Ultra-low frequency pneumatic–mechanical–electrical active vibration isolator considering internal resonance

With the rapid advancement of semiconductor manufacturing equipment, particularly lithography systems, the demand for low- and ultra-low-frequency vibration isolation has become increasingly stringent. The effective suppression of ultra-low-frequency micro-vibrations has become a critical engineering challenge. A novel pneumatic–mechanical–electrical active vibration isolation (PME-AVI) system is designed in this paper. The proposed system provides ultra-high load capacity and exhibits quasi-zero stiffness (QZS) characteristics in both the vertical and horizontal directions. The isolation mechanism of the PME-AVI system employs an air-flotation bearing with a tapered pressure-equalization micro-orifice restrictor (TPMR), which effectively suppresses sleeve–piston tilting in conventional air bearings and ensures stable non-contact, friction-free operation. In addition, a hybrid control strategy combining model predictive feedback control (MPC) and full-order filtered-x Gauss–Newton (FO-FxGN) feedforward control is developed for the PME-AVI system. The proposed strategy effectively addresses the internal resonance issues inherent in ultra-low-frequency air-flotation isolation systems. Simulation and experimental results demonstrate that the designed PME-AVI system achieves natural frequencies below 0.5 Hz in the X, Y, and Z directions, and provides an isolation efficiency of 99.55% (−47 dB) at 10 Hz. In addition, the proposed hybrid control strategy reduces the internal resonance peaks by more than 15 dB. This paper shows significant potential for micro-vibration isolation applications in semiconductor manufacturing equipment.