Patent Publication Number: US-2019167909-A1

Title: Medication injector apparatus with drive assembly that facilitates reset

Description:
BACKGROUND OF THE INVENTION 
     The present invention pertains to medication delivery devices, and, in particular, to portable medication delivery devices such as injection pens. 
     Patients suffering from a variety of diseases, such as diabetes, frequently must inject themselves with medication, such as insulin solutions. To permit a person to conveniently and accurately self-administer proper doses of medicine, a variety of devices broadly known as injector pens or injection pens have been developed. 
     In order to permit a person to administer a proper dose, injection pens have been equipped with a wide variety of dosing and injecting mechanisms that enable a particular dosage to be conveniently selected and then dispensed. Generally, these pens are equipped with a cartridge including a plunger and containing a multi-dose quantity of liquid medication. A drive member is movable forward to advance the plunger in the cartridge in such a manner to dispense the contained medication from the opposite cartridge end, typically through a needle that penetrates a stopper at that opposite end. In reusable pens, after the pen has been utilized to exhaust the supply of medication within the cartridge, a user can remove and dispose of the spent cartridge. Then, to prepare for the next cartridge, the plunger-engaging drive member of the pen is reset to its initial position, either manually or automatically during attachment of a replacement cartridge, and the injection pen can then be used to the exhaustion of that next cartridge. 
     In order to allow the reset of the plunger-engaging drive member of reusable injection pens, a variety of assemblies have been utilized. One known assembly utilizes a nut fixed within the housing, such as by ultrasonic welding, which nut threadedly engages a drive screw that when rotated is extendable from the base of the injection pen to advance the plunger of a cartridge within a retainer mounted to the pen base. Rotation of the drive screw to screw it through the fixed nut to advance the plunger is effected by a toothed drive clutch, keyed to rotate with the screw, which engages a toothed drive member that rotates during operation of the injecting mechanism. The drive clutch, which is forced into torque transmitting relationship with the drive member when the cartridge retainer is mounted to the pen base, is spring biased away from the toothed drive member when the cartridge retainer is removed. While effective to advance the drive screw, and to allow that screw to be reset or pushed back into the pen base during the process of mounting the cartridge retainer, this assembly is not without its shortcomings. For example, due to the relatively large size of the drive clutch, a flywheel effect of the rotating clutch during screw resetting may cause the screw to retract so far that the initial priming of the pen may be inconvenient to perform. 
     Injection pens have been equipped with an assortment of mechanisms that generate an audible clicking noise during the injecting process. This clicking noise is intended to inform a user that the pen is operating to administer medication. One known pen uses an injection clicker mechanism which employs a series of radially extending leaf springs arranged around the periphery of a disk-shaped, radially projecting portion of a drive sleeve of the injecting mechanism. As the injecting mechanism of the pen is operated, the drive sleeve rotates, causing rotation of a clutch that has been axially moved during pen assembly so as to be engaged by teeth that axially extend in the distal direction from the drive sleeve radially projecting portion. As the clutch rotates, a drive screw that extends through the drive sleeve and to which the clutch is keyed is caused to rotate, and the drive screw advances axially as it screws through a nut within the pen housing to move a cartridge plunger and expel medicine from the pen. During the drive sleeve rotation, the radially extending leaf springs arranged around the drive sleeve radially projecting portion slip into and out of recesses in the pen housing located radially outward thereof, thereby producing audible clicking noises associated with injection. The leaf springs, when inserted in the housing recesses when drive sleeve rotation is halted, are designed to prevent counter-rotation of the drive sleeve which would allow undesirable back up of the drive screw. While useful, this injection clicker design is not without its shortcomings. For example, modifying the feel and sound of the injection clicks during the design of the pen may involve modifications to the mold cavities of the housing. Still further, the radially extending leaf springs may undesirably increase the overall girth of the injection pen. 
     In another injection pen disclosed in U.S. Pat. No. 5,688,251, an injection clicker is provided by a spring biased distal clutch with axially facing teeth which is coaxially arranged on and splined to a nut that engages an advanceable lead screw. The spring that pushes the distal clutch teeth against the housing bulkhead to create audible clicking during injection also pushes a proximal clutch against a driver to create audible feedback during dose dialing. While perhaps functional, this design is not without its shortcomings. For example, because the spring used within the injection audible feedback design is also used as part of the dialing audible feedback design, the injection audible feedback cannot be tuned or adjusted by modifying that spring without also affecting the dialing audible feedback, and potentially other features such as dialing torque. 
     Another limitation of reusable injection pens is that because different types of medicines, provided in separate cartridges, possibly may be utilized with the same reusable pen body, a user of the injection pen and those various cartridges needs to be vigilant to ensure the pen is used to administer the correct dosage of medicine. In order to assist a user in identifying medicine contained in a cartridge, a cartridge recognition system has previously been disclosed in U.S. Pat. No. 5,954,700. In that system, a medicine-filled cartridge includes an information providing source designed to provide information regarding the cartridge to the electronic delivery device, such as an injection pen for which it is adapted. While useful, the information provided does not necessarily result in the delivery device indicating to a user the actual dose of medicine being administered by the delivery device, and calculation errors on the part of the user are possible, resulting in incorrect doses. 
     Another limitation of some injection pens relates to the dose setting mechanism. One mechanism disclosed in U.S. Pat. No. 5,509,905 includes switches that are used in forming signals when the switches are actuated during rotation by a user of an operating head extending from the pen base. The signals are used in mathematically establishing the number of unit volumes set by the user. However, the use of cams to activate the switches results in the resistance to rotating the operating head noticeably varying during revolution of that operating head. 
     Another problem with some existing injection pens is that dosing and injecting operations of the pen are not intuitive to all users. In particular, with some pens, the user first must rotate a knob of the pen to set the medicine dose to be delivered as indicated by numbers on a marked dial fixedly connected with the knob, and then must apply an axial or plunging force which moves the knob axially to inject the medicine dose. Because for some pen designs the knob and dial will have axially translated away from the pen base while being rotated during dose setting, and further that knob and dial, when plunged during injecting, will also rotate back into the pen base so as to provide via its markings a continuous indication of the amount of medicine remaining to be delivered, a user may come to believe that rotating down the proximally extended knob will inject the medicine. However, such a belief is erroneous for at least one pen design, and therefore a user who operates under such an erroneous belief may not properly self-administer the desired medicine. 
     In a well known disposable injection pen design, a dose is similarly set by rotating out a knob, connected to a number-marked dial, such that the dial translates out while rotating. While the dial is rotated, a sequence of numbers helically arranged on the dial is visible through a viewing window to show the dose the pen is then set to deliver. In this design, application of a plunging force moves the knob and the dial axially and without rotation to inject the medicine dose. However, while useful, this design is not without its shortcomings. For one thing, during plunging, few if any of the dose-indicating numbers which have been passed in setting the pen are displayed, which may be a source of confusion for some users. Furthermore, after the pen is used for injecting, the dial has to be reset before it can be screwed outward to set the next dose for delivery. Resetting requires a rotation of the dial to a zero position, except for a limited number of dose quantities previously injected, followed by an axial shifting of the dial. 
     Thus, it would be desirable to provide a device or method that overcomes one or more of these and other shortcomings of the prior art. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention encompasses a drive assembly that is operable to advance a plunger of a cartridge of a portable injector apparatus such as an injection pen, and which is resettable with minimal effort during replacement of the spent cartridge. 
     The present invention also encompasses an assembly within a portable injector apparatus that during dose injecting provides to a user an audible indication of operation, which audible indication is readily adjustable by the manufacturer by, for example, a substitution of biasing elements. 
     The present invention also encompasses a therapeutic dose indicating apparatus for a medicine delivery device, such as an injection pen, which first determines a therapeutic dose based on a sensed medicine concentration and a sensed dose volume setting, and then visibly displays the determined therapeutic dose. The invention further encompasses a doseable quantity identifier for an injection pen which uses a sensor, such as with electrical contacts, to read a matrix to determine how a dose setting mechanism has been rotationally arranged by a user in setting the pen for dose administration. 
     The present invention also encompasses a medication injector apparatus including an assembly for selectively rotating a drive sleeve, which assembly has a dial that rotates out during dose setting and which translates in without rotation during dose injecting. The dial is keyed to a barrel within the apparatus, and further is threadedly engaged with the drive sleeve that is operably connected to a drive member advanceable to force medication from a fluid container within the apparatus. The relative rotation experienced by the barrel and drive sleeve during dosing and injecting is used by an electrical sensing mechanism in recognizing the arrangement of the apparatus for the purpose of displaying to a user the dose selected and remaining to be injected. 
     In one form thereof, the present invention provides a resettable, cartridge plunger drive assembly of a dose injecting mechanism of a medication injector apparatus which has a reusable base and a cartridge assembly mountable thereto. The base has a rotatable drive member of the dose injecting mechanism within its housing, and the cartridge assembly has a medicine-filled cartridge with a movable plunger at one end and an outlet at the other end. The drive assembly includes a nut, a screw, a drive clutch, and a biasing element. The nut is keyed to the base housing to be both movable relative thereto between first and second axial positions, and rotatably fixed relative thereto at the first and second axial positions. The screw includes a plunger-engaging distal end and external threading in threaded engagement with an internally threaded opening of the nut. The drive clutch is connected to the nut to be axially retained and rotatably movable relative thereto. The drive clutch is keyed to the screw to be rotatably fixed and axially movable relative thereto. The nut is positioned within the base housing to be axially movable from the first axial position to the second axial position by engagement with the cartridge assembly during mounting of the cartridge assembly to the reusable base. The drive clutch is in torque transmitting engagement with the rotatable drive member when the nut is disposed in the second axial position, whereby rotation of the drive member during operation of the dose injecting mechanism rotates the drive clutch and thereby the screw to produce axial movement of the screw in a distal direction through the nut to thereby advance the plunger-engaging distal end of the screw to force medication from the cartridge outlet. The biasing element biases the nut from the second axial position toward the first axial position when the cartridge assembly is not mounted to the reusable base. The drive clutch is disengaged from torque transmitting engagement with the rotatable drive member when the nut is disposed in the first axial position, whereby application of a force in a proximal direction on the plunger-engaging distal end of the screw axially moves the screw in a proximal direction as it screws through the nut to thereby reset the screw. 
     In another form thereof, the present invention provides a resettable, cartridge plunger drive assembly of a dose injecting mechanism of a medication injector apparatus which has a reusable base and a cartridge assembly mountable to the base. The apparatus base has a rotatable drive member of the dose injecting mechanism within its housing, and the cartridge assembly has a medicine-filled cartridge with a movable plunger at one end and an outlet at the other end. The drive assembly includes a nut, a screw, a drive clutch, and a biasing element. The nut is keyed to the base housing to be both movable relative thereto between first and second axial positions, and rotatably fixed relative thereto at the first and second axial positions. The screw includes a plunger-engaging distal end and external threading in threaded engagement with an internally threaded opening of the nut. The drive clutch is keyed to the screw to be rotatably fixed and axially movable relative thereto. The nut is positioned within the base housing to be axially movable from the first axial position to the second axial position by engagement with the cartridge assembly during mounting of the cartridge assembly to the reusable base. The drive clutch is structured and arranged to be shifted from a location out of torque transmitting engagement with the rotatable drive member to a location in torque transmitting engagement with the rotatable drive member when the nut is moved from the first axial position to the second axial position, wherein when the drive clutch is in torque transmitting engagement with the rotatable drive member, rotation of the drive member during operation of the dose injecting mechanism rotates the drive clutch and thereby the screw to produce axial movement of the screw in a distal direction through the nut to thereby advance the plunger-engaging distal end of the screw to force medication from the cartridge outlet. The biasing element is structured and arranged to bias the drive clutch from the location in torque transmitting engagement with the rotatable drive member to the location out of torque transmitting engagement with the rotatable drive member, and thereby move the nut from the second axial position toward the first axial position, when the cartridge is not mounted to the reusable apparatus base, wherein when the drive clutch is out of torque transmitting engagement with the rotatable drive member, application of a force in a proximal direction on the plunger-engaging distal end of the screw axially moves the screw in a proximal direction as it screws through the nut to thereby reset the screw. 
     In another form thereof, the present invention provides an injection clicker assembly of a medication injector apparatus, which apparatus includes a drive screw advanceable in a distal direction to shift a movable plunger of a cartridge so as to force medication from an outlet of the cartridge, a drive sleeve of a dose injecting mechanism rotatable in a first direction within a housing of the apparatus, the drive sleeve including a distal facing surface and defining a longitudinal bore in which the drive screw extends, and a clutch, connected to the drive screw, that is rotated by engagement with the drive sleeve distal facing surface to thereby rotate and advance the drive screw through a nut within the housing. The injection clicker assembly includes a collar arranged coaxially on the drive sleeve at a location proximal of the distal facing surface of the drive sleeve. The collar is connected to the drive sleeve to be axially movable relative thereto and rotatably fixed thereto when the drive sleeve rotates in the first direction. The collar includes a plurality of teeth extending in an axial direction and adapted to engage mating teeth of a stop surface one of integrally formed with and non-rotatably connected to a housing of the apparatus. The injection clicker assembly also includes a biasing element adapted to force the collar axially into meshing engagement with the stop surface. The collar and the stop surface are complementarily configured such that during rotation of the drive sleeve in the first direction, and due to a returning force applied to the collar by the biasing element, the collar oscillates axially on the drive sleeve as the collar teeth slide over the stop surface teeth to provide an audible clicking sound that indicates injecting use of the apparatus. 
     In another form thereof, the present invention provides a therapeutic dose indicating apparatus for a portable medication injector device which includes an adjustable dose setting mechanism and which is loaded with a replaceable medicine container. The apparatus includes a visible display, a container recognizer that recognizes a concentration of medicine within the container, which container recognizer includes an identifier disposed on the container, a doseable quantity identifier that identifies a volume of medicine selected for delivery by the adjustable dose setting mechanism, and a controller adapted to determine a therapeutic dose based on the recognized concentration and the identified volume and cause the therapeutic dose to be displayed in the visible display. 
     In another form thereof, the present invention provides a doseable quantity identifier for a medication injector apparatus having a dose setting mechanism operable to select a volume of medicine to be delivered from a held cartridge. The doseable quantity identifier includes a rotational matrix disposed on a first component of the apparatus, a sensor for electrically sensing the rotational matrix, which sensor is disposed on a second component of the apparatus which experiences rotational motion relative to the first component during operation of the dose setting mechanism, whereby data of the rotational matrix sensible by the matrix sensor is thereby indicative of an arrangement of the dose setting mechanism, a controller circuited with the sensor which interprets data of the rotational matrix sensed by the sensor to determine a quantity of medicine to be delivered from the cartridge during injection, and a visible display that displays the quantity of medicine to be delivered as determined by the controller. 
