Note: Descriptions are shown in the official language in which they were submitted.
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POWDER FILLING APPARATUS AND METHOD
10
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field
of fine powder processing, and particularly to the metered
transport of fine powders. More particularly, the present
invention relates to systems, apparatus and methods for
20 Jfilling receptacles with unit dosages of non-flowable but
dispersible fine powdered medicaments, particularlv for
subsequent inhalation by a patient.
Effective delivery to a patient is a critical aspect
of any successful drug therapy. Various routes of delivery
25 exist, and each has its own advantages and disadvantages.
Oral drug delivery of tablets, capsules, elixirs, and the
like, is perhaps the most convenient method, but many drugs
have disagreeable flavors, and the size of the tablets makes
them difficult to swallow. Moreover, such medicaments are
30 often degraded in the digestive tract before they can be
absorbed. Such degradation is a particular problem with
modern protein drugs which are rapidly degraded by proteolytic
enzymes in the digestive tract. Subcutaneous injection is
frequently an effective route for systemic drug delivery,
35 including the delivery of proteins, but has a low patient
acceptance and produces sharp waste items, e.g. needles, which
are difficult to dispose. Since the need to inject drugs on a
frequent schedule such as insulin one or more times a day, can
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2
be a source of poor patient compliance, a variety of
alternative routes of administration have been developed,
including transdermal, intranasal, intrarectal, intravaginal,
and pulmonary delivery.
Of particular interest to the present invention are
pulmonary drug delivery procedures which rely on inhalation of
a drug dispersion or aerosol by the patient so that the active
drug within the dispersion can reach the distal (alveolar)
regions of the lung. It has been found that certain drugs are
readily absorbed through the alveolar region directly into
blood circulation. Pulmonary delivery is particularly
promising for the delivery of proteins and polypeptides which
are difficult to deliver by other routes of administration.
Such pulmonary delivery can be effective both for systemic
delivery and for localized delivery to treat diseases of the
lungs.
Pulmonary drug delivery (including both systemic and
local) can itself be achieved by different approaches,
including liquid nebulizers, metered dose inhalers (MDI's) and
dry powder dispersion devices. Dry powder dispersion devices
are particularly promising for delivering protein and
polypeptide drugs which may be readily formulated as dry
powders. Many otherwise labile proteins and polypeptides may
be stably stored as lyophilized or spray-dried powders by
themselves or in combination with suitable powder carriers. A
further advantage is that dry powders have a much higher
concentration than medicaments in liquid form.
The ability to deliver proteins and polypeptides as
dry powders, however, is problematic in certain respects. The
dosage of many protein and polypeptide drugs is often critical
so it is necessary that any dry powder delivery system be able
to accurately, precisely and repeatably deliver the intended
amount of drug. Moreover, many proteins and polypeptides are
quite expensive, typically being many times more costly than
conventional drugs on a per-dose basis. Thus, the ability to
efficiently deliver the dry powders to the target region of
the lung with a minimal loss of drug is critical.
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3
For some applications, fine powder medicaments are
supplied to dry powder dispersion devices in small unit dose
receptacles, often having a puncturable lid or other access
surface (commonly referred to as blister packs). For example,
the dispersion devices described in U.S. Patent Nos. 5,785,049
and 5,740,794 are constructed to receive such a receptacle.
Upon placement of the receptacle in the device, a
multi-flow ejector assembly having a feed tube is penetrated
through the lid of the receptacle to provide access to the
powdered medicament therein. The multi-flow ejector assembly
also creates vent holes in the lid to allow the flow of' air
through the receptacle to entrain and evacuate the medicament.
Driving this process is a high velocity air stream which is
flowed past a portion of the tube, such as an outlet end, to
draw powder from the receptacle, through the tube, and into
the flowing air stream to form an aerosol for inhalation by
the patient. The high velocity air stream transports the
powder from the receptacle in a partially de-agglomerated
~o~m, and the final complete de-agglomeration takes place in
tze mixing volume just downstream of the high velocity air
ir._ets.
Of particular interest to the present invention are
the physical characteristics of poorly flowing powders.
