Design and analysis of a variable-stiffness multi-pole 3DOF magnetic suspension vibration isolator

Vibration isolation in marine and aerospace engineering faces increasing challenges under complex random excitations, where conventional passive and semi-active isolators exhibit limited adaptability. To overcome these limitations, this study develops a novel multi-degree-of-freedom variable-stiffness magnetic suspension vibration isolator (3DOF-MSVI) featuring a dual-layer, multi-pole H-shaped armature configuration. A generalized nonlinear magnetic circuit–mechanical coupling model is formulated and validated through finite element simulations and prototype experiments. The proposed design effectively eliminates magnetic flux conflict zones and enables multi-axis suspension force and torque generation. Compared with the baseline MSVI, the 3DOF-MSVI achieves a 79% enhancement in maximum suspension force, while torque output increases by 355.7% relative to the 2DOF-MSVI. Further optimization of the central shaft length contributes an additional 11.4% improvement in suspension force. By modulating input current and structural alignment parameters, the system realizes active stiffness control across multiple degrees of freedom. These findings demonstrate that the 3DOF-MSVI can flexibly adjust the structural stiffness, thereby offering a promising solution for vibration isolation under stochastic excitations in offshore platforms, precision instruments, and aerospace systems.