     In still another form thereof, the present invention provides a method of indicating a therapeutic dose to a user of a portable medication injector apparatus loaded with a cartridge of medicine, the portable medication injector apparatus including a dose setting mechanism operable to select a volume of medicine for delivery. The method includes the steps of recognizing a concentration of the medicine within the cartridge with a cartridge recognizer of the portable medication injector apparatus, identifying a selected delivery volume with a doseable quantity identifier of the portable medication injector apparatus, determining the therapeutic dose with a controller of the portable medication injector apparatus using the recognized concentration and the identified selected delivery volume as input, and displaying the determined therapeutic dose on a display of the portable medication injector apparatus. 
     In still another form thereof, the present invention provides a medication injector apparatus comprising a housing, a fluid container mounted to the housing defining a medicine-filled reservoir and including a movable piston at a proximal end of the reservoir, a needle assembly removably attached to a distal end of the fluid container to have an injection needle of the needle assembly in flow communication with the reservoir, a drive member advanceable within the housing in a distal direction to move the piston toward the injection needle for forcing medicine from the container, and a dose setting element that includes a control portion external to the housing and manually rotatable in a first direction to screw the dose setting element from a plunged position to a plungeable position at which the dose setting element projects farther proximally from the housing than at the plunged position. The apparatus also includes means, operable by translating without rotation the dose setting element from the plungeable position to the plunged position, for advancing the drive member in the distal direction, the advancing means comprising a drive sleeve and a barrel within the housing that experience relative rotation during at least a portion of a movement of the dose setting element between the plunged position and the plungeable position, and an electronics assembly that displays a dose of medicine to be injected based on a sensing of the relative rotational positions of the barrel and the drive sleeve. 
     In still another form thereof, the present invention provides a medication injector apparatus including a housing, a medicine-filled container mounted to the housing and including a movable piston at one end and an outlet at the other end, a drive member advanceable within the housing in a distal direction to move the piston toward the outlet for forcing medicine from the container, a drive sleeve around and operatively connected to the drive member, which drive sleeve is rotatable to advance the drive member distally, a barrel around the drive sleeve and movable in the distal direction within the housing by engagement with the drive sleeve from a first axial position to a second axial position, which barrel is freely rotatable relative to the housing at the first axial position and rotatably fixed relative to the housing at the second axial position, a dose setting element including a manually rotatable portion external to the housing, which dose setting element is keyed with the barrel within the housing to be axially movable and rotatably fixed relative to the barrel, and which is in threaded engagement with the drive sleeve. The manually rotatable portion is rotatable in a first direction such that the dose setting element rotates and moves proximally along the drive sleeve due to the threaded engagement therebetween, whereby the dose setting element moves from a plunged position to a plungeable position at which the dose setting element projects farther proximally from the housing than at the plunged position. When the dose setting element is in the plungeable position, application of a force in a distal direction on the dose setting element first translates distally and without rotation the dose setting element and the drive sleeve and the barrel relative to the housing until the barrel shifts from the first axial position to the second axial position, and then, until the dose setting element reaches the plunged position, translates distally and without rotation the dose setting element relative to the housing while thereby rotating without translation the drive sleeve to advance the drive member distally within the housing. 
     One advantage of the present invention is that a drive assembly can be provided which facilitates reset of an injection pen during installation of a replacement medication cartridge. 
     Another advantage of the present invention is that a drive assembly can be provided which, without increasing the injection force of the injection pen in which it is used, allows for a biasing element strong enough to force the drive clutch out of engagement with the drive member, thereby avoiding a problem found in the prior art in which a more weakly biased drive clutch could bind to the drive member so as to lock the drive screw and prevent reset. 
     Another advantage of the present invention is that a drive assembly can be provided which has a relatively small drive clutch to limit flywheel effects during drive screw reset, which in turn may reduce priming volumes. 
     Another advantage of the present invention is that a drive assembly can be provided which engages a cartridge assembly during its mounting to the pen base so as to reduce play between the cartridge assembly and the pen base, thereby providing an improved fit therebetween and improved quality feel to the injection pen. 
     Another advantage of the present invention is that a drive assembly with a relatively simple design can be provided to reduce costs of assembly and manufacture. 
     Another advantage of the present invention is that a drive assembly can be provided which in one embodiment spring biases forward a loaded cartridge to hold it in place against a forward stop of the holder or retainer of the cartridge assembly to ensure a stable platform for dose delivery. 
     Another advantage of the present invention is that a drive assembly can be provided which in one embodiment is biased together with a loaded cartridge so as to limit relative movement of the cartridge and the drive screw which otherwise could cause drooling of the pen. 
     Still another advantage of the present invention is that an injection clicker assembly can be provided that generates an audible indication to a user of injecting operation of the portable injector in which it is installed. 
     Still another advantage of the present invention is that an injection clicker assembly can be provided that is readily tunable during manufacturing design, such as by altering a spring constant or preload of a biasing element, to provide the desired tone and loudness of the injection audible feedback. 
     Still another advantage of the present invention is that an injection clicker assembly can be provided that can be tuned during manufacture independently of any dialing audible feedback or dialing torque of a pen in which it is installed. 
     Still another advantage of the present invention is that an injection clicker assembly can be provided that can be designed to serve as an anti-backup mechanism for an advanceable drive screw. 
     Still another advantage of the present invention is that an injection clicker assembly can be provided that is structured and arranged to utilize space efficiently so as to not adversely impact the length or girth of the pen in which it is installed. 
     Still another advantage of the present invention is that an injection pen can be provided which electronically displays the dose of therapeutic agent the user has selected for administration by operation of the dose setting mechanism of the pen. 
     Still another advantage of the present invention is that because the therapeutic dose displayed is a medically important, actual amount of medicine to be administered, rather than a number of clicks or injection pen unit volumes, a user need not make mental calculations regarding dosing which may be subject to error. 
     Still another advantage of the present invention is that an injection pen can be provided which can be used with various types of medicines while allowing the pen to display dose information related to the particular type, such as strength of concentration, of medicine in use. 
     Still another advantage of the present invention is that a dose that can be displayed by the injection pen can be determined by the pen after it automatically recognizes the concentration of the contents of a loaded medicine container. 
     Still another advantage of the present invention is that a rotational matrix that can be used to determine the selected dose volume permits a unique signal for a small, such as fifteen degree, rotational position of the dose setting mechanism, has a compact design to fit within a small physical envelope, and provides a low friction contact solution for dose sensing which does not detract from the ease of operation. 
     Still another advantage of the present invention is that a rotational matrix can be provided with a feature that enables the microcontroller of the apparatus to determine if an invalid sensed matrix position code should be ignored as an aberration rather than causing the apparatus to immediately display an error message. 
     Yet another advantage of the present invention is that a medicine injector apparatus can be provided including an assembly for selectively rotating a drive sleeve which has different modes of operation during dose setting and injecting to allow a user to conceptually distinguish between the different stages of apparatus use. 
     Yet another advantage of the present invention is that a medicine injector apparatus can be provided including an assembly for selectively rotating a drive sleeve which includes a dial that rotates while translating during the dose setting operation, yet which translates without rotating during the dose injecting operation. 
     Yet another advantage of the present invention is that a medicine injector apparatus can be provided including an assembly for selectively rotating a drive sleeve which during its injecting operation automatically resets the apparatus to a zero position from which its dial can be rotated outward to set the next dose for delivery. 
     Yet another advantage of the present invention is that a medicine injector apparatus can be provided including a switch within the housing and used in controlling the electronics of the apparatus, such as setting date and time values. 
     Yet another advantage of the present invention is that the switch that can be provided in the medicine injector apparatus is activated by axial motion of a component within the housing during use, and serves to distinguish between dosing and injecting operations, which among other things makes the switch suitable for triggering a last dose memory function of the pen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other advantages and objects of this invention, and the manner of attaining them, will become more apparent, and the invention itself will be better understood, by reference to the following description of embodiments of the invention taking in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a diagrammatic plan view of a medicine injection pen equipped with one form of a dose injecting mechanism including a resettable, cartridge plunger drive assembly of the present invention; 
         FIG. 2  is a plan view in partial cross-section diagrammatically showing the injection pen of  FIG. 1  prior to the mounting of the cartridge assembly to the reusable pen base, and with the drive screw of the drive assembly projecting from the distal end of the pen base; 
         FIG. 3  is a fragmentary plan view in cross-section diagrammatically showing the reusable pen base of  FIG. 2 ; 
         FIG. 4  is a fragmentary plan view in cross-section diagrammatically showing the injection pen of  FIG. 1  with the cartridge assembly fully mounted to the reusable pen base; 
         FIG. 5  is a perspective view of the drive assembly, and a rotatable drive member that powers drive assembly operation, removed from the injection pen of  FIG. 1 ; 
         FIG. 6  is a cross-sectional view in exploded form of an injection nut and drive clutch of a drive assembly of the present invention; 
         FIG. 7  is a fragmentary plan view in cross-section diagrammatically showing another injection pen in which an inventive drive assembly biases forward a cartridge within a retainer mountable to the pen base; 
         FIG. 8  is a fragmentary view in cross-section diagrammatically showing portions of an injection pen equipped with one form of an injection clicker assembly of the present invention; 
         FIG. 9  is a fragmentary view in cross-section diagrammatically showing another form of an injection clicker assembly of the present invention within portions of another injection pen; 
         FIG. 10  is an exploded perspective view of the injection clicker assembly of  FIG. 9  and portions of the injecting mechanism with which it interacts; 
         FIG. 11  is an opposite perspective view of  FIG. 10 ; 
         FIG. 12  is a block diagram representation of one form of a therapeutic dose indicating apparatus of the present invention; 
         FIG. 13  is a diagrammatic plan view of an injection pen as the delivery device equipped with one form of the therapeutic dose indicating apparatus shown in  FIG. 12 ; 
         FIG. 14  is a cross-sectional view of a cartridge assembly removed from the injection pen of  FIG. 13 ; 
         FIG. 15  is a plan view of a first embodiment of a barrel hub of the cartridge assembly of  FIG. 14 ; 
         FIG. 16  is a plan view of a second embodiment of a barrel hub of the cartridge assembly of  FIG. 14 ; 
         FIG. 17  is a plan view of a third embodiment of a barrel hub of the cartridge assembly of  FIG. 14 ; 
         FIG. 18  is a schematic representation of how one form of the therapeutic dose indicating apparatus of the present invention operates; 
         FIG. 19  is a diagrammatic plan view in partial cross-section of a sensor array and a dial-mounted rotational matrix of one form of a doseable quantity identifier of the present invention; 
         FIG. 20  is a plan view of the rotational matrix of  FIG. 19  shown unwrapped and removed from the dose setting dial; 
         FIG. 21  is a plan view of the sensor array removed from the dial-mounted matrix of  FIG. 19 , wherein the sensor contacts are shown in dashed lines; 
         FIG. 22  is a plan view of another embodiment of a doseable quantity identifier of the present invention; 
         FIG. 23  is a top view of one form of an injection pen of the present invention equipped with an assembly for selectively rotating a drive sleeve to inject a set dose; 
         FIG. 24  is a cross-sectional front view of the injection pen of  FIG. 23  prior to the dose setting knob being manually rotated out to set the dose to be delivered by further operation of the injection pen; 
         FIG. 25  is a cross-sectional view conceptually similar to the view of  FIG. 24  after the cap has been removed, the pen is in a primed state, and the dose setting knob has been rotated out to set the dose for delivery; 
         FIG. 26  is a cross-sectional view conceptually similar to the view of  FIG. 25  after the dose setting knob has been slightly plunged so as to mechanically transition the pen to a dose injecting state; 
         FIG. 27  is an exploded rear perspective view of the injection pen of  FIG. 23 ; 
         FIG. 28  is a front perspective view of the slider assembly of  FIG. 27 ; 
         FIG. 29  is another rear perspective view of the contact assemblies of  FIG. 27 ; and 
         FIG. 30  is a plan view of the rotational matrix of  FIG. 27  shown unwrapped and removed from the rest of the injection pen. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments 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 
       FIG. 1  generally illustrates one type of medication delivery device in which a drive assembly of the present invention finds beneficial application. The shown delivery device is a reusable, medication injection pen, generally designated  20 . As is generally known in reusable devices of its type, injection pen  20  includes a medication filled cartridge  22  as part of a cartridge assembly, generally designated  24 , which is connected to a reusable pen base, generally designated  26 . Pen base  26  preferably includes dose setting and injecting mechanisms that function to allow a quantity of medicine to be selected and then expelled from cartridge assembly  24  through the injection needle assembly  27  shown attached thereto. In the shown embodiment, an exposed knob  28  with rotatable button  30  thereon at the rearward or proximal end of pen base  26  is a manually operable portion of the dose setting and injecting mechanisms otherwise housed within pen base  26 . During the dose setting process, knob  28  is designed to be rotatable to set the dose, and when knob  28  is so rotated to increase the selected dose the knob  28  and button  30  translate out of pen base  26  from the axial position shown in  FIG. 1 , or to the right from the perspective of a  FIG. 1  viewer. During the dose injecting process which occurs after the dose setting process, when a plunging force is applied to button  30 , which rotates freely relative to knob  28 , button  30  and knob  28  are designed to be shifted to the left, and back to the axial position shown in  FIG. 1 , to cause the injecting mechanism components housed within the pen base to operate to cause the medicine in the cartridge to be injected. 
     The foregoing is provided as background and is intended to be illustrative and not limiting in any way, as a variety of injectors, having varied manual dose setting and injecting mechanisms, and having varied external shapes and sizes, are known in the injection pen art. The inventive drive assembly may be readily adapted for many of such mechanisms in view of the explanation herein, as the inventive drive assembly described further below in theory may be incorporated into any type of injecting mechanism that during injection rotates a rotatable drive element that inputs a rotational force to the drive assembly. Additionally, the inventive drive assembly is applicable to autoinjectors having rotatable drive elements, and further does not require the presence of a dose setting mechanism that allows variability in the quantity to be delivered. 
     With additional reference to  FIG. 2 , in which the needle assembly is not shown attached thereto, cartridge assembly  24  is assembled from component parts during its production into a unit handled by a user as a single piece, and disposed of as a unit when the contained medicine is exhausted. Cartridge  22  of cartridge assembly  24  includes an open-ended glass housing  32  that defines an internal volume filled with medicine such as human growth hormone or insulin. A slidable plunger  34  engages inner surface  33  of the cartridge housing in a fluid-tight manner. A rod tip  35  used to distribute advancing forces applied to plunger  34 , and which is freely movable within the cartridge internal volume located proximally of plunger  34 , has a base disc  37  integrally formed with a cylindrical collar  38  in which fits the distal end  121  of drive screw  120  of the inventive drive assembly. If rod tip  35  is eliminated, distal end  121  of drive screw  120  can directly, as opposed to indirectly, engage plunger  34 . Alternatively when the pen is to be used with cartridges that lack a rod tip, a foot which has a larger diameter than the drive screw and which is designed to rotate relative to the drive screw may be rotatably mounted on distal end  121  to directly engage the cartridge plunger. 
