Abstract:
An inhaler includes a main body having a canister housing, a medicament canister retained in a central outlet port of the canister housing, and a dose counter having an actuation member for operation by movement of the medicament canister. The canister housing has an inner wall, and a first inner wall canister support formation extending inwardly from a main surface of the inner wall. The canister housing has a longitudinal axis X which passes through the center of the central outlet port. The first inner wall canister support formation, the actuation member, and the central outlet port lie in a common plane coincident with the longitudinal axis X such that the first inner wall canister support formation protects against unwanted actuation of the dose counter by reducing rocking of the medicament canister relative to the main body of the inhaler.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation patent application of U.S. Non-Provisional patent application Ser. No. 14/103,324, filed Dec. 11, 2013, which is a divisional patent application of U.S. Non-Provisional patent application Ser. No. 13/110,532, filed May 18, 2011, now U.S. Pat. No. 8,978,966, issued Mar. 17, 2015, which claims priority to U.S. Provisional Patent Application No. 61/345,763, filed May 18, 2010, and U.S. Provisional Patent Application No. 61/417,659, filed Nov. 29, 2010, each of which is incorporated herein by reference in its entirety for any and all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to dose counters for inhalers, inhalers and methods of assembly thereof. The invention is particularly applicable to metered dose inhalers including dry power medicament inhalers, breath actuated inhalers and manually operated metered dose medicament inhalers. 
     BACKGROUND OF THE INVENTION 
     Metered dose inhalers can comprise a medicament-containing pressurised canister containing a mixture of active drug and propellant. Such canisters are usually formed from a deep-dawn aluminium cup having a crimped lid which carries a metering valve assembly. The metering valve assembly is provided with a protruding valve stem which, in use is inserted as a push fit into a stem block in an actuator body of an inhaler having a drug delivery outlet. In order to actuate a manually operable inhaler, the user applies by hand a compressive force to a closed end of the canister and the internal components of the metering valve assembly are spring loaded so that a compressive force of approximately 15 to 30 N is required to activate the device in some typical circumstances. 
     In response to this compressive force the canister moves axially with respect to the valve stem and the axial movement is sufficient to actuate the metering valve and cause a metered quantity of the drug and the propellant to be expelled through the valve stem. This is then released into a mouthpiece of the inhaler via a nozzle in the stem block, such that a user inhaling through the outlet of the inhaler will receive a dose of the drug. 
     A drawback of self-administration from an inhaler is that it is difficult to determine how much active drug and/or propellant are left in the inhaler, if any, especially of the active drug and this is potentially hazardous for the user since dosing becomes unreliable and backup devices not always available. 
     Inhalers incorporating dose counters have therefore become known. 
     WO 98/028033 discloses an inhaler having a ratchet mechanism for driving a tape drive dose counter. A shaft onto which tape is wound has a friction clutch or spring for restraining the shaft against reverse rotation. 
     EP-A-1486227 discloses an inhaler for dry powered medicament having a ratchet mechanism for a tape dose counter which is operated when a mouthpiece of the inhaler is closed. Due to the way in which the mouthpiece is opened and closed, and actuation pawl of the device which is mounted on a yoke, travels a known long stroke of consistent length as the mouthpiece is opened and closed. 
     WO 2008/119552 discloses a metered-dose inhaler which is suitable for breath-operated applications and operates with a known and constant canister stroke length of 3.04 mm+/−0.255 mm. A stock bobbin of the counter, from which a tape is unwound, rotates on a shaft having a split pin intended to hold the stock bobbin taut. However, some dose counters do not keep a particularly reliable count, such as if they are dropped onto a hard surface. 
     More recently, it has become desirable to improve dose counters further and, in particular, it is felt that it would be useful to provide extremely accurate dose counters for manually-operated canister-type metered dose inhalers. Unfortunately, in these inhalers, it has been found in the course of making the present invention that the stroke length of the canister is to a very large extent controlled on each dose operation by the user, and by hand. Therefore, the stroke length is highly variable and it is found to be extremely difficult to provide a highly reliable dose counter for these applications. The dose counter must not count a dose when the canister has not fired since this might wrongly indicate to the user that a dose has been applied and if done repeatedly the user would throw away the canister or whole device before it is really time to change the device due to the active drug and propellant reaching a set minimum. Additionally, the canister must not fire without the dose counter counting because the user may then apply another dose thinking that the canister has not fired, and if this is done repeatedly the active drug and/or propellant may run out while the user thinks the device is still suitable for use according to the counter. It has also been found to be fairly difficult to assembly some known inhaler devices and the dose counters therefor. Additionally, it is felt desirable to improve upon inhalers by making them easily usable after they have been washed with water. 
     The present invention aims to alleviate at least to a certain extent one or more of the problems of the prior art. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided a dose counter for an inhaler, the dose counter having a counter display arranged to indicate dosage information, a drive system arranged to move the counter display incrementally in a first direction from a first station to a second station in response to actuation input, wherein a regulator is provided which is arranged to act upon the counter display at the first station to regulate motion of the counter display at the first station to incremental movements. 
     The regulator is advantageous in that it helps prevent unwanted motion of the counter display if the counter is dropped. 
     According to a further aspect of the present invention, the regulator provides a resistance force of greater than 0.1 N against movement of the counter display. According to still a further aspect of the present invention, the resistance force is greater than 0.3 N. According to yet a further aspect of the present invention, the resistance force is from 0.3 to 0.4 N. 
     Preferably, the counter comprises a tape. 
     Preferably, the tape has dose counter indicia displayed thereon. The first station may comprise a region of the dose counter where tape is held which is located before a display location, such as a display window, for the counter indicia. 
     The first station may comprise a first shaft, the tape being arranged on the first shaft and to unwind therefrom upon movement of the counter display. 
     The first shaft may be mounted for rotation relative to a substantially rotationally fixed element of the dose counter. 
     The regulator may comprise at least one projection which is arranged on one of the first shaft and the substantially rotationally fixed element and to engage incrementally with one or more formations on the other of the first shaft and the substantially rotationally fixed element. 
     At least two said projections may be provided. Exactly two said projections maybe provided. 
     Each projection may comprise a radiused surface. 
     The at least one projection may be located on the substantially fixed element which may comprise a fixed shaft which is fixed to a main body of the dose counter, the first shaft being rotationally mounted to the fixed shaft. 
     Preferably, the fixed shaft has at least two resiliently flexible legs (or forks). Each leg may have at least one said projection formed in an outwardly facing direction thereon, said one or more formations being formed on an inwardly facing engagement surface of the first shaft, said at least one projection being arranged to resiliently engage said one or more formations. Preferably, a series of said formations are provided. An even number of said formations may be provided. Eight to twelve of said formations may be provided. In one embodiment, ten said formations are provided. 
     Each said formation may comprise a concavity formed on an engagement surface. Each concavity may comprise a radiused surface wall portion which preferably merges on at least one side thereof into a flat wall portion surface. The engagement surface may include a series of said concavities, and convex wall portions of the engagement surface may be formed between each adjacent two said concavities, each said convex wall portion comprising a convex radiused wall portion. 
     Each convex radiused wall portion of each convex wall portion may be connected by said flat wall portion surfaces to each adjacent concavity. 
     The fixed shaft may comprise a split pin with fork legs and each projection may be located on a said fork leg. 
     The first shaft may comprise a substantially hollow bobbin. 
     Said at least one formation may be located on an inner surface of the bobbin. In other embodiments it may be located on an outer surface thereof. Said engagement surface may extend partially along said bobbin, a remainder of the respective inner or outer surface having a generally smooth journal portion along at least a portion thereof. 
     The drive system may comprise a tooth ratchet wheel arranged to act upon a second shaft which is located at the second station, the second shaft being rotatable to wind the tape onto the second shaft. 
     The second shaft may be located on a main body of the dose counter spaced from and parallel to the first shaft. 
