Patent Application
20050145291
The present invention relates to a method and apparatus for introducing powder into a pocket, in particular allowing powder, such as for inhalation, to be transferred from a source and discharged into pockets of a carrier.
It is well known to prepare dry powder for inhalation using a powder bed and to transfer powder from that bed to pockets of a carrier using a dosator. In particular, reference may be made to U.S. Pat. No. 3,847,191, U.S. Pat. No. 4,542,835 and U.S. Pat. No. 5,826,633.
The powder bed is typically constructed as a rotating disk with a doctor blade which is used to smooth the surface of the powder. This provides powder with a consistent bulk density and a smooth surface.
A dosator is provided as a sharp edged tube with a central plunger. The plunger is positioned so as to define a space within the tube equivalent to a required dose of powder. The dosator is then inserted into the powder of the powder bed so as to fill the defined volume. In this way, when the dosator is removed, it brings with it a slug of powder of the required quantity. The powder may be transferred to a carrier and then deposited into a pocket by actuating the plunger.
This known system has a number of disadvantages. In particular, upon removal of the dosator from the powder bed, the powder breaks away from the dosator tip in an unrepeatable way. Furthermore, powder may be lost during transfer from the powder bed to the carrier and powder may be retained on dosator internal and external surfaces rather than being transferred to the pockets as intended. In this way, inaccuracies will result in the quantity of powder introduced into the pockets.
It is an object of the present invention to overcome or at least reduce the problems of previous systems.
According to the present invention, there is provided a method of introducing powder into a pocket having an open side including:
orientating the pocket with the open side facing at least partially upward;
providing the pocket with a volume of powder greater than that of the pocket;
compressing the volume of powder to a predetermined bulk density; and
removing excess powder so as to leave the pocket full of powder with the predetermined bulk density.
In this way, the product is filled reliably and repeatably with the substantially same amount of powder. In particular, this is governed only by the volume of the pocket and the compression applied to the powder. The applied compression can be controlled in a variety of ways. It will be appreciated that, in practice, the predetermined bulk density will include a small range of bulk densities according to various tolerances and the requirements for the powder housed in the pocket. Hence, the techniques for compressing the powder can allow small variations in the actual bulk density. These can all be considered as being the predetermined bulk density and will all result in substantially the same amount of powder as required by the powder's use.
The volume of powder may be confined to a space adjacent to the open side.
According to the present invention, there is provided a method of introducing powder into a pocket using a dosator having an elongate cavity with an open end and a plunger opposite the open end moveable along the cavity so as to define, between the plunger and the open end, a space of variable volume, the method including:
with the plunger defining a volume greater than that of the pocket, inserting the open end into a source of powder so as to fill the volume with powder;
positioning the open end over the pocket;
driving the plunger so as to expel powder from the open end into the pocket and compress it to a predetermined bulk density; and
removing the open end from the pocket so as to leave the pocket full of powder with the predetermined bulk density.
In this way, filling pockets with a predetermined quantity of powder is not dependent on that predetermined quantity being correctly transferred from the source of powder to the pocket. If the amount of powder picked up by the dosator varies, powder falls from the dosator during transfer or variable amounts of powder remain on the dosator after filling the pocket, this will not have a direct corresponding effect on the amount of powder provided in the pocket. In particular, the pocket is completely filled and compressed to a predetermined bulk density. The quantity of powder in the pocket is thus defined only by the volume of the pocket itself and the compression applied to it. Controlling the compression can be achieved in a number of different ways. A further advantage is that, compared to previous systems, the pockets are completely filled and, hence, there is no head space or excess volume. In other words, there is no wasted volume in the pockets. Removal of head space may substantially reduce unwanted moisture and gases in the sealed pocket. Furthermore, the weight of powder filled in the pocket is less dependent on the condition of the powder in the source. In particular, it is not critical that the powder in the source be at an even known density, since the step of compression brings it to the predetermined bulk density any way.
In one embodiment, the dosator has a plurality of said elongate cavities with respective open ends and a respective plurality of said plungers opposite said respective open ends and moveable along the cavities so as to define, between the plungers and the open ends, respective spaces of variable volume, the method further including driving the plurality of respective plungers together, eg simultaneously.
