Drive assembly suitable for use in a medication delivery device and medication delivery device
A drive assembly comprises a housing, a drive member moveable for setting a dose and for delivering the dose. A piston rod adapted to be driven by the drive member in the distal direction during movement of the drive member in the distal direction for dose delivery and a restriction member for restricting proximal movement of the piston rod during proximal movement of the drive member by mechanical interaction of the restriction member with a stop feature. The restriction member and stop feature arranged for the piston rod to be moved proximally a first distance during a first movement of the drive member before the restriction member and stop feature interact mechanically. The first distance the piston rod moves proximally during the first movement of the drive member is different than a subsequent distance the piston rod moves during a subsequent proximal movement of the drive member.
1. A drive assembly for use in a medication delivery device, comprising:
a housing configured to be secured to a cartridge retaining part, the housing having a proximal end and a distal end, wherein the proximal end is an end furthest away from a dispensing end of the medication delivery device,
a drive member moveable in a proximal direction with respect to the housing for setting a dose of a medication to be delivered and in a distal direction with respect to the housing for delivering the dose,
a piston rod adapted to be driven by the drive member in the distal direction with respect to the housing during a movement of the drive member in the distal direction for delivering the dose,
wherein the piston rod comprises
a bearing surface at a distal end of the piston rod to abut a proximal face of a piston and
a plurality of stop features, provided on an external surface of the piston rod, and
a rotationally fixed restriction member for restricting a proximal movement of the piston rod with respect to the housing during a proximal movement of the drive member by mechanical interaction of the restriction member with one stop feature of the plurality of stop features,
wherein
the restriction member and the one a first stop feature of the plurality of stop features are arranged for the piston rod to be moved proximally a first distance during a first proximal movement of the drive member for setting a first dose before the restriction member and the one stop feature interact mechanically,
wherein the drive assembly is configured such that, after a distal movement of the drive member for delivering the first dose, the restriction member mechanically interacts with a second stop feature different than the one stop feature,
wherein the piston rod and the restriction member are arranged for the proximal movement of the piston rod to be restricted during a second and any subsequent proximal movement of the drive member for setting a second and any subsequent dose by the restriction member already mechanically interacting with the second stop feature different from the one stop feature before the second and any subsequent proximal movement of the drive member for setting the second and any subsequent dose, and
wherein the first distance which the piston rod moves proximally during the first proximal movement of the drive member is different than a subsequent distance which the piston rod moves proximally during a subsequent proximal movement of the drive member.
2. The drive assembly according to claim 1 , wherein a priming movement of the drive member comprises the first proximal movement of the drive member.
3. The drive assembly according to claim 1 , wherein the drive member and the piston rod are releasably engaged.
4. The drive assembly according to claim 1 , wherein the restriction member engages the piston rod.
5. The drive assembly according to claim 1 , wherein the restriction member is secured against at least one of or both of rotational movement with respect to the housing and axial movement with respect to the housing.
6. The drive assembly according to claim 1 , wherein the one stop feature is provided on an outer surface of the piston rod.
7. The drive assembly according to claim 1 , wherein the plurality of stop features are arranged equidistantly along the piston rod.
8. The drive assembly according to claim 7 , wherein the piston rod and the restriction member are arranged for the proximal movement of the piston rod to be prevented during the second and any subsequent proximal movement of the drive member for setting the dose by the restriction member already mechanically interacting with the one stop feature before the second and any subsequent proximal movement of the drive member for setting the dose.
9. The drive assembly according to claim 1 , wherein the first distance is greater than a distance which the piston rod moves proximally subsequent to the distal movement of the piston rod for delivering the dose.
10. The drive assembly according to claim 1 , wherein the first distance which the piston rod moves proximally during the first proximal movement of the drive member is larger than the subsequent distance which the piston rod moves proximally during a subsequent proximal movement of the drive member.