Seven-degree-of-freedom redundant manipulators with link offset have many advantages, including obvious geometric significance and suitability for configuration control. Their configuration is similar to that of the experimental module manipulator (EMM) in the Chinese Space Station Remote Manipulator System. However, finding the analytical solution of an EMM on the basis of arm angle parameterization is difficult. This study proposes a high-precision, semi-analytical inverse method for EMMs. Firstly, the analytical inverse kinematic solution is established based on joint angle parameterization. Secondly, the analytical inverse kinematic solution for a non-offset spherical-roll-spherical (SRS) redundant manipulator is derived based on arm angle parameterization. The approximate solution of the EMM is calculated in accordance with the relationship between the joint angles of the EMM and the SRS manipulator. Thirdly, the error is corrected using a numerical method through the analytical inverse solution based on joint angle parameterization. After selecting the stride and termination condition, the precise inverse solution is computed for the EMM based on arm angle parameterization. Lastly, case solutions confirm that this method has high precision, and the arm angle parameterization method is superior to the joint angle parameterization method in terms of parameter selection.
This paper proposes a detumbling motion planning algorithm for free-flying space manipulator with a grasped tumbling target in the post-capturing phase. This algorithm can not only collision-freely guide the space manipulator and the target to terminal stationary states but also suppress the residual vibration of the flexible appendage on the space manipulator. First, considering the avoidances of self-collisions and motion singularities, a smooth detumbling path is planned for the space manipulator by a proposed smoothing rapid random tree star algorithm (SM-RRT*). Second, a quintic polynomial function is implemented to generate a continuous detumbling trajectory along the detumbling path. Then, with the object of minimizing the residual flexible vibrations and the constrains of joint acceleration limits, an optimization model is established to refine the detumbling trajectory. Finally, the optimization model is solved by an improved particle swarm optimization algorithm (PSO), where a potential field term is included in the generation of the particle velocity to enhance the computational efficiency. Simulation results validate the effectiveness of the proposed detumbling motion planning algorithm.
Space robots play a significant role in on‐orbit servicing (OOS) missions, such as inspecting, capturing, refueling, and repairing satellites, assembling and maintaining large space infrastructure, and removing orbital debris. Over the past four decades, many space robot engineering applications and technology verifications for OOS have been accomplished. This article comprehensively reviews the advances by representative space robotic programs on space shuttles, outside/inside the International Space Station and the China Space Station, as well as on satellites, and the development trends of space robots are summarized. In addition, the primary key technologies and challenges are explored, including the following: 1) visual perception for noncooperative targets; 2) motion planning and control with a free‐floating base and flexibility; 3) multifunctional end‐effectors; 4) ground teleoperation with long time delays; and 5) high‐fidelity ground verification. Finally, the prospects for space robot future research are presented.
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