US20090014086A1

US20090014086A1 - Dispensing small quantities of powder

Info

Publication number: US20090014086A1
Application number: US11/571,168
Authority: US
Inventors: Bruce Macmichael; Will Opie; John Poley
Original assignee: Pfizer Inc
Current assignee: Pfizer Inc
Priority date: 2004-07-01
Filing date: 2005-06-28
Publication date: 2009-01-15
Also published as: MX2007000020A; CA2571493A1; CN101027216A; GB0414813D0; BRPI0512955A; EA200602279A1; JP2008504178A; KR20070034602A; AU2005258995A1; WO2006003377A1; EP1765672A1

Abstract

An apparatus for dispensing small quantities of powder into a receptacle, the apparatus comprising a hopper (1), the hopper in use containing powder to be dispensed therefrom, a support for the hopper whereby the hopper can in use be held above a receptacle (8) into which the dispensed powder is to be received, at least one actuator for delivering impact energy to the hopper for causing powder to be dispensed therefrom and powder compaction means for enhancing the compaction of at least some of the powder in the receptacle.

Description

The present invention relates to an apparatus and method for dispensing small quantities of powder. The present invention has particular application in the gravimetric metering of powder, particularly medicament in powder form, which is dispensed gravimetrically into small receptacles such as capsules.
The flow characteristics of powders have a tendency to prevent flow of the powder through small holes, for example in a sieve containing the powder, under the action of gravity because the powder particles tend to agglomerate into larger particles. However it is well known that shaking the hopper causes the powder to flow. It has been shown that applying discrete movements of a well defined nature to the hopper can cause a reproducible amount of powder to flow through the holes.
For example, WO-A-01/33176 discloses an apparatus and method for dispensing small quantities of particles, in particular small amounts of medicament especially in a powder form. The apparatus uses a funnel shaped hopper with a plurality of holes in a membrane at the base of the hopper, forming a sieve-like element, through which powder present in the hopper may fall. A preferred method is to tap the hopper horizontally to cause such a movement, thereby controllably dispensing powder through the membrane. The tapping is achieved by an electromechanical actuator which delivers impact energy to the hopper, which in turn causes a small number of particles to fall through the sieve-like element and onto a weighing measuring balance. The actuator is a horizontally oriented solenoid which taps the side of the hopper via a rod which supports the hopper at one end and has the solenoid mounted at the other end. A tapping action can also be done with a vertical component to the action of the actuator or the resultant movement of the hopper. The dispensed powder falls into a receptacle which is disposed on a weighing pan of a precision weigh scale so that the dispensed powder is progressively weighed in real time, with feedback control of the dispensing actuator so that dispensing is terminated when the desired weight of powder has been dispensed.
In order for very small amounts of powder to be dispensed to within a very fine tolerance with respect to a target total dispensed weight, the powder particles which are dispensed though the holes of the sieve have a very small dimension which means that when the individual powder particles are compacted together into agglomerate particles prior to dispensing, the agglomerates are broken up before they pass through the holes. This means that the powder progressively dispensed into the receptacle has a low bulk density, and correspondingly a high bulk volume. This can lead to problems of overfilling of capsules. This is particularly encountered when a common capsule size is required to contain different medicaments having different densities, or different amounts of the same medicament.
There is a need for a dispensing system which can avoid the problem of overfilling of capsules.
Furthermore, the controlled dispensing of the powder is achieved by continually measuring the weight of the dispensed powder, and using a computer program to control the tapping action of the actuator. This calculates the weight of powder dispensed per tap, based on previous weight increases from previous taps, and predicts whether a further tap is required in order to increase the total dispensed weight up to a predetermined target value. The software also accounts for any time delay between additional powder actually producing a particular total powder weight, and the weigh scale which weighs the powder weight in real time accurately indicating that weight, because a time period is required before each measurement for the weigh scale pan to reach a stable condition in order for an accurate measurement to be made.
However, this method leads to the problem of slow dispensing of powder, particularly when larger amounts of powder are dispensed, leading to long measurement cycle times.
There is a need for a dispensing apparatus and method which can retain the measurement accuracy of this known system, yet operate at faster cycle times. Such faster cycle times would extend the use of this dispensing apparatus and method to the large scale commercial production of pharmaceutical capsules containing individually weighed and recorded amounts of medicament therein. There is a need for such an application.
For use in such a large scale commercial production of pharmaceutical capsules containing individually weighed and recorded amounts of medicament therein, there is yet further a need for an apparatus and method for automatically feeding empty receptacles to be filled to the weigh scale and removing filled receptacles from the weigh scale so that a large number of receptacles can be quickly and accurately filled with the required weight of powder. It is crucial that the feeding and removing system does not interfere with the precision weighing of the powder, which is obviously important when medicaments are being gravimetrically metered into capsules.
In addition, the known system, while providing high accuracy in the attainment of a target weight value for the medicament, nevertheless could be improved by providing yet smaller tolerances in the target weight, but without increasing dispensing cycle times.
The present invention aims at least partially to overcome these problems of the known apparatus and method and to meet these needs.
Accordingly, the present invention provides an apparatus for dispensing small quantities of powder into a receptacle, the apparatus comprising a hopper, the hopper in use containing powder to be dispensed therefrom, a support for the hopper whereby the hopper can in use be held above a receptacle into which the dispensed powder is to be received, at least one actuator for delivering impact energy to the hopper for causing powder to be dispensed therefrom and powder compaction means for enhancing the compaction of at least some of the powder in the receptacle.
The present invention also provides a method of dispensing small quantities of powder into a receptacle, the method comprising the steps of: disposing in a hopper a powder to be dispensed therefrom; supporting the hopper above a receptacle into which the dispensed powder is to be received; delivering impact energy to the hopper by at least one actuator thereby to cause powder to be dispensed therefrom into the receptacle; and, at any stage in the method, compacting at least some of the powder thereby to enhance the compaction of the powder in the receptacle.
This invention relates in particular to a gravimetric metering system primarily for dispensing medicament in powder form into small receptacles such as capsules. The apparatus preferably includes a transfer mechanism which can feed a plurality of receptacles successively on to the pan of a weigh scale in such a way that they can be filled with a medicament in powder form whilst on the weigh scale pan and then removed successively from the pan after the filling is completed.
The transfer mechanism employed to place the receptacles on the pan uses a lateral motion to bring the receptacles over the centre of the pan and then a vertical motion to rest the receptacles on to the pan so that the pan, and the receptacle thereon, is free of any contact with the transfer mechanism.
A particularly preferred arrangement uses a rotary transfer mechanism which employs a rotary motion to bring the receptacles successively in turn over the pan and then a vertical motion of either the pan or the receptacle, depending upon the type of weigh scale that is used, to deposit the receptacle on or remove the receptacle from the weigh scale pan.
This apparatus therefore provides that the receptacles to be filled can be automatically fed onto and removed from the pan of a precision weigh scale. A dispensing system gradually fills the receptacle on the weigh scale pan with the powder stopping when the desired weight of powder has been placed in the receptacle. The filled receptacle is then removed from the pan and replaced by an empty one for the next filling cycle.
In order for the measurement to be made as rapidly as possible it is important that the loading and unloading operations are as fast as possible whilst minimising any disturbance to the weighing system.
This requires gentle placement of the capsule on the pan; gentle removal of the capsule from the pan; movement of the capsule in a way that prevents powder spillage; and rapid movement of the capsule without generating air movements or heating.
The transfer mechanism which has been developed to achieve the transfer onto and off of the pan requires motion both in the plane of the pan, to bring the receptacle to the desired position over the pan, and normal (or orthogonal) to the plane of the pan to lower the receptacle onto the pan and lift it off again.
The transfer mechanism of the preferred embodiments implements the required motions in a way which is smooth, quiet, cleanable and generates a minimum of spilled powder. As the mechanism is typically fabricated from stainless steel to comply with conventional regulations or requirements for pharmaceutical process equipment, any simplification to the mechanism provides benefits in reducing the equipment cost, and simplifying the operation and cleaning of the mechanism in use.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

