Research On The Quasi-zero Stiffness Vibration Isolation System Based On Positive And Negative Stiffness Of Parallel Structure

When dealing with the low-frequency(less than 2Hz) vibration isolation in the precision and ultra-precision matching would encounter problems such as too much static deformation and instability, which make low-frequency vibration isolation become a big challenge in the design of isolator. This paper design and analysis an isolator which use positive and negative stiffness structure in parallel. The developed isolator possess the characteristics of high-static-low-dynamic stiffness(HSLDS).Mathematical model of the vibration isolation system has established and the forcedisplacement characteristics of the negative stiffness structure and combined system are analyzed in deep. Acquire the quasi-zero stiffness condition and compare three different stiff system: hardening stiffness system, softening stiffness and combined system.The dynamic characteristics of the system under harmonic excitation are analyzed, amplitude-frequency characteristic of the system are acquired by using the method of Harmonic Balance. As the system is nonlinear, the amplitude-frequency curve of the system jumped in some point, which is a phenomenon of dynamic bifurcation. The condition of the stability of the periodic solution and the approximate calculation expression of jump-frequency are calculated. The designed system has hardening characteristics in small displacement while as increasing of the displacement, softening characteristics appeared in large displacement. Compared with the linear system, it is found that under the appropriate parameter HSLDS system has a lower vibration isolation frequency and transmissibility.Using the method of numerical calculation and analyze the phase diagram, Poincare section diagram and the bifurcation diagram discussed the bifurcation and chaos characteristics of the system which caused by the changes of the system parameter. Based on maximum lyapunov exponents to determine whether a system is in chaos condition it is found that by using the method of random phase control and weak periodic signal control chaos state of the system can be eliminated.Vibration isolation experimental platform is designed to verify the theory. Displacement transmissibility experiment are carried on the vibration table. Both quasizero stiffness system and linear system displacement transmissibility are tested for compare. The experimental results of quasi-zero stiffness system have large error in the low frequency, only when excitation frequency higher than 2.5Hz the system are effected while through compare with the linear system it is verified that the non-linear system can reduce the nature frequency and enlarge the range of vibration isolation frequency.