Split piston metering pump

1 . A micropump for delivery of medication by infusion, comprising:

a reservoir; a cannula; a motor; and a gear;

a floating pump housing having a first aperture in fluid communication with the reservoir and a second aperture in fluid communication with the cannula, the floating pump housing having a drive rack engaged with the gear to move the pump housing axially;

a fixed piston and a floating piston axially oriented within the pump housing;

the fixed piston and the floating piston being positioned to close the first and second aperture at first and second axial positions, respectively, of the fixed piston and floating piston within the floating pump housing; wherein

the motor is engaged to the gear and the gear is engaged to the drive rack to translate the floating pump housing axially with respect to the fixed piston and the floating piston, wherein translating the drive floating piston with respect to the fixed piston defines a pump volume space within the floating pump housing;

wherein the fixed piston is in a fixed position, the floating piston is not coupled to the floating piston, and the floating pump housing is translated by the motor and gear to obtain said first and second axial positions; and

further comprising a cradle having a first keying rib receiving the fixed piston and maintaining the drive fixed piston in said fixed position, and a second keying rib receiving the floating piston, the floating piston having a groove contacting the second keying rib, wherein axial ends of the groove define the limits of axial movement of the floating piston against the second keying rib.

2 . The micropump of claim 1 , wherein axial movement of the floating pump housing first translated the floating piston, then translates the pump volume from a position oriented with the first aperture to a position oriented with the second aperture.

3 . A micropump for delivery of medication by infusion, comprising:

a reservoir; a cannula; a motor; a gear;

a pump housing having a first aperture in fluid communication with the reservoir and a second aperture in fluid communication with the cannula;

a drive piston comprising a rack, and a floating piston axially oriented within the pump housing;

the drive piston and the floating piston being positioned to close the first and second aperture at first and second axial positions, respectively, of the drive piston and floating piston within the pump housing; wherein

the motor is engaged to the gear and the gear is engaged to the rack to translate the drive piston axially with respect to the floating piston,

wherein the floating piston comprises a bore receiving a portion of the drive piston to define a pump volume space in the bore, and a through-hole on the floating piston fluidly connecting the bore and an outer surface of the floating piston, said through hole positioned to provide access to the reservoir via the first aperture in a first position and access to the cannula via the second aperture in a second position.

4 . The micropump according to claim 3 , comprising a radially positioned O-ring sealon the drive piston radially compressed against an interior surface of the bore in the floating piston.

5 . A micropump for delivery of medication by infusion, comprising:

a reservoir; a cannula; a motor; a gear;

a tubular pump housing having a first aperture in fluid communication with the reservoir and a second aperture in fluid communication with the cannula;

a drive rack operatively connected to the gear; a drive piston in the pump housing;

a floating piston axially aligned with the drive piston and coupled to the drive piston; at least one radial seal on the floating piston in frictional engagement with an interior surface of the pump housing, and at least one radial seal on the drive piston in frictional engagement with an interior surface of the pump housing; wherein

the motor is engaged to the gear, the gear is engaged to the drive rack and the drive rack is engaged to the drive piston to translate the drive piston and the floating piston axially within the pump housing; wherein

translating the drive piston with respect to the floating piston defines a pump volume space within the pump housing; and wherein

the floating piston closes the first aperture and the drive piston closes the second aperture at different axial positions of the drive piston and floating piston within the pump housing;

further comprising a first hook on the floating piston;

a second hook on one end of the drive piston coupled to the first hook on the floating piston;

a third hook on a second end of the drive piston axially opposite said first end of the drive piston; and

a fourth hook on the drive rack coupled to the third hook on the drive piston;

a gap between the first hook and the second hook permitting defined axial movement of the floating piston with respect to the drive piston; and

a gap between the third hook and the fourth hook permitting defined axial movement of the drive rack with respect to the drive piston.

6 . The micropump according to claim 5 , comprising a travel limit sensor operatively communicating with the gear when the drive rack is fully extended toward the pump housing and fully retracted from the pump housing.

7 . A micropump for delivery of medication by infusion, comprising:

a reservoir; a cannula; a motor; a gear; a drive piston comprising a rack;

a pump housing having a first aperture in fluid communication with the reservoir and a second aperture in fluid communication with the cannula;

the drive piston received in a floating piston axially arranged in the pump housing, the drive piston having a portion received in a bore in the floating piston, defining a pump volume space between the bore and the drive piston;

a through-hole on the floating piston fluidly connecting the bore and an outer surface of the floating piston,

said through hole positioned to provide access from the reservoir to the pump volume space via the first aperture in a first position and access from the pump volume space to the cannula via the second aperture in a second position.

8 . The micropump according to claim 7 , further comprising a coupling pin received through a slot in the floating piston and received into the drive piston, wherein the slot in the floating piston is elongated in the axial direction and has opposite axial ends defining the extent of axial movement of the drive piston in the bore of the floating piston.

9 . The micropump according to claim 7 , further comprising

a radial seal on the drive piston in frictional engagement with an interior surface of the bore of the floating piston;

two pairs of radially positioned seals on the floating piston in frictional engagement with an interior surface of the tubular pump housing.

10 . The micropump according to claim 7 , wherein

the drive piston comprises a single unitary element.

11 . The micropump according to claim 7 , wherein

the floating piston is provided with an elongated opening permitting access by the gear to the drive rack through the opening.

12 . The micropump according to claim 7 , wherein the drive piston comprises a rack portion and a piston portion, and the rack portion is coupled to the piston portion by a first hook on the rack portion engaging a second hook on the piston portion, wherein a gap between the first hook and the second hook permits axial movement of the rack portion with respect to the piston portion before the rack portion engages the piston portion.

13 . The micropump according to claim 7 , wherein the drive piston is completely received within the bore of the floating piston throughout the pump cycle.