     The ratchet wheel may be fixed to the second shaft is arranged to rotate therewith. The ratchet wheel may be secured to an end of the second shaft and aligned coaxially with the second shaft. 
     The dose counter may include anti-back drive system which is arranged to restrict motion of the second shaft. The anti-back drive system may include a substantially fixed tooth arranged to act upon teeth of the ratchet wheel. 
     According to a further aspect of the present invention, a dose counter includes an anti-back drive system which is arranged to restrict motion of the second shaft in a tape winding direction. 
     According to a further aspect of the present invention there is provided a shaft for holding counter tape in a dose counter for an inhaler, the shaft having an engagement surface including incrementally spaced formations located around a periphery thereof, the formations comprising a series of curved concavities and convex portions. 
     The shaft may comprise a hollow bobbin. 
     The engagement surface may be a generally cylindrical inwardly directed surface. 
     The engagement surface may include a flat surface wall portion joining each concavity and convex wall portion. 
     Each concavity may comprise a radiused wall portion. 
     Each convex wall portion may comprise a radiused wall portion. 
     Said concavities may be regularly spaced around a longitudinal axis of the shaft. 
     Said convex wall portions may be regularly spaced around a longitudinal axis of the shaft. 
     In some embodiments there may be from eight to twelve said concavities and/or convex wall portions regularly spaced around a longitudinal axis thereof. 
     One embodiment includes ten said concavities and/or convex wall portions regularly spaced around a longitudinal axis of the shaft. 
     According to a further aspect of the present invention there is provided a shaft and counter tape assembly for use in a dose counter for an inhaler, the assembly comprising a rotatable shaft and a counter tape which is wound around the shaft and is adapted to unwind therefrom upon inhaler actuation, the shaft having an engagement surface which includes incrementally spaced formations located around a periphery thereof. 
     According to a further aspect of the present invention there is provided an inhaler for the inhalation of medication and the like, the inhaler including a dose counter as in the first aspect of the present invention. 
     A preferred construction consists of a manually operated metered dose inhaler including a dose counter chamber including a dose display tape driven by a ratchet wheel which is driven in turn by an actuator pawl actuated by movement of a canister, the tape unwinding from a stock bobbin during use of the inhaler, a rotation regulator being provided for the stock bobbin and comprising a wavelike engagement surface with concavities which engage against control elements in the form of protrusions on resilient forks of a split pin thereby permitting incremental unwinding of the stock bobbin yet resisting excessive rotation if the inhaler is dropped onto a hard surface. 
     According to another aspect of the present invention there is provided a dose counter for a metered dose inhaler having a body arranged to retain a medicament canister of predetermined configuration for movement of the canister relative thereto; the dose counter comprising: an incremental counting system for counting doses, the incremental counting system having a main body, an actuator arranged to be driven in response to canister motion and to drive an incremental output member in response to canister motion, the actuator and incremental output member being configured to have predetermined canister fire and count configurations in a canister fire sequence, the canister fire configuration being determined by a position of the actuator relative to a datum at which the canister fires medicament and the count configuration being determined by a position of the actuator relative to the datum at which the incremental count system makes an incremental count, wherein the actuator is arranged to reach a position thereof in the count configuration at or after a position thereof in the canister fire configuration. 
     This arrangement has been found to be highly advantageous since it provides an extremely accurate dose counter which is suitable for use with manually operated metered dose inhalers. It has been found that dose counters with these features have a failure rate of less than 50 failed counts per million full canister activation depressions. It has been found in the course of making the present invention that highly reliable counting can be achieved with the dose counter counting at or soon after the point at which the canister fires. It has been is covered by the present inventors that momentum and motion involved in firing the canister, and in some embodiments a slight reduction in canister back pressure on the user at the time of canister firing, can very reliably result in additional further motion past the count point. 
     The actuator and incremental counting system may be arranged such that the actuator is displaced less than 1 mm, typically 0.25 to 0.75 mm, more preferably about 0.4 to 0.6 mm, relative to the body between its location in the count and fire configurations, about 0.48 mm being preferred. The canister, which can move substantially in line with the actuator, can reliably move this additional distance so as to achieve very reliable counting. 
     The incremental count system may comprise a ratchet mechanism and the incremental output member may comprise a ratchet wheel having a plurality of circumferentially spaced teeth arranged to engage the actuator. 
     The actuator may comprise an actuator pawl arranged to engage on teeth of the ratchet wheel. The actuator pawl may be arranged to be connected to or integral with an actuator pin arranged to engage and be depressed by a medicament canister bottom flange. The actuator pawl may be generally U-shaped having two parallel arms arranged to pull on a central pawl member arranged substantially perpendicular thereto. This provides a very reliable actuator pawl which can reliably pull on the teeth of the ratchet wheel. 
     The incremental count system may include a tape counter having tape with incremental dose indicia located thereon, the tape being positioned on a tape stock bobbin and being arranged to unwind therefrom. 
     The actuator and incremental output member may be arranged to provide a start configuration at which the actuator is spaced from the ratchet output member, a reset configuration at which the actuator is brought into engagement with the incremental output member during a canister fire sequence, and an end configuration at which the actuator disengages from the ratchet output during a canister fire sequence. 
     The actuator may be arranged to be located about 1.5 to 2.0 mm, from its location in the fire configuration, when in the start configuration, about 1.80 mm being preferred. 
     The actuator may be arranged to be located about 1.0 to 1.2 mm, from its location in the fire configuration, when in the reset configuration, about 1.11 mm being preferred. 
     The actuator may be arranged to be located about 1.1 to 1.3 mm, from its location in the fire configuration, when in the end configuration, about 1.18 mm being preferred. 
     These arrangements provide extremely reliable dose counting, especially with manually operated canister type metered dose inhalers. 
     The main body may include a formation for forcing the actuator to disengage from the incremental output member when the actuator is moved past the end configuration. The formation may comprise a bumped up portion of an otherwise generally straight surface against which the actuator engages and along which it is arranged to slide during a canister firing sequence. 
     The dose counter may include a counter pawl, the counter pawl having a tooth arranged to engage the incremental output member, the tooth and incremental output member being arranged to permit one way only incremental relative motion therebetween. When the incremental output member comprises a ratchet wheel, the tooth can therefore serve as an anti-back drive tooth for the ratchet wheel, thereby permitting only one way motion or rotation thereof. 
     The counter pawl may be substantially fixedly mounted on the main body of the incremental count system and the counter pawl may be arranged to be capable of repeatedly engaging equi-spaced teeth of the incremental output member in anti-back drive interlock configurations as the counter is operated. The counter pawl may be positioned so that the incremental output member is halfway, or substantially halfway moved from one anti-back drive interlock configuration to the next when the actuator and incremental output member are in the end configuration thereof. This is highly advantageous in that it minimises the risk of double counting or non-counting by the dose counter. 
     According to a further aspect of the invention there is provided an inhaler comprising a main body arranged to retain a medicament canister of predetermined configuration and a dose counter mounted in the main body. 
     The inhaler main body may include a canister receiving portion and a separate counter chamber, the dose counter being located within the main body thereof, the incremental output member and actuator thereof inside the counter chamber, the main body of the inhaler having wall surfaces separating the canister-receiving portion and the counter chamber, the wall surfaces being provided with a communication aperture, an actuation member extending through the communication aperture to transmit canister motion to the actuator. 
     According to a further aspect of the present invention there is a provided an inhaler for metered dose inhalation, the inhaler comprising a main body having a canister housing arranged to retain a medicament canister for motion therein, and a dose counter, the dose counter having an actuation member having at least a portion thereof located in the canister housing for operation by movement of a medicament canister, wherein the canister housing has an inner wall, and a first inner wall canister support formation located directly adjacent the actuation member. 
     This is highly advantageous in that the first inner wall canister support formation can prevent a canister from rocking too much relative to the main body of the inhaler. Since the canister may operate the actuation member of the dose counter, this substantially improves dose counting and avoids counter errors. 
