Beams with spatial compliance can be deformed as bending in a plane, twisting, and extending. In terms of the screw theory on rigid body motions, the concept of ＂deflection screw＂ is introduced, a spatial compliant beam theory via the deflection screw is proposed, and the spatial compliance of such a beam system is presented and analysed based on the material theory and fundamental kinematic assumptions. To study the dynamics of the spatially compliant beam, the potential energy and the kinetic energy of the beam are discussed by using the screw theory to obtain the Lagrangian. The Rayleigh-Ritz method is used to compute the vibrational frequencies based on discussions of boundary conditions and shape functions. The eigenfrequencies of the beam with spatial compliance are compared with those of individual deformation cases, pure bending, extension, or torsion. Finally, dynamics of a robot with two spatial compliant links and perpendicular joints is studied using the spatial compliant beam theory. Coupling between the joint rigid body motions and the deformations of spatial compliant links can easily be found in dynamic simulation. The study shows the effectiveness of using the screw theory to deal with the problems of dynamic modeling and analysis of mechanisms with spatially compliant links.
This article introduces the working principles of a spacecraft hatch including its operating process and moving trajectory. On this basis, an operating mechanism is designed to execute automatic open and close action of the hatch and measure the operating torques. Analysis on the mechanism＇s configuration and topological structure of each phase of movement proves that it is a typical variable freedom mechanism. The mechanism manipulates the hatch in accordance with the moving trajectory requirements through configuration transformation. Kinematic analysis and simulation of some typical configurations show that the velocity differences among mechanism components themselves and the components and their abutting components could exert influences on its working stability during configuration transformation. To solve the problem, stability conditions of configuration transformation are proposed. Appropriate control models are established for the output velocity curves of the driving servo motor and solved based on the stability conditions and rules of movement. Results from another simulation demonstrate that the proposed control models ensure smooth configuration transform and stable operation.