     Cartridge  22  is further protected by an outer housing  42 , which is shown as being transparent but may be otherwise constructed. At its rearward end, outer housing  42  includes an externally threaded, stepped-down neck portion  44 , and a further stepped-down rear hub  46  in which extends the rearward end of rod tip  35 . Threaded neck portion  44  allows for a threaded or screw attachment of cartridge assembly  24  to pen base  26 . Cartridge assembly  24  includes cap  50  that is secured during production, such as by ultrasonic welding, to outer housing  42  to capture cartridge  22  within the outer housing. A pierceable rubber septum  54  is pressed by cap  50  against cartridge housing  32  to seal the open forward end of the housing. External threads on cap  50  allow mounting of injection needle assembly  27 . When assembly  27  is so mounted, the rear end of its needle pierces septum  54 , and medicine is expressed from cartridge  22  through the needle when plunger  34  is driven to the left in  FIG. 1  during injecting use of pen  20 . 
     The cartridge assembly which is acted upon by the drive assembly of the present invention may be differently configured such as is known in the art. For example, and as further shown in  FIG. 7 , the cartridge assembly may be provided as a reusable retainer which is connectable in suitable fashion, such as via threads, to a reusable pen base, and which retainer defines a chamber into which a disposable cartridge is loaded for use. After the contents of the given cartridge are exhausted by multiple uses of the injection pen, a user disconnects the retainer from the pen base, removes the spent cartridge from the open proximal end of the retainer and disposes of that cartridge, and then inserts a replacement disposable cartridge into the retainer which is then reconnected to the pen base for use, which cartridge replacement process can be repeated as necessary. Still further, other cartridge assemblies may be used, such as a cartridge assembly that includes a disposable cartridge made of plastic and without an outer protective cover, and which attaches directly to the pen base, as well as a cartridge assembly that includes a replaceable cartridge, which mounts or inserts within a chamber of the device, and a cover element for the cartridge-receiving device chamber, such as a separate cap piece or an access door that is slidably or pivotally connected to the device. 
     With additional reference to  FIGS. 3-6 , the drive assembly includes a floating nut  60  located within the interior hollow of pen base  26  defined by the pen base exterior housing. In the embodiment diagrammatically shown in  FIG. 3 , the distal end of the pen base exterior housing includes a cartridge interface member  62  fixedly secured, such as by gluing, plastic snap fit or ultrasonic welding, to a rearwardly extending housing body portion  64 . Interface member  62  is internally threaded at  66  for connection to the externally threaded stepped-down neck portion  44  for mounting cartridge assembly  24  to pen base  26 . External threading  63  of interface member  62  allows mounting of a not shown main cap of injection pen  20 . The inventive drive assembly also may be used with other housing configurations. 
     Floating nut  60  is molded in one piece from plastic and includes a generally cylindrical, tubular body section  70  which is preferably keyed to the pen base housing to allow the nut to travel in an axial direction therein while preventing rotational motion of the nut within the housing at any given axial position. A suitable keying includes radially projecting keys  74  located adjacent the rearward end of nut body section  70  which fit within axially aligned grooves or keyways  65  formed in housing body portion  64 . In the shown embodiment, three equally angularly spaced keys  74  are provided, but additional keys, or fewer keys including only a single key, may be employed. In addition, nut  60  may be keyed to the pen base housing by keys furnished on the housing that fit within keyways formed in the exterior of the nut. 
     The hollow interior  71  of tubular body section  70  is spanned by disk portion  80  of nut  60 . The portion of hollow interior  71  located forward of disk portion  80  is sized to freely rotatably receive hub  46 . A central opening  81  defined by disk portion  80  is formed with internal threads  82  designed to mate with external threading  124  of the drive assembly screw  120 . A pair of drive clutch retainers  85  are provided on opposite sides of central opening  81 . Each drive clutch retainer  85  is a rim or latch portion  87  integrally formed with and projecting radially inwardly from body section  70 . 
     Floating nut  60  is forced toward the forward end of pen base  26  by a biasing element acting between nut  60  and, for example, the pen base housing. One suitable biasing element is a metal, helical compression spring  90  having a forward end  91  that directly abuts the annular end face  72  of body section  70 , and a rearward end  92  that directly abuts a protruding bulkhead  93  of housing body portion  64 . The rear end surface  67  of interface member  62  provides an axial stop against which the forward face  75  of each nut key  74  abuts to limit forward axial movement of nut  60  by spring  90 . Alternate biasing elements, such as different types of springs and different materials of construction, may be substituted in other embodiments. The rearward end of the biasing element alternatively may abut a pen component that is connected to, rather than integrally formed with, the housing. 
     In the embodiment of  FIG. 3 , drive clutch  100  of the inventive drive assembly is connected to floating nut  60  to be rotatably free and axially fixed. Drive clutch  100  has a disk shaped body  102  ringed completely by a radially outwardly projecting snap ring  104 . When arranged as shown in  FIG. 6  during the device assembly process, movement of drive clutch  100  toward nut  60  results in snap ring  104  ramping up the resilient clutch retainers  85  with the nut and clutch resiliently deforming slightly until snap ring  104  axially passes rim portions  87 , at which time the pieces snap back to their original form to axially capture snap ring  104  between rim portions  87  and a protruding surface portion  89  of the proximal face of disk portion  80  which rings central opening  81 . Protruding surface portion  89  has a smaller diameter than the distal surface  106  of drive clutch  100  to provide a smaller contact area to limit frictional resistance to rotation therebetween. Other types of latching mechanisms to axially retain the drive clutch within the floating nut while permitting relative rotation therebetween, including different numbers of rim portions or rearwardly extending, axially aligned prong portions from which a latch portion projects radially inward, also may be substituted in alternate embodiments. 
     Body  102  of drive clutch  100  defines a central opening  110  and has at least one inwardly extending V-shaped portion or key  112  projecting within the opening. Key  112  fits within a corresponding keyway channel  122  longitudinally extending along the length of drive or lead screw  120 , which includes external threading  124  that engages threading  82  of floating nut  60 . As shown in  FIG. 5 , two diametrically arranged keys  112  fit within longitudinal keyways  122  located on opposite sides of the drive screw. The interfitting of keys  112  with keyways  122  causes forced rotation of drive clutch  100  during injection to rotate drive screw  120 , and similarly causes forced rotation of drive screw  120  during reset to rotate drive clutch  100 . 
     Drive clutch  100  is adapted to engage a rotatable drive member of the injecting mechanism for torque transmission. The outer radial region of proximal surface  113  includes a series of axially projecting, generally triangular shaped teeth  114  arranged in an annulus, which teeth are structured and arranged to mate with similarly configured teeth  130  provided on drive member  135 . Each tooth  114  includes a ramped side  116 , and an axially aligned side  118  to which force is directly applied by a tooth  130  during driving rotation of drive clutch  100  by drive member  135 . In alternate embodiments, different torque transmitting configurations, including flat plates relying exclusively on friction for non-slipping torque transmission, may be substituted for the particular toothed configuration shown. 
     The rotatable drive member  135  rotates when injection pen  20  is operated to cause fluid to be ejected through needle assembly  27 . Drive member  135  is diagrammatically shown as an annular disc  140  rotatably fixed to a sleeve  142  journaled within the injection pen and through which extends drive screw  120 . Annulus  140  includes the forwardly extending teeth  130 . The inventive drive assembly may be driven by differently designed rotatable drive members within the scope of the invention. 
     The inventive drive assembly will be further understood in view of the following explanation of aspects of the operation of injection pen  20 , starting with the injection pen configured as shown in  FIG. 2  which occurs when a new cartridge assembly  24  is replacing an exhausted cartridge assembly that is not shown. The user will first assemble cartridge assembly  24  to pen base  26 . 
     Typically, a user will hold reusable pen base  26  in one hand, and cartridge assembly  24  in the other hand, and first maneuver the components such that distal end  121  of drive screw  120  is inserted within hub  46  and rod tip collar  38 , and into contact with rod tip base disc  37 . Pen base  26  and cartridge assembly  24  are then manually moved together in an axial direction until hub  46  is axially introduced into the pen base hollow interior and the external threads of stepped-down neck portion  44  initially abut internal threads  66  of cartridge interface portion  62 . In the course of this movement, rod tip  35  is first moved farther into cartridge  22  to close up any spacing that may have existed between it and plunger  34 , and then drive screw  120  is forced axially and screws through floating nut  60  while drive clutch  100  freely spins with drive screw  120  and within floating nut  60 . The drive screw  120  is so pushed back or reset, rather than plunger  34  being forced to slide within cartridge  22 , due to the relatively low frictional resistance to reset of the drive assembly. 
     To continue its mounting, cartridge assembly  24  is then rotated relative to pen base  26  to screw the components together. During an early stage of this rotation, within the housing interior volume, annular shoulder  45  contacts end surface  76  of floating nut  60  that is in a forward axial position due to biasing by spring  90 . In alternate embodiments, other portions of the cartridge assembly, such as the rearward end of hub  46 , may be the point of contact with nut  60 . In addition, rather than a direct contact or engagement with the nut, the cartridge assembly may indirectly engage the nut, such as via an interposed member made of a low friction material. Continued screwing in of cartridge assembly  24  by the user shifts floating nut  60  rearward against a resisting force generated by the compressing of spring  90 . In particular, shoulder  45  slides along floating nut end surface  76  as the cartridge assembly rotates and move axially, while nut  60  moves axially without simultaneously rotating. The resisting force generated by spring  90 , which increases as the insertion progresses, reduces play between cartridge assembly  24  and pen base  26  to provide injection pen  20  with a more solid or well-constructed feel to a user, and to limit pen drooling that can occur during relative movement of the cartridge and the drive screw. 
     Cartridge assembly  24  is fully mounted after it has been screwed in until end face  43  of barrel  42  abuts the distal face of cartridge interface member  62 , which arrangement is shown in  FIG. 4 . When cartridge assembly  24  is so mounted, nut  60  and the retained clutch  100  are in a rearward axial position at which teeth  114  of drive clutch  100  are positively engaged with teeth  130  of drive member  135  in a non-slip fashion so clutch  100  can be rotated by rotation of drive member  135 . 
     Subsequently, and with respect to the injection pen  20  shown in  FIG. 1 , after knob  28  has been dialed out to set a dose, the plunging of button  30 , which is mechanically interconnected with sleeve  142  of drive member  135 , rotates drive member  135  to rotate the drive clutch  100  and thereby drive screw  120 , which screws out through nut  60  to advance plunger  34  to force medicine from the needle equipped cartridge assembly  24 . 
     Referring now to  FIG. 7 , there are diagrammatically shown portions of another injection pen equipped with a drive assembly of the present invention. In this embodiment, the reusable pen base  226  is similarly constructed to that shown in  FIG. 3 , and further the drive assembly is the same as that shown in  FIG. 3  other than end  121  of drive screw  120  being configured to rotatably support an added foot  123 . Foot  123  is attached so as to be freely rotatable about the axis of screw  120  during use and serves to distribute pressure on plunger  34 . The cartridge assembly in  FIG. 7  is in the form of a reusable retainer  230  with a disposable cartridge loaded therein, which cartridge is similar to cartridge  22  but lacks a rod tip  35 . Retainer  230  is connectable to the pen base housing such as via threads shown at  232 . Cartridge  22  is insertable into, and removable for replacement from, the retainer through the open rearward end of the retainer when the retainer is not connected to pen base  226 . When a retainer  232  with a loaded cartridge  22  is mounted to pen base  226 , floating nut  60  directly contacts the cartridge housing  32 , and the spring biasing of the nut forces cartridge  22  forward within the retainer against the interior surface of a not shown forward end of the retainer. Cartridge  22  is thereby prevented from moving relative to nut  60 . 
     In still another alternate embodiment which is not shown, the drive clutch need not be held by the floating nut, but instead is simply shifted into engagement with the drive member by, for example, abutting contact with the floating nut. In such a configuration, the spring operably engages the drive clutch to bias it out of engagement with the rotatable drive member when no cartridge assembly is properly mounted to the pen base. For example, the forward end of a spring may abut a washer member which holds forward the drive clutch, such as in contact with the floating nut. 
       FIGS. 8-11  show injection clicker assemblies of the present invention, which assemblies may find beneficial application in injection pens, such as injection pen  20  of  FIG. 1 . However, and while descriptions of these assemblies below may make reference to such a pen  20  in general, such assemblies are not limited to being incorporated into pens similar to pen  20 . The inventive injection clicker assembly may be readily adapted for many alternately configured injectors in view of the explanation herein, as the inventive injection clicker assembly described further below in theory may be mounted on rotatable drive sleeves of injecting mechanisms which are turned by operation of differently configured components of those injecting mechanisms. Additionally, the injection clicker assembly does not require the presence of a dose setting mechanism that allows variability in the quantity to be delivered. 
     As shown in  FIG. 8 , one form of the injection clicker assembly of the present invention includes a ring-shaped collar or clicker element, generally designated  240 . In the description below of the operation of the pen portion shown in  FIG. 8 , such pen portion is described as being a part of pen  20  shown in  FIG. 1  to facilitate explanation, but it will be appreciated that the pen shown in  FIG. 8  includes, for example, a drive assembly which is slightly different than that which is described above with respect to pen  20 , as well as a cartridge assembly that comprises a reusable retainer  238 , which is threadably connected to the pen base housing, and a disposable cartridge  22  loaded therein. 
     Annular collar  240  defines a central bore through which drive sleeve  242  extends such that collar  240  is coaxially mounted on drive sleeve  242 . At least one rib or key, such as a pair of diametrically opposed keys  244 , inwardly project within the central bore of collar  240  and slidably fit within longitudinally extending slots or keyways  246  on opposite sides of drive sleeve  242 . The keying of collar  240  with drive sleeve  242  results in collar  240  being rotatably fixed but axially movable relative to drive sleeve  242 . In an alternate embodiment, collar  240  can be keyed to drive sleeve  242  with mating keys and keyways that are on the drive sleeve and collar respectively. 
     The proximal face of collar  240  is formed with a ring of axially extending teeth  248 . Teeth  248  mesh with complementary teeth  250  that are molded into bulkhead  252 . The number of collar teeth  248  and teeth  250  to which it engages need not be in a 1 to 1 ratio, as the clicker may have, for example, every other tooth removed. Bulkhead  252  is an additional component splined to the pen outer housing portion  254 , which outer housing is shown as an assembly of multiple component parts, such that bulkhead  252  is rotatably fixed relative to the pen housing during injecting use of the pen. Bulkhead  252  is axially fixed in the embodiment of  FIG. 8  by being pressed by a spring  256  against a lip portion of the pen outer housing. In alternate embodiments, mating teeth  250  may be part of a bulkhead integrally formed with the pen outer housing. 
