Patent ID: 9597459
Date: 2017-03-21
CPC Classifications: A61M

Claim:
1. A drive mechanism for a drug delivery device which can be switched between a normal operation mode and a reset mode, the drive mechanism comprising a housing having a proximal end and a distal end; a piston rod which is adapted to be displaced in a distal direction with respect to the housing for delivering a dose in a normal operation mode of the drive mechanism, and which is adapted to be displaced in the proximal direction with respect to the housing in a reset mode of the drive mechanism; a retractable spline connection that releasably engages the piston rod in the normal operation mode and disengages the piston rod in the reset mode; a drive member which is rotationally moveable in a rotation direction with respect to the housing, wherein, in the normal operation mode, the drive member is rotationally locked with the piston rod through engagement of the retractable spline connection so that rotational movement of the drive member in the rotation direction with respect to the housing is converted into movement of the piston rod in the distal direction with respect to the housing yet allowing axial movement between the drive member and the piston rod, and wherein, in the reset mode, the piston rod is decoupled from the drive member by retraction of the spline connection; and a stop member configured to prevent rotational movement of the drive member relative to the housing during dose setting and to allow the the drive member to rotate with respect to the stop member during dose delivery, wherein, in the normal operation mode, the drive member is splined to the piston rod such that the drive member cannot rotate relative to the piston rod and rotational movement in the rotation direction of the drive member with respect to the housing is converted into rotational movement of the piston rod in the same direction, and in the reset mode the piston rod being rotatable with respect to the drive member for displacing the piston rod in the proximal direction.