Abstract
An extracorporeal magnetically levitated blood pump, which consists of an axial magnetic bearing, a levitated impeller and an axial flux motor, has been developed to recover cardiac function of acute heart failure patients. Rotating speed of a levitated impeller is changed in synchronization with heart beat to increase coronary flow of a natural heart or reduce load of the natural heart. The transient change in the rotating speed of the impeller causes a detection error of rotating angle, which prevents maintaining constant phase difference between rotor flux and control flux. Increase/decrease in axial attractive force produced by the motor due to the variation of phase difference deteriorates suspension stability of the maglev motor. In this study, a magnetic coupling mechanism which can reduce the variation of phase difference was employed to transfer torque to the levitated impeller. Dynamic characteristics of the maglev motor with the developed magnetic coupling mechanism were then evaluated. The rotating speed of the levitated impeller was transiently changed from 1200 rpm to 2400 rpm in physiological saline medium. Maximum oscillation amplitude of 0.13 mm in the previous maglev motor was successfully decreased to 0.05 mm by utilizing the magnetic coupling mechanism. In contrast, there was no significant change in radial displacement of the levitated impeller according to the motor drive mechanism. In the future, magnetic levitation stability will be improved by optimizing the size and arrangement of the rotor permanent magnets for magnetic coupling motor.
