Abstract:
A dose indicator or dose counter is disclosed which includes an indexable first display unit indexable about a first display axis, an indexable second display unit indexable about a second display axis, the second display axis being transverse to the first display axis, and a chassis comprising a chassis frame, a displacement portion comprising a drive means to engage the first display unit, and at least one hinge means directly or indirectly connecting the displacement portion and chassis frame. The drive means is preferably configured to index the dose indicator. The dose indicator/counter has a small number of components yet is effective, reliable and compact.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to United Kingdom Application No. 1312448.2, filed Jul. 11, 2013, which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    The present specification relates to dose indicators or dose counters, and more particularly to dose indicators or dose counters for pressurised metered dose inhaler (pMDI) devices. The present invention also relates to actuators comprising such dose indicators/counters and to inhalers comprising such actuators. 
         [0003]    Patients who use inhalers, such as pMDI devices, need to monitor their inhaler usage, and regulators of medicines have begun to require that some method of dose indication is included into the inhaler. Dose counters (providing a precise count of the number of doses remaining) and dose indicators (providing an indication of the number of doses remaining) for inhalers are known. 
         [0004]    In most dose counters and dose indicators, the display is indexed each time the inhaler device is used. Many dose counters and/or dose indicators are complex, requiring a number of small mechanical parts, which may increase cost, may lead to difficulties in assembly, and may require tight dimensional tolerances. 
         [0005]    International Publication No. WO 2011/071788 discloses dose counters for dispensers and in particular dose counters for use with metered dose inhalers. 
         [0006]    U.S. Pat. No. 6,752,153 discloses an inhaler for aerosolization of medicament with a dose counter. The dosage counter has a first and a second counting ring and a coupling device that connects the counting rings. 
         [0007]    International Publication No. WO 1998/52634 discloses a dosing device and in particular relates to dosing devices for drug delivery such as injectors and inhalers and a mechanism for use in such devices. 
         [0008]    It would be advantageous to provide a dose indicator or dose counter that has fewer essential parts. It would also be advantageous if the dose indicator were designed to fit within typical existing pMDI actuators and to be compatible with existing pMDI valves. 
         [0009]    In this specification, the term “dose indicator” is intended to refer to both dose counter devices and dose indicator devices. 
       SUMMARY 
       [0010]    In a first aspect, there is provided a dose indicator comprising, an indexable first display unit indexable about a first display axis, an indexable second display unit indexable about a second display axis, the second display axis being transverse to the first display axis, and a chassis comprising a chassis frame, a displacement portion comprising a drive means to engage the first display unit, and at least one hinge means directly or indirectly connecting the displacement portion and chassis frame. The drive means is preferably configured to index the dose indicator. 
         [0011]    This is advantageous because it provides a dose indicator/counter that has a small number of components yet is effective, reliable and compact. Furthermore, the invention allows the provision of a cheap, simple and reliable dose-by-dose counter that is capable of counting 200 doses or puffs. It may count down from 200 to 0 and is able to fit within a pMDI actuator of similar shape and comparable size to existing actuators. 
         [0012]    The hinge means (e.g. hinge or hinges) may generally be any connecting portion including such that allows restricted but controlled relative movement of the displacement portion and the chassis frame, including relative rotational and/or translational movement. 
         [0013]    The second display axis and the first display axis may be arranged so that they do not intersect. However, generally the second display axis will intersect the first display axis. 
         [0014]    The second display axis may, preferably, be at an acute or an obtuse angle to the first display axis. In some circumstances, the second display axis may be substantially orthogonal to the first display axis. 
         [0015]    Generally, the first display unit and/or the second display unit will be substantially circular in a cross-section (usually a cross section transverse, preferably generally orthogonal, to the first and/or second display axis respectively) and will be rotatably indexable about the first display axis and/or about the second display axis respectively. The term “substantially circular” in this context includes annular or disc-shaped embodiments and polygonal shapes with at least five sides. 
         [0016]    The drive means is preferably adapted to engage the first display unit. In particular, it is preferred if the drive means is adapted to engage the first display unit on a curved path, the drive means being driven by a force from outside the circumference of the first display unit. This improves the stability of indexing because it allows freer movement of the drive means past the first display unit and reduces the risk of advancing an additional, unwanted count. 
