MAGNETIC SUSPENSION CONTROLS FOR A NEW CONTINUOUS-FLOW VENTRICULAR ASSIST DEVICE

A new continuous flow ventricular assist device (CFVAD III) using a fu ll magnetic suspension has been constructed. The magnetic suspension c enters the centrifugal impeller within the clearance passages in the p ump, thus avoiding any contact. This noncontact operation gives very h igh expected mechanical reliability, large clearances, low hemolysis, low thrombosis, and relatively small size compared with current pulsat ile devices. A unique configuration of a system of magnetic actuators on the inlet side and exit sides of the impeller gives full five axis control and suspension of the impeller. The bearing system is divided into segments that allow for three displacement axes and two angular c ontrol axes. For the first suspension tests, a decentralized set of pr oportional, derivative, and integral (PID) controllers acting along th e modal coordinates are used to suspend the impeller. The controller d esign takes into account the blood forces acting on the magnetically s uspended impeller, the unbalance forces on the impeller and gravitatio nal loads during various body motions. In the final design, the bearin g control axes will be coupled together through fluidic forces so the electronic feedback controller is a centralized multiple input, multip le output controller. The control system design must be robust against these types of externally imposed loads to keep the impeller centered and avoid blood damage. This article discusses the dynamic model, con troller, and controller implementation for the magnetic suspension con troller of CFVAD III.