FIG. 1 is a schematic section, from one side, through a hopper of a powder dispensing apparatus for use in the method and apparatus of the present invention for dispensing powder into a receptacle;

FIG. 2 is a schematic section, from one side, through a hopper and a tapping device of a powder dispensing apparatus for use in the method and apparatus of the present invention for dispensing powder into a receptacle;

FIG. 3 is a schematic view, from one side, of a first embodiment of a transfer mechanism for loading and unloading receptacles onto and from a weighing balance pan under a filling apparatus in accordance with the present invention;

FIG. 4 is a schematic plan view of a second embodiment of a rotary transfer mechanism for loading and unloading receptacles onto and from a weighing balance pan under a filling apparatus in accordance with the present invention;

FIG. 5 is a schematic view, from one side, of the rotary transfer mechanism of FIG. 4;

FIG. 6 is an enlarged schematic plan view of part of the rotary transfer mechanism of FIG. 4 showing the interrelationship between the rotary carousel and a carrier for a receptacle;

FIG. 7 is a schematic side sectional view on line A-A of part of the carousel and the carrier of FIG. 6;

FIG. 8 is a schematic view, from one side, of a compaction apparatus for use in the method and apparatus of the invention for dispensing powder into a receptacle;

FIG. 9 is a graph representing the relationship between measured weight and time when using the apparatus of FIG. 8;

FIG. 10 is a schematic view, from one side, of another embodiment of a compaction apparatus for use in the method and apparatus of the present invention for dispensing powder into a receptacle;

FIG. 11 is a graph representing the relationship between measured weight and time when using the compaction apparatus of FIG. 10;

FIG. 12 is a schematic view, from one side, of another embodiment of a compaction apparatus for use in the method and apparatus of the present invention for dispensing powder into a receptacle;

FIGS. 13( a), (b), (c), (d) and (e) are schematic views, from one side, showing sequential steps in a process scheme for filling receptacles with powder in accordance with another embodiment of the present invention;

FIGS. 14( a), (b), (c) and (d) are schematic plan views showing sequential steps in a process for dispensing powder into a receptacle in accordance with another embodiment of the present invention;

FIG. 15 is a graph showing the relationship between measured weight and time for the process of FIG. 14; and

FIGS. 16( a), (b), (c) and (d) are schematic plan views showing sequential steps in a process for dispensing powder into a receptacle in accordance with, another embodiment of the present invention.

