Abstract:
The invention provides a injection device for administering an injectable product, including a base section adapted to receive a container from which a product dose is dispensed through a needle by displacement of a piston in the container, and a drive unit including a driven member, a drive element and a damping arrangement, the drive unit for applying a force to advance the piston in the container to dispense a dose, wherein the damping arrangement generally counteracts the drive force and counter forces. The invention also encompasses a needle safety sleeve and a blocking structure for use with injection devices.

Description:
RELATED APPLICATIONS 
   This application is a continuation of U.S. application Ser. No. 09/902,091, filed on Jul. 10, 2001, now issued as U.S. Pat. No. 7,128,728, issued on Oct. 31, 2006, which is a continuation of U.S. application Ser. No. 09/311,434, filed on May 14, 1999, now issued as U.S. Pat. No. 6,258,068, issued on Jul. 10, 2001, which claims priority to German Application No. 198 219 334.4, filed on May 15, 1998, the contents of which are incorporated in their entirety by reference herein. 

   BACKGROUND 
   The invention relates to devices for administering injectable products, in particular the injection of medically or cosmetically effective products. 
   Devices which the invention also concerns are known as injection pens. Generally, an injection pen comprises an elongated, hollow cylindrical housing in which a container, having the shape of an ampoule, filled with the product to be administered, is received. An injection needle is attached to the container and when so attached is generally axially aligned with or parallel to the central longitudinal axis of the housing, extending generally from one end of the housing. A drive unit for a piston within the container is also arranged in the housing. The piston is advanced in forward direction within the container under the effect of a driven member of the drive unit, thus causing a predetermined product dose to be dispensed. For advancing the piston, the driven member itself is advanced in the forward direction (i.e., toward the needle) in relation to the housing, either manually or by the drive force of a drive element of the drive unit. In the latter case, energy is stored in the drive unit, which energy is converted into a drive force driving the driven member forward upon the drive unit being actuated. 
   In the course of advancement of the driven member, the stored energy or at least part of the same is consumed. The drive force exerted by the drive element on the driven member is consequently reduced while the driven member is being advanced. Typically towards the end of the injection or dispensing cycle, the advancing or forward speed of the driven member decreases and, therefore, the dispensing rate will decrease, i.e., dispensing is not uniformly distributed over the total injection or dispensing cycle. Other interferences or counter forces may be caused by irregularities in the internal diameter of the ampoule, resulting in the wall frictional forces affecting the piston, causing non-constant piston movement over the stroke of the piston and making uniform dispensing or injection difficult. 
   SUMMARY 
   It is an object of the invention to provide for the uniform dispensing or injecting of an injectable product in devices for administering such products. 
   In one embodiment, the invention is an injection device comprising a base section and a drive unit including a driven member, a drive element and a damping arrangement. Typically, the base section may accommodate a container from which a product dose is dispensed through a needle by displacement of a piston in the container. The drive unit applies a force to advance the piston in the container to dispense a dose, and the damping arrangement is adapted to generally counteract the drive force and other counter forces produced during use of the device. 
   In another embodiment according to the invention, a device for administering an injectable product comprises a base section, a container arranged in or on the base section, from which container a product is dispensed through a needle by displacement, in a forward direction, of a piston being arranged in the container, and a drive unit comprising a driven member and a drive element, wherein the drive element exerts a drive force on the driven member upon the drive unit being actuated, thus displacing the driven member in the direction of forward advancement of the piston (toward the needle), thereby advancing the piston within the container. The drive force may be exerted on the driven member by a spring, but also by a pressurized fluid, such as compressed air. For actuation of the drive unit, a blocking means, preventing advancement of the driven member, is released. Preferably, in some embodiments, the drive force is not exerted on the driven member before the release of the blocking means. According to the invention, the device comprises means for generating a controlled damping force, counteracting said drive force in the course of the piston being advanced, in addition to unavoidable counter forces. The unavoidable counter forces essentially are frictional forces acting on the piston when the piston is advanced and any forces generated by the work of displacement the piston performs. Since in addition to these unavoidable counter forces a damping force is generated which counters the drive force, the force difference acting on the driven member and resulting from the drive force, the unavoidable counter forces and the damping force can be controlled much more accurately than is the case in prior art devices. 
   The damping force is advantageously set to ensure that the product is administered with the most constant dispensing rate possible. In most applications, the dispensing rate is constant upon the piston being advanced at constant speed. Accordingly, the damping force in one embodiment is generated relative to or dependent on the advancing speed of the piston, preferably directly dependent on the advancing speed of the driven member. An acceleration increases the damping force and a deceleration decreases the damping force. If the advancing speed is kept constant, the damping force remains constant. Self-regulation is particularly preferred. 
