Claims for Patent: 9,084,853

Summary for Patent: 9,084,853

Title:	Drive mechanism for a drug delivery device and drug delivery device
Abstract:	A lead screw, a lead screw nut and a drive member are aligned with an axis. A coupling between the lead screw and the lead screw nut allows a helical movement of the lead screw. The drive member is rotationally locked with the lead screw nut. The lead screw is coupled with the drive member to generate a helical movement of the lead screw when the drive member is moved in one axial direction. The coupling is overridden when the drive member is moved in the opposite axial direction. Spline features are arranged on the lead screw in a row parallel to the axis with alternatingly small and large gaps between succeeding spline features. A stop feature of the drive member has a dimension in the direction of the axis which is larger than the small gaps and at most as large as the large gaps.
Inventor(s):	Plumptre; David Aubrey (Worcestershire, GB)
Assignee:	Sanofi-Aventis Deutschland GmbH (Frankfurt am Main, DE)
Application Number:	13/825,813
Patent Claims:	1. A drive mechanism for a drug delivery device, comprising: a lead screw comprising a first screw thread, a lead screw nut and a drive member, aligned with an axis defining an axial direction and an opposite axial direction, a coupling between the lead screw and the lead screw nut allowing a helical movement of the lead screw with respect to the lead screw nut at least in the axial direction, the drive member being 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, spline features of the lead screw, the spline features being arranged in at least one row parallel to the axis with alternatingly small and large gaps between succeeding spline features, and a stop feature of the drive member, the stop feature facing the lead screw, a dimension of the stop feature in the direction of the axis being larger than the small gaps and at most as large as the large gaps. 2. The drive mechanism according to claim 1, further comprising: a second screw thread of the lead screw, the first screw thread and the second screw thread comprising the same pitch and being intertwined. 3. The drive mechanism according to claim 2, wherein the spline features are each arranged adjacent to the first screw thread or adjacent to the second screw thread. 4. The drive mechanism according to claim 1, wherein the spline features are protruding elements of the lead screw. 5. The drive mechanism according to claim 1, 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. 6. The drive mechanism according to claim 1, 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. 7. The drive mechanism according to claim 6, wherein at least some of the spline features are arranged adjacent to the stop features of the lead screw. 8. The drive mechanism according to claim 1, wherein the drive member is a drive sleeve, the lead screw passing through the drive member, and the stop feature of the drive member is a protruding element or two separate protruding elements or a plurality of separate protruding elements located on an inner sidewall of the drive member. 9. The drive mechanism according to claim 1, wherein the spline features are arranged in at least two rows parallel to the axis, the rows being equi-spaced around a circumference of the lead screw. 10. 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. 11. The drug delivery device according to claim 10, further comprising: a guide feature of the drive member, the guide feature preventing a rotation of the drive member with respect to the body, and the lead screw nut being rotationally locked with the body, the drive member thus being rotationally locked with the lead screw nut.