FIG. 1 shows schematically the dispensing head of a precision powder metering system for use in the method and apparatus of the invention. Such a dispensing head is known from WO-A-01/33176.
Referring to FIG. 1, the device consists of a hopper 1 for a powder, for example a medicament used for administration to the lungs of a patient via a powder inhaler. The hopper 1 is of generally frusto-conical form with the larger end 2 open and uppermost. The smaller end 3 is closed by a plate 4 in which a plurality of holes 5 are formed, thereby forming a sieve. When a powder 7 is placed in the hopper 1, some powder 7 may initially fall through the holes 5 but thereafter, in general, the powder flow stops as the powder 7 jams in the holes 5. The flow of powder 7 through the holes 5 can be made controllable and reproducible by the choice of appropriate dimensions for the holes to match the properties of the powder. Typically, the holes lie in the range of from 100 microns to 2000 microns.
In order to use the apparatus for precision dispensing, a receptacle 8 for the powder 7 is placed under the plate 4 and the hopper 1 is tapped on the sidewall 9 thereof at a location 6. The tap may be in a form that results from the impact of a mass travelling at a controlled velocity. The resulting motion of the hopper 1 and powder 7 causes the powder 7 to flow through the holes 5 in the plate 4 for a small period of time following the impact, after which the powder flow stops. Thus a discrete amount of powder 7 is controllably dispensed into the receptacle 8 as a result of each tap.
In order to accurately dispense a desired total amount of the powder 7, a plurality of taps are used to fill each receptacle 8 and the total weight of powder 7 dispensed into the receptacle 8 is measured in real time so that as soon as the required amount has been dispensed, the tapping can be stopped.
FIG. 2 shows a particular hopper and tapping device of a powder dispensing apparatus for use in the present invention for dispensing powder into a receptacle. In this embodiment, a frusto-conical hopper 20 has a sieve 21 at its smaller lower end 22 and a larger upper end 23 for receiving bulk powder 24, such as medicament, to be dispensed through the sieve 21. The hopper 20 is supported by a cantilever arm 25, which is attached to or bears against a sidewall 26 of the hopper 20. Within the cantilever arm 25 is provided a longitudinally directed cavity 27, and in the cavity 27 is disposed an electro-mechanical actuator.
The electromechanical actuator may have the structure and operation of the actuator disclosed in WO-A-01/33176, the disclosures of which are incorporated herein by reference. In particular, the actuator may comprise a solenoid which is energisable so as to be moved in a single direction, against a biasing force of a spring, so as to impart a tapping force on the cantilever arm. However, in the present illustrated embodiment, by way of example, the actuator is a double-acting solenoid, energisable so as to be movable successively in two opposed directions against the biasing force of a respective one of two springs.
Accordingly, in this embodiment, in the cavity 27 are disposed, in a longitudinally mutually spaced configuration, a pair of longitudinally oriented first and second solenoid coils 28,29 of a solenoid 30, comprising the electromechanical actuator. The coils 28,29 are rigidly attached to the cantilever arm 25. An armature 31 of the solenoid 30 comprises a longitudinally extended body having a central bush 32 and two opposed first and second projecting portions 33,34, each of the projecting portions 33, 34 extending within a respective one of the coils 28,29, and with the bush 32 centrally disposed between the two coils 28,29. If desired, a pair of opposed helical compression springs (not shown) may be provided, with each spring located between the bush 32 and a respective coil 28,29, thereby to urge the armature 31 into a central position in the absence of any actuating force on the armature 31. The first and second projecting portions 33,34 have respective first and second end walls 35,36 which are each spaced from a respective first and second end face 37,38 of the cavity 27 when the armature 31 is in the central position.
When a first current pulse is passed through the first coil 28, the armature 31 is accelerated towards the second end face 38 of the cavity 27 and the end wall 36 impacts it. The impact momentum is transferred by the cantilever arm 25 to the hopper 20 and the bulk powder 24 therein and causes a discrete amount of the powder 24 to fall into a receptacle 39 located, in use, beneath the sieve 21 of the hopper 20. Thereafter, when a second current pulse is passed through the second coil 28, the armature 31 is accelerated towards the first end face 37 of the cavity 27 and the end wall 35 impacts it. The impact momentum is again transferred by the cantilever arm 25 to the hopper 20 and the bulk powder 24 therein and causes a discrete amount of the powder 24 to fall into the receptacle 39. Accordingly, alternate energising of the two coils 28,29 causes the armature 31 to move in opposite directions in an alternating manner.
With this arrangement it is possible to tap the hopper 20 in either direction along the cantilever arm 25. Accordingly, powder dispensing may occur either by alternating the direction of tapping in successive tapping steps corresponding to successive powder dispense actions or alternatively by always using a pair of taps closely separated in time in a single tapping step to achieve a single powder dispense action.
The use of a solenoid 30 to generate the impact on the hopper 20 and the bulk powder 24 therein allows the magnitude of the impact to be altered by controlling the voltage driving the first and second coils 28,29 of the solenoid 30. Thus even if the mechanical arrangement causes some difference between the magnitude or effect of the forward and reverse taps associated with the energization of the two coils 28,29, the overall cumulative effect can be balanced by using different forward and reverse drive voltages. The same effect can be achieved by changing the pulse width, i.e. the period of time during which each coil 28,29 is switched on.
In other embodiments of the invention, it may be advantageous in some instances to use a different actuator arrangement to stimulate powder flow and as such the means of averaging the direction of excitation would be altered for optimal performance with that arrangement. Alternatively, the actuator may have only a single coil so that the armature only impacts the hopper in a single direction.
Although the actuator comprising the hopper impact mechanism is described in the illustrated embodiment as a solenoid, this is only one possible actuator. Alternative actuators may comprise an electric motor and cam; a piezoelectric actuator; or a voice coil linear actuator. Alternative arrangements can include a vertically directed solenoid or linkage such that the horizontal action of the solenoid causes the hopper to have a vertical as well as a horizontal response to the tapping action.
In accordance with this invention, the receptacles to be filled with powder from the hopper are dispensed on a weighing balance pan of a weigh scale while they are being so filled.
FIG. 3 shows a transfer mechanism for loading and unloading receptacles onto and from a weighing balance pan under the hopper and actuator system as described above. The receptacles 42, which typically comprise a bottom half of a capsule for containing a powdered medicament, are each mounted in respective carriers 41 which have an annular flange 51 arranged so that the carriers 41 can be lifted vertically by a transfer arm 44.
The empty receptacles 42 in their carriers 41 are brought to the gravimetric dispenser head, comprising the hopper and actuator, on a transport system such as a conveyor belt 55. The transfer arm 44 for transferring the carriers 41 is moved to a pick up position 43, inserted under the flange 51 and raised to remove the receptacle 42 in the carrier 41, supported by the arm 44, from the belt 45. The transfer arm 44 is then moved laterally until it is over the centre of the weighing balance pan 48. The arm 44 is then lowered until the carrier 41 rests on the upper surface 46 of the pan 48. The arm 44 is moved a small additional amount downwards so that the arm 44 has no further contact with either the pan 48 or the carrier 41.
