Air spring (AS) vibration isolators have a large load capacity and can effectively attenuate base vibration; therefore, they are widely applied to support precision instruments. Lowering the stiffness of the isolator with additional mechanisms is the key to improving its performance. However, for AS isolators with stiffness requirements in multiple directions, it is intricate to integrate all the necessary stiffness mechanisms. To address this, a magnetic spring (MS) exhibiting anisotropic stiffness is introduced, forming a parallel pneumatic–magnetic vibration isolator (PPMVI). In the vertical direction, the MS delivers negative stiffness, lowering the overall stiffness to improve performance. In the horizontal directions, it provides positive stiffness to counteract the negative stiffness brought by the unstable horizontal isolation mechanism and restores overall stability. Stiffness characteristics of the MS are investigated, and stiffness coupling is reduced through optimized parameter design. Stability of the PPMVI is verified by simulation, and the vertical isolation performance, in the form of acceleration transmissibility, is validated by experiments. The results show that the PPMVI regains stability in horizontal directions. In the vertical direction, it has 55.5% lower stiffness than the AS isolator under the same conditions, and transmissibility is also reduced.
Du et al. (2026) studied this question.