     Teeth  248  and  250  are configured such that when in meshed engagement, only unidirectional rotation of collar  240  relative to bulkhead  252 , and thereby to the pen housing, is permitted. During such relative rotation, the collar teeth  248 , when traveling across teeth  250 , generate audible clicking noises. The unidirectional rotatability of collar  240  allows it to function as an anti-backup mechanism for the drive sleeve and injection screw as described further below. In alternate embodiments in which no anti-backup feature need be performed by collar  240 , teeth  248  and  250  may be differently configured so as to not prevent reverse rotation and to thereby allow bi-directional collar rotation. 
     Injection clicker  240  is biased in the proximal axial direction along drive sleeve  242  by a biasing element, generally designated  258 . In the shown embodiment, the biasing element is a coiled compression spring made of metal which is coaxially mounted on drive sleeve  242 , but other types of springs or materials of construction alternatively may be employed. During injecting use of the pen, spring  258  backs up collar  240  to provide injection clicks and rotational positioning. During manufacture, springs of various strength can be tested in order to select a spring that provides a suitable clicking noise without modifying either the bulkhead or the collar design. 
     The distal end of spring  258  abuts a proximal facing surface of a radially protruding disk portion  260  of drive sleeve  242 . The distal facing surface of disk portion  260  includes a ring of axially extending teeth  262  that are used to transmit rotational motion of the drive sleeve to a drive assembly that advances the injection screw. In the shown embodiment, which is intended to be illustrative and not limiting, the drive assembly includes a clutch  266  with proximal teeth  264  that mate with disk portion teeth  262  when the pen is fully assembled as shown in  FIG. 8 . Clutch  266  is keyed to threaded injection screw  270  via keys  268  that fit within diametrically disposed keyways  272  longitudinally aligned along the screw that extends through drive sleeve  242 . Clutch  266  is axially retained within, but rotatable relative to, a floating nut, generally designated  275 , by way of tangs  277  that snap fit over the clutch during assembly. Floating nut  275  is keyed to the pen housing to be axially movable but rotatably fixed. Floating nut  275  is biased distally by spring  256  when cartridge retainer  238  and cartridge  22  is disassembled from the pen base so as to disengage the drive sleeve teeth  262  from clutch teeth  264  to allow injection screw reset. When floating nut  275  moves distally during pen disassembly, for an injecting mechanism shown in which the drive sleeve is not axially fixed, drive sleeve  242  is moved distally by the action of spring  258  against disk portion  260 , but is prevented from engaging clutch  266  by the abutment of disk portion  260  against the not shown keys of pen housing portion  255  to which floating nut  275  is keyed. 
     The injection clicker assembly of  FIG. 8  will be further understood in view of the following explanation of its operation within a pen such as pen  20 . When pen  20  is in the configuration shown in  FIG. 1 , which is a ready state prior to dose dialing for injection, the teeth of drive sleeve disk portion  260  and clutch  266  are engaged, and the teeth of collar  240  and bulkhead  252  are engaged as shown in  FIG. 8 . During dose dialing or selection, spring  258  maintains collar teeth  248  in meshing engagement with bulkhead teeth  252 . Due to the unidirectional rotatability of collar  240  and its keying to drive sleeve  242 , this teeth meshing rotationally locks drive sleeve  242 . With the drive sleeve assembly locked rotationally, the clutch  266 , and therefore the drive screw  270  keyed thereto, cannot rotate, thereby providing an injection screw anti-back up feature. During the plunging of button  34  in the dose injecting process described above, drive sleeve  242 , and thereby collar  240  keyed thereto, is caused to rotate in the direction permitted by the tooth configuration of collar  240 . Rotation of disk portion  260  of drive sleeve  242  rotates clutch  266  and thereby drive screw  270 , which screws through an internal threading  279  of nut  275  to advance in the distal direction to shift the movable plunger of cartridge  22  so as to force medication from an outlet of the cartridge. As collar  240  rotates, it oscillates axially, against a proximal directed force applied by spring  258 , as its teeth ride over bulkhead teeth  250  and create audible clicks that indicate injecting operation. 
     Referring now to  FIG. 9-11 , another form of an injection clicker assembly of the present invention is shown in a different partially shown injection pen. This injection clicker assembly is particularly adapted for an injecting mechanism having a drive sleeve part that shifts axially during injecting operation. The injection clicker assembly includes a ring-shaped collar or clicker element, generally designated  290 . Annular collar  290  defines a central bore  292  through which tubular base  335  of the drive sleeve extends. At least one rib or key, such as a pair of diametrically opposed keys  294 , inwardly project within bore  292 . Keys  294  fit within longitudinally extending keyways  340  on opposite sides of drive sleeve base  335  such that collar  290  is rotatably fixed but axially movable relative to the drive sleeve. 
     The proximal face of collar  290  is formed with a ring of axially extending teeth  296 . Teeth  296  mesh with complementary teeth  347  molded into a bulkhead  348  integrally formed with the diagrammatically shown pen outer housing. 
     Each tooth of teeth  296  includes an axially aligned surface  297  and a ramped surface  298  extending to the axially aligned surface of the successive tooth, which teeth configuration permits unidirectional rotation of collar  290  relative to the pen housing that allows the collar to function as an anti-backup mechanism. During such relative rotation, the collar teeth  296 , when traveling across the pen housing teeth  347 , generate audible clicking noises. 
     Injection clicker  290  includes a distal surface  300  which at times during pen operation is abutted by a radially aligned, outer region  307  of a retainer ring, generally designated  305 . Ring  305  includes a forwardly angled, central portion  309  which interference fits during pen assembly into a circumferential groove  343  formed in drive sleeve base  335 . This connection causes retainer ring  305  to follow the axial movement of drive sleeve base  335  during operation, which axial movement is a function of the particular injecting mechanism of the pen. Retainer ring  305  serves to restrict axial motion of collar  290  when the drive sleeve is axially positioned as shown in  FIG. 9 , such as during dose dialing, by its outer region  307  engaging surface  300 , thereby preventing the disengagement of collar teeth  296  from housing teeth  347 . 
     Collar  290  is biased in the proximal axial direction by a coiled metal compression spring  320  coaxially oriented around drive sleeve body  335 . The proximal end  321  of spring  320  fits around a stepped-down diameter neck portion  302  of collar  290 . Spring end  321  is pressed over and retained by six ribs  303  spaced at even intervals around the neck portion circumference. 
     The distal end  322  of spring  320  fits around a stepped-down diameter neck portion  332  of a radially protruding, torque-transmitting member  330  of the drive sleeve, generally designated  325 . Drive member  330  is the portion of the drive sleeve which transmits rotational drive sleeve motion to a clutch  350  keyed to drive screw  354 . Six ribs  331  evenly spaced around neck portion  332  are pressed into the distal end  322  of spring  320  during pen assembly to retain spring  320  to drive member  330 . The distal facing surface of drive member  330  includes distally, axially extending teeth  333  that mate with teeth on clutch  350  when the pen is assembled for use. 
     In the embodiment shown in  FIGS. 9-11 , the drive sleeve is a two part assembly, as radially protruding drive member  330  is configured to allow limited axial movement relative to tubular base  335  of the drive sleeve, which base is caused to rotate when the injecting mechanism of the pen is operated. This ability of relative motion aids in preventing clutch binding when a cartridge assembly is mounted to the pen base. In particular, during cartridge assembly mounting, in the condition that the clutch mechanism is meeting tooth to tooth, drive member  330  can back up allowing the cartridge assembly to be fully installed without locking up or damaging the clutch teeth, and any tooth to tooth condition that remains after installation is automatically addressed upon pen priming. This ability of relative motion also allows for the axial movement of the drive sleeve tubular base during injecting operation, which movement is a function of the overall injecting mechanism of the pen. 
     Within a central bore  334  of drive member  330  through which fits tubular base  335 , a pair of diametrically opposed keys  337  project radially inwardly. Keys  337  fit within longitudinally extending keyways  340  such that member  330  is rotatably fixed but axially movable relative to drive sleeve base  335 . A pair of diametrically opposed snaps or ribs  338  also project within bore  334  at locations offset ninety degrees from keys  337 . During manufacturing assembly of drive member  330  to base  335 , ribs  338  snap-fit into recesses  341  formed on the periphery of drive sleeve base  335  and in spaced apart relationship from distal end  342 . Recesses  341  extend in the axial direction greater than the thickness of ribs  338  so as to permit the limited axial movement of drive member  330  relative to base  335 . The snap-fit connection prevents the drive sleeve assembly from coming apart axially when a medication cartridge is disassembled from the pen base, and further insures that the forward travel of drive member  330  is limited by drive sleeve base  335  to aid in disengagement of drive member  330  from clutch  350  when a cartridge assembly is removed. 
     The teeth  333  of drive member  330  mate with a clutch of a drive assembly utilized to shift the injection screw distally. The drive assembly shown in  FIG. 9  has a clutch  350  internally keyed to a threaded drive screw  354  that extends through drive sleeve base  335 . Clutch  350  is connected to a rotatably fixed floating nut  360  which threadedly engages drive screw  354 . Rotation of clutch  350  via the drive sleeve  325  rotates drive screw  354 , which screws through nut  360  to advance in the distal direction beyond the end of the reusable pen base to shift movable plunger  365  of cartridge  367  so as to force medication from an outlet of the cartridge. Floating nut  360  is biased distally by spring  369  when the cartridge assembly is removed so as to disengage the drive assembly from drive sleeve teeth  333  to allow injection screw reset. This drive assembly is more fully described above. Other drive assemblies with a clutch that operably engages drive sleeve member  330  when the pen is assembled for use may be used in devices with the inventive injection clicker assembly. 
     The injection clicker assembly of  FIGS. 9-11  will be further understood in view of the following explanation of its operation within the pen. When the pen is assembled as shown in  FIG. 9 , the teeth  333  of drive sleeve member  330  and clutch  350  are engaged and the teeth of injection clicker  290  and the pen housing are engaged. During dose dialing, drive sleeve base  335  is proximally retained, such as by a not shown spring, causing retainer ring  305  to abut collar surface  300  to keep clicker teeth  296  in meshed engagement with housing teeth  347 . Due to the keying of collar  290  to drive sleeve base  335 , this teeth meshing rotationally locks the drive sleeve base  335 , and therefore the drive member  330  due to its keying to base  335 . With the drive sleeve assembly locked rotationally, the clutch  350 , and therefore the injection screw  354  keyed thereto, cannot rotate, thereby providing an injection screw anti-back-up feature. 
     When the injecting mechanism is manually operated during an injecting use of the dialed up pen, drive sleeve base  335  first moves distally to shift retainer ring  305  distally such that collar  290 , subject to overcoming the biasing force of spring  320 , is movable distally. The drive sleeve body  335  then begins to rotate, and teeth  296  of collar  290  shift in and out of engagement with the housing teeth producing injection clicks. The drive sleeve rotation also causes the drive clutch  350  to rotate which screws the injection screw  354  through floating nut  360 . During this injecting process, if the floating nut floats proximally slightly, the compressed spring  369  forces it back toward the pen distal end to finish the injection. 
     In one form shown in block diagram in  FIG. 12 , a therapeutic dose indicating apparatus of the present invention is housed in a delivery device  420  and utilizes an automatic container recognizer  422 , a doseable quantity identifier  424 , a controller  426 , and a display  428 . One type of delivery device for which the system is particularly well suited is an injection pen, but other types of portable devices, such as a pulmonary device or inhaler, may be similarly equipped. 
     Automatic container recognizer  422  functions first to recognize a characteristic of a container insert into delivery device  420 , which characteristic in one embodiment relates to a concentration of the medicine within the container, and then to input that information to controller  426  as shown at  430 . Doseable quantity identifier  424  functions first to sense the arrangement to which the dose setting mechanism of delivery device  420  has been manipulated by a user to prepare the device to deliver a finite volume of medicine, and then to input that information to controller  426  as shown at  432 . In response to the input information, controller  426  calculates the therapeutic dose to be delivered and instructs display  428  via line  434  to visibly display that dosage to a user of delivery device  420 . 
     The delivery device with therapeutic dose indicating capabilities of  FIG. 12  is shown in  FIG. 13  as a reusable injection pen, generally designated  440 . As is conventional in reusable devices of its type, injection pen  440  includes a cartridge assembly, generally designated  442 , which is connected to a pen base, generally designated  444 , which houses dose setting and injecting mechanisms that when operated cause a quantity of medicine to be selected and then expelled from cartridge assembly  442  through injection needle assembly  467 . 
     One form of cartridge assembly  442  is further shown in cross-sectional view in  FIG. 14  and is, but for the identifier described below, the same as the cartridge assembly  24  of  FIG. 2 . Thus, cartridge assembly  442  includes a cartridge  446  with a glass housing  448  that defines a medication-filled internal volume. The cartridge includes slidable plunger  449 , rod tip  452 , cap  464  and septum  466 . Cartridge  446  is further protected by an outer housing or barrel  458  that includes an externally threaded, stepped-down neck portion  460 , and a further stepped-down rear hub  462 . External threads  468  on cap  464  allow mounting of injection needle assembly  467  that pierces septum  466 . 
     The automatic container or cartridge recognizer  422  of injection pen  440  includes an identifier associated with cartridge assembly  442  which is designed to work with a sensor that signals controller  426  within pen base  444  based on the identifier sensed. As described in U.S. Pat. Nos. 5,954,700 and 6,110,152, the disclosure of which are hereby incorporated herein by reference in their entirety, the identifier can take many forms and be used to indicate a variety of facts to the user. 
     In one form, the identifier is used to represent the concentration of the therapeutic contents of the cartridge assembly, and which concentration identifier is disposed on the outer housing hub  462  of cartridge assembly  442 . The concentration identifier possesses specific characteristics, such as dimensional and spatial characteristics, recognizable by the sensor of automatic cartridge recognizer  422 . In alternate embodiments, and with corresponding modifications to the sensor of automatic cartridge recognizer  422 , the identifier may be placed on other portions of the cartridge assembly, including but not limited to cartridge housing  448 , and rod tip  452 , and further may be used to represent, for example, which one of different possible insulin types is contained in the cartridge assembly. 
     The concentration identifier is permanently affixed to the cylindrical exterior surface of hub  462 . For cartridge recognition systems that sense or otherwise read the identifier with elements other than radially outwardly located electrical contacts as described below, for example when the concentration identifier is adapted for use with optical or magnetic sensors, the identifier need not be exposed on the periphery of hub  462 , and may be differently positioned such as affixed to the interior surface of hub  462 . 