At this point the receptacle 42 is available to be filled from a filling system 47 (comprising the hopper and actuator system described hereinabove) whilst its weight is being measured by the weigh scale 52. When filling is complete the transfer arm 44 is raised to remove the carrier 41 and the receptacle 42 therein from the weigh scale pan 48 and then the transfer arm 44 is moved horizontally to a put down position 49 where the carrier 41 is located over a second conveyor belt 50. At this point the carrier 41 is lowered, freeing the carrier 41 from contact with the transfer arm 44, such that the carrier 41 rests on the second conveyor belt 50. The transfer arm 44 is then free to return to the pick up position 43 to repeat the filling/weighing process in a subsequent receptacle-filling cycle.
FIGS. 4 and 5 show an alternative rotary transfer mechanism for loading and unloading receptacles onto and from a weighing balance pan under a hopper and actuator system as described above, which uses a carousel (or rotary disk) for holding a plurality of carriers/receptacles at respective angular positions around the carousel rather than a transfer arm for holding one carrier/receptacle at a time in association with a pair of conveyor belts as employed in the embodiment of FIG. 3.
FIGS. 4 and 5 show the main components of the mechanism. The incoming receptacle to be filled which has been previously mounted in a carrier 61, is placed, together with the carrier 61, in a selected one of a plurality of holes 63 located circumferentially around a rotary transfer mechanism 60 in the form of a carousel. The hole 63 holds the carrier 61 at a specific angular location of the outer circumference, and at a specific orientation as the rotary transfer mechanism 60 moves. The preferred structure of the hole 63 and the associated carrier 61 are shown in greater detail in FIG. 6.
FIG. 6 shows in an enlarged view only a part of the rotary transfer mechanism 60 in that only two carrier locations, constituted by the holes 63, are shown whereas the rotary transfer mechanism 60 may have as many holes 63 for the carriers 61 on it as required. FIG. 7 shows in greater detail the structure of the holes 63 and of the carrier 61. The holes 63 in the rotary transfer mechanism 60 each have a slot 62 communicating with the outer circumference 70 of the carousel 60 through which a central part 64 of the carrier 61 can pass to allow the longitudinal axis of the carrier 61 to be centred in a central circular part 69 of the hole 63. The central circular part 69 and the slot 62 of each hole 63 resemble a keyhole-like structure. The upper edges 80 of the circular parts 69 of the holes 63 are tapered to match a corresponding angle of taper of the edge 66 of the top flange 67 of the carrier 61. Thus without support the carrier 61 can sit in the central circular part 69 of the hole 63, being held in place by gravity and centred in the hole 63 by the conical tapered shape of the touching surfaces of the edge 80 of the carousel 60 and the edge 66 of the top flange 67 of the carrier 61.
The flat base 65 of the carrier 61 is made a larger diameter than the central region 64 so that when the base of the carrier 61 is pushed upwards or supported by a flat surface, such as the upper surface 46 of the pan 48, then the carrier 61 will rest stably on that flat surface. If the carrier 61 is thus raised relative to the transfer mechanism 60 so that the tapered edge 66 of the flange 67 is just no longer in contact with the upper edge 80 of the circular part 69 of the hole 63, then the carrier 61 will be free of any contact with the transfer mechanism, and rest solely, and stably and securely, on the flat supporting surface underneath the carrier 61.
The upper part 68 of the carrier 61 is shaped to accept the receptacle to be filled. In the case illustrated this is in the form of one half 81 of a capsule for containing medicament. Thus incoming capsules to be filled may be loaded at a loading station 59 into the transfer mechanism 60 either by being placed in carriers 61 already in place in the transfer mechanism 60 or by being placed in the carriers 61 by a separate mechanism (not shown) before the carriers 61 are loaded in the holes 63 of the transfer mechanism 60.
Once the receptacle is in place in the respective carrier 61 the transfer mechanism 60 which is free to rotate about the vertical axis 84 can be angularly indexed to move an unfilled receptacle to its fill position 83 over the weigh scale pan 48. The whole transfer mechanism 60 may then be lowered a distance sufficient for the base 65 of the carrier 61 to contact the upper surface 46 of the weigh scale pan 48.
Other capsules and carriers 61 on the transfer mechanism 60 remain in place as it is arranged that there are no surfaces below them, which they would otherwise contact when the transfer mechanism 60 is lowered.
After filling, the transfer mechanism 60 is raised, thereby reseating the carrier 61 in the respective hole 63 of the transfer mechanism 60. Thus, as the next unfilled capsule is transferred onto the pan 48, the previously filled capsule is transferred to the unloading station 82 where it is removed.
Both loading and unloading mechanisms can utilise conventional capsule handling systems such as are found on capsule filling lines. In some cases it may be preferred to incorporate the application of the capsule cap to the filled body whilst the filled body is still on the transfer mechanism so as to ensure no powder is lost during transport. In this case the carrier design would be made compatible with this requirement.
The indexing, raising and lowering of the transfer mechanism can be accomplished by servo motor drivers or linear actuators to enable smooth and accurate motion to be achieved.
In accordance with one aspect of the present invention, the powder, for example, of medicament, which has been dispensed into the receptacle, for example one half of a gelatine capsule, is subjected to a compaction step while the powder is in the receptacle. The compaction is achieved by applying a force to the powder particles, either directly or indirectly, so as to increase the degree of particle packing in the powder in the receptacle. The compaction may be carried out intermittently, or continuously. When the compaction is carried out intermittently, the compaction may be carried out between successive dispensing steps for dispensing additional powder into the receptacle. When the compaction is carried out continuously, it may be carried out during dispensing of the powder into the receptacle. The compaction of the powder in the receptacle may be achieved directly by physically contacting the powder in the receptacle so as to press it down into a more closely packed form, thereby to increase the bulk density of a powder in the receptacle, and so as to reduce its bulk volume. For example, a vertically reciprocal plunger may be employed to push down on the powder in the receptacle, thereby to compact it. When the compaction is achieved indirectly, the receptacle itself, or a carrier for the receptacle, may be tapped once or periodically in one or a plurality of directions or alternatively the powder in the receptacle may be subject to vibration, for example ultrasonic vibration. This causes the powder already dispensed into the receptacle to settle under its own weight under the action of gravity so as to increase its close packing, thereby to increase its bulk density and reduce its bulk volume.
Referring to FIGS. 8 and 9 there is shown one embodiment of the compaction apparatus and method in accordance with the invention. In this embodiment, the receptacle 100 into which powder 102 such as powdered medicament is to be dispensed, typically comprises a bottom half of a gelatine capsule for containing a powdered medicament. The receptacle 100 is mounted in a carrier 104, which may have the construction as described above. In the dispensing and weighing steps, the carrier 104 rests on the upper surface 106 of a weighing balance pan 108 of a weigh scale. In such a configuration, the receptacle 100 is available to be filled from a gravimetric dispenser head, such as the hopper and actuator system described hereinabove, whilst its weight is being measured by the weigh scale during the dispensing step until a target weight is achieved, measured and recorded.
