Type Synthesis Of Parallel Mechanisms Utilizing Submechanisms Digital Topological Graphs And New Method With Skew-Symmetric Matrixes

The research of modern mechanisms is mainly aimed at the mechanisms with better performance and can be used in more application fields.In this dissertation,a new approach for constructing various novel parallel mechanisms with sub-mechanisms is proposed by using the series limbs,planar closed loop mechanisms and less mobility parallel mechanisms as the sub-mechanisms and combining with the digital topology graphs.The constructed mechanisms have the advantages of large in stiffness,large in workspace,simple in control,good in stability,simple in structure and strong in bearing capacity.the parallel mechanism with a planar closed loop sub-mechanism is more appropriate to be used as the mechanisms of a parallel manipulator with redundant constraints,a rigid-flexible hybrid manipulator and other manipulators.In addition,a new skew-symmetric matrix theory which can be used to slove Hessian of the complex mechanism is proposed,and a new unified acceleration model of the parallel mechanism is established based on the new theory.The main contents studied in this dissertation are as follows:(1)The basic principle of constructing complex closed-loop mechanisms by associated linkages is studied an analyzed.The relationships between the degree of freedom?the redundant constraints ?the complexity coefficient and links of a complex mechanism with redundant constraints are revealed,and the mathematical models for solving different numbers of associated linkages are derived.(2)The construction method of the contracted graphs of the ternary / quaternion links are discussed because they are more often used in the synthesis of new type of parallel manipulators.The process of constructing the contracted graphs of the ternary / quaternion links is determined,and the characteristic string groups are used to represent the contracted graphs.Then,some rules for judging the isomorphism and validity are put forward according to each evolutionary process.(3)The theoretical foundation for synthesizing the parallel mechanisms with the submechanism and digital topology diagram is studied.The method of synthesizing the parallel mechanisms with sub-mechanisms by digital topology graphs is put forward.By using arrays to represent the digital topology graphs,the method for solving the effective arrays and constructing the effective digital topology graphs are investigated.The conditions for synthesizing the parallel mechanisms with sub-mechanisms by digital topology graphs are determined.The structural characteristics of sub-mechanisms are studied,and the expressions of the equivalent sub-mechanisms are established.(4)The synthesis method of the parallel mechanisms with planar closed loop submechanism is studied.A synthesis method for modifying the original digital topology graph is proposed,and the principles and the process of the modification are determined.A method of synthesizing closed-loop parallel mechanism with sub-plane based on modified original digital topology graph is established.Based on the proposed method,many novel parallel mechanisms with planar closed-loop sub-mechanisms are synthesized.(5)A synthesis method for synthesizing PM with sub-mechanism is proposed and studied.Based on the general principle that the number of drives equals to the number of degrees of freedom(DOF)of the parallel mechanism,the sub-mechanism modular synthesis model of the complex parallel mechanisms is constructed.and the theory for synthesizing the parallel mechanisms with sub-mechanisms by digital topology graphs is established.Based on the proposed method,many novel parallel mechanisms with sub-mechanisms are synthesized.(6)The issue of solving the Hessian matrix of complex parallel mechanism is studied.The New Skew-symmetric method is proposed.The Jacobian matrix of the new parallel mechanism is differentiated and the Hessian matrix is solved,and the unified acceleration model of the parallel mechanism is established.