Abstract:
A needleless hypodermic injection system for injecting a liquid medication, which system comprises a disposable cartridge which contains a medication and which comprises a propellant and an igniter, and a reusable application device which comprises a pressure chamber for receiving the medication cartridge, actuation means including an ignition system and means for ensuring reliability and safety of the system. The reusable application device comprises: (a) a housing including a fist housing section and a second housing section which are adapted to be assembled together by a screwing operation, the first housing section comprising a front part having an injection outlet and a chamber adapted to receive a the cartridge contains the medication to be injected and also contains a propellant and an igniter, and (b) means for selectively activating said igniter of said cartridge when predetermined conditions are fulfilled.

Description:
PRIORITY TO RELATED APPLICATIONS  
       [0001]     This application is a Continuation of Ser. No. 10/101,400, filed Mar. 19, 2002 which is pending. This application claims the benefit of U.S. Provisional Application Ser. No. 60/278,042, filed Mar. 22, 2001. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention concerns a needleless hypodermic injection system for injecting a liquid medication.  
         [0003]     The invention also concerns a reusable application device which is a first part of such a system.  
         [0004]     The invention further concerns a disposable medication cartridge which is a second part of such a system.  
       BACKGROUND OF THE INVENTION  
       [0005]     Prior art systems and devices of the above mentioned kind have important disadvantages. They have a complex structure and are therefore not easy to assemble and to use, in particular for patients which have some handicaps or are not in full possession of their handling capabilities. Moreover they lack reliable means for preventing accidental release of injections and their negative consequences, e.g. loss of expensive medications and possible injures inflicted to the user.  
         [0006]     The main aim of the instant invention is therefore to provide a system an application device, and a medication cartridge of the above mentioned kind with which the above mentioned drawbacks can be eliminated or at least substantially reduced.  
       SUMMARY OF THE INVENTION  
       [0007]     According to a first aspect of the invention the above mentioned aim is attained with a needleless hypodermic injection system for injecting a liquid medication, which system comprises: 
        (a) a disposable cartridge which contains a medication and which includes a propellant and an igniter, and     (b) a reusable application device which comprises a pressure chamber for receiving said cartridge, and actuation means including an ignition system and means for ensuring reliability and safety of the system.        
 
         [0010]     According to a second aspect of the invention the above mentioned aim is attained with a reusable application device for a needleless hypodermic injection system for injecting a liquid medication contained in a cartridge inserted into said application device, said application device comprising 
        (a) a housing including a first section and a second section which are adapted to be connected with each other to form a housing assembly,     said first housing section comprising a chamber for receiving a cartridge containing a medication unit which contains a liquid medication,     said first housing section having a symmetry axis which extends along its length and a front part having an outer contact surface which is adapted to be applied on a skin surface, said contact surface having an opening through which liquid medication ejected from said cartridge can pass and be injected through said skin surface,     (b) ejection means for causing ejection of said liquid medication contained in said cartridge in order to perform an injection, a first part of said ejection means being contained in said cartridge and a second part of said ejection means being contained in said second housing section,     c) assembly detecting means which reach a first predetermined state when said first housing section is properly and completely assembled with said second housing section to form said housing assembly, said assembly detecting means being located within said housing assembly,     d) position detecting means which are located in part within said first housing section and in part in said second housing section, said position detecting means reaching a second predetermined state when the following conditions are simultaneously satisfied by the relative position of said housing assembly with respect to said skin surface,     d.2) said contact surface of said first section exerts a predetermined pressure on said skin surface, the distribution of said pressure over the area of said contact surface being substantially uniform, and     d.3) said symmetry axis of said first section is positioned substantially normal to said skin surface, and     e) actuator means for activating said ejection means, said actuator means being normally disabled and becoming operable only upon being enabled by a combination of predetermined effects provided by     said assembly detecting means after they reach said first predetermined state, and     said position detecting means when they reach said second predetermined state.        
 
         [0022]     According to a third aspect of the invention the above mentioned aim is attained with a reusable application device for a needleless hypodermic injection system for injecting a liquid medication contained in a cartridge inserted into said application device, said cartridge containing a propellant adapted to be ignited by application of electrical energy to two electrical contacts which are part of said cartridge, said application device comprising 
        a) a housing including a first section and a second section, each of these sections having a length axis and said first and second housing sections being adapted to be connected with each other to form a housing assembly, said housing assembly being so configured and dimensioned that it is adapted to be held by a user with one hand,     b) said first housing section comprising a chamber for receiving a cartridge containing a liquid medication, said first section having an outer contact surface which is adapted to be applied on a skin surface through which an injection is to be applied,     c) said second housing section containing electrical means for causing ignition of a propellant contained in a cartridge arranged in said chamber of said first housing section and actuator means for activating said electrical means, and     d) position detecting means for detecting whether said contact surface of said first section exerts a predetermined pressure on said skin surface and whether at the same time said length axis of said first section is positioned substantially normal to said skin surface, the distribution of said pressure over the area of said contact surface being substantially uniform, said means for detecting enabling said actuator means when the latter conditions are satisfied.        
 