     The canister housing may have a longitudinal axis which passes through a central outlet port thereof, the central outlet port being arranged to mate with an outer canister fire stem of a medicament canister, the inner wall canister support formation, the actuation member and the outlet port lying in a common plane coincident with the longitudinal axis. Accordingly, this construction may prevent the canister from rocking towards the position of the dose counter actuation member, thereby minimising errors in counting. 
     The canister housing may have a further inner canister wall support formation located on the inner wall opposite, or substantially opposite, the actuation member. Accordingly, the canister may be supported against rocking motion away from the actuator member so as to minimise count errors. 
     The canister housing may be generally straight and tubular and may have an arrangement in which each said inner wall support formation comprises a rail extending longitudinally along the inner wall. 
     Each said rail may be stepped, in that it may have a first portion located towards a medicine outlet end or stem block of the canister housing which extends inwardly a first distance from a main surface of the inner wall and a second portion located toward an opposite end of the canister chamber which extends inwardly a second, smaller distance from the main surface of the inner wall. This may therefore enable easy insertion of a canister into the canister housing such that a canister can be lined up gradually in step wise function as it is inserted into the canister housing. 
     The inhaler may include additional canister support rails which are spaced around an inner periphery of the inner wall of the canister housing and which extend longitudinally therealong. 
     At least one of the additional rails may extend a constant distance inwardly from the main surface of the inner wall. 
     At least one of the additional rails may be formed with a similar configuration to the first inner wall canister support formation. 
     The dose counter may, apart from said at least a portion of the actuation member, be located in a counter chamber separate from the canister housing, the actuation member comprising a pin extending through an aperture in a wall which separates the counter chamber and the canister housing. 
     According to a further aspect of the present invention there is provided an inhaler for inhaling medicaments having: a body for retaining a medicament store; the body including a dose counter, the dose counter having a moveable actuator and a return spring for the actuator, the return spring having a generally cylindrical and annular end; the body having a support formation therein for supporting said end of the return spring, the support formation comprising a shelf onto which said end is engageable and a recess below the shelf. 
     This shelf and recess arrangement is highly advantageous since it allows a tool (such as manual or mechanical tweezers) to be used to place the return spring of the actuator onto the shelf with the tool then being withdrawn at least partially via the recess. 
     The shelf may be U-shaped. 
     The support formation may include a U-shaped upstanding wall extending around the U-shaped shelf, the shelf and upstanding wall thereby forming a step and riser of a stepped arrangement. 
     The recess below the shelf my also be U-shaped. 
     At least one chamfered surface may be provided at an entrance to the shelf. This may assist in inserting the actuator and return spring into position. 
     A further aspect of the invention provides a method of assembly of an inhaler which includes the step of locating said end of said spring on the shelf with an assembly tool and then withdrawing the assembly tool at least partly via the recess. This assembly method is highly advantageous compared to prior art methods in which spring insertion has been difficult and in which withdrawal of the tool has sometimes accidentally withdrawn the spring again. 
     The cylindrical and annular end of the spring may be movable in a direction transverse to its cylindrical extent into the shelf while being located thereon. 
     According to a further aspect of the present invention there is provided an inhaler for inhaling medicament, the inhaler having a body for retaining a medicament store; and a dose counter, the dose counter having a moveable actuator and a chassis mounted on the body; the chassis being heat staked in position on the body. This is be highly advantageous in that the chassis can be very accurately positioned and held firmly in place, thereby further improving counting accuracy compared to prior art arrangements in which some movement of the chassis relative to the body may be tolerated in snap-fit connections. 
     The chassis may have at least one of a pin or aperture heat staked to a respective aperture or pin of the body. 
     The chassis may have a ratchet counter output member mounted thereon. 
     The ratchet counter output member may comprise a ratchet wheel arranged to reel in incrementally a dose meter tape having a dosage indicia located thereon. 
     According to a further aspect of the present invention there is provided a method of assembling an inhaler including the step of heat staking the chassis onto the body. The step of heat staking is highly advantageous in fixedly positioning the chassis onto the body in order to achieve highly accurate dose counting in the assembled inhaler. 
     The method of assembly may include mounting a spring-returned ratchet actuator in the body before heat staking the chassis in place. The method of assembly may include pre-assembling the chassis with a dose meter tape prior to the step of heat staking the chassis in place. The method of assembly may include attaching a dose meter cover onto the body after the heat staking step. The cover may be welded onto the body or may in some embodiments be glued or otherwise attached in place. 
     According to a further aspect of the present invention there is provided an inhaler for inhaling medicament and having a body, the body have a main part thereof for retaining a medicament store; and a dose counter, the dose counter being located in a dose counter chamber of the body which is separated from the main part of the body, the dose counter chamber of the body having a dosage display and being perforated so as to permit the evaporation of water or aqueous matter in the dose counter chamber into the atmosphere. 
     This is high advantageous since it enables the inhaler to be thoroughly washed and the dose counting chamber can thereafter dry out fully. 
     The display may comprise a mechanical counter display inside the dose counter chamber and a window for viewing the mechanical counter display. The mechanical counter display may comprise a tape. The perforated dose counter chamber may therefore enable reliable washing of the inhaler, if desired by the user, and may therefore dry out without the display window misting up. 
     The dose counter chamber may be perforated by a drain hole formed through an outer hole of the body. The drain hole may be located at a bottom portion of the body of the inhaler, thereby enabling full draining of the inhaler to be encouraged after washing when the inhaler is brought into an upright position. 
     According to a further aspect of the present invention there is provided a dose counter for an inhaler, the dose counter having a display tape arranged to be incrementally driven from a tape stock bobbin onto an incremental tape take-up drive shaft, the bobbin having an internal bore supported by and for rotation about a support shaft, at least one of the bore and support shaft having a protrusion which is resiliently biased into frictional engagement with the other of the bore and support shaft with longitudinally extending mutual frictional interaction. This arrangement may provide good friction for the bobbin, thereby improving tape counter display accuracy and preventing the bobbin from unwinding undesirably for example if the inhaler is accidentally dropped. 
     The support shaft may be forked and resilient for resiliently biasing the support shaft and bore into frictional engagement. 
     The support shaft may have two forks, or more in some cases, each having a radially extending protrusion having a friction edge extending therealong parallel to a longitudinal axis of the support shaft for frictionally engaging the bore of the support shaft with longitudinally extending frictional interaction therebetween. 
     The bore may be a smooth circularly cylindrical or substantially cylindrical bore. 
     Each of the above inhalers in accordance with aspects of the present invention may have a medicament canister mounted thereto. 
     The canister may comprise a pressurised metered dose canister having a reciprocally movable stem extending therefrom and movable into a main canister portion thereof for releasing a metered dose of medicament under pressure, for example by operating a metered dose valve inside the canister body. The canister may be operable by pressing by hand on the main canister body. 
     In cases in which one or more support rails or inner wall support formations are provided, the canister may at all times when within the canister chamber have a clearance of about 0.25 to 0.35 mm from the first inner wall support formation. The clearance may be almost exactly 0.3 mm. This clearance which may apply to the canister body itself or to the canister once a label has been applied, is enough to allow smooth motion of the canister in the inhaler while at the same time preventing substantial rocking of the canister which could result in inaccurate counting by a dose counter of the inhaler, especially when lower face of the canister is arranged to engage an actuator member of the dose counter for counting purposes. 
     According to a further aspect of the invention, a method of assembling a dose counter for an inhaler comprises the steps of providing a tape with dosing indicia thereon; providing tape positioning indicia on the tape; and stowing the tape while monitoring for the tape positioning indicia with a sensor. The method advantageously permits efficient and accurate stowing of the tape, e.g. by winding. 
     The dosing indicia may be provided as numbers, the tape positioning indicia may be provided as one or more lines across the tape. The stowing step comprises winding the tape onto a bobbin or shaft, and, optionally, stopping winding when the positioning indicia are in a predetermined position. The tape may be provided with pixelated indicia at a position spaced along the tape from the positioning indicia. The tape may also be provided with a priming dot. 
