DOSE COUNTING MECHANISM

The present invention relates to dose counting mechanisms for medicament inhaler devices, for example metered-dose inhaler (MDI) devices. In particular, the invention relates to a counter comprising a counting component (20,620), a locking element (46,646) for resisting movement of the counting component (20,620), and a distinct driving element (70,670) for driving movement of the counting component (20,620). The locking and driving elements are actuated by movement of a common element to move the locking element (46,646) out of engagement with the counting component (20,620) and to move the driving element (70,670). The driving element (70,670) applies a motive force to the counting component (20,620) before the locking element (46,646) fully disengages from the counting component (20,620).

The present invention relates to dose counting mechanisms for medicament inhaler devices, for example metered-dose inhaler (MDI) devices. In particular, the invention relates to an improvement of the indexing of a rotating wheel forming at least a part of the mechanical dose counting mechanism.

Accurate and reliable counting of doses is an important consideration for inhaler devices of all types, so that a user can be confident of the number of doses remaining for delivery. Counters can be broadly categorised into electronic dose counters and mechanical dose counters. Electronic counters are typically used where large numbers of doses need to be counted, but mechanical counters have the benefit of needing no power supply to register or display a dose count, so are generally preferred wherever possible.

Where a mechanical counter is required to count a large number of doses, multiple linked count wheels or drums are often employed to display the count. This avoids having to provide a physically large display surface on a single element of the counter, because each wheel need only display digits 0-9, and maybe end-of-life indicators/positions. A problem can arise, however, in ensuring that the first wheel, displaying the units value of the count, is sufficiently advanced/indexed during use of the device.

For a press-and-breathe pressurised metered-dose inhaler (pMDI) device, the indexing mechanism should be operated as part of the normal use-sequence. This generally means that the counter will be actuated by the movement of the medicament canister between its rest position and its fire point. This movement occurs over a relatively short distance, typically between 2 mm and 3 mm. For a counter where individual doses are registered by movement of a units wheel in a multi-wheel counter, the small movement must effect a relatively large rotation of 36° of the units wheel (i.e. a tenth of a rotation).

The timing, appearance, and accuracy of this indexing has potential implications for the user experience. Slowly indexing the counter throughout the act of depressing the canister can be slightly confusing to the user, especially if the counter is front-mounted and thus potentially visible during use. The partial indexing that may result can also be confusing, particularly if the counter remains in that state once the user has (even if just temporarily) stopped interacting with the device.

To avoid these problems, most dose counters only start to index at a defined commitment-point during the depression of the canister. There will also be a fire-point, i.e. a distance of canister depression at which the canister fires. Known inhaler devices are typically unable to tie these two points to the same depression distance unless some form of firing sensor is provided, but it is important that they are situated as close to each other as possible. However, care must be taken to ensure that, in all tolerance conditions, the counting commitment-point does not occur after the fire-point. After the commitment-point the dose counter will tend to complete an index, either during depression or on return to the rest position of the canister, regardless of whether the user continues depressing the canister or just releases it. Counting of a dose when there has been no delivery is undesirable, but delivery of a dose without indexing the counter should be minimised as far as is reasonably possible.

A counter indexing system will require energy-input, which can come directly from the user (in the form of increased canister-depression-force) and/or be harvested from unused force applied by the canister spring as the canister returns to its rest position. The lack of information surrounding the force-requirements for the canister spring may present reliability risks for the latter option, rendering it undesirable. However, care must be taken to ensure that the peak force experienced by the user during operation, if user force is directly harvested on the downward stroke, does not exceed a specified maximum force.

According to a first aspect of the invention there is provided an indexing mechanism as defined in the appended claim1. Further optional features are recited in the associated dependent claims.

