Design And Theoretical Research Of Deployable Truss Antenna Mechanism Based On Tetrahedral Units

As an important means to realize large aperture and high precision space antenna,the deployable antenna has many advantages,such as high rigidity,high deployment rate and high profile precision,and has been used in orbit many times at home and abroad.The deployable antenna is a multi-degree of freedom(DOF)multi-output complex space multi-loop coupling overconstrained mechanism composed of a certain number of basic deployable units,and its design and research are difficult.At present,there are few basic deployable units which can form parabolic reflector antennas.In this paper,the profile division methods of antenna reflector are studied,and the asymmetric and symmetric deployable antenna mechanisms which are suitable for two types of units of profile division methods are systematically designed and studied theoretically.The main research contents are as follows:In view of the reflector of parabolic antenna,a method of profile division based on triangular asymmetric design is analyzed,and a new method based on hexagon symmetric design is proposed.Taking the parabolic antenna reflector with the same parameters as an example,the improved three-way grid method is used to divide the reflector surface based on two methods of profile division,and the results of the profile division are compared and analyzed.Based on the triangle asymmetric profile division,three basic tetrahedral deployable units and their combined units which can form asymmetric deployable antenna mechanisms are given: 3RR-3RRR,3RR-3URU and 3UU-3URU tetrahedron.Based on the hexagon symmetric profile division,a novel symmetric deployable antenna mechanism based on tetrahedral combined unit is proposed by using the constraint synthesis method based on the screw theory.The DOF characteristics of three tetrahedral basic units and their combined units are analyzed by using the screw theory and the method based on link-demolishing and equivalent idea.The DOFs of mechanisms are verified by the dynamic simulation software Adams.The comparison and analysis of the asymmetric deployable antenna mechanisms based on three basic units is carried out.The DOFs of the symmetric truss deployable antenna mechanisms based on 3RR-3RRR and 3RR-3URU combined units are analyzed by using the equivalent method and the screw theory.The antenna mechanism based on tetrahedral unit is a multi-joint multi-DOF mechanism.The conditions and results of adding reasonable actuation position are obtained by using the screw topological graph and screw coefficient matrix.The relationship between the position,velocity,and orientation of each disc node with time is deduced,and the kinematic simulation verification is carried out.The asymmetric and symmetric truss deployable antenna mechanism based on tetrahedrons are passive-input overconstrained mechanisms,which makes it difficult to analyze the force during the deployment process.The overconstrained mechanism is divided into passive overconstrained mechanism,active overconstrained mechanism and passive-input overconstrained mechanism.A method of force analysis of overconstrained mechanism based on equivalent stiffness is proposed.Taking 2SS+P and 7-SS passive overconstrained structures,2SPS+P and 7-SPS active overconstrained mechanisms,2SPS+P and 7-SPS passive-input overconstrained mechanisms as examples,the equivalent stiffness matrix of three types of overconstrained mechanisms is derived,and the analytical relations between driving force,output displacement and branch stiffness are established.The adaptability of equivalent stiffness to three types of overconstrained mechanisms is discussed,and the mechanism of the influence of branch stiffness on the distribution of force of three types of overconstrained mechanisms is analyzed.The dynamic equation of the passive-input overconstrained mechanism of the deployable antenna mechanism with tetrahedrons is established,and the internal relationship between the equivalent stiffness and the driving torque of the mechanism is studied.The comprehensive performance of a variety of asymmetric and symmetric deployable antenna mechanisms is compared.The 3D sketch model of large symmetric deployable antenna mechanism is constructed by programming design method,and the detailed structure design of parts is carried out.A symmetric modular prototype based on3RR-3URU unit is developed and experimental research is carried out.The results will provide theoretical and technical basis for the design and development of this kind of deployable antenna mechanism.