重力梯度对自由漂浮空间机器人姿态扰动分析

Analysis of Effect of Gravity Gradient on Attitude Disturbances of Free-Floating Space Robots

分析重力梯度对在轨运行的自由漂浮空间机器人姿态运动影响。由Lagrange方法建立自由漂浮空间机器人受重力梯度扰动的非线性动力学模型。首先,考虑无控关节自由状态,分析重力梯度对关节运动的影响。其次,利用相平面轨迹分析重力梯度对自由漂浮系统姿态运动影响。最后,由速度偏差曲线分析重力梯度对机械臂的影响。结果表明,当作用时间接近轨道周期或更长时,重力梯度引起的关节偏差已十分显著,且这种扰动作用主要由轨道偏心率决定;关节锁定时俯仰姿态受扰运动有周期振动与翻滚两种形式,若初始角速度满足一定限值可以保证俯仰运动不发生翻滚;当机械臂长时间工作时,忽略重力梯度将产生明显的末端定位误差。

The purpose of this paper is to investigate the effect of gravity gradient torques on attitude dynamics of onorbit free-floating space robots. Nonlinear dynamics of the free-floating system subject to gravity gradient effect is derived by Lagrange equation. Firstly, the effect of nonlinear disturbances caused by gravity gradient torques on the motion free manipulator joints of free-floating space robot is analyzed. Secondly, when manipulator configuration is required to be fixed, the stability of pitch motion of the free-floating system in circular orbit is investigated by using phase phane portrait. Finally, the calculated errors of velocities of manipulator end with and without gravity gradient torques are developed. Disturbances to pose of the controlled manipulator end are talk about. Results show that the manipulator joints are significantly disturbed when time span is about an orbit period or longer, so that it cannot be neglected. Moreover, these disturbances are mainly determined by the eccentricity of orbit. The system with fixed configuration vibrates or tumbles along pitch axis. If initial angular rates are properly chosen, such system can avoid tumbling. For long time manipulation, large control errors are induced if the gravitational gradient effect is neglected.