Design And Deployment Dynamics Of Ring Truss-type Deployable Antenna Mechanism

With the rapid development of communication technology,space science and earth observation technology,the requirements for large aperture space antennas become more and more urgent.Due to the limitation of the vehicle's storage space,the antenna must be able to fold and deploy,so the best candidates for space antennas is the large deployable antenna.Due to the advantage of light quality,large aperture and high precision,more and more researchers pay the attention to the mesh deployable antenna.This dissertation takes the ring truss-type deployable antenna mechanism as the research objective,gives extensive research in terms of mobilty analysis,design of deployable mechanism,form-finding and precision adjustment of cable net,deployment dynamics modeling and ground experiments of the principle prototype.The large space deployable mechanism is composed of several simple single closed-loop mechanisms,so based on the analysis of the single loop equations of closed-loop mechanism,one mothod for the mobility analysis of multi-loop deployable mechanism is presented.The single closed-loop mechanism can be transferred to one equivalent open-loop kinematic chain with variable parameters,then the multi-loop deployable mechanism can be simplified to one single closedloop mechanism for mobility analysis.On this basis,the loop equations of 5R Myard linkage and plane-symmetry Bricard linkage could be derived by using the D-H method,and through using them as basic unit,the large space deployable mechanism can be constructed,the geometric coordinate condition for the machnism keeping continuous movement is obtained,a variety of new space deployable mechanisms network are gotten.In order to construct the large space deployable antenna,one large ring deployable mechanism is presented,which is composed of planar six bar linkages.The novel mechanism has very good folding and unfolding performance,and can be as the support structure of space antenna.By using the closed-loop synchronous cable system and the double crank-slider mechanism,the synchronous motion can be realized.Two driving modes including cable driven and torsion spring driven are presented,and the high rigidity driving joints are designed.The kinematics model of the ring mechanism is established,and the velocity and acceleration analysis are done,the model was verified through the example simulation.The design of antenna cable net structure is directly related to the accuracy of the deployable antenna.Therefore,taking the three-dimensional grid cable net as the research object,the methods of form-finding and accuracy adjustment for cable net strcuture are investigated.By using the grid generation method with considering sag-to-span ratio,the ideal lengths of cable segment in the paraboloid cable net reflector are determined.Based on the force density method,the dual-objective optimization form-finding for the antenna cable net are established,the goals of this model are both appropriate surface accuracy and uniform tension,then the optimal prestress distribution of cable network in equilibrium state is obtained.On this basis,the form-finding method with considering the effect of surrounding truss' s deformation are proposed to solve the best accurate result.Based on the nodes adjustment method,the optimization mathematical model for precision adjustment of cable net is built,two solving algorithm are proposed,including multidimensional advance-retreat method and minimum step approximation method,then the fast adjustment of cable net precision is realized.In order to forecast the change of the mechanism's dynamics characteristic during the deploment process,the dynamics model of the deployable mechanism must be setted and the simulation experiment should be done.Based on the theory of multi-body dynamics,the deployment angle is taken as the generalized coordinate variable,by using the Lagrange method,the deployment dynamic model of ring deployable antenna is established,which considers the influence of flexible cable net,joint damping,torsion spring driving force and movement control cables to ring mechanism.A kind of motion planning method based on speed control is proposed,and the control equations of the cables are deduced.Through positive and inverse dynamics simulation experiment,the change rule of system energy is solved and the influence of joint damping to the mechanism deployment is analyzed.The force control curve of the control cables are aslo obtained,and improvements of control cable arrangement are proposed.In order to validate the feasibility of the proposed antenna scheme,a ground experimental prototype and the experimental system are fabricated.The repeated deploy-fold experiments,precision experiments,stiffness and control cable tension testing experiments are done,and the experimental results show that the mchanism has good deploy/fold performance,very high repeat positioning accuracy.The results of cable tension experiment verify the validity of the established deployment dynamic model,which provides reference for the design of the motor control parameters.