AU1860697A — Pen-type injector drive mechanism

USPTO Abstract

A medication injection mechanism, for delivering a dosage of medication from a medication cartridge having a piston, includes a two-piece drive shaft, a rachet mechanism, and a drive mechanism. The two-piece drive shaft includes a plunger portion and a drive portion. The plunger portion has an end that contacts the piston of the medication cartridge, ratchet teeth disposed on the sides of the plunger portion that define a thickness of the plunger portion, and an opening to provide a passage through the plunger portion of the two-piece drive shaft. The drive portion is formed by rails that are coupled together by a connector that passes through the opening in the plunger portion so that the drive portion is coupled to the plunger portion, and can move relative to the plunger portion. Each of the rails forming the drive portion has threads on a surface that extend beyond the defined thickness of the plunger portion. The ratchet mechanism engages with the ratchet teeth of the plunger portion to permit the movement of the plunger portion toward the piston of the medication cartridge and to inhibit movement of the plunger portion away from the piston of the medication cartridge. Also, the drive mechanism engages with the threads on the rails of the drive portion, but is free of contact with the ratchet teeth on the plunger portion to adjust the position of the drive portion relative to the plunger portion so that the drive portion can be moved toward the piston of the medication cartridge a fixed distance and the plunger portion is moved a distance that is less than or equal to the fixed distance.