DYNAMICS MODELING AND EXPERIMENT OF A FLEXIBLE CAPTURING MECHANISM IN A SPACE MANIPULATOR 1)

An end-effector with flexible capturing mechanisms, which can accomplish on-orbit capturing operations with large tolerance, is a vital component of a large-scale space manipulator. Dynamics modeling and theoretical analysis of the flexible capturing mechanisms are very important for on-orbit servicing task simulation and prediction. In this paper, a dynamics model of a flexible capturing mechanism with three cables in a space end-effector is developed firstly. The three-dimensional absolute nodal coordinate formulation (ANCF) is used to create nonlinear finite elements of flexible cables. Both bending and longitudinal deformation of the cables are considered, furthermore, contact between the flexible cables and the rigid target is analyzed by introducing an intermediate cylinder reference coordinate system. Then, an experiment with passive spring suspension is built to validate the proposed model and signals of both motions and forces of the target are collected and compared with the simulation results. The comparison shows that the values of the simulation match well with the experimental measuring ones. The presented model could be used as supplements for the two-dimension planar air-bearing experiment and could be used for capturing task simulations of large-scale space manipulators. At last, capturing simulations of two representative on-orbit operations are conducted by co-simulation with the proposed model and a dynamics model of a large-scale space manipulator. One of the operations is the soft capturing process of an inspection task on the spacecraft surface, the other is the soft capturing of a floating target. The main difference between the two simulations is that the target in the first simulation is fixed on the base of the manipulator. Results of these simulations show that the soft capturing process can be accomplished on the prescribed condition.