Delay mechanism suitable for compact automatic injection device

A delay mechanism for an automatic injection device having a housing and a medication filled syringe. The delay mechanism includes a shuttle, a follower, a damping compound, at least one biasing member, and a biased plunger element. When moved in the device housing from a first location to a second location, the biased plunger element is adapted to drive the syringe piston within syringe barrel to force medication through the syringe needle for an injection. The follower, when the plunger element is so moved, is freed to move, under urging of the at least one biasing member, from a first position on the housing toward a second position to thereby move the shuttle for retracting the syringe needle into the housing after injection. The damping compound dampens or slows rotation of the follower as the follower moves from the first position toward the second position.

BACKGROUND OF THE INVENTION

The present invention pertains to pharmaceutical injection devices, and, in particular, to a mechanism used to delay needle retraction for an automatic injection device.

Patients suffering from a number of different diseases frequently must inject themselves with pharmaceuticals. A variety of devices have been proposed to facilitate these injections. One type of device is an automatic injection device. This type of device, when triggered by a user or someone helping the user, automatically inserts into the user a needle of a syringe that prior to triggering was disposed within the device housing, and then automatically injects a dose of medication through that inserted needle. One known type of automatic injection device then automatically advances a shroud to cover the needle when the dose is completed. In another type of automatic injection device having a configuration more desirable to some, and instead of having an advancing shroud, the device will automatically retract the needle into the housing when the dose is completed. To ensure that the full desired contents of the syringe have been injected prior to the syringe being retracted, a variety of differently configured delay mechanisms have been proposed for such automatic injection devices.

One problem with at least some automatic injection devices having delay mechanisms is that the devices are longer than some users may like when placed by the user on an injection site. All things being equal, a shorter device for a given delivery volume may be provided by making the syringe shorter but with a larger diameter. However, as causing such syringes to inject tends to require the application of more force and therefore a more robust drive system, constraints can result as to where the delay mechanism can be accommodated within the device housing. Still further, some delay mechanisms are not as compact axially as would be desirable to allow for the injection devices in which they are used to be short or compact.

Another problem with at least some automatic injection devices having delay mechanisms is that the means for holding the needle in a retracted position after use is less reliable than desired. It is possible with such devices for the needle to be released accidentally from a locked position after use despite the device experiencing a relatively minor impact or external force.

Thus, it would be desirable to provide an automatic injection device that can overcome one or more of these and other shortcomings of the prior art.

BRIEF SUMMARY OF THE INVENTION

In one form thereof, the present invention provides a delay mechanism for an automatic injection device having a housing and a medication filled syringe having a barrel, a piston, and an injection needle, the device being operable for moving the syringe in a first direction relative to the housing to extend the injection needle beyond the housing. The delay mechanism includes a shuttle, a follower, a damping compound, at least one biasing member, and a biased plunger element. The shuttle is rotatably fixed relative to the housing and configured for engaging the syringe for retraction. The follower is adapted for shifting the shuttle in a direction opposite to the first direction. The follower is keyed with the housing for movement from a first position on the housing to a second position on the housing, the second position being axially spaced from the first position in the direction opposite to the first direction, the second position being rotationally spaced from the first position. The damping compound is between surfaces of the follower and at least one of the shuttle and the housing to dampen rotation of said follower. The at least one biasing member provides a force urging the follower from the first position to the second position. The biased plunger element is adapted to drive the piston within the barrel to force medication through the injection needle for an injection. The biased plunger element is biased in the first direction within the housing from a first location to a second location, and is rotatably fixed relative to the housing. The follower is prevented from moving from the first position toward the second position when the plunger element is in the first location, and the follower freed to move from the first position toward the second position when the plunger element moves from the first location to the second location such that the at least one biasing member shifts the follower from the first position to the second position to thereby move the shuttle for retracting the injection needle into the housing after injection.

