Title of Invention	A COMPACT INJECTION DEVICE FOR AUTOMATIC EXTENSION AND RETRACTION OF ITS SYRINGE AFTER CONTENT DISCHARGE
Abstract	The invention relates to a compact injection device (110) for automatic extension and retraction of its syringe after content discharge, comprising a housing (112) adapted to receive a syringe (114) having a discharge nozzle (118): first and second drive elements (132,134), of which the first is acted upon and the second acts upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the discharge nozzle, the first drive element being capable of movement relative to the second when the former is acted upon and the latter is restrained by the syringe; and a coupling that prevents the first drive element from moving relative to the second until they have been advanced to a nominal decoupling position relative to the syringe.

Title of Invention

A COMPACT INJECTION DEVICE FOR AUTOMATIC EXTENSION AND RETRACTION OF ITS SYRINGE AFTER CONTENT DISCHARGE

Abstract

The invention relates to a compact injection device (110) for automatic extension and retraction of its syringe after content discharge, comprising a housing (112) adapted to receive a syringe (114) having a discharge nozzle (118): first and second drive elements (132,134), of which the first is acted upon and the second acts upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the discharge nozzle, the first drive element being capable of movement relative to the second when the former is acted upon and the latter is restrained by the syringe; and a coupling that prevents the first drive element from moving relative to the second until they have been advanced to a nominal decoupling position relative to the syringe.

