Patent ID: 8617109

Claim:
A device for delivering predetermined doses of liquid medicament, the device having a medicament delivery state and a medicament non-delivery state and comprising: a cartridge configured to contain the liquid medicament and a piston sealingly and slidably arranged in the cartridge; an energy accumulating member configured to stepwise accumulate energy when the device is in the medicament non-delivery state; an elongated threaded plunger rod arranged in an interior of the device; a plunger rod driving member configured to engage the threaded plunger rod and be in a driven state when the device is in the medicament delivery state and in a non-driven state when the device is in the medicament non-delivery state, wherein rotation of the plunger rod driving member due to output torque of the energy accumulating member drives the threaded plunger rod, enabling the threaded plunger rod, which is in contact with the piston, to be driven toward a proximal end of the cartridge by a predetermined distance and expel a predetermined dose of the liquid medicament from the cartridge; and an axial bearing coupled to an outer cover and configured to pick up forces acting on a proximal part of the device in a longitudinal direction thereof and arising from driving the threaded plunger rod, whereby more of the accumulated energy that results from stepwise rotational tensioning of the energy accumulating member positioned at a distal end of the device is converted to output torque; wherein the energy accumulating member is a flat spiral spring.