Abstract: A multi-dimensional quasi-zero stiffness vibration isolation method combining flexible suspension and inverted pendulum is proposed to meet the requirements of ultra-low frequency vibration isolation for precision equipment mounted on aerospace launch vehicles and other aircraft. By connecting the flexible suspension to specific positions below the centroid of payload, the horizontal quasi-zero stiffness is achieved through the pendulum effect of flexible suspension and the inverted pendulum effect caused by upward centroid shift of payload. The vibration equation of the flexible suspension-inverted pendulum composite isolation system is established, and its multidimensional vibration isolation characteristics are analyzed. Key parameters including suspension stiffness, horizontal and vertical positions of suspension points relative to payload centroid are investigated for their influences on system stability, natural frequencies, and vibration transmissibility. Results indicate that the stability of isolation system decreases with reduced suspension stiffness, increased payload centroid height, and decreased horizontal spacing of suspension points, requiring rational parameter configuration to ensure stability. For given payload, vertical isolation performance mainly depends on suspension stiffness, while horizontal high-frequency isolation performance is primarily determined by suspension working length. Reducing suspension stiffness and suspension point spacing while increasing payload centroid height can improve low-frequency horizontal isolation performance. The coupling between horizontal translation and rotational motion creates an anti-resonance phenomenon near the main rotational natural frequency, enabling excellent horizontal isolation in specific frequency bands. A prototype is developed and tested for natural vibration characteristics and vibration transmissibility, with experimental results verifying the theoretical analysis.

Key words: flexible suspension, inverted pendulum, vibration isolation, quasi-zero stiffness, stability, transmissibility