Injection device
An injection device for injection of set doses of medicine from a cartridge, in which syringe a dose is set by screwing a nut up along a threaded piston rod, whereby a dose setting drum, which carries on its cylindrical surface along a helix a scale of which a number corresponding to the set dose is shown in a window in the housing of the syringe, and an injection button, which is elevated over the end of the syringe, are moved axially a distance which is larger than the axial movement of the nut. A gear wheel transmission is established between the nut and the injection button.
1. A method for expelling medication from a cartridge of medication having a moveable piston in an injection device having a rack and pinion transmission that couples an injection button with a piston driver; the method comprising the steps of:
moving a first rack rearward during setting of a dose, the rack remaining in continuous meshed engagement with a first pinion causing the first pinion to rotate during setting of a dose;
moving the first rack forward during injection of a dose and causing the first pinion to rotate in an opposite direction;
rotating a second pinion, which has a different diameter than the first pinion, in unison with the first pinion when the first rack is moved forward, wherein the second pinion remains in continuous meshed engagement with a second rack,
driving the piston driver forward during forward motion of the first rack thereby causing medication to be expelled from the injection device, wherein the first rack moves longitudinally in unison with the injection button and wherein when the injection button is pressed to move the first rack forward, the first and second pinion move longitudinally in a forward direction; and
expelling medication from the cartridge contained in the device.
2. The method of claim 1 , further comprising multiplying a force exerted on the injection button and transferring the multiplied value of the force to the piston driver via the rack and pinion transmission.
3. The method of claim 1 , wherein the first rack moves forward by a distance greater than the piston is driven forward during injection.
4. A method for expelling medication from an injection device having a rack and pinion transmission that couples an injection button with a piston in a medication cartridge; the method comprising the steps of:
setting a dose to be expelled;
while setting the dose, moving a first rack rearward while maintaining a constant meshed engagement between the first rack, which in unison with the injection button, and a pinion;
maintaining a constant meshed engagement between the pinion and a second rack that is longitudinally fixed within the device during rearward movement of the first rack;
moving the first rack forward by pressing the injection button and maintaining constant meshed engagement of the pinion with the second rack;
multiplying a force from the injection button with the rack and pinion transmission so that the force exerted the piston driver is greater than the force exerted on the injection button;
moving the pinion longitudinally in a forward direction during injection; and
expelling medication from the device.