Nonlinear dynamics design for in-space assembly motion of manipulators on flexible base structures

The construction of ultra-large space structures necessitates advanced in-space assembly technologies. Due to the requirement for lightweight designs, these structures usually consist of numerous slender beams, which may experience large-amplitude vibrations while the onboard manipulators operate at high speeds. These nonlinear structural vibrations can greatly reduce both the accuracy and efficiency of manipulation. Based on multibody system dynamics, this paper presents how to plan the motion of manipulators via a two-step optimization strategy. The nonlinear finite elements of Absolute Nodal Coordinate Formulation are used to model and simulate the motion of the manipulators and their base structures. The first optimization step based on rigid multibody dynamics is performed with Particle Swarm Optimization to minimize the impact on satellite attitudes. Subsequently, the second optimization step based on flexible multibody dynamics is achieved through the application of Gradient Descent method combined with sensitivity analysis to suppress large vibrations of the flexible bases. Finally, three case studies demonstrate that both vibration reduction of very flexible components and fast operation of manipulators can be effectively achieved. Thus, the proposed method is applicable to collaborative motion planning of manipulators on complex space structures for various space tasks.