     According to a further aspect of the invention, a tape system for a dose counter for an inhaler has a main elongate tape structure, and dosing indicia and tape positioning indicia located on the tape structure. The tape positioning indicia may comprise at least one line extending across the tape structure. The tape system may comprise pixelated indicia located on the tape structure and spaced from the positioning indicia. The tape system may comprise a priming dot located on the tape structure. The positioning indicia may be located between the timing dot and the pixelated indicia. The main elongate tape structure may have at least one end thereof wound on a bobbin or shaft. 
     A further aspect of the invention provides a method of designing an incremental dose counter for an inhaler comprising the steps of calculating nominal canister fire and dose counter positions for a dose counter actuator of the inhaler; calculating a failure/success rate for dose counters built to tolerance levels for counting each fire of inhalers in which the dose counter actuators may be applied; and selecting a tolerance level to result in said failure/success rate to be at or below/above a predetermined value. This is highly advantageous in that it allows an efficient and accurate prediction of the reliability of a series of inhaler counters made in accordance with the design. 
     The method of designing may include selecting the failure/success rate as a failure rate of no more than one in 50 million. The method of designing may include setting an average count position for dose counters built to the tolerances to be at or after an average fire position thereof during canister firing motion. The method of designing may include setting the average count position to be about 0.4 to 0.6 mm after the average fire position, such as about 0.48 mm after. The method of designing may include setting tolerances for the standard deviation of the fire position in dose counters built to the tolerances to be about 0.12 to 0.16 mm, such as about 0.141 mm. The method of designing may include setting tolerances for the standard deviation of the count positions in dose counters built to the tolerances to be about 0.07 to 0.09 mm, such as about 0.08 mm. A further aspect of the invention provides a computer implemented method of designing an incremental dose counter for an inhaler which includes the aforementioned method of designing. 
     A further aspect of the invention provides a method of manufacturing in a production run a series of incremental dose counters for inhalers which comprises manufacturing the series of dose counters in accordance with the aforementioned method of designing. 
     A further aspect of the invention provides a method of manufacturing a series of incremental dose counters for inhalers, which comprises manufacturing the dose counters with nominal canister fire and dose count positions of a dose counter actuator relative to a dose counter chassis (or inhaler main body), and which includes building the dose counters with the average dose count position in the series being, in canister fire process, at or after the average canister fire position in the series. 
     According to a further aspect of the invention, the method provides fitting each dose counter in the series of incremental dose counters to a corresponding main body of an inhaler. 
     These aspects advantageously provide for the production run of a series of inhalers and dose counters which count reliably in operation. 
     According to a further aspect of the invention, an incremental dose counter for a metered dose inhaler has a body arranged to retain a canister for movement of the canister relative thereto, the incremental dose counter having a main body, an actuator arranged to be driven and to drive an incremental output member in a count direction in response to canister motion, the actuator being configured to restrict motion of the output member in a direction opposite to the count direction. This advantageously enables an inhaler dose counter to keep a reliable count of remaining doses even if dropped or otherwise jolted. 
     The output member may comprise a ratchet wheel. The actuator may comprise a pawl and in which the ratchet wheel and pawl are arranged to permit only one-way ratcheting motion of the wheel relative to the pawl. The dose counter may include an anti-back drive member fixed to the main body. In a rest position of the dose counter, the ratchet wheel is capable of adopting a configuration in which a back surface of one tooth thereof engages the anti-back drive member and the pawl is spaced from an adjacent back surface of another tooth of the ratchet wheel without positive drive/blocking engagement between the pawl and wheel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention may be carried out in various ways and preferred embodiment of a dose counter, inhaler and methods of assembly, design and manufacture will now be described with reference to the accompanying drawings in which: 
         FIG. 1  is an isometric view of a main body of an embodiment of an inhaler related to the invention together with a mouthpiece cap therefor; 
         FIG. 2  is a top plan view of the components as shown in  FIG. 1 ; 
         FIG. 3A  is a section on the plane  3 A- 3 A in  FIG. 2 ; 
         FIG. 3B  is a view corresponding to  FIG. 3A  but with a dose counter fitted to the main body of the inhaler; 
         FIG. 4A  is an exploded view of the inhaler main body, mouthpiece cap, dose counter and a dose counter window; 
         FIG. 4B  is a view in the direction  4 B in  FIG. 4C  of a spring retainer of the dose counter; 
         FIG. 4C  is a top view of the spring retainer of  FIG. 4B ; 
         FIG. 5  is a bottom view of the assembled inhaler main body, mouthpiece cap, dose counter and dose counter window; 
         FIGS. 6A, 6B, 6C, 6D, 6E, 6F, 6G and 6H  are various views of dose counter components of the inhaler; 
         FIGS. 7A and 7B  are sectional views showing canister clearance inside the main body of the inhaler; 
         FIG. 7C  is a further sectional view similar to that of  FIG. 7B  but with the canister removed; 
         FIG. 7D  is a top plan view of the inhaler main body; 
         FIGS. 8A, 8B, 8C and 8D  show the inhaler main body and dose counter components during assembly thereof; 
         FIG. 9  shows a sectional side view of a datum line for an actuator pawl of the dose counter; 
         FIGS. 10A, 10B, 10C, 10D, 10E and 10F  show various side views of positions and configurations of the actuator pawl, a ratchet wheel, and a count pawl; 
         FIG. 11  shows distributions for tolerances of start, reset, fire, count and end positions for the actuator of the dose counter; 
         FIG. 12  is an enlarged version of part of  FIG. 4A ; 
         FIG. 13  shows an end portion of a tape of the dose counter; 
         FIG. 14  shows a computer system for designing the dose counter; 
         FIG. 15  is an isometric view of a stock bobbin modified in accordance with the present invention for use in the dose counter of the inhaler of  FIGS. 1 to 14 ; 
         FIG. 16  shows an end view of the stock bobbin of  FIG. 15 ; 
         FIG. 17  is a section through a longitudinal axis of the stock bobbin of  FIGS. 15 and 16 ; 
         FIGS. 18A, 18B and 18C  are views of the stock bobbin of  FIGS. 15 to 17  mounted in the dose counter chassis of  FIGS. 1 to 14 , with the control elements of the forks of the second shaft (or split pin) having a profile slightly different to that in  FIG. 6F , with the forks in a compressed configuration; 
         FIGS. 19A, 19B and 19C  are views equivalent to  FIGS. 18A to 18C  but with the forks in a more expanded configuration due to a different rotational position of the stock bobbin; 
         FIG. 20  is an isometric view of the chassis assembled and including the stock bobbin of  FIGS. 15 to 17  but excluding the tape for reasons of clarity; 
         FIG. 21  is a view of a preferred embodiment of a dry powder inhaler in accordance with the present invention; 
         FIG. 22  is an exploded view of the inhaler of  FIG. 21 ; 
         FIG. 23  is a view of a dose counter of the inhaler of  FIG. 21 ; 
         FIG. 24  is an exploded view of the dose counter shown in  FIG. 23 ; 
         FIG. 25  is an exploded view of parts of the inhaler of  FIG. 21 ; and 
         FIG. 26  is a view of a yoke of the inhaler of  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a main body  10  of a manually operated metered dose inhaler  12  in accordance with an embodiment related to the present invention and having a mouthpiece cap  14  securable over a mouthpiece  16  of the main body. 