Poorly flowing powders are those powders having physical
characteristics, such as flowability, which are dominated by
cohesive forces between the individual units or particles
(hereinafter "individual particles") which constitute the
powder. In such cases, the powder does not flow well because
the individual particles cannot easily move independently with
respect to each other, but instead move as clumps of many
particles. When such powders are subjected to low forces, the
powders will tend not to flow at all. However, as the forces
acting upon the powder are increased to exceed the forces of
cohesion, the powder will move in large agglomerated "chunks"
of the individual particles. When the powder comes to rest,
the large agglomerations remain, resulting in a non-uniform
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4
powder density due to voids and low density areas between the
large agglomerations and areas of local compression.
This type of behavior tends to increase as the size
of the individual particles becomes smaller. This is most
likely because, as the particles become smaller, the cohesive
forces, such as Van Der Waals, electrostatic, friction, and
other forces, become large with respect to the gravitational
and inertial forces which may be applied to the individual
particles due to their small mass. This is relevant to the
present invention since gravity and inertial forces produced
by acceleration, as well as other effected motivators, are
commonly used to process, move and meter powders.
For example, when metering the fine powders prior to
placement in the unit dose receptacle, the powders often
agglomerates inconsistently, creating voids and excessive
density variation, thereby reducing the accuracy of the
volumetric metering processes which are commonly used to meter
in high throughput production. Such inconsistent
agglomeration is further undesirable in that the powder
agglomerates need to be broken down to the individual
particles, i.e. made to be dispersible, for pulmonary
delivery. Such de-agglomeration often occurs in dispersion
devices by shear forces created by the air stream used to
extract the medicament from the unit dose receptacle or other
containment, or by other mechanical energy transfer mechanisms
(e.g., ultrasonic, fan/impeller, and the like). However, if
the small powder agglomerates are too compacted, the shear
forces provided by the air stream or other dispersing
mechanisms will be insufficient to effectively disperse the
medicament to the individual particles.
Some attempts to prevent agglomeration of the
individual particles are to create blends of multi-phase
powders (typically a carrier or diluent) where larger
particles (sometimes of multiple size ranges), e.g.
approximately 50 m, are combined with smaller drug particles,
e.g. 1 m to 5 m. In this case, the smaller particles attach
to the larger particles so that under processing and filling
the powder will have the characteristics of a 50 m powder.
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Such a powder is able to more easily flow and meter. One
disadvantage of such a powder, however, is that removal of the
smaller particles from the larger particles is difficult, and
the resulting powder formulation is made up largely of the
5 bulky flowing agent component which can end up in the device,
or the patient's throat.
Current methods for filling unit dose receptacles
with powdered medicaments include a direct pouring method
where a granular powder is directly poured via gravity
(sometimes in combination with stirring or "bulk" agitation)
into a metering chamber. When the chamber is filled to the
desired level, the medicament is then expelled from the
chamber and into the receptacle. In such a direct pouring
process, variations in density can occur in the metering
chamber, thereby reducing the effectiveness of the metering
chamber in accurately measuring a unit dose amount of the
medicament. Moreover, the powder is in a granular state which
can be undesirable for many applications.
Some attempts have been made to minimize density
variations by compacting the powder within, or prior to
depositing it in the metering chamber. However, such
compaction is undesirable, especially for powders made up of
only fine particles, in that it decreases the dispersibility
of the powder, i.e. reduces the chance for the compacted
powder to be broken down to the individual particles during
pulmonary delivery with a dispersion device.
It would therefore be desirable to provide systems
and methods for the processing of fine powders which would
overcome or greatly reduce these and other problems. Such
systems and methods should allow for accurate and precise
metering of the fine powder when divided into unit doses for
placement in unit dose receptacles, particularly for low mass
fills. The systems and methods should further ensure that the
fine powder remains sufficiently dispersible during processing
so that the fine powder may be used with existing inhalation
devices which require the powder to be broken down to the
individual particles before pulmonary delivery. Further, the
systems and methods should provide for the rapid processing of
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6
the fine powders so that large numbers of unit dose
receptacles can rapidly be filled with unit dosages of fine
powder mzdicaments in order to reduce cost.