     As further illustrated in the various embodiments shown and described with reference to  FIGS. 15-17 , the cartridge concentration identifier is shown formed by a single strip of electrically conductive material fixedly associated with hub  462 . The shown strip extends the entire hub circumference, but may span only a part of the circumference if the associated sensor contacts of container recognizer  422  described below are configured to achieve a satisfactory connection despite one or more circumferential gaps in the strip. The conductive strip may be in the form of a pad printed conductive ink applied to the hub, however, other means of accomplishing the identifier strip may be employed. For example, the strip may be a crimped metal band, or a conductive electroplating of a material insert molded into the hub, or a conductive paint, or a pad printed ink, or a metallic self-adhesive label, or a non-conductive adhesive label onto which an appropriate electrically-conductive pattern has been applied. 
     Referring now to  FIGS. 15-17 , hubs  462   a ,  462   b  and  462   c  of three different cartridge assemblies  442   a ,  442   b  and  442   c  each compatible with pen base  444 , are shown. The type of content identifier shown being used on hubs  462   a ,  462   b  and  462   c  uses the dimensional aspect of the width of the conductive strip, along with the spatial aspect of the placement of that strip on a hub, to represent the cartridge contents. This type of content identifier has particular applicability to identifying the concentration of hGH, which has a limited number of common concentrations, and therefore the three cartridge assemblies shown in  FIGS. 15-17  each contain hGH in a different concentration. In other types of content identifiers within the scope of the invention, the dimensional aspect of the identifier strip may be different than the width, such as the thickness or texture of the strip. 
     In  FIG. 15 , representing a first concentration, a conductive strip  472  having a relatively small width, such as about 4.8 mm, encircles hub  462   a  of cartridge assembly  442   a  near the distal end of the hub which is adjacent the threaded neck  460   a  of the barrel. In  FIG. 16 , representing a second concentration, a conductive strip  474  having a relatively small width, such as about 4.8 mm, encircles hub  462   b  of a second cartridge assembly  442   b  near the proximal end of the hub. Although the widths of strips  472  and  474  are identical to reduce the number of differently constructed parts needed for manufacture of the various cartridge assemblies, as will be appreciated from the explanation of the device operation that follows, different widths for strips  472  and  474  may be utilized so long as appropriate electrical circuits between the sensors result. Finally, in  FIG. 17 , representing a third concentration, a conductive strip  476  having a relatively large width, such as about 7.1 mm, encircles hub  462   c  of a third cartridge assembly  442   c  and covers nearly the entire hub axial length. The axial region of hub  462   c  covered by strip  476  is the same as would be covered by strips  472  and  474  if positioned on hub  462   c  at the same locations as such strips are positioned on hubs  462   a  and  462   b , respectively. 
     Once any of the cartridge assemblies shown in  FIGS. 15-17  has been properly mounted to injection pen  440 , such as by screwing that cartridge assembly into pen body  444  of  FIG. 13 , the content identifier of that mounted cartridge assembly provides a conductive path between a series of sensor contacts within the device which are spaced along the axial length of the inserted hub. The varying widths and locations of the content identifiers of the various cartridge assemblies provide different conductive paths between the sensor contacts. 
     For example, as schematically shown during operation in  FIG. 18 , the sensor includes electrical contacts  480 ,  481  and  482 . Although these sensor contacts are shown in  FIG. 18  as being in exact axial alignment, each of sensor contacts  480 - 482  may be angularly spaced from the other sensor contacts, such as within a 60° circumferential span or 120° apart, or such other angular spacing as may be possible within the pen base interior hollow. Furthermore, each sensor contact naturally could comprise a plurality of contacts circuited in parallel and positioned at the same axial hub location. The sensor contacts may be resilient metal fingers extending from a subassembly base pivotally mounted to, for example, the housing, and circuitry on the base is electrically connected to a circuit board of controller  426 . The subassembly base is rotationally biased such that hub contact portions of the metal fingers are in a radially retracted position when no cartridge assembly is mounted to pen base  444 . When the hub is inserted during connection of cartridge assembly  442  to pen base  444 , through movement of the hub, or of a movable part of the pen base engageable with the hub, such as a floating nut described above, a pivot arm of the subassembly base is contacted, causing the subassembly base to rotate such that the contact portions of the fingers are moved into communication with the content identifier. In an alternate embodiment, rather than pivotable sensor contacts, the fingers may be resilient or leaf spring type metal fingers which are biased radially inward into contact with the hub and which are mounted, for example, to the pen base housing or to a part movable within the housing of pen base  444  itself, which fingers slide along the hub as the hub inserts during connection of cartridge assembly  442  to pen base  444 . 
     Controller  426  processes the data related to which of the sensor contacts within injection pen  440  are in communication with the conductive strip of the content identifier and derives information from a look-up table to essentially read what is represented as being within the cartridge assembly. For example, sensor contacts  480  and  482  are directly circuited with controller  426  by lines  484  and  486 , which lines may be patterns imprinted on a circuit board of controller  426 . Sensor contact  481  is similarly circuited to controller  426  by line  488  which is grounded at  490 . When cartridge assembly  442   b  with content identifier  474  is loaded as shown in  FIG. 18 , grounded sensor contact  481  is in communication with identifier  474 , and the conductivity of identifier  474  is used to ground sensor contact  482  and thereby line  486  to controller  426 . Because sensor contact  480  is not in communication with identifier  474 , line  484  is not grounded. As a result, controller  426  is effectively signaled that line  484  remains open while line  486  has been closed, and controller  426  equates this input to a certain hGH concentration, such as 12 mg, being present within the loaded cartridge assembly  42   b . (This concentration, as well as other hGH concentrations referred to herein, is indicated in mg units, as opposed to mass per volume units as might otherwise be expected, because that is how these concentrations for hGH are normally referenced, such as by physicians to their patients. Such an indication is a result of the numeric value relating to the mass in mg of lyophilized drug before its reconstitution, which results in the cartridge contents being in liquid form. The concentration in mg/ml can be readily obtained by dividing the referenced milligram mass by the 2.88 milliliter volume of the cartridge contents when reconstituted.) In a similar manner, when cartridge assembly  442   a  with content identifier  472  is loaded, grounded sensor contact  481  is in communication with identifier  472 , and identifier  472  is used to ground sensor contact  480  and line  484  to controller  426 , but sensor contact  482  and line  486  is not grounded, thereby resulting in controller  426  being signaled that line  486  remains open while line  484  has been closed such that controller  426  equates this input to a different hGH concentration, such as 6 mg, being present within the loaded cartridge assembly  442   a . Similarly, when cartridge assembly  442   c  with content identifier  476  is loaded, grounded sensor contact  481  is in communication with identifier  476 , and identifier  476  is used to ground sensor contacts  480  and  482  and lines  484  and  486  to controller  426 , thereby resulting in controller  426  being signaled that lines  484  and  486  have each been closed such that controller  426  equates this input to a different hGH concentration, such as 24 mg, being present within the loaded cartridge assembly  442   c . Finally, when no cartridge assembly is loaded, or a cartridge assembly without an identifier or with a defective identifier is loaded, controller  426  is signaled that lines  484  and  486  each remain open such that no concentration information is available as input. 
     It will be appreciated that the cartridge recognition system could have more or less than the three contact points shown in  FIG. 18 , and could use recognizable electrical signals other than ground, such as a small voltage, to activate the content identifiers. In addition, in other forms of the present invention, the cartridge assembly may be differently configured such as is known in the art, and such as described above. In an embodiment where a disposable cartridge and a reusable retainer is used, the content identifier will be provided on the disposable cartridge, and pen base  444  will be correspondingly modified to permit recognition of that cartridge, such as by incorporating part of the recognition system, for example electrical contacts and wiring, into the retainer, or by configuring the pen base components, such as the contacts, to extend within the chamber of the retainer. 
     Referring now to  FIG. 19 , one form of a doseable quantity identifier of injection pen  440  is diagrammatically shown. Doseable quantity identifier  424  includes a rotational matrix, generally designated  500 , and a sensor array, generally designated  502 , which together are arranged to identify adjustments of the pen mechanism used at least in dose setting, as well as preferably in dose injecting after its dose setting. A variety of mechanisms for setting and injecting a dose are known in the injection pen art and are therefore not explained in exhaustive detail herein. Moreover, as the inventive doseable quantity identifier may be readily adapted for such and newly developed mechanisms in view of the explanation herein, the particulars of such mechanisms explained further herein are intended to be illustrative and not limiting. Furthermore, in alternate embodiments of the invention in its most general form, doseable quantity identifiers of known design which communicate with a controller may be substituted for the rotational matrix/sensor array within the therapeutic dose indicating apparatus of the present invention. 
     Rotational matrix  500  and sensor array  502  are operably connected to first and second components of injection pen  440  which experience relative rotational motion during operation of the dose setting mechanism by a user to select a volume desired to be injected. 
     In the embodiment of  FIG. 19 , the dose setting mechanism includes a rotatable dial  506  into which is incorporated rotational matrix  500 . Dial  506  is rotationally fixed to an exposed knob  508  that is rotatable by the user to select the dose to be delivered by use of the injection pen. In the described embodiment, dial  506  when rotated via knob  508  translates out of pen base  444 , or to the right from the perspective of a  FIG. 13  viewer, during the dialing up of a dose in preparation for dose injecting. However, the inventive matrix need not be on a dial that so translates, but may be on another rotatable component such as a drive sleeve. In addition, although only one of the first and second relatively rotatable pen components is part of the dose setting mechanism in the embodiment of  FIG. 19 , as the other of these components to which sensor array  502  is connected may be the outer housing of pen base  444 , the first and second components each may be parts of the dose setting mechanism in other embodiments. 
     Shown removed from dial  506  and two-dimensionally in  FIG. 20 , matrix  500  is data arranged in a rectangular array formed of multiple orthogonally intersecting rows and columns. The number of columns is a function of the internal workings of the injection pen, and corresponds to the number of rotational positions within one of its revolutions at which dial  506  can be set to have the injection pen deliver different volumes of medicine. The movement of dial  506  between adjacent rotational positions corresponds to a change by one dose volume unit of the quantity to be injected by pen operation, and such change is known as a “click” due to the setting mechanism, as a result of its configuration, producing an audible click-like noise during such movement. The actual quantity of such dose volume unit, for example 0.024 ml, is a function of the design of the dose setting mechanism as is known in the art. 
     The data populating matrix  500  is in the form of the presence or absence of an electrically conductive material at the intersections of the rows and columns, which electrically conductive data points are shown contiguous or all linked to form a pattern  501  structured and arranged in conjunction with the sensor contacts of array  502  to convey information to controller  426  of pen  440 . The linking allows an electrical signal delivered to a single data point on pattern  501 , such as a grounding of that point, to travel along the entire pattern as described further below. 
     Each of the six rows  509 ,  510 ,  511 ,  512 ,  513  and  514  of matrix  500  extends around the entire circumference of dial  506 . The twenty-four matrix columns  516 ,  517 ,  518 ,  519 ,  520 ,  521 ,  522 ,  523 ,  524 ,  525 ,  526 ,  527 ,  528 ,  529 ,  530 ,  531 ,  532 ,  533 ,  534 ,  535 ,  536 ,  537 ,  538  and  539  are equal width, so as each to span  150  of the dial circumference, and are aligned in parallel with the axial length of dial  506 . In the shown embodiment, column  516  is unpopulated by any electrically conductive data points and is formed by a circumferential gap between the ends of the conductive pattern portion that otherwise fills row  509  (i.e. columns  517 - 539 ) when matrix  500  encircles dial  506 . The twenty-four column matrix design permits twenty-four distinct rotational positions of dial  506  to be recognized. However, fewer or additional columns than the twenty-four shown may be provided within the scope of the invention. In addition, matrix rows different in number than the six shown may also be used as long as a suitable pattern recognizable by controller  526  results. 
     The electrically conductive pattern  501  of matrix  500  may be fabricated by two-shot molding a platable material, such as filled styrene plastic, into an electrically non-conductive or insulating sleeve, which molded material is then plated with a conductive material, such as successive layers of copper, nickel and then gold, so as to be electrically conductive. After plating, the sleeve is fixedly attached to dial  506 . To facilitate manufacture, such as to provide a fixturing point needed to position the required pattern, the conductive pattern  501  of matrix  500  may include a not shown extension beyond the matrix rows or columns, but which extension is not used by sensor array  502 . In alternate embodiments, the matrix pattern may be otherwise manufactured, such as a sheet metal matrix insert molded onto a sleeve, or such as in ways similar to those described above with reference to the cartridge content identifiers, for example via a metallic pattern on a non-conductive self-adhesive label or flexible circuit board attached to the dial, or by conductive paint or pad printed conductive ink applied directly to the dial. 
     Sensor array  502  operationally engages matrix  500  to sense the matrix data. For the electrically conductive matrix pattern  501  shown in  FIGS. 19 and 21 , sensor array  502  includes resilient or leaf-spring type metal contacts  546 ,  547 ,  548 ,  549 ,  550  and  551  which extend radially inward from a cylindrical base sleeve  544  coaxially arranged on dial  506 . Each of sensor contacts  546 - 551  abuts matrix  500  within a different row, and in the shown embodiment sensor contacts  546 ,  547 ,  548 ,  549 ,  550  and  551  are respectively aligned with matrix rows  509 ,  510 ,  511 ,  512 ,  513  and  514 . Sensor contacts  546  and  549  are installed at a first circumferential position of base sleeve  544 , sensor contacts  547  and  550  are installed at a second circumferential position of base sleeve  544  which is spaced 1200 from the position of contacts  546  and  549 , and sensor contacts  548  and  551  are installed at a third circumferential position of base sleeve  544  which is spaced 120′ from the positions of both contacts  546  and  549 , and contacts  547  and  550 . This even angular spacing of the sensor contacts around the matrix serves to center the matrix and limit frictional resistance. For this 120° spacing, when dial  506  is rotationally oriented relative to sensor array  502  such that contacts  546  and  549  each abut matrix  500  within, for example, column  516 , contacts  547  and  550  each abut matrix  500  within column  524 , and contacts  548  and  551  each abut matrix  500  within column  532 . 
     When sensor contact  546 , which serves as the grounding contact as described below, is aligned with column  516 , in the shown embodiment this is the “home” or “zero” position of the dial. When the pen is manipulated such that no volume of medicine will be delivered if the injecting mechanism of the pen is operated, the dial will be in this home position. At the home position, the ground is not electrically connected with any of the other contacts  547 - 551 . The matrix pattern can be adapted to indicate this home position even if, for example, the conductive pattern filled all of row  519  including column  516 . For such a matrix pattern, the pattern would also be configured to not be in contact with any of the other sensor contacts  547 - 551  when sensor contact  546  was aligned with column  516 . 