         [0027]     According to a fourth aspect of the invention the above mentioned aim is attained with a reusable application device for a needleless hypodermic injection system for injecting a liquid medication, which application device comprises: 
        (a) a housing including a fist housing section and a second housing section which are adapted to be assembled together by a screwing operation,     said first housing section comprising a front part having an injection outlet and a chamber adapted to receive a cartridge containing a medication unit which contains the medication to be injected, a propellant, and an igniter, and     (b) means for selectively activating said igniter of said cartridge when predetermined conditions are fulfilled.        
 
         [0031]     According to a fifth aspect of the invention the above mentioned aim is attained with a medication cartridge for a needleless hypodermic injection system for injecting a liquid medication, said cartridge comprising a housing adapted to contain: 
        (a) a first chamber containing a medication unit configured and dimensioned to store a volume of liquid to be injected, said medication unit having a first region and a second region that are in liquid communication with each other, said first region being deformable and said second region having an injection outlet, and     (b) a second chamber containing a propellant,     said first chamber being divided by an elastic barrier in two zones, a first zone containing said medication unit and a second zone which is communication with said second chamber, so that upon ignition of the propellant in the second chamber gas generated thereby expands into said second zone of said first chamber, exerts pressure on and deforms said barrier which in turn transfers that pressure to and deforms said deformable first region of said medication unit and thereby causes ejection of said medication through said injection outlet, and     (c) means for mechanically setting the volume available within said cartridge for gas said expansion, so that said volume has a selected predetermined size.        
 