2. Descriotion of the Background Art
U.S. Patent No. 5,765,607 describes a machine to
meter products into containers and includes a metering unit to
supply the product into containers.
U.S. Patent No. 4,640,322 describes a machine which
applies sub-atmospheric pressure through a filter to pull
material directly from a hopper and laterally into a non-
rotatable chamber.
U.S. Patent 4,509,568 describes a granular material
processing apparatus employing a rotating paddle to stir the
=5 granular material.
U.S. Patent No. 2,540,059 describes a powder filling
apparatus having a rotating wire loop stirrer for stirring
powder in a hopper before directly pouring the powder into a
metering chamber by gravity.
German patent DE 3607187 describes a mechanism for
the metered transport of fine particles.
Product brochure, "E-1300 Powder Filler" describes a
powder filler available from Perry Industries, Corona, CA.
U.S. Patent No. 3,874,431 describes a machine for
filling capsules with powder. The machine employs coriilg
tubes that are held on a rotatable turret.
British Patent No. 1,420,364 describes a membrane
assembly for use in a metering cavity employed to measure
quantities of dry powders.
British Patent No. 1,309,424 describes a powder
filling apparatus having a measuring chamber with a piston
head used to create a negative pressure in the chamber.
Canadian Patent No. 949,786 describes a powder
filling machine having measuring chambers that are dipped into
the powder. A vacuum is then employed to fill the chamber
with powder.
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7
SUMMARY OF THE INVENTION
The invention provides systems, apparatus and
methods for the metered transport of fine powders into unit
dose receptacles. In one exemplary method, such fine powders
are transported by first agitating the fine powders with a
vibrating element, and then capturing at least a portion of
the fine powder. The captured fine powder is then transferred
to a receptacle, with the transferred powder being
sufficiently uncompacted so that it can be substantially
dispersed upon removal from the receptacle. Usually, the fine
powder will comprise a medicament with the individual
particles having a mean size that is less than about 100 m,
usually less than about 10 m, and more usually in the range
from about 1 m to 5 m.
The fine powder will preferably be placed into a
hopper having an opening at a bottom end. The element is
vibrated to agitate the fine powder. Vibration of the powder
in the vicinity of the opening assists in the transfer of a
portion of the fine powder through the opening where it may be
captured into a chamber. Vibration of the element also
assists in de-agglomerating powder within the metering chamber
so that the metering chamber may more uniformly be filled.
The vibratable element is preferably vibrated in an
up and down, i.e. vertical, motion relative to the powder in
25# the hopper. In one aspect, an ultrasonic horn is employed to
vertically vibrate the element. Alternatively, the element
may comprise a rod that is vibrated back and forth, i.e.
laterally, within the powder. In another alternative, the
vibratable element is vibrated in an orbital manner. In one
aspect, the rod is operably attached to a piezoelectric motor
which vibrates the rod. Preferably, the element is vertically
vibrated at a frequency in the range from about 1,000 Hz to
about 180,000 Hz, and more preferably from about 10,000 Hz to
about 40,000 Hz, and most preferably from about 15,000 Hz to
about 25,000 Hz. The rod is preferably vibrated laterally at
a frequency in the range from about 50 Hz to about 50,000 Hz,
and more preferably in the range from about 50 Hz to about
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8
5,000 Hz, and most preferably in the range from about 50 Hz to
about 1,000 Hz.
In another aspect, the element has a distal end
which is placed near the opening. Further, the distal end has
an end member which is vibrated over the chamber to assist in
transfer of the fine powder from the hopper to the chamber.
The end member preferably projects laterally outward from the
element. In one aspect, the end member comprises a cylinder
when the element is vibrated vertically. In another aspect,
the end member comprises a cross-member when the rod is
laterally vibrated. Preferably, the end-member is vertically
spaced apart from the chamber by a distance in the range from
about 0.01 mm to about 10 mm, and more preferably from about
0.5 mm to about 3.0 mm. Such a distance assists in keeping
the powder uncompacted when transferred to the chamber.
