Structural Synthesis And Performance Study Of Generalized Parallel Mechanisms

Conventional parallel manipulators have been widely studied both in industry and academia in the past several decades.However,the structural synthesis of non-conventional parallel mechanisms is seldom studied,especially for the generalized parallel mechanisms(GPMs)with coupling sub-chains or configurable moving platforms.Compared with conventional parallel mechanisms with smaller working space and limited rotational ability,GPMs allow for improved performance and functionality,and present potential significance.For example,the advantages of stiffness,workspace and rotational ability.Since GPMs can improve the kinematic and dynamic performance,it has been widely studied in both mechanisms and robotics in the past decades.To address the problems that the GPMs having been rarely presented in the current stage and the existed generalized parallel mechanisms have the disadvantage of unsatisfactory actuation scheme,a new method for constructing GPMs is proposed.The contracted graphs in connection with Euler's equation are constructed based on permutation and combination,and the isomorphism is identified through connective array method.Then,fractionation and simplification process of the contracted graph of the resulting manipulators are analyzed.Finally,two-layer and two-loop mechanisms which are the basic units of GPMs are derived.As for the two-layer and two-loop mechanisms,the approach of adding serial open kinematic chains(SOCs)on the top of single loop mechanisms is adopted.Based on constraint synthesis and virtual work,a class of SOCs and single loop mechanisms are synthesized and common mechanisms and equivalent SOCs are analyzed.The mutual constraints between two loops are analyzed and the general procedure for constructing two loops mechanisms is proposed.Finally,a class of two-layer and two-loop mechanisms is presented.For the application of the GPMs in reconfigurable mechanisms,the constraint singularity of closed-loop chains is applied in constructing reconfigurable kinematic chains.Closed-loop chains are connected with serial kinematic chains and coupling sub-chains.With different configuration phases of closed-loop chains,the configuration and motion of the kinematic limbs are changeable.Subsequently,the configuration and mobility variation of the GPMs are performed.Four kinematotropic chains are proposed,and a class of novel reconfigurable GPMs with different configurations and mobilities are designed.To accommodate the specific requirement in modern manufacturing process,a partially decoupled 4-DOF GPM is presented.A completed system is formed from the number synthesis and graph synthesis to the design and analysis of the mechanism.The kinematic model for position analysis of the GPM is established and the analysis of the overall Jacobian matrix is conducted.Besides,the workspace and singularity are discussed.The advocated method will contribute to the topological design and structure synthesis of GPMs,and is helpful to the analysis of GPMs.