The mechanism comprises a counting component, a locking element for resisting movement of the counting component and a distinct driving element for driving movement of the counting component. The locking and driving elements have an initial position in which the locking element is engaged with the counting component, and the locking and driving elements are actuated by movement of a common element to move the locking element out of engagement with the counting component and to move the driving element, wherein the driving element applies a motive force to the counting component before the locking element fully disengages from the counting component. Engagement of the first element with the counting component may prevent movement of the counting component.

WO 2012/150427 discloses a dose counter mechanism where an actuator2,102,202drives an index wheel18,118,218to advance a count wheel26,126,226once for every ten doses released. A hook10,210on the actuator drives the index wheel, and an engagement feature17,217on the actuator holds the count wheel in position between actuations. Both the hook and the engagement feature are moved simultaneously as the actuator is moved, so that engagement feature disengages from the count wheel as the hook moves towards engagement with the index wheel.

The count wheel is free to advance when the hook engages and drives the index wheel.

AU 2016204147 relates to a dose counter for a metered dose inhaler. As a canister is initially depressed, an actuator240moves anticlockwise to the position shown inFIG. 10b. This moves a first pawl242into engagement with a wheel230as a second pawl244moves away. Continued depression of the canister causes rotation of the wheel230to the position shown inFIG. 10c, which represents the end of a compression/firing stroke of the canister. On the return stroke, as shown inFIG. 10d, the first pawl242moves clear of the wheel230, and continued rotation of the wheel is then driven by engagement of the second pawl244during the rest of the rebound stroke until the mechanism reaches the position shown inFIG. 10e. The two pawls are never simultaneously engaged with the wheel.

The driving element of the present invention may move into contact with the counting component from the first position to apply the motive force, or may be pre-engaged and apply a force in the first position prior to movement of the common element. Movement of the counting element may be driven by movement of the driving element from the first position.

The mechanism may incorporate some means of storing or charging energy behind or within the driving element. For example, the driving element may be provided on a resilient arm. The resilient arm may be deformed on/during engagement of the driving element with the counting component, or with a chassis or some other feature of a device housing the mechanism, such as an inhaler device, to store potential energy in the resilient arm.

The resilient arm may comprise a hinged or bent section. The hinged or bent section may be deformable or collapsible to adjust the spring rate of the resilient arm, or to provide a specific region with a different spring rate.

The resilient arm may comprise an abutment feature, for example a slot, loop, slot or similar, to resist deformation of the hinged or bent section in a first direction. This may provide a higher spring rate/resistance to deformation in said first direction than in one or more other directions.

The driving component may be out of engagement with the counting component in the initial position, and actuation of the driving element by the common element may then move the driving element into engagement with the counting component to apply a motive force to the counting component.

The driving element may engage with a slot in the counting component.

The slot in the counting component may comprise a cam surface for engagement with the driving element. The slot in the counting component may comprise first and second cam surfaces for engagement with the driving element. The first and second cam surfaces may be engaged in opposite movement directions of the of the driving element, so as to deform the resilient arm in opposite directions during use. Different spring rates/resistances to deformation may be provided, for example by an abutment feature as previously described.

The indexing mechanism may further comprise a restoring element providing a biasing force to urge the locking and/or driving element back to the initial position. Providing different spring rates as discussed may reduce the biasing force needed to urge the locking and/or driving element back to the initial position. The restoring element may comprise a spring, for example a metal or polymer spring.

The spring may be a leaf spring and may be part of an integrally formed component which also comprises the locking and/or driving element.

The locking element may engage with a recess in the counting component.

The locking and driving elements may be provided on separate components such that the indexing mechanism may comprise an indexing actuator and a locking actuator, or the locking and driving elements may provided on a common component such that the mechanism comprises a single indexer component.

The counting component may be a rotatable component and movement of the counting element may comprise rotation. The rotatable component may be a count wheel of a dose counter.

Movement of the common element may comprise depression of the common element, for example by a user. The common element may be an MDI canister.

The invention also provides a method of indexing a counter as defined in the appended claim22. Further optional features are recited in the associated dependent claims.