In still another aspect, the element is preferably
moved across the opening while being vibrated. For instance,
the element may be translated along the opening at a rate that
is preferably less than about 100 cm/s. However, the
particular rate of translation will typically depend on the
vibrational frequency of the element. In this way, the
element is swept across the chamber while being vibrated.
Movement of the element along the opening is
particularly preferable when multiple chambers are aligned
with the opening. In this way, the element may be employed to
assist in the transfer of fine powder from the hopper into
each of the chambers. Optionally, a plurality of elements or
rods may be vibrated within the hopper in the vicinity of the
openings. Preferably, the rods will be aligned with each
other and will be translated along the opening while being
vibrated, although in some cases the rods or elements may
remain stationary over each chamber.
To assist in the capture of the fine powder in the
chamber, air is preferably drawn through the chamber bottom to
draw the fine powder into the chamber. Following capture of
the fine powder, the powder is preferably transferred to a
receptacle. Transferring of the fine powder is preferably
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9
accomplished by introducing a compressed gas into the chamber
to expel the captured powder into the receptacle.
In another aspect of the method, the powder in the
hopper is periodically levelled. As one example, the powder
may be levelled by placing a projecting member above the
distal end of the vibratable element. In this way, the
projecting member vibrates along with the vibratable element.
As the element is translated along the hopper, the projecting
member tends to level the powder in the hopper. In one
aspect, transfer of the powder is performed in a moisture
controlled environment.
In still another aspect, the powder captured by the
chamber is adjusted to be a unit dose amount. This may be
accomplished by placing a thin plate (or doctor sheet) between
the hopper and the chamber. The plate has an aperture to
allow for the transfer of the powder from the hopper and into
the chamber. The chamber is then moved relative to the plate,
with the plate scraping any excess powder from the chamber.
Alternatively, a doctor blade may be employed to scrape any
excess powder from the chamber as the chamber is rotated.
In one particular aspect, the powder is transferred
to the hopper from a secondary hopper. Preferably, the
secondary hopper is vibrated to transfer the powder onto a
chute where it passes into the primary hopper. In still yet
another aspect, the chamber is periodically removed and
replaced with a chamber of a different size to adjust the
volume of the chamber. In this way, different unit dosages
may be produced by the invention.
The invention further provides an exemplary
apparatus for transporting a fine powder. The apparatus
comprises a hopper for holding the fine powder. The apparatus
further includes at least one chamber which is moveable to
allow the chamber to be placed in close proximity to an
opening in the hopper. A vibratable element is also provided
having a proximal end and a distal end, with the element being
placed within the hopper such that the distal end is near the
opening. A vibrator is provided to vibrate the element when
within the fine powder. In this way, the element may be
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vibrated to agitate the fine powder to assist in its transfer
from the hopper to the chamber. Preferably, the vibrator
comprises an ultrasonic horn which vibrates the element in an
up and down or vertical motion. Alternatively, a
5 piezoelectric motor may be employed to laterally vibrate the
element.
In one exemplary aspect, the apparatus further
includes a mechanism for translating the vibratable element or
rod over the chamber as the element is vibrated. Such a
10 mechanism is particularly advantageous when a plurality of
chambers are provided in a rotatable member which is rotated
to align the chambers with the opening. The translating
mechanism may then be employed to translate the element over
the rotatable member so that the vibrating element passes over
each chamber to assist in the filling of each with powder.
The translating mechanism preferably comprises a linear drive
mechanism which translates the rod along the opening at a rate
that is less than about 100 cm/s.
In another aspect, the vibrator is configured to
vibrate the element in an up and down motion at a frequency in
the range from about 1,000 Hz to about 180,000 Hz, and more
preferably in the range from about 10,000 Hz to about 40,000
Hz, and most preferably in the range from about 15,000 Hz to
about 25,000 Hz. When vibrated up and down, the vibratable
element preferably comprises a cylindrical shaft having a
diameter in the range from about 1.0 mm to about 10 mm. When
vibrated laterally, the element preferably comprises a rod or
wire having a diameter in the range from about 0.01 inch to
about 0.04 inch.