Full Text	Background Technology The present invention relates to an injection device of the type that receives a syringe, extends it, discharges its contents and then retracts it automatically. Devices of this general description arc shown in WO 95/35126 and EP-A-0 516 473 and tend to employ a drive spring and some form of release mechanism that releases the syringe from the influence of the drive spring once its contents are supposed to have been discharged, to allow it to be retracted by a return spring. Because of the stack-up of tolerances of the various components of the device, a certain margin of safety must be built into the activation of the release mechanism, to ensure that it is effective. The consequence of underestimating the safety margin is that the release mechanism may fail to operate even once the syringe contents have been discharged, which is unsatisfactory in a device that is supposed to retract automatically, particularly for self-administered drugs. On the other hand, overestimating the safety margin may mean that some of the syringe contents arc discharged after the syringe has retracted, which results firstly in a short dose and secondly in what may be termed a "wet" injection. Wet injections are undesirable for the squeamish, particularly in connection with self-administered drugs. UK patent applications nos. 0210123, 0229384 and 0325596 describe a series of injection devices designed to deal with this problem. Each makes use of a neat trick that delays the release of the syringe for a certain period of time after the release mechanism has been activated, in an attempt to ensure that the syringe has been completely discharged. The devices illustrated in UK patent application no. 0325596 make use of a two-part drive incorporating a fluid-damped delay mechanism that is particularly effective in ensuring complete discharge of the syringe contents. In each case, the device relies upon two unlatching mechanisms. The first unlatching mechanism initiates the fluid damping mechanism and the second releases the syringe from the actuator, allowing it to be withdrawn. The unlatching mechanisms are activated by components of the injection device having been advanced to nominal unlatching positions relative to the device casework. A device 10 of this general character is illustrated schematically in figure 1. The sequence of operation is as follows. Firstly, the device 10 is armed. The user presses a release button and the syringe 14 is advanced a distance d, by a drive spring 30, thereby compressing the retraction spring 26. This movement inserts the needle 18 into the patient. The plunger 23 is advanced a distance d2 by the drive spring 30, injecting most of the dose. Once nearly the entire dose has been injected, the first unlatching mechanism is activated, an operation illustrated schematically by the coincidence of components 1 and 3. The plunger 23 is then advanced a further distance d3 by the drive spring 30, injecting the rest of the dose. Finally, the second unlatching mechanism is activated, an operation illustrated schematically by the coincidence of components 2 and 4, and the retraction spring 26 then causes the needle 18 to be retracted by the distance d\|. Since the drive spring acts upon the same component of the device throughout, here referred to as the "actuator", the distance that component must move between the device being armed and the second unlatching mechanism being activated is, subject to tolerance stack-up, equal to the sum of d1, D2 and d3. In the devices described in the applications mentioned above, all of this movement takes place to the rear of the syringe, which means that the overall length of the device must be greater than the sum of the length of the actuator, the distances d1, d2, and d3, and the length of the syringe body not including the needle. The best design of injection device is one that is compact. This is important both to the ergonomics of the device and to its manufactured cost. The length of the device can be reduced by allowing the actuator to move past the syringe, and by having the unlatching mechanisms activated in front of the syringe. However, this would require the actuator and its unlatching mechanisms to pass around the space occupied by the syringe, involving an increase in diameter of the device that negates the length savings. Summary of the Invention It is an objective of the present invention to provide a more compact device. Instead of triggering release of the unlatching mechanisms using a fixed point on the device casework, the present invention does it using one of more features that move forward with the syringe as it is advanced. In other words, the nominal positions at which the unlatching mechanisms are activated are defined relative to the syringe, not relative to the device casework. As illustrated in figure 2, these nominal positions also move forwards a distance d1 as the syringe is initially advanced. This in turn means that the initial distance between the actuator and the syringe plunger can be reduced by the distance d1. The length of the device can be reduced by d1 at a stroke. More modest improvements arc available when only one of the nominal positions at which the unlatching mechanisms are activated is defined relative to the syringe. Accordingly, a first aspect of the present invention provides an injection device comprising: a housing adapted to receive a syringe having a discharge nozzle; first and second drive elements, of which the first is acted upon and the second acts upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the discharge nozzle, the first drive element being capable of movement relative to the second when the former is acted upon and the latter is restrained by the syringe; a coupling that prevents the first drive element from moving relative to the second until they have been advanced to a nominal decoupling position relative to the syringe. In this case, the nominal decoupling position, i.e. the first nominal unlatching position, is defined relative to the syringe and not relative to the housing. Preferably, the device includes: an actuator that acts upon the first drive element; means for biasing the syringe from an extended position in which the discharge nozzle extends from the housing to a retracted position in which the discharge nozzle is contained within the housing; and a release mechanism, activated when the first drive element has been advanced to a nominal release position that is more advanced than the said nominal decoupling position, and adapted to release the syringe from the action of the actuator, whereupon the biasing means restores the syringe to its retracted position. In preferred embodiments of the invention, the nominal decoupling position is defined either by one of the drive elements interacting with a decoupling component that moves with the syringe as it is advanced. For ease of manufacture and assembly, the coupling may comprise flexible arms on one of the drive elements that engage with a drive surface on the other, in which case the decoupling component causes the flexible arms to move when the said nominal decoupling position is reached, thus disengaging them from the drive surface to allow the first drive element to move relative to the second. A second aspect of the present invention provides an injection device comprising: a housing adapted to receive a syringe having a discharge nozzle, the housing including means for biasing the syringe from an extended position in which the discharge nozzle extends from the housing to a retracted position in which the discharge nozzle is contained within the housing; first and second drive elements, of which the first is acted upon and the second acts upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the discharge nozzle, the first drive element being capable of movement relative to the second when the former is acted upon and the latter is restrained by the syringe; a coupling that prevents the first drive element from moving relative to the second until they have been advanced to a nominal decoupling position; and a release mechanism, activated when the first drive element has been advanced to a nominal release position relative to the syringe that is more advanced than the said nominal decoupling position, and adapted to release the syringe, whereupon the biasing means restores the syringe to its retracted position. Mere, the nominal release position, i.e. the second nominal unlatching position, is defined relative to the syringe and not relative to the housing. Again, in preferred embodiments, the nominal release position is defined by an actuator or the first drive element interacting with a decoupling component that moves with the syringe as it is advanced. It may be defined by the actuator interacting with the first drive element once the nominal decoupling position has been reached, at which position the first drive element is restrained by the syringe against further movement. Once again, for case of manufacture and assembly, of the actuator and the first drive element, one preferably comprises second flexible arms that engage with a second drive surface on the other, and the release mechanism preferably comprises the said decoupling component, which causes the second flexible arms to move when the said nominal release position is reached, thus disengaging them from the drive surface. Alternatively, of an actuator and the first drive element, one preferably comprises second flexible arms that engage with a second drive surface on the other, allowing the actuator to act upon the first drive element and preventing the former from moving relative to the latter until the nominal release position has been reached, the second flexible arms are preferably biased toward a position at which they engage the second drive surface and the release mechanism preferably causes them to move against their bias, thus disengaging them from the drive surface. Brief Description of the Drawings The invention will now be described by way of example with reference to the accompanying drawings, in which: figures 1 and 2 are schematic illustrations to which reference has already been made; Figure 3 is an illustration of a first embodiment of the invention; and Figure 4 is likewise a second. Detailed Description Figure 3 shows an injection device 110 in which a housing 112 contains a hypodermic syringe 1 14. The syringe 114 is of conventional type, including a syringe body 116 terminating at one end in a hypodermic needle 118 and at the other in a flange 120. The conventional