The method comprises sequential steps of:A. engaging a locking element with a counting component to prevent movement of the counting component; and subsequentlyB. moving a driving element to apply a motive force the counting component; andC. moving the locking element out of engagement with the counting component.

The locking and driving elements are moved in steps B and C by movement of a common element, the driving element applies the motive force to the counting component before the locking element fully moves out of engagement with the counting component and the driving element drives movement of the counting component once the locking element is fully out of engagement with the counting component.

The locking and driving elements may be moved simultaneously in steps B and C. Step B may comprise storing energy to drive movement of the counting component.

The counting component may be rotatable and the driving element may drive rotation of the counting component. The driving element may further hold the counting component in a rotated position after driving rotation.

The method may comprise the further step of:D. moving the locking element back into engagement with the counting component. The locking element may be moved in step D by a spring biasing force.

Movement of the locking and/or driving element may comprise rotation around a pivot.

Movement of the common element may comprise depression of the common element.

The method may be implemented using an indexing mechanism as previously described.

An exploded view of a press-and-breathe pressurised metered-dose inhaler (pMDI) device2is shown inFIG. 1. The pMDI2comprises a rear housing/body4, for receiving a canister6of medicament with a valve stem at a lower end16as shown, and a front housing8. Components of a dose counter10are shown between the front and rear housings4,6. The individual components include a counter wheel20, a locking actuator40and an indexing actuator60, all of which will be described more fully later.

The front housing8further comprises a window12through which a portion of the counter wheel20can be viewed, and a mouthpiece14providing fluid connection to the medicament canister6when the pMDI is assembled. The precise internal geometry of the rear housing4to provide the fluid communication and facilitate release of a dose from the canister6is unimportant to the present invention, and various suitable configurations will be familiar to a skilled reader. A mouthpiece cover18for closing and protecting the mouthpiece14is also provided, as is conventional.

A rear perspective view of the counter wheel20is shown inFIG. 2. The counter wheel20comprises a generally flat disc portion22and a charging feature24raised from the rear surface of the disc portion22. A centrally positioned mounting hole26is provided for mounting the counter wheel20on a peg provided in the rear housing4.

The charging feature24comprises ten evenly spaced curved fingers28defining ten slots30therebetween. Each curved finger28provides a first camming surface32and a second camming surface34, with each slot30provided between the first camming surface32of one curved finger28, and the second camming surface34of an adjacent curved finger28. The curved fingers28are shaped so that each slot30is wider at an end that is nearest the outer circumference of the counter wheel20.

The outer circumference of the disc portion22of the counter wheel20is provided with ten evenly spaced locking recesses36, each of which comprises one chamfered edge38, angled to the radius of the counter wheel20.

The various features on the rear of the counter wheel20, specifically the first and second camming surfaces32,34and locking recesses, cooperate with parts of the locking actuator40and indexing actuator60to provide an indexing system in accordance with the present invention.

As shown inFIG. 3, the locking actuator40comprises a central mounting pin42to be received in recesses in the front and rear housings4,8to provide a pivoting connection. A substantially rigid arm44extends from the mounting pin42, and a locking peg46is supported on an elevated part48of the substantially rigid arm44. The locking peg46extends laterally from the elevated part48of the substantially rigid arm44, generally parallel to the mounting pin42. Also provided on the substantially rigid arm44, but spaced from the locking peg46is a bearing surface50. A spring arm52also extends from the mounting pin42, generally perpendicular to the substantially rigid arm44.

The indexing actuator60is shown inFIG. 4. Like the locking actuator40, the indexing actuator60comprises a central mounting pin62to provide a pivoting connection in the front and rear housings4,8, and a substantially rigid arm64extends from the mounting pin62and provides a bearing surface66. The indexing actuator60also provides an indexing arm68, generally perpendicular to the mounting pin62, with an indexing peg70provided at its upper end remote from the mounting pin62. A spring arm72is provided as in the locking actuator44previously described.

