MECHANISM FOR AN AUTOMATIC MEDICAMENT DELIVERY DEVICE

A mechanism for an automatic medicament delivery device comprises a housing; a dose setting element; a button; a piston rod that is rotationally fixed and axially movable with respect to the housing; a nut; and a spring. The dose setting element is configured to be gripped by a user of the device to set a dose to be delivered by rotation of the dose setting element with respect to the housing when the mechanism is in a dose setting state, wherein the rotation of the dose setting element stores energy in the spring. Furthermore, the rotation of the dose setting element causes the nut to move by a dose distance in a proximal direction with respect to the piston rod, the dose distance being proportional to the dose. The mechanism further is configured to switch from the dose setting state into a dose delivery state upon moving the button, for example in an axial direction, with respect to the housing. A transfer into the dose delivery state couples the spring to the nut to cause automatic movement of the nut in a proximal direction by releasing the energy stored during dose setting. The piston rod is configured to move together with the nut by the dose distance in the proximal direction to deliver the dose when the mechanism is in the dose delivery state. Furthermore, the dose setting element is configured to remain axially stationary with respect to the housing when the dose is being delivered.