         [0036]     The main advantages attained with the invention are as follows: 
        Injections can only be performed when plurality of predetermined necessary conditions for a correct injection are satisfied. Therefore, the risk of accidentally released injections and their negative consequences, e.g. loss of expensive medications and possible injure of user, are substantially reduced.     A device and a system according to the invention are easy, safe and comfortable to use, so that they can be assembled and used by patients or other persons without any training or special instructions.     The manufacturing cost of a device and a system according to the invention is not higher than prior art devices for the same purpose.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]     The subject invention will now be described in terms of its preferred embodiments with reference to the accompanying drawings. These embodiments are set forth to aid the understanding of the invention, but are not to be construed as limiting.  
         [0041]      FIG. 1  shows a schematic cross sectional view of a basic structure of a medication cartridge  11  used in a needleless injection system according to the invention.  
         [0042]      FIG. 2  shows a schematic cross sectional view of the basic structure of an application device according to the invention including a representation of a medication cartridge  11  according to  FIG. 1 .  
         [0043]      FIG. 3  shows a schematic cross sectional view of the pressure chamber and locking means which are part of the application device according to  FIG. 2  and which are adapted to enclose and contain a medication cartridge  11  of the type shown by  FIG. 1  during a high-pressure injection.  
         [0044]      FIG. 4  shows a schematic cross sectional view of a complete application device according to the invention without a medication cartridge inserted thereinto.  
         [0045]      FIG. 5  shows a side view of the nose section  42  of an application device of the kind shown by  FIG. 4 .  
         [0046]      FIG. 6  shows a first perspective view of the nose section  42  shown by  FIG. 5 .  
         [0047]      FIG. 7  shows a second perspective view of the nose section  42  shown by  FIG. 5 .  
         [0048]      FIG. 8  shows a first exploded view of components of the nose section  42  shown by  FIGS. 5-7 .  
         [0049]      FIG. 9  shows a second exploded view of components of the nose section  42  shown by  FIGS. 5-7 .  
         [0050]      FIG. 10  shows a first schematic representation of the electrical ignition circuit of an application device of the kind shown by  FIG. 4 .  
         [0051]      FIG. 11  shows a second schematic representation of the electrical ignition circuit of an application device of the kind shown by  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0052]     According to the invention a reusable application device is used as part of a needleless hypodermic injection system for injecting a liquid medication contained in a cartridge inserted into said application device.  
       Medication Cartridge Assembly  
       [0053]     As shown by  FIG. 1 a  medication cartridge assembly  11  according to the invention comprises components described hereinafter.  
         [0054]     A cartridge shell  12  made e.g. of a plastic material contains among other components a sealed medication module which comprises a nozzle body  13  and a flexible container wall  14  that hermetically encloses a portion of the nozzle and forms a reservoir  15  for a liquid medication  16  stored in the sealed medication module. This sealed module including liquid medication  16  stored therein is manufactured under sterile conditions.  
         [0055]     A part of the container wall  14  forms a break-off protective cap  17  that covers a jet orifice  18  of nozzle body  13 . Cap  17  is removed by the user just prior to use.  
         [0056]     An envelope  21  made e.g. of rubber surrounds the flexible container wall  14  and serves as a protective barrier. Envelope  21  protects flexible wall  14  from direct hot gas contact, and prevents hot gas from entering a fluid channel  22  within nozzle body  13  and jet orifice  18  of nozzle body  13  even in the event of a break in the flexible container wall  14 . Envelope  21  also forms a gas seal between the cartridge shell  12  and the medication module containing the liquid medication  16 .  
         [0057]     Cartridge shell  12  unifies the components contained therein and contains also gas generated within cartridge shell  12  by a gas generator contained therein during actuation. The wall of cartridge shell  12  may be relatively thin since it transfers the gas pressure forces generated within cartridge shell  12  to a surrounding high strength chamber that is part of a reusable actuation device described hereinafter.  
         [0058]     Injection energy is provided by a gas generator located in the rear part of cartridge shell  12 . This gas generator is a subassembly consisting of a metal gas generator body  23  which has a propellant containing chamber  24  located between an outlet orifice plate  25  and a closure plug or closure plate  26 . When the gas generator is actuated in order to provide the energy necessary for performing an injection of the liquid medication, a propellant contained in propellant chamber  24  is ignited by an electrically heated wire and produces hot gas that flows to gas pressure chamber  27  surrounding envelope  21 , flexible container wall  14  and medication reservoir  15  and an annular co-volume  28  the size of which is defined by the axial position of a co-volume seal ring  34 .  
         [0059]     Heating wire adapted to be electrically heated is arranged within propellant chamber  24 . This heating wire is electrically connected with ignition contacts  31 ,  32  arranged in closure plate. When the medication cartridge assembly is properly positioned within the reusable application device ignition contacts  31 ,  32  engage corresponding electrical contacts which are part of the application device described hereinafter. Electric power is deliverable to the heating wire  35  (shown in  FIG. 11 ) arranged within propellant chamber  24  through the latter contacts and ignition contacts  31 ,  32  engaged therewith.  
         [0060]     Cartridge shell  12  further contains an internal support  33  which e.g. a structure made of a plastic material that snaps into cartridge shell  12  and holds the above described sealed medication module and the gas generator in position. When cartridge assembly  11  is inserted into and properly positioned within an application device described hereinafter in order to perform an injection, a part of this application device pushes on the rear of cartridge assembly  11  and clamps the closure plate  26  of the gas generator, internal support  33 , envelope  21  and the above described sealed medication module into the nose of cartridge shell  12 . Cartridge assembly  11  remains so clamped during actuation thereof by the application device for performing the injection. This clamping action on cartridge assembly  11  assures that this assembly is hermetically sealed to prevent hot gas leakage around jet orifice  18  of nozzle body  13 .  
         [0061]     When a cartridge assembly is actuated by the application device, pressure exerted by gas surrounding a part of the sealed medication module within cartridge shell  12  is transmitted to liquid medication  16  contained in the sealed medication module through flexible container wall  14 . The pressure exerted in this way on the liquid medication causes a collapsing of flexible container wall  14  and this drives the liquid medication through jet orifice  18  at high velocity. Peak pressure, up to 300 bar, occurs at the beginning of the injection and forces a jet of liquid medication to penetrate through a skin layer and thereby form a fluid delivery channel into the subcutaneous tissue. The pressure then drops to about 100 bar to complete the medication injection through the so formed fluid delivery channel.  
         [0062]     Ease of jet penetration varies between patients or between injection sites on the same patient. The initial peak injection pressure is therefore adjusted to control the jet penetration force to an appropriate value. This adjustment is effected by positioning co-volume seal ring  34  at a suitable axial position with respect to cartridge shell  12  in order to set the value of the annular co-volume  28 .  
         [0063]     Increasing co-volume  28  increases the expansion volume of the gas generated and delivered by the gas generator and reduces the initial peak pressure to a lower value. A co-volume setting ring  48  that is part of the application device described hereinafter slides into the rear of cartridge  11  during loading of cartridge  11  into the application device, brings co-volume seal ring  34  into a selected position and holds this ring in this position.  
