机器人组装超大型结构的姿-轨-柔耦合动力学仿真

Orbit-Attitude-Structure Coupled Dynamic Simulation for Ultra-large Structure Assembled by Robot

机器人空间组装是建造超大型航天器的重要方式。当前针对空间组装的研究大多集中于小型结构,没有考虑万有引力梯度和姿-轨-柔耦合效应的影响。本文针对主结构-空间机器人-待组装结构组成的系统,建立姿-轨-柔耦合动力学模型,研究万有引力梯度和姿-轨-柔耦合效应对组装过程的影响。首先,将空间机器人看作刚体,将主结构和待组装结构看作柔性体,分别采用自然坐标法和绝对节点坐标法进行运动学描述;然后,考虑刚体和柔性体的动能、万有引力势能和弹性势能推导系统的Hamilton方程,计入万有引力和万有引力梯度的影响;最后,通过轨迹规划和轨迹跟踪控制实现空间机器人空间组装超大型结构的姿-轨-柔耦合动力学仿真,给出组装过程中系统的轨道运动、姿态运动、空间机器人关节空间和笛卡尔空间、结构振动等动力学响应。研究发现:万有引力梯度和姿-轨-柔耦合效应对空间机器人的控制力矩和组装精度产生显著影响,在组装方案设计和控制系统设计中必须予以考虑。

Using robot to assemble spatial components is an essential way to build ultra-large spacecraft. Available studies on space assembly mostly focus on small structures,without considering the effects of gravity gradient and orbitattitude-structure coupling. In this paper,an orbit-attitude-structure coupled dynamic model is established for the space assembly system including space robot and flexible structure to study the effects of gravity gradient and orbit-attitudestructure coupling on the assembly process. First,the space robot is regarded as rigid,and the main structure and the structure to be assembled are regarded as flexible. Moreover,natural coordinates are used to model the rigid space robot,and absolute nodal coordinates are adopted to model the flexible structures. Then,the Hamilton equation of the system is derived with the consideration of the kinetic energy,the gravitational potential energy,and the elastic energy of the rigid and flexible bodies,taking the effects of gravitational force and gravity gradient into account. Finally,orbitattitude-structure coupled dynamic simulations are conducted by trajectory planning and trajectory tracking control,and the dynamic responses of the system are studied,including the orbital motion,attitude motion,control results in both the joint space and the Cartesian space of the robot,and structural vibrations of the flexible structures. The results show that the effects of gravity gradient and orbit-attitude-structure coupling are vital to the control moment of the space robot and the assembling precision,which must be considered in the assembly process design and control system design.