Drive mechanism for a drug delivery device and a method for assembling a drug delivery device

A method for assembling a drug delivery device, the method comprising:

• providing a first piston rod member, a second piston rod member and an adjustment member;
• arranging the adjustment member at least partly inside the second piston rod member;
• operating the adjustment member to move the first piston rod member with respect to the second piston rod member;
• and
• coupling the first piston rod member with the second piston rod member such that movement between the first piston rod member and the second piston rod member is prevented,
• wherein the drive mechanism has a first state in which the first and the second piston rod member are moveable with respect to each other by operating the adjustment member, thereby adjusting a length of the piston rod, wherein coupling the first piston rod member with the second piston rod member comprises moving the adjustment member completely into the second piston rod member such that the adjustment member is arranged inside the second piston rod member to a greater extent than in the first state of the drive mechanism.

A drive mechanism for a drug delivery device, the drive mechanism comprising:

• a piston rod comprising a first piston rod member and a second piston rod member;
• and
• an adjustment member, wherein the drive mechanism has a first state in which the first and the second piston rod member are moveable with respect to each other by operating the adjustment member, thereby adjusting a length of the piston rod,
• wherein the adjustment member is arranged at least partially inside the second piston rod member,
• wherein the adjustment member comprises a third connection member,
• wherein the second piston rod member comprises a fourth connection member, and wherein the third connection member and the fourth connection member are configured to prevent a rotational movement of the adjustment member and the second piston rod member relative to each other and to permit a relative axial movement of the adjustment member and the second piston rod member when the third connection member and the fourth connection member are connected to each other, and
• wherein the first piston rod member is moveable relative to the second piston rod member when the third connection member and the fourth connection member are not connected to each other.

A drive mechanism for a drug delivery device, the drive mechanism comprising:

• a piston rod comprising a first piston rod member and a second piston rod member;
• and
• an adjustment member, wherein the drive mechanism has a first state in which the first and the second piston rod member are moveable with respect to each other by operating the adjustment member, thereby adjusting a length of the piston rod,
• wherein the adjustment member is arranged at least partially inside the second piston rod member,
• wherein the first piston rod member comprises a fifth connection member and the second piston rod member comprises a sixth connection member, and
• wherein when the fifth connection member and the sixth connection member are connected to each other such that a movement between the first and the second piston rod member is restricted to a concurrent rotational and translational movement.