According to the present invention, there is also provided an apparatus for introducing powder into a pocket, the apparatus including a dosator and the dosator having:
an elongate cavity with an open end;
a plunger opposite the open end movable along the cavity so as to define, between the plunger and the open end, a space of variable volume for receiving powder; and
a driver for driving the plunger along the cavity, the driver being operable to drive the plunger towards the open end so as to compress the powder to a predetermined bulk density.
Thus, powder can be introduced into a pocket and compressed to a predetermined bulk density. It becomes possible to fill pockets completely and obtain the advantages mentioned above.
Furthermore, fine adjustments may be made to the process by altering the compression provided by the plunger. This allows variations in the powder properties and pocket dimensions to be accommodated.
In one embodiment, the dosator has a plurality of said elongate cavities with respective open ends; and
a respective plurality of said plungers opposite said respective open ends and moveable along the cavities so as to define, between the plungers and the open ends, respective spaces of variable volume; and wherein
the driver drives all of the plurality of respective plungers together.
Preferably, the dosator is returned to the source of powder and the plunger is driven to or at least partly through the open end so as to expel any remaining powder from the dosator and return the remaining powder to the source.
In this way, the dosator may be cycled to fill consecutive pockets. By returning the remaining powder to the source, that powder may be used again for the filling of other pockets. Furthermore, returning it to the source allows the source to process the powder and return it to its uncompressed state.
The system fills pockets with excellent accuracy. However, the surface of the powder in the pocket can be doctored to remove any small amounts of excess powder. This may be achieved by wiping with a blade the surface of the carrier in which the pocket is formed and, hence, wiping the surface of the powder so as to remove any such excess powder.
In this way, the system is less dependent upon the precise nature in which the remaining powder in the open end breaks away from the powder in the pocket. The doctoring ensures that all pockets are filled to the same extent and also cleans surrounding surfaces of powder, thereby facilitating subsequent adhesion of a sealing layer.
The driver may cause the compression of the powder by driving the plunger or the plungers towards the open end with a predetermined force.
Alternatively, the plunger can be pushed down to a controlled distance with the gap between the dosator tube and the surface surrounding the pocket defining the pressure at the pocket opening. In particular, excess powder will flow sideways with the gap defining the pressure at the pocket entrance, such that it does not matter if the resistance to plunger motion is variable.
The driver may drive the plunger or group of plungers towards the open end with a force which is independent of displacement of the plunger or the group of plungers.
The driver may be a pneumatic mechanism which drives the plunger or group of plungers with a predetermined pressure.
This provides a convenient mechanism by which the powder may be compressed to the predetermined bulk density.
Preferably, the dosator is in the form of a tube, the profile of the edge of the tube formed around the open end being chosen to optimise the two processes of picking up the powder and dispensing it into the container. A sharp edge is advantageous in allowing the dosator to be inserted into the source of powder so as to fill the space with powder. However, a flat end can be advantageous in sealing against surfaces around respective pockets without damaging the surface so as to ensure that powder from the space is contained within the pocket and compressed as required. The edge profile used is therefore specific to the container design and the properties of the powder.
This is advantageous in allowing the dosator to be inserted into the source of powder so as to fill the space with powder. Furthermore, the sharp edge can be advantageous in mating with surfaces around respective pockets so as to ensure that powder from the space is introduced into the pockets and compressed as required.
Preferably, the apparatus further includes a transfer mechanism for moving the dosator between the source of powder and the pocket and a control system controlling the transfer mechanism and the driver.
In this way, the system may be automated so as to allow consecutive pockets to be filled with powder from the source. As will be discussed below, with the use of multiple dosators, consecutive groups or arrays of pockets can be filled consecutively.
Preferably, the control system controls the transfer mechanism and the driver to automatically in turn insert the open end into a source of powder, position the open end over a pocket, drive the plunger so as to expel powder from the open end into the pocket and compress it to a predetermined bulk density, remove the open end from the pocket, return the dosator to the source of powder and drive the plunger to expel any remaining powder.
Hence, the control system provides a cycle which can be repeated for consecutive pockets.
Preferably, the control system controls the driver before the open end is inserted into the source of powder to position the plunger to define a volume greater than that of the pocket. The control system need not necessarily control the return position itself, but might merely initiate the return or release the plunger for return. The plunger can be driven to the returned position with any suitable mechanical mechanism. Its final position could be determined merely by the extent of travel of the plunger in the cavity or some adjustment means, such as a screw, could be provided to adjust the position of a stop.
