Alternating pump gaps

1. A blood pump system, comprising:

a pump housing;

an impeller for rotating in a pump chamber within the housing;

a stator comprising drive coils for applying force to the impeller;

a field oriented control (FOC) device for controlling the drive coils;

at least one bearing mechanism for suspending the impeller within the pump chamber;

a sensing circuit for determining an axial position of the impeller; and

a position control mechanism for moving the impeller in an axial direction between a first eccentric position and a second eccentric position within the pump chamber by controlling, based on the axial position of the impeller, a stator coil flux current provided to the FOC device, independent of a quadrature current provided by a speed control device to the FOC device to control a torque applied to the impeller.

2. The blood pump system of claim 1 , wherein:

the position control mechanism is configured to move the impeller based on a triggering event.

3. The blood pump system of claim 1 , wherein:

the position control mechanism is configured to move the impeller based on the impeller crossing a speed threshold.

4. The blood pump system of claim 3 , wherein:

the speed threshold is a low speed threshold.

5. A blood pump system, comprising:

a pump housing;

an impeller for rotating in a pump chamber within the housing;

a stator comprising drive coils for applying force to the impeller;

a field oriented control (FOC) device for controlling the drive coils;

a first bearing for suspending the impeller relative to a first end of the pump chamber, a first blood gap defined between the impeller and a first bearing surface;

a second bearing for suspending the impeller relative to a second end of the pump chamber, a second blood gap defined between the impeller and a second bearing surface;

a sensing circuit for determining an axial position of the impeller; and

a position control mechanism for moving the impeller in an axial direction between a first eccentric position and a second eccentric position within the pump chamber by controlling, based on the axial position of the impeller, a stator coil flux current provided to the FOC device, independent of a quadrature current provided by a speed control device to the FOC device to control a torque applied to the impeller.

6. The blood pump system of claim 5 , wherein:

the position control mechanism is configured to move the impeller based on the impeller crossing a speed threshold.

7. The blood pump system of claim 5 , wherein:

the sensing circuit is configured to:

receive two measured currents corresponding to a first phase and a second phase of the drive coils;

calculate a current corresponding to a third phase of the drive coils; and

estimate the axial position of the impeller.

8. The blood pump system of claim 5 , wherein:

the position control mechanism is configured to move the impeller based on a triggering event.

9. The blood pump system of claim 8 , wherein:

the triggering event comprises an impeller speed threshold or a time threshold.

10. The blood pump system of claim 5 , wherein:

the position control mechanism is configured to move the impeller in the axial direction to reduce the first blood gap and to increase the second blood gap thereby increasing a washout rate at the second blood gap.

11. A method of operating a blood pump including a housing and an impeller for rotating within a pump chamber within the housing, comprising:

rotating the impeller within the pump chamber with a stator, the impeller being suspended within the pump chamber by a first bearing at a first end of the pump chamber and a second bearing at a second end of the pump chamber; and

moving the impeller in an axial direction between a first eccentric position and a second eccentric position within the pump chamber by engaging a position control mechanism which controls a stator coil flux current provided to a field oriented control (FOC) device controlling drive coils of the stator, independent of a quadrature current provided to the FOC device to control a torque applied to the impeller.

12. The method of operating a blood pump including a housing and an impeller for rotating within a pump chamber within the housing of claim 11 , wherein:

moving the impeller comprises adjusting a magnetic flux between the impeller and the drive coils.

13. The method of operating a blood pump including a housing and an impeller for rotating within a pump chamber within the housing of claim 11 , wherein:

the method further comprises:

receiving two measured currents corresponding to a first phase and a second phase of the drive coils;

calculating a current corresponding to a third phase of the drive coils; and

estimating an axial position of the impeller; and

wherein controlling the stator coil flux current is based on the axial position of the impeller.

14. The method of operating a blood pump including a housing and an impeller for rotating within a pump chamber within the housing of claim 11 , wherein moving the impeller comprises:

moving the impeller periodically and intermittently.

15. The method of operating a blood pump including a housing and an impeller for rotating within a pump chamber within the housing of claim 11 , wherein moving the impeller comprises:

moving the impeller based on a triggering event.

16. The method of operating a blood pump including a housing and an impeller for rotating within a pump chamber within the housing of claim 15 , wherein:

the triggering event comprises an impeller speed threshold or a time threshold.