Patent Abstract:
The present invention relates to a medical delivery device comprising a generally elongated housing, a container containing medicament to be delivered, a drive means capable of acting on said container for expelling said medicament, wherein said drive means comprises at least two force spring means arranged between a fixed part of the device and a movable part of the device.

Full Description:
TECHNICAL FIELD 
     The present invention relates to an injection device and in particular an injection device capable of handling medicament in fluid form having high viscosity. 
     BACKGROUND ART 
     The present invention relates to injection devices for injecting medicament and other types of fluids to be used in for example cosmetic treatment. 
     This type of drugs often have a high viscosity which means that they require high forces in order to press the fluid through a hollow needle when injecting them. 
     Auto-injectors having an automated injection function often work with spirally wound compression springs, where the springs act on a plunger rod, which in turn acts on a stopper inside a medicament container, for expelling medicament through an attached needle. The other end of the spring is often abutting an inner end surface of the housing of the device, which means that the housing has to be dimensioned to the forces of the spring. 
     When handling fluids with high viscosity this becomes even more pronounced because of the high forces required to expel the medicament. Further the spring becomes very large both regarding the diameter of the wound spring and also the diameter of the thread of the wire. The size of the spring means that the device becomes large, and for some applications and customers, such sizes of the devices are not acceptable. 
     Document WO 9421316 discloses an injection device arranged with two coil springs of different diameter working in concert. The idea of having two springs is to handle the rather long travel of the drive member, which could be difficult with a single spring because of a tendency of buckling when fully compressed and becoming entangled with interior components of the device. 
     With the dual spring arrangement one spring is arranged between an end plate and the base of an elongated cup. The cup has also an outwardly flange and the second spring acts between this and a wall across the cylindrical drive member. 
     This design can be used for handling long travel but cannot be utilised when larger forces are required. It is not possible to add the forces of the two springs because of the intermediary cup. The rear spring acts to move the cup forward, and thus the front spring, and then the front spring should act on the drive member. This means that the rear spring has to be so strong that the cup will not be moved backward due to the force of the front spring. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The aim of the present invention is to provide an injector being capable of handling the expelling of liquids having high viscosity without increasing the size of the injector in any substantive way. 
     This aim is obtained with an injector according to the features of claim  1 . Preferable embodiments of the invention are the subject of the dependent claims. 
     According to a main aspect of the invention it is characterised by a medical delivery device comprising a generally elongated housing, a container adapted to contain medicament and a stopper sealingly and slidable arranged inside said container, energy accumulating means, drive means arranged with an outer front end in contact with said stopper, such that, when a force from said energy accumulating means is applied to the drive means, the stopper moves towards the front end of the container and expels the medicament, wherein said energy accumulating means comprises at least two force spring means arranged inside the drive means between inner walls of said driving means and a rear fixed part of the device. 
     According to another aspect of the invention, said driving means is a tubular plunger rod having at its rear end a tubular enlargement forming a cylindrical space. 
     According to a further aspect of the invention, one force spring means is arranged inside said tubular plunger rod, and at least a second force spring means is arranged inside said tubular enlargement. 
     According to yet an aspect of the invention, it further comprises holding means capable of acting on said drive means for holding said at least two force spring means in a loaded state. 
     According to a further aspect of the invention, it further comprises an actuating means capable of acting on said holding means for releasing said drive means and thereby said at least two loaded force spring means. 
     According to yet an aspect of the invention, it further comprises a needle shield arranged slidable in said housing capable of acting on said actuating means when said needle shield is pressed against an injection site. 
     According to yet an aspect of the invention, said actuating means further comprises a resilient means for urging said needle shield towards the front end of the device when said device is removed from the injection site. 
     The advantages with the present invention are several. Because the device is arranged with at least two spring force means, a large force can be obtained in the device without having to use a very large single spring. The device is thus capable of handling liquid medicament having high viscosity, without the device having to be large and bulky, and thus not very attractive to users. 
     The size of the device can be kept within reasonable dimensions since preferably one spring force means is arranged inside the plunger rod and a second spring force means is arranged outside the plunger rod. 
     Also preferably, the injector is arranged with automatic penetration and injection functions, which functions are activated by the needle shield being pressed against an injection site. 
     These and other aspects of and advantages with the present invention will become apparent from the following detailed description and from the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following detailed description of the invention, reference will be made to the accompanying drawings, of which 
         FIGS. 1   a - b  are cross-sectional views of an injector according to the present invention in a state when delivered to a user, where cross-section b is taken 90° in relation to cross-section a in all the figures, 
         FIGS. 2   a - b  are cross-sectional views of the injector of  FIG. 1  where it is ready for use, 
         FIGS. 3   a - b  are cross-sectional view of the injector of  FIG. 1  where penetration has been initiated, 
         FIGS. 4   a - b  are cross-sectional view of the injector of  FIG. 1  where penetration has been completed, 
         FIGS. 5   a - b  are cross-sectional view of the injector of  FIG. 1  where injection has been completed, and 
         FIGS. 6   a - b  are cross-sectional view of the injector of  FIG. 1  where it has been withdrawn from the injection site. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiment of the injector shown in the drawings comprises an elongated housing  10  with a front end  12 , to the left in the figures, which is pressed against the injection site during use, as will be described below, and an opposite rear end  14 . At the front end of the housing a generally tubular needle shield  16  is slidably arranged. The rear end of the needle shield extends into the rear part of the housing, in a manner that will be described below. 