In another form thereof, the present invention provides a delay mechanism for an automatic injection device having a housing and a syringe. The delay mechanism includes a shuttle for retracting the syringe in a first direction within the housing, a follower, means for moving the follower relative to the housing from a first position to a second position, the follower being configured to move the shuttle to retract the syringe in the first direction when the follower moves from the first position to the second position, means on the follower and the housing for guiding motion of the follower relative to the housing from the first position to the second position, a plunger adapted to force medication from the syringe, means to prevent the follower from being rotated from the first position toward the second position until the plunger has started to force medication from the syringe, and a means for damping rotational motion of the follower when the follower moves from the first position toward the second position.

One advantage of the present invention is that a delay mechanism may be provided which is compact in design.

Another advantage of the present invention is that a delay mechanism may be provided which allows for the secure retention after use of a retracted needle of an automatic injection device.

Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent an embodiment of the present invention, the drawings are not necessarily to scale, and certain features may be exaggerated or omitted in some of the drawings in order to better illustrate and explain the present invention.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1, there is shown a perspective view of a first embodiment of an automatic injection device, generally designated20, with a delay mechanism of the present invention. InFIGS. 2-4, device20is shown abstractly with a simple needled syringe, and with its needle cover, which during use is collapsed and pierced during an injection, not being shown. InFIG. 2, device20is shown being unlocked by rotating the safety sleeve32as indicated by arrow23about the housing main body34to an unlocked angular position. After device unlocking, and when the trigger button21is depressed as indicated by arrow24, the needled syringe25of the device20is automatically driven downward such that the injection needle27of syringe25projects beyond the bottom end of the device housing to penetrate the user as shown inFIG. 3. The device then proceeds to inject automatically, that is without further user action, the medication contents of the syringe25through the needle27, after which the syringe is retracted automatically, as indicated by arrow29, such that the needle27is returned to within the housing as shown inFIG. 4. The inventive delay mechanism within device20helps to stage the operation to ensure that the medication contents are properly delivered prior to the needled syringe being retracted. The delay mechanism is also useful as a means of compensating for axial tolerances in the syringe and other device components.

Although the inventive delay mechanism is shown finding beneficial application in the device20described herein, such application is merely illustrative and not intended to be limiting. The inventive delay mechanism can be used in many differently configured automatic injection devices where its benefits are desired.

With reference again toFIG. 1and toFIG. 5, device20includes an outer housing30in which are operationally disposed working components of the device. At the top or distal end of the housing and protruding axially therefrom is button21. When safety sleeve32is rotatably oriented to unlock the button21that is then plunged by a user, or someone helping the user, the plunged button21allows rotation of a lock ring140within the housing and shown inFIG. 5which disengages the plunger element230so as to trigger or start the automatic operative function of device20. The safety sleeve32and trigger assembly for the device is further described in a provisional patent application filed with the United States Patent and Trademark Office on Mar. 14, 2013 as Application No. 61/782,929, and in an international patent application, with the same listed inventors as this case, filed with the United States Patent and Trademark Office as receiving office on the same date of this application and entitled “Trigger Assembly for an Automatic Injection Device”, the entire disclosures of both those applications are hereby incorporated herein by reference.

As used herein, distal and proximal refer to axial locations relative to an injection site when the device is oriented for use at such site, whereby, for example, proximal end of the housing refers to the housing end that is closest to such injection site.

The axial height of housing30is formed by safety sleeve32, a main body34and a base plate35. Main body34is further shown inFIGS. 6A-6D. Main body34is formed from a two part molding process with a base portion37and an encircling sleeve portion38. Base portion37is made of a transparent plastic material to allow visibility of the syringe contents, and sleeve portion38is made from an opaque plastic material. Above sleeve portion38, the upper region, generally designated41, of base portion37includes a disc portion42and is configured to mount safety sleeve32and button21. A radially recessed bottom region43of main body34defines a central opening and is provided with external threading45.

Housing base plate35, further shown inFIGS. 8A and 8B, is made of the same transparent material as base portion37. The rim52of base plate35is threaded along its inner periphery at54that engages threading45to securely attach base plate35to main body34. A positive locking detent feature between base plate35and body34may also be provided to ensure the base plate does not unscrew from the body. A small, central aperture55in the disc-shaped base57of base plate35through which a syringe needle moves out from and then back into the housing during use is ringed by a tube portion60that distally extends from base57.