plunger that would normally be used to discharge the contents of the syringe 114 manually has been removed and replaced with a drive element 134 as will be described below, to which is attached a bung 122. The bung 122 constrains a drug 124 to be administered within the syringe body 116. Whilst the syringe illustrated is of hypodermic type, this need not necessarily be so. Transcutaneous or ballistic dermal and subcutaneous syringes may also be used with the injection device of the present invention. Generally, the syringe must include a discharge nozzle, which in a hypodermic syringe is the needle 118. As illustrated, the housing includes a return spring 126 that biases the syringe 114 from an extended position in which the needle 118 extends from an aperture 128 in the housing 112 to a retracted position in which the discharge nozzle 118 is contained within the housing 112. The return spring 126 acts on the syringe 114 via a sleeve 127. At the other end of the housing is a compression drive spring 130. Drive from the drive spring 130 is transmitted via a multi-component drive to the syringe 114 to advance it from its retracted position to its extended position and discharge its contents through the needle 118. The drive accomplishes this task by acting directly on the drug 124 and the syringe 114. Hydrostatic forces acting through the drug 124 and. to a lesser extent, static friction between the bung 122 and the syringe body 116 initially ensure that they advance together, until the return spring 126 bottoms out or the syringe body 116 meets some other obstruction that retards its motion. The multi-component drive between the drive spring 130 and the syringe 114 consists of three principal components. A drive sleeve 131 takes drive from the drive spring 130 and transmits it to flexible latch arms 133 on a first drive element 132. This in turn transmits drive via flexible latch arms 135 to a second drive element, the drive element 134 already mentioned. The first drive element 132 includes a hollow stem 140, the inner cavity of which forms a collection chamber 142 in communication with a vent 144 that extends from the collection chamber through the end of the stem 140. The second drive element 134 includes a blind bore 146 that is open at one end to receive the stem 140 and closed at the other. As can be seen, the bore 146 and the stem 140 define a fluid reservoir 148, within which a damping fluid is contained. A trigger (not shown) is provided on one side of the housing 112. The trigger, when operated, serves to decouple the drive sleeve 131 from the housing 112, allowing it to move relative to the housing 112 under the influence of the drive spring 130. The operation of the device is then as follows. Initially, the drive spring 130 moves the drive sleeve 131, the drive sleeve 131 moves the first drive element 132 and the first drive element 132 moves the second drive element 134. in each case by acting through the flexible latch arms 133, 135. The second drive element 134 and the bung 122 move and, by virtue of static friction and hydrostatic forces acting through the drug 124 to be administered, move the syringe body 116 against the action of the return spring 126. The return spring 126 compresses and the hypodermic needle 118 emerges from the exit aperture 128 of the housing 112. This continues until the return spring 126 bottoms out or the syringe body 116 meets some other obstruction that retards its motion. Because the static friction between the bung 122 and the syringe body 116 and the hydrostatic forces acting through the drug 124 to be administered are not sufficient to resist the full drive force developed by the drive spring 130, at this point the second drive element 134 begins to move within the syringe body 116 and the drug 124 begins to be discharged. Dynamic friction between the bung 122 and the syringe body 116 and hydrostatic forces acting through the drug 124 to be administered are, however, sufficient to retain the return spring 126 in its compressed state, so the hypodermic needle 118 remains extended. Before the second drive element 134 reaches the end of its travel within the syringe body 116, so before the contents of the syringe have fully discharged, the flexible latch arms 135 linking the first and second drive elements 132, 134 reach a constriction 137. The constriction 137 is formed by a component 162 that is attached to the syringe flange 120, so it will be understood that when the syringe 114 advances from its retracted position to its extended position, the component 162 advances with it. The constriction 137 moves the flexible latch arms 135 inwards from the position shown to a position at which they no longer couple the first drive element 136 to the second drive element 134, aided by the bevelled surfaces on the constriction 137. Once this happens, the first drive element 136 acts no longer on the second drive element 134, allowing the first drive element 132 to move relative to the second drive element 134. Because the damping fluid is contained within a reservoir 148 defined between the end of the first drive element 132 and the blind bore 146 in the second drive element 134, the volume of the reservoir 148 will tend to decrease as the first drive element 132 moves relative to the second drive element 134 when the former is acted upon by the drive spring 130. As the reservoir 148 collapses, damping fluid is forced through the vent 144 into the collection chamber 142. Thus, once the flexible latch arms 135 have been released, the force exerted by the drive spring 130 does work on the damping fluid, causing it to flow through the constriction formed by the vent 144, and also acts hydroslatically through the fluid, to drive the second drive element 134. Losses associated with the flow of the damping fluid do not attenuate the force acting on the body of the syringe to a great extent. Thus, the return spring 126 remains compressed and the hypodermic needle 118 remains extended. After a time, the second drive element 134 completes its travel within the syringe body 116 and can go no further. At this point, the contents of the syringe 114 are completely discharged and the force exerted by the drive spring 130 acts to retain the second drive element 134 in its terminal position and to continue to cause the damping fluid to How through the vent 144, allowing the first drive element 132 to continue its movement. Before the reservoir 148 of fluid is exhausted, the flexible latch arms 133 linking the drive sleeve 131 with the first drive element 132 reach another constriction 139, also provided by the component 162 that is attached to the syringe flange 120. The constriction 139 moves the flexible latch arms 133 inwards from the position shown to a position at which they no longer couple the drive sleeve 131 to the first drive element 132, aided by the bevelled surfaces on the constriction 139. Once this happens, the drive sleeve 131 acts no longer on the first drive element 132, allowing them to move relative to each other. At this point, of course, the syringe 114 is released, because the force developed by the drive spring 130 is no longer being 226 bottoms out or the syringe body 216 meets some other obstruction that retards its motion. The multi component drive between the drive spring 230 and the syringe 214 again consists of three principal components. The drive sleeve 231 takes drive from the drive spring 230 and transmits it to flexible latch arms 233 on a first drive element 232. These elements are shown in detail "A". The first drive element 232 in turn transmits drive via flexible latch arms 235 to a second drive element 234. These elements are shown in detail "B'\ As before, the first drive element 232 includes a hollow stem 240, the inner cavity of which forms a collection chamber 242. The second drive element 234 includes a blind for 246 that is open at one end to receive the stem 240 and closed at the other. As can be seen, the bore 246 and the stem 240 define a fluid reservoir 248, within which a damping fluid is contained. A trigger (not shown) is provided in the middle of the housing 212. The trigger, one operated, serves to decouple the drive sleeve 231 from the housing 212 allowing it to move relative to the housing 212 under the influence of the drive spring 230. The operation of the device is then as follows. Initially, the drive spring 230 moves the drive sleeve 231, the drive sleeve 231 moves the first drive element 232 and the first drive element 232 moves the second drive element 234, in each case by acting through the flexible matching arms 233, 235. The second drive element 234 moves and, by virtue of static friction and hydrostatic forces acting through the drug 224 to be administered, moves the syringe body 216 against the action of the return spring 226. The return spring 226 compresses and the hypodermic needle 218 emerges from the exit aperture 228 of the housing 212. This continues until the return spring 226 bottoms out or the syringe body 216 meets some other obstruction that retards its motion. Because the static friction between the bung 222 and the syringe body 216 and the hydrostatic forces acting through the drug 224 to be administered are not sufficient to resist the full drive force developed by the drive spring 230, at this point the second drive element 234 begins to move within the syringe body 216 and the drug 224 begins to be discharged. Dynamic friction between the bung 222 and the syringe body 216 and hydrostatic forces acting through the drug 224 to be administered are, however, sufficient to retain the return spring 226 in its compressed state, so the hypodermic needle 218 remains extended. Before the second drive element 234 reaches the end of its travel within the syringe body 216, so before the contents of the syringe have fully discharged, the flexible latch arms 235 linking the first and second drive elements 232, 234 reach a constriction 237. The constriction 237 is formed by a component 262 that is attached to the syringe carrier. Additional flexible arms 247 overlie the flexible arms 235 on the first drive element 232, by means of which drive is transmitted to the second drive element 234. Figure 4 illustrates the injection device 210 at the position where the additional flexible arms 247 are just making contact with the constriction 237 in the component 262. The constriction 237 moves the additional flexible arms 247 inwards, aided by the bevelled surfaces on both, and the additional flexible arms 247 in turn move the flexible arms 235. by means of which drive is