Injection device
View Patent ↗Injection devices are known for the self administration of medicament by patients, in which the medicament is typically contained within a cartridge located within the injection device. It is a problem that injection devices should be small enough to fit into a jacket pocket or a hand bag without difficulty. Also, the injection device must be of a size that enables a piston or the like used to drive the cartridge bung within the cartridge to be moved both to a maximum dispense position within the cartridge and to be fully withdrawn from the cartridge to allow for replacement of the cartridge. A drive mechanism for an injection device is disclosed in which a piston 42 comprises a first piston part 44 guided for linear movement to selectively drive a bung 18 and a second piston part 46 connected for pivoting movement with respect to the first piston part 44.
1. A drive mechanism for an injection device, comprising:
a piston that is successively moved in relation to a first end of a medicament cartridge containing a medicament selectively to drive a bung closing a first end of the medicament cartridge into the medicament cartridge to expel medicament through a delivery member located at a second end of the medicament cartridge, the piston further comprising:
a first piston part guided for linear movement to selectively drive the bung; and
a second piston part connected for pivoting movement with respect to the first piston part,
wherein the piston is driven through a dispense gear by a dosing shaft.
2. A drive mechanism according to claim 1 , further comprising a transmission mechanism between a dial dose mechanism and the piston.
3. An injection device incorporating a drive mechanism according to claim 2 .
4. A drive mechanism according to claim 2 , wherein the transmission mechanism comprises a dose setting mechanism connected to drive the piston through the dispense gear.
5. An injection device incorporating a drive mechanism according to claim 4 .
6. A drive mechanism according to claim 4 , wherein the dose setting mechanism comprises a spline connecting the dosing shaft to the dial dose mechanism, the dosing shaft having an abutment surface at one end.
7. An injection device incorporating a drive mechanism according to claim 6 .
8. A drive mechanism according to claim 6 , wherein a button has a stop surface for abutment with the abutment surface of the dosing shaft.
9. An injection device incorporating a drive mechanism according to claim 8 .
10. An injection device incorporating a drive mechanism according to claim 1 .
11. An injection device according to claim 10 , further comprising a drive means selectively to drive the bung having a button displaceably housed in the injection device.