Configuration Synthesis And Networking Of Units For Spatial Deployable Mechanism

Deployable mechanisms refer to the mechanisms that can be folded into a compact configuration and be deployed into a large predetermined shape.With the development of aerospace technology,the scale of the spacecraft is bigger and bigger,but the payload capsule of the rocket stays the same,so deployable mechanisms become one of the best choices for the large scale spacecraft.Large-scale,big folding ratio,high stiffness and light weight have become the trend of deployable mechanisms.Traditional deployable mechanisms use planar linkage as the basic units,which cannot meet the requests.Spatial single-loop overconstainted linkages(SLOLs)possess the advantages of big folding ratio and high stiffness,which become the research focus of the deployable mechanism.Different from the planar linkages,the movement of the SLOL is spatial and complex.There are some common problems for the SLOL,such as configuration synthesis,networking method of the units,geometry parametric design of the mechanical network,stiffness reinforcement of mechanical network,etc.These problems hinder the application of SLOLs on the deployable mechanism.These problems are studied in this thesis.This thesis presents a rod overlapping method to synthesize the SLOLs.By overlapping the rod with the same parameters of basic units,a new single-loop kinematic chain is obtained.The motion screw equation of the new kinematic chain is obtained on the basis that motion screw equation is independent of coordinate system.Following the degree of freedom(DOF)of the kinematic chain is calculated,the kinematic chain with one DOF is SLOL.Taking Bennett linkage as an example,25 kinds of 5R and 6R SLOLs are obtained.The singular states of the linkages are analyzed according to the motion screw equation.Then the relationship between the symmetry and the folding feature of the SLOLs is analyzed.The symmetry of the obtained SLOLs is evaluated,and 7 linkages with line and plane symmetry are generated.At the same time,a series of feed deploying mechanisms are synthesized with one dimensional deployable function,which adopting the kinematic chains with stable structure.According to the characteristics of SLOLs,this thesis puts forward a transition unit method to network the SLOLs.The proportion change of the rod length does not affect the loop equation of the SLOL.Using this feature,transition units are constructed between the SLOLs,of which only rod length is proportional shortened between the transition units and basic units,the rest parameters are the same.The movements of basic units are harmonized through the transition units,so a large scale deployable network is constructed.Using the relationship between the units,the constraint screw matrix of the network is deduced.Through linear column transformation,the constraint matrix is simplified,and the DOF of the network is obtained.Taking the synthesized 6R-B-A,6R-B-D and 6R Altmann linkage as basic units,mechanical networks are constructed with transition unit method.Then the mobility of a mechanical network constructed by Altmann linkages is analyzed,and the singulation and deployable performance of the network are analyzed.Using the alternative form of Bennett linkages as the basic units,a parameterized deployable mechanical network with excellent deployable performance is proposed.The relationship between the alternative form and the original form of Bennett linkage is analyzed,and the mapping relationship between the two forms are solved.By the transition unit method,new Bennett linkages between the alternative froms of Bennett linkages are constructed,and a modular network is obtained.The network profile is analyzed.Taking cylindrical network as the object,the unit parameters of the network are analyzed.According to the networking process,the DOF of the network is calculated,following,the relationship between the unit parameters and the mobility of the network is analyzed.The deployable profile of the network is analyzed,and a method to fit parabolic shape antenna by Bennett network is put forward.A prototype is manufactured.The deploy experiment of the prototype verifed the feasibility of the fit method.A double layer network is proposed on the basis of single layer netwok in this thesis.The movement of equilateral Bennett linkage is analyzed,then it is concluded that the diagonal revolate joint axis rotate about a virtual axis.Using this feature,a hybrid linkage is proposed by combining the equilateral Bennett linkage and symmetric four bar linkage,which makes the spatial movement of the Bennett linkage into a regular movement.Using the hybrid mechanism as a pillar between the layers,double layer truss networks and cable-truss hybrid network are put forward,respectively.A process to fit deployable mechanism profile is put forward.The link planar density of the network is analyzed,results show that the double layer network improves the link efficiency.Using the hybrid network,an offset parabolic antenna is designed,and the mode of the antenna is analyzed.The impact of cable layer on the network stiffness is analyzed.Simulation and experimen results show that the double layer network can improve the stiffness of the antenna.