transmitted from the first drive element 232 to the second drive element 234, inwards from the position shown to a position at which they no longer couple the first and second drive elements together. Once this happens, the first drive element 232 acts no longer on the second drive element 234, allowing the first drive element 232 to move relative to the second drive element 234. Because the damping fluid is contained within a reservoir 248 defined between the end of the first drive element 232 and the blind bore 246 in the second drive element 234, the volume of the reservoir 248 will tend to decrease as the first drive element 232 moves relative to the second drive element 234 when the former is acted upon by the drive spring 230. As the reservoir 248 collapses, damping fluid is forced into the collection chamber 242. Thus, once the flexible latch arms 235 have been released, the force exerted by the drive spring 230 does work on the damping fluid, causing it to flow into the collection chamber 242, and also acts hydrostatically through the fluid, thence via the second drive element 234. Losses associated with the flow of the damping fluid do not attenuate the force acting on the body of the syringe to a great extent. Thus, the return spring 226 remains compressed and the hypodermic needle remains extended. Alter a time, the second drive element 234 completes its travel within the syringe body 216 and can go no further. At this point, the contents of the syringe 214 are completely discharged and the force exerted by the drive spring 230 acts to retain the second drive element 234 in its terminal position and to continue to cause the damping fluid to How into the collection chamber 142, allowing the first drive element 232 to continue its movement. A flange 270 on the rear of the second drive element 234 normally retains the flexible arms 233 in engagement with the drive sleeve 231. However, before the reservoir 248 of fluid is exhausted, the flexible latch arms 233 linking the drive sleeve 231 with the first drive element 232 move sufficiently far forward relative to the second drive element 234 that the flange 270 is brought to register with a rebate 272 in the flexible arms 233. whereupon it ceases to be effective in retaining the flexible arms 233 in engagement with the drive sleeve 231. Now, the drive sleeve 231 moves the flexible latch arms 233 inwards from the position shown to a position at which they no longer couple the drive sleeve 231 to the first drive element 232, aided by the bevelled latching surfaces 274 on the flexible arms 233. Once this happens, the drive sleeve 231 acts no longer on the first drive element 232, allowing them to move relative to each other. At this point, of course, the syringe 214 is released, because the forces developed by the drive spring 230 are no longer being transmitted to the syringe 214, and the only force acting on the syringe will be the return force from the return spring 226. Thus, the syringe 214 now returns to its retracted position and the injection cyele is complete. We Claim: 1. A compact injection device (110) for automatic extension and retraction of its syringe after content discharge, comprising: a housing (112) adapted to receive a syringe (114) having a discharge nozzle (118): first and second drive elements (132,134), of which the first is acted upon and the second acts upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the discharge nozzle, the first drive element being capable of movement relative to the second when the former is acted upon and the latter is restrained by the syringe; and a coupling that prevents the first drive element from moving relative to the second until they have been advanced to a nominal decoupling position relative to the syringe. 2. The injection device as claimed in claim 1 comprising: an actuator (130) that acts upon the first drive element; means (126) for biasing the syringe from an extended position in which the discharge nozzle extends from the housing to a retracted position in which the discharge nozzle is contained within the housing; and a release mechanism, activated when the first drive element has been advanced to a nominal release position that is more advanced than the said nominal decoupling position, and adapted to release the syringe from the action of the actuator, whereupon the biasing means (126) restores the syringe to its retracted position. 3. The injection device as claimed in claim 1 or claim 2, wherein the nominal decoupling position is defined by one of the drive elements interacting with a decoupling component that moves with the syringe as it is advanced. 4. The injection device as claimed in any one claims 1-3, wherein the coupling comprises cooperating features of the first and second drive elements that allow the first to act upon the second. 5. The injection device as claimed in claim 4, wherein the cooperating features comprise flexible arms on one of the drive elements that engage with a drive surface on the other. 6. The injection device as claimed in any preceding claim wherein the coupling comprises a decoupling mechanism, activated when the drive elements have been advanced to the said nominal decoupling position and adapted to decouple the first drive element from the second, thus allowing the first drive element to move relative to the second. 7. The injection device as claimed in claim 3, wherein: the coupling comprises flexible arms (135) on one of the drive elements that engage with a drive surface on the other: and the decoupling component causes the flexible arms to move when the said nominal decoupling position is reached, thus disengaging them from the drive surface to allow the first drive element lo move relative to the second. 8. The injection device as claimed in claim 4 wherein: the coupling comprises flexible arms (235) on one of the drive elements that engage with a drive surface on the other: and the decoupling component causes the flexible arms to move when the said nominal decoupling position is reached, by acting on an intermediate component, thus disengaging the flexible arms from the drive surface to allow the first drive element to move relative to the second. 9. The injection device as claimed in claim 8, wherein the intermediate component is a flexible component (247) of the drive element upon which the said drive surface is to be found. 10. The injection device as claimed in any one of claims 5, 7 and 8, wherein the flexible arms are biased toward a position at which they engage the drive surface and the decoupling component causes them to move against their bias, thus disengaging them from the drive surface. 11. The injection device as claimed in claim 2, wherein the release mechanism is activated when the first drive element has been advanced to a nominal release position relative to the syringe. 12. The injection device as claimed in claim 11, wherein the nominal release position is defined by the first drive element, or an actuator that acts upon it, interacting with a decoupling component that moves with the syringe as it is advanced. 13. The injection device as claimed in claim 11, wherein the nominal release position is defined by an actuator interacting with the first drive element once the nominal decoupling position has been reached. 14. The injection device as claimed in any of claims 11 to 13, wherein the release mechanism is adapted to decouple the first drive element from an actuator once the said nominal release position has been reached, thus releasing the syringe from the action of the actuator. 15. The injection device as claimed in any of claims 11-14, comprising a second coupling, between an actuator and the first drive element, that prevents the actuator from moving relative to the first drive element until the nominal release position has been reached. 16. The injection device as claimed in claim 15, wherein the second coupling comprises cooperating features of the actuator and the first drive element allowing the former to act upon the latter. 17. The injection device as claimed in claim 16, wherein: the cooperating features of the actuator and the first drive element include second flexible arms (133) on one of them engaged with a second drive surface on the other: and the release mechanism comprises a decoupling component that causes the second flexible arms to move when the said nominal release position is reached, thus disengaging them from the drive surface to allow the actuator to move relative to the first drive element. 18. The injection device as claimed in claims 2 or claim 12,wherein: of the actuator and the first drive element, one comprises second flexible arms (133) that engage with a second drive surface on the other, allowing the actuator to act upon the first drive element and preventing the former from moving relative to the latter until the nominal release position has been reached; the release mechanism comprises the said decoupling component, which causes the second flexible arms to move when the said nominal release position is reached, thus disengaging them from the drive surface to allow the actuator to move relative to the first drive element. 19. The injection device as claimed in claim 13, wherein: of the actuator and the first drive element, one comprises second flexible arms (133) that engage with a second drive surface on the other, allowing the actuator to act upon the first drive element and preventing the former from moving relative to the latter until the nominal release position has been reached; and the second flexible arms are biased toward a position at which they engage the second drive surface and the release mechanism causes them to move against their bias, thus disengaging them from the drive surface. ABSTRACT TITLE: "A compact injection device for automatic extension and retraction of its syringe after content discharge" The invention relates to a compact injection device (110) for automatic extension and retraction of its syringe after content discharge, comprising a housing (112) adapted to receive a syringe (114) having a discharge nozzle (118): first and second drive elements (132,134), of which the first is acted upon and the second acts upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the discharge nozzle, the first drive element being capable of movement relative to the second when the former is acted upon and the latter is restrained by the syringe; and a coupling that prevents the first drive element from moving relative to the second until they have been advanced to a nominal decoupling position relative to the syringe.

