Pen-type injector
The present invention relates to injectors, such as pen-type injectors, that provide for administration of medicinal products from a multidose-cartridge and permit a user to set the delivery dose. The injector may include a housing, a piston rod adapted to operate through the housing, a dose dial sleeve located between the housing and the piston rod, and a drive sleeve located between the dose dial sleeve and the piston rod. The dose dial sleeve may have a helical thread of first lead and the drive sleeve may have a helical groove of second lead. The first lead of the helical thread and the second lead of the helical groove may be the same.
1. A drive mechanism for use in a drug delivery device comprising:
a housing having a longitudinal axis and comprising an inner surface with an insert that is rotationally and axially fixed relative to the housing;
a piston rod positioned and aligned with the longitudinal axis having a first thread on a first end that is engaged with the insert; and
a drive sleeve that extends about the piston rod and has internal and outer surfaces, where the internal surface is engaged with the piston rod;
wherein longitudinal axial movement of the drive sleeve causes the piston rod to rotate through the insert relative to the housing.
2. The drive mechanism of claim 1 where the rotation of the piston rod advances a piston in a cartridge.
3. The drive mechanism of claim 1 where the piston rod has a second thread on a second end.
4. The drive mechanism of claim 3 where the drive sleeve has an internal surface comprising a helical groove that engages the second thread of the piston rod.
5. The drive mechanism of claim 4 further comprising a dose dial sleeve having an outer surface having a helical thread with a lead, where the helical groove of the drive sleeve has a lead that is equal to the lead of the helical thread of the helical thread on the dose dial sleeve.
6. The drive mechanism of claim 5 where the first thread and second thread have opposing directions to prevent the piston rod from rotating when the dose dial sleeve is extended axially from the housing.
7. The drive mechanism of claim 3 where the first thread has a different lead than the second thread.
8. The drive mechanism of claim 3 where the second thread comprises a series of part threads.
9. The drive mechanism of claim 3 where the first thread of the piston rod is oppositely disposed to the second thread of the piston rod.
10. The drive mechanism of claim 3 where the piston rod further comprises a receiving recess at the second end that accepts a stem of a button.