     The main body has a canister chamber  18  into which a canister  20  ( FIG. 7A ) is slideable. The canister  20  has a generally cylindrical main side wall  24 , joined by a tapered section  26  to a head portion  28  having a substantially flat lower face  30  which has an outer annular drive surface  32  arranged to engage upon and drive an actuation pin  34  of a dose counter  36  as will be described. Extending centrally and axially from the lower face  30  is a valve stem  38  which is arranged to sealingly engage in a valve stem block  40  of the main body  10  of the inhaler  12 . The valve stem block  40  has a passageway  42  leading to a nozzle  44  for directing the contents of the canister  20 , namely active drug and propellant, towards an air outlet  46  of the inhaler main body  12 . It will be appreciated that due to gaps  48  between the canister  20  and an inner wall  50  of the main body  10  of the inhaler  12  an open top  52  of the main body  10  forms an air inlet into the inhaler  12  communicating via air passageway  54  with the air outlet  46 , such that canister contents exiting nozzle  44  mix with air being sucked by the user through the air passageway  54  in order to pass together through the air outlet and into the mouth of the user (not shown). 
     The dose counter  36  will now be described. The dose counter  36  includes an actuation pin  34  biased upwardly from underneath by a return spring  56  once installed in the main body  10 . As best shown in  FIGS. 4A, 6H and 8A , the pin  34  has side surfaces  58 ,  60  arranged to slide between corresponding guide surfaces  62 ,  64  located in a dose counter chamber  66  of the main body  10 , as well as an end stop surface  68  arranged to engage a corresponding end stop  70  formed in the dose counter chamber  66  to limit upward movement of the pin  34 . The pin  34  has a top part  72  which is circularly cylindrical and extends through an aperture  74  formed through a separator wall  76  which separates the canister chamber  18  from the dose counter chamber  66 . The top part  72  of the pin  34  has a flat top surface  78  which is arranged to engage the outer annular drive surface  32  of the canister  20 . 
     The actuation pin  34  is integrally formed with a drive or actuator pawl  80 . The actuator pawl  80  has a generally inverted U-shape configuration, having two mutually spaced and parallel arms  82 ,  84  extending from a base portion of the actuation pin  34 , each holding at respective distal ends  88  thereof opposite ends of a pawl tooth member  90  which extends in a direction substantially perpendicular to the arms  82 ,  84 , so as to provide what may be considered a “saddle” drive for pulling on each of the 11 drive teeth  92  of a ratchet wheel  94  of an incremental drive system  96  or ratchet mechanism  96  of the dose counter  36 . As shown for example in  FIG. 10B , the pawl tooth member  90  has a sharp lower longitudinal side edge  98  arranged to engage the drive teeth  92 , the edge-to-surface contact provided by this engagement providing very accurate positioning of the actuator pawl  80  and resultant rotational positioning of the ratchet wheel  94 . 
     The dose counter  36  also has a chassis preassembly  100  which, as shown in  FIGS. 4A and 6A , includes a chassis  102  having a first shaft  104  receiving the ratchet wheel  94  which is secured to a tape reel shaft  106 , and a second shaft (or split pin)  108  which is parallel to and spaced from the first shaft  104  and which slidably and rotationally receives a tape stock bobbin  110 . 
     As shown in  FIG. 6B , when the inhaler has not been used at all, the majority of a tape  112  is wound on the tape stock bobbin  110  and the tape  112  has a series of regularly spaced numbers  114  displayed therealong to indicate a number of remaining doses in the canister  20 . As the inhaler is repeatedly used, the ratchet wheel  94  is rotated by the actuator pawl  80  due to operation of the actuation pin  34  by the canister  20  and the tape  112  is incrementally and gradually wound on to the tape reel shaft  106  from the second shaft  108 . The tape  112  passes around a tape guide  116  of the chassis  102  enabling the numbers  114  to be displayed via a window  118  in a dose counter chamber cover  120  having a dose marker  132  formed or otherwise located thereon. 
     As shown in  FIGS. 6A and 6D , the second shaft  108  is forked with two forks  124 ,  126 . The forks  124 ,  126  are biased away from one another. The forks have located thereon at diametrically opposed positions on the second shaft  108  friction or control elements  128 ,  130 , one on each fork. Each control element extends longitudinally along its respective fork  124 ,  126  and has a longitudinally extending friction surface  132 ,  134  which extends substantially parallel to a longitudinal axis of the second shaft and is adapted to engage inside a substantially cylindrical bore  136  inside the tape stock bobbin  110 . This control arrangement provided between the bore  136  and the control elements  128 ,  130  provides good rotational control for the tape stock bobbin  110  such that it does not unwind undesirably such as when the inhaler is dropped. The tape force required to unwind the tape stock bobbin  110  and overcome this friction force is approximately 0.1 N. 
     As can be seen in  FIG. 6D , as well as  FIGS. 6G and 10A to 10F , the chassis  102  is provided with an anti-back drive tooth  138  or count pawl  138  which is resiliently and substantially fixedly mounted thereto. As will be described below and as can be seen in  FIGS. 10A to 10F , when the actuation pin  34  is depressed fully so as to fire the metered valve (not shown) inside the canister  20 , the actuator pawl  80  pulls down on one of the teeth  92  of the ratchet wheel  94  and rotates the wheel  94  anticlockwise as shown in  FIG. 6D  so as to jump one tooth  92  past the count pawl  138 , thereby winding the tape  112  a distance incrementally relative to the dose marker  122  on the dose counter chamber  120  so as to indicate that one dose has been used. 
     With reference to  FIG. 10B , the teeth of the ratchet wheel  94  have tips  143  which are radiused with a 0.1 mm radius between the flat surfaces  140 ,  142 . The ratchet wheel  94  has a central axis  145  which is 0.11 mm above datum plane  220  ( FIG. 9 ). A top/nose surface  147  of the anti-back drive tooth  138  is located 0.36 mm above the datum plane  220 . The distance vertically (i.e. transverse to datum plane  220 — FIG. 9 ) between the top nose surface  147  of the anti-back drive tooth is 0.25 mm from the central axis  145  of the wheel  94 . Bump surface  144  has a lateral extent of 0.20 mm, with a vertical length of a flat  145 ′ thereof being 1 mm, the width of the bump surface being 1.22 mm (in the direction of the axis  145 ), the top  149  of the bump surface  144  being 3.02 mm vertically below the axis  145 , and the flat  145 ′ being spaced a distance sideways (i.e. parallel to the datum plane  220 ) 2.48 mm from the axis  145 . The top surface  78  of the pin  34  ( FIG. 6H ) is 11.20 mm above the datum plane  220  ( FIG. 9 ) when the actuator pawl  80  and pin  34  are in the start configuration. The length of the valve stem  22  is 11.39 mm and the drive surface  32  of the canister  20  is 11.39 mm above the datum plane  220  when the canister is at rest waiting to be actuated, such that there is a clearance of 0.19 mm between the canister  20  and the pin  34  in this configuration. 
       FIGS. 10A and 10B  show the actuator pawl  80  and ratchet wheel  94  and count pawl  138  in a start position in which the flat top  78  of the pin  34  has not yet been engaged by the outer annular drive surface  32  of the canister  20  or at least has not been pushed down during a canister depression. 
     In this “start” position, the count pawl  138  engages on a non-return back surface  140  of one of the teeth  92  of the ratchet wheel  94 . The lower side edge  98  of the actuator pawl is a distance “D” ( FIG. 9 ) 1.33 mm above datum plane  220  which passes through bottom surface or shoulder  41  of valve stem block  40 , the datum plane  220  being perpendicular to a main axis “X” of the main body  10  of the inhaler  12  which is coaxial with the centre of the valve stem block bore  43  and parallel to a direction of sliding of the canister  20  in the main body  10  of the inhaler  12  when the canister is fired. 
     As shown in  FIG. 10B , an advantageous feature of the construction is that the pawl tooth/actuator  90  acts as a supplementary anti-back drive member when the inhaler  12  is not being used for inhalation. In particular, if the inhaler  12  is accidentally dropped, resulting in a jolt to the dose counter  36  then, if the wheel  94  would try to rotate clockwise (backwards) as shown in  FIG. 10B , the back surface  140  of a tooth will engage and be blocked by the tooth member  90  of the pawl  80 . Therefore, even if the anti-back drive tooth  138  is temporarily bent or overcome by such a jolt, undesirable backwards rotation of the wheel  94  is prevented and, upon the next canister firing sequence, the pawl  90  will force the wheel  94  to catch up to its correct position so that the dose counter  36  continues to provide correct dosage indication. 