         [0017]    Thus, in a second aspect, there is provided a dose indicator comprising, an indexable first display unit rotatably indexable about a first display axis, and a chassis comprising a chassis frame, a displacement portion comprising a drive means to engage the first display unit, and at least one hinge means directly or indirectly connecting the displacement portion and chassis frame, wherein the drive means is adapted to engage the first display unit on a curved path, the drive means being driven by a force from outside the circumference of the first display unit. Optionally there is also an indexable second display unit, indexable about a second display axis. 
         [0018]    Preferably, the first display unit is rotatable in a first plane transverse to the first display axis, and the curved path is at least partly outside the first plane. It is also preferred that the drive means is driven by a force that has a component generally in the first plane, the component of the force that is in the first plane being outside the circumference of the first display unit. This is advantageous because it allows that the first display unit may be of generally disc-like or polygonal ( 5  sides or greater) cross section with the indexing features (e.g. indexing teeth) being on the outer circumference of the unit. 
         [0019]    Preferably, the drive means is angled into the first display unit to improve engagement and to reduce the chance of the drive means unintentionally disengaging from the first display unit. 
         [0020]    Preferably, the chassis is moulded as a unitary piece. Preferably, the first display unit is also moulded as a unitary piece. It is also preferred if the second display unit is moulded as a unitary piece. This is advantageous because it enables the reduction of the number of parts of the dose indicator, with consequent benefits of cost and simplicity of assembly. The components of the dose indicator may therefore number just three corresponding to chassis, first display unit and second display unit. However, in some circumstances additional components may be advantageous. 
         [0021]    It is preferred if the chassis, first display unit and second display unit are each independently designed so they may be injection moulded without the requirement for a side action in the moulding tool. This reduces flash in the moulded components. 
         [0022]    It is preferred if the drive means is integrally comprised in the displacement portion. 
         [0023]    In preferred embodiments, the drive means comprises a drive pawl. In some embodiments it is advantageous if the engaging end of the drive pawl is outside the cylindrical envelope of the first display unit (i.e. outside its circumference) in the rest position, and is brought within this envelope during actuation. Thus, during actuation preferably the drive pawl follows a path from outside the circumference of the first display unit. 
         [0024]    Usually, the displacement portion will be adapted so that it may be displaced along a displacement path that is preferably at least partly transverse to the first display axis. It is preferred if the displacement path is at least partly arcuate. This may be achieved, for example, if the drive means is located on the displacement portion at a position remote from the hinge or hinges, preferably at a position distal to the hinge or hinges. The hinges may be configured for substantially pivotal (rotational) movement of the displacement portion. 
         [0025]    Usually, the displacement portion will comprise at least one press member that acts as an interference portion for interference with the valve during actuation. The press member or members may for example be a press knuckle or press knuckles. It is advantageous if the contact points (e.g. press knuckles) between the valve and the displacement portion include points that are radially in different directions from the valve stem, as this helps to compensate for effects of the patient tilting the canister slightly during actuation. Thus, preferably there are two or more contact points (e.g. press knuckles) distributed on the displacement portion. 
         [0026]    The dose indicator will usually further comprise at least a first display non-return means, the first display non-return means being preferably at least partly located on the chassis frame. The non-return means may be for example a frictional non-return means, but in a preferred embodiment the first display non-return means comprises a non-return arm adapted to interact with one or more detents on the first display unit. 
         [0027]    The chassis preferably further comprises at least one return means. The return means will usually comprise at least one spring. Preferably, the at least one spring comprises a leaf spring, preferably a curved leaf spring. The at least one return means (preferably a curved leaf spring) will usually directly or indirectly connect the displacement portion and chassis frame, preferably at a position remote from the hinge or hinges. 
         [0028]    Usually, the first and/or the second display unit will be adapted to index through between 5 and 25 indicia, preferably 8 to 12 indicia. 
         [0029]    The dose indicator may comprise a first display unit mounting means for mounting the display unit on the chassis frame so that it is indexable about the first display axis. 
         [0030]    The internal profile of the first display unit may include an axle bearing and the chassis may include an axle with an external profile designed to engage closely with the axle bearing to allow relative rotational movement without wobble. This may be achieved by close circumferential engagement of the internal profile of the first display unit and the external profile of the first display unit axle over most of the circumference corresponding to positions on the first display unit axle that are axially separated by some distance. This distance is preferably greater than the thickness of the portion of the first display unit that bears indicia. 
         [0031]    The first display unit axle may be substantially cylindrical, or it may have cylindrical sections of different diameter. For example the section closer to the first display unit&#39;s indicia may have the larger diameter. The first display unit axle may have a lead-in surface at the distal end to facilitate placing of the first display unit. This first display unit axle may be configured to hold the first display unit in position and to prevent its axial translation along the first display unit axle, e.g. by the provision of circumferential detents. 
