Patent ID: 7195616

Claim:
A resettable, cartridge plunger drive assembly of a dose injecting mechanism of a medication injector apparatus, the apparatus including a reusable base and a cartridge assembly mountable to the base, the base having a rotatable drive member of the dose injecting mechanism within a base housing, the cartridge assembly having a medicine-filled cartridge with a movable plunger at one end and an outlet at the other end, the drive assembly comprising: a nut keyed to the base housing to be both movable relative thereto between first and second axial positions, and rotatably fixed relative thereto at said first and second axial positions, said nut including an internally threaded opening; a screw including a plunger-engaging distal end and external threading in threaded engagement with said internally threaded opening of said nut; a drive clutch connected to said nut to be axially retained and rotatably movable relative thereto, said drive clutch keyed to said screw to be rotatably fixed and axially movable relative thereto; said nut positioned within the base housing to be axially movable from said first axial position to said second axial position by engagement with the cartridge assembly during mounting of the cartridge assembly to the reusable base, wherein said drive clutch is in torque transmitting engagement with the rotatable drive member when said nut is disposed in said second axial position, whereby rotation of the drive member during operation of the dose injecting mechanism rotates said drive clutch and thereby said screw to produce axial movement of said screw in a distal direction through said nut to thereby advance the plunger-engaging distal end of said screw to force medication from the cartridge outlet; and a biasing element that biases said nut from said second axial position toward said first axial position when the cartridge assembly is not mounted to the reusable base, wherein said drive clutch is disengaged from torque transmitting engagement with the rotatable drive member when said nut is disposed in said first axial position, whereby application of a force in a proximal direction on said plunger-engaging distal end of said screw axially moves said screw in a proximal direction as it screws through said nut to thereby reset said screw.