     Matrix pattern  501  shown in  FIG. 20  is designed complementary to this contact arrangement. Matrix pattern  501  uses a gray code coding scheme to reduce the risk of an error in dial position sensing going undetected. In the gray code coding scheme, the pattern is configured in view of the sensor positioning such that rotational dial movement, in either direction and in an amount equal to one column, causes only a single one of sensor contacts  547 - 551  to switch its electrical circuiting relationship with the pattern, which single switching can be monitored by the controller (i.e. only one sensor contact changes from being out of contact with the pattern to being in contact with the pattern, or vice versa, when dial rotation causes each sensor contact in its respective given column to be moved to a column on either side of that given column). In the shown embodiment, each of the twenty-four rotational set positions of dial  506  relative to sensor sleeve  544  results in a unique set of information being recognized by operation of sensor contacts  546 - 551 . 
     It will be appreciated that column positionings of the sensor contacts different than the three 120° spaced sets described above may be used, for example all of sensor contacts  546 - 551  being aligned with one of the matrix columns, as long as appropriate modifications are made to the conductive matrix pattern. 
     To maintain the proper alignment of the sensor contacts with matrix pattern  501 , sensor array  502  and rotational matrix  500  are rotatably free and axially fixed relative to one another. For the sensor array/rotational matrix shown in  FIG. 19 , sensor array  502  may be keyed to, for example, the housing of pen base  444  so as to be free to translate with, but not rotate with, dial  506  when the dial is rotated and thereby caused to translate during dose setting. Not shown connections between dial  506  and sensor array  502  may be used to cause sensor array to translate with the dial. 
     Sensor contacts  546 - 551  of array  502  are each circuited to controller  426  as abstractly represented at line  432  such that sensor input can be used by controller  426  to derive the matrix positioning using a look-up table in a similar manner as described above with respect to the automatic container recognizer. For example, during use a ground signal is sent to sensor contact  546 , which is in contact with and grounds matrix pattern  501  at all rotational dial positions except when sensor contact  546  is aligned in matrix column  516 . When electrically conductive matrix pattern  501  is so grounded, each of sensor contacts  547 - 551  that is in contact with conductive matrix pattern  501  is also grounded. The set of grounded/ungrounded signals received by controller  426  via line  432  for all of the sensor contacts is used to derive the rotational position of the matrix  500 , and thereby dial  506 , relative to sensor array  502 . When sensor contact  546  is aligned with matrix column  516 , none of the contacts are grounded, which information also is recognized by controller  426  as indicative of a particular one of the twenty-four rotational positions of dial  506 . 
     The data of matrix  500  including areas of electrically conductive material is due to such data serving to complete electrical circuits with electrical contacts of the sensor. In alternate embodiments, different matrix data forms may be used with corresponding modifications to the sensor array. For example, if optical or magnetic sensing elements are to be employed in sensor array  502 , the matrix data may be markings or magnets, as appropriate. 
     The matrix/sensor array shown in  FIG. 19  is merely one suitable form and may be differently arranged within the scope of the present invention. For example, the locations of the sensor array and matrix may be reversed, such that a sensor array  502  circuited to controller  426  is mounted on dial  506  and arranged to engage a rotational matrix disposed on the inner circumference of coaxial sleeve  544 . 
     In addition, and as further described with reference to the embodiment of  FIGS. 23-30 , both the matrix and sensor array may be disposed on components of the reusable pen base which rotate at different times during dose setting and injecting use of injection pen  440 . To facilitate the signal communication between controller  426  and such a rotating sensor array, a slider assembly is disposed therebetween. As diagrammatically shown in  FIG. 22 , an array of sensor contacts  546 ′- 551 ′ are installed on a partially shown first pen component  558  coaxially mounted on a partially shown second pen component  559 . Pen component  558  is completely ringed by six electrically conductive, metal bands  560 - 565  that fit within channels in its outer radial periphery. Bands  560 - 565  are in contact with the outward ends of sensor contacts  546 ′- 551 ′, respectively, that extend through the radial thickness of component  558 . Sensor contacts  546 ′- 551 ′ are similarly structured and arranged to the sensor contacts of the embodiment of  FIGS. 19-21 , and contact a not shown rotational matrix, similar to matrix  500 , that encircles pen component  559 . Slider assembly  570  includes six resilient electrical contacts  571 - 576  having free ends which slide along bands  560 - 565  as pen component  558  rotates, and such sliding contact results in an electrical connection between sensors  546 ′- 551 ′ and slider contacts  571 - 576  at any rotational position of pen component  558  relative to slider assembly  570 . 
     If the internal workings of the injection pen are configured such that pen components  558  and  559  do not translate or move axially during operation, slider assembly  570  may be mounted to a stationary pen base component, such as a microprocessor containing flexible circuit board fixed to the injection pen housing and which serves as controller  426 . Slider contacts  571 - 576  are connected to circuits on this circuit board routed to the controller microprocessor. For this type of slider assembly mounting, other than limited axial play as may be required for the working parts of the injection pen, slider assembly  570  is axially and rotationally fixed within pen base  444 . If pen components  558  and  559  translate together during pen operation, slider contacts  571 - 576  are wired to controller  426  and slider assembly  570  is keyed to, for example, the pen outer housing and connected to pen component  558  so as to translate with but not rotate with the array of sensor contacts  546 ′- 551 ′. 
     The injection pen controller  426  that processes signals from the sensor contacts of the automatic container recognizer  422  and doseable quantity identifier  424  to determine display information may be constructed and installed within pen base  444  in any suitable fashion known in the art. In one embodiment of the invention, controller  426  includes a battery-powered, programmable microcontroller mounted on a main printed flexible circuit board that is generally U-shape and flexible so as to conform to the interior of the pen base housing and to provide a hollow in which extend the internal working parts of pen base  444 . The flexible circuit board is connected to the housing with locating pins and adhesive. In an alternate embodiment, an application specific integrated circuit or ASIC may be substituted for the microprocessor. 
     Injection pen display  428  is operatively coupled to the microcontroller  426  and is visible through a transparent housing window of pen base  444 . Display  428 , such as a liquid crystal display, visibly displays to a user information useful to the operation of the injection pen. For example, as best shown in  FIG. 13 , display  428  is caused by microcontroller  426  to display at  580  information about the medicine within the held cartridge as recognized by automatic cartridge recognizer  422 , at  582  the amount of therapeutic the injection pen stands ready to administer upon the operation of the injecting mechanism of pen  440  as described further below, and at  584  the remaining strength of the battery that powers the electronic components of injection pen  440 . The information shown at  580  relates to the concentration of the medicine, as explained further above, but other types of information may be provided. The units of the dose to be administered is shown in  FIG. 13  as being imprinted on the underside of the housing window at  586 , but may be part of the display controlled by microcontroller  426 . 
     The design of the therapeutic dose indicating apparatus in injection pen  440  will be further understood in view of the following explanation of its operation. While cartridge assembly  442  is mounted to pen base  444 , controller  426  remains in a ready state with all of the display elements turned off so as to not display any information to a user. In this ready state, controller  426  processes signals received from the sensor contacts of automatic cartridge recognizer  422  to identify, for example, the concentration of the medicine contained within the cartridge assembly as represented by the identifier band. In this ready state, controller  426  also processes signals received from the sensor contacts of doseable quantity identifier  424  to identify the position of matrix  500  relative to sensor array  502 . 
     Controller  426  advances from the ready state into the operational state, and display  428  is thereby activated, when controller  426  senses further user action on pen  440 . For example, such action sensing will typically be a recognition that matrix  500  is being moved relative to sensor array  502  during manipulation by the user of the dose setting mechanism. Other action which may be sensed is operation of a not shown on/off button which may be located on pen base  444 , or as part of knob  508  of the injecting mechanism. 
     When advanced to the operational state, controller  426  causes the concentration identified with automatic cartridge recognizer  422  to be displayed at  580 . If controller  426  fails to recognize any concentration information, an error message such as “--,” or no message at all, is displayed at  580  instead of any numerical concentration value. Recognition failure may result from a cartridge assembly being entirely absent from, or not properly mounted to, pen base  444 , or from a cartridge identifier being damaged or absent from the assembly, or from an internal failure in the automatic cartridge recognizer circuit. When concentration information is not automatically recognized, the concentration used by controller  426  may be user configurable. For example, set button  588  shown in  FIG. 13  is circuited with controller  426  and is depressable to select, and have displayed at  580 , any of the standard concentration values, such as 6, 12 and 24 mgs in the case of hGH, preprogrammed into controller  426 . 
     While controller  426  is in the operational state, as knob  508  is rotated by a user to set the dose to be delivered, controller  426  continually receives input in real time from the sensor contacts of doseable quantity identifier  424  to identify the position of matrix  500  relative to sensor array  502 . Controller  426  processes the input to determine to which position the dial  506 , and therefore matrix  500  in the shown embodiment, has been rotated from the “zero” dial position at which no volume of medicine will be delivered if the injecting mechanism of the pen is operated. For example, if the “zero” dial rotational position is when sensor  546  engages column  516 , controller  426  recognizes when sensor  546  is in engagement with each of columns  517 - 539  to determine which percentage of a dial revolution has been made. Typically, automatically during, or manually after, injection of the set dose the dial is returned to its original “zero” position for subsequent use. However, controller  426  may be designed to determine dose setting based on any starting point of the dial. 
     Controller  426  senses the rotational position of the dose setting dial via the matrix/sensor array interface whether the dial is being rotated, or dialed up, so as to increase the set dose, or being dialed down to decrease the set dose. In addition, controller  426  is programmed to account for one or more complete dial revolutions during dose setting. During dose setting, by recognizing the matrix position relative to the sensor array at the orientation from which the dial is being rotated, controller  426  recognizes in which direction the dial is being rotated during movement to the “zero” dial rotational position. Specifically, if the “zero” dial rotational position is when sensor  546  engages column  516 , controller  426  recognizes that the set dose is being increased if sensor  546  reaches column  516  immediately after being in column  539 , and that the set dose is being decreased if sensor  546  reaches column  516  immediately after being in column  517 . 
     For example, with the dial initially arranged in the “zero” dial rotational position, during dialing up when that “zero” dial rotational position is reached for the first time and the dialing up continues, and then the “zero” dial rotational position is reached for the second time and the dialing up continues, when controller  426  senses via the matrix/sensor array that, for example, dial rotation is halted by a user when the dial reaches the sixth rotational position from the “zero” position, controller  426  recognizes that a fifty-four unit volume dose has been set for injection (i.e. two complete revolutions each of twenty-four positions or unit volumes in the shown embodiment plus the six additional positions). If a dose is initially set at too large an amount by a user who then reduces that dose setting before injecting, dialing down through the “zero” rotational position attained at one or more complete dial revolutions will be accounted for by controller  426 . 
     The dose volume that controller  426  identifies with doseable quantity identifier  424  is used to display the actual therapeutic amount to be injected. Specifically, controller  426  essentially multiplies the concentration displayed at  580  by the volume set by rotation of dial  506  and causes the injectable amount of therapeutic to be displayed at  582 . The multiplication step described above is normally performed by controller  426  referencing a look-up table populated with data based on therapeutic concentration and the number of dial “clicks” selected. The display at  582  displays the injectable amount at all times throughout the dose setting process. For example, when each “click” corresponds to a unit dose volume of 0.024 milliliters, when the cartridge concentration is 6 mg as explained above, each dialing up of dial  506  in an amount of 15 degrees, or one click, causes display  582  to be increased by 0.05 for the shown milligram labeling, and similarly when the cartridge concentration is 24 mg, each one click dialing up of dial  506  causes display  582  to be increased by 0.20 for the shown milligram labeling. Thus, at all times the amount of therapeutic displayed at  582  is the medically significant amount actually injectable by operation of injection pen  440 . No calculations based on the concentration of hGH loaded in the cartridge assembly  442  need be made by the user to figure out how much hGH is being injected. 
     In addition, the display amount at  582  also works throughout injection (i.e., displays the quantity still to be injected) if the pen components on which the matrix and sensor array are disposed are designed to appropriately rotate relative to each other during injection. 
     After injection pen  440  is used to inject the set dose, such as by axially pressing on knob  508  and moving dial  506  back into pen base  444 , controller  426  automatically returns to an off state, and the display elements of display  428  all turn off, following a certain time period of inactivity. In the event after dose setting no injection is immediately made, the display remains on until the injection is made, after which the pen turns off after the above-described inactivity. 
     As further described below, the doseable quantity indicator may be used in delivery devices that lack the automatic cartridge recognition system described herein, such as in devices in which different medicines each having only a single concentration are being delivered. In such devices, the display at  582  can be a numerical value or another piece of information representative of the actual doseable volume. 
     Referring now to  FIG. 23 , there is shown an exemplary embodiment of a medication injector apparatus with an assembly for selectively rotating a drive sleeve of the present invention. The apparatus, generally designated  620 , is shown in the form of a reusable injection pen, although other forms of portable injectors are within the scope of the invention. 
     Injection pen  620  includes a reusable pen base, generally designated  622 , to which is attached a cartridge assembly generally designated  624  and further referenced in  FIG. 25 . In  FIG. 23 , the cartridge assembly is shown substantially encased within a removable cap assembly  626 . As further shown in  FIG. 27 , cap assembly  626  comprises a metal tip clip  627  swaged to metal cap shell  629 , and a plastic tubular cap insert  633  that is secured within shell  629  and includes modules for attachment to the cartridge holder. Insert  633  is not shown in  FIG. 24  to facilitate illustration. Pen base  622  houses a dose setting and injecting assembly that when operated causes a quantity of medicine to be selected and then expelled from cartridge assembly  624  through pen needle assembly  628  further referenced in  FIG. 24 . 
     With additional reference to  FIGS. 24-27 , cartridge assembly  624  is of a general type known in the art and includes a reusable cartridge holder or retainer  630 . The proximal end  631  of holder  630  is connectable in a suitable fashion, such as via an internal threading, to the distal end of pen base  622 . Holder  630  defines a chamber into which a disposable cartridge  632  is loaded for use. 
     Cartridge  632  is of a standard design generally described above and includes a medication-filled glass housing  634 , piston  638 , septum  644  and cap  646 . A foot  640  that is rotatably secured via a one time snap-fit on the distal end of a drive screw  780  extendable from pen base  622  distributes moving force on piston  638 . Openings or windows  642  on opposite sides of cartridge holder  630  allow visual observation of the quantity of medicine remaining within the held cartridge. External threads  650  on the distal end of cartridge holder  630  allow mounting of hub portion  652  of pen needle assembly  628 . When assembly  628  is mounted as shown in  FIG. 24 , the proximal end  654  of needle cannula  656  held in hub portion  652  pierces septum  644 , and medicine is expelled from cartridge  632  through needle cannula  656  during injecting use of pen  620 . Although the needle assembly is shown as having a single injection needle, needle assemblies which may be used with pen  620  may be of various pen types known in the art, including, but not limited to, assemblies with one or more shortened injection needles, including microneedle arrays. 