An end-member is preferably operably attached to the
distal end of the vibratable element to assist in agitation of
the fine powder. The end-member is preferably vertically
spaced apart from the chamber by a distance in the range from
about 0.01 mm to about 10 mm, and more preferably from about
0.5 mm to about 3.0 mm. In one alternative, the apparatus is
provided with a plurality of vibratable elements so that
multiple elements may be vibrated within the fine powder.
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In still another aspect, the chamber is disposed
within a rotatable member which is placed in a first position
having the chamber aligned with the opening in the hopper, and
a second position having the chamber aligned with a
receptacle. In this way, the chamber may be filled with
powder when in the first position. The rotatable member is
then rotated to the second position to allow the powder to be
expelled from the chamber and into the receptacle. The
chamber preferably includes a port which is in communication
with a vacuum source to assist in drawing the fine powder from
the hopper and into the chamber. A filter is preferably
disposed across the port to assist in capturing the powder. A
source of compressed gas is preferably also in communication
with the port to eject the captured powder from the chamber
and into the receptacle. A controller may be provided for
controlling actuation of the gas source, the vacuum source and
operation of the vibrator.
The apparatus may also include a mechanism for
adjusting the amount of captured powder in the chamber due to
the chamber volume. In this way, the captured amount will be
a unit dose amount. Such an adjustment mechanism may comprise
an edge for removing fine powder extending above the chamber.
In one embodiment, the adjustment mechanism comprises a thin
plate having an aperture which may be aligned with the chamber
during filling.. As the rotatable member is rotated, the edge
of the aperture scrapes the excess powder from the chamber.
In one particular aspect, the vibratable element
includes a projecting member which is spaced above the distal
end. The projecting member serves as a leveller to level
powder within the hopper as the vibratable element is
translated along the hopper.
In another aspect, a secondary hopper is provided to
store the powder until delivered to the primary hopper. A
shaking mechanism is provided to vibrate the secondary hopper
when powder is to be transferred to the primary hopper.
Preferably, the powder passes down a chute so that the powder
may be transferred without interfering with the translation of
the vibratable member along the primary hopper.
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In still another aspect, the chamber is formed in a
change tool. In this way, the size of the chamber may be
varied simply by attaching a change tool with a different
sized chamber to the rotatable member.
The invention further provides an exemplary system
for transporting fine powders. The system comprises a
plurality of rotatable members which each include a row of
chambers. A hopper is disposed above each rotatable member
and has an opening to allow powder to be transferred to the
chambers. A vibratable element is disposed in each hopper,
and vibrators are provided to vibrate the elements in an up
and down motion. A translation mechanism is further provided
to translate the vibratable members along the hoppers to
assist in transferring the powder from the hoppers and into
the chambers. Conveniently, a controller may be provided to
control operation of the rotatable members, the vibrators, and
the translation mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross-sectional side view of an
exemplary apparatus for transporting fine powders according to
the invention.
Fig. 2 is an end view of the apparatus of Fig. 1.
Fig. 3 is a more detailed view of a chamber of the
apparatus of Fig. 1 showing a vibrating rod being translated
over the chamber according to the invention.
Fig. 4 is a left front perspective view of an
exemplary system for transporting powder according to the
invention.
Fig. 5 is a right front perspective view of the
system of Fig. 4.
Fig. 6 is a cross-sectional view of the system of
Fig. 4.
Fig. 7 is a schematic view of an alternative
apparatus for transporting fine powders according to the
invention.
*rB
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Fig. 8 is a schematic view of still another
alternative apparatus for transporting fine powders according
to the invention.
Fig. 9 is a schematic view of still another
alternative apparatus for transporting fine powders according
to the invention.
Fig. 10 is a perspective view of a further
embodiment of an apparatus for transporting fine powders
according to the invention.
Fig. 11 is a cross-sectional view of the apparatus
of Fig. 10 taken along lines 11-11.