         [0032]    Usually, in embodiments of the invention, the first display unit is a units display unit. 
         [0033]    Preferably, the second display unit is a tens display unit. 
         [0034]    In preferred embodiments the first display unit comprises a drive arm adapted to index the second display unit. This is particularly suited to embodiments in which the second display unit is a tens display unit. 
         [0035]    An angled edge may be provided on the trailing side of the drive arm and/or the indexing teeth of the second display unit may be provided with angled leading edges. This reduces the chances of a double second (e.g. tens) count occurring whilst maximizing the overlap between the drive arm and indexing teeth. A rounded leading edge may be provided on the leading edge of the drive arm. This ensures that the point contact with an indexing tooth has a high incident angle for most of an indexing movement of the second display unit. 
         [0036]    In some embodiments the first display unit has a substantially circular cross section, preferably a cross section on a plane transverse (more preferably substantially orthogonal) to the first display axis. 
         [0037]    In some embodiments the second display unit has a substantially circular cross section, more preferably a substantially annular cross section. It is preferred if the cross section is on a plane transverse (more preferably substantially orthogonal) to the second display axis. 
         [0038]    In preferred embodiments, the first and/or the second display unit comprises a zero stop means. It is particularly preferred that the second display unit comprises a zero stop means to stop the second display unit from advancing beyond the zero count (e.g. of ten if the second display units is a tens display unit) corresponding to a nearly empty inhaler, and the second display unit is preferably further configured to prevent indexing of the first display unit beyond the ensuing zero units count. This configuration of the stop means may be achieved by using positive engagement between the first (e.g. the units) display unit and the second (e.g. tens) display unit. In embodiments where the first and/or the second display unit comprises a zero stop means, the drive member may be configured to deflect or collapse to allow continued use of the inhaler after the displayed overall count has reached zero. 
         [0039]    Preferably, the zero stop means interacts with a stop arm located on the chassis. Advantageously, the chassis comprises polyoxymethylene (i.e. POM, acetal). 
         [0040]    The polyoxymethylene is preferably in homopolymer form. 
         [0041]    In a third aspect, the invention provides an actuator for an inhaler, the actuator comprising a dose indicator as discussed in the first or second aspect. 
         [0042]    In a fourth aspect, the invention provides an inhaler comprising an actuator as discussed in the third aspect. 
         [0043]    The dose indicator of the present invention is of simple construction, whilst being robust and reliable in its indication of doses. It is suitable for use in a pressurized metered dose inhaler (pMDI) or other dispensing devices (e.g. dry powder inhalers, aqueous pump dispensers) to indicate usage (e.g. number of doses used or number of doses remaining) by means of numbers and/or coloured regions or other indicia in its display. Typically doses are counted downwards, and an indication of when the inhaler canister needs to be replaced may be provided in addition to an indication of the number of doses that have been dispensed. 
         [0044]    When adapted for a pMDI, the dose indicator may be of a suitable size and configuration to fit into existing inhaler actuators, including breath actuated actuators or actuators with breath coordination means incorporated, without appreciable changes to the dimensions or shape of the existing actuator designs. Actuators will typically be provided with a window for viewing the dose indication or count. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]    So that the present specification may be more completely understood, reference is made to the accompanying drawings in which like elements are given like reference numerals (with the addition of 100 or multiples of 100 to the numerals of different embodiments): 
           [0046]      FIG. 1  shows a bottom perspective view of an exemplary dose indicator. 
           [0047]      FIG. 2  shows a top perspective view of a chassis of the dose indicator of  FIG. 1 . 
           [0048]      FIG. 3  shows a bottom perspective view of the chassis of the dose indicator of  FIG. 1 . 
           [0049]      FIG. 4  shows a side perspective view of the units display unit of the dose indicator of  FIG. 1 . 
           [0050]      FIG. 5  shows a reverse side perspective view of the units display unit of the dose indicator of  FIG. 1 . 
           [0051]      FIG. 6  shows a bottom perspective view of the tens display unit of the dose indicator of  FIG. 1 . 
           [0052]      FIG. 7  shows a side view of the dose indicator of  FIG. 1 , illustrating its operation. 
           [0053]      FIG. 8  shows a perspective view of a second exemplary dose indicator. 
           [0054]      FIG. 9  shows a bottom perspective view of a third exemplary dose indicator. 
