Bearing Dynamic Characteristics of the Ventrassist Rotary Blood Pump

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. A shaftless impeller, which also acts as the rotor of the brushless DC motor, is passively suspended in the pump cavity by hydrodynamic forces. The paper presents experimental investigation of the displacement of the impeller within the cavity, which will play an integral role in obtaining approval for clinical trials. Displacement of the impeller is measured using Hall effect sensors located at different positions on the pump under different pump-operating conditions. Voltage output from the sensors are converted into impeller movement in five degrees of freedom (x, y, z, Ox and Oy). The sixth degree of freedom (Oz), the rotation about the impeller axis, is determined by the commutation performed by the motor controller. To determine experimentally the undamped dynamic characteristic of the hydrodynamic bearing, future measurements of bearing forces combined with the results of impeller displacement presented in this paper will allow for the calculation of stiffness coefficients for the hydrodynamic bearing.