     In the shown embodiment, pen needle assembly  628  further includes a needle cover  658  which has an interference fit to hub portion  652 . Cap assembly  626  fits over the distal end of cartridge assembly  624  when pen  620  is not being used, and is removably snap fit to cartridge holder  630  using mating detents and indents. A camming feature on cartridge holder  630  serves to rotationally align cap assembly  626  properly on cartridge holder  630  when being connected together, and further pushes cap assembly  626  axially away from the cartridge holder  630  to disengage any snap fit therebetween when the cap assembly is rotated relative to the cartridge holder during its removal therefrom. A decorative trim ring  662  is fixedly connected, such as via adhesives, around proximal end  631  of cartridge holder  630  for aesthetic purposes. 
     In pen  620 , after the contents of a given cartridge  632  are exhausted by use of the injection device, a user disconnects holder  630  from the pen base  622 , removes and disposes of the spent cartridge  632 , and then inserts a replacement, disposable cartridge into the reusable holder which is then reconnected to pen base  622  for use. Windows  642  help in gripping the cartridge during the removal of the cartridge from holder  630 . 
     In an alternate embodiment not shown, and rather than the separable cartridge and holder shown, the cartridge assembly may be differently configured as is known in the art, and such as described above. For example, the cartridge assembly  624  may be assembled from component parts during production into a disposable unit handled by a user as a single piece. 
     Cartridge holder  630  is removably mounted to pen base  622  by screwing its internally threaded proximal end onto the external threading  664  of a tubular front housing  666 . Front housing  666  is snap fit via angularly spaced detents  667  to a distal end of a housing main body, generally designated  670 . Angularly spaced keys  668  of front housing  666  fit within keyways  671  of housing main body  670  to prevent relative rotation therebetween. 
     The housing main body  670  is molded in one piece, but a multiple piece assembly may be employed. Housing end cap  676  is snap fit via its protruding collar  677  to the proximal end of main body  670  to be axially fixed together. 
     Proximally extending beyond and axially shiftable through the central opening of end cap  676  is a cylindrical sleeve-shaped dial  680 . A set of three angularly spaced notches or keyways  681  located along the proximal edge of dial  680 , and a set of three snap slot recesses  682  in the dial, respectively accommodate keys  692  and latching ribs  693  of a base  690  of a dial assembly to provide a rigid, permanent assembly of dial knob base  690  with dial  680  via a one-time snap fit. The dose knob assembly includes a cover  695  that is fixed to base  690  with adhesive, and with keys  696  of cover  695  fitting in notches  694  of base  690 . In one embodiment, dose knob base  690  is plastic and cover  695  is a die-cast component. Gripping features  697  formed in the exterior periphery of cover  695  enhance gripping of the dial knob assembly during its rotating or dialing to set the dose. Within its interior, dial knob cover  695  includes a centering protrusion, or alternately a ring-shaped seat, which centers the distal end of priming spring  699 . 
     Adjacent its distal end, dial  680  includes a pair of radially protruding keys  683  which insert within longitudinally extending keyways (not shown) formed in the interior surface of barrel  700 . This keying provides consistent rotational movement between dial  680  and barrel  700  while permitting dial  680  to move axially relative to barrel  700 . A double start helical threading  685  radially inwardly protruding from the cylindrical interior surface of dial  680  mates or screws into helical grooves  712  formed in the exterior surface of a drive sleeve  710  of a drive sleeve assembly, generally designated  708 . By making one of the double start threads  685  and its corresponding groove  712  thinner than the other thread and groove, a one way assembly of the dial to the drive sleeve is achieved. Different thread configurations, including a single thread and groove connection, may be used in alternate embodiments. An arrowhead  686  formed on dial  680  shows the direction dial  680  is inserted onto drive sleeve  710  to facilitate assembly. Zero stop  713  is the distal end of grooves  712  which is abutted by dial threading  685  to prevent the dial  680  from being dialed below a zero setting of the pen. A maximum dose stop, formed of a collar  720  with a pair of axially extending latching prongs  721  that snap fit into recesses  714  in drive sleeve  710 , fits around the proximal end of drive sleeve  710  to engage dial threading  685  at the proximal end of grooves  712  to prevent the dial  680  from being dialed above a maximum setting. 
     Barrel  700  is formed with an annular rib  702  at its proximal end that extends continuously around the outer circumference of the barrel. The distal face of barrel rib  702  includes a series of axially extending, unidirectional teeth  703  for engagement with an annular dial clicker  725 . The proximal face of dial clicker  725  includes a ring of axially extending, unidirectional teeth  726  that mate with barrel teeth  703 . The distal face of dial clicker  725  includes a ring of axially extending, unidirectional teeth  728  that mate with axially extending, unidirectional teeth  732  on the proximal face of an annular dial clutch  730 . 
     A set of four keys  733  protrude radially outwardly from the external periphery of clutch  730  and slidably fit within axially extending keyways  673  in housing main body  670  to prevent rotation of clutch  730  relative to the housing. A helical compression spring  735  having one end abutting a bulkhead  672  formed in housing main body  670  and the other end seated on the distal face of dial clutch  730  biases clutch  730  into clicker  725  into barrel rib  702  to provide audible clicks during dose dialing and to provide rotational positioning during dialing. In particular, when dial  680  is dialed up so as to axially move proximally, clicker teeth  728  slide past clutch teeth  732  as the meshing of clicker teeth  726  with the teeth  703  of the rotating barrel  700  causes rotation of clicker  725 . When dial  680  is dialed down, the barrel teeth  703  slide past clicker teeth  726  as clicker  725  is rotatably fixed by the meshing of clicker teeth  728  with teeth  732  of the rotatably fixed clutch  730 . As is known in the art, this sliding motion of the teeth produces the dial clicks. 
     Barrel spring  735  biases barrel  700  proximally such that except during injecting operation of pen  620  as described below, the axially extending external splines  704  at the barrel distal end do not mesh with complementarily internal splines of bulkhead  718  formed in housing main body  670 . The splines of bulkhead  718  are twenty-four in number and equally angularly spaced circumferentially around the drive sleeve. The proximal retraction of barrel  700  is halted when the proximal face of barrel lip  705  abuts drive sleeve flange  716  and the drive sleeve has been retracted proximally until ring  760  has pressed clicker  754  into full engagement with splines of the housing bulkhead  718 . Splines  704  are integrally formed on inward lip  705  of the barrel in four arcuate segments, the spacing between segments providing clearance for lugs  655 . The proximal face of lip  705  also serves as a contact face for injection force that is placed on drive sleeve  710 , as well as a bearing surface for the relative rotational movement of drive sleeve  710  and barrel  700 . 
     When barrel  700  is shifted distally so as to compress barrel spring  735  during injecting, barrel splines  704  mesh with internal splines of bulkhead  718  to prevent rotation of barrel  700  relative to housing  670 . In an alternate embodiment, the prevention of rotation of barrel  700  relative to housing  670  may be accomplished with interfacing, unidirectional teeth. 
     The distal region of drive sleeve  710  is generally cylindrical, although shown with slight facets for improving manufacturability, and includes circumferential groove  748 , diametrically opposed recesses  750  and diametrically opposed longitudinal slots  746 . Injection clicker  754  is rotatably fixed with drive sleeve  710  by four 90° spaced apart lugs  655  integrally formed with the drive sleeve which fit into four corresponding recesses  647  in the proximal face of clicker  754 . Clicker  754  is biased in the proximal direction by clutch spring  758 . Retainer ring  760  fits in groove  748  and prevents disassembly of the clicker from the drive sleeve. When drive sleeve  710  is biased proximally by operation of barrel spring  735 , lugs  655  engage the splines of bulkhead  718  and prevent rotation of drive sleeve  710 . When the biasing of barrel spring  735  is overcome and the drive sleeve is shifted distally during injecting, lugs  655  are shifted away from bulkhead  718  to allow lugs  655  to disengage from splines of bulkhead  718 , thereby allowing the drive sleeve  710  to rotate. Clicker  654  is allowed to move axially with respect to the drive sleeve allowing clicker teeth  656  to slide over the ramped end faces of the splines of bulkhead  718  when drive sleeve  710  is rotated to create an audible clicking indication of operation and to provide a rotational positioning during injection. The distal end of clutch spring  758  abuts the proximal face of an injection clutch  762  that is rotatably fixed with drive sleeve  700  by keys  764  that slide within slots  746 . Clutch  762  is further snap fit within recesses  750  so as to have a limited axial play on drive sleeve  710  to accommodate the axial motion of the drive sleeve during injecting, and axial travel of the floating nut  776  during installation of the cartridge assembly  624 . The distal face of clutch  762  includes a ring of torque transmitting teeth  766 . 
     Clutch teeth  766  selectively mate with teeth  772  of a drive clutch  770  axially retained within injection nut  776 . Internal keys  774  of clutch  770  slide within two longitudinal keyways or slots in threaded drive screw  780  and cause the drive screw to be rotated with the clutch. The drive screw keyways or slots are formed by corner or right-triangular shaped cuts in the screw along its length, which cuts are generally on opposite sides of the screw. The lead edge of the first corner cut is radially aligned in the screw, as well as diametrically aligned with the lead edge of the second corner cut, resulting in the non-aligned or trail edges of the first and second corner cuts being parallel. Drive screw  780 , which extends within an axial bore through drive sleeve  710 , threadedly engages an internally threaded bore within injection nut  776 . Nut  776  is rotatably fixed but axially movable within housing  670  via angularly spaced keys  777  that slide within axially aligned recesses  674  in housing main body  770 . When drive screw  780  is caused to be rotated by the forced rotation of drive clutch  770 , the drive screw advances in the distal direction as it screws through nut  776 . Priming spring  699  press fits onto the proximal end of drive screw  780 . During cartridge replacement, when screw  780  is driven back when being reset during mounting of a replacement cartridge-filled cartridge assembly  624  to pen base  622 , spring  699  is compressed upon contacting the dial knob cover  695  to bias the drive screw forward toward cartridge piston  638 . Injection nut  776  is biased in the distal direction by an injection spring  784  that acts between a housing bulkhead and the proximal face of nut  776 , which biasing is overcome by engagement with the distal end of cartridge  632  during mounting of cartridge assembly  624 . 
     In the embodiment shown, electronics are used in determining and displaying the dose that is set and remaining to be injected during subsequent use of pen  620 . Therefore, in the shown embodiment, dial  680  need not be furnished with any numbers or other markings that provide a user with a visual indication as to what quantity of medicine the pen has been manipulated to inject upon use, and the dial thus serves as an extension of the grippable knob. The electronics include an electrically conductive matrix pattern  800  around a plastic sleeve  802  that is fixed, through a method such as adhesive bonding, a snap fit or press fit, to drive sleeve  710 . A not shown, axially extending key of sleeve  802  fits within an opening in annular flange  716  of drive sleeve  710  to prevent relative rotation, and allows for a proper orientation of the matrix  800  relative to drive sleeve  710 . Flange  716  also provides a bearing surface for the relative motion between drive sleeve  710  and barrel  700 , takes the distal axial load of injection, as well as takes the proximal axial load of retraction by spring  735 . The matrix-including sleeve  802  together with drive sleeve  710  form the drive sleeve assembly  708  that rotates and translates as a single unit during operation. 
     Matrix sleeve  802  is electrically contacted by contact ends of a pair of insert molded leaf spring contact assemblies, generally designated  805  and  806 , further shown in  FIG. 29 . Contact assembly  805  includes a plastic base  807  that inserts within the cross portion of a T-shaped opening  808  in barrel  700 . A wedge shaped periphery of base  807  prevents over insertion. Four metal leaf springs  810 ,  811 ,  812  and  813  are captured in base  807 . The matrix contact ends  810   a ,  811   a ,  812   a  and  813   a  of leaf springs  810 - 813  extend through the base of opening  808  and brush against the matrix sleeve to make electrical contact with the conductive pattern  800 . Wire contact ends  810   b ,  811   b ,  812   b  and  813   b  of leaf springs  810 - 813  extend external to barrel  700  and fit within the four most proximal circumferential grooves  706  of a set of six such grooves in the exterior of barrel  700  which accommodate contact rings. 
     Contact assembly  806  is similarly constructed to contact assembly  805  with a plastic base  814  holding three metal leaf springs  816 ,  817  and  818  including matrix contact ends  816   a ,  817   a  and  818   a , and wire contact ends  816   b ,  817   b  and  818   b . Plastic base  814  inserts within a not shown barrel opening that is longitudinally and angularly offset from barrel opening  808 . Wire contact ends  816   b ,  817   b  and  818   b  extend external to barrel  700  and fit within the three most distal circumferential grooves  706  of the set of six such grooves. By placing contacts  813  and  816  at the same longitudinal position and in the same groove  706 , a redundant contact for grounding the matrix pattern is provided. In the shown embodiment, matrix contact ends  816   a ,  817   a  and  818   a  are angularly offset 180 degrees from matrix contact ends  810   a ,  811   a ,  812   a  and  813   a , but other spacings may be employed. 
     With reference again to  FIG. 27 , encircling barrel  700  are six contact rings made of metal wraps or coiled springs  820 - 825 . Rings  820 - 825  seat within the six axially spaced, circumferential grooves  706  in the exterior of barrel  700 , as well as grooves  809  formed in base  807  and grooves  815  of base  814 , and are in electrical contact with wire contact ends  810   b ,  811   b ,  812   b ,  813   b  and  816   b ,  817   b  and  818   b , respectively. Rings  820 - 825  allow contacts of a rotationally stationary slider assembly  838  to remain in contact with the rings regardless of the relative rotational positions of the rings. 
     Matrix  800  is designed and constructed conceptually similar to matrix  500 , but is adapted to work with the angular positionings of matrix contact ends  810   a ,  811   a ,  812   a ,  813   a ,  816   a ,  817   a  and  818   a  such that twenty-four different angular orientations of barrel  700  relative to drive assembly  710  can be recognized. One suitable matrix  800  is shown two-dimensionally in  FIG. 30 . The rounded protrusions shown on the matrix in  FIG. 30  are not part of the effective pattern, but rather are used to help hold the pattern in the part into which it is insert molded. Still further, the pattern of matrix  800  is designed so that single-point errors in contacts related to matrix data associated with the contact ends  810   a ,  811   a ,  812   a ,  817   a  and  818   a , and not the ground contact ends  813   a  and  816   a , that are different than the change expected by moving from one matrix position to an adjacent matrix position in either direction are readily detected by controller  867  for the purpose of detecting errors in the pen operation at all times the pen is on. Specifically, the matrix  800  is designed such that during relative rotational motion of the pen components which moves the matrix one position from its current position (e.g., a movement of 15° for the twenty-four column matrix shown), the change of one of the signals associated with matrix contacts ends other than contacts  813   a  and  816   a  results in only one of the following: (a) a shift to the code corresponding to an adjacent position, (b) a shift to a code corresponding to none of the twenty-four positions, or (c) a shift to a code corresponding to a position outside of a given range, such as a range from two to six positions inclusively away from the current position. Other ranges, from two to three or four or five positions, or two to eight or more positions, may alternative be employed. In other words, for any of the twenty-four rotational positions, the code of the matrix data within the range of two to six positions away from a given position in either direction differs by at least two data points from the given position. Thus, during pen use, whether during manual dialing up a dose, or manual dialing down a dose, or during medicine injecting, if the controller receives information suggesting a movement of greater than six rotational positions from the previously recognized position, which such movement is considered by the pen to be too large a movement and therefore an error, unless within a short period of time set by the manufacturer, such as the time between display updates, during which time the controller continues to check the matrix data, the received information is back within the accepted range of positions from the previously recognized position, the controller causes an error message to be displayed. If the received information does return to the accepted range within the set period, the pen controller recognizes the erroneous reading as being an aberration and ignores it as such, and does not display an error message or require a resetting of the pen. 
