Simulation Investigation In Active Vibration Isolation By Using A Nonlinear Isolator

Generally speaking, an elastic element, damping element and inertial element compose the traditional passive vibration isolation system in which the isolator is installed between the vibration source and the receiver to reduce the vibration transmissibility. The passive isolation system can isolate high frequency responses effectively but not for the low frequencies. The high static and low dynamic stiffness isolator as a nonlinear one has good static bearing capacity and low dynamic stiffness, which is beneficial to reduce the natural frequency and extend the vibration isolation range of such an isolation system. The active vibration control is an important method to control low frequency vibrations,it can also adapt to the disturbance frequency change. So it can be expected that the control force will be decreased by combine the active vibration control with high static and low dynamic stiffness isolator together in addition to better isolation performances. The problems such as cost, reliability and stability of an active vibration isolation system will be solved by an active vibration isolation system using high static and low dynamic stiffness isolators,since the actuator will cost less energy and reduce its dimension and weight.Firstly, the effects on the responses of a high static and low dynamic stiffness isolation system by excitation amplitude,structure parameters and damping are discussed by making a mathematical model of a high static and low dynamic stiffness isolator. Then measurements of the static characteristic of a high static and low dynamic stiffness iso lator-a bubble steel wire rope isolator are finished.Then a feedforward control system by using the high static and low dynamic stiffness isolator is compared with the feedforward control system by using the equivalent linear isolator. When the control force only acts on the base of the isolation system or between the mass and the base, the nonlinear active control system need less output force. When the control force only acts on the mass of the isolation system, control forces of these two cases are the same.At last, the acceleration, velocity and displacement feedback control systems by using the high static and low dynamic stiffness isolator are compared with the linear case. The nonlinear feedback system needs less control force in the intermediate frequency range than the equivalent linear one while the control forces they need are the same in high frequency range. The vibration control performance when the control force only acting on the mass is superior to that of the control force acting between the mass and base. When the control force only acts on the mass, the acceleration feedback system is propitious to extend the isolation frequency range and the velocity feedback system can suppress the resonance peak and the displacement feedback system will reduce the isolation frequency range. When the feedback control force only acts on the base, the acceleration feedback system has disadvantage to isolate the high frequency vibrations and the velocity feedback system does not work well and the displacement feedback system has good control results.