           [0055]      FIG. 10  shows another bottom perspective view of the third exemplary dose indicator. 
           [0056]      FIG. 11  shows a top view of the third exemplary dose indicator 
           [0057]      FIGS. 12 a  and 12 b    show vertical cross sections, taken centrally through the back and front of each dose indicator, of the dose indicator of  FIGS. 1 to 7  and a similar, alternative embodiment respectively. 
           [0058]      FIG. 13  shows a cross section through a pressurised metered dose inhaler incorporating a dose indicator as illustrated in  FIGS. 10 and 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0059]    This invention relates to a two-component (with an optional third component) dose indicator for a pMDI. The indicator may be indexed by the displacement generated when a patient actuates a pMDI valve. 
         [0060]    In the embodiment illustrated in  FIGS. 1 to 7 , the dose counter  1  comprises a dose-by-dose counter for a pMDI (that is capable of being configured to count down from 200 to 0) which comprises a chassis  2 , a units display unit  33  and an optional tens display unit  42 . The dose counter  1  can be inserted into a standard pMDI actuator. 
         [0061]    As shown in  FIG. 1  and  FIG. 7 , a dose counter  1  comprises a chassis  2  with a chassis frame  4  of generally annular form. The annular form of the chassis frame  4  is designed to fit snugly into an inhaler actuator to provide support and to prevent deformation in use. Optionally the support may be enhanced by one or more ledges on the actuator for seating a horizontal surface of the chassis, or ribs/grooves to prevent deformation and relative rotation of the chassis frame in the actuator. The chassis  2  incorporates a number of features including springs, hinges and indexing features that are used to actuate and reset the device. The features are formed integrally (i.e. moulded in a unitary piece) with the chassis  2 . 
         [0062]    The dose counter  1  also comprises a units display unit  33  that comprises a units display unit boss  41  and a series of units display unit indexing teeth  38 . A drive pawl  6  formed integrally with the chassis  2  contacts the indexing teeth  38  and indexes the teeth when chassis  2  is pressed against by a valve of a medicament canister pressing downwards on indexing knuckles  26  (not visible in  FIG. 1 ; see  FIG. 2 ) on the top side of the chassis  2 . When pressed downwards, the displacement plate  19  (see  FIG. 2 ) of the chassis  2  moves downwards and hinges  20 , integrally formed with the chassis frame  4  and displacement plate  19 , deform. Spring arms  12  return the chassis  2  to its original position after indexing. 
         [0063]    A non-return arm  8  also formed integrally with the chassis  2  contacts a series of non-return teeth  40  arranged coaxially with the indexing teeth  38 , and prevents backwards movement of the units display unit  33 . A units display unit stop arm  32  integrally formed with the chassis  2  is positioned adjacent to the units display unit boss  41  and guards against the units display unit  33  jumping off its mounting. 
         [0064]    The dose counter  1  also comprises an optional tens display unit  42  in the form of a ring with tens display unit indexing teeth  46  indexed by the tens display unit drive tooth  39  (not visible in  FIG. 1 ; see  FIG. 7 ) and generally prevented from backwards movement by the tens display unit non-return arm  28 . 
         [0065]    Lugs  22  reduce rotation of the dose counter  1  when mounted in the actuator in such a way as to allow the stem post of the actuator to pass through stem post aperture  14 . 
         [0066]      FIGS. 2 and 3  show the chassis  2  from a top view and a side bottom view respectively. In addition to the features visible in  FIG. 1 , the chassis  2  comprises indexing knuckles  26  (see  FIG. 2 ) that are contacted by the valve of a medicament canister when it is displaced downwards to actuate the metered dose valve to dispense a metered dose. As discussed above, upon actuation the displacement plate  19  moves downwards and the hinges  20  deform. The spring arms  12  are resilient and resist displacement and return the displacement plate  19  to its original position after actuation. 
         [0067]    Thus, an indexing element is attached to a displacement plate  19  that is anchored to a chassis frame  4  at one end by two hinges and at the other end by two spring arms  12  that are also anchored to the chassis frame  4 . The two spring arms  12  have a long active length in order to reduce stress concentration. This is advantageous because it reduces strain in the springs over time. 
         [0068]    Having the spring arms  12  separate from the hinges is also advantageous, as each feature is only required to perform a single function. 
         [0069]    In alternative embodiments, the hinges could be used to provide the spring force, but due to a short active spring length the stresses and strain in the hinges would be higher. 
