Analysis And Optimization Of 5R And 4R1S Spatial Single Loop Mechanisms As Deployable Mechanisms

In aerospace field, various space mechanisms have been widely applied. With the advancement of related space technology and the diversification of demands, the sizes of space mechanisms are bigger and bigger. The carrying capacity of the rockets or space shuttles, however, cannot be enlarged effectively because of the limit of the fuel and cost. So, the deployable mechanisms were created to solve this kind of problem. Before the launch of the rocket, the deployable mechanisms were folded in a very compact configuration in the fairing. And after the arrival at the predetermined orbit, the deployable mechanisms will be extended into the working configuration which may be very large.One kind of deployable mechanism which is articulated, truss, bidimensional system will be discussed and investigated in this dissertation.At the beginning, the single loop mechanisms with only revolute joints and spherical joints are synthesized. Then a kind of mechanism with four revolute joints and one spherical joint is selected as the basic deployable unit. Another mechanism with five revolute joints proved to be homologous with the 4R1S linkage is also confirmed. The degrees of freedom of two mechanisms are analyzed using Lie-group and Lie-algebra theory. Both the 4R1S linkage and 5R linkage have single DOF, and the 5R linkage is a typical over-constrained mechanism.Several basic deployable units are assembled into a deployable module which can be infinitely developed to an enormous deployable network. After the two schemes with 4R1S and 5R unit are obtained, kinematic and dynamic analysis is the next work.The D-H coordinates are set in a unit. Then the kinematic relationship among the links can be solved by the coordinate transformations. The centre of spherical joint in 4R1S linkage is selected as a characteristic point. The trace, velocity, acceleration of the point can be depicted. At last of kinematics, the kinematic relationship between two adjacent modules is analyzed.Respectively considering the elasticity of connecting rods and the clearances of joints, four kinds of dynamic models are built. A series of conclusions are compared about the clearances of joints using software ADAMS, which illustrate the feasibility of the models.A comprehensive comparison between 4R1S and 5R is elaborated. The merit and demerit of the over-constrained mechanisms and the spherical joint are discussed. At the end of the dissertation, the mass and first-order nature frequency of the mechanism are optimized by changing the offsets and the diameters of rods.