The indexing arm68comprises a hairpin bend74, hereafter referred to as a hairpin74, part way along its length, and is thicker at a lower end, adjacent the mounting pin62, than at the upper end, adjacent the indexing peg70. A diagonal brace76is also provided between the substantially rigid arm66and the indexing arm68, at a position between the mounting pin62and the hairpin74. A first part of the indexing arm68therefore has a relatively high rigidity, and a second part is more easily deformable.

FIG. 5shows the assembly of the counter wheel20, locking actuator40and indexing actuator60within the rear casing4of the inhaler2to provide a complete dose counter mechanism. In the described embodiment, each of the counter wheel20locking actuator40and indexing actuator60is moulded as a single piece component in a plastics material.

Each of the locking actuator40and indexing actuator60is pivotally mounted to the rear housing4at its respective mounting pin42,62, and the free ends of the spring arms57,72are bearing against an inner surface of the rear housing4. The counter wheel20is mounted via its central mounting hole26so at to be rotatable relative to the rear housing4.

The lower end16of a canister6can be seen just above the bearing surfaces50,66of the locking actuator40and indexing actuator60. In this position, the indexing peg70of the indexing actuator60is adjacent but spaced from the end on one of the curved fingers28, and the locking peg46of the locking actuator40is engaged with one of the locking recesses36provided around the edge of the counter wheel20. The chamfered edge38at one side of each of the locking recesses36can also be seen clearly inFIG. 5.

Operation of the dose counter will now be described with reference toFIGS. 6A to 6F. The locking actuator40and indexing actuator60are both rotated from their rest positions during use by movement of the canister6, and both are rotated back to their rest position after indexing by their respective spring arms52,72, which are anchored on the caseworks/rear housing4of the inhaler device2.

InFIG. 6A, the cannister6has been depressed a small amount so that its lower end16has moved vertically downwards to bear on the bearing surfaces50,66of the locking actuator and indexing actuator40,60. This rotates the substantially rigid arm64of the indexing actuator60clockwise around its mounting pin62and rotates the substantially rigid arm44of the locking actuator40anticlockwise around its mounting pin42. Rotation of the substantially rigid arm64of the indexing actuator60causes corresponding rotation of the indexing arm68so that the indexing peg70engages with the first camming surface32of a slot30of the counter wheel20. The simultaneous rotation of the substantially rigid arm44of the locking actuator40causes the locking peg46to start moving out of the locking recess36. The spring arms52,72are prevented from rotating by the walls of the rear housing4, so they resiliently deform to provide a restoring force to the locking actuator and indexing actuator40,60.

Further downward movement of the lower end16of the canister6further rotates the indexing actuator60, causing the indexing peg70to move along the first camming surface32towards the centre of the counter wheel20. The locking actuator40also continues to rotate, but the locking peg46remains in engagement with a locking recess36. Accordingly, the counter wheel20is prevented from rotation, and the indexing arm68resiliently deforms as the indexing peg70moves along the first camming surface32. As shown inFIG. 6Bthe locking peg46is just moving clear of a locking recess36, and the hairpin74has opened out as part of the deformation of the indexing arm68.

The length of the indexing arm68locates the drive peg70relatively far from the mounting pin62of the of the indexing actuator60, which serves to amplify movement of the drive peg70during operation.

FIG. 6Cshows the dose counter part-way through an indexing operation. The locking peg46has moved clear of the locking recess36to an unlocked position so that the counter wheel20is free to rotate. Energy stored by the resilient deformation of the indexing arm68can then drive the anticlockwise rotation of the counter wheel20, moving the indexing peg70further along the first camming surface32. The amplified movement of the indexing peg70helps to ensure that sufficient elastic potential energy is stored in the indexing arm68to power an index and advance the counter wheel20the required distance.

The point at which the locking peg46clears the locking recess36to unlock the counter wheel20represents a commitment point before which depression of the canister6will not result in a dose being counted. The location of the locking peg46relatively close to the mounting pin42of the locking actuator40helps to minimise variation of this commitment point due to manufacturing tolerances.

