Type Synthesis of Fully Decoupled Three Translational Parallel Mechanism with Closed loop Units and High Stiffness

Abstract

In this paper, a new synthesis method of fully decoupled three translational (3T) parallel mechanisms (PMs) with closed loop units and high stiffness is proposed based on screw theory. Firstly, a new criterion for the full decoupled of PMs is presented that the reciprocal product of the transmission wrenc h screw matrix and the output twist screw matrix of PMs is a diagonal matrix, and all elements on the main diagonal are nonzero constants. The forms of the transmission wrench screws are determined by the criterion. Secondly, the forms of the actuated and unactuated screws can be obtained according to their relationships with the transmission wrench screws. The basic decoupled limbs are generated by combination of the above actuated and unactuated screws. Finally, a closed loop units construction method is investigated to apply the decoupled mechanisms in a better way on the high stiffness occasion. The closed loop units are constructed in the basic decoupled limbs to generate a high stiffness fully decoupled 3T PM. Kinematic and stiffness analys e s show that the Jacobian matrix is a diagonal matrix, and the stiffness is obviously higher than that of the orthogonal coupling mechanisms, which verifies the correctness of the proposed synthesis method. The mechanism synthesized by this method has a good applicati on prospect in vehicle durability test platform.