Full Text

Background Technology
The present invention relates to an injection device of the type that receives a syringe,
extends it, discharges its contents and then retracts it automatically. Devices of this
general description arc shown in WO 95/35126 and EP-A-0 516 473 and tend to
employ a drive spring and some form of release mechanism that releases the syringe
from the influence of the drive spring once its contents are supposed to have been
discharged, to allow it to be retracted by a return spring.
Because of the stack-up of tolerances of the various components of the device, a
certain margin of safety must be built into the activation of the release mechanism, to
ensure that it is effective. The consequence of underestimating the safety margin is
that the release mechanism may fail to operate even once the syringe contents have
been discharged, which is unsatisfactory in a device that is supposed to retract
automatically, particularly for self-administered drugs. On the other hand,
overestimating the safety margin may mean that some of the syringe contents arc
discharged after the syringe has retracted, which results firstly in a short dose and
secondly in what may be termed a "wet" injection. Wet injections are undesirable for
the squeamish, particularly in connection with self-administered drugs.
UK patent applications nos. 0210123, 0229384 and 0325596 describe a series of
injection devices designed to deal with this problem. Each makes use of a neat trick
that delays the release of the syringe for a certain period of time after the release
mechanism has been activated, in an attempt to ensure that the syringe has been
completely discharged. The devices illustrated in UK patent application no. 0325596
make use of a two-part drive incorporating a fluid-damped delay mechanism that is
particularly effective in ensuring complete discharge of the syringe contents. In each
case, the device relies upon two unlatching mechanisms. The first unlatching
mechanism initiates the fluid damping mechanism and the second releases the syringe
from the actuator, allowing it to be withdrawn. The unlatching mechanisms are
activated by components of the injection device having been advanced to nominal
unlatching positions relative to the device casework.
A device 10 of this general character is illustrated schematically in figure 1. The
sequence of operation is as follows. Firstly, the device 10 is armed. The user presses a
release button and the syringe 14 is advanced a distance d, by a drive spring 30, thereby

compressing the retraction spring 26. This movement inserts the needle 18 into the
patient. The plunger 23 is advanced a distance d2 by the drive spring 30, injecting most
of the dose. Once nearly the entire dose has been injected, the first unlatching
mechanism is activated, an operation illustrated schematically by the coincidence of
components 1 and 3. The plunger 23 is then advanced a further distance d3 by the drive
spring 30, injecting the rest of the dose. Finally, the second unlatching mechanism is
activated, an operation illustrated schematically by the coincidence of components 2
and 4, and the retraction spring 26 then causes the needle 18 to be retracted by the
distance d|.
Since the drive spring acts upon the same component of the device throughout, here
referred to as the "actuator", the distance that component must move between the device
being armed and the second unlatching mechanism being activated is, subject to
tolerance stack-up, equal to the sum of d1, D2 and d3. In the devices described in the
applications mentioned above, all of this movement takes place to the rear of the syringe,
which means that the overall length of the device must be greater than the sum of the
length of the actuator, the distances d1, d2, and d3, and the length of the syringe body not
including the needle.
The best design of injection device is one that is compact. This is important both to the
ergonomics of the device and to its manufactured cost. The length of the device can be
reduced by allowing the actuator to move past the syringe, and by having the unlatching
mechanisms activated in front of the syringe. However, this would require the actuator
and its unlatching mechanisms to pass around the space occupied by the syringe,
involving an increase in diameter of the device that negates the length savings.
Summary of the Invention
It is an objective of the present invention to provide a more compact device. Instead of
triggering release of the unlatching mechanisms using a fixed point on the device
casework, the present invention does it using one of more features that move forward
with the syringe as it is advanced. In other words, the nominal positions at which the
unlatching mechanisms are activated are defined relative to the syringe, not relative to
the device casework. As illustrated in figure 2, these nominal positions also move

forwards a distance d1 as the syringe is initially advanced. This in turn means that the
initial distance between the actuator and the syringe plunger can be reduced by the
distance d1. The length of the device can be reduced by d1 at a stroke. More modest
improvements arc available when only one of the nominal positions at which the
unlatching mechanisms are activated is defined relative to the syringe.
Accordingly, a first aspect of the present invention provides an injection device
comprising:
a housing adapted to receive a syringe having a discharge nozzle;
first and second drive elements, of which the first is acted upon and the second
acts upon the syringe to advance it from its retracted position to its extended position
and discharge its contents through the discharge nozzle, the first drive element being
capable of movement relative to the second when the former is acted upon and the
latter is restrained by the syringe;
a coupling that prevents the first drive element from moving relative to the
second until they have been advanced to a nominal decoupling position relative to the
syringe.
In this case, the nominal decoupling position, i.e. the first nominal unlatching
position, is defined relative to the syringe and not relative to the housing.
Preferably, the device includes:
an actuator that acts upon the first drive element;
means for biasing the syringe from an extended position in which the
discharge nozzle extends from the housing to a retracted position in which the
discharge nozzle is contained within the housing; and
a release mechanism, activated when the first drive element has been advanced
to a nominal release position that is more advanced than the said nominal decoupling
position, and adapted to release the syringe from the action of the actuator, whereupon
the biasing means restores the syringe to its retracted position.

In preferred embodiments of the invention, the nominal decoupling position is defined
either by one of the drive elements interacting with a decoupling component that
moves with the syringe as it is advanced.
For ease of manufacture and assembly, the coupling may comprise flexible arms on
one of the drive elements that engage with a drive surface on the other, in which case
the decoupling component causes the flexible arms to move when the said nominal
decoupling position is reached, thus disengaging them from the drive surface to allow
the first drive element to move relative to the second.
A second aspect of the present invention provides an injection device comprising:
a housing adapted to receive a syringe having a discharge nozzle, the housing
including means for biasing the syringe from an extended position in which the
discharge nozzle extends from the housing to a retracted position in which the
discharge nozzle is contained within the housing;
first and second drive elements, of which the first is acted upon and the second
acts upon the syringe to advance it from its retracted position to its extended position
and discharge its contents through the discharge nozzle, the first drive element being
capable of movement relative to the second when the former is acted upon and the
latter is restrained by the syringe;
a coupling that prevents the first drive element from moving relative to the
second until they have been advanced to a nominal decoupling position; and
a release mechanism, activated when the first drive element has been advanced
to a nominal release position relative to the syringe that is more advanced than the
said nominal decoupling position, and adapted to release the syringe, whereupon the
biasing means restores the syringe to its retracted position.
Mere, the nominal release position, i.e. the second nominal unlatching position, is
defined relative to the syringe and not relative to the housing.
Again, in preferred embodiments, the nominal release position is defined by an
actuator or the first drive element interacting with a decoupling component that moves
with the syringe as it is advanced. It may be defined by the actuator interacting with