         [0064]     A cartridge assembly  11  clamped into the actuation device described hereinafter is a hermetically sealed assembly, and retains as much as 100 bars pressure after actuation. The application device must therefore release the clamping force in a controlled way and allow that the gas pressure within cartridge  11  forces closure plug  26  of the gas generator out to break the seal with the gas generator body  23  and vent the gas. This controlled pressure release makes it easy to open the application device after it is used to perform an injection and prevents that the amount of pressure remaining in the cartridge after an injection may cause an undesirable forceful opening of the application device that may cause an injury to a user of the device.  
       Structure of an Application Device According to the Invention  
       [0065]     The above described characteristics of cartridge assembly  11  define the basic functional requirements the application device has to satisfy. Additional requirements ensure safe and easy operation of the application device.  
         [0066]     The force a user has to apply for loading a cartridge  11  into an application device and the force a user has to apply for removing a cartridge  11  from the application device after use for performing an injection must be low enough to allow easy and sure operation of the application device by ill or elderly patients.  
         [0067]     Actuation of the application device must not be possible unless the device is fully closed and locked. Otherwise partial engagement of the locking mechanism might lead to failure and possible injury caused by the high pressure created during an injection operation.  
         [0068]     To ensure that actuation of the application device is not possible unless the device is fully closed and locked, operation of an application device according to the invention requires that the nose part of the application device is pressed uniformly and with a predetermined force against the skin surface to be injected before actuation of the application device is enabled. Main objectives of this security measure are to prevent accidental actuation resulting in ejection of a liquid jet that might cause eye injury and also to prevent wasted injections due to premature actuation of the application device before the nose part thereof is properly pressed against the skin surface at the injection site.  
         [0069]     The outer surface of the application device should not have any sharp edges or pinch points and the design of the application device has to satisfy ergonomic requirements.  
         [0070]     The shape of the application device has to be well adapted to the function it has to perform and therefore the procedures for loading and unloading a cartridge  11  into the application device and for actuating the application device should be so obviously and intuitively clear to the user that a minimum of user instruction is necessary to ensure proper use of the application device.  
         [0071]     Moreover, the application device and in particular the area around the cartridge nozzle that contacts the skin during the injection should be adapted to be easily cleaned.  
         [0072]     The injection system formed by cartridge  11  and the application device described hereinafter should be fail-safe and resistant to tampering. Any faults in the device should result in failure of device actuation rather than in an unexpected or dangerous actuation. The design of the latter injection system should be such that it discourages a “clever” person from modifying or tricking the device so that it operates improperly.  
         [0073]     The application device described hereinafter meets the requirements outlined above.  
         [0074]     As shown by  FIG. 2 , an application device  41  according to the invention comprises two sections: a nose section  42  which comprises a pressure chamber  49  defined by the interior of a shell  43  and adapted for receiving a cartridge assembly  11 , and a base section  44  which comprises among other components a breech block  45  and an electrical ignition system (not shown in  FIG. 2 ).  
         [0075]     Nose section  42  and a base section  44  are assembled in two steps. In a first step a cartridge  11  is inserted into pressure chamber  49  of nose section  42  and after that nose section  42  and the cartridge  11  inserted thereinto are mechanically connected to base section  44 . For this purpose, nose section  42  and base section  44  are twisted with respect to each other ¼ turn to provide engagement of a set of locking lugs.  
         [0076]     In a second step nose section  42  is twisted of about one turn with respect to base section  44  for tightening a screw mechanism that clamps cartridge assembly  11  with a required preload of e.g. 200 Newton. At this point application device  41  is ready for performing an injection. For this purpose, the user removes break-off protective cap  17  from cartridge  11 , presses jet orifice  18  of nozzle body  13  against a skin surface at the injection site, and then presses an actuation switch to release an injection.  
         [0077]     Interlocks prevent actuation of the application device if it is not fully closed and if the skin contact surface of its nose section  42  is not uniformly pressed against the skin surface.  
         [0078]     A spent cartridge is removed by reversing the loading process. For this purpose, nose section  42  is twisted of about one turn with respect to base section  44  to release the clamp screw mechanism and vent the residual cartridge gas pressure. The locking lugs are then disengaged by a further ¼ turn, and nose section  42  and base section  44  are separated from each other so that the spent cartridge may be removed and discarded.  
         [0079]     Application device  41  is a tightly integrated system that comprises the following subsystems:  
         [0000]     Pressure Chamber and Lock  
         [0080]     Pressure chamber  49  and a lock which includes the above mentioned breech block are a set of mechanical components that enclose and contain a cartridge assembly  11  during a high-pressure injection.  
         [0000]     Housing  
         [0081]     A housing encloses and supports the other subsystems which form part of an application device according to the invention. This housing also forms the surfaces the user grips to administer injections and to open and close the application device for loading, respectively unloading of a cartridge  11 .  
         [0000]     Electric Ignition System  
         [0082]     An electric ignition system includes a battery, an actuation switch, safety interlock switches and electrical connection leads. The electrical ignition system supplies electric current to the ignition contacts  31 ,  32  of cartridge  11  and thereby to ignition wire  35  (see  FIG. 11 ) to start an injection process when the user presses the actuation switch.  
         [0000]     Object Sensor  
         [0083]     An object sensor comprises a mechanical structure surrounding jet orifice  18  of nozzle body  13  of cartridge  11 . This mechanical structure comprises a skin contact surface of nose section  42 . Two diametrically opposite places of this skin contact surface must be pressed against the injection site in order to enable application device  41  to actuate a cartridge  11  which has been loaded into application device  41 .  
         [0084]     The following sections describe each of the above mentioned subsystems in detail.  
         [0000]     Pressure Chamber and Lock Mechanism  
         [0085]      FIG. 3  shows a general arrangement of a pressure chamber  49  and a lock mechanism  51 . Pressure chamber  49  is the interior of a generally cylindrical shell  43  with a reduced diameter opening  46  at one end and a full diameter opening  47  at the other end. The shell  43  of pressure chamber  49  is manufactured from high strength steel and dimensioned such that it will withstand about 900 bar internal pressure (that is three times a 300 bar maximum working pressure) without damage.  
         [0086]     Lock mechanism  51  is part of a mechanical structure contained in and carried by base section  44 . In order to load a new cartridge into the application device or to unload an spent cartridge from the application device, nose section  42  and base section  44  are disassembled as described above in order to separate the shell  43  of pressure chamber  49  from lock mechanism  51 .  
         [0087]     When cartridge  11  is inserted into pressure chamber  49  break-off protective cap  17  and the outer end of nozzle body  13  extend through the reduced diameter opening  46  of the shell  43  of pressure chamber  49 . The shell  43  of pressure chamber  49  has a clearance fit with respect to cartridge shell  12 . During an injection process the internal pressure within cartridge shell  12  expands it elastically and its outer wall contacts the internal surface of the shell  43  of pressure chamber  49 , thereby transfers the pressure load to the shell  43  of pressure chamber  49  during the injection process, and limits the mechanical stress on cartridge shell  12 . After an injection, the residual pressure in cartridge shell is released by venting (as described above) and cartridge shell elastically contracts. This restores the clearance fit of cartridge shell  12  with respect to the shell  43  of pressure chamber  49  and this allows easy removal of a used cartridge. Nozzle body  13  of cartridge  11  has sufficient strength to bridge the reduced diameter opening  46  and withstand the internal pressure in cartridge  11  during an injection process.  