In this embodiment, the receptacle 100 and/or the carrier 104 is or are additionally tapped either intermittently or continually by one or more tapping elements 110,112 acting thereon. The or each tapping element 110,112 may act on the receptacle 100 and/or the carrier 104 in any suitable direction, for example horizontally (as shown by arrow A in FIG. 8), or vertically downwardly (as shown by arrow B in FIG. 8), or any angle therebetween, or in a plurality of directions. The or each tapping element 110,112 may be moved by a dedicated actuator (not shown), or by a common actuator (not shown), or by the actuator (such as the actuator 30 of FIG. 2) which is configured to tap the hopper 114.
Alternatively, as also shown in FIG. 8, the hopper 114 may be constructed and located so that a part of the hopper 114 (such as a downwardly depending tube 115), or an additional tapping element connected thereto, engages the receptacle 100 and/or the carrier 104 so that when the hopper 114 is moved by the actuator 30 so as to dispense powder 102 through the sieve 116 into the receptacle 100, the hopper 114 also applies a tapping force onto the receptacle 100 and/or the carrier 104, thereby to cause settling of the already dispensed powder in the receptacle 100.
As shown in FIG. 9, which shows the relationship between the measured weight of powder 102 dispensed and time, in this particular embodiment there may be an initial dispensing phase (Dispense #1) in which the hopper 114 is repeatedly tapped by the actuator 30 so as progressively to dispense only a substantially predetermined portion of the total target amount of the powder 102 into the receptacle 100. Thereafter, the first dispense phase is stopped and in a first compaction phase (Tap #1) the already dispensed powder 102 is compacted for example by tapping on the receptacle 100 and/or the carrier 104. During this compaction phase, the tapping on the receptacle 100 and/or the carrier 104 causes fluctuations in the measured weight of the receptacle 100 and its contents. There then follows a second dispense phase (Dispense #2) in which an additional portion of the total desired weight of the powder 102 is dispensed into the receptacle 100, and following this stage a second compaction phase (Tap #2) in which the already dispensed powder 102 is again compacted by tapping the receptacle 100 and/or the carrier 104. This sequence may be repeated a number of times. At the end of the weighing process, there is a final dispense phase (Final dispense), where the final amount of the powder 102 is dispensed into the receptacle 100, and a final weighing (Final weigh) phase, where the total weight of the dispensed powder is weighed by the weigh scale.
In the arrangement where the movement of the hopper 114 by the actuator 30 causes a tapping movement on the receptacle 100 and/or the carrier 104, then during the compaction phase(s) additional powder may be dispensed into the receptacle 100 as a result of such movement of the hopper 114.
In accordance with a second embodiment of the invention, as shown in FIGS. 10 to 11, when the carrier 104 holding the receptacle 100 is disposed on the weigh scale pan 108, the dispensed powder 102 in the receptacle 100 is subjected to external vibration, for example from a vibrating element 116 represented generally by a speaker element in FIG. 10, which causes non-contacting vibration of the powder 102 in the receptacle 100. The vibrational force applied to the powder 102 causes the particles to settle into a more closely packed morphology, thereby increasing the bulk density of the powder. The vibration has a frequency selected so that it does not affect the operation of the weigh scale, for example ultrasonic vibration having a frequency of 20,000 Hz or greater. The ultrasonic vibration may optionally be focussed, for example by a lens element 118 as schematically represented in FIG. 10, onto the receptacle 100. The vibration may be imparted to the powder 102 in the receptacle 100 either periodically or, as shown in FIG. 11, continuously during the dispensing of the powder 102 into the receptacle 100.
Referring to FIG. 11, this shows the relationship between measured weight and time during the dispensing and weighing of the powder 102 in the receptacle 100. The powder 102 is continuously dispensed into the receptacle 100 and the dispensed weight is continuously measured by the weigh scale. During the dispensing phase, the powder which has been dispensed is continuously subjected to vibration, thereby causing continuous settling, and consequential increase in bulk density of the powder which been already dispensed into the receptacle. Dispensing is stopped when the weigh scale, with its associated software and processor, has calculated that the required weight of powder 102 has been dispensed, following which, after elapsing of a time period sufficient to permit the weigh scale of the balance to settle to a final stable reading, a final stable weight of the powder 102 is measured. The ultrasonic vibration is terminated before the weighing of the final stable weight, thereby to ensure that the final stable weight is determined accurately.
In a further embodiment, as shown in FIG. 12, the powder 102 which has been dispensed into the receptacle 100 is subjected to physical compaction. After the powder 102 has been dispensed from the hopper 114 into the receptacle 100 which is carried in the carrier 104 which is in turn disposed on the weigh scale pan 108, a compaction element 120, for example a plunger as shown in FIG. 14, is inserted into the receptacle 100 thereby physically to press down and compact the powder 102 in the receptacle 100. The physical compaction step may be carried out once or a number of times in the dispense and weighing cycle. Although the physical compaction may be carried out at the end of the dispensing cycle, before the final stable weight has been measured, this is not preferred because there is a possibility that the compaction element 120 may inadvertently reduce the actual weight from the target value by inadvertently removing some of the powder 102 from the receptacle 100. Typically, the sequence of the dispense and compaction steps are the same as shown in FIG. 9.
In accordance with a further aspect of the invention, compaction of powder in the receptacle is achieved by depositing into the receptacle a pre-compacted body of powder so as partially to fill the receptacle with a substantially predetermined portion of the target weight of the powder, and thereafter completing the filling of the receptacle to the desired final target weight by dispensing the remainder of the powder from the hopper of the gravimetric dispenser head. In accordance with this aspect, as well as providing the benefit of a higher bulk density of the total powder in the receptacle being achieved, additionally this aspect provides the surprising combination of benefits that not only can the speed of filling a receptacle be increased, but also the accuracy of achieving the required target weight can be enhanced.
FIGS. 13( a),(b),(c),(d) and (e) accordingly show sequential steps in a process scheme for filling receptacles with powder in accordance with another embodiment of the present invention.
Referring to FIG. 13 (a), initially the receptacle 100, comprising the bottom half of a gelatine capsule for containing a powdered medicament, is disposed in the carrier 104 which in turn is supported on the weigh scale pan 108 of a weigh scale. The tare weight of the empty receptacle 100 and its associated carrier is measured by the weigh scale 104. This step is however optional and in particular may be omitted, for example when it is known that any manufacturing tolerances in the weight of the receptacles 100 are small, and in particular are within the target tolerances of the final capsule weight of the filled capsule.