the first drive element once the nominal decoupling position has been reached, at
which position the first drive element is restrained by the syringe against further
movement.
Once again, for case of manufacture and assembly, of the actuator and the first drive
element, one preferably comprises second flexible arms that engage with a second
drive surface on the other, and the release mechanism preferably comprises the said
decoupling component, which causes the second flexible arms to move when the said
nominal release position is reached, thus disengaging them from the drive surface.
Alternatively, of an actuator and the first drive element, one preferably comprises
second flexible arms that engage with a second drive surface on the other, allowing
the actuator to act upon the first drive element and preventing the former from moving
relative to the latter until the nominal release position has been reached, the second
flexible arms are preferably biased toward a position at which they engage the second
drive surface and the release mechanism preferably causes them to move against their
bias, thus disengaging them from the drive surface.
Brief Description of the Drawings
The invention will now be described by way of example with reference to the
accompanying drawings, in which:
figures 1 and 2 are schematic illustrations to which reference has already been
made;
Figure 3 is an illustration of a first embodiment of the invention; and
Figure 4 is likewise a second.
Detailed Description
Figure 3 shows an injection device 110 in which a housing 112 contains a hypodermic
syringe 1 14. The syringe 114 is of conventional type, including a syringe body 116
terminating at one end in a hypodermic needle 118 and at the other in a flange 120.
The conventional plunger that would normally be used to discharge the contents of
the syringe 114 manually has been removed and replaced with a drive element 134 as
will be described below, to which is attached a bung 122. The bung 122 constrains a

drug 124 to be administered within the syringe body 116. Whilst the syringe
illustrated is of hypodermic type, this need not necessarily be so. Transcutaneous or
ballistic dermal and subcutaneous syringes may also be used with the injection device
of the present invention. Generally, the syringe must include a discharge nozzle,
which in a hypodermic syringe is the needle 118.
As illustrated, the housing includes a return spring 126 that biases the syringe 114
from an extended position in which the needle 118 extends from an aperture 128 in
the housing 112 to a retracted position in which the discharge nozzle 118 is contained
within the housing 112. The return spring 126 acts on the syringe 114 via a sleeve
127.
At the other end of the housing is a compression drive spring 130. Drive from the
drive spring 130 is transmitted via a multi-component drive to the syringe 114 to
advance it from its retracted position to its extended position and discharge its
contents through the needle 118. The drive accomplishes this task by acting directly
on the drug 124 and the syringe 114. Hydrostatic forces acting through the drug 124
and. to a lesser extent, static friction between the bung 122 and the syringe body 116
initially ensure that they advance together, until the return spring 126 bottoms out or
the syringe body 116 meets some other obstruction that retards its motion.
The multi-component drive between the drive spring 130 and the syringe 114 consists
of three principal components. A drive sleeve 131 takes drive from the drive spring
130 and transmits it to flexible latch arms 133 on a first drive element 132. This in
turn transmits drive via flexible latch arms 135 to a second drive element, the drive
element 134 already mentioned.
The first drive element 132 includes a hollow stem 140, the inner cavity of which
forms a collection chamber 142 in communication with a vent 144 that extends from
the collection chamber through the end of the stem 140. The second drive element
134 includes a blind bore 146 that is open at one end to receive the stem 140 and
closed at the other. As can be seen, the bore 146 and the stem 140 define a fluid
reservoir 148, within which a damping fluid is contained.

A trigger (not shown) is provided on one side of the housing 112. The trigger, when
operated, serves to decouple the drive sleeve 131 from the housing 112, allowing it to
move relative to the housing 112 under the influence of the drive spring 130. The
operation of the device is then as follows.
Initially, the drive spring 130 moves the drive sleeve 131, the drive sleeve 131 moves
the first drive element 132 and the first drive element 132 moves the second drive
element 134. in each case by acting through the flexible latch arms 133, 135. The
second drive element 134 and the bung 122 move and, by virtue of static friction and
hydrostatic forces acting through the drug 124 to be administered, move the syringe
body 116 against the action of the return spring 126. The return spring 126
compresses and the hypodermic needle 118 emerges from the exit aperture 128 of the
housing 112. This continues until the return spring 126 bottoms out or the syringe
body 116 meets some other obstruction that retards its motion. Because the static
friction between the bung 122 and the syringe body 116 and the hydrostatic forces
acting through the drug 124 to be administered are not sufficient to resist the full drive
force developed by the drive spring 130, at this point the second drive element 134
begins to move within the syringe body 116 and the drug 124 begins to be discharged.
Dynamic friction between the bung 122 and the syringe body 116 and hydrostatic
forces acting through the drug 124 to be administered are, however, sufficient to
retain the return spring 126 in its compressed state, so the hypodermic needle 118
remains extended.
Before the second drive element 134 reaches the end of its travel within the syringe
body 116, so before the contents of the syringe have fully discharged, the flexible
latch arms 135 linking the first and second drive elements 132, 134 reach a
constriction 137. The constriction 137 is formed by a component 162 that is attached
to the syringe flange 120, so it will be understood that when the syringe 114 advances
from its retracted position to its extended position, the component 162 advances with
it. The constriction 137 moves the flexible latch arms 135 inwards from the position
shown to a position at which they no longer couple the first drive element 136 to the
second drive element 134, aided by the bevelled surfaces on the constriction 137.