   In preferred embodiments, the damping force will be reduced at least once during forward movement. Preferably, the damping force cycle exerted over the advance stroke of the piston is adapted to the cycle of the drive force exerted by the drive element. When the energy of the drive element decreases, the damping force decreases. 
   In one variation, the damping force is generated by the fact that a volume change work must be performed for the advancement of the piston, due to a chamber increasing or decreasing in volume upon the piston being advanced, with pressure compensation in the chamber only taking place at a delayed rate. This system is self-regulatory since change in speed brings about a corresponding change in the damping force. 
   In another variation, the damping force itself is a frictional force. Due to the design of the components being in frictional engagement for this purpose, the damping force, in this case caused by friction, is controlled. 
   The invention is preferably used in injection devices. However, it is not limited to this application. In principle, it may be profitably used in all devices for administering products in which a drive force causes advancement of a driven member, including such devices wherein the drive force directly causes movement of the drive member, and/or in which the advancement of a piston results from the interaction of a drive force with unavoidable counter forces which are predetermined within or result from manufacturing tolerances. 
   Another object of the invention is to improve removal of a needle safety cap typically applied to the needle in injection devices, in which the needle is surrounded by a needle safety sleeve during transport of the device and only projects over or from a front end of the needle safety sleeve during an injection. In prior art devices of this type, in particular semi-automatic injection devices and fully-automatic injection devices, so-called auto-injectors, the needle safety sleeve is slotted in order to allow the user to remove the needle safety cap by access through the slot. However, this means that the needle is visible in the transport position of the device and, in particular, when inserting the needle, thus possibly producing in the user a psychological barrier against insertion of the needle. 
   The present invention in large part solves this problem by connecting a stripper to the device in such a way that the stripper is displaceable against the direction of advancement when inserting the needle. Once the stripper has fulfilled its function, i.e. stripped the needle safety cap from the needle, thus allowing simple, complete removal of the cap from the device, the stripper according to the invention does not impede injection, although it is still connected to the device, due to the stripper being either shifted into or over the needle safety sleeve when the needle is being inserted. The needle then also projects over or beyond a front end of the stripper. The stripper is provided with engaging means for clamping or gripping the needle safety cap, but which do not impede forward movement of the needle in relation to the stripper and the needle safety sleeve after the needle safety cap has been removed. 
   It is another object of the invention to provide a device according to the invention, which can be safely handled after administration of a product, as a uncovered projecting needle poses a safety problem after administration of a product dose. This object is addressed by the invention in that a needle safety sleeve connected to the device, displaceable in and against the direction of needle advancement, is blockable against retraction from a base position in which it surrounds the needle beyond its tip as a protection. Preferably blocking is effected by providing a blocking element or, in a solution that is preferred, by automatic retraction of the inserted needle after or injection. 
   An advantage of the present invention is the operational safety is enhanced. In a device according to the invention, particularly in an auto-injection device in which the needle is automatically advanced by advancement of the container in relation to the base section, the container is advanced against an elastic restoring force, returning the container for replacement into its rear position. 
   This advantage is based on the knowledge that when the needle safety cap covering the needle is retracted, the container is pulled slightly forward against said elastic restoring force, followed by rapidly and abruptly bouncing back into its rear position immediately after the cap has been pulled off due to the restoring force. The container can thereby be damaged. Operational safety is not only jeopardized by the risk of damage to the container, but also by any splinters possibly breaking off from the container which may block an advancement of the container required for inserting the needle. This risk is prevented according to the invention by releasably locking or blocking the container in its rear position, i.e., the base position prior to inserting the needle, against unintentional forward movement. 
   In one preferred variation of this embodiment, the same blocking element which is already used for blocking the displaceable needle safety sleeve, as described above, is also used for blocking the container against forward movement, i.e., the same blocking element may be optionally used for the two blocking functions described. 
   The stripper, the blocking of the needle safety sleeve and the blocking of the container may advantageously be used in connection with controlled damping, but may also be applied individually and in a suitable combination with each other. 