Preferably, the volume greater than that of the pocket is sufficient that when the powder in said space is compressed to the predetermined bulk density, the resulting volume of compressed powder is greater than that of the pocket.
This is required when the powder reduces in volume under compression.
Preferably, with the open end positioned over the pocket, substantially all of the open area of the pocket lies within the open end.
This ensures that the pocket is effectively filled with powder.
It should be appreciated that centering of the dosator on the pocket may be important, but the diameter of the dosator tube need not be larger than the diameter of the pocket. For certain filling parameters, the process could work equally successfully with a dosator tube diameter smaller than that of the pocket.
Preferably, a plurality of dosators are provided in the apparatus arranged in an array corresponding to at least part of an array of pockets in a carrier.
In this way, a plurality of pockets may be filled simultaneously. In particular, with one cycle of the apparatus, some or all of the pockets of a carrier can be filled.
The method and apparatus are particularly advantageous when used for introducing dry powder for inhalation into pockets of carriers, such as blister packs.
In particular, it is proposed to use a carrier holding inserts, each insert forming a respective pocket. The inserts may be displaced out of the carrier to facilitate dispensing of the contained powder. In a preferred arrangement, the carrier is formed as a plate with through holes, each through hole containing a respective insert. The inserts and hence the pockets can be formed by a process of insert moulding in the carrier or, alternatively, moulded separately and later inserted into the carrier.
The invention will be more clearly understood from the following description, given by way of example only, with reference to the accompanying drawings, in which:
FIGS. 1(a) and (b) illustrate schematically apparatuses embodying the present invention;
FIGS. 2(a) to (g) illustrate the steps of a preferred method of the present invention; and
FIGS. 3(a) and (b) illustrate alignment of a dosator tube with a pocket.
As illustrated in
It should be appreciated that
It is also possible for the apparatus to include a plurality of dosators arranged in an array corresponding to at least part of an array of pockets of a carrier or, as illustrated in
Operation of the overall system will now be described with reference to FIGS. 2(a) to (g).
As illustrated, the dosator 10 includes a plunger or tamper 12. The dosator 10 is preferably in the form of a tube and has an axial passage forming an elongate cavity. The cavity extends from an open end 14 and the plunger 12 is able to move to and from the open end 14 along the passage or cavity. In this way, a space 16 of variable volume is formed between the open end 14 and the plunger 12. The driver 40 drives the plunger 12 along the cavity of the dosator 10 so as to vary the volume of the space 16 as required.
The cross section of the cavity and the plunger are preferably circular though any cross sectional shape could be used. The cross sectional shapes and areas of the plunger 12 and cavity correspond to one another so as to provide a normal piston/cylinder arrangement.
As will be described below, the cavity is used to receive powder. The fit between the plunger 12 and the walls of the cavity is chosen accordingly. For an apparatus used with powder for inhalation, the powder is extremely fine and, hence, it is likely that some powder will find its way between the plunger 12 and the walls of the cavity. In this respect, therefore, the fit between the plunger 12 and the walls of the cavity is not made too tight, since powder will become trapped and the force required to move the plunger 12 will be adversely affected. On the other hand, of course, if the fit is too loose, significant amounts of powder will travel between the plunger 12 and the walls of the cavity such that metering will be adversely affected.
As illustrated in
When the dosator 10 is inserted into the powder 22, the plunger 12 is in a position retracted from the open end 14 so as to provide a space 16 having a volume greater than that of the pocket to which powder is to be supplied.
As illustrated, the dosator 10 is in the form of a sharp edged tube. The sharp edge 18 around the periphery of the open end 14 is advantageous in enabling the dosator to be pushed easily and neatly into the powder 22. Indeed, this is further enhanced by providing the dosator 10 with a thin wall along its length for at least the depth to which it must be inserted into the powder 22.
As illustrated in
FIGS. 3(a) and (b) are provided to illustrate factors relating to alignment of the dosator tube to the pocket.
As illustrated in these Figures, the dosator tube 10 is misaligned with the pocket 32 by the dimension L. It has been determined that significant misalignment can result in variation of the bulk density in the pocket. The alignment of the pocket to the dosator should be better than 20% of the width of the pocket and more preferably better than 10%.