In the second step, the receptacle 100 is partially filled with a body of powder. This body of powder has been pre-compacted, in the sense of having a bulk density which is higher than that achievable by dispensing the powder out of the hopper 114, which is used in the final dispensing and gravimetric weighing step. The pre-compacted body of the powder has preferably been volumetrically measured so as to have a controlled volume. Alternatively, the body has been gravimetrically measured so as to have a controlled weight. In either case, the approximate volume or weight of the body has been selected so as to constitute a proportion, for example from 80 to 95% by weight, of the total target weight of the powder to be dispensed into the receptacle 100.
When the body of powder has been volumetrically measured, preferably the body is in the form of a plug of powder which has been formed and dispensed into the receptacle 100 using a powder dispensing apparatus, known in the art as a “dosator”, which is conventionally used in the art of filling gelatine capsules with powdered medicament.
Referring to FIGS. 13( b) and (c), the dosator 122 comprises a tube 124, typically a cylindrical tube, which has disposed therein a longitudinally reciprocal piston member 120. Prior to filling of the tube 124 with a controlled volume of powder, the piston member 126 is retracted and the tube 124 is oriented vertically whereby the bottom open end 128 of the tube 124 defines the lowermost part of a volume 129 in the tube 124 for receiving a plug of powder of controlled volume. The dosator 122 in this configuration is pushed downwardly into a powder bed 130 containing the powder 132. The powder 132 in the bed 130 is homogeneously dispersed and, as is well known in the art, the properties such as the density, flow properties, temperature, etc. of the powder 132 in the bed are carefully controlled so that when the dosator 122 is pushed downwardly into the powder bed 130 to a predefined depth, a repeatable particular volume 134 of the powder is introduced into and retained in the bottom volume 129 of the tube 124 as a plug of the powder. The downward urging of the dosator 122 into the powder bed 130 causes a degree of compaction of the powder to form the plug 134 of powder in the tube. Typically, the volume of the plug 134 is not defined by the position of the piston, but rather by the properties of the powder 132, the dimensions of the tube 124 and the speed, force and depth of pushing of the dosator tube 124 into the powder bed 130.
When the dosator tube 124 has been filled with a plug 134 of powder in this way, the dosator tube 124 is lifted from the powder bed 130 and laterally moved to a location above the receptacle 100 as shown in FIG. 13( d). The piston 126 is then urged downwardly thereby to push the plug 134 of pre-compacted powder out of the tube 124 so that it falls under gravity into the receptacle 100 as a pre-formed plug 134. Preferably, the receptacle 100, and the associated carrier 104, are not carried on a weigh scale pan 108 during this step. However, the receptacle and the associated carrier may be still carried by the weigh scale which was employed to measured the tare weight of the empty receptacle 100.
Thereafter, as shown in FIG. 13( e) the receptacle 100 carrying the pre-compacted plug 134 of powder and its associated carrier 104 are transferred (for example by the transfer apparatus described hereinabove) to the weigh scale pan 136 of a second weigh scale where the remainder of the powder 102 is dispensed from a hopper 114 into the receptacle 100 and the total amount of the powder 102 is weighed to achieve the final desired target weight as described hereinabove.
This embodiment provides the advantages that a larger amount of a given powder 102 can be incorporated into a receptacle 100 such as a gelatine capsule as compared to the filling of the receptacle 100 only using the dispenser tapping head and the gravimetric weighing system, as the initial plug 134 of powder is pre-compacted relative to the powder which is finally dispensed into the receptacle 100 in order to provide an accurate measurement of the final gravimetric weight of the total powder in the receptacle 100 This is achieved without compromising the accuracy of weighing the final weight and accuracy of achieving a target final weight. Also, the speed of dispensing as a whole is increased, because the time taken to dispense the preformed plug 134 of powder into the receptacle 100 using the dosator 122 can be reduced as compared to dispensing a corresponding amount of the powder into the receptacle 100 using only the dispenser tapping head and the gravimetric weighing system, without compromising weighing accuracy.
A further embodiment of the present invention is illustrated with reference to FIGS. 14 to 15. In this embodiment, which is a modification of the previous embodiment of FIG. 13, two weigh scales are employed, one for weighing the final stable weight of the volumetrically measured initial volume of pre-compacted powder from the dosator head and a second thereafter to measure the final stable weight of the total amount of powder dispensed into the receptacle, including the remainder gravimetrically measured from the hopper of the dispenser tapping head. The two weigh scales are operated in synchronism with a receptacle transfer mechanism, such as that described hereinabove, which is configured sequentially to deliver receptacles first to the first weigh scale, and then to the second weigh scale, whereby when a leading receptacle is being weighed on the second weigh scale, a lagging receptacle immediately upstream thereof is being weighed on the first weigh scale.
Referring in particular to FIGS. 14( a), (b), (c) and (d), these schematically show sequential steps in a process in accordance with this embodiment of the present invention. Referring first to FIG. 14( a) there is shown schematically two weigh scales. The first weigh scale 140 is associated with a dosator 122 which is arranged (as described hereinabove) to deposit a plug 134 of pre-compacted powder into the receptacle 100 which is carried in the carrier 104 which in turn is disposed on the first weigh scale 140. The second weigh scale 142 is adapted to operate in conjunction with a gravimetric tapping dispenser including a hopper 114 for dispensing powder 102 into the receptacle 100 which has already received the plug 134 of powder, with the second weigh scale 142 being arranged to weigh the final total weight of the powder 102 cumulatively deposited into the receptacle 100. As schematically represented in FIG. 14, a plurality of receptacles 100 are transferred, using a transfer apparatus (not shown) such as that described hereinabove, sequentially first to the first weigh scale 140, and then to the second weigh scale 142. In FIG. 14, three receptacles 100 are shown for the purposes of illustration and it will be immediately apparent to the skilled person that a continuous series of receptacles 100 may be fed to the first and second weigh scales 140,142 for sequential filling of the receptacles 100.
Referring to the drawings, a first receptacle 100 a is initially delivered by the transfer system to the first weigh scale 140. As described with respect to the previous embodiment, the tare weight of the receptacle 100 a is then measured by the first weigh scale 140. Then, a plug 134 of pre-compacted powder is deposited by the dosator 122 into the receptacle 100 a, for example to fill the receptacle with from 80 to 95%, most typically about 90%, by weight of the total amount of powder to be filled into the receptacle 100 a. The first weigh scale 140 is then employed to measure the final stable weight of the partially filled receptacle 100 a.
Thereafter, the partially filled receptacle 100 a is transferred in a transfer step from the first weigh scale 140 to the second weigh scale 142 and simultaneously the transfer mechanism transfers the next following empty receptacle 100 b in a corresponding transfer step onto the first weigh scale. The next but one following empty receptacle 100 c is also transferred by the transfer mechanism into position immediately upstream of the first weigh scale 140.
