| Parabolic cylindrical antenna has been proved to have the advantages of wide swath,strong directional,high gain and easy for beam automatic scanning,etc.,all the major countries in the aerospace industry attach great importance to the research and application of this kind of antenna in the aerospace field,and the mission requirements has been put forward which requiring it to continuously develop towards the direction of large diameter and high precision.In order to meet the development requirements of large parabolic cylindrical deployable antenna,a cylindrical net-shell deployable truss structure which may be suitable for the support structure of the antenna is proposed in this paper.The configuration,dimension synthesis,precision analysis,ground test and other aspects of the proposed truss structure are addressed,and the feasibility of using the deployable structure to support large parabolic cylindrical antenna is demonstrated.In order to meet the application requirements of large parabolic cylindrical antenna support structure,the construction method of a cylindrical net-shell deployable truss structure with single degree-of-freedom is proposed.The proposed structure has a regular cuboid shape in the folded state and a truss structure in the deployed state,and it can fit cylindrical surface,parabolic cylindrical surface,sine cylindrical surface,etc.In order to verify the mobility and the rationality of the drivers,the mobility analysis method based on equivalent model and deduction is proposed by combining reciprocal screw theory,screw synthesis and translation theory,and the constraint characteristics and instantaneous degrees of freedom during the deployment of the structure are studied.Results show that the deployable structure can be fully deployed and its degree of freedom is one which indicates that its deploying process can be easily controlled.In addition,the reflector supporting solution of parabolic cylindrical antenna is also presented based on the proposed deployable structure.To improve the deployment stability and drive efficiency,the dimensional synthesis of antenna deployable support structure is addressed.First,to evaluate the deployment stability,the transmission ratio stability index(TRSI)is designed based on Jacobian matrix.Second,the motion/force transmissibility is used to analyze the drive efficiency.A local transmission index(LTI)analysis method based on sub-closed-loop is proposed to analyze the LTI of the parallel mechanism whose sub-closed-loop contains actuator.An improved global transmission index(IGTI)is proposed to analyze the global motion/force transmissibility for the mechanism without good transmission workspace.Finally,based on TRSI and IGTI,the dimensional parameter optimization model of the deployable support structure is established and the configuration with better comprehensive performance is obtained.Results show that the deployment stability and driving efficiency of the optimized deployable support structure have been improved,and the designed indexes is useful.In order to estimate the support structure precision,the effect of 3D joint clearance on the position accuracy of spatial mechanism is studied and an approach to estimate the precision of the large complex spatial mechanism is proposed.Firstly,a 3D clearance model of paired bearing support joint(PBS-Joint)is established.And the solution of the basic unit deviation configuration with 3D joint clearance being considered is presented.Then,by equating the basic unit as a feature link,and based on the error space constraints of the feature link,the cascade approach for solution the deviation configuration of basic loop is presented.Moreover,the mosaic equivalence approach for solution the deviation configuration of complex spatial mechanism is proposed.And by studying the precision differences of 1/8 deployable support structure calculated by mosaic equivalence approach and cascade approach,the optimal registration accuracy threshold is determined.Finally,the precision of the complete support structure is obtained.Results show that,when all the PBS-Joints equipped with Metric 628/6 bearings in standard clearance,the surface precision of support structure can obtain a relatively high accuracy.Finally,in order to verify the validity of the deployable support structure and find the potential problems of the structure,the prototype of structure and a set of zero-gravity experimental device are manufactured,and its motion performance is tested.First,according to the motion trajectories of the hanging points,the tracking requirements of the hanging points are determined.Then,a hanging points tracking system with passive and active combined based on a large-span truss support frame is designed,and the zero-gravity experimental device is manufactured.In addition,the optimization model of balance forces on hanging points is established,and an optimization method based on genetic algorithm with MATLAB and Nastran co-simulation is proposed.Then,the balance forces are optimized,and the influence of balance forces on experiment has been effectively reduced as a result of the deployable support structure deformation has been reduced 49%.At last,based on the prototype of deployable support structure and the zero-gravity experimental device,the motion performance of deployable support structure has been tested.The experimental results show that the designed zero-gravity experimental device can meet the requirements of ground test,and the deployable support structure is reasonable and has a smooth motion performance. |
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