   Other objects, features and advantages of the device and method of the present invention will become more fully apparent and understood with reference to the following description and appended drawings and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts one embodiment of a device according to the present invention, and  FIGS. 1   a  and  1   b , taken from  FIG. 1 , depict details thereof; 
       FIG. 2   a  depicts the stripper shown in  FIG. 1  in a rear position, 
       FIG. 2   b  depicts the stripper in a frontal position, 
       FIG. 3  depicts another embodiment of a device according to the invention, 
       FIG. 3   a  depicts details of the embodiment shown in  FIG. 3 , 
       FIG. 4   a - e  depicts an auto-injection embodiment including blocking of the needle safety sleeve, 
       FIG. 5   a - e  depicts the auto-injection device in accordance with  FIG. 4   a - e  including blocking of the container, 
       FIG. 6   a - b  depicts the auto-injection device in accordance with  FIGS. 4   a - e  and  5   a - e  comprising an alternative release means, and 
       FIG. 7   a - c  depicts an auto-injection device also including blocking of the needle safety sleeve. 
   

   DETAILED DESCRIPTION 
   The accompanying Figures and this description depict and describe embodiments of the injection device and method of the present invention, and features and components thereof. With regard to means for fastening, mounting, attaching or connecting the components of the present invention to form the device as a whole, unless specifically described otherwise, such means are intended to encompass conventional fasteners such as threaded connectors, snap rings, clamps such as screw clamps and the like, rivets, toggles, pins and the like. Components may also be connected by adhesives, glues, welding, ultrasonic welding, and friction fitting or deformation, if appropriate. Unless specifically otherwise disclosed or taught, materials for making components of the present invention may be selected from appropriate materials such as metal, metallic alloys, natural and manmade fibers, vinyls, plastics and the like, and appropriate manufacturing or production methods including casting, extruding, molding and machining may be used. 
   Any references to front and back, right and left, top and bottom and upper and lower are intended for convenience of description, not to limit the present invention or its components to any one positional or spacial orientation. 
     FIG. 1  is a longitudinal section of an injection pen, comprising an elongated, hollow cylindrical housing as a base section. The housing comprises a rear housing sleeve  4  being provided with an internal thread in a front section, and a front housing sleeve  7  being provided with an external thread in a rear section. The two housing sleeves  4  and  7  are screwed to each other in the sections of the two threads. A container  1  is arranged within the area of the front housing sleeve  7  and filled with an injectable product, in particular a fluid medicament. 
   The container  1  is an ampoule, common to such injection pens, including a piston  2  arranged in the same. By advancing the piston  2  towards an outlet at a front end of the container  1 , a product dose is displaced from the container  1 . An injection needle N is arranged on the container outlet pointing in the direction of advancement of the piston  2 . The needle N is covered by a needle safety cap  3 . 
   The container  1  is arranged in and centered by a container holder  30 . The container holder  30 , too, is formed by a sleeve and comprises in a front area three centering tongues  31  for centering the container  1 . Further tongues  32  are formed evenly distributed over the circumference of the container holder  30  between the centering tongues  31  and projecting over the front ends of the centering tongues  31 . The further tongues  32  act as stops when pushing back the needle safety sleeve  10 . 
   An intermediate sleeve  20  is arranged in an annular gap between the container holder  30  and the front housing sleeve  7 . The rear circumference of said intermediate sleeve  20  is provided with recesses through which the container holder  30  projects. Thereby, the container holder  30  is connected to the front housing sleeve  7  non-shiftably in relation to the front housing sleeve  7 ; in embodiment, the container holder  30  is screwed to the front housing sleeve  7 . In contrast, the intermediate sleeve  20  is displaceable in relation to the front housing sleeve  7  and the container holder  30  after release of a blocking means  21 , against the forward direction of the piston. 
   A releasing sleeve  35  is arranged in the rear housing sleeve  4 , a front face of which is in contact with a rear face of the intermediate sleeve  20 . The releasing sleeve  35  is essentially a hollow cylinder. A piston rod, extending rearwards from the piston  2 , projects through it. The releasing sleeve  35  is arranged in the rear housing sleeve  4  and longitudinally displaceable in either direction. It is driven by a restoring spring  9  into its frontal position, as shown in  FIG. 1 , in which it is positioned flush in contact with a rear face of the intermediate sleeve  20  and a rear flange face of the container  1 . A rear face  36  of the releasing sleeve  35  is chamfered outwards from a rear edge of an internal jacket face. When driving the releasing sleeve  35  back, said chamfered face  36  releases a drive unit for advancement of the piston  2  and dispensing the product. 