Fig. 12 is a cross-sectional view of the apparatus
of Fig. 10 taken along lines 12-12.
Fig. 13 is an exploded view of a rotatable member of
the apparatus of Fig. 10.
Fig. 14A is a schematic view of a scraping mechanism
for scraping excess powder from a chamber of a rotatable
member.
Fig. 14B is an end view of the scraping mechanism of
Fig. 14A as mounted above the rotatable member.
Fig. 14C is a perspective view of an alternative
mechanism for scraping excess powder from a chamber of a
rotatable member according to the invention.
Fig. 15 is a perspective view of a particularly
preferable system for transporting powders according to the
invention.
DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS
The invention provides methods, systems, and
apparatus for the metered transport of fine powders into
receptacles. The fine powders are very fine, usually having a
mean size in the range that is less than about 20 m, usually
less than about 10 m, and more usually from about 1 m to
5 m, although the invention may in some cases be useful with
larger particles, e.g., up to about 50 m or more. The fine
powder may be composed of a variety of constituents and will
preferably comprise a medicament such as proteins, nucleic
acids, carbohydrates, buffer salts, peptides, other small
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biomolecules, and the like. The receptacles intended to
receive the fine powder preferably comprise unit dose
receptacles. The receptacles are employed to store the unit
dosage of the medicament until needed for pulmonary de.liverv.
To extract the medicament from the receptacles, an inhalation
device, such as those described in U.S. Patent Nos. 5,785,049
and 5,740,794 may be employed.
However, the methods of the invention are
also useful in preparing powders to be used with other
inhalation devices which rely on the dispersement of the fine.
powder.
The receptacles are preferably each filled with a
precise amount of the fine powder to ensure that a patient
will be given the correct dosage. When metering and
transporting the fine powders, the fine powders will be
delicately handled and not comnressed, so that the unit dosage
amount delivered to the receptacle is sufficiently dispersible
to be useful when used with existing inhalation devices. The
fine powders prepared by the invention will be especially
useful with, although not limited to, "low energy" inhalation
devices which rely on manual operation or solely upon
inhalation to disperse the powder_ With such inhalation
devices, the powder will preferably be at least 20% (by
weight) dispersible or extractable into a flowing air stream,
more preferably be at least 60% dispersible, and most
preferably at least 90% dispersible as defined in U.S. Patent
No. 5,785,049. Since
the cost of producing the fine powder medicaments are usually
quite expensive, the medicament will preferably be metered and
transported into the receptacles with minimal wastage.
Preferably, the receptacles will be rapidly filled with the
unit dosage amounts so that large numbers of receptacles
containing the metered medicament can economically be
produced.
According to the invention, the fine particles are
captured in a metering chamber (which is.preferably sized to
define a unit dosage volume). A preferable method of
capturing is by drawing air through the chamber so that the
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drag force of the air will act upon the small agglomerates or
individual particles as described in U.S. Patent No.
5,775,320.
In this way, the fluidized fine
5 powder fills the chamber without substantial compactiori and
without substantial formation of voids. Further, capturing in
this manner allows the fine powder to be accurately and
repeatably metered without unduly decreasing the
dispersibility of the fine powder. The flow of air.through
10 the chamber may be varied in order to control the density of
the captured powder.
After the fine powder is metered, the fine powder is
ejected into the receptacle in a unit dosage amount, with the
ejected fine powder being sufficiently dispersible so that it
15 may be entrained and aerosolized in the turbulent air flow
created by an inhalation or dispersion device. Such an
ejection process is described in U.S. Patent No. 5,775,320.
Agitation of the fine powders is preferably
accomplished by vibrating a vibratable member within the fine
powder in the vicinity just above the capture chamber.
Preferably, the element is vibrated in an up and down, i.e.,
vertical, motion. Alternatively, the element may be laterally
vibrated. A variety of mechanisms may be employed to vibrate
the elements including an ultrasonic horn, a piezoelectric
bending motor, a motor rotating a cam or a crank shaft, an
electric solenoid, and the like. Alternatively, a wire loop
may be rotated within the fine powder to fluidize the powder.
