Medication injector apparatus with drive assembly that facilitates reset

摘要

A medication injector apparatus such as an injection pen. The injection pen includes a resettable, cartridge plunger drive assembly including an axially floating nut, a cartridge plunger engaging screw, and a drive clutch movable with the nut and which when rotated causes the screw to screw through the nut. When a cartridge assembly is mounted to the pen base, the floating nut and drive clutch are shifted proximally such that the drive clutch is in torque transmitting engagement with a rotatable drive member of the pen, such that rotation of that drive member results in drive screw advancement through the nut in the distal direction. When the cartridge assembly is not mounted to the pen base, the floating nut and drive clutch are biased distally to disengage the drive clutch from torque transmitting engagement with the rotatable drive member and to thereby allow the drive screw to be reset proximally through the nut to a position more retracted within the pen base. The injection pen further may include an assembly for selectively rotating a drive sleeve (710) of the pen, which assembly has a dial (680) that rotates out during dose setting and which translates in without rotation during dose injecting.