Hybrid passive levitation mechanism utilizing thrust force and magnetic force for a pump application

The durability of a blood pump has been enhanced owing to the development of contactless bearings. According to Earnshaw’s law, levitation in all six degrees of freedom cannot be realized using a static magnetic field. Therefore, the combination of passive magnetic bearings and active magnetic bearings or passive magnetic bearings and hydrodynamic bearings are commonly adopted in the blood pump. However, the active magnetic bearings exhibit a risk of malfunctioning of their control system, and the hydrodynamic bearings exhibit a risk of blood trauma owing to their narrow gaps. Therefore, the objective of this study is to develop a passive levitation system for an impeller with a large gap without active control. The large gap prevents blood damage, and passive levitation contributes to reduce the risk of device malfunction. In this study, hybrid passive levitation mechanism utilizing thrust force and magnetic force is proposed. The thrust force generated by the rotation of the impeller changes depending on the interaction between the housing geometry and impeller position, even with a large gap. Considering this characteristic, the impeller was levitated by balancing the magnetic force generated by the permanent magnets and the thrust force in the axial direction. The movements in the radial and angular directions are passively supported by the restoring force and torque generated by the permanent magnets. The geometry of the pump and dimensions of the permanent magnets were designed so that the mechanism had positive stiffness in all directions. The levitation of the impeller in the axial direction was confirmed in the experiment by the pump prototype.