Drive mechanism for a drug delivery device

Abstract

The present invention relates to a drive mechanism for a drug delivery device as well as to a drug delivery device for dispensing of a dose of a medicinal product, wherein the drive mechanism comprises: a holder for a product-containing cartridge, the cartridge having a piston slidably arranged therein in an axial direction, a piston rod to be operably engaged with the cartridge's piston for dispensing of a dose of the medicinal product, at least one adjusting member slidably arranged in axial direction relative to the piston and/or relative to the piston rod for eliminating axial clearance between the piston and the piston rod, an interlock means adapted to interact with the adjusting member for mutually locking in position the piston and the piston rod irrespective of the relative distance between piston and piston rod.

1 . Drive mechanism for a drug delivery device for dispensing of a dose of a medicinal product, comprising:
 a holder for a product-containing cartridge, the cartridge having a piston slidably arranged therein in an axial direction,   a piston rod to be operably engaged with the cartridge's piston for dispensing of a dose of the medicinal product,   at least one adjusting member displaceably arranged in axial direction relative to the piston and/or relative to the piston rod for eliminating axial clearance between the piston and the piston rod, wherein the adjusting member is attached to a proximal end of the piston or is pre-assembled to a distal portion of the piston rod and further comprises a receptacle to receive a distal portion of the piston rod,   an interlock means adapted to interact with the adjusting member for locking the piston rod's distal portion in place at an arbitrary position inside the adjusting member's receptacle.   
     
     
         2 . The drive mechanism according to  claim 1 , wherein the interlock means is adapted to provide a retention force substantially larger than an axial force required to displace the adjusting member and/or the piston. 
     
     
         3 . The drive mechanism according to  claim 1 , wherein the interlock means is designed as positive, frictional or adhesive lock. 
     
     
         4 . The drive mechanism according to  claim 1 , wherein the adjusting member's receptacle and a distal portion of the piston rod are bonded or welded. 
     
     
         5 . The drive mechanism according to  claim 1 , wherein a deformable adhesive disposed in the adjusting member's receptacle is adapted to provide a clearance-eliminating axial displacement of piston rod and adjusting member, and wherein the adjusting member and the piston rod are to be mutually interlocked by curing of said adhesive. 
     
     
         6 . The drive mechanism according to  claim 4 , wherein in a pre-assembly configuration, the adjusting member is pre-assembled to the distal portion of the piston rod by means of the deformable nun-cured adhesive. 
     
     
         7 . The drive mechanism according to  claim 5 , wherein in a pre-assembly configuration, the adjusting member comprises a first adhesive component and the piston rod at its distal portion comprises a second adhesive component of a two-component adhesive. 
     
     
         8 . The drive mechanism according to  claim 1 , wherein the interlock means is adapted to radially clamp the adjusting member's receptacle and the piston rod's distal portion. 
     
     
         9 . The drive mechanism according to  claim 1 , wherein piston rod at its distal portion comprises at least one radially movable jaw to interact with the adjusting member's receptacle, wherein the jaw has a slanted inner surface to engage with a correspondingly slanted surface of an axially movable lock rod. 
     
     
         10 . The drive mechanism according to  claim 1 , wherein the interlock means comprises an eccentrically supported clamping member to mutually clamp the adjusting member and the piston rod. 
     
     
         11 . The drive mechanism according to  claim 1 , wherein the interlock means comprises a blocking ring arranged on the outer circumference of the piston rod's distal portion to radially prop against an inside facing wall of the adjusting member's receptacle, wherein the blocking ring is further adapted to impede an axial movement of piston rod and adjusting member towards each other. 
     
     
         12 . The drive mechanism according to  claim 1 , wherein the piston rod comprises a hollow shaft adapted for axial insertion of a lock rod for activating a locked mode or for eliminating axial clearance. 
     
     
         13 . The drive mechanism according to  claim 1 , wherein the adjusting member and the piston rod are threadedly engaged and rotatably biased by a spring member. 
     
     
         14 . The drive mechanism according to  claim 13 , wherein an interlock member movably arranged in radial direction at the piston rod radially engages with a corresponding recess at an inner surface of the adjusting member for selectively releasing and/or interlocking of a clearance-eliminating relative rotation between piston rod and adjusting member. 
     
     
         15 . The drive mechanism according to  claim 13 , wherein the adjusting member and the distal portion of the piston rod comprise threaded receptacles facing towards each other, wherein the receptacles are threadedly engaged by means of a threaded adjustment sleeve, rotatably biased by the spring member relative to the piston rod or relative to the adjusting member. 
     
     
         16 . The drive mechanism according to  claim 13 , wherein the threaded engagement of adjusting member, adjusting sleeve and/or piston rod is of self-locking type. 
     
     
         17 . A drug delivery device for dispensing of a dose of a medicinal product, comprising a housing and a cartridge comprising the medicinal product, the cartridge further comprising a piston slidably arranged in an axial direction, wherein the device further comprises a drive mechanism according to any one of the preceding claims. 
     
     
         18 . The drug delivery device according to  claim 17 , wherein the housing comprises a through opening or a transparent window to deliver an adhesive or an electromagnetic radiation for locking in position of piston and piston rod. 
     
     
         19 . A method of eliminating clearance between a piston and a piston rod in a drive mechanism of a drug delivery device, wherein the drive mechanism comprises a holder for a product-containing cartridge having a piston slidably arranged therein in an axial direction, wherein the piston rod is to be operably engaged with the cartridge's piston for dispensing of a dose of the medicinal product, further comprising an adjusting member attached to a proximal end of the piston or being pre-assembled to a distal portion of the piston rod, wherein the adjusting member comprises a receptacle to receive a distal portion of the piston rod, the method of eliminating said clearance during or after assembly of the drive mechanism comprises the steps of:
 axially moving of the piston rod relative to the adjusting member and/or axially moving the adjusting member relative to the piston for eliminating axial clearance between the piston and the piston rod,   locking the piston rod's distal portion in place at an arbitrary position inside the adjusting member's receptacle by an interlock means adapted to interact with the adjusting member.