The housing also includes a central inner portion formed by a rod-shaped part or shaft62shown inFIG. 5that depends from housing disc portion42in the center of main body34. To facilitate manufacture and assembly, shaft62is separately formed and then fixedly secured, such as with a shown fastener64to be at all times rotabably and axially fixed relative to housing main body34.

Housing shaft62supports a follower or delay element, generally designated70, that is further shown inFIGS. 12A-12E. Delay element70is formed as one rigid piece and includes a central collar72having a pair of facing ribs or keys74that extend radially inward into an otherwise open center76. Keys74extend the full axial height of collar72. Two tabs or ears78project radially outward from diametric portions of collar72at the distal end of the collar. A ring-shaped damping fin80is concentric with collar72. Fin80is connected to collar72by a spanning flange82that extends between the proximal end of fin80and the central axial region of collar72. Although a single, continuous fin is provided, it could be replaced with differently shaped or numbers of fins in alternate embodiments.

Two holes84are provided through flange82centered one hundred eighty degrees apart to receive the upper ends of keys264of plunger element230. Two openings86through fin80are provided directly radially outward of tabs78and angularly centered between the holes84. Openings86are used during manufacture for molding of tabs78, and also serve to allow damping fluid to move to opposite radial sides81,83of fin80.

A pair of legs90extends proximally from flange82. Legs90are bowed in the angular direction to partially define a cylindrical hollow91below collar72. The angular sides92of each leg90are made thicker for robustness and are angularly spaced from the opposing sides of the other leg90to provide axially extending openings94that are diametrically opposed.

Openings94serve as keyways for the plunger element keys264as their keyed engagement is used in the shown embodiment to maintain the follower70rotationally fixed relative to the housing shaft62to prevent, until such time as the plunger element230has moved axially a sufficient distance after triggering, the follower from moving toward another position, at which other position the syringe has been retracted. In alternate embodiments, the follower need not be keyed to the plunger element and can be otherwise prevented from moving along a track in the housing, which movement prevention is undone by the plunger element as it moves axially. For example, the follower could be directly connected to the housing, or a part rotatably fixed with the housing, such as the shuttle, via a latch or snap, or blocked from moving by a lock member that is rotatably fixed with but axially slidable relative to the housing. As the plunger element moves proximally, the plunger element unlatches or unsnaps the follower, or moves the lock member out of its position blocking the follower, such that the follower is then free to move on the housing track. Such alternate embodiments will be further understood in view of International Publications Nos. WO2011/109205 and WO2008/112472, the entire disclosures of which applications are hereby incorporated herein by reference.

Housing shaft62and delay element70are complementarily designed with keying to guide the movement of the delay element70both axially and rotatably relative to shaft62. For this purpose and with reference toFIGS. 13A-13C, shaft62includes a generally cylindrical body100with a pair of recess or keyway regions102and a pair of recess or keyway regions104that are connected by axially extending channels106, all of which closely accommodate keys74. Regions102and104connected by channels106form tracks or keyways for the axially elongated keys74. Only one such keyway is necessary, but two angularly spaced keyways balances the parts. Only one set of recess regions102,104and channel106is visible inFIGS. 13B and 13C, but it will be appreciated that the sides of shaft62opposite to those sides shown inFIGS. 13B and 13C, other than with respect to disc section132, are similar Each recess region102includes bottom shoulder110that extends the full angular span of that region, a top shoulder112that extends the full angular span other than where channel106opens into that region, an axially extending shoulder114that spans shoulders110and112, and an end shoulder116that leads to channel106. Each recess region104includes a top shoulder120that extends the full angular span of that region other than channel122, a bottom shoulder124that extends the full angular span other than where channel106opens into that region, an end shoulder126continuing from channel106, and a stop shoulder128that axially extends from bottom shoulder124to channel122. Each of recess regions102are shown configured to produce strictly rotational motion of the follower70, but each or both could be configured to produce an axial component of motion as well, meaning the follower moves both rotationally and axially while moving in recess regions102.

