PERFORMANCE OF A CONTINUOUS-FLOW VENTRICULAR ASSIST DEVICE - MAGNETICBEARING DESIGN, CONSTRUCTION, AND TESTING

A new centrifugal continuous flow ventricular assist device, the CFVAD III, which is fully magnetic bearing suspended, has been developed. I t has only one moving part (the impeller), has no contact (magnetic su spension), is compact, and has minimal heating. A centrifugal impeller of 2 inch outer diameter is driven by a permanent magnet brushless DC motor. This paper discusses the design, construction, testing, and pe rformance of the magnetic bearings in the unit. The magnetic suspensio n consists of an inlet side magnetic bearing and an outlet side magnet ic bearing, each divided into 8 pole segments to control axial and rad ial displacements as well as angular displacements. The magnetic actua tors are composed of several different materials to minimize size and weight while having sufficient load capacity to support the forces on the impeller. Flux levels in the range of 0.1 T are employed in the ma gnetic bearings. Self sensing electronic circuits (without physical se nsors) are employed to determine the impellar position and provide the feedback control signal needed for the magnetic bearing control loops . The sensors provide position sensitivity of approximately 0.025 mm. A decentralized 5 axis controller has been developed using modal contr ol techniques. Proportional integral derivative controls are used for each axis to levitate the magnetically supported impeller.