       FIG. 10C  shows a configuration in which the actuator pawl  80  has been depressed with the pin  34  by the canister  20  to a position in which the side edge  98  of the pawl tooth member  90  is just engaged with one of the teeth  92  and will therefore upon any further depression of the pin  34  begin to rotate the wheel  94 . This is referred to as a “Reset” position or configuration. In this configuration, the lower side edge  98  of the actuator  80  is 0.64 mm above the datum plane  220 . 
       FIG. 10D  shows a configuration in which the actuator pawl  80  has been moved to a position lower than that shown in  FIG. 10C  and in which the metered dose valve (not shown) inside the canister has at this very position fired in order to eject active drug and propellant through the nozzle  44 . It will be noted that in this configuration the count pawl  138  is very slightly spaced from the back surface  140  of the same tooth  92  that it was engaging in the configuration of  FIG. 10D . The configuration shown in  FIG. 10D  is known as a “Fire” configuration. In this configuration the lower side edge  98  of the actuator  80  is 0.47 mm below the datum plane  220 . 
       FIG. 10E  shows a further step in the sequence, called a “Count” position in which the actuator pawl  80  has rotated the ratchet wheel  94  by the distance circumferentially angularly between two of the teeth  92 , such that the count pawl  138  has just finished riding along a forward surface  142  of one of the teeth  92  and has resiliently jumped over the tooth into engagement with the back surface  140  of the next tooth. Accordingly, in this “Count” configuration, a sufficiently long stroke movement of the pin  34  has occurred that the tape  112  of the dose counter  36  will just have counted down one dose. In this configuration, the lower side edge  98  of the actuator is 0.95 mm below the datum plane  220 . Accordingly, in this position, the actuator  80  generally, including edge  98 , is 0.48 mm lower than in the fire configuration. It has been found that, although the count configuration happens further on than the fire configuration, counting is highly reliable, with less than 50 failed counts per million. This is at least partially due to momentum effects and to the canister releasing some back pressure on the user in some embodiments as its internal metering valve fires. 
     In the configuration of  FIG. 10F , the pawl  80  has been further depressed with the pin  34  by the canister  20  to a position in which it is just disengaging from one of the teeth  92  and the actuator pawl  80  is assisted in this disengagement by engagement of one of the arms  84  with a bump surface  144  on the chassis  102  (see  FIG. 6G ) and it will be seen at this point of disengagement, which is called an “End” configuration, the count pawl  138  is positioned exactly halfway or substantially halfway between two of the drive teeth  92 . This advantageously means therefore that there is a minimum chance of any double counting or non-counting, which would be undesirable. In the end configuration, the side edge  98  of the actuator is 1.65 mm below the datum plane  220 . It will be appreciated that any further depression of the actuator pawl  80  and pin  34  past the “End” configuration shown in  FIG. 10F  will have no effect on the position of the tape  112  displayed by the dose counter  36  since the actuator pawl  80  is disengaged from the ratchet wheel  94  when it is below the position shown in  FIG. 10F . 
     As shown in  FIGS. 7C and 7D , the inner wall  50  of the main body  10  is provided with a two-step support rail  144  which extends longitudinally along inside the main body and is located directly adjacent the aperture  74 . As shown in  FIG. 7B  a diametrically opposed two-step support rail  146  is also provided and this diametrically opposed in the sense that a vertical plane (not shown) can pass substantially directly through the first rail  144 , the aperture  74 , a central aperture  148  of the valve stem block  40  (in which canister stem  25  is located) and the second two-step support rail  146 . As shown in  FIG. 7A  and schematically in  FIG. 7B , the rails  144 ,  146  provide a maximum clearance between the canister  20  and the rails  144 ,  146  in a radial direction of almost exactly 0.3 mm, about 0.25 to 0.35 mm being a typical range. This clearance in this plane means that the canister  20  can only rock backwards and forwards in this plane towards away from the actuation pin  34 . A relatively small distance and this therefore prevents the canister wobbling and changing the height of the actuation pin  34  a as to undesirably alter the accuracy of the dose counter  36 . This is therefore highly advantageous. 
     The inner wall  50  of the main body  10  is provided with two further two-step rails  150  as well as two pairs  152 ,  154  of rails extending different constant radial amounts inwardly from the inner wall  50 , so as to generally achieve a maximum clearance of almost exactly 0.3 mm around the canister  20  for all of the rails  144 ,  146 ,  150 ,  152 ,  154  spaced around the periphery of the inner wall  50 , in order to prevent undue rocking while still allowing canister motion freely inside the inhaler  12 . It will be clear from  FIG. 7C  for example that the two-step rails have a first portion near an outlet end  156  of the canister chamber  18 , the first portion having a substantially constant radial or inwardly-extending width, a first step  160  leading to a second portion  162  of the rail, the second portion  102  having a lesser radial or inwardly extending extent than the first portion  156 , and finally a second step  164  at which the rail merges into the main inner wall  50  main surface. 
     A method of assembling the inhaler  12  will now be described. 
     With reference to  FIG. 8A , the main body  10  of the inhaler  12  is formed by two or more plastics mouldings which have been joined together to the configuration shown. 
     As shown in  FIG. 8B , the actuator pawl  80  and pin  34  are translated forward into position into a pin receiving area  166  in the dose counter chamber  66  and the pin  34  and actuator  80  may then be raised until the pin  34  emerges through the aperture  74 . 
     Next, the return spring  56  may be inserted below the pin  34  and a generally cylindrical annular lower end  168  of the spring  56  may be moved by a tweezer or tweezer-like assembly tool (not shown) into engagement with a shelf  170  of a spring retainer  172  in the dose counter chamber  66 . The spring retainer  172  is U-shaped and the shelf  170  is U-shaped and has a recess  174  formed below it. As shown in  FIGS. 4B, 4C and 12  shelf  170  includes three chamfer surfaces  176 ,  178 ,  180  arranged to assist in moving the lower end of the spring  168  into position onto the shelf using the assembly tool (not shown). Once the lower end of the spring  168  is in place, the assembly tool (not shown) can easily be removed at least partly via the recess  174  below the lower end  168  of the spring  56 . 
     The tape  112  is attached at one end (not shown) to the tape stock bobbin  110  and is wound onto the bobbin by a motor  200  ( FIG. 13 ) having a hexagonal output shaft  202  which engages in a hexagonal socket  204  ( FIG. 6B ) of the bobbin. During winding, the tape is monitored by a sensor  206 , which may be in the form of a camera or laser scanner, which feeds data to a computer controller  205  for the motor  200 . The controller  205  recognises three positioning markers  210  in the form of lines across the tape  112  and stops the motor  202  when the tape  112  is nearly fully wound onto the bobbin  110 , such that the distal end  212  of the tape  112  can be secured, e.g. by adhesive, to the tape reel shaft  106 . The controller  205  also recognises a pixelated tape size marker  214  observed by the sensor  206  and logs in a stocking system data store  217  details of the tape  112  such as the number of numbers  114  on the tape, such as one hundred and twenty or two hundred numbers  114 . Next, the tape reel shaft is wound until an appropriate position of the lines  210  at which a priming dot  216  will, once the bobbin  110  and reel shaft  106  are slid onto the second shaft  108  and second shaft  104 , be in a position to be located in the window  118  when the inhaler  12  is fully assembled. In the embodiments, the bobbin  110  and reel shaft  106  may be slid onto the shafts  108 ,  104  before the tape  112  is secured to the reel shaft  106  and the reel shaft may then be wound to position the priming dot  216 . 
