Type Synthesis And Design Of The Tetrahedral Deployable Antenna Support Mechanism

The deployable antenna with large diameter,high precision and high rigidity,designed on the basis of spatial deployable mechanism,has played a more and more important role in aerospace engineering,and is one of the key equipments for human to complete space exploration activities.Taking the deployable supporting mechanism for antenna based on tetrahedral deployable unit as research object,type synthesis of the tetrahedral unit mechanism,combination method of the tetrahedral unit and the improved tetrahedral units are carried out,and the surface fitting,structural design and modal analysis of the minimum combination unit of the deployable supporting mechanism for antenna are conducted.Firstly,the deployable tetrahedral unit constituting the developable antenna supporting mechanism is analyzed.On the basis of the two different motion forms of the nodes,using the constraint-synthesis method based on reciprocal screw theory,and combining the dual relationship between constraint and motion,a series of tetrahedral unit mechanisms are constructed.And through configuration optimization,the simplest tetrahedral deployable unit with single degree of freedom of 3RR-3RRR structure is obtained.Based on the process of type synthesis,other different forms of deployable unit mechanisms are obtained by expanding the tetrahedral deployable unit.Against the problem that the combination mechanism composed of the tetrahedral deployable units with single degree of freedom cannot be completely folded,the obtained tetrahedral deployable unit mechanism are improved,such as the 3RR-3URU deployable unit mechanism with multi degrees of freedom are obtained.The combination method for the the improved deployable tetrahedral unit is studied,so the large scale surface the deployable supporting mechanism with large diameter for the curverd-surface antenna are obtained,which can realize complete fold.Based on the unity of all the links and the consistency of all the units,the comparative analysis of four kinds of surface division methods is completed.The deviation between the best fitting paraboloid obtained by the different surface division methods and the designed paraboloid is obtained by using the least squares method,so as to choose the better surface division methods.Considering the rotational symmetry of the minimum combination unit at the center of the paraboloid,a hexagonal division method containing the center node is proposed.For this method,each hexagonal unit can be divided into three isosceles triangle units,which can increase the unity of the links and the consistency of the units.According to the results of the surface division of the parabolic surface with certain parameters,and combining the geometric parameters of the tetrahedral unit,the parameters of the deployable supporting mechanism for antenna,such as axes of the kinematic joints and the length of the links,are gradually determined,by using the Solidworks software,and then the structural design of all parts and assembly of various forms of deployable units are completed.Selecting the minimum combination unit at the center of the supporting mechanism,the modal analysis is carried out and its modal characteristics is obtained by using Workbench software.