Each top shoulder120may be provided with a not shown notch along a middle section of its angular extent, which notches serve as catches for holding the spring-loaded follower during an assembly step.

The shown tracks formed by recess regions102and axial channels106effectively produces a square jog in the tracks. During follower movement, when each key74moving along a recess region102reaches a position in the square jog of its respective track, the damped and slow rotation of the follower ends, and an undamped and rapid movement of follower70then occurs as key74shifts along channel106to recess region102. This rapid movement provides a nearly instantaneous follower retraction and thereby makes the syringe retraction it achieves visibly, audibly and tactilely apparent to the user.

In an alternate embodiment, and to guide the follower as the follower moves from its rotationally locked position prior to device use to the position at which it has caused syringe retraction prior to being further moved to effect a locking of that retraction, the track may be formed to produce along all or part of its length a gradual helical sweep of the follower.

A grooved portion130of shaft62located proximally of recess regions102ends at a disc section132, from which a stub135used in device assembly proximally extends. Disc section132includes an axially oriented opening134in which inserts an axially protruding proximal end or tip152of a biasing member150.

Biasing member150, shown best inFIG. 14, functions to bias follower70rotatably as well as axially relative to shaft62. Biasing member150is shown as a cylindrical spring formed of a helically coiled wire154. Spring150is selected to provide suitable torsional and axial forces within the available space, and the selection is dependent upon the device operation, such as the delay required, and the design of the cooperating components, such as the damping compound and follower and shuttle configurations. Other designs of biasing members, such as a metal or plastic flexure configured to perform the dual functions, may be substituted for the single metal coil spring shown. In alternate embodiments, and although the part count would increase, the single biasing member150may be replaced with two or more biasing members to serve the axial and rotational biasing functions, or may be replaced with an axial spring coupled with an additional piece, or driver, that provides the torsional preload via a cam or thread surface.

The internal opening156of spring150freely receives shaft62, while the outer diameter of spring150freely fits within cylindrical hollow91of follower70. The axially extending distal tip158of spring150inserts within a not shown blind pocket formed in the underside of collar72. The opposite end coils of spring150act against the underside of collar72and the distal face of shaft disc section132. Spring150is symmetric such that ends158and152are interchangeable.

A shuttle member, generally designated170, is axially held by delay member70within the device housing30. Shuttle member170, which is further shown inFIGS. 9A-9E, cooperates with a shuttle clip element216to form a shuttle for syringe retraction. Shuttle member170is molded in one piece and includes an annular plate portion172that includes a pair of diametrically disposed arcuate slots174for receiving the plunger element230and a pair of diametrically disposed openings176used in device manufacturing assembly. At the center of plate portion172is an upstanding collar180which rings a center portion182that is recessed proximally from the distal face of collar180. Center portion182defines a keyed opening184shaped to receive therethrough the inserted distal end of follower collar72and tabs78during manufacturing assembly. During such assembly, rotation of the inserted collar72results in center portion182being captured between collar tabs78and spanning flange82such that shuttle member170is axially fixed relative to follower70throughout device operation. A pair of diametrically opposed tabs188project radially outward from collar180and serve to locate lock ring140axially relative to shuttle member170.

The U-shaped underside190of collar180defines an annular hollow or pocket192and provides a support surface for damping fluid as follower70rotates relative to the shuttle member170.

A damping compound or fluid indicated as195inFIG. 5, such as a silicone grease thickened with Teflon available from Nye Lubricants as Nye fluorocarbon gel 880, fills annular pocket192. Follower fin80fits within hollow192such that damping compound195is disposed both radially inward and outward of the fin, resulting in a damping or delay effect as the follower fin80tries to rotate relative to the collar underside190with the viscous damping fluid providing a resistance to this rotation during operation. Other compounds with different properties may be selected by one of skill in the art.

Furthermore, the positioning of the fluid filled pocket and the fin that inserts therein on the shuttle member and follower respectively may be switched to the follower and shuttle member respectively in an alternate embodiment.

