Multi-degree-of-freedom ultra-low frequency vibration isolation system for precision devices with decoupled control

High precision devices are sensitive to low frequency background vibration. In order to meet the requirement of vibration isolation and adaptation to different working modes, a multi-DOF (Degree-of-Freedom) ultra-low frequency vibration isolation system is proposed. The system uses diaphragm bellow isolators to bear static load and electromagnetic actuators to exert control forces. Auxiliary isolators of variable stiffness are used to make the system adaptive to operation and transportation. The dynamic model of the vibration isolation system is established to analyze vibration characteristics and investigate control laws. A broadband control law based on the actuation-measurement state decoupling is proposed and the mixed feedback and feedforward control is adopted to realize ultra-low frequency vibration isolation. Numerical and experimental results have demonstrated that the proposed system is able to isolate ground vibration effectively. The initial vibration isolation frequency is reduced to 0.5 Hz and the transmissibility reaches -8.3 dB at 1 Hz and -21.9 dB at 2 Hz.