Once this happens, the first drive element 136 acts no longer on the second drive
element 134, allowing the first drive element 132 to move relative to the second drive element 134.
Because the damping fluid is contained within a reservoir 148 defined between the
end of the first drive element 132 and the blind bore 146 in the second drive element
134, the volume of the reservoir 148 will tend to decrease as the first drive element
132 moves relative to the second drive element 134 when the former is acted upon by
the drive spring 130. As the reservoir 148 collapses, damping fluid is forced through
the vent 144 into the collection chamber 142. Thus, once the flexible latch arms 135
have been released, the force exerted by the drive spring 130 does work on the
damping fluid, causing it to flow through the constriction formed by the vent 144, and
also acts hydroslatically through the fluid, to drive the second drive element 134.
Losses associated with the flow of the damping fluid do not attenuate the force acting
on the body of the syringe to a great extent. Thus, the return spring 126 remains
compressed and the hypodermic needle 118 remains extended.
After a time, the second drive element 134 completes its travel within the syringe
body 116 and can go no further. At this point, the contents of the syringe 114 are
completely discharged and the force exerted by the drive spring 130 acts to retain the
second drive element 134 in its terminal position and to continue to cause the
damping fluid to How through the vent 144, allowing the first drive element 132 to
continue its movement.
Before the reservoir 148 of fluid is exhausted, the flexible latch arms 133 linking the
drive sleeve 131 with the first drive element 132 reach another constriction 139, also
provided by the component 162 that is attached to the syringe flange 120. The
constriction 139 moves the flexible latch arms 133 inwards from the position shown
to a position at which they no longer couple the drive sleeve 131 to the first drive
element 132, aided by the bevelled surfaces on the constriction 139. Once this
happens, the drive sleeve 131 acts no longer on the first drive element 132, allowing
them to move relative to each other. At this point, of course, the syringe 114 is
released, because the force developed by the drive spring 130 is no longer being

226 bottoms out or the syringe body 216 meets some other obstruction that retards its
motion.
The multi component drive between the drive spring 230 and the syringe 214 again
consists of three principal components. The drive sleeve 231 takes drive from the
drive spring 230 and transmits it to flexible latch arms 233 on a first drive element
232. These elements are shown in detail "A". The first drive element 232 in turn
transmits drive via flexible latch arms 235 to a second drive element 234. These
elements are shown in detail "B'\ As before, the first drive element 232 includes a
hollow stem 240, the inner cavity of which forms a collection chamber 242. The
second drive element 234 includes a blind for 246 that is open at one end to receive
the stem 240 and closed at the other. As can be seen, the bore 246 and the stem 240
define a fluid reservoir 248, within which a damping fluid is contained.
A trigger (not shown) is provided in the middle of the housing 212. The trigger, one
operated, serves to decouple the drive sleeve 231 from the housing 212 allowing it to
move relative to the housing 212 under the influence of the drive spring 230. The
operation of the device is then as follows.
Initially, the drive spring 230 moves the drive sleeve 231, the drive sleeve 231 moves
the first drive element 232 and the first drive element 232 moves the second drive
element 234, in each case by acting through the flexible matching arms 233, 235. The
second drive element 234 moves and, by virtue of static friction and hydrostatic forces
acting through the drug 224 to be administered, moves the syringe body 216 against
the action of the return spring 226. The return spring 226 compresses and the
hypodermic needle 218 emerges from the exit aperture 228 of the housing 212. This
continues until the return spring 226 bottoms out or the syringe body 216 meets some
other obstruction that retards its motion. Because the static friction between the bung
222 and the syringe body 216 and the hydrostatic forces acting through the drug 224
to be administered are not sufficient to resist the full drive force developed by the
drive spring 230, at this point the second drive element 234 begins to move within the
syringe body 216 and the drug 224 begins to be discharged. Dynamic friction between
the bung 222 and the syringe body 216 and hydrostatic forces acting through the drug

224 to be administered are, however, sufficient to retain the return spring 226 in its
compressed state, so the hypodermic needle 218 remains extended.
Before the second drive element 234 reaches the end of its travel within the syringe
body 216, so before the contents of the syringe have fully discharged, the flexible
latch arms 235 linking the first and second drive elements 232, 234 reach a
constriction 237. The constriction 237 is formed by a component 262 that is attached
to the syringe carrier. Additional flexible arms 247 overlie the flexible arms 235 on
the first drive element 232, by means of which drive is transmitted to the second drive
element 234. Figure 4 illustrates the injection device 210 at the position where the
additional flexible arms 247 are just making contact with the constriction 237 in the
component 262.
The constriction 237 moves the additional flexible arms 247 inwards, aided by the
bevelled surfaces on both, and the additional flexible arms 247 in turn move the
flexible arms 235. by means of which drive is transmitted from the first drive element
232 to the second drive element 234, inwards from the position shown to a position at
which they no longer couple the first and second drive elements together. Once this
happens, the first drive element 232 acts no longer on the second drive element 234,
allowing the first drive element 232 to move relative to the second drive element 234.
Because the damping fluid is contained within a reservoir 248 defined between the
end of the first drive element 232 and the blind bore 246 in the second drive element
234, the volume of the reservoir 248 will tend to decrease as the first drive element
232 moves relative to the second drive element 234 when the former is acted upon by
the drive spring 230. As the reservoir 248 collapses, damping fluid is forced into the
collection chamber 242. Thus, once the flexible latch arms 235 have been released,
the force exerted by the drive spring 230 does work on the damping fluid, causing it
to flow into the collection chamber 242, and also acts hydrostatically through the
fluid, thence via the second drive element 234. Losses associated with the flow of the
damping fluid do not attenuate the force acting on the body of the syringe to a great
extent. Thus, the return spring 226 remains compressed and the hypodermic needle
remains extended.

Alter a time, the second drive element 234 completes its travel within the syringe
body 216 and can go no further. At this point, the contents of the syringe 214 are
completely discharged and the force exerted by the drive spring 230 acts to retain the
second drive element 234 in its terminal position and to continue to cause the
damping fluid to How into the collection chamber 142, allowing the first drive
element 232 to continue its movement.
A flange 270 on the rear of the second drive element 234 normally retains the flexible
arms 233 in engagement with the drive sleeve 231. However, before the reservoir 248
of fluid is exhausted, the flexible latch arms 233 linking the drive sleeve 231 with the
first drive element 232 move sufficiently far forward relative to the second drive
element 234 that the flange 270 is brought to register with a rebate 272 in the flexible
arms 233. whereupon it ceases to be effective in retaining the flexible arms 233 in
engagement with the drive sleeve 231. Now, the drive sleeve 231 moves the flexible
latch arms 233 inwards from the position shown to a position at which they no longer
couple the drive sleeve 231 to the first drive element 232, aided by the bevelled
latching surfaces 274 on the flexible arms 233. Once this happens, the drive sleeve
231 acts no longer on the first drive element 232, allowing them to move relative to
each other. At this point, of course, the syringe 214 is released, because the forces
developed by the drive spring 230 are no longer being transmitted to the syringe 214,
and the only force acting on the syringe will be the return force from the return spring
226. Thus, the syringe 214 now returns to its retracted position and the injection cyele
is complete.

