A Study On Magnetic-Mechanical Coupled Multistable Mechanism And Its Design Method

Possessing the excellent mechanical properties of simple structure, threshold snapping, fast response, precise positioning and low energy consumption, multistale mechanisms have great potentials in the fields of optical switches, crash sensors, mechanical memories, actuators, robotics, and so on. Besides the pure mechanical multistable mechanisms, a novel multistable mechanism using the nonlinear interaction between the magnetic force and elastic force was proposed in this paper. According to the form of the spatial arranged permanent magnets, the multistable mechanisms (MPMM) can be divided into three types:Line-MPMM, Plane-MPMM, and Space-MPMM. A magnetic-mechanical coupled method for designing multistable mechanism was proposed based on pseudo-rigid-body model (PRBM) and magnetic charge model. To the knowledge of the authors, due to the imperfect analyzing models, it is difficult to control the multistable parameters of the mechanism such as stable state number, travelling range, and driven load.In this paper, two key issues for magnetic-mechanical coupling modeling process and optimization of multi-steady-state characteristics were studied.First, a method for designing Line-MPMM was proposed. The two parallel beams of large deformation mechanics and interactions among multi-permanent magnets were systematically analyzed. And, the force balance equation of the Line-MPMM considering the influence of the axial deformation of the beam on the magnetic field distribution was established. With the nonlinear balance equation, the nonlinear coupling relation among multi-parameters including the magnet number, magnetization, arrangement, stable state number, travelling distance, and driving load was analyzed.Second, by optimizing the layout of the permanent magnet and considering the relative axial displacement attributed by the large deformation of the parallel beams, a heptastable mechanism was designed, which stable characteristics such as the number of the states, the position of the states and the snapping threshold were analyzed. The nearly consistent between the experimental and theoretical results adequately validated the correctness of the proposed analyzing model.Third, to increase the number of triggering directions of the bistable mechanisms, a universal bistable mechanism was proposed by incorporating the cylindrical cantilever and permanent magnet ring,which could snap-through from one stable state to the other one in all in-plane direction. The nonlinear mechanics of the magnetic-mechanical coupling mechanism was analyzed by considering the influence of the tip rotation angle and relative displacement of the moving circular magnet on the magnetic field strength. The experimental and theoretical results were in reasonable agreement, which sufficiently validated the proposed model.Consequently, the proposed design method was very useful for design the newly proposed magnetic-mechanical coupled mechanism.