The rotation of the counter wheel20continues until, as shown inFIG. 6D, the hairpin74returns to its undeformed position. The indexing peg70moves into an end portion31of the slot30which is angled relative to the remainder so that further movement of the indexing peg70towards the centre of the counter wheel20imparts no rotational drive to the counter wheel20, and indeed maintains the rotational position of the counter wheel20. This provides some dwell time at the end of an indexing operation. The locking peg46, at this point, is aligned with the next locking recess36′ around the circumference of the counter wheel20.

When pressure on the canister6is released, its lower end16begins to move vertically upwards clear of the bearing surfaces50,66of the locking actuator40and indexing actuator60, as shown inFIG. 6E. The energy stored by resilient deformation of the spring arms52,72causes clockwise rotation of the locking actuator40and anticlockwise rotation of the indexing actuator60around their mounting pins42,62. The clockwise rotation of the locking actuator40causes the locking peg46to engage with the chamfered edge48of the next locking recess36′, and then move into a locked position in the next locking recess36′ to again resist rotation of the counter wheel20. The chamfered edge38provides a lead-in feature to help account for any slight misalignment of the counter wheel20. The anticlockwise rotation of the indexing actuator60causes the indexing peg70to move radially outwards along the slot30. The indexing peg70engages with the second camming surface34of the slot30during this movement, and this causes a compression in the hairpin74of the indexing arm.

FIG. 6Fshows the end of an indexing operation, with the mechanism essentially returned to its rest configuration as shown inFIG. 5, but advanced by one dose. The continued rotation of the locking actuator40and indexing actuator60has fully engaged the locking peg46with the recess36′ in the counter wheel20and moved the indexing peg70clear of the end of the second camming surface24. The energy stored during compression of the hairpin74causes the indexing peg70to spring up past the end of the second camming surface24ready to engage with the next slot30′ of the counter wheel20. Compressing the indexing arm68also counteracts the effects of applying tensile stress during indexing, ensuring that any creep effects are minimised.

It will be appreciated that the operation described inFIGS. 6A-6Fcorresponds to one full depression and release of the canister6, i.e. the delivery of a single dose of medicament. Since the counter wheel20provides ten slots30and ten locking recesses36, ten actuations will result in one full rotation of the counter wheel20.

It will be understood that the indexing arm68can be resiliently deformed and stressed during operation by the camming surface32,34via compression or extension of the hairpin74or simply by bending in the arm68. Although primarily designed to rely on deformation at the hairpin74, it is likely that some bending of the arm68will also occur. Indeed, it is possible to design an alternative indexing arm that will store elastic potential energy by deforming more equally in both of these modes simultaneously.

The applicant has also investigated the possibility of using different deformation modes and/or directions to achieve differential spring forces in an indexing arm during its two stages of being stressed. This would allow, for example, a higher spring force to be provided when an indexing arm is deformed during engagement with the first camming surface32, and a lower spring force to be provided by the same arm during engagement with the second camming surface34. The energy input for the indexing of the counter wheel20needs to be relatively high, to ensure that the indexing operation is reliably completed. In contrast, the spring force during reset of the arm should ideally be as low as possible, since it directly impacts the size and strength of the spring arm required to return the indexing arm under all environmental and/or tolerance conditions, and thus the force that the user must put into depressing the canister6and stressing the spring arm during use.

Some possible alternative indexing actuators for the present invention are illustrated inFIGS. 7 to 11B.

FIGS. 7 and 8show indexing actuators160,260that are broadly similar to the indexing actuator described above. The indexing actuator160ofFIG. 7comprises an alternative hairpin174in the indexing arm168. Essentially, the hairpin174of this first alternative indexing actuator160is rotated relative to that shown inFIG. 4. The remaining components of the indexing actuator160, such as the indexing peg70, mounting pin62, spring arm72and bearing surface66are as previously described.