Shuttle member170further includes two legs200that are bowed in the radial direction and which proximally extend from annular plate portion172. Legs200are spaced from the outer radial periphery of plate portion172such that an overhanging region202of plate portion172provides an annular surface against which the distal end of a plunger biasing spring205directly abuts. A pair of not shown, diametrically opposed, depending hooks may be provided on the outer radial periphery of plate portion172to ensure spring205remains centered on the shuttle member170. The axially extending, angular sides204of each leg200are angularly spaced from the opposing sides of the other leg200to provide axially extending and diametrically opposed openings206in which interfit the plunger element legs232to rotatably fix the plunger element230relative to the shuttle member170. Legs200are bowed in the radial direction to partially define a cylindrical hollow203. The inner radial surfaces207of legs200include longitudinally extending ribs209that serve as stops to prevent the syringe from moving upward within shuttle member170.

The lower regions of the outer radial periphery212of legs200are recessed at214to accommodate resilient flanges218of a clip element, generally designated216, that is further shown inFIGS. 11A and 11B. Clip element216is made of a single piece of stainless steel. Flanges218resiliently grip legs200to fixedly secure the clip element216with the shuttle member170so that they act as a single part. Flanges218extend to a ring-shaped base220having a central opening222. Opening222is sized to allow the syringe barrel352, but not distal flange354, to fit therethrough. Ring-shaped base220is sized to engage syringe flange354and designed to stay axially clear of the top of tube portion60. Notches223in base220allow passage of sleeve arms318described further below.

A plunger element that during use is axially shifted within housing30to drive both needle insertion and medication delivery is generally indicated at230and further shown inFIGS. 7A-7E. Plunger element230includes axially extending legs232with outward directed flanged ends236at the proximal ends of the legs. The upper regions240of legs232above plate portion248are sized and shaped to insert within slots174of shuttle plate portion172. Upper regions240include cam faces244that engage complementary portions of the lock ring140. Until the trigger assembly of device20is activated by the user to disengage the lock ring portions from cam faces244, plunger element230is effectively latched and prevented from axially moving proximally under the biasing force of compressed spring205.

Plunger element230also includes a central plate portion248that spans legs232. A cylindrical tube250with a partially closed bottom end252depends from plate portion248between plunger legs232. Bottom end252directly engages the sealing piston or plunger356of the device syringe350. Tube250is sized with a transverse cross-section that allows its insertion into barrel352of syringe350. A radial gap254between the outer radial periphery of tube250and the inner radial periphery of legs232is sized to receive the upper extent, in the shown case the flange354and adjacent barrel352, of syringe350when the plunger element tube250inserts into the syringe barrel352. The hollow interior256of tube250is sized to house follower legs90therein until device operation. Four openings260in end252provide clearance in which initially fit the extending tabs or extensions95on follower legs90, which extensions are to keep the follower70and shuttle element230engaged for a longer portion of the axial travel of the plunger element. The upper region of hollow interior256is interrupted by a pair of inwardly projecting keys264. Keys264fit within openings94of follower70to prevent the follower70from rotating relative to plunger element230until the keys264drop below openings94when the plunger element230is moved during an injection such that the follower70, relative to the plunger element230, rises out from within tube250. Keys264extend above plate portion248to fit into clearance holes84of follower70. Keys264extend above plate portion248to keep the follower70and shuttle element230engaged for a longer portion of the axial travel of the plunger element.

Plunger element230is rotatably keyed with shuttle member170at all times within device20due to the interfitting of plunger element legs232with shuttle member legs200. Projecting rib portions280are the portions of legs232that engage plunger leg sides204. Rib portions280are radially reduced for the sleeve arms318to pass over during device assembly.

Plunger element230is surrounded along most of its axial length by a syringe support member, generally designated290, that is further shown inFIGS. 10A-10D. Syringe support member290includes a tubular body or sleeve292extending from a distal end294to a proximal end296. A pair of diametrically opposed flanges298projecting from distal end294each include a radially outwardly projecting key300that slide axially within diametrically arranged channels or keyways304provided on housing main body34via vertically extending ribs308formed on the interior surface311of base portion37.

