Abstract:
The VentrAssist implantable rotary blood pump, intended for long term ventricular assist, is under
development and is currently being tested for its rotor-dynamic stability. The pump consists of a shaftless
impeller, which also acts as the rotor of the brushless DC motor. The impeller remains passively
suspended in the pump cavity by hydrodynamic forces, which result from the small clearances between
the outside surfaces of the impeller and the pump cavity. These small clearances range from
approximately 50 um to 230 um in size.
This paper presents experimental investigation of the displacement of the impelIer within the cavity.
Displacement of the impeller was measured using eddy-current proximity sensors and laser displacement
proximity sensors, located at different positions on the pump, under different pump-operating conditions.
All transducers have been calibrated prior to any experimental. Voltage output from the transducers were
converted into impeller movement in five independant physical coordinates (x, y, z, 0x and 0y). The sixth
degree of freedom (0z), the rotation about the impeller axis, is determined by the commutation performed
by the motor controller.
To determine experimentally the dynamic characteristics of the hydrodynamic bearing, a computer
program was developed to calculate the axial bearing force exerted on an impeller blade. By combining
the calculated force with the measured impeller displacement, the stiffness and damping coefficients were
determined.