Then, in a second filling step, the final remaining amount of the powder is filled, using the hopper 114, into the partially filled receptacle 100 a to achieve the desired target weight of the filled receptacle 100 a and the second weigh scale 142 is employed to measure the final stable weight of the filled receptacle 100 a. The second weigh scale 142 receives not only the partially filled receptacle, but also information from the first weigh scale 140 concerning the final stable weight of the partially filled receptacle 100 a. At the same time, the next following receptacle 100 b disposed on the first weigh scale 140 is partially filled by the dosator 122, and the final stable weight of the partially filled receptacle 100 b is weighed.
In a subsequent transfer step, the leading filly filled receptacle 100 a, and with the final weight now having been measured, is transferred from the second weigh scale 142 and the receptacle 100 a is closed, for example, by the top half of the gelatine capsule being closed over the bottom half of the gelatine capsule. In synchronism, the following partially filled receptacle 100 b is transferred to the second weigh scale 142, and the next but one empty receptacle 100 c is transferred to the first weigh scale 140. The sequence is then repeated until all of the receptacles 100 are filled.
FIG. 15 shows the relationship between weight as measured by the first and second weigh scales 140,142, and time. The solid line represents the weight of the leading receptacle 100 a and the dashed line represents the weight of the lagging receptacle 100 b. In the initial transfer step, the first leading receptacle 100 a is transferred onto the first weigh scale 140. Once the balance has stabilised, the empty (tare) weight of the receptacle is recorded. Then, the dosator 122 dispenses the pre-compacted body 134 of powder into the receptacle 100 a, the weight measured by the weigh scale 140 is permitted to stabilise and then the final stable weight is measured. This step requires a first time period for permitting the empty capsule to stabilise and a second time period for (a) dispensing of the plug 134 of powder from the dosator 122, (b) permitting the measured weight to stabilise again, and (c) recording the final stable weight of the partially filled receptacle 100 a. In a next step, the leading partially filled receptacle 100 a is transferred from the first weigh scale 140 to the second weigh scale 142 and simultaneously the immediately upstream empty receptacle 100 b is transferred to the first weigh scale 140 using the transfer mechanism. In a subsequent dispensing and weighing step, the upstream partially filled receptacle 100 a is filled to the required calculated amount gravimetrically by the hopper 114, the weight is progressively weighed and the final weight is permitted to stabilise on the weigh scale 142 and thereafter a final weight measurement is made by the second weigh scale 142. Simultaneously, the immediately downstream 100 b receptacle thereof is partially filled by the dosator 122 and the final stable weight of the partially filled receptacle 100 b is determined by the first weigh scale 140. These two steps for filling the two receptacles 100 s and 100 b operate in synchronism and the total time required is determined by the longer of the two steps, so that the transfer steps can also operate in synchronism thereafter. This sequence of steps is repeated for a succession of receptacles 100 to be filled.
Using the sequence of steps of this embodiment, it may be seen that although each receptacle 100 may take substantially the same time to fill with the desired final amount of powder as for the previous embodiment, by synchronising the operation of the dosator 122 with a first weigh scale 140 and the gravimetric tapping head including the hopper 114 with the second weigh scale 142 and transfer therebetween, a filled receptacle 100 is transferred from the final, second, weigh scale 142 at approximately twice the rate as in the previous embodiment. Therefore the rate of production of the filled and weighed receptacles 100 is approximately doubled.
However, and surprisingly, the accuracy, with respect to a target weight value, of the actual weight of the powder 100 in the receptacle is also increased even though the speed has increased. This is because the proportion of the total weight of powder in the ultimately filled receptacle 100 which has been dispensed by the gravimetric tapping head is typically from 5 to 20% of the total weight of the powder in the receptacle 100, since the dosator 122 has dispensed from 80 to 95% by weight of the total amount of the powder to be filled into any receptacle 100. Correspondingly, the amount of powder dispensed by the hopper 114 and gravimetrically weighed in any dispensing and gravimetric weighing step is reduced as compared to using only a gravimetric tapping dispenser to dispense all of the powder. Accordingly, the gravimetric weight of the powder required to be dispensed per tap by the gravimetric tapping dispenser (in particular the hopper 114 containing the sieve 116) can be reduced, which is achieved for example by configuring the hopper and its associated sieve to dispense a smaller amount of powder per tap on the hopper 114. Most particularly, the sieve mesh size may be reduced, the sieve area may be reduced and/or the tapping force on the hopper 114 may be reduced. This in turn leads to the result that since the weight per tap is reduced, the total weight of powder dispensed into the receptacle 100 can be much more accurately controlled. For example, if the weight per tap is reduced from 2x micrograms to x micrograms, the total weight of the powder in the receptacle 100 can be dispensed to within a tolerance of x micrograms rather than 2x micrograms.
In this embodiment, instead of using a dosator 122, a second gravimetric tapping head may be employed, but configured to dispense significantly greater weight of powder per tap than that of the gravimetric tapping head associated with the second weigh scale 142.
A yet further embodiment of the present invention is illustrated with respect to FIGS. 16( a), (b), (c) and (d) which show sequential steps in the powder dispensing process. In this embodiment, a single weigh scale is employed in conjunction with a dosator and a gravimetric tapping dispenser, which are selectively laterally moved above the weigh scale when dispensing powder, and remote from the weight scale when not dispensing.
As shown in FIG. 16( a), in the first step of the process of this embodiment a receptacle 100 to be filled, together with the associated carrier 104, is disposed on the weigh scale pan 150 of the weigh scale 152 using a transfer apparatus such as that described hereinabove. The tare weight of the receptacle 100 and its carrier 104 is measured by the weigh scale 152. In this step, the dosator 122 and the gravimetric tapping dispenser, including the hopper 114, are both remote from the weigh scale 152. In a second step as shown in FIG. 16( b), the dosator 122 is laterally moved over the receptacle 100 carried on the weigh scale 152, and the volumetrically measured plug 134 of pre-compacted powder is deposited into the receptacle 100 by the dosator 122. In a third step as shown in FIG. 16( c), the dosator 122 is removed from the receptacle 100 and in synchronism therewith the hopper 114 of the gravimetric tapping dispenser is moved over the receptacle 100, following which the receptacle 100 is filled to the required weight of the powder. Thereafter, in the final step as shown in FIG. 16( d), the hopper 114 is removed away from the weigh scale 152, the pan 150 of the weigh scale is permitted to stabilise and a final stable weight of the filled receptacle 100 is made. The filled receptacle 100 is thereafter removed from the weigh scale pan by the transfer apparatus (not shown) and a subsequent empty receptacle 100 to be filled is deposited on the weigh scale pan for filling in a subsequent cycle.
Again, this embodiment provides the advantages that the total amount of powder has a greater bulk density, and thereafter is more compacted, as compared to the prior art. Furthermore, since the gravimetric tapping dispenser including the hopper 114 is employed only partially to fill the receptacle 100, this results in a reduced weight of powder being dispensed per tap from the hopper 114, which in turn results in a more accurate final weight, with respect to a desired target weight, of the filled receptacle 100 being achieved.

