A Piston Rod Drive for an Injection Device
AssigneeNovo Nordisk A/S
InventorSimon Munch Pedersen
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Abstract
The invention relates to a piston rod drive arrangement for an injection device used for self-administration of a plurality of individually set doses. The drive arrangement is made from a first element (10) mating the non-circular cross-section (3) of a piston rod (1) and a second element (20) having an inner thread (21) mating the outer thread of the piston rod. Whenever the first element (10) and the second element (20) are rotated in relation to each other the piston rod (1) is moved in an axial direction. In order to minimise the play in the threaded connection a resilient element (23) is proved to apply a force to the piston rod (1) in a longitudinal direction.
Claims15
A piston rod drive arrangement for an injection device, comprising;
- a piston rod having an outer surface with an outer thread which outer thread extend helically in a longitudinal direction along a centre line (X) and which outer surface further is provided with a longitudinal extending engagement surface such that the outer surface of the piston rod has a non-circular cross-section,
- a first element engaging the longitudinal extending engagement surface of the non-circular cross-section of the piston rod,
- a second element having an inner thread mating the outer thread of the piston rod,
- such that the piston rod is moved in the longitudinal direction when the first element and the second element are rotated in relation to each other, and wherein,
- a resilient element apply a force to the piston rod in the longitudinal direction.
Dependencies are inferred from the claim text.