Novel non-contact adjustable torsional electromagnetic negative stiffness device: theoretical analysis and application

To address the issue that traditional quasi-zero-stiffness (QZS) torsional vibration isolation systems struggle to adapt to time-varying loads due to their fixed structural parameters, this paper proposes a novel non-contact adjustable torsional electromagnetic negative stiffness device (ATENSD). Through the axial electromagnetic coupling between the iron-core coils and the permanent magnets, the ATENSD can generate rotational negative stiffness which can be dynamically adjusted by regulating the current of the iron-core coil. Firstly, the fundamental configuration of the ATENSD is introduced, and the principle of its variable negative stiffness is analyzed. Subsequently, electromagnetic finite element analysis are employed to elucidate the influence of the permanent magnet shape, the permanent magnet thickness, the pole-pair number and the magnetic-pole angle on the ATENSD stiffness characteristics, for guiding the prototype design. Moreover, the analytical electromagnetic-force model of the ATENSD is established by the magnetic energy method. And a comparative analysis is then conducted to examine the influence laws of the control current and the air gap on the electromagnetic torque and stiffness characteristics of the ATENSD. Finally, stiffness characterization experiments and vibration transmission test experiments are conducted on the ATENSD prototype. The results demonstrate that the designed ATENSD achieves continuously adjustable negative stiffness with good linearity during current regulation. And the QZS adjustable electromagnetic torsional isolator (QZS-AETI), integrated with the ATENSD, has a good vibration transmission suppression effect across the entire frequency range.