Evolution Design of Multiple Metamorphic Mechanisms Inspired by the Concept of Assur Group

Metamorphic mechanisms that can adapt to a variety of working conditions with distinct configurations, have gained widespread attention in recent years. However, it's always difficult to design metamorphic mechanisms with various motion branches. In this paper, the evolution design of a family of novel multiple metamorphic mechanisms is conducted by the inspiration from the concept of Assur group. Adopting some class II groups which are derived from the combination of three basic links, a novel 7R multiple metamorphic mechanism is first presented and analyzed. Kinematic analysis illustrates that the mechanism contains totally 11 motion branches including three types of effective joints, i.e., non-overconstrained 7R motion branches, overconstrained 6R motion branches, and planar 4R motion branches. Reconfiguration analysis of the mechanism is presented by the kinematic curves, and it shows that there are totally ten bifurcation points. Moreover, the transformations among all the motion branches are analyzed. Then, adopting different combinations of the elements, the evolution design of more 7R multiple metamorphic mechanisms is presented. This paper proposes a family of multiple metamorphic mechanisms which can achieve a large number of motion branches, and the construction process of the mechanisms in this paper provides a new reference for designing multiple metamorphic mechanisms.