The cause of the error is that if powder 44 is trapped between the plunger 12 and the surface surrounding the pocket 32, then it may provide sufficient resistance to motion to stop the plunger. In addition the larger gap G on the other side allows powder to escape as plunger pressure is applied.
In many cases, the dosator tube will contact the surface 45 surrounding the pocket 32 such that the height H of the dosator tube above the pocket will be zero. However, in some case, this height may be chosen to some value greater than zero. In particular, this can be chosen to avoid damage to the dosator tube or pocket or to allow some powder to escape to prevent excessive compaction.
Additionally, where, as illustrated in
If the gap becomes sufficient to allow powder to escape sideways during the transfer, then compression may be lost.
The dimensions required will be a function of the powder particle size and flow characteristics and can be determined by the skilled person according to the particular embodiment.
The dosator tubes can be chosen to have a width, relative to the pocket width, that is smaller, equal or larger.
The choice can be made by considering the accuracy of the mechanics for the apparatus and the flow characteristics of the powder.
Using a dosator which is smaller than the pocket permits some misalignment of the dosator with pocket without affecting performance as the dosator will still be above the pocket. Smaller dosators may be necessary with large pockets as wide dosators will not pick up powder. However, the compression force from the dosator will not be applied over the whole of the surface and, for free flowing powders, this may give unreliable density control.
Using a dosator of equal size to the pocket gives best uniformity of compression density control but requires accurate alignment.
Using a dosator which is larger than the pocket reduces the alignment requirements and reduces the height of powder in the dosator tube compared to the normal tubes. However, for poorly flowing powders the powder around the edges may jam preventing the desired pressure being applied to the powder in the pocket.
The ratio between pocket and dosator widths should therefore be chosen depending upon the accuracy that can be achieved in positioning and the characteristics of the powder. Typically the preferred ratio will be within ±20% of unity.
In the context of filling carriers with doses of inhalation powder, it is suggested that the edge 18 of the open end 14 contacts the surface of the carrier 30 a little outside the periphery of the opening of the pocket 32, for instance approximately 0.5 mm. However, the edge 18 should not be much bigger, since then powder will not flow and there will be some compaction of the trapped powder.
Following on from the description above, for this embodiment, the joint between the edge 18 and the surface of the carrier 30 should be tight enough to prevent too much powder from escaping, but loose enough to allow air to escape.
This arrangement is illustrated in
The plunger 12 may then be driven towards the open end 14. This forces powder to be ejected from the dosator into the pocket 32. The driver 40 drives the plunger 12 in this regard such that the powder 24 is compressed to a predetermined bulk density. In this preferred embodiment, the plunger is driven with a predetermined force. In particular, the force provided to (and from) the plunger is preferably independent of displacement. In this respect, the driver 40 is preferably embodied as a pneumatic mechanism such that for the pocket filling operation at least the plunger may be driven with a predetermined air/gas pressure so as to ensure that the powder 24 is compressed to the corresponding predetermined bulk density. For the embodiment of
At this point, it is to be appreciated that, as mentioned above, the volume of the space 16 during the powder insertion step illustrated in
It should be appreciated that the volume of the powder 24 may be reduced when it is compressed by the plunger 12. In this case, the initial volume of the space 16 used when the dosator 10 is inserted into the powder 22 as illustrated in
In the next step, as illustrated in
It is important for successful implementation of the method that as the dosator is separated from the pocket, the powder in the dosator remains in place and breaks away from the powder in the pocket cleanly at the surface of the pocket leaving the pocket filled to just above the surface of the pocket.
This enables simple doctor blading of the excess to leave the pocket full and with no excess powder piled up over the pocket. For many powders it has been found that this occurs reliably simply by raising the dosator tube perpendicularly away from the pocket opening plane. However, for some powders, the point of separation may not be sufficiently reliable. In these cases additional separation measures may be required. These may include:
Where lateral movements of the dosator can position the open end of the dosator over a flat surface adjacent to the surface, the plunger in the dosator may be activated again to compress further the powder, ensuring that it remains in the dosator as it is lifted up. The dosator tube therefore has been used as a doctor blade to ensure a clean, flat surface to the powder in the pocket.
