This article studies the attitude control problem for spacecraft staring-mode observation. The staring mode of spacecraft is initially presented, and its advantages for observation are analysed. Then, based on the dynamic equation and kinematic equation using error quaternion and angular velocity error, a sliding-mode controller is designed to improve control effect, which prolongs observation time and enhances observation precision. Afterwards, a disturbance observer is devised and included in this proposed controller to reduce inherent chattering of sliding-mode control and to improve the stability of the spacecraft platform. Besides, the convergence of the proposed disturbance observer is proved theoretically. Finally, simulations are performed, and the results demonstrate that the proposed controller has quicker response, better robustness to uncertainty of spacecraft inertia parameters and external disturbance, and effectively weakens the chattering.
An obstacle avoidance and path planning algorithm for a multi-joint manipulator in a space robot is presented in this paper. In this paper, the end-effector of the manipulator is used to capture some special target in a space environment with obstacles. To ensure the safety of the operation, a collisionfree path from the initial position to the target position is essential. Therefore, an obstacle avoidance and path planning algorithm based on the Rapidly-Exploring Random Tree (RRT) algorithm and the Forward and Backward Reaching Inverse Kinematics (FABRIK) algorithm is presented in this paper. First, a path planning algorithm based on the Rapidly-Exploring Random Tree (RRT) algorithm is designed for the multi-joint manipulator. Further, a method to generate a random point by artificial guidance is introduced for a higher searching speed. The RRT algorithm can effectively explore the entire workspace and find a feasible path without collision for the end-effector. To calculate the positions of each joint, the Forward and Backward Reaching Inverse Kinematics (FABRIK) algorithm is introduced and improved for the problem of inverse kinematics. The FABRIK algorithm avoids the use of rotational angles or matrices, and instead finds each joint position by locating a point on a line, and thus, it has a low computational cost. Therefore, the improved obstacle avoidance and path planning algorithm can quickly plan a feasible path for the multijoint manipulator in a space environment with obstacles. A numerical simulation is carried out to analyze the proposed obstacle avoidance and path planning method. It is observed that the method finds a feasible path without collision for the multi-joint manipulator with a low computational cost. These results validated the effectiveness of the proposed method for path planning to avoid the obstacles. INDEX TERMS FABRIK, multi-joint manipulator, obstacle avoidance, path planning, rapidly-exploring random tree.
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