         [0070]    In an alternative embodiment, the hinge means may be provided by one or more springs. 
         [0071]    The units display unit  33  is mounted on the units display unit axle  18 , which is angled at an acute angle with respect to the chassis  2  to take account of the arcuate movement of the drive pawl  6  owing to its position distal to the hinges  20  on the displacement plate  19 . The chassis frame  4  includes tens display unit clips  10  and tens display unit locating ledge  24  to mount the tens display unit  42 , and zero stop arm  16 . 
         [0072]      FIGS. 4 and 5  show the units display unit  33 . The units display unit  33  is generally circular in end view and comprises two coaxial sets of gear teeth: units display unit indexing teeth  38  and units display unit non-return teeth  40 . The units display unit indexing teeth  38  interact with the drive pawl  6  when the units display unit  33  is mounted on the chassis  2 . The units display unit non-return teeth  40  interact with the non-return arm  8  when the units display unit  33  is mounted on the chassis  2 , thereby preventing return of the units display unit  33  after an indexing stroke. 
         [0073]    The profiles of the indexing teeth  38  and non-return teeth  40  have been designed with a hooked edge that prevents or reduces the chance of the pawls or arms from disengaging or slipping off the tooth during actuation. 
         [0074]    The axle bearing  34  of the units display unit  33  is mounted on the units display unit axle  18  of the chassis  2 . The internal profile of the units display unit  33 , including axle bearing  34 , and the external profile of the units display unit axle  18  are designed to engage closely to allow relative rotational movement without wobble. This may be achieved by close circumferential engagement of the internal profile of the units display unit  33  and the external profile of the units display unit axle  18  over most of the circumference corresponding to positions on the units display unit axle  18  that are axially separated by some distance. This distance is preferably greater than the thickness of the portion of the units display unit  33  that bears indicia. The units display unit axle  18  may be substantially cylindrical, or it may have cylindrical sections of different diameter such that the proximal section is the larger diameter section. The units display unit axle  18  may have a lead-in surface at the distal end to facilitate placing of the units display unit  33 . The units display unit  33  may be prevented from axial translation by the units display unit stop arm  32  protruding from the displacement plate  19 . 
         [0075]    An advantage of embodiments of the invention is achieved because the drive means is adapted to engage the first display unit on a curved path, the drive means being driven by a force starting from outside the circumference of the first display unit. This improves the stability of indexing when the units display unit  33  is mounted on the chassis  2  because it allows freer movement of the drive pawl  6  past the display unit  33  without advancing an additional, unwanted count. In the rest position, the drive pawl  6  sits above the first of the units display unit  33  indexing teeth  38  and the non-return arm  8  is engaged with the first of the units display unit non-return teeth  40  (that prevent reverse rotation of the units display unit  33 ). 
         [0076]    Preferably the drive pawl  6  and non-return arm  8  act at opposite sides of the units display unit axle  18 , which allows less stringent tolerance requirements for the dimensions of the axle  18  and axle bearing  34 . 
         [0077]    The units display unit  33  has on its face a units display surface  36  with a plurality (ten numerals 0 to 9 in the illustrated embodiment) of units indicia  37  to indicate the remaining doses. 
         [0078]    Between the units display unit indexing teeth  38  and units display unit non-return teeth  40 , there is a tens display unit drive tooth  39  that, when the tens display unit is fitted to the dose indicator, drives the indexing teeth of the tens display unit once per cycle of the units display unit  33 . In the embodiment of  FIG. 4  with ten drive teeth  38 , the tens display unit would be driven once every 10 cycles. 
         [0079]    The units display unit  33  has been designed such that it can be injection moulded without the requirement for a side action in the moulding tool. This is advantageous, as it will reduce the capital cost of tooling and reduce the risk of flash on components. 
         [0080]      FIG. 6  shows the tens display unit  42  which is of generally annular form with 21 tens display unit indexing teeth  46  evenly distributed around the circumference of the tens display unit  42 . The tens display unit drive tooth  39  has been given a rounded leading edge to ensure that the point contact with the tens display unit indexing teeth  46  has a high incident angle for as long as possible. An angled edge has been provided on the trailing side of the drive tooth  39  and the leading edges of the tens display unit indexing teeth  46  to reduce the chances of a double tens count occurring whilst maximizing the overlap between these teeth. 
         [0081]    A zero stop  44  (in the form of a boss) protrudes from the tens display unit  42  and interacts with the zero stop arm  16  of the chassis  2  at the end of the life of the dose indicator i.e. when the maximum number of counts has been made, e.g. when the displayed indication reaches zero. 