     Next, the assembled dose counter components of the chassis preassembly  100  shown in  FIG. 6B  may as shown in  FIG. 8C  be inserted into the dose counter chamber  66 , with pins  182 ,  184 ,  186  formed on the main body  10  in the dose counter chamber  66  passing through apertures or slots  188 ,  190 ,  192  formed on the chassis  102 , such that the pins  182 ,  184 ,  186  extend through (or at least into) the apertures or slots  188 ,  190 ,  192 . With the chassis  102  being relatively firmly pushed towards the main body  10 , the pins  182 ,  184 ,  186  are then heat staked and the chassis  102  is therefore after this held very firmly in position in the main body and is unable to move, thereby assisting in providing great accuracy for the dose counter  36 . Next, as shown in  FIG. 8D , the dose counter chamber cover  120  may be fitted over the dose counter chamber  66  and may be secured in place such as by welding, with the priming dot  216  being displayed through the window. 
     The user can, when readying the inhaler  12  for first use, prime the inhaler by depressing the canister  20  three times which will bring the first number  114  on the tape into display through the window  118  in place of the priming dot  216 , the number  114  shown in  FIG. 8D  being “200”, thereby indicating that 200 doses are remaining to be dispensed from the canister  20  and inhaler  12 . 
     As shown in  FIG. 8D , and in  FIG. 5 , an open drain hole  194  is provided at the bottom of the dose counter chamber  66  by a substantially semi-circular cut-out or recess formation  196  in a lower surface  198  of the main body  10  of the inhaler. Accordingly, if the user (not shown) should decide to wash the main body  10  of the inhaler, for example after encountering an unhygienic situation or simply as a matter of choice, the drain hole  194  allows initial draining of water from inside the dose counter chamber  66  and also thereafter evaporation of water or any aqueous matter in the dose counter chamber  66  so that the window  118  does not mist up undesirably. 
       FIG. 14  shows a computer system  230  for designing the dose counter  36  and in particular for calculating distributions representative of average positions and standard deviations in a production series of inhalers of the start, reset, fire, count and end positions of the actuator lower side edge  98  relative to the datum plane  220  ( FIG. 9 ) and therefore of the actuator pawl  80  generally relative to the ratchet wheel  94 , chassis  102  and, when the inhaler  12  is fully assembled, the main body  10  of the inhaler  12 . The computer system  230  includes a data store  232 , a CPU  234 , an input device  236  (such as a keyboard or communication port) and an output device  238  (such as a communications port, display screen and/or printer). A user may enter data via the input device  236  which may be used by the CPU  234  in a mathematical calculation to predict count failure rates when the various dose counters are to be built in a series with dose counter positions set with given averages and standard deviations and taking into account any momentum/inertia effects and metering valve user-back-pressure reduction effect which will occur upon canister firing of a given type of canister. The computer system  230  is thus mathematically used to design the distributions. For the inhaler  12  described herein with the dose counter  36  and canister  20 , the distributions are designed as shown in  FIG. 11 . The x axis shows distance of the lower side surface  98  of the actuator  80  above the datum plane  220  and the y axis is representative of the distribution. Thus, curve  240  shows that the start configuration has an average 1.33 mm above the datum plane  200  (standard deviation is 0.1 mm), curve  242  shows that the reset configuration has an average of 0.64 mm above the datum plane  220  (standard deviation is 0.082 mm), curve  244  shows the fire configuration has an average 0.47 mm below the datum plane  220  (standard deviation is 0.141 mm), curve  246  shows the count configuration has an average 0.95 mm below the datum plane  220  (standard deviation is 0.080 mm), and curve  248  shows the end configuration has an average of 1.65 mm below the datum plane  220  (standard deviation is 0.144 mm). 
       FIGS. 15 to 20  show a version of the inhaler modified in accordance with the present invention. In these drawings, the same reference numerals have been used to those in the earlier drawings to denote the equivalent components. The inhaler  12  is the same as that in  FIGS. 1 to 14  apart from the following modifications. 
     First, it can be seen that there is a modification in that the drive teeth  92  of the ratchet wheel  94  have a different profile to that in  FIGS. 1 to 14 . There are also only nine ratchet teeth  94  in this embodiment instead of eleven. 
     Additionally, as shown in  FIGS. 18C and 19C , the control elements  128 ,  130  on the forks  124 ,  126  of the second shaft  108  have a tapered profile which is different to the profile of the control elements  128 ,  130  shown in  FIG. 6F . Either profile can be used in the embodiment of  FIGS. 15 to 20  however. 
     Furthermore, as shown in  FIG. 15 , the tape stock bobbin  110  has an inwardly facing generally cylindrical engagement surface  300  with a wavelike form extending partially therealong. The engagement surface  300  has a cross-section  301  perpendicular to the longitudinal length of the stock bobbin  110  which is constant therealong. This cross-section  301  can be seen in  FIG. 16  and consists of a series of ten regularly spaced concavities  302  and ten convex wall portions  304 . The convex wall portions  304  are equi-spaced between the concavities  302 . Each concavity  302  has a radius of 0.2 mm. Each convex wall portion  304  also has a radius of 0.2 mm. Finally, the cross section  301  also includes flat wall portions  306  between all of the radiused wall portions of the concavities  302  and convex wall portions  304 . The geometry of the cross-section  301  is therefore defined by the radii of the concavities  302  and convex wall portions  304 , the flat wall portions  306  and the fact that there are ten concavities  302  and convex wall portions  304 . 
     The minor diameter of the engagement surface  300 , i.e. between the tips of opposite convex wall portions  304 , is 2.46 mm. The major diameter of the engagement surface  300 , i.e. between the outermost portions of the concavities  302 , is 2.70 mm. The undeformed tip to tip maximum diameter of the forks  124 ,  126  of the split pin (the second shaft)  108 , i.e. in the region of the maximum radio extent of the control elements  128 ,  130 , is 3.1 millimeters and it will therefore be appreciated that the forks  124 ,  126  are resiliently compressed once the stock bobbin  110  has been assembled onto the split pin  108  in all rotational configurations of the stock bobbin  110  relative to the split pin  108 . The minimum gap between the forks  124 ,  126  in the plane of the cross sections of  FIGS. 18C and 19C  is 1 mm when the split pin  108  is in the undeformed, pre-inserted state. When the split pin  108  is at maximum compression, as shown in  FIGS. 18A to 18C  when the control elements  128 ,  130  are shown to be engaged on top of the convex wall portions  304 , the gap  308  between the tips  310 ,  312  of the forks  124 ,  126  is 0.36 mm. On the other hand, when the split pin  108  is at minimum compression (once inserted into the stock bobbin) as shown in  FIGS. 19A to 19C , when the control elements  128 ,  130  rest in the concavities  302 , the gap between the tips  310 ,  312  of the forks  124 ,  126  is 0.6 mm. The control elements  128 ,  130  are outwardly radiused with a radius also of 0.2 mm such that they can just rest on the concavities  302  with full surface contact (at least at an axial location on the split pin where the tapered control elements are at their maximum radial extent), without rattling in, locking onto or failing to fit in the concavities  302 . The radii of the control elements  128 ,  130  is therefore preferably substantially the same as the radii of the concavities  302   
     It will be appreciated that whereas  FIGS. 18B and 19B  are end views along the coaxial axis of the stock bobbin  110  and split pin  108 ,  FIGS. 18A and 19A  are cross-sections.  FIG. 19A  is a section on the plane A-A′ in  FIG. 19C  and  FIG. 18A  is a section at the same plane, but of course with the stock bobbin  110  rotated relative to the split pin  108 . 
     As the inhaler  12  is used and the ratchet wheel  94  rotates in order to count used doses, the stock bobbin rotates incrementally through rotational positions in which rotation is resisted, i.e. due to increasing compression of the split pin  108  at such rotational positions, and rotational positions in which rotation is promoted, i.e. due to decreasing compression of the split pin  108  at such rotational positions and this may involve a click forward of the stock bobbin  110  to the next position equivalent to that in  FIGS. 19A to 19C  in which the control elements  128 ,  130  of the split pin art located in the concavities  302 . This functionality firstly allows the stock bobbin to unwind during use as required, but also prevents the tape  112  from loosening during transit if the inhaler  12  is dropped, such as onto a hard surface. This is highly advantageous, since the tape  11  is prevented from moving to a position in which it will give an incorrect reading regarding the number of doses in the canister. 
