Parallel Mechanisms With Bifurcation of Schoenflies Motion

Type synthesis of lower mobility parallel mechanisms (PMS) has attracted extensive attention in research community of robotics over the last seven years. One important trend in this area is to synthesize PMs with prespecified motion properties. This paper focuses on the type synthesis of a special family of PMs whose moving platform can undergo a bifurcation of Schoenflies motion. First, bifurcation of Schoenflies motion in PMs is interpreted in terms of displacement group theory and the basic limb bond {X(y)) {R(N, x)} is identified. Further, the geometric condition for constructing a PM with bifurcation of Schoenflies motion is presented. The kinematic equivalence between {X(y)} {R(N, x)} and {X(y)} {X(x)} is proven. Four subcategories of irreducible representation of the product {X(y)}{X(x)} are proposed and the limb chains that produce the desired limb bond are synthesized. Finally, the partitioned mobility of PMs with bifurcation of Schoenflies motion and its effect on actuation selection are discussed.