Sleeve292includes a spring-supporting shelf310provided on the interior surface312near proximal end296. Shelf310is buttressed by a series of angularly spaced gussets314along the underside of shelf310. Two diametrically arranged pairs of support arms318upwardly project at an angle from interior surface312below shelf310. The flattened upper tips320of arms318are spaced within the hollow325of sleeve292to engage the underside of flange354of syringe barrel352. Arms318serve to hold the syringe350within the housing30prior to the device being used.

The end coil of spring205that drives medication injection abuts the top face of shelf310. As best shown inFIG. 5, spring205acts against the plunger element ends236via the interposed shelf310. Flanged ends236of plunger element230nest between the lower ends325of arms318such that the plunger element230is rotatably fixed with syringe support member290and thereby device housing30. This operative connection means that syringe support member290acts as a part of the drive plunger of device20with plunger element230. The medication filled, needled syringe for use with the inventive delay mechanism of the present invention290may be one of a variety of syringe designs, such as a staked needle syringe that would generally have a configuration as shown inFIGS. 2-4. Different needle covers could also be employed. Device20is shown inFIG. 5as having a needle syringe, generally designated350with a needle cover380. Syringe350and cover380will be further understood in view of a conceptually similar syringe design described in International application no. PCT/US2012/051702, the entire disclosure of which application is hereby incorporated herein by reference.

Needle syringe350includes a barrel352with a radially outwardly extending, circumferential rib or flange354at its distal end. An elastomieric ring355under flange354cushions inpact of flange354on shuttle base220. An elastomeric piston356slidably seals with the barrel interior to prevent the medication contents from exiting the top end of barrel352. A collar portion360at the proximal end of barrel352connects with a hub362that has a resilient portion that forms a pierceable septum364that seals the bottom of the medication reservoir.

A needle carrier370holds a double-ended cannula372. Needle carrier370is axially movable in a keyed or rotatably fixed fashion within hub362between detented axial positions. Needle carrier370is shown abstractly inFIG. 5, but is further shown inFIGS. 15-17as having resilient arms with detents on their upper ends that engage nubs provided in the interior surface of hub362. Distal tip374of cannula372is for piercing septum364and cannula proximal tip376is for piercing cover380and penetrating a user.

Needle cover380maintains the sterility of cannula372prior to device use and is made of a single air-tight elastomeric piece. Cover380includes ring portion382that mounts to hub362and a hinging region383at the upper end of a collapsing body384with a needle penetrable end region386.

The construction of device20will be further understood in view of a description of its operation. The device is initially configured as shown inFIG. 5andFIG. 15, with spring205under compressive preloading to acting to provide a biasing force on plunger230relative to shuttle member170. Despite this biasing force, plunger230can not move axially proximally relative to the shuttle as it is effectively latched with the lock ring140mounted to shuttle member170. Spring150is under a torsional preloading and an axial preloading each tending to bias follower70relative to the housing30and more particularly shaft62. Despite this biasing, follower70can not move distally within the housing as the interfitting of follower keys74within recess regions102results in keys74abutting top shoulders112, and the keying of follower70with plunger element230by keys264fitting within openings94of follower70prevents rotation of the follower within the housing. Follower70, and the held shuttle member170, can not move proximally as follower keys74abut shaft shoulders110. To allow for an injection, safety sleeve32is manually rotated by a user, or someone helping the user, to unlock button21and the device20is placed on an injection site. When the trigger assembly is then operated by depressing button21, plunger element250is released to be shifted by spring205proximally within the housing.

Plunger element250, due to the direct engagement of the bottom end252of its tube250with syringe plunger356, drives plunger356proximally which initially moves barrel352downward to cause cannula tip384to pierce cover region386and extend through base plate opening55to penetrate the user's skin. Cover380begins to axially collapse when the barrel352moves downward. Cannuala tip374has yet to pierce septum364as it is still axially retained within hub360.

As the plunger element230is continued to be shifted downward by spring205, syringe barrel352is continued to be driven proximally, with cover380continuing to collapse. When needle carrier370abuts housing base57, with the cover region386sandwiched therebetween, it can travel no further proximally, and further proximal motion of barrel352causes the hub360to move downward relative to the needle carrier370such that septum364is pierced by needle tip374.

