Injection Device

Abstract

An injection device for injection of set doses of medicine from a cartridge has a nut (13) that is screwed up along a threaded piston rod (4) during a dose setting operation. The nut is screwed along the piston rod by rotating a dose setting member (17. A rotational coupling mechanism includes an axially displaceable coupling member (25) which is rotated as a function of axial displacement. During dose setting, the nut is allowed to rotate relative to the coupling member. During injection, the coupling member is rotationally locked to the nut. This provides a dose setting and injection mechanism wherein the nut member is both rotated during dose setting and during injection.

Description

[0001]The present invention relates to syringes having a piston drive element for engaging and moving a piston within a medication cartridge, by which a dose can be set by rotating a nut along the piston drive element during dose setting, and wherein a set dose can be expelled by driving the nut to its initial position.BACKGROUND OF THE INVENTION[0002]An almost classic pen which adopts the above described dose setting and injecting scheme is described in EP 327 910.[0003]By setting a dose on this pen a tubular member forming an injection button is screwed up along a threaded piston rod a distance corresponding to the distance said piston rod must be moved to inject the set dose. The tubular member simply forms a nut which is during the dose setting screwed away form a stop and which is during the injection pressed back to abutment with said stop and the force exerted on the button is directly transmitted to the a piston closing one end of an ampoule in the syringe which ampoule cont...

AI Technical Summary

Benefits of technology

[0033]The term “housing” according to instant invention shall preferably mean an exterior housing (“main housing”, “body”, “shell”) or interior housing (“inner body”, “insert”) having internal and external threads. The housing may be designed to enable the safe, correct, and comfortable handling of the drug delivery device or any of its mechanisms. Usually, it is designed to house, fix, protect, guide, and/or engage with any of the inner components of the drug delivery de

Problems solved by technology

This development is not quite favourable, as especially users having reduced finger strength have their difficulties in pressing the injection button, a problem that is further increased when still thinner needles are used to reduce the pain by injection.

Also with quite small movements of the button it is difficult to feel whether the button is moved at all and by injection of one unit from a 3 ml ampoule the piston and consequently the injection button has to be moved only about 0.1 mm.

However, by this kind of gearing relative large surfaces are sliding over each other so that most of the transformed force is lost due to friction between the sliding surfaces.

A disadvantage by this construction is that the teeth of the racks and gearwheels alternating have to be brought in and out of engagement with each other with the inherit danger of clashing.

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