Research On Multi-degree Of Freedom Force Loading System Based On Parallel Mechanism

In space flight of the spacecraft, space docking mechanism plays a crucial role of connecting the cabin. In order to maintain the stable flight state of the spacecraft, the space docking mechanism will bear the force and moment of the multiple degrees of freedom in a long time. In order to ensure the reliability of the docking mechanism combination on orbit working, in the design process of space docking mechanism, the multi degree of freedom loading fatigue test of docking mechanism combination on the ground is needed. This thesis is based on the project of the fatigue life test platform of the docking mechanism, and studies the multi DOF load test system based on parallel mechanism.Different from most previous multi-dimensional force loading system, the first innovation of this paper lies in design, verification and validation of the a new parallel loading structure, and the design of the control method based on driving force closed loop, using the inverse solution of the force and torque on the load for each loading hydraulic actuator output force, through precise control of the hydraulic loading actuator output force to achieve the force and moment loading in various degrees of freedom. Another innovation point is through the simulation software of load stiffness change on the loading performance of multi degree of freedom of the loading system, the coupling characteristics and simulate the loading force loading system, it has guiding significance for engineering practice and scientific research projects.In this paper, the basic structure and loading principle of the multi axis load system based on the orthogonal six DOF parallel platform are introduced. According to the performance index, this kind of orthogonal parallel mechanism can be applied to a combination of the docking mechanism with six degrees of freedom and torque. Secondly, according to the mechanical structure of the loading mechanism the kinematics model of the loading system is established, and further solving the kinetic equation, and the inverse solution model of loading system with multiple degree of freedom of the six axis force and moment is established by using Matlab / Simulink software.Then the hydraulic actuator force of the closed-loop system is modeled and analysed, a detailed model of the valve controlled hydraulic cylinder of the closed-loop system is established. And the force simulation of the closed-loop system is completed. It is worth mentioning that the design of the single force closed-loop controller improves the stability of the closed-loop control system driving force greatly.In order to establish the complete model of the parallel loading system in this paper, using the dynamics simulation software ADAMS, the mechanical system of the loading system has been modeled and simulated and analyzed with the simulated load instead of docking mechanism. In the end, the parallel six component force loading system of a joint simulation analysis using Matlab and ADAMS is established. The parallel multi axial loading system of static and dynamic loading simulation have been realized. And the impact of the docking mechanism stiffness on the whole system has been analyzed. At last the parallel multi axial loading system of each degree of freedom force coupling characteristics has been analyzed which lays a foundation for the future study on force control decoupling.