Zhao Sikai, Zheng Tianjiao, Sui Dongbao, Zhao Jie, Zhu Yanhe
State Key Laboratory of Robotics and Systems, Harbin Institute of Technology, Harbin, China.
Front Neurorobot. 2023 Feb 15;17:1093718. doi: 10.3389/fnbot.2023.1093718. eCollection 2023.
As astronauts perform on-orbit servicing of extravehicular activity (EVA) without the help of the space station's robotic arms, it will be rather difficult and labor-consuming to maintain the appropriate position in case of impact. In order to solve this problem, we propose the development of a wearable robotic limb system for astronaut assistance and a variable damping control method for maintaining the astronaut's position. The requirements of the astronaut's impact-resisting ability during EVA were analyzed, including the capabilities of deviation resistance, fast return, oscillation resistance, and accurate return. To meet these needs, the system of the astronaut with robotic limbs was modeled and simplified. In combination with this simplified model and a reinforcement learning algorithm, a variable damping controller for the end of the robotic limb was obtained, which can regulate the dynamic performance of the robot end to resist oscillation after impact. A weightless simulation environment for the astronaut with robotic limbs was constructed. The simulation results demonstrate that the proposed method can meet the recommended requirements for maintaining an astronaut's position during EVA. No matter how the damping coefficient was set, the fixed damping control method failed to meet all four requirements at the same time. In comparison to the fixed damping control method, the variable damping controller proposed in this paper fully satisfied all the impact-resisting requirements by itself. It could prevent excessive deviation from the original position and was able to achieve a fast return to the starting point. The maximum deviation displacement was reduced by 39.3% and the recovery time was cut by 17.7%. Besides, it also had the ability to prevent reciprocating oscillation and return to the original position accurately.
在宇航员执行舱外活动（EVA）的在轨服务且没有空间站机械臂帮助的情况下，万一发生碰撞，要保持合适的位置将非常困难且耗费体力。为了解决这个问题，我们提出开发一种用于辅助宇航员的可穿戴机器人肢体系统以及一种用于保持宇航员位置的可变阻尼控制方法。分析了宇航员在舱外活动期间的抗冲击能力要求，包括抗偏差、快速返回、抗振荡和精确返回的能力。为满足这些需求，对带有机器人肢体的宇航员系统进行了建模和简化。结合这个简化模型和强化学习算法，获得了机器人肢体末端的可变阻尼控制器，它可以调节机器人末端的动态性能以抵抗碰撞后的振荡。构建了带有机器人肢体的宇航员失重模拟环境。仿真结果表明，所提出的方法能够满足舱外活动期间保持宇航员位置的推荐要求。无论阻尼系数如何设置，固定阻尼控制方法都无法同时满足所有四个要求。与固定阻尼控制方法相比，本文提出的可变阻尼控制器自身完全满足了所有抗冲击要求。它可以防止过度偏离原始位置，并能够快速回到起始点。最大偏差位移减少了39.3%，恢复时间缩短了17.7%。此外，它还具有防止往复振荡并精确回到原始位置的能力。
