Study On Degree Of Freedom And Dynamics Of The Deployable Structure With Scissor Like Element

Because the deployable structure is able to fold or unfold,and configuration keeping,it is widely applied in many fields,such as aviation,aerospace,construction and so on.As a special structure,the deployable structure is a kind of mechanical structure,which is able to change the configuration between mechanism and structure.There are many kinds of units which are composed to be the deployable structures.The scissor like element,which owns the advantage of large contraction ratio and so on,is one of the common units composed to form the deployable structures.And the scissor like element is able to form the different deployable structures by the different array methods.But the deployable structure with scissor like element is a multibody composing structure with many closed loops and many redundant constraints.Because of the structure characteristics of deployable structure with scissor like element,its kinematics and dynamics characteristic are not only studied,but also its motion synchronization and structure stability are analyzed during the unfold process,for the design and analysis of deployable structure.Therefore,this paper focuses on t he research and analysis about the deployable structure with scissor like element which integrate mechanism and structure,and the research works and innovation points are as follows:(1)The paper proposes the technology with decomposing and composing for deployable structure with scissor like element,and computes the degree of freedom based on s crew theory.First of all,the deployable structure with scissor like element is decomposed into some basic units as its geometry characteristic,and draws the constraint topology geometry figure according to geometry theory.Then constraint screw equations are built based on screw theory.Second,these basic units are composed for the original deployable structure as it geometry characteristic,and the degree of freedom of deployable structure is computed based on screw theory.Finally,this paper computes degree of freedom of two kinds of deployable structure and simulates their process of motion.The computing method of degree of freedom provides an analysis method for computing the other degrees of freedom of complex deployable structures.(2)According to the geometrical characteristics of spatial deployable structure with three scissor like elements,the mathmetical model is built and the topological geometry is drawn.Kinematics formula of spatial deployable structure with three scissor like elements is derived,and the connection between screw velocity and screw acceleration and the velocity and acceleration of point in the spatial coordinates is given in the paper.Local coordinate systems of scissor like elements are built,and jacobian matrices of the center of mass of deployable structure are derived.Based on the expression form of screw theory and principle of virtual work,the simple equations of dynamics of deployable structure with scissor like element are built.The kinematics and dynamics of deployable structure are studied.(3)The paper studies the influcence of joint clearance on t he dynamics and motion synchronization of deployable structure with scissor like element.Based on L-N clearance model,equations of dynamics considering clearance are built.Three factors,size of clearance,position of clearance and velocity of unfold inflection on deployable structure with scissor like element are studied separately.Given the relevant parameters,the results are obtained and this three factors inflection on deployable structure is analyzed.(4)According to the geometry of the deployable structure,equations of boundary constraint and joint constraint are built in the theory of absolute nodal of coordinate formulation.Combined with the system stiffness matrix and mass matrix,equations of dynamics considering the constraint condition of deployable structure are derived.The equations of dynamics are solved by the Newmark numerical methods.Dynamics response of deployable structure is studied under the force and velocity separately.(5)The deployable structure with scissor like element is designed and manufactured,and the experimental platform is built and test.Based on the platform,the vibration acceleration of deployable structure with scissor like element are tested,and the data results are obtained and analyzed.For solving the degree of freedom of the deployable structure,the technology about decompose and compose structure is proposed,namely the deployable structure is decomposed into the basic units,and they are composed again.Under the system of screw theory,because the deployable structure is a mechanical structure with the characteristics of many closed loops and redundant constraints,its equations of motion and jacobian matrix of center of mass are derived.Based on the theory of virtual work,the simpler expression of equations of motion is built.Because the joint clearance is unavoidable,and it plays an important role in dynamics characteristic of deployable structure during the process of unfold,this paper studies systematically the clearance inflection on the dynamics of deployable structure under the unfold process.When the deployable structure unfolds the word position and is working,it will be locked and a mechanical structure.If the locked and working deployable structure is affected by disturbing,it will be vibration and not be work normally.Based on t he absolute nodal coordinate formulation,the paper studies the problem about structure dynamics response which it influences the stability of deployable structure.The degree of freedom and the dynamics characteristic during the process of unfold and configuration keeping are studied systemly in this paper.The research work not only provides a theoretical basis for the development of mechanism theory and structure theory,but also is helpful for the further application of the deployable structure.