A Novel Six Degree-of-Freedom Parallel Manipulator With Three Legs

Abstract

In this paper, a novel six degrees-of-freedom (6-DOF) parallel manipulator actuated by three base-mounted partial spherical actuators is proposed. The parallel manipulator consists of a base, a moving platform and three connecting legs. Each leg has spherical (S), prismatic (P) and universal (U) joints (SPU) in serial manner. The spherical joints are partially actuated due to the fact that the actuators of each leg are used only to specify its leg’s direction. The inverse and forward pose kinematics as well as the singularity points of the aforementioned mechanism is described in the article. In the inverse pose kinematics, active joint variables could be calculated with no need for the evaluation of passive joint variables. It will be shown that the inverse pose kinematics has sixty-four (64) solutions (64 different configurations exists for the inverse pose problem). In the forward pose kinematics, instead of twelve nonlinear equations derived by equaling the transformation matrices of each leg through Denavit-Hartenberg notation, only three nonlinear equations with less nonlinearity could be solved via numerical method, and therefore the numerical method converges more rapidly to the answer. Finally two different sets of singularity points with different natures are obtained.