Analysis Of The Configuration And The Influence Of Structural Constraints On The Mechanical Performances Of 2R1T Overconstrained Parallel Mechanism

Overconstrained parallel mechanisms have higher stiffness,stronger bearing capacity and higher precision than ordinary parallel mechanisms,which has a broad application prospect in the field of high-grade CNC machine tools.However,there are only a few overconstrained parallel mechanisms in practice at present,and the lack of excellent performance and configuration is one of the important reasons why they are not widely used.In view of the great influence of structural constraints on mechanical properties of such mechanisms,this project intends to take 2R1T(R represents rotation,T represents movement)over-constrained parallel mechanism suitable for constructing five-axis hybrid machining center as the research object,and analyze the influence of configuration and structural constraints on mechanical properties of the mechanism.The main research contents are as follows:The theoretical and practical constraint combinations of the branches of a 2R1 T three-branch overconstrained parallel mechanism are systematically analyzed.Then,based on the reciprocity relationship between the kinematic screw and the constrained screw,the branch configurations are analyzed in four categories according to the number of kinematic pairs with one degree of freedom.Finally,under the condition that the maximum constrained linear independent group of the moving platform remains unchanged,All global configurations of 2R1 T overconstrained parallel mechanisms are obtained and five overconstrained characteristics are summarized.A method was proposed to solve the statically indeterminate force problem of overconstrained parallel mechanism based on Moore-Penrose inverse and deformation coordination relation.The driving force and non-over-binding screw system amplitudes were directly solved based on Moore-Penrose inverse and deformation coordination relation.The stress problems of four kinds of 2R1 T overconstrained parallel mechanisms are analyzed by using the proposed method.Finally,the influence of structural constraints on the static distribution results of the mechanism is compared.The global stiffness matrices of the general overconstrained parallel mechanism for the branch stiffness matrix,the driving force helix and the binding helix system were established,and four kinds of 2R1 T overconstrained parallel mechanisms were taken as the research object to analyze the six-dimensional micro-displacement of the dynamic platform when the mechanism was subjected to the same external load,which indirectly reflected the linear stiffness and angular stiffness of four different configurations.Finally,the stiffness of the four configurations is compared and analyzed.Four kinds of rigid and flexible hybrid models of 2R1 T overconstrained parallel mechanism are established based on Solid Works,ANSYS and Adams.By comparing the numerical simulation results with the theoretical analysis results,the correctness of the theoretical analysis method and the obtained results for the stress problem of2R1 T overconstrained parallel mechanism is verified.