A Research On Topology And Dynamics Of Generalized Mechanisms

With mechanism developing rapidly, more and more new mechanisms appear which involved something different from traditional mechanisms. It is hard to study these new mechanisms with the research method of traditional mechanisms, therefore, it is essential to apply some new concepts and methods on them. Li Xuerong and Zou Huijun proposed the theory system of generalized mechanisms, based on which, this dissertation researches generalized mechanisms from several aspects as follow and obtains some results.1. This dissertation researches the structure of generalized mechanisms, including topological components, geometrical components and physical components. The relation of the structure of generalized mechanisms to the structure of components is discussed. The topological components are mainly studied, especially for space deployable mechanisms. The components of generalized mechanisms are defined as generalized components. The performance of generalized components is analyzed. There are two description methods for generalized mechanisms, i.e. weighting topological graph and matrix notation. The weighting topological graph can describe the topological components entirely and tersely. According to the weighting topological graph, one can obtain the corresponding matrix notation of generalized mechanisms, including incidence matrix and adjacency matrix. The generalized degree of freedom of generalized mechanisms is studied, including degree of freedom of movement transmission and degree of freedom of force transmission. The degree of freedom of movement transmission describes the velocity transmission relation with the driving member to driven member, while the degree of freedom of force transmission describes the force transmission with the same, they can be used to evaluate the dynamics performance of generalized mechanisms, then the calculation of generalized degree of freedom is obtained.2. The problem of dynamics of generalized mechanisms is researched by the screw theory based Lagrangian method. The basic principle of screw theory is overviewed, including Chasles theorem and Poinsot theorem. The structure equation of closed chain included generalized mechanisms are studied, i.e. the generalized mechanisms is divided into several branch kinematic chains with common rack and end components, then make these equations equal to each other. The kinetic energy and potential energy of components of rigid, flexible, spring and cable are studied based on screw theory, and then the dynamics equation of branch kinematic chains is obtained. Cut some components of generalized mechanisms to form open chain tree system is useful to obtain the dynamics equation of the corresponding generalized mechanisms. This dissertation takes the generalized mechanisms of ETS-VIII deployable antenna as an example to obtain its dynamics model and solve it.3. This dissertation studies the optimization design with the generalized mechanisms of ETS-VIII deployable antenna as an example. The main structural factors which influence the performance of generalized mechanisms are analyzed. Based on the concepts of generalized degree of freedom, this paper selects the statistical characteristics, the mean and standard deviation of generalized degree of freedom, weighting sum to describe the dynamics performance. The constraint condition is obtained by the relation of geometrical factor of each component. The constraint conditions, designable variables, and objective function can form the optimization model. Then it can be solved by the multi-island genetic algorithm with the result of several different weight values. The relationship of the mean and standard deviation of degree of freedom of force transmission to the distant of driving of deployable process is analyzed, and then some conclusion is obtained.