A Three-dof Tripod for Generating Spherical Rotation

Abstract

A novel three degree-of-freedom manipulator, which includes three in-parallel limbs between a fixed frame and a platform that moves by spherical rotation about a fixed point, is described. This mechanism is not overconstrained and has the structural type of the translational Tsai platform. Each limb is a sequence of a universal joint, a prismatic pair and a universal joint (UPU). The spherical rotation of the moving platform is obtained by variation of length in the linear actuators that are mounted on the prismatic pairs of the three limbs. Under some geometric constraint changes, we obtain a generalised structure of the mechanism. This arrangement belongs to a more general family of mechanisms, which is presented succinctly and can be obtained from deductive reasoning.