Research On The Isolation Characteristics Of Variable Stiffness Maglev Floating Raft Vibration Isolation System

In the methods of reducing and eliminating harmful vibration, vibration isolation technology has long been receiving people's attention. Floating raft vibration isolation technology is developed after the single-layer and double-layer vibration isolation technology. Now it has been widely used in the engineering. Supporting stiffness is a very important parameter in all vibration isolation systems. It will directly affect the vibration isolation performance of vibration isolation systems.The supporting stiffness of isolator in conventional vibration isolation system is usually a fixed value, which makes the vibration isolation system has limitation when it works. That means the vibration isolation effect is good at high frequencies but is bad at low frequencies and nearby the resonant frequency. When the frequency range of vibration that is produced by machine units under different working conditions changes greatly, conventional vibration isolation system can effectively isolate higher frequency vibration, but can not do well with lower frequency vibration.So we use variable stiffness magnetic suspension isolator and conventional isolator in parallel, by changing the current in the coil of magnetic suspension isolator to adjust the vibration isolation system's stiffness and make it can effectively isolate the vibration produced by machine units in the whole working range.This paper researches the vibration isolation characteristic of conventional floating raft isolation system with two machine units, through comparing theoretical analysis results and simulation results, and using force transmission rate as a standard to measure the vibration isolation effect. The results show that, in high frequencies, the force transmission rate of floating raft vibration isolation system under single excitation is very close to the double-layer vibration isolation system which has equivalent parameters and the force transmission rate of floating raft vibration isolation system under double excitation is smaller than that under single excitation.The current upper limit of magnetic suspention isolator can be determined after analysing the supporting stiffness characteristic of multipled magnetic suspention isolator and conventional isolator. Compare the vibration isolation effects between magnetic suspension vibration isolation system and conventional vibration isolation system, it is found that with current increases, the magnetic suspension vibration isolation system's stiffness decreases, its force transmission rate curve moves down, and the vibration isolation effect of vibration isolation system is improved within the working frequency range of machine unit. It is also found that magnetic suspension isolator's nonlinear characteristics make the system can isolate the external vibration more effectively, when the displacement is large.Finally, the isolation characteristics of double-layer vibration isolation system is researched, and the experiment results agrees well with simulation results. Just because the actual damping is smaller than the simulation value, the experimental curves' peaks at the natural frequencys are larger than the simulation curves' peaks.