FIG. 8shows a second alternative indexing actuator260, which illustrates how the dimensions and design of an indexing actuator may be modified according to different packaging constraints. A shorter indexing arm268is provided, with the hairpin274located at the upper end of the indexing arm268immediately adjacent the indexing peg70. The mounting pin262and bearing surface266are longer than those in the previously described indexing actuators60,160. A spring arm72is again included to provide a restoring force as before.

This indexing actuators160,260ofFIGS. 7 and 8do not feature any clear differentiation between the index-energy spring rate (during depression of the canister6) and the reset spring rate. Both modes of use will cause a similar mixture of bending along the length of the indexing arm168,268and extension or retraction of the length of the arm168,268via expansion or contraction of the hairpin feature174,274.

FIG. 9Ashows a front view of a further alternative indexing actuator360, which has a slightly more complex design to provide different spring forces in the two modes of use outlined above. The side view ofFIG. 9Ashows the indexing actuator360as moulded. The design of the lower part of the indexing actuator360, including the mounting pin62, bearing surface66and spring arm72, is essentially the same as that of the indexing actuators60,160shown inFIGS. 4 and 7. The indexing arm368has a more complex design, with two branches368a,368bat an upper end. The indexing peg70is provided at the end of the first branch368a, which incorporates a hairpin374similar to the hairpin74of the first indexing actuator60ofFIG. 4. The second branch368bincludes a lip/end-stop378at its free end.

A perspective view of the same indexing actuator360in its primed condition is shown in the perspective view ofFIG. 9B. The end of the first branch368a, with the end of the indexing arm368comprising the indexing peg70, has been hooked underneath the end-stop378at the end of the second branch368b. The indexing peg70can still move downwards, or towards the mounting pin62, with a relatively low force by contracting the hairpin374. However, the end-stop378prevents the hairpin374from opening/expanding from the position shown inFIG. 9Bso that movement of the indexing peg70relative to the arm368away from the mounting pin62is resisted. As a result of this design, depression of a canister6results in energy storage solely through bending of the indexing arm368as the indexing actuator360is rotated during the indexing operation. This provides a relatively high spring force, which can be reduced if required by including a thinner region380in the indexing arm368, to ensure there is sufficient energy to index the counter. During a return or reset stroke, in the opposite direction, the hairpin374can also collapse to providing a lower overall spring force, meaning that the size and strength of the spring arm72can be minimised.

FIGS. 10A and 10Bshow similar views of a fourth alternative indexing actuator460, which achieves a similar outcome via a different design. Again,FIG. 10Ashows the indexing actuator460as moulded, andFIG. 10Bin its primed condition. In the fourth alternative indexing actuator460a loop478is provided part way up the indexing arm468, and a stop peg482is provided on the end of an extension portion484extending from the indexing peg70at the end of the indexing arm468.

In the primed condition the stop peg482is engaged with the loop478by bending the hairpin474. The engagement of the stop peg482with the loop478essentially performs a similar function to the end-stop378in the third alternative indexing actuator360, providing a cam track to limit the movement of the indexing peg70. During depression of the canister6the indexing peg70cannot move away from the mounting pin62through expanding the hairpin474, because this movement is prevented by the stop peg482and loop478. Movement during the indexing can therefore only be achieved through bending of the indexing arm468as the indexing actuator460rotates. In contrast, the stop peg482can move within the loop478, towards the mounting pin62, during reset. The hairpin474is therefore free to compress in this mode of operation, which provides a relatively lower spring force. As above, this provides a desirable balance of a larger spring force during indexing, and a lower spring force for reset.

