Modeling and Control of Dual-Arm Space Robots

Abstract

With the rapid growth of space technology, space robots play a critical role in on-orbit servicing missions, such as assembling, repairing, refueling, and transporting missions. Space robots can autonomously carry out on-orbit missions, avoiding dangerous and expensive tasks for astronauts. Unlike ground robots with fixed bases, the coupled dynamics between the free base and the manipulator of space robots need to be considered. Compared with single-arm space robots, dual-arm space robots can implement more complex tasks with a higher probability of success. Therefore, the modeling, motion control, hybrid position/force control, and post-capture control of a dual-arm space robot are investigated and presented in this thesis. The mathematical models of dual-arm space robots are developed by considering the reaction wheels (RWs) in the base. The kinematic model is constructed by the Generalized Jacobian Matrix (GJM). The dynamic models are inferred by the Newton-Euler method and the Lagrangian method, which are used in different application scenarios. The motion control of the two manipulators is used to implement a novel strategy to approach a defunct spinning target in space. By the nonlinear model predictive controller (NMPC), the end-effectors can track and plan smooth trajectories to approach and synchronize with a defunct spinning target. Meanwhile, the base attitude is regulated by the RWs to be stable at zero. The hybrid position/force control is applied to the dual-arm space robot to conduct contact operations. Novel capture and on-orbit assembly strategies are investigated. With the model uncertainties of the space robot, a robust sliding mode controller (SMC) is developed for better robust performance than the conventional computed torque controller. Furthermore, the unknown inertial parameters of the target can be precisely estimated during the capture phase. When a space robot and a target are rigidly connected during the post-capture phase, they form a combined system. The combined system can be stabilized to rest status by the space robot. The space robot can also release the target at the desired velocity. The proposed modeling, capturing of a spinning target, on-orbit assembling, and post-capturing processes are validated in the numerical simulations, which show the feasibility and effectiveness. The proposed work will improve the accuracy and efficiency of space robot technology.