Theoretical Model Of A Nonlinear Electromagnetic Vibration Isolator And Its Semi-active Damping Control Method

Mechanical vibrations can detrimentally influence the working performance and operating life of machinaries and equipments.Therefore,researchers made their efforts to utilize all kinds of methods for reducing or avoiding the damage.With the development of science and technology,a low level vibration response is required in the harsh working environment.Traditional linear vibration isolators are limited in high precision instruments due to their narrow vibration isolation band.Nonlinear vibration isolators are widely concerned and studied because they can greatly increase the vibration isolation bandwidth,reduce the peak response and improve the static carrying capacity.Considering the advantages of nonlinear vibration isolators,this paper studies the theoretical model of a novel nonlinear electromagnetic nonlinear vibration isolator and utilizes a semi-active damping control method to realize the high vibration attenuation performance in a wide band.The thesis focuses on:1.A novel nonlinear vibration isolator based on the permanent magnets(PMs)is designed,which develops the design method of nonlinear vibration isolators.The nonlinear magnetic force among the PMs is derived according to the ampere current model.Then the effects of the distance and angle among the PMs are theoretically studied.Nonlinear magnetic force is tested and the experimental results agree well with the theoretical results.2.The vibration isolation performance of the proposed nonlinear vibration isolator is evaluated theoretically,numerically and experimentally.The response of the nonlinear vibration isolator is derived via the harmonic balance method(HBM)and the corresponding numerical simulation is carried out.The experimental test system is carried out to verify the favorable vibration isolation performance under the symmetrical and asymmetrical distribution of the PMs and the large amplitude excitation.One can obtain the hardening or softening characteristic of the nonlinear vibration isolator by changing the poles of the PMs.The experimental results demonstrate that the peak frequency and corresponding response of the nonlinear vibration isolator reduce to 60%and 20%correspondingly compared with those of equivalent linear vibration isolators.The experimental results verify the simulation results.3.The dynamic and vibration islation characteristics of a two-state(monostable and bistable)isolator is studied.The theoretical model of the two-state isolator and its dynamic and isolation performance test system are established.Numerical and experimental results show that both bistable and monostable isolators can effectively improve the isolation performance.The monostable isolator presents periodic vibrations with the change of the excitation frequency.The bistable vibration isolator presents the periodic or chaotic vibrations alternatively with the change of the excitation displacement or excitation frequency.4.The semi-active damping control method based on electromagnetic shunt damping is applied to the nonlinear vibration isolator to achieve the high vibration isolation performance.The dynamic model of the semi-active coupling system is established and the response is derived through the HBM.The test system of vibration isolation performance is established.The numerical simulations and experiments are carried out,which show that the semi-active nonlinear vibration isolator is able to further improve the vibration isolation performance and eliminate the "jump-down" phenomenon in the coupled system.5.The shock isolation performance of the semi-active nonlinear vibration isoaltiors is investigated.The coupling model of the system is established,three indices of the shock isolation performance are introduced,which are shock acceleration ratio(SAR),shock displacement ratio(SDR)and relative displacement ratio(RDR).Then some numerical simulations are carried out.The test system of shock isolation performance is established.Both numerical and experimental results demonstrate that SDR and RDR become better when the negative resistance electromagnetic shunt damping is used.This paper established the design method,theoretical analysis method and experimental verification method of a novel permanent magnet nonlinear vibration isolator and also studied the semi-active damping control method based on electromagnetic shunt damping.The results demonstrate that:1.The PMs based nonlinear vibration isolator is able to improve the vibration isolation performance and broaden the vibration isolation band.2.The semi-active shunt damping can further reduce the vibration response and avoid the "jump-down" phenomenon of the nonlinear vibration isolator.3.The semi-active nonlinear vibration isolator has a favorable shock isolation performance.In summary,this work could provide a new method for the vibration control field.