         [0082]    The tens display unit  42  has a tens display unit display surface  48  which rotates as the tens display unit  42  is indexed.  FIG. 6  shows the tens display unit display surface  48  as having a series of indentations  49 . In a more preferred embodiment, these would be replaced by tens indicia (not shown), e.g. in the form of a sequence of numerals “20”, “19”, . . . down to either “00” or “0” or a blank. These numerals, and those of the units indicia  37 , may advantageously be produced by hot foil printing, moulding, embossing, laser marking, or other suitable means. A viewing cut out  30  in the chassis frame  4  of the chassis  2  allows the juxtaposition of the indicia on the tens display unit  42  and those from the units display unit  33  to be seen, such that together they display the count or indication of doses (e.g. of remaining doses). 
         [0083]    The tens display unit  42  has a rim on its outermost edge which acts as a bearing surface whilst ensuring that the printed display cannot rub against the inside wall of the chassis  2 . The tens display unit  42  is located centrally in the chassis  2  by the bearing rim on the outermost surface. It is located axially by a series of clip and location features  10 ,  24  on the chassis  2 . 
         [0084]    The tens display unit non-return arm  28  interacts with the tens display unit indexing teeth  46  and prevents rotation in the reverse direction and restricts rotation in the drive direction except when receiving an impulse from the tens display unit drive tooth  39  on the units display unit  33 . 
         [0085]    The tens display unit  42  has been designed such that it can be injection moulded without the requirement for a side action in the moulding tool. This is advantageous, as it will reduce the capital cost of tooling and reduce the risk of flash on components. To assemble the dose counter  1 , the units display unit  33  is mounted on the units display unit axle  18  on the chassis frame  4 . The tens display unit  42  is then hooked under the tens display unit locating ledge  24  and pushed past the two tens display unit clips  10 . Once assembled, the dose counter  1  can then be inserted into an actuator as an assembled unit. 
         [0086]      FIG. 7  shows the dose counter part way through actuation. During operation of the dose counter  1  upon actuation of the pMDI valve, the displacement plate  19  bends at its hinges and follows a generally arcuate displacement path. The drive pawl  6  also follows an arcuate path. The drive pawl  6  is angled into the units display unit indexing teeth  38 , to further help secure engagement and to reduce the chance of the drive pawl  6  unintentionally disengaging from the units display unit indexing teeth  38 . 
         [0087]    The engagement of the drive pawl  6  with the units display unit indexing teeth  38  advances the display of the units display unit  33  by one count, and the drive pawl  6  then continues its travel as far as it continues to be driven by the user, up to the limit of travel of the pMDI valve. The rotation of the units display unit  33  by one count results in the non-return arm  8  being forced to flex and to ride over the next one of the units display unit non-return teeth  40 . 
         [0088]    On the return stroke, the spring force of the spring arms  12  causes the drive pawl  6  to return to its original, rest position. The non-return arm  8  engages with the next of the units display unit non-return teeth  40 , thus preventing reverse rotation of the units display unit  33 . Since the units display unit  33  is unable to rotate, the drive pawl  6  is forced to ride over the next of the units display unit indexing teeth  38  and return to its rest position. 
         [0089]    On a tens count (e.g. for a displayed count changing from “190” to “189”), as the counter is indexed the rotation of the units display unit  33  causes the tens display unit drive tooth  39  (on the units display unit  33 ) to engage with tens display unit indexing teeth  46 . The tens unit display unit non-return arm  28  resiliently distorts under the driving force, and once the stroke is completed it detains the tens display unit  42  on the next of the tens display unit indexing teeth  46 . 
         [0090]    Once the dose counter  1  reaches a display of zero, the zero stop arm  16  on the chassis frame  4  and zero stop  44  on the tens display unit  42  come into engagement and prevent further rotation of the tens display unit  42 . Interference between the last of the tens display unit indexing teeth  46  and the tens display unit drive tooth  39  on the units display unit  33  in turn prevents the units display unit  33  from rotating further. Due to the resilient flexibility in the chassis  2 , spring arms  12  and drive pawl  6 , the inhaler can still be actuated once the stop-at-zero features become engaged. 
         [0091]    The indexing of the units display unit  33  and tens display unit  42  occurs on the down-stroke of the actuation. This is advantageous, as work on the dose counter  1  is being carried out by the user (rather than, for example, by spring return force, which would be limited). This leads to a more reliable device, as the function of the spring arms  12  is only to reset the counter. 
