A Study On Threshold Acceleration Switches Based On Bistable Characteristic

Acceleration switch is an inertial device which integrates functions of sensing, judging and actuating, which not only senses acceleration signals and then perform the on-off functions under the effects of the threshold forces, but also meet the demands of fast response, large contact force, large electric current, long cut-off time and anti-jamming performance. So it shows widely application potentials in aircraft systems, automobile safety systems, consuming electrical equipents, medical instruments, and weapon systems, etc. However, the domestic and even abroad research status show that there are still some difficulties and problems to be solved in its basic design theory, research methods and fabrication technologies. Moreover, the present research process mainly relies on the trial and error method, which contributes to high costs, resulting in the absence of micro-acceleration switch with high performance in our domestic markets.Now, the key technology in designing acceleration switches involves the intersection and coupling of multiphysical subjects such as mechanical nano-contact theory, film damping theory, elastic theory, permanent magnetic, bistable mechanics, and mechanical-electrical dynamic theory. And The research on threshold characteristics of bistable structures are especially important in the function realization of the micro-switch.With the basis work on bistable mechanics, this paper aims to establish the design theory of bistable mirco acceleration switch. First, the shortage of small deflection theory in analyzing the bistable mechanics is pointed out, and then, the dynamic post-buckling control equations of the inclined slender beam under complex loads are established, which are based on the large deflection and elastic theories. Later, the post-buckling configurations and the nonlinear variable stiffness of the large deflection inclined beam are obtained by utilizing the numerical methods.Based on the switch characteristics and its working principles, the static design theory of the threshold acceleration switch with bistable structures is proposed. And after that, considering the effects of inertial force, post-buckling force, permanent magnetic force, film damping force and contact force on the switch performances, the dynamic design model under these coupled forces is therefore established to guide the design process. Samples of the switch are made thereby after analyzing the effects of the different design factors on the switch performances. The numerical simulation results are consistent with those by our experiments, which validate the feasibility and effectiveness of the theoretical design model, which provides the theoretical basis and for the micro-acceleration switch and bistable devices.Based on the generalized variation principles, the nonlinear relationship between the transversal force and displacement is deduced considering the effects of axial compression on the beam length constraint.While the second bifurcation buckling occurs during the snap-through process, the nonlinear coupled relations among the transverse critical force, the axial compression, arc height and the buckling modes are also analyzed by utilizing the meromorphic function method and buckling mode method. The simulation results have a good agreement with those from experiments, hence, its applications in designing MEMS bistable device.The effects of the geometric parameters of the cosine arc-beam and the compliant structures on the snap-through and stable holding characteristics are analyzed. By comparing the results from the large deflection post-buckling theory, energy variation methods and experiments, the shortage of the energy variation method in analyzing bistable mechanics are pointed out.Based on the geometrical nonlinear theory of large deflection elastic beams, the dynamic governing differential equations of post-buckling behavior of clamped-clamped inclined beams subjected to combined forces are established. By using the implicit compatibility conditions to solve the nonlinear statically-indeterminate problems of elastic beams, the strongly nonlinear equations formulated in terms of elliptic integrals are directly solved in the numerical sense. When the applied force exceeds the critical value, the numerical simulation shows that the inclined beam snaps to the other equilibrium position automatically. It is in the snap-through process that the accurate configurations, nonlinear variation stiffness, and the stress distribution of the post-buckling inclined beam with different angles are presented, and the effects of the structure parameters on the bistability and buckling modes are analyzed. The numerical results are in good agreement with those obtained in the experiments, which demonstrates the validity of the post-buckling deductions, which provides theoretical basis for the accurate post-buckling analysis of flexible micro-structures.Based on the nonlinear relations between the permanent magnetic force and displacement, a novel bistable mechanism with permanent magnetic structures is designed, and the effects of structure parameters on the bistability and stable holding performance are analyzed.Aimed to the analyzing of the bistability caused by the pull-in phenomena, based on the magneto motive model, the effects the magnetic core reluctance on the snap through positions of different magnetic micro-devices are analyzed, and the control method of the snap position is given.Aimed to solving the problems in the design process, based on the threshold characteristics of the bistable structures and the switch working principle, the concept of a novel threshold acceleration switch with nonlinear bistable structures is put forward and the corresponding static design theory of the acceleration switch with post-buckling structures and permanent magnetic structures is given. Considering the effects of inertial force, post-buckling force, permanent magnetic force, film damping force and contact force on the switch performances, the electromechanical dynamic design model under coupled forces is established to guide the design process. The relationships between the switch parameters and the dynamic characteristics such as fast response, time maintaining, frequency response and the contact reliability, are analyzed by numerical simulation method. With in the tests error range, the simulation results are consistent with those obtained by experiments, which validate the feasibility of the switch design theory.Owing to the lack of the unified standard to test the acceleration switch performance, which slows down the development of the research, based on the switch working characteristics and principles, the system and detailed evaluation standards are proposed objectively, which is very helpful for the design of micro-threshold acceleration switch.