         [0088]     Full diameter opening  47  of the shell  43  of pressure chamber  49  is closed when shell  43  is engaged with lock mechanism  51 . Lock mechanism  51  has several functions. A first function of lock mechanism  51  is that it locks to the shell  43  of pressure chamber  49  and carries the axial pressure force (which is a function of the cartridge internal diameter and the gas pressure) which tends to separate lock mechanism  51  from the shell  43  of pressure chamber  49 . A second function of lock mechanism  51  is that it carries the ignition contacts of the application device that engage the ignition contacts  31 ,  32  of cartridge  11 . A third function of lock mechanism  51  is that it carries an interchangeable co-volume setting ring which serves for setting the axial position of the co-volume seal ring  34  in cartridge  11 . A fourth function of lock mechanism  51  is that it comprises a clamp screw  52  that allows the user to apply the necessary clamping force on cartridge  11  prior to actuation thereof, and to release the residual pressure in cartridge  11  in a slow and controlled way after an injection process. A fifth function of lock mechanism  51  is that it contains a mechanical interlock that assures that locking lugs are fully engaged before clamp screw  52  can be turned to prepare and bring the system composed by the application device and cartridge  11  to a state that allows actuation of cartridge  11  by the application device. Each of these functions is described in more detail in the following sections.  
         [0089]     A pair of male locking lugs  53  on the shell  43  of pressure chamber  49  engage female pockets  54  in a receiver ring  55  of lock mechanism  51  to form a structural connection. The user makes this connection by inserting locking lugs  53  into receiver ring  55  with an axial motion, and then rotating the shell  43  of pressure chamber  49  ¼ turn with respect to receiver ring  55  to engage locking lugs  53  with female pockets  54 . This type of connection is widely used in firearms and hose couplings because of its strength and reliability.  
         [0090]     After locking lugs  53  are fully engaged with female pockets  54 , clamp screw  52  is turned to push breechblock  45  into cartridge  11 . Clamp screw  52 , the shell  43  of pressure chamber  49 , receiver ring  55  and breechblock  45  are all on a common axis, i.e. they are coaxially arranged. This screw action preloads the sealing of cartridge  11  with a force of about 200 Newtons, sets the axial position of co-volume seal ring  34  to a selected position, and pushes the ignition contacts of the application device against the ignition contacts of cartridge  11  so that electrical contact is established between these ignition contacts.  
         [0091]     After an injection process is terminated, a 100 bar residual pressure in cartridge  11  generates a force of about 1600 Newtons on clamp screw  52 . Under this mechanical load, the user turns clamp screw  52  to retract breechblock  45  and vent cartridge  11 . One of the ends of clamp screw  52  has right hand threads that engage matching threads in receiver ring  55 , whereas the opposite end of clamp screw  52  has left hand threads that engage matching threads in breechblock  45 . One or more pins in receiver ring  55  engage matching axial slots in breechblock  45 , and prevent rotation of breechblock  45  while allowing axial motion thereof. The provision of clamp screw  52  with the above mentioned different threads makes it possible to obtain an axial displacement of breechblock  45  per revolution of clamp screw  52  that is twice as long as the axial displacement that would be obtained if clamp screw  52  had only a single type of thread with the same thread pitch distance. A suitable choice of thread diameter and pitch favorably influences the amount of effort needed for disassembling, respectively assembling application device  41 . This is discussed in more detail hereinafter.  
         [0092]     A pair of interlock levers  56 ,  57  consisting each of a latch portion  69  and an arm portion  68  are pivot mounted on a pivot  70  to the receiver ring  55 . Interlock levers  56 ,  57  lie in a plane that includes the symmetry axis of receiver ring  55 , and the pivot axes are perpendicular to this plane and symmetrically placed on each side of the symmetry axis of the receiver ring. Interlock levers  56 ,  57  are spring biased by a bias spring  60  so that the latch portions  69  engage a pair of grooves (not shown) in clamp screw  52 , preventing screw rotation. When the shell  43  of pressure chamber  49  is inserted into receiver ring  55 , the arm portions  68  of interlock levers  56 ,  57  slip into a pair of cam grooves  58 ,  59  in the shell  43  of pressure chamber  49 . Cam grooves  58 ,  59  are shaped to move the arm portions  68  of interlock levers  56 ,  57  as the shell  43  of pressure chamber  49  is rotated to engage locking lugs  53 , so that the latch portions  69  are removed from the clamp screw grooves. The result is that rotation of clamp screw  52  is only possible when the locking lugs  53  are fully engaged with pockets  54 .  
         [0093]     A second function of interlock levers  56 ,  57  is to prevent rotation of lugs  53  and disengagement thereof from pockets  54  once clamp screw  52  is rotated from the starting position to clamp cartridge  11  and thereby the closure plug of cartridge  11  and pressure chamber  49  by means of breechblock  45 . When clamp screw  52  is rotated, the latch portions  69  of the interlock levers  56 ,  57  ride on the outside diameter of clamp screw  52 , and can no longer enter the clamp screw grooves and rotate about pivots  70 . The arm portions  68  of interlock levers  56 ,  57  are therefore immovable, and bear against the sides of the cam grooves  58 ,  59  in the shell  43  of pressure chamber  49  and block rotation of locking lugs  53 . This ensures that lugs  53  remain fully engaged with pockets  54  during actuation of cartridge  11  and can only be disengaged after clamp screw  52  is returned to the starting position. At this point the latch portions  69  of interlock levers  56 ,  57  can again drop into the clamp screw grooves, allowing the latches  69  of interlock levers  56 ,  57  to rotate about the pivots  70 .  
         [0094]     A third function of interlock levers  56 ,  57  is to prevent shell  43  of pressure chamber  49  from being inserted if clamp screw  52  is not in the starting position. In this condition the latch portions  69  of the interlock levers  56 ,  57  ride on the outside diameter of clamp screw  52 , displacing the arm portions  68  of the levers so that they do not enter the cam grooves in the shell  43  of pressure chamber  49 . This blocks the shell  43  of pressure chamber  49  from entering the receiver ring  55  far enough for the locking lugs  53  to engage pockets  54 . The situation in which the shell  43  of pressure chamber  49  is removed and the clamp screw  52  is not in the starting condition is not normal, and indicates damage or tampering. Correction of this anomalous state requires device service or replacement.  
         [0095]     By careful selection of the design parameters of clamp screw  52 , the required effort to assembly and disassembly application device  41  are approximately equal and this results in greatly improved ease of use.  
         [0096]     Frictional torque of clamp screw  52  varies in function of axial load, screw thread diameter, and friction coefficient. Load reaction torque varies in function of axial load and thread pitch. The reaction torque adds to the friction torque in the closing direction (when assembling application device  41 ), and increases the user effort. Conversely, the reaction torque subtracts from the friction torque in the opening direction (when disassembling application device  41 ) and assists the user. Since the axial force is about 200 Newtons in the closing direction and about 1600 Newtons in the opening direction, according to the invention the parameters of clamp screw  52  are selected to equalize the opening and closing torque. The following table summarizes the results of a typical design calculation.  
                                                                     Parameter   Value                                        Clamp screw diameter   8   mm           Screw thread friction coefficient   0.12               Peak closing force   200   N           Peak opening force   1600   N           Equalized opening and closing torque   20   N-cm           Screw pitch (Total of left and right   6   mm           hand clamp screw sections)                      
 