   The drive unit is formed by a driven member  40  and a drive spring acting as a drive element  49 , clamped between the driven member  40  and the rear housing sleeve  4 . The driven member  40  is pot-shaped, comprising a sleeve body open at its rear, formed by a simple circular cylindrical sleeve, projecting backwards from a closed sleeve bottom  41 . Said sleeve body is arranged in a surrounding internal sleeve  5  of the rear housing sleeve  4 , projecting forward from a rear face of the rear housing sleeve  4 . The internal sleeve  5  forms a slideway for the driven member  40 . In addition, it retains the driven member  40  against the force of the drive element  49  by a number of snap-on elements  6  being evenly distributed over a frontal circumference of the internal sleeve  5  (only one such element  6  is visible in the sectional view of  FIG. 1 ) and surrounding a front face of the driven member  40 . 
     FIG. 1  shows the injection device in its base position prior to injection, in which the driven member  40  is blocked by means of the snap-on elements  6  and the needle N is surrounded by the needle safety sleeve  10 . Due to the needle N being surrounded by the needle safety sleeve  10 , the needle is covered for the user of the injection device, in particular when being inserted into the skin, thus reducing a psychological block against inserting the needle N into one&#39;s own skin. 
   For insertion, the needle safety sleeve  10 , together with the intermediate sleeve  20  and the releasing sleeve  35 , in relation to the housing sleeves  4  and  7  and the container holder  30  with the container  1 , can be shifted back against the forward direction (i.e., away from the needle). Furthermore, a sleeve-shaped stripper  60  is supported by the needle safety sleeve  10 . Said stripper  60  projects over a front face of the needle safety sleeve  10  and can be shifted against a restoring element  69  provided in the needle safety sleeve  10 , formed in the embodiment by a restoring spring, into the needle safety sleeve  10 . The stripper  60  serves to strip off a needle safety cap, already removed in  FIG. 1 . Its removal function will be described with reference to  FIGS. 2   a  and  2   b.    
   For injecting the product the injection device is positioned on and pressed against the surface of a tissue, generally the human skin. This pressure initially pushes the stripper  60 , forming the front end of the injection device, against the force of the restoring element  69 , into the needle safety sleeve  10  up to a stop position, in which it is completely or almost completely surrounded by the needle safety sleeve  10 . As soon as the stripper  60  has reached its stop position in the needle safety sleeve  10 , the user releases the blocking means  21  by pressing the releasing button  8 , thus releasing blocking against shifting of the intermediate sleeve  20  in relation to the front housing sleeve  7 . 
   Since the injection device is still pressed against the tissue, the needle safety sleeve  10 , and subject to the pressure exerted by the needle safety sleeve  10 , the intermediate sleeve  20  and therefore the releasing sleeve  35 , are pushed back within the housing. The needle N penetrates the tissue. Prior to injection, the needle safety sleeve  10  with a rear stop face, formed by an all-round shoulder  12  projecting inwards from a rear section of the needle safety sleeve  10 , pushes against the tongues  32  of the container holder  30 , acting as a stop, the chamfered face  36  of the releasing sleeve  35  engages the snap-on elements  6 , and releases the fixation of the driven member  40  upon the sleeves  10 ,  20  and  35  being driven back further. Release of the fixation occurs at the point in time when the needle N has reached its desired predetermined penetration depth. 
   At this point in time, the driven member  40  is driven by the drive force of the drive element  49  in forward direction against a rear face of the piston rod and drives the piston  2  forward within the container while being driven forward itself. Pushing the piston  2  forward dispenses the product from the container through its outlet and the needle connected to it. In some embodiments, the full content of the container is dispensed upon the drive unit being released. In such embodiments, the content of the container is the product dose. In principle, however, by a constructive further development of the injection device, several selectable product doses could be dispensed during a plurality of injections. 
   During advancement of the driven member  40 , the drive force stored in the drive element is gradually consumed when using a drive spring as a drive element  49 , for instance, in accordance with the characteristics of the spring. The advance speed of the piston  2  would therefore decrease during the course of advancement and the dispensing rate would decrease. In order to compensate for the reduction in drive force while the piston  2  is being advanced, a pneumatic damping force acting on the drive member  40  is generated. 
   For this purpose, the driven member  40  and the housing, i.e., the rear housing sleeve  4  form walls of a low-pressure chamber K, the volume of which increases during advancement of the driven member  40 . In this embodiment, the chamber K is formed by the sleeve bottom  41  and the sleeve body of the driven member  40  projecting from the same, and the rear face of the rear housing sleeve  4  and the internal sleeve  5  projecting from the same. The sleeve body of the drive member  40  and the internal sleeve  5  are displaced like telescopic sleeves in relation to each other. In the area of the slideways, i.e., between the external jacket face of the driven member  40  and the internal jacket face of the internal sleeve  5 , a surrounding seal  42  is arranged. In the embodiment, a washer is placed in a circumferential groove of the sleeve body of the driven member  40 . 
