| In the activity of space exploration and space station construction, equipments can not be all launched into aerospace in deployed status as the limit of rocket's carrying capacity. Deployable structures obtain unprecedented development opportunities and have been widely applied in many areas with the advancement of related space technology. Deployable structure is the broad category of prefabricated structures that can be transformed from a closed compact or folded configuration to a predetermined expanded form of a complete stable structure capable of supporting loads. Space deployable truss is one kind of deployable structures that has simpler mechanical structure relative to other deployable structures and it is always used in large space structures. It is usually used as support structures of solar panels, space telescope and synthetic aperture radar, etc. The main technique requirements of deployable truss are high rigidity, high reliability, large stowage ratio and light weight. Current researches on space trusses are focusing on the kind of identical cross section. In this paper, a kind of truss that has tapering cross section is proposed. Tapered truss performs more excellent mechanical characters compared to normal truss. This issue will promote the development of deployable truss in a certain degree.As deployable truss can be converted to the equivalent beam model, this paper first analyzes and compares the strength and stiffness performance of tapered beam and normal beam. Then the feasibility of tapered deployable truss is discussed. Configuration and driving mechanism of developable module is devised. The extending or retracting principle of tapered mast is briefly depicted. Taking the complexity of 1-DOF (degree of freedom) tapered deployable truss into account, screw theory is adopted to analyze the degree of freedom, and the mobility is also pointed out. The result proves this design is correct. Using mechanism synthesis theory, a 3-DOF tapered deployable truss is brought out. Geometry conditions this mechanism must satisfy and stowage radio is derived.The performance of tapered deployable truss is significantly affected by cross sectional area of bars, taper of truss, etc. And it is not intuitive. Optimization analysis can make truss obtain optimum performance. After establishing optimal mathematical model, Parametric Design Language APDL of finite element analysis software ANSYS is used to model and optimize the truss. Comparison of tapered truss and consistent-cross-sectional truss on equal mass or stiffness is then implemented. The result shows that tapered truss can have higher quality truss stiffness ratio. Through modal analysis, natural frequencies and corresponding vibration mode of truss is acquired. The control frequency of spacecraft should avoid the natural frequencies of truss in order to avoid resonance. Solid model of 1-DOF tapered deployment truss is founded and kinematics analysis is analyzed with multi-system dynamic analysis software ADAMS. The simulation result gives the deployment process and displacement, velocity, acceleration curves of truss when extending. Kinematics analysis of 3-DOF tapered deployment truss is executed and the simulation results are acquired with MATLAB. |