 Housing 
 
         [0097]      FIG. 4  shows a cross section of application device  41  including the housing components. As well as containing the functional components, the housing has important functions of its own. The nose section  42  of the housing is rigidly connected to the shell  43  of pressure chamber  49 , and serves as one handle through which the user applies opening and closing torque. The base section  44  of the housing is rigidly connected to clamp screw  52 , and serves as the other handle. The base section  44  of the housing rotates relative to the receiver ring  55  and breechblock  45 . In combination, the nose section  42  and the base section  44  of the housing also act as visual and tactile indicators, since they have oval profiles that line up when the device is fully closed. Closure of application device  41  is assisted by a spring-loaded pin and detent  61  that latch the application device  41  in the closed position. Additional functions and features of the housing will become evident in the descriptions of other aspects of application device  41 .  
         [0098]     FIGS.  5  to  9  show various views of the nose section  42  and of some of its components.  FIG. 5  shows a side view of the nose section  42  of an application device of the kind shown by  FIG. 4 .  FIG. 6  shows a first perspective view of the nose section  42  shown by  FIG. 5 .  FIG. 7  shows a second perspective view of the nose section  42  shown by  FIG. 5 .  FIG. 8  shows a first exploded view of components of the nose section  42  shown by  FIGS. 5-7 .  FIG. 9  shows a second exploded view of components of the nose section  42  shown by  FIGS. 5-7 .  
         [0000]     Electric Ignition System  
         [0099]      FIGS. 10 and 11  show schematic representations of the electric ignition system of application device  41 .  
         [0100]     In its simplest form, the electric ignition system of application device  41  consists of a battery  62 , an actuation switch  63  controlled by the user, electrical contacts that engage electrical contacts of cartridge  11 , and interconnection conductors. The user loads a fresh cartridge  11  into application device  41 , closes and locks this device, removes break-off protective cap  17 , presses jet orifice  18  against the skin at the injection site, and then presses push button  63  of the actuation switch. Current passing through an electrically heated wire in the gas generator of cartridge  11  lights the propellant and starts the injection. The invention uses this basic approach, and adds interlock mechanisms to reduce the chance of premature actuation that could cause a hazard or waste an injection cartridge.  
         [0101]     The physical configuration of the electric ignition system of this invention is illustrated in  FIG. 4 . Except as noted, the ignition components are attached to the base section  44  of the housing. Battery  62  is permanently connected by soldering or a similar means, and will normally last the life of application device  41 . The positive battery terminal  64  is electrically connected to the input terminal of the normally open actuation microswitch  71 , and the negative terminal  65  is connected to the input terminal of the normally open interlock microswitch  72 . The output terminal of the actuation microswitch  71  is connected to a conductive spring member  73  that is biased into contact with the central ignition contact pin  66 . This contact connection is required since the central ignition contact pin  66  rotates with the receiver ring  55 , not with the base section  44  of the housing. The output terminal of the interlock microswitch  72  is connected to a conductive spring member  67  that is biased into contact with the sliding conductive transfer pin  74  in the receiver ring  55 . The transfer pin  74  forms a conductive path from the conductive spring member  67  to the co-volume setting ring  48  and then to the breechblock  45 . Because the base section  44  of the housing and the receiver ring  55  have rotational and axial relative motion, contact takes place and ignition is possible only when clamp screw  52  is in the predetermined actuation position.  
         [0102]     The central ignition contact pin  66  presses against the cartridge center ignition contact  32 . The pin head  75  is structurally connected to the sliding breechblock  45 , but electrically isolated by an insulating bushing  76 . The pin shaft passes through clearance holes in the breechblock  45  and clamp screw  52 , and is supported on center by an insulating sleeve bearing  77  to maintain electrical isolation.  
         [0103]     The electrically conductive sliding breechblock  45  presses against the outer ignition contact  31  of cartridge  11 . As described above, current can only flow to the breechblock  45  when the clamp screw  52  is in the actuation position and the transfer pin  74  makes contact with the conductive spring member  67 .  
         [0104]     When the interlock microswitch  72  is closed and the clamp screw  52  is in the actuation position, the actuation microswitch  71  is the only remaining barrier to current flow through the ignition contacts and the electrically heated wire  35  in cartridge  11 . This results in the battery voltage appearing between the input and outlet terminals of the actuation microswitch  71 . This “ready to actuate” condition is visually indicated by a LED  78  connected across the terminals. Actuation then takes place when the user closes the actuation microswitch  71  by pressing push button  63 .  
         [0105]     A mechanism consisting of a pushbutton  63 , coil spring  81 , pin lever  82  and flat spring  83  is used to close the actuation microswitch  71  when the user presses the push button  63 . This arrangement allows the pushbutton  63  to be positioned so that it is convenient for the user, while the actuation microswitch  71  is positioned where housing space is available. The pushbutton  63  slides in a sleeve  84  in the housing, and is biased out by the coil spring  81 . The pin lever  82  serves a dual purpose. First, it is pressed into the pushbutton  63  and extends into openings in the sides of the sleeve  84  to retain the pushbutton  63  in the housing. Second, it acts as a lever that transfers the pushbutton motion to the flat spring  83  that engages the actuation microswitch operating plunger  85 . The pin lever  82  pivots in a hole in the side of the sleeve  84  nearest the nose section  42  of the housing of the application device  41 , and swings through a slot  86  in the opposite side. The flat spring  83  is anchored at one end, and passes over the microswitch  71  and extends to engage the end of the pin lever  82 . When the pin lever  82  swings, it deflects the flat spring  83  towards the actuation microswitch  71  and pushes the actuation plunger  85 . The sleeve  84  in the housing is made of translucent plastic that is illuminated by the “ready to actuate” LED  78 .  
