Ultra-low frequency air flotation vibration isolation system with a dual-chamber structure using adaptive control strategy

Vibration isolation systems for ultra-precision instruments are strongly influenced by internal resonances, leading to an increase in vibration transmissibility of up to 10–30 dB at the resonance frequencies. The dual-chamber air-floating vibration isolation system exhibits an extremely low natural frequency. However, the presence of the expansion chamber introduces internal resonance problems at mid-to-high frequencies. To enhance the vibration isolation performance of the dual-chamber air-floated isolation system, this paper proposes an adaptive control strategy tailored to such systems to address internal resonance beyond the natural frequency. The dual-chamber air-floated isolation system is accurately modeled and systematically analyzed in this paper. The results reveal that the fundamental cause of internal resonance in the dual-chamber isolation system is Helmholtz resonance. To address this issue, a novel orthogonal basis function infinite impulse response (OBF-IIR) controller is designed in this paper to efficiently compensate for vibrations induced by the dual-chamber Helmholtz resonance effect. On this basis, a fast, accurate online adaptive algorithm is developed to update the controller zeros in real time, enabling adaptive, synchronous compensation of internal resonances in the dual-chamber isolation system. The proposed OBF-IIR controller not only suppresses internal resonances induced by the spring–damper model and the dual-chamber Helmholtz resonance effect, but also compensates for resonances arising from other sources. The proposed adaptive control strategy demonstrates faster convergence and higher accuracy, reducing the vibration transmissibility of the isolation system by 10–30 dB in the 2–100 Hz range and decreasing the cumulative power spectral density at 100 Hz by 23.8%–84.9%.