   Referring to  FIG. 1 , and  FIGS. 1   a  and  1   b , the rear face of the rear housing sleeve  4  comprises a passage “P” into which a seal  50 , having a calibrated through-bore “T”, but otherwise being airtight, has been inserted. Instead of a calibrated through-bore, a one-way or non-return valve “V” could be used, allowing the unimpeded escape of air upon the driven member  40  being driven back, but pressing against a valve seat on aspiration, this leaving only a defined, narrow through-bore, as predetermined in the design. The volume flow admitted per time unit into the chamber K is in any case less per time unit than the increase in volume of the chamber occurring during the advancement of the driven member  40 , with a damping force therefore always being generated as long as the driven member  40  is advanced by the resulting drive force. The faster the driven member  40  is advanced the larger the generated damping force, i.e., the larger the effectively exerted drive force the larger the damping force generated. The type of damping force generation will therefore automatically compensate an energy consumption taking place in the drive unit, since with a decrease of the drive force a deceleration of the driven member  40  and a reduction of the damping force occurs. Simultaneously, other unavoidable or practically unavoidable counter forces are also compensated. Such superficial and other irregularities which cause deceleration or acceleration of the driven member  40 , are automatically accompanied by a change in the volume change work to be performed by the drive element  49 . An exemplary counter force is wall friction between the container  1  and the piston  2 , which is not identical everywhere over the stroke of the piston  2  within the container  1 . In addition, damping is further reduced due to the compressibility of the medium and the increase in chamber volume during the course of advancement of the driven member  40 , thus compensating twice for energy consumption. 
     FIGS. 2   a  and  2   b  show how a needle safety cap  3  may be removed by means of the stripper  60 .  FIG. 2   a  shows the needle safety cap  3  completely covering or surrounding the injection needle. This corresponds to the state of the injection device directly after inserting the container  1  and screwing the two housing sleeves  4  and  7  together. At the same time, this represents the transport position of the injection device until just prior to injection. For preparation for an injection, the needle safety cap  3  is initially removed. 
     FIG. 2   a  shows how the removal of the needle safety cap  3  is initiated. For this, initially, the sleeve-shaped stripper  60  is pushed into the needle safety sleeve  10  against the pressure of the restoring element  69  until it presses against the needle safety cap  3  with two diametrically opposed engaging elements  61 . The two engaging elements  61  project obliquely inwards, like barbs, from the rear interior jacket face of the stripper. When pushing back the stripper  60 , the engaging elements  61  are more and more strongly pressed against the needle safety cap  3  which is widened towards the rear. 
   After firmly clamping the needle safety cap  3  between the engaging elements  61 , the stripper  60  may be released. It is returned by the restoring element  69  to its frontal position, as shown in  FIG. 2   b , pushing it against a stop shoulder  11  of the needle safety sleeve  10 , thus stripping the needle safety cap  3  from the container  1 . In this position, the needle safety cap  3 , which now only loosely covers the needle N, may be easily and completely removed manually from the front. In order to simplify manual removal, the stripper  60  is provided with at least two gripping recesses  62 . 
   As the stripper  60  is permanently attached to the injection device, the user does not have to first tediously introduce it for removal of the needle safety cap  3 . On the other hand, it does not interfere in any way during injection. Another advantage resides in the fact that the needle safety sleeve  10  can be designed completely closed, i.e., without any gripping slot for removal of the needle safety cap  3 , thus allowing the needle N to be completely covered. 
     FIG. 3  shows an auto-injection device not only for automatically dispensing the product but also for automatically inserting the needle. Where the same references are used in  FIG. 3  as in the embodiments described above, components of a substantially identical function are identified. As to the basic mode of operation of the auto-injection device, reference is made to the applicant&#39;s parallel German patent application No. 198 22 031 and the corresponding U.S. application Ser. No. 09/311,435, the disclosures of which are incorporated herein by reference: 
   In contrast to the embodiment of  FIG. 1 ,  FIG. 3  depicts an exemplary embodiment of a damping mechanism in an auto-injection device wherein damping of the drive force exerted on the driven member  40  is effected by friction. This damping frictional force is exerted between a contact pressure element  45 , designed as a pliable ring, clamped between the sleeve-shaped driven member  40  and a transfer member  46 , which is also sleeve-shaped and surrounds the driven member  40  during advancement. This damping frictional force is exerted between a contact pressure element  45 , designed as a pliable ring, clamped between the sleeve-shaped driven member  40  and a transfer member  46  which is also sleeve-shaped and surrounds the driven member  40  during advancement. 
