Tri-chamber nutating pump

1. A nutating pump, comprising:

a nutating piston disposed in a pump housing, the pump housing comprising an inlet and an outlet, the pump housing further comprising a middle passage extending through the pump housing and intersecting the inlet and the outlet, the middle passage including a middle section disposed between the inlet and the outlet and a distal section disposed opposite the inlet from the outlet and terminating at an enclosure,

the nutating piston comprising a proximal section and a distal end with a pump section disposed therebetween, the pump section at least partially and slidably accommodated in the middle section of the middle passage with the pump section extending at least partially across the inlet to the distal section of the middle passage, the proximal section of the nutating piston extending at least partially across the outlet, the pump section of the nutating piston comprising a recess extending across at least part of the pump section to the distal end of the nutating piston,

the proximal section of the nutating piston having a first maximum outer diameter, the pump section of the nutating piston having a second maximum outer diameter that is greater than the first maximum outer diameter, the proximal section connected to the pump section at a transition section, the proximal section of the nutating piston coupled to a drive shaft,

the pump housing and the nutating piston defining two pump chambers including a first pump chamber and a second pump chamber, the first pump chamber defined by the distal end and the recess of the nutating piston and the distal section of the middle passage,

the second pump chamber defined by the transition section and a portion of the proximal section of the nutating piston that extends across the outlet of the pump housing and between the outer passage and the outlet,

the outlet in communication with a through passage of a compensating housing, the through passage extending past a compensating piston at a third pump chamber disposed in the through passage, the compensating piston being slidably and sealably accommodated in the compensating housing, the compensating piston including a distal end directed towards the through passage and a proximal end engaging a bearing, the bearing engaging a cam, the cam coupled to the drive shaft,

wherein rotation of the drive shaft causing rotation of the cam, which imparts reciprocating movement to the bearing and the nutating piston thereby causing reciprocating movement of the distal end of the nutating piston into and out of the through passage.

2. The nutating pump of claim 1 wherein the middle passage of the pump housing extends at least substantially perpendicular to the inlet and the outlet and the outer passage of the pump housing extends at least substantially parallel to the middle passage.

3. The nutating pump of claim 1 wherein the outlet of the pump housing is connected to an outlet housing disposed between the outlet and the compensating housing, the outlet housing having an outlet passage providing communication between the outlet and the through passage.

4. The nutating pump of claim 1 wherein the compensating piston is slidably accommodated in a liner, the liner having a distal end facing the through passage of the compensating housing and a proximal end engaging a primary seal for inhibiting leakage between the compensating piston and the liner.

5. The nutating pump of claim 4 wherein the primary seal is annular and has an outer periphery, the outer periphery comprising a slot for accommodating an O-ring, the O-ring sandwiched between the outer periphery of the seal and a seal retainer, the seal retainer including a proximal end with an opening through which the compensating piston passes, the proximal end connected to a distal end by a continuous sidewall, the distal end of the seal retainer being biased against the compensating housing by a spring, the spring also biasing the proximal end of the compensating piston against the bearing.

6. The nutating pump of claim 1 wherein the cam, the compensating piston and the nutating piston are arranged so that when a cumulative output from the first and second pump chambers is at a maximum, a compensating output from the third pump chamber is at a minimum.

7. The nutating pump of claim 1 wherein the cam, the compensating piston and the nutating piston are arranged so that when a cumulative output from the first and second pump chambers is at a minimum, a compensating output from the third pump chamber is at a maximum.

8. The nutating pump of claim 1 wherein the drive shaft is coupled to a stepper motor.

9. The nutating pump of claim 1 wherein the pump housing and the compensating housing are molded from a plastic material.

10. A method for providing a steady state output flow from a nutating pump that is operating at a constant motor speed, the method comprising:

providing a nutating pump with a first pump chamber, a second pump chamber, and a nutating piston, the first pump chamber producing a first output in response to a first 180° of rotation of the nutating piston, the second pump chamber producing a second output in response to a second 180° of rotation of the nutating piston, the nutating pump including an outlet,

providing a compensating piston with a distal end that faces the outlet when the compensating piston is in a retracted position and that extends into the outlet when the compensating piston is in an extended position,

extending the compensating piston into the outlet when a cumulative output from the first and second pump chambers approaches a maximum level, and

retracting the compensating piston from the outlet when the cumulative output from the first and second pump chambers approaches a minimum level.