|Abstract:||An injection syringe comprises a housing (1), a piston rod (6) with a non-circular cross-section and an outer thread (7), a piston rod drive which includes a piston rod guide (85) mating with the cross-section of the piston rod (6), and a nut (4) which is not axially displaceable and which mates with the thread (7) of the piston rod (6) to form a self-locking thread connection. Rotation of a dose setting element (81) causes an injection button to be screwed out to project from the housing (1). When the injection button (88) is pushed axially, such axial movement is transformed, by way of the threaded coupling, into a rotation of one of the piston drive elements (85) relative to the other one (4). A unidirectional coupling between the nut member (4) and the piston rod guide (85) allows rotation in one direction by which the piston rod (6) is transported in a distal direction. The coupling has an initial reluctance to be overcome before rotation takes place, said reluctance being large enough to resist torques exerted during the dose setting.|
|Inventor(s):||Steenfeldt-Jensen; S.o slashed.ren (Hornb.ae butted.k, DK), Hansen; Steffen (Hiller.o slashed.d, DK)|
|Assignee:||Novo Nordisk A/S (Bagsvaerd, DK)|
1. An injection syringe for apportioning set doses of a medicine from a cartridge containing an amount of medicine sufficient for the preparation of a number of therapeutic doses,
a piston rod having a not circular cross-section and an outer thread
a piston rod drive comprising two elements
a) a piston rod guide mating the not circular cross-section of the piston rod to allow axially displacement but not rotatation of the piston rod in relation to said piston rod guide, and
b) a nut member which is not axially displaceable in the housing and which has an inner thread mating the thread of the piston rod to form a self locking thread connection,
a dose setting mechanism comprising a not self locking thread connection along which an injection button by rotation of a dose setting element relative to said housing is screwed out from the proximal end of the housing to project from this proximal end a distance determined by the angle of said rotation and which thread connection by axial returning of the injection button transforms this axial movement to a rotation of one of the piston drive elements relative to the other, characterised in that a unidirectional coupling is provided between the nut member and the piston rod guide allowing rotation of these parts relative to each other in one direction but not in the opposite direction, the allowed rotation being one by which the piston rod is transported in a distal direction in the syringe, the coupling being so designed that an initial reluctance set large enough to resist a torque exerted on the coupling by the dose setting has to be overcome before rotation takes place.
2. An injection syringe according to claim 1, characterised in that a click coupling providing an moderate resistance against rotation in either directions is established between the housing and the element rotated relative to this housing to set a dose.
3. An injection syringe according to claim 1, characterised in that the unidirectional coupling comprises a pawl sliding over a pawl wheel with teeth having a steep front edge and a ramp shaped trailing edge.
4. An injection syringe according to claim 3, characterised in that the trailing edges of the pawl wheel teeth has a depression engaged by a mating protrusion on the pawl.
5. An injection syringe according to claim 1, characterised in that a dose scale drum has in its surface a helical track engaged by a helical rib on the inner side of the housing to form a not self locking thread connection between the housing, and that the dose scale drum and is coupled to the injection button to be moved axially with this button.
6. An injection syringe according to claim 5, characterised in that the thread connection by which the injection button is lifted by setting a dose is the thread connection between the dose scale drum and the housing.
7. An injection syringe according to claim 1, characterised in that the element rotated relative to the housing is the injection button and that the not self locking thread connection which determines the lifting of the injection button is an inner thread in a bore in the injection button engaging an outer thread on a part with enlarged diameter of the piston rod.
8. An injection syringe according to claim 1, characterised in that the piston rod guide is mounted in a driver tube in which tube the piston rod is axially displaceable but is rotated with said tube, and that the not self locking thread connection which determines the lifting of the injection button is provided between the driver tube and a part which is axially displaceable with the injection button.