Drive mechanism for an injection device
View Patent ↗A drive mechanism for an injection device is disclosed in which piston means are selectively driven to expel medicament from within a medicament cartridge. The drive mechanism comprises a drive means ( 270 ), first means ( 278 ) associated with the drive means, second gear means ( 274 ) being moveable between a first position in wich only movement along its longitudinal axis is permitted and a second position in which the second gear means ( 274 ) is free to rotate about the longitudinal axis, the piston means ( 280 ) being associated with the second gear means ( 274 ), a housing ( 276 ) within which the first gear means ( 278 ) and the second gear means ( 274 ) are constrained for movement, and biassing means ( 282 ) located between the housing ( 276 ) and a second gear means ( 274 ) to bias the second gear means ( 274 ) to the first position.
1. A drive mechanism for an injection device in which piston means are selectively driven to expel medicament from within a medicament cartridge, the drive mechanism comprising:
a drive means;
a first gear means associated with the drive means;
a second gear means moveable between a first position in which only movement along a longitudinal axis of the second gear means is permitted and a second position in which the second gear means is free to rotate about the longitudinal axis;
a piston means associated with the second gear means;
a housing within which the first gear means and the second gear means are constrained for movement; and
a biasing means located between the housing and the second gear means to bias the second gear means to the first position.
2. A drive mechanism according to claim 1 , wherein one of the second gear means and the housing is provided with a plurality of splines and the other of the second gear means and the housing is provided with keyways within which the splines are located when the second gear means is in the first position.
3. A drive mechanism according to claim 1 , wherein a first movement of the drive means causes the first gear means to advance from an initial position towards the second gear means causing the second gear means to be displaced from the first position to the second position and a second movement of the drive means causes the first gear means to return to the initial position thereby allowing the second drive means to rotate and return to the first position under the action of the biasing means.
4. A drive mechanism according to claim 1 , wherein the drive means comprised a push pull solenoid.
5. A drive mechanism according to claim 1 , wherein the biasing means comprised a helical spring.
6. A drive mechanism according to claim 1 , wherein the piston means comprises a lead screw.
7. A drive mechanism according to claim 2 , wherein a first movement of the drive means causes the first gear means to advance from an initial position towards the second gear means causing the second gear means to be displaced from the first position to the second position and a second movement of the drive means causes the first gear means to return to the initial position thereby allowing the second drive means to rotate and return to the first position under the action of the biasing means.
8. A drive mechanism according to claim 2 , wherein the drive means comprised a push pull solenoid.
9. A drive mechanism according to claim 3 , wherein the drive means comprised a push pull solenoid.
10. A drive mechanism according to claim 2 , wherein the biasing means comprised a helical spring.
11. A drive mechanism according to claim 3 , wherein the biasing means comprised a helical spring.
12. A drive mechanism according to claim 4 , wherein the biasing means comprised a helical spring.
13. A drive mechanism according to claim 2 , wherein the piston means comprises a lead screw.
14. A drive mechanism according to claim 3 , wherein the piston means comprises a lead screw.
15. A drive mechanism according to claim 4 , wherein the piston means comprises a lead screw.
16. A drive mechanism according to claim 5 , wherein the piston means comprises a lead screw.