Further downward advancement of plunger element230continues to move barrel352proximally until barrel flange354, cushioned by ring355, abuts clip element base220, at which point the barrel352can not move proximally, the cover380is fully collapsed, and further proximal motion of plunger element230drives plunger365further downward within barrel352as tube250inserts farther into barrel352, causing the syringe contents to be forced through cannula372and into the user.

As plunger element230moves proximally under bias of spring205, keys264slide down follower legs90within openings94until clearing tips95, at which point the follower70is rotationally unlocked from the plunger element230. This unlocking typically will be designed to occur shortly before the end of proximal travel of the plunger, but can be earlier depending on the designed for delaying effect of the delay mechanism.FIG. 16illustrates device20at this point of operation.

When rotationally unlocked, follower70, as urged by the torsional preloading of biasing member150, starts to rotate around shaft62with keys74sliding angularly within recess regions102. This follower rotation is also relative to shuttle member170that remains rotationally fixed within the housing via its keyed relationship to plunger element230. The viscous damping compound195between follower fin80and shuttle collar180dampens or offers a resisting force to this follower rotation, which resistance results in a passage of time before the follower shifts distally as described below, during which time remaining medication can be properly expelled from the syringe through the needle tip376.

Rotation of follower70about shaft62as driven by spring150continues until follower keys74abut end shoulders116, at which point keys74are aligned with channels106. By then, plunger element230has completed its proximal travel to fully move syringe plunger356into syringe barrel112to expel a suitable dose, and under the axial force provided by spring150, follower70is then driven distally within housing30such that keys74slide through channels106and into recess regions104until abutting top shoulders120. This distal motion of follower70simultaneously and identically moves the shuttle member170, and the shuttle clip element216, distally. As clip element216so moves, and due to its engagement of clip base220with the underside of flange354, syringe350is carried by the shuttle distally so as to retract the proximal376of the injection needle372to a protected position within the housing30.

After needle retraction, a further follower rotation produces a locking of the retracted needle. In particular, when keys74abut shoulders120, keys74are disposed within recess regions104. The torsional preloading of biasing member150still remaining restarts the rotation of follower70in the same angular direction around shaft62, with keys74sliding angularly within recess regions104. When keys74abut stop shoulders128, the follower rotation is halted. If top shoulders120are notched to provide follower catch features as described above, follower rotation is instead halted when keys74slip into these notches. Keys74do not continue into channels122, which channels are used during assembly of the follower70to shaft62, as during assembly of shaft62to housing disc portion42the fastener64effectively makes channel122impassable to the keys74. Because follower70, and therefore the shuttle including shuttle member170, then can not be shifted proximally due to the abutting engagement of shoulders124by keys74, the needled syringe350is locked in a retracted position. At this point, device20is configured as inFIG. 17, and the user then can dispose or otherwise handle the device in the normal course.

While this invention has been shown and described as having preferred designs, the present invention may be modified within the spirit and scope of this disclosure. For example, the inventive delay mechanism can have differently shaped parts or can be used in devices with different other components, such as alternate triggers. Furthermore, the manner in which the various parts are keyed together, and the fact that certain parts are keyed directly to other parts, may be changed in alternate embodiments. For example, the keys and keyways on various parts may by switched, or the shuttle could be directly keyed with the housing to be rotatably fixed rather than indirectly keyed, such as through the plunger element. Still further, and while the described plunger element drives both syringe advancement as well as advancement of the syringe piston within the barrel, the delay mechanism could be employed in a device in which the plunger element that it engages merely drives piston advancement within the barrel. Still further, while the damping compound is provided directly between the shuttle and the follower in the shown embodiment, in alternate embodiments, and instead of or in addition to such follower and shuttle direct damping feature, the damping feature can be provided between the follower and the housing directly, though such may delay the axial movement of the follower relative to the housing and thereby slow syringe axial retraction. This application is therefore intended to cover any variations, uses or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.