We Claim:
1. A compact injection device (110) for automatic extension and retraction of its
syringe after content discharge, comprising:
a housing (112) adapted to receive a syringe (114) having a discharge nozzle
(118):
first and second drive elements (132,134), of which the first is acted upon and
the second acts upon the syringe to advance it from its retracted position to its
extended position and discharge its contents through the discharge nozzle, the
first drive element being capable of movement relative to the second when the
former is acted upon and the latter is restrained by the syringe; and
a coupling that prevents the first drive element from moving relative to the
second until they have been advanced to a nominal decoupling position relative
to the syringe.
2. The injection device as claimed in claim 1 comprising:
an actuator (130) that acts upon the first drive element;
means (126) for biasing the syringe from an extended position in which the
discharge nozzle extends from the housing to a retracted position in which the
discharge nozzle is contained within the housing; and

a release mechanism, activated when the first drive element has been advanced
to a nominal release position that is more advanced than the said nominal
decoupling position, and adapted to release the syringe from the action of the
actuator, whereupon the biasing means (126) restores the syringe to its
retracted position.
3. The injection device as claimed in claim 1 or claim 2, wherein the nominal
decoupling position is defined by one of the drive elements interacting with a
decoupling component that moves with the syringe as it is advanced.
4. The injection device as claimed in any one claims 1-3, wherein
the coupling comprises cooperating features of the first and second drive
elements that allow the first to act upon the second.
5. The injection device as claimed in claim 4, wherein the cooperating features
comprise flexible arms on one of the drive elements that engage with a drive
surface on the other.

6. The injection device as claimed in any preceding claim wherein the coupling
comprises a decoupling mechanism, activated when the drive elements have
been advanced to the said nominal decoupling position and adapted to decouple
the first drive element from the second, thus allowing the first drive element to
move relative to the second.
7. The injection device as claimed in claim 3, wherein:
the coupling comprises flexible arms (135) on one of the drive elements that
engage with a drive surface on the other: and
the decoupling component causes the flexible arms to move when the said
nominal decoupling position is reached, thus disengaging them from the drive
surface to allow the first drive element lo move relative to the second.
8. The injection device as claimed in claim 4 wherein:
the coupling comprises flexible arms (235) on one of the drive elements that
engage with a drive surface on the other: and
the decoupling component causes the flexible arms to move when the said
nominal decoupling position is reached, by acting on an intermediate component,
thus disengaging the flexible arms from the drive surface to allow the first drive
element to move relative to the second.

9. The injection device as claimed in claim 8, wherein the intermediate
component is a flexible component (247) of the drive element upon which the
said drive surface is to be found.
10. The injection device as claimed in any one of claims 5, 7 and 8, wherein the
flexible arms are biased toward a position at which they engage the drive surface
and the decoupling component causes them to move against their bias, thus
disengaging them from the drive surface.
11. The injection device as claimed in claim 2, wherein the release
mechanism is activated when the first drive element has been advanced to a
nominal release position relative to the syringe.
12. The injection device as claimed in claim 11, wherein the nominal
release position is defined by the first drive element, or an actuator that acts
upon it, interacting with a decoupling component that moves with the syringe as
it is advanced.

13. The injection device as claimed in claim 11, wherein the nominal
release position is defined by an actuator interacting with the first drive element
once the nominal decoupling position has been reached.
14. The injection device as claimed in any of claims 11 to 13, wherein the release
mechanism is adapted to decouple the first drive element from an actuator once
the said nominal release position has been reached, thus releasing the syringe
from the action of the actuator.
15. The injection device as claimed in any of claims 11-14, comprising a
second coupling, between an actuator and the first drive element, that prevents
the actuator from moving relative to the first drive element until the nominal
release position has been reached.
16. The injection device as claimed in claim 15, wherein the second coupling
comprises cooperating features of the actuator and the first drive element
allowing the former to act upon the latter.

17. The injection device as claimed in claim 16, wherein:
the cooperating features of the actuator and the first drive element include
second flexible arms (133) on one of them engaged with a second drive surface
on the other: and
the release mechanism comprises a decoupling component that causes the
second flexible arms to move when the said nominal release position is reached,
thus disengaging them from the drive surface to allow the actuator to move
relative to the first drive element.
18. The injection device as claimed in claims 2 or claim 12,wherein:
of the actuator and the first drive element, one comprises second flexible arms
(133) that engage with a second drive surface on the other, allowing the
actuator to act upon the first drive element and preventing the former from
moving relative to the latter until the nominal release position has been reached;
the release mechanism comprises the said decoupling component, which
causes the second flexible arms to move when the said nominal release position
is reached, thus disengaging them from the drive surface to allow the actuator to
move relative to the first drive element.

19. The injection device as claimed in claim 13, wherein:
of the actuator and the first drive element, one comprises second flexible arms
(133) that engage with a second drive surface on the other, allowing the
actuator to act upon the first drive element and preventing the former from
moving relative to the latter until the nominal release position has been reached;
and
the second flexible arms are biased toward a position at which they engage the
second drive surface and the release mechanism causes them to move against
their bias, thus disengaging them from the drive surface.

ABSTRACT

TITLE: "A compact injection device for automatic extension and retraction of its
syringe after content discharge"
The invention relates to a compact injection device (110) for automatic extension
and retraction of its syringe after content discharge, comprising a housing (112)
adapted to receive a syringe (114) having a discharge nozzle (118):
first and second drive elements (132,134), of which the first is acted upon and
the second acts upon the syringe to advance it from its retracted position to its
extended position and discharge its contents through the discharge nozzle, the
first drive element being capable of movement relative to the second when the
former is acted upon and the latter is restrained by the syringe; and a coupling
that prevents the first drive element from moving relative to the
second until they have been advanced to a nominal decoupling position relative
to the syringe.

A COMPACT INJECTION DEVICE FOR AUTOMATIC EXTENSION AND RETRACTION OF ITS SYRINGE AFTER CONTENT DISCHARGE

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