As illustrated in
It will be appreciated that, as illustrated schematically in
Finally, though not illustrated, the plunger is moved back to the position of
Thus, in conclusion, with pockets 32 of predetermined size, it is possible to reliably and repeatably transfer predetermined masses of powder to those pockets. In particular, the mass of powder is determined by the volume of the pocket and the predetermined bulk density created by the plunger 12.
It will be appreciated that this system can be used for transferring powders of any sort. However, it is of particular application to filling carriers with powder used for inhalation. For such powders, it is extremely important that predetermined masses or doses be reliably and repeatably provided in the carriers.
The carriers may be of any desired shape and size, for instance carriers commonly known as blister packs. Preferably, however, the surface of the carrier surrounding the periphery of the pockets 32 should be approximately planar so as to allow correct mating of the edge 18 of the open end 14 and also improved doctoring by the blade 70. Of course, it is possible to conceive of other shapes and forms for complementary edges 18 and surfaces of the carrier 30, together with appropriately shaped blades 70.
Although the invention has been described with reference to a dosator, it can also be embodied in other ways. For instance, with the pockets facing upwards, the volume of powder may be provided to the pockets in any convenient manner and compressed to the predetermined bulk density. For each pocket, the associated volume of powder may be confined to a space adjacent the open side of the pocket before being compressed into the pocket.
As described above, in order to control the powder mass in the pocket the density must be accurately controlled to the predetermined value. For many powders this will be achieved by the force or pressure exerted by the plunger as the powder is transferred from the dosator to the pocket.
However, for some powders and pocket shapes, it may be difficult to ensure that the force applied to the plunger is reproducibly conveyed through the powder in the dosator tube to compress the powder in the pocket to the required bulk density.
This will be especially the case for lightly compressed cohesive powders where even a short length of powder in a tube will jam rather than slide forward when pushed.
In these cases it may be necessary to augment the motion of the plunger by some additional mechanism that ensures the powder flows fully into the pocket. Transfers of powder into the pocket from the dosator in these cases might be achieved by:
In these cases a separate process, after the bulk of the powder has been transferred from the tube to the pocket, may be used to set the bulk density of the powder in the pocket to the predetermined value. This could be achieved by:
Where the present invention is used for filling containers with medicament, the powder may be made up of two components, the drug and the excipient. However, the drug concentration may vary between batches. If this is the case, then to ensure that each pocket has the same amount of drug, from batch to batch, it would be preferred to maintain the same pocket volume and to be able to adjust the bulk density during the filling operation.
To accomplish this, it is proposed that the bulk density in the pocket is changed during or after filling.
With typical medicament powders, where the excipient is lactose, the bulk density can be controlled over sufficient range to accommodate normal batch to batch drug concentration variation which is rarely above ±5%. For these powders the bulk density control can be achieved by controlling the force on the plunger during the filling of the pocket. Pressures between 1 bar and 10 bar, exerted by the plunger on the powder, are suitable for good compaction of the powder into the pocket.
The variation of bulk density with the plunger force depends upon the powder and pocket geometry. For a plunger with an area of 28 mm2 and an aspect ratio of approximately 3:1, the bulk density of lactose powder can be increased by 10% by increasing the plunger pressure from 2 bar to 4 bar.
As mentioned above, where the method is to be used to fill a plurality of pockets simultaneously an array of dosator tubes will be required, either as an array of separate dosators or, as illustrated in
Where this is undertaken, a number of detailed implementation issues need to be considered.
If the distance between dosator tubes is similar to the width of the dosator tubes then powder will tend to bridge the space between tubes. This is undesirable. To overcome this, the spacing can be increased or the powder removed whilst the dosator array is still over the powder bed.
Where the method is implemented with an array of dosators having respective tubes each dosator can have an independent means for generating the force on its plunger. This however may be over complicated for a cost effective implementation.
So as to allow the use of a singe dosator in some instances, it may be preferable to implement an approximation to independent force control by means such as:
Whilst, as a particular advantage of the present invention, the final control of the bulk density in the pocket is set after filling, there are also benefits to be obtained by controlling the bulk density of the powder as picked up by the dosator tube. This may be used to:
The bulk density in the dosator tube(s) can be varied by the parameters set for how the dosator penetrates the powder in the powder bed. The parameters include:
The values of each parameter can be determined experimentally and will be specific for a particular powder formulation and pocket geometry.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0202912.2 | Feb 2002 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB03/00528 | 2/6/2003 | WO |
