Plunger segments drive mechanism for a medicament delivery device

1. A drive mechanism for a medicament delivery device, wherein the drive mechanism comprises an elongated plunger rod, wherein the plunger rod comprises a number of discrete segments, interlocking elements arranged between adjacent segments operably arranged to releasably lock adjacent segments, drive force elements operably arranged to act between adjacent segments, and release elements operably arranged to act on the interlocking elements such that the segments are released in sequence,

wherein the interlocking elements comprise form-engaging elements, and

wherein the interlocking elements comprise interlocking protrusions and recesses arranged on adjacent segments, the protrusions and recesses arranged generally radially in relation to each other.

2. The drive mechanism according to claim 1 , wherein the interlocking elements are arranged such that the radially innermost of the interlocking elements is movable inwards in the generally radial direction.

3. The drive mechanism according to claim 2 , wherein the release elements are operably connected to the innermost interlocking elements such as to prevent movement inwards until activation of the drive mechanism.

4. The drive mechanism according to claim 3 , wherein the release element is a part of an adjacent, distally positioned, segment.

5. The drive mechanism according to claim 4 , wherein a segment is arranged with a passage in its distal end, that an adjacent, distally positioned, segment is arranged with a protrusion fitting into the passage, the protrusion fitting comprising the release elements.

6. The drive mechanism according to claim 5 , wherein the protrusion fitting is arranged flexible in a generally radial direction and wherein the release elements comprise an elongated element in contact with the protrusion fitting for preventing flexing in the generally radial direction.

7. The drive mechanism according to claim 6 , wherein the flexible arrangement comprises a generally longitudinally extending slit, the slit dividing the protrusion fitting in at least two parts, and wherein the elongated element extends into the slit.

8. The drive mechanism according to claim 1 , further comprising support elements arranged to support a segment when a proximally positioned segment has been distally displaced.

9. The drive mechanism according to claim 8 , wherein the support elements are arranged to prevent movement in the distal direction.

10. The drive mechanism according to claim 8 , wherein the support elements are comprised in the elongated element, the support elements comprising a proximally directed surface.

11. The drive mechanism according to claim 10 , wherein the proximally directed surface is arranged on a flexing arm that flexes in a generally transversal direction when the elongated element is moved out of contact with the slit.

12. The drive mechanism according to claim 10 , wherein the drive force elements are operably arranged such that the gap of the slit is reduced when the elongated element is moved out of the slit.

13. The drive mechanism according to claim 1 , wherein characteristics of the drive force elements are selected independently for meeting injection force requirements.

14. A medicament delivery device comprising a drive mechanism according to claim 1 .