Buffer Compliance Control of Space Robots Capturing a Non-Cooperative Spacecraft Based on Reinforcement Learning

Abstract

Aiming at addressing the problem that the joints are easily destroyed by the impact torque during the process of space robot on-orbit capturing a non-cooperative spacecraft, a reinforcement learning control algorithm combined with a compliant mechanism is proposed to achieve buffer compliance control. The compliant mechanism can not only absorb the impact energy through the deformation of its internal spring, but also limit the impact torque to a safe range by combining with the compliance control strategy. First of all, the dynamic models of the space robot and the target spacecraft before capture are obtained by using the Lagrange approach and Newton-Euler method. After that, based on the law of conservation of momentum, the constraints of kinematics and velocity, the integrated dynamic model of the post-capture hybrid system is derived. Considering the unstable hybrid system, a buffer compliance control based on reinforcement learning is proposed for the stable control. The associative search network is employed to approximate unknown nonlinear functions, an adaptive critic network is utilized to construct reinforcement signal to tune the associative search network. The numerical simulation shows that the proposed control scheme can reduce the impact torque acting on joints by 76.6% at the maximum and 58.7% at the minimum in the capturing operation phase. And in the stable control phase, the impact torque acting on the joints were limited within the safety threshold, which can avoid overload and damage of the joint actuators.

A Fuzzy Logic Reinforcement Learning Control with Spring-Damper Device for Space Robot Capturing Satellite

“…In order to maintain a stronger effect, the food and the bell are matched to generate the enhancement signal. Compared to RL in our published previously work [3], this paper enhanced the primary reinforcement signal to become an enhancement signal containing more information (which ultimately makes the calm control of the hybrid system more stable).…”

“…At present, it is feasible to use a space robot to complete the capture task. This has therefore become one of the research hot spots of space exploration [1][2][3][4][5][6][7][8]. Generally, the process of capture operation can be divided into four stages: (1) the space robot observes the target satellite; (2) a pre-operation stage before capture operation, such as deceleration and detumbling control of the target satellite;…”

“…However, the space robot is a rootless system, and it works in both microgravity and a vacuum. If the SEA is added in the joints of space robot (refer to our published previously work [3,22]), the flexible vibration caused by SEA will be difficult to suppress. Therefore, the controller was divided into a fast subsystem controller and slow subsystem controller, wherein the slow subsystem controller realizes trajectory tracking and the fast subsystem controller suppresses the flexible vibration.…”

Integrated Fixed Time Sliding Mode Control for Motion and Vibration of Space Robot with Fully Flexible Base–Link–Joint

“…Space robots are rootless multi-body systems used to perform exploration, assembly, construction, service, repair, or assist astronauts in extravehicular missions in the special space environment, and play an integral role in the space exploration process, and have been the focus of research by space workers [1][2][3][4][5][6]. Space missions are complex and diverse, and space robots have different configurations [7].…”

Repetitive Learning Sliding Mode Stabilization Control for a Flexible-Base, Flexible-Link and Flexible-Joint Space Robot Capturing a Satellite

“…The use of robotic systems to carry out on-orbit operations is highly desirable because it limits the need for astronaut intervention in extreme environments, meaning missions can be executed within shortened timescales and with higher levels of human safety. Therefore, the study of related theories and technologies has received considerable attention [1][2][3][4][5][6], etc. The first space robot is the "Canadian Arm" developed in Canada.…”