A final example showing a fifth alternative indexing actuator560in moulded and primed configurations is provided with reference toFIGS. 11A and 11B. In this embodiment, the indexing arm568can again be considered to split into first and second branches568a,568bat an upper end, with the indexing peg70provided at the end of the first branch568a. A locating peg582projects from an opposite side of the first branch568aaligned with the indexing peg70, and is received in a cam-slot578provided on the second branch568bto limit the movement of the indexing peg70to a single radial line to or from the mounting pin62of the indexing actuator560. The first branch568aalso comprises first and second hinges586,588. The first hinge586is provided at a lower end of the first branch568a, and the second hinge588is provided between two halves of the first branch568aso that the first branch forms a ‘V’ shape. The second hinge588includes an open section590towards its outer side, with the apex of the ‘V’ being provided by two abutting end-stops592.

In use, radial movement of the indexing peg70away from the mounting pin62, while storing up energy for indexing, quickly causes the end-stops592in the second hinge588to engage and ‘lock out’ the hinge588preventing further opening/expansion. Further movement of the pin is possible only by bending the two limbs of the first branch568ato open out the ‘V’. This results in a relatively high spring force, sufficient for the indexing operation.

Radial movement of the indexing pin70towards the mounting pin62, during reset, can be achieved with a relatively lower force, because the end-stops592move apart allowing the two hinges586,588to collapse the V with minimal bending of either limb of the first branch568aso that the indexing pin70can move down the cam slot578under minimal resistance. The necessary restoring force to be provided by the spring arm72is therefore minimised.

It will be understood that the movement of the indexing pin70in the fifth alternative indexing actuator560regulated by the first branch568aof the indexing arm568and the cam slot578. The remainder of the indexing arm568, including the second branch568b, can be made relatively stiff to minimise bending in the arm568, so that the behaviour of the indexing actuator560under load, and in particular the precise position of the indexing pin70, is as predictable as possible.

All of the indexing actuators60,160,260,360,460,560described above are intended to be used with a locking actuator40substantially as shown and described inFIG. 3.

An alternative embodiment602of the invention is shown in an exploded perspective view inFIG. 12, and an assembled side view inFIG. 13. This alternative embodiment602combines the indexing actuator60and locking actuator40of the invention into a single indexer component650. As shown, the alternative embodiment602is in ‘rig’ form for experimental/development purposes. The counter wheel620and indexer650are mounted to a stand604and secured in place by a front plate608, and the indexer650includes a lever666to be operated either by hand or by force-testing equipment, rather than specific features for interacting with a pMDI canister. It will be understood, however, that the arrangement could readily be modified for use in a pMDI device by a skilled reader.

In a similar manner to the counter wheel20ofFIG. 2, the counter wheel620of this alternative embodiment comprises ten evenly spaced curved slots630and ten evenly spaced locking recesses636. The indexer650is broadly ‘J’ shaped, having a generally horizontal top section664providing the lever666and a curved indexing arm668with a flexible end section. The top section664comprises a locking hook646at the end opposite the lever666, and an indexing tooth670is provided at the end of the curved indexing arm668.

As shown in the assembled view ofFIG. 13, the locking hook646is engaged with one of the locking recesses636in the counter wheel620, and the indexing tooth670is positioned below the counter wheel620. The mounting pivot626of the indexer650is located adjacent the locking hook646and is spaced by a greater distance from the indexing tooth670so that rotation of the indexer650will cause a greater movement of the indexing tooth670than the locking hook646.

In use, a downward pressure is applied to the lever666to cause anticlockwise rotation of the indexer650. The anticlockwise rotation causes a locating peg682on the indexing arm668to move over a small camming surface694on the front plate608, flexing the end of the indexing arm668towards the pivot626in the direction indicated by arrow696. Continued rotation of the indexer650brings the indexing tooth570into contact with an angled surface of one of the slots630which acts as a first camming surface632on the counter wheel620. The locking hook646remains engaged with a locking recess636at this stage, so that continued anticlockwise rotation of the indexer650results in the indexing arm668flexing further in the direction of arrow696.