         [0092]    Due to the properties required for the spring arms and ratchets, the chassis  2  is preferably made from polyoxymethylene (also known as POM or acetal) or material with similar properties (high stiffness, low friction and good dimensional stability). 
         [0093]    Preferably the acetal is an acetal homopolymer. POM and materials with similar properties tend to be opaque hence the need for a cut out portion in the chassis and corresponding window in the actuator body so that the indicia are visible. 
         [0094]    The chassis  2  has been designed such that it can be injection moulded without the requirement for a side action in the moulding tool. This is advantageous, as it reduces the capital cost of tooling and reduces the risk of flash on components. 
         [0095]      FIG. 8  shows an alternative embodiment of a dose indicator  101  part way through actuation, comprising a chassis  102  with a chassis frame  104  of generally annular form. The embodiment of  FIG. 8  also has spring arms  112 , a drive pawl  106  driving the indexing teeth  138  of a units display unit  133 , and a tens display unit  142  with tens display unit indexing teeth  146 . The units display unit has non-return teeth  140  that interact with the non-return arm  108  of the chassis  102  and, in this embodiment, a boss protrusion  143  on the boss  141  which on pressing down of the displacement plate  119  during actuation interacts with a forked deadstop  145  moulded integrally with the displacement plate  119 . This is advantageous because is prevents the springs  112  and hinges being overstressed during use, e.g. if the user presses with a force significantly in excess of that needed to operate the dose indicator and to actuate the valve. 
         [0096]    As shown in  FIG. 9 , a third embodiment of a dose counter  201  according to the invention comprises a chassis  202  with a chassis frame  204  of generally annular form. The chassis  202  incorporates a number of features including springs, hinges and indexing features that are used to actuate and reset the device. These features are formed integrally with the chassis  202 . 
         [0097]    The dose counter  201  is somewhat similar to that shown in  FIG. 1 , so only those features that differ will be described. 
         [0098]    A displacement plate  219  is attached to the chassis  202  by two hinges  220 . The hinges  220  have bridge-shaped features to direct most of the flexing to the thinner regions at the apex of each bridge. The displacement plate  219  is also attached to the chassis  202  by two spring arms  212 , joined to the chassis  202  on the opposite side to the hinges, and joined to the displacement plate  219  by lateral extensions to the plate that are just to the side of the stem post aperture  214  further from the hinges  220 . The spring arms  212  are designed to flex transversely to the axis of the hinges, to provide additional return force for the displacement plate  219  without any twisting of the spring arms. The hinges  220  are slightly further forward towards the units display unit  233  than are the hinges  20  of the embodiment in  FIG. 1 : this reduces the distance of pMDI metering valve stem movement needed to cause the dose counter to index. The displacement plate  219  has an integral drive pawl  206 , and is formed integrally with the spring arms  212 , hinges  220  and chassis  202 . The displacement plate  219  does not have a units display unit stop arm, however, as this feature  216  is provided instead on the tens display unit locating ledge  224  of the chassis frame  204  ( FIG. 11 ). The design provides for the boss  241  to sit close to the actuator valve stem post of the inhaler (not shown) when the dose counter is assembled into the inhaler. 
         [0099]    The units display unit  233  has a single set of gear teeth  238 , corresponding to the indexing teeth  38  (see e.g.  FIG. 1 ), that also serve to engage a non-return arm  208  and so also act as non-return teeth. When it is assembled into the chassis  202 , the units display unit  233  is retained on the chassis  202  because the non-return arm  208  goes around the units display unit  233  and engages the gear teeth  238 . 
         [0100]    During a return stroke, the drive pawl  206  must ride over a tooth while the non-return arm  208  prevents the units display unit  233  from rotating backwards. The gear teeth  238  are shaped such that the long side of each tooth has a convex surface. The component of force from the flexing drive pawl  206  that acts to resist return of the displacement plate  219  is thereby reduced later in the travel when the force applied by the spring arms  212  is reducing: return is less hindered by the drive pawl  206  having to ride over a gear tooth with a convex surface. 
         [0101]    The chassis  202  has downwardly directed legs  247  on either side of the chassis and integrally formed with it, for precisely positioning the dose counter in an inhaler actuator. The legs have vertical grooves  248 , which may engage internal vertical ribs of the actuator to prevent any rotational movement of the dose counter. The legs have feet  249  that are turned inwards to form clips that locate in recesses located on the floor of a pMDI actuator (not shown). Alternatively, the feet may locate on top of ribs or other features in the actuator. The dose counter may advantageously be located in the actuator by an interference (friction) fit; alternatively clipping features may be provided. 