     It will be recognized that one skilled in the art, in view of the teachings herein, can provide other ways for controller  867  to determine the validity of a sensed position code, based upon a previously recognized position code. For example, it is not necessary for the matrix  800  to provide unique patterns for all twenty-four positions of a revolution, but only for those positions within a valid range, such as one to six positions, on either side of any given position. The controller would compare a sensed position code to the position codes within the range adjacent the previous code to determine around which of the non-unique position codes was being sensed. The foregoing approach would allow the twenty-four positions to be captured through a five-row matrix, which is a four-bit signal, instead of the shown six-row matrix  800 , which is a five-bit signal. The reduction to a five-row matrix is not required, but could be used to reduce the number of parts or decrease device length. If a five-bit signal were still to be used, such may improve the overall reliability of the device without increasing device length because redundancy may be added. 
     Still further, a matrix  800  could be created where matrix data associated with two matrix contact ends other than contact ends  813   a  and  816   a  change when shifting one column of the matrix  800 , instead of only one data point as described directly above. Such an approach would allow controller  867  to reject all single-point error of such sensor contacts instead of only those that would result in a change of more than one data point, thereby improving the reliability of the device. For such a two-bit shift, if twenty-four unique rotational positions are desired, a seven-row matrix pattern, as opposed to the six-row pattern shown, will be required. 
     Each of contact rings  820 - 825  is directly engaged by one of six sliding contacts  840 - 845  of a slider assembly, generally designated  838 , shown further in  FIG. 28 . Sliding contacts  840 - 845  are made of metal in a leaf spring form and are mounted on a plastic chassis  847  between a pair of keys  849  that radially project from the chassis. Keys  849  insert within a pair of circumferential grooves or keyways  707  in barrel  700  that flank on either axial side the set of six grooves  706 . The fitting of keys  849  within grooves  707  causes slider assembly  838  to move axially with barrel  700 , but allows barrel  700  to be rotated relative to slider assembly  838 , all the while with sliding contacts  840 - 845  in electrical communication with contact rings  820 - 825 . 
     Slider assembly  838  is fixedly connected to a flexible circuit board  865  such that the contacts can transmit to the microcontroller via the circuit board  865  the sensed matrix pattern. Slider assembly  838  is positioned on the board during manufacture via a pair of nubs that project from the back of chassis  847  and fit within notches  851  in the board. Slider assembly chassis  847  fits within opening  678  of housing main body  670 , which opening serves as a keyway in which slider assembly  838  is axially movable but rotatably fixed relative to the housing. 
     To accomplish sensing of relative motion of barrel  700  and drive sleeve assembly  708 , the matrix  800  on sleeve  802  provides a selective conductive path between the six contact rings  820 - 825 . Contact ring  823  is always grounded, and that grounded ring, via its associated matrix contact ends  813   a  and  816   a , is always in contact with and thereby grounds the conductive matrix  800 , except at the home rotational position when none of the other rings  820 ,  821 ,  822 ,  824  and  825  via their associated matrix contact ends is in contact with the matrix pattern  800 . The matrix pattern  800  selectively shorts the current JO across the appropriate rings to form a code that is then picked up by slider contacts  840 - 845  and sent to the microcontroller for recognition. 
     Although described above as the matrix being grounded, in other embodiments, the matrix could be activated not by a ground signal, but rather by any voltage that is distinctly recognizable by the controller. For example, for a controller where the only options are logic high and ground, rather than the ground signal described above as being the activating signal, a logic high signal of approximately three volts may be used to activate the matrix. 
     Slider assembly  838  also includes an injection switch, generally designated  853 . Switch  853  has a resilient contact  855  made of metal in a leaf spring form and with a ramped region  857 . When barrel  700 , and thereby slider assembly  838 , are moved axially a short distance during a first phase of injecting operation, ramped region  857  is pressed radially outward by contact with housing surface  679  such that resilient contact  855  completes a circuit with fixed contact  861  of the injection switch. Resilient contact  855  includes a contact end  859 , and fixed contact  861  includes a contact end  863 , that are each electrically connected to circuit board  865  to convey electrical signals to the microcontroller. During this slider assembly axial movement, the portion of flexible circuit board  865  to which the slider assembly is mounted also moves axially relative to the remainder of the board. The closing of injection switch  853  is recognized by microcontroller  867  as the start of the injecting operation of the pen, rather than the pen being dialed down or up in preparation for injecting. 
     Flexible circuit board  865  is a two-layer flexible circuit board that wraps around the housing main body  670  and is connected to main body  670  with locating pins and adhesive. Flexible circuit board  865  serves as the base to which are mounted microcontroller  867 , which is programmed to control the electronic operations of pen  620 , batteries  869  for powering the electronics, and an LCD display  871 . 
     The electronics of pen  620  are capable of sensing the relative rotational motion of the drive sleeve assembly  708  within the barrel  700 , which barrel and drive sleeve assembly are maintained in a consistent axial position with respect to each other. During dose setting, barrel  700  rotates while drive sleeve assembly  708  is rotationally fixed within the housing, and during dose injecting the barrel is rotationally fixed and the drive sleeve assembly rotates within the housing. 
     A clear plastic lens  873  is adhered to housing main body  670 , and protectively covers display  871  and provides magnification of the display readout. Push button  875  used in controlling the pen electronics is pivotally mounted to lens  873  and interfaces with a switch actuator  874  that activates a snap dome switch that is electrically connected to circuit board  865 . The microcontroller  867  is programmed to turn on the display for operation when button  875  is manually depressed. In one embodiment, button  875  can be used to change data stored in memory, or a setting of a clock associated with the microprocessor. For example, data stored in memory associated with the microprocessor, such as the date, is adjustable by first pressing and holding button  875  for a set period, such as three seconds, to transition the pen into an adjust mode, and then by axially pressing on the dial knob assembly to move slider assembly  838  and activate injection switch  853  to increment the data being changed. A bezel  877  adhered to housing main body  670  serves as a decorative trim piece and along with lens  873  and push button  875  is exposed through a window  879  of an outer skin  880  formed from metal and which is adhered to housing main body  670 . 
     A seal  882  made of foam is captured between the underside of lens  873  and an upper surface of the flexible circuit board  865 . Seal  882  resists any fluid that may be present on the pen exterior along the interconnection of the push button  875  and lens  873  from reaching the internal electronics of pen  620 . A frame filler  885 , which is provided to facilitate pen assembly and fits within notches in housing main body  670 , serves as an additional base on which display  871  is adhered, and is an additional bonding surface for skin  880 . 
     A cover portion  887  is adhered to the underside of housing main body  670 , and has internal relief to allow room for the electronics. A metal outer skin  880  is adhesively mounted to both housing main body  670  and cover portion  887  to provide an attractive appearance to pen  620 . 
     The structure of injection pen  620  will be further understood in view of the following explanation of its operation. When the user needs to inject herself with a dose of the medication, pen  620  first is turned on by depressing button  875 , which causes display  871  to display the current date and time according to the pen&#39;s internal clock, and a “0” as to the amount of medicine the pen is prepared to deliver. Pen  620  also may be turned on by beginning to rotate the dial knob assembly, or alternatively by pressing the dial knob assembly to trigger the injection switch. If after the pen is turned on via button  875  or by pressing the dial knob assembly, the dial knob assembly is axially pushed distally such that injection switch  853  is activated, the date, time and amount of the last injection is caused to be displayed. If the memory of pen  620  is adapted for multiple dose memory, each additional distal plunging of the dial knob assembly will cause the then previous injection date time and amount to be displayed, so that the user can cycle through the stored previous doses, which may be ten or more doses. To exit the dose memory mode, the user can wait for a set period of time, such as eight seconds, without dialing the dose knob or pressing any buttons, or by dialing the dose knob from the “0” position, or by pressing and releasing the dose knob a sufficient number of times to cycle through the entire multiple dose memory. 
     Pen  620  is then manipulated such that the user selects the dose to be administered. The following explanation will assume pen  620  has already been primed as is suggested, which priming step merely involves operating the pen in the manner described below to discharge a small dose to expel any air from the cartridge. In a pen having multiple dose memory, an indication that such dose was a priming dose can be tagged in memory, such as by pressing and releasing mode button  875  immediately following the prime delivery so long as the microprocessor  867  senses the injection switch  853  is no longer activated, such as prior to the completion of a five-second post injection timer. When a user reviews the doses in memory, a priming dose may be indicated by that dose alternating over time with a “P” in the display. The prime tag alternatively may involve a press and release of mode button  875  by the user upon reaching a prime dose when reviewing the doses stored in the dose memory. 
     To select the dose, the user grips the cover  695  of the dial knob assembly between typically a thumb and forefinger and begins to rotate it relative to the rest of pen base  622 . This rotation causes corresponding rotation of dial  680 , and further barrel  700  rotates simultaneously due to its keying with the dial. As dial  680  and the dial knob assembly rotate, they also axially translate in the proximal direction as dial  680  screws up drive sleeve  710  due to its threaded engagement therewith. As the dial screws out, it proximally extends farther beyond the pen base housing, and the dial knob assembly is shifted proximally and farther away from the housing. Drive sleeve  710  is held in rotatably fixed fashion by the engagement of lugs  655  within the housing splines. If the user rotates beyond a desired dose, the dose knob assembly and dial  680 , and therefore the barrel  700 , may be rotated in the opposite direction, which operation spins the dial  680  back down the drive sleeve  710 . During this dialing down, the drive sleeve is held in rotatably fixed fashion due to its resistance to rotation attributable to lugs  655 . During the rotation of barrel  700 , which is axially stationary relative to the drive sleeve, display  871  displays a continuously changing value of the amount of medication that pen  620  would inject if operated via plunging at any given point during that rotation. In particular, display  871  is controlled by microprocessor  867 , which recognizes the rotational position of barrel  700  relative to drive sleeve  710  based on input from the workings of the matrix pattern  802 , rings  820 - 825 , slider assembly  838 , and circuit board  865 . The user halts the dial rotation when she observes that display  871  indicates the quantity of medication desired to be injected. At this point, injection pen  620  is configured as shown in the cross-sectional view of  FIG. 25 , as the cap assembly and cover  658  have previously been taken off during the priming step as is conventional. 
     The user is now prepared to inject the set dose, which injecting operation is performed in two phases. Initially, and in the first phase, the pen is mechanically transitioned from a dosing mode to an injecting mode by proximally shifting the dose knob and dial a small distance, such as 0.080 inches of travel back into the pen housing. In particular, the user, typically with her thumb, applies a plunging force on the proximal face of dial knob cover  695 . This plunging places an axial load on dial threads  685 , which loading, via the drive sleeve thread  712 , advances drive sleeve assembly  708  distally within pen  620  and without rotation of dial  680  relative to drive sleeve assembly due to frictional forces. This drive sleeve motion moves barrel  700  distally or forward due to the direct contact of the distal face of flange  716  with barrel lip  705 . Distal travel of dial  680 , drive sleeve  710 , and barrel  700  is halted when barrel  700  reaches a location at which splines  704  mate with the housing bulkhead splines, at which time the barrel is rotatably fixed, and the dial, being rotatably keyed to the barrel, is also rotatably fixed. 
     When pen  620  has reached this state, which is shown in  FIG. 26 , the second phase of the injecting operation begins, as any further plunging force applied to the dial knob translates the dial knob assembly and dial  680  distally and without rotation, which translation produces rotation of drive sleeve  710 . As drive sleeve  710  is rotated, the injection clutch  762  is also caused to rotate, which forces the rotation of the injection screw  780 , which due to its engagement with the injection nut, advances the screw within the cartridge to force medicine out of the needle. As drive sleeve  710  rotates, the injection clicker  754  bounces in and out of the housing splines to produce injection clicks. The dial  680  is plunged until it reaches a plunged axial position corresponding to the position shown in  FIG. 24 , at which position dial thread  685  abuts zero stop  713  and rotation of drive sleeve  708  is halted. During this second phase, if the injection nut  776  has floated backward at all, the injection nut spring  784  finishes the injection by moving nut  776  distally when plunging of the dial is complete. 
     During both phases of the injecting operation, microcontroller  867  continuously receives the input from the electronic sensors that pick up relative rotational motion of the barrel  700  and the drive sleeve assembly  708 . Display  871 , throughout the entire injection process, displays the quantity still to be injected in real time, subject to the limitations of the electronics, which may allow the display to be updated only, for example, eight times per second. Because the injection switch  853  is activated when the barrel is moved distally, the microprocessor uses input from switch  853  to distinguish between dialing a dose and injection. The switch signal also may be used by the microprocessor to cause the time, date and amount being injected to be stored in memory for later reference. 
     After injection pen  620  is used to inject the set dose, controller  867  automatically returns to an off state, and the display elements of display  871  all turn off, following a certain time period of inactivity. In the event after dose setting no injection is immediately made, the display remains on until the injection is made, after which the pen turns off after the above-described inactivity. As the process of fully plunging the dose setting knob assembly and dial  680  during pen use automatically resets them, setting the dose the next time pen  620  is used simply requires rotating the dial knob assembly and dial  680  from their plunged position and without further manipulation. 
     Microcontroller  867  can use input received from injection switch  853  and the electronic sensors that pick up relative rotational motion of the barrel and the drive sleeve assembly to diagnose whether the injection pen is operating properly. For example, the pen can be programmed to display an error if the microcontroller senses the injection switch  853  is activated while the electronic sensors are indicating that the dose is being dialed up. In addition, an error message can also be communicated to the user via the display if the microcontroller senses that the injection switch  853  has not been activated, yet the input from the electronic sensors suggest that the dial sensing is of dubious accuracy, such as caused by the dial being manually rotated too rapidly by the user. 
     While one particular mechanism for converting rotation of the drive sleeve into an axial motion of the cartridge piston is disclosed in  FIGS. 23-27 , other less complicated mechanisms known in the art, such as one in which the drive sleeve is directly threaded with a drive screw, can be substituted within the scope of the present invention. 
     While this invention has been shown and described as having multiple designs, the present invention may be modified within the spirit and scope of this disclosure. 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.