Research on path planning of free-floating space robot based on dual mode switching

Large amount of space debris is bound to pose a threat to the safety of on-orbit spacecraft. How to deal with and remove space debris has become a top priority mission. The free-floating space robot (FFSR) is one of important tools for completing the debris removing task. Safe and effective path planning is the basis of trajectory tracking operations for FFSR. When the optimal path planning is carried out under the multiple constraints(such as the manipulator end error control limits, the joint torque limits, non-integrity constraints, coupling constraints, etc.),the optimal solution maybe do not exist due to the strict constraints. This will directly lead to the failure of the path planning task. Aim to avoid the unsolved situation and ensure to get the executable operation path, a path planning method based on dual mode switching is proposed in this paper. The basic idea of the dual mode switching method is that: In each control cycle, 'mode 1' is solved first, and if the solution exists, the calculation will be completed. If the solution can't be obtained, it will be converted to 'mode 2' according to the set conditions. Where, the 'mode 1' is to carry out the optimal solution of path planning under the condition that all the constraints are satisfied, and obtain the joint angular velocity value in accordance with the optimal objective function, while the 'mode 2' is to get an effective planning solution which can realize trajectory tracking task but is not the optimal solution. For the 'mode 2', realizing trajectory tracking task means the direction of the 'mode 2' solution is as the same as the designed control law while the size of it is as close as possible to the designed control law. The simulation results show that the proposed path planning method based on dual mode switching can smoothly realize the switching between the two modes, and can get a valid executable path under severe constraint conditions, also meet the requirements of trajectory tracking task of FFSR.