         [0102]      FIG. 10  shows a view in which the tens display unit drive tooth  239  is about to engage a tens display unit indexing tooth  246   b . The angled forward surface of each indexing tooth  246  combined with the relative planes in which the tens display unit  242  and units display unit  233  lie, ensure that the tens display unit drive tooth  239  has clearance whilst having an adequate vertical rear surface of the indexing tooth  246   b  to engage with to rotate the tens display unit  242  to just past the desired amount. Thence the tens display unit non-return arm  228  (not visible in  FIG. 10 : see  FIG. 9 ) will adjust the position of the tens display unit, e.g. by slight back rotation, to align indicia thereon with the viewing cut out  230  (see  FIG. 2  for the corresponding part  30 ). 
         [0103]      FIG. 11  shows zero stop arm  216  of the chassis  202  engaging the zero stop  244  of the tens display unit  242 . Once this point of travel is reached, a further count of nine can be made on the units display unit  233 . After that, the tens display unit drive tooth  239  is stopped by the last indexing tooth  246 , and the units display unit  233  can no longer rotate. Downward movement of the displacement plate  219  causes the drive pawl  206  to engage a tooth  238  that does not move, due to the stopping of the tens display unit. Under this load, the drive pawl  206  deflects allowing additional doses to be taken upon this and subsequent actuations with minimal additional resistance to actuation. The drive pawl  206  is angled (relative to a vertical line) both away from the axis of the hinges  220  and also inwardly towards the axis of the tens display unit  242 . 
         [0104]      FIGS. 12 a  and 12 b    respectively show the embodiment of  FIGS. 1 to 7  and an alternative embodiment, similar except in the detail of the mounting means for mounting the units display unit.  FIG. 12 a    shows the units display unit  33 , the units display unit axle  18  and the axis of the axle X. The external surface of the axle is shown in close engagement with the internal surface  35  of the units display unit axle bearing  34 , for a substantial part of the length of the axle bearing.  FIG. 2  shows that one side of the axle  18  has a flat, which avoids the possibility of compressing air between the axle and bearing during assembly and thereby making them susceptible to separation. In  FIG. 12 b   , the units display unit axle  18  has two circumferential engagement surfaces  51 ,  53  for engagement, at least for most of the circumference, with an internal double-cylindrical profile  55  of the units display unit  33 . The two surfaces are separated along the axis of the axle  18  to provide stability against wobble. A slight lead-in (e.g. a radiussed or chamfered edge) is provided on the distal end (the end that is engaged deepest into the units display unit) of the axle  18  to help with assembly. 
         [0105]      FIG. 13  shows a pressurised metered dose inhaler (pMDI)  260  comprising a canister  263  including a metered dose-dispensing valve  265  mounted via a ferrule  264  on to the neck of a vial  272  component of the canister  263  with an elastomeric gasket  266  to create a seal. The inhaler  260  comprises an actuator  261  including a mouthpiece  268  (in an alternative form, suitable for nasal drug delivery, the actuator may comprise a nosepiece rather than a mouthpiece). The canister  263  is placed within the actuator  261  by inserting the valve stem  269  of the valve  265 , which protrudes outside the ferrule  264 , into a stem socket  273  of a stem post  262  of the actuator  261 . The valve stem  269  has a dispensing passage that allows for passage of substance from a metering chamber of the valve  265  out through the valve stem  269  and actuator mouthpiece  268  (or nosepiece) to the user. To actuate (fire) the valve  265  to deliver a dose of medicament formulation, the valve stem  269  is pushed inwardly relative to the aerosol container from its resting position, allowing formulation to pass from the canister through the valve  265  and through the actuator nozzle  270  and then out to the patient. The actuator  261  has a dose counter  201  mounted around the stem post  262 . The dose counter  201  has a units display unit  233 , a tens display unit  242  a chassis frame  204  and a displacement plate  219 . During actuation, the canister  263  is pressed down by the user. As the canister  263  is pressed into the actuator  261 , the ferrule face  271  surrounding the valve stem  269  contacts indexing knuckles  226  and displaces the displacement plate  219 . The result is that the drive pawl ( 206 ; not visible in  FIG. 13 ) indexes the units display unit  233  in the manner described above.