     Inside the needle shield a medicament container holder  18  is arranged, and inside the container holder a container  20 , e.g. a cartridge, a syringe or the like, is arranged containing medicament to be delivered through a needle  22  attached to the container. 
     The rear part of the container holder is arranged with tongues  24  having inwardly directed ledges  26 . These ledges cooperate with an outwardly directed circumferential ledge  28  of a generally tubular part  30 , creating a snap-on fit between these components. At the rear end of the tubular part an inwardly directed annular ledge  32  is arranged. 
     Inside the tubular part a drive means  34 , e.g. a tubular plunger rod, is arranged with a front end in contact with a stopper  36  in the medicament container. Inside the tubular plunger rod a first energy accumulating means  38 , e.g. a first coil drive spring, is arranged between a front end inner wall of the tubular plunger rod and a rear inner wall of the housing. The tubular plunger rod is further arranged with a generally tubular enlargement  40  forming a cylindrical space, in which a second energy accumulating member  42 , e.g. a second coil drive spring, is arranged between a front end inner wall of the space and the rear inner wall of the housing. On the outer surface of the tubular enlargement a circumferential groove  44  is arranged. 
     Outside the tubular enlargement of the plunger rod a generally tubular holding sleeve  46  is arranged. A part of the holding sleeve is arranged with a number of elongated slots whereby arms  48  are formed between the slots. The ends of the arms are arranged with inwardly directed ledges  50  as well as outwardly directed ledges  52 . 
     Outside the holding sleeve an actuator sleeve  54  is arranged, having a diameter somewhat larger than the cross-sectional measure of the arms of the holding sleeve. The actuator sleeve is arranged with a ledge  56  around its circumference and the tongues  58  of the needle shield snap into the space behind the ledges, thereby locking the needle shield to the actuator sleeve. The actuator sleeve is further arranged with a rearwardly facing ledge  60 , and a resilient means  62 , e.g. a coil spring, is arranged between the ledge and a circumferential ledge  64  of the holding sleeve, thus urging the actuator sleeve and needle shield towards the front of the device. 
     The device is intended to function as follows. When the device is delivered to a user, a protective cap  70  is arranged at the front end of the device. The protective cap comprises a tubular sheath  72  covering the needle in a sterile way. When the cap is removed, so is also the sheath. This also causes the needle shield  14  to move forward and protrude somewhat at the front end of the injector,  FIG. 2 . 
     The injector is now ready to use. The front end with the needle shield  16  is pressed against the injection site, whereby the needle shield is pushed into the housing of the device,  FIG. 3 . Since the needle shield is connected to the actuator sleeve  54 , the latter is moved rearwardly in the housing. 
     The movement of the actuator sleeve causes it to be moved past the outwardly protruding ledges  52  of the arms  48  of the holder  46 . The arms are thus free to flex radially whereby the inwardly directed ledges of the arms are moved out of holding engagement with the groove  44  of the cylindrical part  40  of the tubular plunger rod  34 . The tubular plunger rod is now free to move forward due to the forces of the first and second drive springs  38 ,  42  acting together on the tubular plunger rod. The inwardly directed ledge  32  of the tubular part  30  is still arranged in the groove  44  of the tubular plunger rod, and since the tubular part is connected to the container holder  18 , they are moved forward due to the force of the springs,  FIG. 4 . When the container holder has moved a certain distance, performing the penetration of the needle, it comes in contact with a stop ledge  74  arranged in the housing. The force of the springs will however move the tubular plunger rod further forward, whereby the inwardly directed ledge  32  is moved out of engagement with the annular groove  44  of the tubular plunger rod  34 ,  FIG. 5 . 
     The further movement of the tubular plunger rod  34  moves the stopper  36  inside the medicament container, whereby the pressure from the dual springs  38 ,  42  will cause the medicament to be pressed through the passage of the needle  22  and to be expelled into the tissue of the patient. The injection is completed when the stopper is at the front end of the container and/or when the front end of the tubular part of the tubular plunger rod comes in contact with the rear end wall of the container. 
     The device may now be removed from the injection site. The spring  62  acting on the actuator sleeve  54  will cause the needle shield  16  to move forward,  FIG. 6 , since the needle shield is connected to the actuator sleeve, thereby covering the needle. The device is now ready to be discarded. 
     It is to be understood that the embodiment described above and shown in the drawings is to be regarded only as non-limiting examples of the present invention and that it may be modified within the scope of the patent claims.

Technology Classification (CPC): 0