   In the auto-injection device of  FIG. 3 , the injection cycle is essentially as follows: a blocking unit blocking the advancement of the driven member  40  is released by pressing a release tongue  8 , and the driven member  40  is driven forward to the left in  FIG. 3 , by the drive force of the drive element  49 , which is also a compression spring in this embodiment. Initially, the contact pressure element  45  forms a coupling between the driven member  40  and the transfer member  46 , as shown specifically in detail in  FIG. 3   a . The driven member  40  drives the transfer member  46  via this coupling The transfer member  46 , in turn, advances the container  1 , including the needle N attached to the same at the front end, in relation to the housing. 
   Thereby, the needle N is pushed forward out of the needle safety sleeve  10   a  and is inserted. The needle safety sleeve  10   a , in this embodiment, is firmly attached to the housing. Insertion is limited by stopping of the container holder  30  at the housing. When stopped, the coupling between the driven member  40  and the transfer member  46  is released, as clearly shown in  FIG. 3   a . During further advancement, the driven member  40  is driven forward in relation to the transfer member  46 , presses against the piston rod and advances by its own further advancement the piston  2  in the container  1 , thus allowing the product to be dispensed. 
   The contact pressure element  45  is a slotted spring washer similar to a piston ring. This washer is placed in an all-round groove  44  on an external circumference of the driven member  40 , pressing elastically and radially against the driven member and the internal jacket slideway  43  of the transfer member  46 , i.e., a type of counter element. The external circumference of the driven member  40  or the internal jacket slideway  43  of transfer member  46  may provide a contact pressure surface for contact pressure element  45 . The wall frictional force exerted between the contact pressure element  45  and the transfer member  46  decreases during the course of advancement of the driven member  40  due to the internal jacket slideway  43  of the transfer member  46  being widened in the forward direction. This compensates for a decrease of the drive force of the drive element  49 . 
   A guide ring  47  is placed in a rear section of the transfer member  46 , serving as a straight guide for the driven member  40 . Said guide ring  47  may also be formed as a sealring comprising one or several calibrated through-bores or a non-return valve in accordance with the embodiment of  FIG. 1 . In this way a pneumatic damping force instead of or in addition to the frictional damping force could be generated. In such an embodiment, the low-pressure chamber would be formed in the gap section between the transfer member  46  and the driven member  40  being shifted into the transfer member  46 . 
   A tensioning handle  8   a , projecting through the housing  4 , is used for returning into rear position and tensioning a holding  4   a  and release sleeve  4   b  together with the driven member  40 , the holding  4   a  and release sleeve  4   b  being displaceably arranged in the housing and jointly connected with the driven member  40 . 
     FIGS. 4   a - e  and  5   a - e , which include elevational, sectional and cross-sectional views, show an auto-injection device in which the advancement of the container  1  for inserting the needle is effected in the conventional way by the piston  2 , in contrast to the device of  FIG. 3 , i.e. advancement of the container  1  is not decoupled from the advancement of the piston  2 , but is rather effected by the piston  2 . However, the injection device of  FIGS. 4   a - e  and  5   a - e , like that shown in  FIG. 1 , comprises a needle safety sleeve  10 , displaceable in either longitudinal direction in relation to the housing. This displaceable needle safety sleeve  10  covers the needle after injection, i.e. after retraction, which is not possible in the auto-injection device depicted in  FIG. 3 . 
   In contrast to the embodiment of  FIG. 1 , however, a stripper  65  is provided, not permanently connected to the injection device, but which must be inserted between the needle safety cap  3  and the needle safety sleeve  10  for removing the needle safety cap  3  until it grips behind the needle safety cap  3  like a claw, thus allowing removal of the needle safety cap  3  together with the stripper  65 . 
     FIG. 4   a - e  shows an injection device after injection and retraction of the needle with the needle safety cap  3  already inserted on it for future transport. A special feature of this embodiment is the blocking of the needle safety sleeve  10 . 
   Blocking of the needle safety sleeve  10  securely ensures that the tip of the needle cannot freely project, thus eliminating any risk of damage to the needle N and in particular injury. The needle safety sleeve  10  is blocked by a blocking element  80  relative to the housing in such a way as to prevent the needle safety sleeve  10  being pushed back against forward direction. 
