion branches can be obtained and when two joints are under geometric constrained, three 4R motion branches can be obtained. Further, three further motion branches with coaxial joints are obtained and motion branch transformation is illustrated with kinematic curves. For each of the motion branches, motion screws of this novel 6R metamorphic mechanism present corresponding geometry morphology and are analysed with screw algebra.