Drive mechanism for a drug delivery device and drug delivery device
The drive mechanism comprises a lead screw ( 5 ) and a lead screw nut, which are aligned with an axis ( 4 ). The lead screw has screw threads ( 6, 16 ) having the same pitch and being intertwined.
1. A drive mechanism for a drug delivery device, comprising:
a lead screw and a lead screw nut aligned with an axis defining an axial direction, and an opposite axial direction, and radial directions diverging from the axis,
the lead screw comprising (i) a screw thread and (ii) at least one further screw thread, the screw thread and the at least one further screw thread having the same pitch and being intertwined, and
a drive feature of the lead screw nut, the drive feature comprising three angularly equi-spaced drive portions;
the drive feature engaging the screw thread and the further screw thread and allowing for a dispense operation of a fixed dose,
the dispense operation comprising a helical movement of the lead screw with respect to the lead screw nut at least in the axial direction,
the lead screw advancing a piston in a distal direction.
2. The drive mechanism according to claim 1 , further comprising:
a drive member rotationally locked with the lead screw nut,
the lead screw being coupled with the drive member, the coupling generating a helical movement of the lead screw with respect to the drive member when the drive member is moved in the axial direction with respect to the lead screw, and the coupling being overridden to prevent a helical movement of the lead screw with respect to the drive member when the drive member is moved in the opposite axial direction with respect to the lead screw.
3. The drive mechanism according to claim 2 , further comprising:
a flexible guide feature of the lead screw, and
a screw thread of the drive member,
the flexible guide feature of the lead screw and the screw thread of the drive member providing the coupling of the lead screw with the drive member.
4. The drive mechanism according to claim 3 , wherein the screw thread of the drive member has two separate co-axial helical features.
5. The drive mechanism according to claim 2 , further comprising:
stop features of the lead screw, the stop features inhibiting the helical movement of the lead screw when the drive member is moved in the opposite axial direction with respect to the lead screw.
6. The drive mechanism according to claim 1 , wherein the drive feature of the lead screw nut comprises at least two separate parts protruding from an inner surface of the lead screw nut.
7. The drive mechanism according to claim 1 , wherein the drive feature of the lead screw nut is tapered towards the screw thread of the lead screw.
8. The drive mechanism according to claim 1 , wherein
two or more portions of the drive feature of the lead screw nut engage a same screw thread of the lead screw.
9. A drug delivery device, comprising:
a drive mechanism according to claim 1 , and
a body having a distal end and a proximal end, which are spaced apart in the direction of the axis.