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

[0023]According to such a configuration, a prolongation or reduction of the stroke of the injection button compared to the stroke of the piston rod may be obtained. Further, as this configuration implies a change in the rate of rotation of the dose setting member for a given dose to be injected, a dose scale reading with a different layout may be obtained. In this way, a scale reading with increased distance between consecutive numbers may be obtained, which provides the possibility of increasing the font size of the labels of the scale reading. Also, this configuration provides the possibility of fine tuning the gearing ratio, if the injection device is so configured.

[0027]According to a fifth aspect of the invention, the rotational coupling mechanism comprises an incremental feedback mechanism providing incremental clicks during dose setting corresponding to dose volume. This aspect provides an easy adjustment of the rotational movement of the dose setting drum for each click, relatively to the housing part. In combination with the third aspect, an increase or a decrease of distance between the numbers on the dose setting drum or dose setting scale and thus the rotation for each click can be varied by choosing a specific pitch of the thread of the housing which engages the thread of the coupling member. By varying the inclination of the track along the extension of the track, it is possible to vary the rotation per click in a nonlinear way.

[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 device (e.g., the drive mechanism, cartridge, plunger, piston rod) by limiting the exposure to contaminants, such as liquid, dust, dirt etc. In general, the housing may be unitary or a multipart component of tubular or non-tubular shape. Usually, the exterior housing serves to house a cartridge from which a number of doses of a medicinal product may by dispensed. However, a cartridge may be directly coupled to the housing so as to be partly or fully external to the housing.

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.

Although broadly being considered state of the art, the injection device disclosed in U.S. Pat. No. 6,663,602 presents important mechanical constraints due to the construction principle of the linear gearing system which acts during dosing.

As the gear is an integrated part of the construction and as the gear can only be designed to certain transmission ratios, the gear implies important constraints on the obtainable ratio of movement of the injection button relative to the movement of the piston.

Due to the direct proportionality between the movement of the piston rod and the administered dose of medication, the same syringe can not easily be adapted to different medications.

Although adaptation is possible by changing the transmission ratio of the linear gear, this solution will in general be very complex and imply a complete redesign of the syringe.

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