         [0106]     The schematic representation of the electrical ignition system shown by  FIG. 10  illustrates the fact that in order that an injection can be performed with application device  41  the following switches have to be closed: switches  71 ,  72 , and switch formed by lock mechanism  51 , spring-loaded pin and detent  61  and electrical conductive transfer pin  74 . This latter switch is only then closed when the application device  41  is completely assembled, that is when the components contained in nose section  42 , in base section  44 , and the cartridge  11  are all in the proper position with respect to each other.  
         [0107]     The schematic representation of the electrical ignition system shown by  FIG. 11  illustrates the state of this system when the application device  41  is completely assembled and all necessary contacts for the ignition are established with exception of switches  71  and  72  which are still open. In this state LED  78  received a current limited by resistor  79 . This current is well below the value necessary to cause ignition by electrically heating ignition wire  35 , but is large enough to cause light emission by LED  78  and thereby signalize that application device  41  would become ready for performing an injection if and when properly positioned on the injection site.  
         [0108]     When the application device  41  reaches a proper position on the injection site, switch  72  is closed by this positioning, and actuation of push button  63  by the user can then cause closure of switch  71 . If this happens, the electrical ignition circuit is closed and a sufficiently large current is fed to ignition wire  35  to cause ignition of the propellant in cartridge  11 .  
         [0000]     Object Sensor/Position Detector  
         [0109]     The object sensor or position detector requires the nose section  42  of the housing of the application device  41  to be pressed uniformly against the skin surface at the injection site before actuation is possible/allowed. The object sensor/position detector is illustrated in  FIG. 4 . The nose section  42  of the housing includes a flat annular surface  91  which surrounds the end of the shell  43  of pressure chamber  49  that protrudes from the housing and the injection nozzle. A pair of diametrically opposed sensor pins  92 ,  93  slide in holes in the housing, and their ends extend a short distance above the surface in the rest position. The interlock system according to the invention requires that both sensor pins  92 ,  93  are pushed flush with the annular surface  91  to enable execution of an injection. Sensor pins  92 ,  93  support a concentric rigid metal sensor ring  94  that is free to pivot at the contact points with the sensor pins  92 ,  93 . This defines the condition that two or more separate points must be pressed to push the sensor ring  94  and both pins  92 ,  93  flush with the annular surface  91  and enable execution of an injection. If the sensor ring  94  is pressed at any one point around its circumference it will tip, and at most one of the two sensor pins  92 ,  93  will be pushed flush with the annular surface  91 . The annular area, including the sensor ring  94  and sensor pins  92 ,  93 , is covered by a flexible rubber boot  95 . The inner edge of the boot  95  is bonded to the shell  43  of the pressure chamber  49  at a bond point  105 , and the outer edge of boot  95  fits in a groove in the nose section  42  of the housing. The boot  95  forms a smooth, easily cleaned surface and protects the mechanism. It also retains the sensor ring  94  and holds it in the proper spatial relationship with the sensor pins  92 ,  93  at the rest position.  
         [0110]     The sensor pins  92 ,  93  push a relay ring  96  inside the nose section  42  of the housing. The relay ring  96  in turn pushes a tilt plate  97 . The tilt plate  97  contacts the relay ring  96  with two diametrically opposed raised pivot points  98  ( 98   a  respectively  98   b ), and two diametrically opposed legs  99  ( 99   a  respectively  99   b ) extend towards the base section  44  of the housing. The legs  99  are offset 90 degrees from the pivot points  98 , and lie in the same plane as the sensor pins  92 ,  93 . A return spring  101  formed from sheet spring material pushes the tilt plate  97 , relay ring  96  and sensor pins  92 ,  93  towards the nose section  42  of the housing so that the sensor ring  94  is pushed out to the rest position. A cover plate  102  on the surface of the nose section  42  of the housing that abuts the base section  44  of the housing supports the return spring  101  and shields the mechanism. The tilt plate legs  99  pass through holes in the cover plate  102 , with their ends flush with the outer surface in the rest position.  
         [0111]     When the nose section  42  of the housing is attached to the base section  44  of the housing and the clamp screw  52  is locked, one of the two tilt plate legs  99  is aligned with the interlock push pin  103 . This pin contacts the interlock microswitch plunger  104 , and closes the interlock microswitch  72  when it is pushed by one of the tilt plate legs  99 . The other tilt plate leg contacts the base section  44  of the housing and forms a pivot point. If the sensor ring  94  pushes both sensor pins fully, then the relay ring  96  is pushed uniformly against the two tilt plate pivot points. This causes the tilt plate  97  to rotate around the pivot point formed by the leg in contact with the housing so that the other leg extends, pushes the interlock push pin  103 , and closes the interlock microswitch  72 . In the event that only one sensor pin  92  or  93  is pushed, the relay ring  96  tilts rather than moving uniformly. The two points on the relay ring  96  that contact the tilt plate  97  pivots move only half the full distance, with the result that the tilt plate leg  99  moves only half the full distance and does not close the interlock switch  72 .  
         [0112]     This above described object sensor/position detector has a number of useful features. First, it is electromechanical, and does not contain any electronic devices that are sensitive to and whose operation can be affected by spurious signals from electrostatic discharge or other sources of electromagnetic interference. Second, the electric ignition circuit is totally within the base section  44  of the housing, with no connections to the removable nose section  42  of the housing that could compromise reliability. Third, additional safety is provided by the fact that the device must be fully closed and locked to align the tilt plate leg  99  with the interlock push pin  103 . Fourth, the structure of the object sensor/position detector is symmetrical, so that the nose section  42  of the housing may be connected to the base section  44  of the housing in either of two positions which are angularly spaced from each other of 180 degrees.  
         [0000]     List of Reference Numbers  
         [0000]    
       