When the lever666has been depressed sufficiently to rotate the locking hook646clear of the locking recess636in the counter wheel, the spring force stored in the indexing arm668will then be transferred to the counter wheel620via the indexing tooth670, rotating the counter wheel620anticlockwise. The disengagement of the locking hook646defines a commitment point that would, in practice, be coordinated with the release of a dose from a pMDI canister6.

Anticlockwise rotation of the counter wheel620is limited by engagement of the indexing tooth670with a second camming surface634on the opposite side of the slot630from the first camming surface632. Continued downward pressure on the lever666, indicative of further downward movement of a pMDI canister6, results in continued rotation of the indexer650and moves the indexing tooth within the slot630. This maintains a rotational position of the counter wheel620and provides some dwell time at the end of an indexing operation.

During subsequent rotation of the indexer650in a clockwise direction, the engagement of the indexing tooth670in the slot630initially maintains the rotational position of the counter wheel620until the locking hook646engages with the next locking recess636′. A chamfered edge638is provided so that the engagement can to help account for any slight misalignment of the counter wheel620if necessary.

With the counter wheel620again locked against rotation, continued movement of the indexing tooth670along the second camming surface634as the indexer rotates clockwise serves to flex the indexing arm668in the opposite direction to arrow696. This stores energy in the indexing arm668so that is springs past the end of the slot630once disengaged, ready for a subsequent indexing operation. A coil spring may be provided at the pivot626to store energy during the anticlockwise rotation and drive the clockwise rotation of the indexer650. In a fully realised system, other resilient/spring biasing means, such as a torsion spring or integrated leaf spring(s), may be provided to provide a restorative force to the indexer650.

It should be understood that the embodiments described above comprise a single counter wheel for simplicity. The principles described would be scalable for a larger number of doses by using larger wheels with a greater number of slots30,630and locking recesses46,646, or by employing multiple linked count wheels with the described counter wheel20,620providing the unit count.

As noted above, the distance of translation of the canister during depression is relatively small compared to the required movement of the dose-counter wheel. Therefore, it may be beneficial for the distance of movement of the feature that interacts with the counter-wheel, and enables the component to store the required energy for rotation of the counter wheel, to be ‘geared up’ or otherwise amplified. This will help to provide enough movement to effect the necessary index, but may also increase the tolerances on the position of that feature at any given moment. To counteract the poor positional tolerances on this indexing feature, the locking feature of the mechanism—which sets the trigger-point for the indexing of the counter wheel relative to the position of the canister—can be kept as a separate feature, and situated close to its axis of rotation (or other point joining it to the chassis) to ensure good tolerances and good positional control of the trigger-point.

Once the trigger-point has been reached, and the indexing feature has indexed the counter wheel, there are a variety of possible ways in which the counter wheel can be stopped in the desired angular position:The indexing feature can be allowed to stop in its natural, unstressed position;To improve the angular positioning of the previous option, the path of the indexing feature can be planned in such a way that its final movements are substantially radial relative to the counter wheel, and/or interact with a cam profile such that said final movements do not induce rotation in the counter wheel, meaning that loose tolerances on the final position of the indexing feature can be translated to tight tolerances on the angular position of the counter wheel;The indexing feature, or another feature of the component on which it is borne, may be designed to hit an end-stop that positions it—and thus the counter wheel—more closely than relying on the final position of the loosely-toleranced indexing feature;The locking feature may function as a form of escapement, both releasing and catching the counter wheel to provide a tightly-toleranced end-stop to its rotation; this would probably involve two instances of indexing movement per complete index of the counter wheel.

Various other modifications would also be apparent to a skilled reader. As such, it is emphasised that the forgoing description is provided by way of example only, and is not intended to limit the scope of protection as defined with reference to the appended claims.

Examples of alternative configurations include reversing the direction of rotation of the counter wheel, reversing the direction of radial movement of the indexing peg/tooth (i.e. from towards the centre of the counter wheel toward its outer edge) and/or providing a similar dual charge/release system in a non cam-driven system, for example using a more direct, tangential driving of the counter wheel.