Claims

1. An apparatus for dispensing. small quantities of powder into a receptacle, the apparatus comprising a hopper, the hopper in use containing powder to be dispensed therefrom, a support for the hopper whereby the hopper can in use be held above a receptacle into which the dispensed powder is to be received, at least one actuator for delivering impact energy to the hopper for causing powder to be dispensed therefrom and powder compaction means for enhancing the compaction of at least some of the powder in the receptacle.

2. An apparatus according to claim 1 wherein the powder compaction means comprises a device for compacting the powder after the powder has been dispensed into the receptacle.

3. An apparatus according to claim 2 wherein the compacting device comprises at least one tapping element for tapping the receptacle.

4. An apparatus according to claim 3 wherein the at least one tapping element is adapted to tap the receptacle directly.

5. An apparatus according to claim 4 wherein the at least one tapping element comprises a part of the hopper.

6. An apparatus according to claim 4 wherein the tapping element is adapted to tap the receptacle indirectly by tapping a carrier for the receptacle.

7. An apparatus according to claim 3 further comprising a control means for controlling the operation of the at least one tapping element and the at least one actuator.

8. An apparatus according to claim 7 wherein the control means is adapted alternately to operate the at least one tapping element and the at least one actuator.

9. An apparatus according to claim 2 wherein the compacting device comprises a vibrator device for vibrating the receptacle.

10. An apparatus according to claim 9 wherein the vibrator device comprises a source of ultrasonic radiation which is located remote from the receptacle.

11. An apparatus according claim 9 further comprising a control means for controlling the at least one actuator and the source of ultrasonic radiation in synchronism.

12. An apparatus according to claim 2 wherein the powder compaction means comprises a reciprocable element for pushing downwardly onto the powder dispensed into the receptacle.

13. An apparatus according to claim 12 wherein the reciprocable element comprises a plunger.

14. An apparatus according to claim 1 wherein the powder compaction means comprises a powder compacting device for compacting powder before the powder has been dispensed into the receptacle, and further comprising a dispensing device for dispensing compacted powder into the receptacle prior to dispensing of the powder into the receptacle from the hopper.

15. An apparatus according to claim 14 wherein the powder compacting device and the dispensing device together comprise a common device for forming and depositing into the receptacle a volumetrically measured amount of compacted powder.

16. An apparatus according to claim 15 wherein the common device comprises a tube having a bottom open end and reciprocable piston disposed in the tube.

17. An apparatus according to claim 14 further comprising a receptacle transfer mechanism for selectively moving the receptacle from a first position at which the receptacle is located to receive compacted powder from the dispensing device to a second position at which the container is disposed on a weigh scale and at which the receptacle is located for dispensing of powder thereinto from the hopper.

18. An apparatus according to claim 14 further comprising first and second moving devices for respectively moving the hopper and the dispensing device between respective first and second positions above and remote from a receptacle carried on a weigh scale.

19. An apparatus according to claim 14 further comprising first and second weigh scales and a transfer mechanism which is adapted to transfer a succession of receptacles onto the first weigh scale, from the first weigh scale onto the second weigh stale, and away from the second weigh scale.

20. An apparatus according to claim 19 wherein the powder compaction means is adapted to dispense pre-compacted powder into a receptacle when that receptacle is on the first weigh scale.

21. An apparatus according to claim 20 wherein the hopper is adapted to dispense powder into a receptacle when that receptacle is on the second weigh scale.

22. An apparatus according to claim 19 wherein the transfer mechanism is adapted to transfer successive receptacles in synchronism.

23. An apparatus according to claim 19 wherein the first and second weigh scales are adapted to weigh respective receptacles in synchronism.

24. A method of dispensing small quantities of powder into a receptacle, the method comprising the steps of: disposing in a hopper a powder to be dispensed therefrom; supporting the hopper above a receptacle into which the dispensed powder is to be received; delivering impact energy to the hopper by at least one actuator thereby to cause powder to be dispensed therefrom into the receptacle; and, at any stage in the method, compacting at least some of the powder thereby to enhance the compaction of the powder in the receptacle.

25. A method according to claim 24 comprising compacting the powder after the powder has been dispensed into the receptacle.

26. A method according to claim 25 wherein the compacting step comprises tapping the receptacle thereby to settle the powder in the receptacle.

27. A method according to claim 26 comprising tapping the receptacle directly.

28. A method according to claim 27 wherein a part of the hopper taps the receptacle.

29. A method according to claim 26 comprising tapping the receptacle indirectly by tapping a carrier for the receptacle.

30. A method according to claim 25 further comprising alternately tapping the receptacle and dispensing powder from the hopper.

31. A method according to claim 25 wherein the compacting step comprises vibrating the receptacle.

32. A method according to claim 31 wherein the receptacle is vibrated by ultrasonic radiation.

33. A method according claim 32 wherein the delivery of impact energy to the hopper and the vibration by ultrasonic radiation are in synchronism.

34. A method according to claim 25 wherein the powder is compacted by pushing downwardly onto the powder dispensed into the receptacle.

35. A method according to claim 24 comprising compacting the powder before the powder has been dispensed into the receptacle, and dispensing the compacted powder into the receptacle from a dispensing device prior to dispensing of the powder into the receptacle from the hopper.

36. A method according to claim 35 comprising forming and depositing into the receptacle a volumetrically measure amount of compacted powder.

37. A method according to claim 35 further comprising selectively moving the receptacle from a first position at which the receptacle is located to receive compacted powder from the dispensing device to a second position at which the receptacle is disposed on a weigh scale and at which the receptacle is located for dispensing of powder thereinto from the hopper.

38. A method according to claim 35 further comprising respectively moving the hopper and the dispensing device between respective first and second positions above and remote from a receptacle carried on a weigh scale.

39. A method according to claim 35 further comprising transferring a succession of receptacles onto first weigh scale, from the first weigh scale onto the second weigh scale, and away from the second weigh scale, dispensing pre-compacted powder into a receptacle from the dispensing device when that receptacle is on the first weigh scale, and dispensing powder from the hopper into a partially filled receptacle when that receptacle is on the second weigh scale.

40. A method according to claim 39 comprising transferring successive receptacles in synchronism.

41. A method according to claim 39 comprising weighing respective receptacles in synchronism on the first and second weigh scales.

42. An apparatus for dispensing small quantities of powder into a receptacle substantially as hereinbefore described with reference to the accompanying drawings.

43. A method of dispensing small quantities of powder into a receptacle substantially as hereinbefore described with reference to the accompanying drawings.