Patent ID: 9675760
Date: 2017-06-13
CPC Classifications: A61M

Claim:
1. A drive mechanism for a drug delivery device, comprising: a housing, a piston rod, which is displaced in a distal direction for a delivery of a dose and in a proximal direction for a reset, a lock nut releasably rotationally locked to the housing and threadedly engaged with the piston rod, a rotatable drive member, which is threadedly engaged with the piston rod, and a biasing member, which is loaded and tends to rotate the piston rod with respect to the drive member in such a way that the piston rod is screwed into the drive member and thereby advanced in the proximal direction wherein the rotatable drive member rotates during the delivery of the dose, wherein the biasing member is latched to the lock nut and to the drive member, so that the biasing member is loaded when the drive member rotates relative to the housing during the delivery of the dose, and wherein the biasing member relaxes when the rotational locking of the lock nut is removed, resulting in a rotation of the lock nut and a corresponding rotation of the piston rod with respect to the drive member.