Patent ID: 7442186

Claim:
A medication pump comprising: a cartridge chamber for receiving a medication cartridge, the chamber comprising a first open end for receiving the medication cartridge, a second end defining a drive rod opening, and a cartridge chamber wall extending from the first open end to the second end; wherein the cartridge chamber wall is generally cyclindrical; a motor; a drive rod comprising an interface end, wherein the interface end of the drive rod extends into the cartridge chamber through the drive rod opening, wherein the drive rod is configured to be axially moved by the motor; and a light sensor positioned near the second end of the cartridge chamber configured to detect whether the medication cartridge is located within the cartridge chamber near the second end of the cartridge chamber, wherein the light sensor comprises an emitter and a detector, wherein the emitter and the detector are positioned on the cylindrical cartridge chamber wall at opposite ends of chord through the cartridge chamber, wherein the chord connects two points on the cylindrical cartridge chamber wall.