   The blocking element  80  is formed by means of a ring section comprising two engaging elements  81 , having the shape of two webs, projecting from an inner jacket face of said ring. As best shown in  FIG. 5   a - e  on the bottom left-hand side, the needle safety sleeve  10  comprises two slots  15  gripped by one each of the engaging elements  81  upon the blocking element  80  being placed on the housing. The engaging elements  81  then form stops for those walls of the slots  15  which extend in circumferential direction. The blocking element  80  is obtained by cutting a sleeve open, which sleeve is a circular annular sleeve in the embodiment, wherein cutting open occurs in longitudinal direction and outside of the central longitudinal axis of the sleeve, so that the blocking element  80  comprises a shell which when seen in cross-section, projects a little over the semicircle. Thus, the blocking element  80  as explained hereafter with reference to  FIG. 4   a - e , is insertable over the rear housing sleeve  4  and projects over the largest diameter of the rear housing sleeve  4  when inserted over it. 
   As best shown in cross-sections B-B and C-C of  FIG. 4   a - e , the blocking element  80  in carrying out its function as a block is retained on the needle safety sleeve  10  by means of its snap-in connection. For this the engaging elements  81  are designed flexibly and elastically and provided with snap-in projections at the front, gripping one of the internal slot edges after passing through each slot  15 , thus retaining the blocking element  80  like a snapper in blocked position, but allowing easy removal when required. 
     FIG. 5   a - e  shows the blocking element  80  in its second function, in which it blocks the container  1  against advancement. Without this blocking, during removal of the needle safety cap  3 , the container  1  would be carried along in forward direction over a certain distance against the force of the elastic restoring element  29  and would snap back into its rear position depicted in  FIG. 5   a - e  the moment the needle safety cap  3  is removed, due to the force of the restoring element  49 . When snapping back, there would be a risk of damaging the container and an ensuing risk of possibly blocking forward movement of the container  1  when inserting the needle N. 
   In order to prevent this, the blocking element  80  is attached to a section of the housing covering the rear edge of the container  1  while the injection device is in its transport position until the needle safety cap  3  is removed. In this position, as shown in the longitudinal section of  FIG. 5   a - e , the shell body of the blocking element  80  closely surrounds the housing, as shown in particular in cross-section E-E, and is retained to the rear housing sleeve  4  due to its ends projecting over the semicircle. The engaging elements  81  do not assume any retention function for the blocking element  80 , but now serve as a block for the container  1 . For this purpose, the engaging elements  81  grip through the housing and are positioned in front of an all-round flange provided at the rear end of the container  1  upon the blocking element  80  being attached. Since this rear flange of the container  1 , extending radially outwards, pushes against the engaging elements  81  of the blocking element  80  when removing the needle safety cap  3 , the container  1  is blocked in rear position and cannot therefore be advanced. 
   In its position shown in  FIG. 5   a - e , the blocking element  80  fulfills a third function, namely to prevent release of the drive unit by blocking the movement of a release means  70 . The release means  70  is then able to release the driven member  40  from its blocked position when the blocking element  80  is removed from the housing, thus only allowing advancement of the release means  70  in relation to the housing at this point. 
     FIG. 6   a - b  shows an auto-injection device which corresponds to the injection device of  FIGS. 4   a - e  and  5   a - e , except for the release means  70  for the driven member  40 . A release means  70   a  of  FIG. 6   a - b , too, consists of a sleeve-shaped body comprising a rear sleeve bottom. The driven member  40  is both blocked in its rear position by the release means  70   a  and released when operating the release means  70   a  accordingly. 
   The rear end of the driven member  40  ends in snap means, projecting through a rear face wall of the housing and surrounding its rear circumferential edge, with the snap means of the driven member  40  being pushed outwards due to their inherent elasticity and retained in their positions. As an additional security against unintentional disengagement, for instance due to impact, a blocking part  71  of the release means  70   a , which projects from its sleeve bottom and is formed as a small rectangle when seen in cross section, engages with its long side between two diametrically opposed snap means of the driven member  40 . In this rotational position, it prevents both snap means bending towards each other in the position of the release means  70   a  shown in  FIG. 6   a - b , which would release the snap-in connection. Furthermore, two contact pressure members  72  are projecting from the sleeve bottom of the release means  70   a  at a distance from both sides of the blocking part  71 , which when seen in cross section have the shape of circular segments. The blocking part  71  projects over the contact pressure members  72 . The blocking element  80  is initially removed for release of the driven member  40 , followed by rotating the release means  70   a  at least so far around its longitudinal axis that the snap means of the driven member  40  can be bent towards each other. During rotation of the release means  70   a , the contact pressure members  72  are positioned over the snap means of the driven member  40  when seen in cross section. When pushing the release means  70   a  towards the driven member  40 , the impression elements  72  push against the snap means of the driven member  40 , which comprise chamfered rear faces, thus allowing them to bend towards each other under the pressure of the impression members  72 , thereby releasing the snap-in connection of the driven member  40  with the housing. Due to the pressure exerted by the drive unit  49  the driven member  40  is then driven forward. 
