自由浮动柔性双臂空间机器人系统的动力学控制

DYNAMIC CONTROL OF A FREE-FLOATING FLEXIBLE DUAL-ARM SPACE ROBOTIC SYSTEM

基于假设模态法对柔性连杆的变形进行近似描述,采用拉格朗日方程分析柔性臂的动力学关系,忽略高阶弹性振动模态,根据柔性双臂和物体的动力学方程、末端约束关系以及系统的动量守恒原理,推导一种自由浮动柔性双臂空间机器人闭链系统的动力学模型。针对系统柔性状态的高频特征,采用奇异摄动法将该系统模型分离为慢变和快变两个子系统,对二者分别采用滑模变结构控制和非线性PD控制,保证刚性、柔性状态输出达到要求,由此得到的组合控制使得系统能较好地跟踪期望的轨迹,抑制弹性振动,并减小对本体运动的影响,内力、内力矩均能平稳跟踪期望值。最后进行数字仿真,验证上述方法的有效性。

Based on the assumed modes method, deformation for the flexible link is approximately described. Dynamics of the flexible arm with ignoring high-order elastic modes is analyzed using Lagrange principle. In terms of dynamics of the flexible dual-arm and the object, the constraint relationship between end of the flexible arm and the object as well as the momentum conservation, the dynamic model of the closed chain system for a free-floating flexible dual-arm space robot holding a rigid payload is derived. Aiming at a high frequency characteristic of the flexible state, a slow subsystem and a fast subsystem have been separated based on the singular perturbation method in which the sliding-mode control method and the nonlinear PD control method are adopted in each subsystem respectively to have state outputs of stiffness and flexibility reach desired outputs. Using this combined control method, the payload can track the expected trajectory preferably and the elastic vibration is suppressed. At the same time, there are few effects to the motion of the spacecraft, and internal force and internal torque can smoothly track the given values. Finally, some simulation tests have conducted to verify the effectiveness of the proposed methods.