Type Synthesis And Performance Analysis Of Parallel Mechanism

The parallel mechanism which is famous of the advantages of high stiffness,the heavy loader,quick response has wide potential application in metal-cutting machine tools,industry automation and medical instrument fields.However,the complex kinematics and dynamics of parallel mechanism make it very hard to use parallel mechanism in practical application.Thus,the most urgent problem of parallel mechanism research is to optimize the kinematics and dynamics performance of parallel mechanism to satisfy the practical need.The thesis focused on instantaneous motion,singularity,decoupled mechanism and full-isotropic mechanism.The main work of the thesis includes:(1) The research of parallel mechanism is reviewed.The performance analysis and type synthesis of parallel mechanism is summarized,and the problem existed is also presented.The significances of research on instantaneous motion,singularity and coupled motion problems are proposed.(2) A novel approach of spatial mechanism based on screw theory is proposed, according to the multiple closed-loop structure characteristics of parallel mechanism. The parallel mechanism can be divided into two parts:kinematic chains and moving-platform,and the internal forces between kinematic chains and moving-platform,which can be calculated by screw theory according to the structure of parallel mechanism,are used to analyze instantaneous motion,singularity and coupled motion problems.(3) Based on the geometric features between constraint wrench and motion twist, the design principle of instantaneous motion-free parallel mechanism is proposed. Based on the principle,a number of novel two rotational and one translational Dofs parallel mechanisms are found.(4) Based on the geometric features of linear-related screws,the design principle of singularity-free parallel mechanism is proposed.Based on the principle,a novel three rotational Dofs 3-RRR parallel mechanism and a two rotational and one translational Dofs 2RPS - PS parallel mechanism are presented. (5) Based on the constraint force of kinematic chains,which can be calculated from the structure of the given parallel mechanism,the design principle of decoupled parallel mechanism is proposed.Based on the principle,a number of novel decupled one rotational and two translational Dofs parallel mechanisms are found.(6) The parallel mechanisms with homogeneous stiffness are found,and these special parallel mechanisms are proved to be full-isotropic parallel mechanisms, according to the stiffness matrix of parallel mechanism.The type synthesis method of full-isotropic parallel mechanism is obtained,and some two translational Dofs parallel mechanisms and three rotational Dofs mechanisms are synthesized.