   The blocking element  80  may be designed as a rotary element instead of a plug-in element and could, therefore, remain on the housing after blocking of the container has been released. 
     FIGS. 7   a ,  7   b  and  7   c  show the mode of operation of the needle protection apparatus which prevents the needle N from freely projecting from the housing after retraction from the tissue when it could be broken and/or cause injury if not handled carefully. A feature of the needle protection apparatus is that the needle safety sleeve  10 , which is displaceable in relation to the housing for the purpose of insertion, is blocked in a needle protection position after retraction of the needle, so that it can no longer be pushed into the housing. Pushing over the housing externally would also be feasible. The mode of operation of the pen for inserting the needle N and dispensing the product corresponds to that of the pen shown in  FIG. 3 . 
     FIG. 7   a  shows the front section of the pen in its base position directly before injection.  FIG. 7   b  shows the pen in the frontal position of the container  1 , i.e. in injecting position. The needle safety sleeve  10  has been pushed against the force of the restoring element  19  into its most rear displacement position in relation to the housing sleeve  7 . The needle N projects out of the housing and the needle safety sleeve  10  by the desired length. 
   The needle safety sleeve  10  comprises a rear stop face and a front stop face, limiting the displacement path of the needle safety sleeve  10  in relation to the front housing sleeve  7  in and against forward direction. When moving the needle safety sleeve  10  in either direction, it passes over a blocking sleeve  80 ′ provided in the housing and secured against displacement and preferably also rotation, said blocking sleeve  80 ′ comprising at its front end at least one hook  82  which is chamfered outward obliquely or curved. In an internal jacket section, with which it slides over the hook  82 , the needle safety sleeve  10  comprises a widened section, extending approximately over the length of its maximum displacement path, the widened section being preferably a slightly widened internal diameter. A transitional section  14  extending between the widened section and the adjacent internal cross section is chamfered, thus enabling the needle safety sleeve  10  to slide over the hook  82 , subject to the pressure of the restoring element  19 , up to a point behind the transitional area  14 . Behind the transitional area  14 , in a central section the needle safety sleeve  10  is provided with longitudinal slots  15 , the front faces  16  of which, as best shown in  FIG. 7   c , form stop faces each for one of the hooks  82 . 
   The blocking sleeve  80 ′ ends in a number of elastic and flexible tongues  83 , evenly distributed over the circumference of the sleeve, the free front ends of which are each formed as a hook  82 . The container holder  30  also ends in tongues  33  towards its free front end. When advancing the container holder  30  against the force of the restoring element  29 , these tongues  33  are positioned below the tongues  83  of the blocking sleeve  80 ′. Each of the tongues  83  is thus supported radially towards the inside and can no longer be bent radially inward when the container is in its frontal position. The tongues  83  are not only supported by the tongues  33  but are in addition pushed radially outwardly. In comparison with the tongues  83 , the tongues  33  are rigidly formed and may be more rigid than tongues  83 . 
   After retraction of the needle N, the needle safety sleeve  10  is pushed forward again by the restoring element  19 . Due to the chamfered face  14  and/or the chamfered shape of the at least one hook  82 , the needle safety sleeve  10  is pushed over said hook  82 , the end tip of which is, furthermore, elastic and flexible. However, as soon as the needle safety sleeve  10  has been advanced again to a point at which its stop face  16  is positioned in front of the hook  82 , when seen in forward direction, it is blocked against return by the hook  82  positioned against the stop face  16  in stop position. The hook  82  and the needle safety sleeve  10  are in contact with each other by their stop faces which point vertically to the direction of displacement. In its safety position shown in  FIG. 7   c , the needle N is protected after injection by means of the needle safety sleeve  10 . 
   The container holder  30  is therefore simultaneously used as a displaceable support for the at least one hook  82  and fulfills, according to the invention, the dual function of retaining the container  1  and blocking the needle safety sleeve  10 . The needle safety apparatus does not require the auto-injection device to be designed according to the invention, although it is used most preferably in combination with the same. It may also be used to advantage in generic auto-injection devices. 
   The foregoing description of embodiments of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. The above described embodiments were chosen and described to provide an illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when the claims are interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.