           11  medication cartridge/cartridge assembly  
           12  cartridge shell  
           13  nozzle body  
           14  flexible container wall  
           15  medication reservoir  
           16  liquid medication  
           17  break-off protective cap  
           18  jet orifice  
         
           19 
         
         
           20 
         
           21  envelope  
           22  fluid channel  
           23  gas generator body  
           24  propellant chamber  
           25  outlet orifice plate  
           26  closure plug/closure plate  
           27  gas pressure chamber  
           28  annular co-volume  
         
           29 
         
         
           30 
         
           31  ignition contact  
           32  ignition contact  
           33  internal support  
           34  co-volume seal ring  
           35  electrically heated wire/ignition wire  
         
           36 
         
         
           37 
         
         
           38 
         
         
           39 
         
         
           40 
         
           41  application device  
           42  nose section  
           43  shell of pressure chamber  
           44  base section  
           45  breech block  
           46  reduced diameter opening  
           47  full diameter opening  
           48  co-volume setting ring  
           40  pressure chamber  
         
           50 
         
           51  lock mechanism  
           52  clamp screw  
           53  male locking lugs  
           54  female pockets  
           55  receiver ring  
           56  interlock lever  
           57  interlock lever  
           58  cam groove  
           59  cam groove  
           60  bias spring  
           61  spring-loaded pin and detent  
           62  battery  
           63  push button/actuation button  
           64  positive terminal  
           65  negative terminal  
           66  central ignition contact pin  
           67  conductive spring member  
           68  arm portion  
           69  latch portion  
           70  pivot  
           71  actuation micro-switch  
           72  interlock micro-switch  
           73  electrical conductive spring member  
           74  electrical conductive transfer pin  
           75  pin head  
           76  insulating bushing  
           77  insulating sleeve bearing  
           78  Light Emitting Diode (LED)  
           79  electrical resistance  
         
           80 
         
           81  coil spring  
           82  pin lever  
           83  flat spring  
           84  sleeve  
           85  operating plunger/actuation plunger  
           86  slot  
         
           87 
         
         
           88 
         
         
           89 
         
         
           90 
         
           91  flat annular surface  
           92  sensor pin  
           93  sensor pin  
           94  metal sensor ring  
           95  flexible rubber boot  
           96  relay ring  
           97  tilt plate  
           98  pivot point ( 98   a,    98   b )  
           99  leg ( 99   a,    99   b )  
         
           100 
         
           101  return spring  
           102  cover plate  
           103  interlock push pin  
           104  interlock microswitch plunger  
           105  bond point  
       
     
         [0208]     Although a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.