     During compression and expansion of the forks in the radial direction between the two configurations shown in  FIGS. 18C and 19C , the forks  124 ,  126  rotate about a point  316  on the split pin where the forks  124 ,  126  come together. This rotational action means that there is a camming action between the forks  124 ,  126  and the engagement surface  300  without significant friction but, nevertheless, the resilient forces provided by the regulator formed by the engagement surface  300  and forks  124 ,  126  are able to regulate unwinding of the tape such that it does not easily occur during transit or if the inhaler  12  is dropped. It has been found during testing that a force of 0.3 to 0.4 N needs to be applied to the tape  112  to overcome the regulator at the stock bobbin  110 . 0.32 N is achieved with the control elements  128  having the profile shown in  FIG. 19C  and 0.38 N is achieved with the profile of the control elements  128  altered to be as shown as described with reference to  FIG. 6F . These forces are substantially higher than the 0.1 N force mentioned above and undesirable movement of the tape is substantially avoided even if the inhaler is dropped onto a hard surface. The modified arrangement of  FIGS. 15 to 20  does not provide this force “constantly” such that there is overall not an undesirably high friction of the tape  112  as it passes over the other components of the dose counter because, due to the incremental nature of the resilient forces at the regulator, the tape  112  can incrementally relax as it slides over the stationary chassis components. 
     Instead of having ten concavities  302  and convex wall portions  304 , other numbers may be used, such as 8 or 12. However, it is preferred to have an even number, especially since two control elements  128 ,  130  are provided, so that all of the control elements  128 ,  130  will expand and contract simultaneously. However, other arrangements are envisaged with 3 or more forks and the number of concavities/convex wall portions may be maintained as an integer divisible by the number of forks to maintain a system with simultaneous expansion/contraction. For example, the use of 9, 12 or 15 concavities/convex wall portions with 3 forks is envisaged. 
     Instead of having the engagement surface  300  on the inside of the stock bobbin  110 , it could be placed on the outside of the stock bobbin  110  so as to be engaged by flexible external legs/pawls or similar. 
     It will be noted that the regulator provided by the engagement surface  300  and forks  124 ,  126  does not only allow rotation of the stock bobbin in one direction as is the case with the ratchet wheel  94 . Rotation in both directions is possible, i.e. forwards and backwards. This means that during assembly, the stock bobbin  110  can be wound backwards during or after fitting the bobbin  100 , shaft  106  and tape  112  onto the carriage  102 , if desired. 
     The stock bobbin  110  and the carriage  102  including the split pin  108  are both moulded of polypropylene material. 
     It will be seen from  FIG. 16  that the cross-sectional shape  301  is not symmetrical within the hexagonal socket  204 . This has enabled the hexagonal socket  204  to be maintained at a useful size while still allowing the desired size and geometry of the cross section  301  to fit without interfering with the hexagonal shape of the hexagonal socket  204  and also permits moulding to work during manufacture. 
     As shown in  FIG. 17 , the stock bobbin  110  has a series of four circumferential ribs  330  inside it and a spaced therealong. These hold the stock bobbin  110  on the correct side of the mould tool during moulding. 
       FIGS. 21 and 22  show a preferred embodiment in accordance with the invention of an inhaler  510  for dispensing a dry-powdered medicament in metered doses for patient inhalation. The inhaler  510  is as disclosed in  FIGS. 1 to 16  or EP-A-1330280, the contents of which are hereby fully incorporated herein by reference, but with the stock bobbin  110  and second shaft  108  of the dose counter  516  modified so as to be as in  FIGS. 15 to 20  hereof. Thus, the dry powder inhaler  510  generally includes a housing  518 , and an assembly  512  received in the housing (see  FIG. 21 ). The housing  518  includes a case  520  having an open end  522  and a mouthpiece  524  ( FIG. 25 ) for patient inhalation, a cap  526  secured to and closing the open end  522  of the case  520 , and a cover  528  pivotally mounted to the case  520  for covering the mouthpiece  524 . As shown in  FIG. 22 , the inhaler  510  also includes an actuation spring  569 , first yoke  566  with opening  572 , bellows  540  with crown  574 , a reservoir  514 , second yoke  568  with hopper  542  and dose counter  516  mounted thereto, and case  520  has transparent window  5130  thereon for viewing dose counter tape indicia  5128 . The dose metering system also includes two cams  570  mounted on the mouthpiece cover  528  and movable with the cover  528  between open and closed positions. The cams  570  each include an opening  580  for allowing outwardly extending hinges  582  of the case  520  to pass therethrough and be received in first recesses  584  of the cover  528 . The cams  570  also include bosses  586  extending outwardly and received in second recesses  588  of the cover  528 , such that the cover  528  pivots about the hinges  582  and the cams  570  move with the cover  528  about the hinges  582 . As described in EP-A-1330280, cams  570  act upon cam followers  578  to move second yoke  568  up and down and thereby operate dose counter by engagement of pawl  5138  on the second yoke  568  with teeth  5136 . Remaining components of the inhaler are provided as, and operate as described, in EP-A-1330280. 
     The dose counting system  516  therefore includes a ribbon or tape  5128  ( FIGS. 23 &amp; 24 ), having successive numbers or other suitable indicia printed thereon, in alignment with a transparent window  5130  provided in the housing  18  (see  FIG. 22 ). The dose counting system  516  includes the rotatable stock bobbin  110  (as described above), an indexing spool  5134  rotatable in a single direction, and the ribbon  5128  rolled and received on the bobbin  110  and having a first end  5127  secured to the spool  5134 , wherein the ribbon  5128  unrolls from the bobbin  110  so that the indicia are successively displayed as the spool  5134  is rotated or advanced. In  FIGS. 23 and 24  the wavelike engagement surface  300  of the bobbin  110  is not shown for the purposes of clarity. 
     The spool  134  is arranged to rotate upon movement of the yokes  566 ,  568  to effect delivery of a dose of medicament from reservoir  514 , such that the number on the ribbon  5128  is advanced to indicate that another dose has been dispensed by the inhaler  510 . The ribbon  5128  can be arranged such that the numbers, or other suitable indicia, increase or decrease upon rotation of the spool  5134 . For example, the ribbon  5128  can be arranged such that the numbers, or other suitable indicia, decrease upon rotation of the spool  5134  to indicate the number of doses remaining in the inhaler  510 . Alternatively, the ribbon  5128  can be arranged such that the numbers, or other suitable indicia, increase upon rotation of the spool  5134  to indicate the number of doses dispensed by the inhaler  10 . 
     The indexing spool  5134  includes radially extending teeth  5136 , which are engaged by pawl  5138  extending from a cam follower  578  of the second yoke  568  upon movement of the yoke to rotate, or advance, the indexing spool  5134 . More particularly, the pawl  5138  is shaped and arranged such that it engages the teeth  5136  and advances the indexing spool  5134  only upon the mouthpiece cover  528  being closed and the yokes  566 ,  568  moved back towards the cap  526  of the housing  518 . 
     The dose counting system  516  also includes a chassis  5140  that secures the dose counting system to the hopper  542  and includes shafts  108 ,  5144  for receiving the bobbin  110  and the indexing spool  5134 . As described above with reference to  FIGS. 1 to 20 , the bobbin shaft  108  is forked and includes radially nubs  5146  for creating a resilient resistance to rotation of the bobbin  110  on the shaft  108  by engaging with the wavelike engagement surface  300  inside the bobbin  110 . A clutch spring  5148  is received on the end of the indexing spool  5134  and locked to the chassis  5140  to allow rotation of the spool  5134  in only a single direction. 
     Various modifications may be made to the embodiment shown without departing from the scope of the invention as defined by the accompanying claims as interpreted under patent law.