Although agitation is preferably accomplished by vibrating the
vibratable member within the fine powder, in some cases it may
be desirable to vibrate the vibratable member just above the
powder to fluidize the powder.
Referring to Figs. 1 and 2, an exemplary embodiment
of an apparatus 10 for metering and transporting unit dosages
of a fine powder medicament will be described. Apparatus 10
comprises a trough or hopper 12 having a top end 14 and a
bottom end 16. At bottom end 16 is an opening 18. Held
within hopper 12 is a bed of fine powder 20. Positioned below
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hopper 12 is a rotatable member 22 having a plurality of
chambers 24 about its periphery. Rotatable member 22 may be
rotated to align chambers 24 with opening 18 to allow powder
20 to be transferred from hopper 12 and into chambers 24.
Positioned above hopper 12 is piezoelectric bending
motor 26 having a rod 28 attached thereto. Piezoelectric
motor 26 is positioned above hopper 12 such that a distal end
29 of rod 28 is placed within the fine powder bed 20 while
being spaced apart from rotatable member 22. Bottom end 16 of
hopper 12 is positioned just above rotatable member 22 so that
powder held within hopper 12 will not escape between bottom
end 16 and rotatable member 22. At distal end 29 of rod 28 is
a cross-member 30 which is aenerally perpendicular to rod 28.
Cross-member 30 will pre-ferably be at least as long as the top
diameters of chambers 24 to assist in agitating fine powder
into the chambers as described in greater detail hereinafter.
As best illustrated in Fig. 1, upon actuation of
piezoelectric bending motor 26, rod 28 is caused to vibrate
back and forth as indicated b_v arrows 32. Further, as
illustrated by arrow 34, piezoelectric bending motor 26 is
translatable along the length of rotatable member 22 to allow
cross-member 30 to be vibrated over each of the chambers 24.
Referring now co Fig. 3, the transfer of powder from
hopper 12 (see Fig. 1) to chamber 24 will be described in
greater detail. Disposeci within chamber 24 is a top filter 36
and a back-up filter 38. Top filter 36 is disposed in
rotatable member 22 such that it is at a known distance
relative to the top of chamber 24. A line 40 is in
communication with chamber 24 to provide suction within
chamber 24 during filling and compressed gas when expelling
the powder from cham.ber 24 in a manner similar to that
described ir, U.S. Patent No. 5,826,633.
When read_l for filling, a vacuum is created within
line 40 to draw air through chamber 24. Further, rod 28 is
vibrated as shown by arrows 32 when positioned above chamber
24 to assist in agitating powder bed 20. Such a process
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assists in transferring the powder from bed 20 and into
chamber 24. While vibrating, rod 28 is translated over
chamber 24 as indicated by arrow 34. In this way, agitation
of the powder bed 20 will occur over substantially the entire
ooening of the chamber 24. Further, translation of rod 28
will also move rod 28 over other chambers so that they may be
f"illed in a similar nianner.
As illustrated by arrows 42, rod 28 will preferably
be vertically spaced from rotatable member 22 by a distance in
the range from about 0.01 mm to about 10 mm, and more
preferably from about 0.1 mm to about 0.5 mm. Such vertical
spacing is preferred to ensure that the powder immediately
above the cavity is fluidized and can be drawn into the
cha~lber 24. Referring now to Figs. 4-6, an exemplary
embodiment of a powder transferring and metering system 44
will be described. System 44 is patterned after the
orinciples previously set forth in connection with apparatus
=0 of Figs. 1-3. System 44 comprises a base 46 and a frame 48
=or rotatably holding a rotatable member 50. Rotatable member
50 includes a plurality of chambers 52 (see Fig. 6).
.otatable member 50, including chambers 52, will preferably be
n--ovided with vacuum and compression lines similar to that
pYeviously described in U.S. Patent No. 5,826,633.
In brief, a vacuum is created to assist in drawing powder into
chambers 52. Upon filling of chambers 52, rotatable member 50
_s rotated until chambers 52 are facing downward. At that
point, compressed gas is forced through chambers 52 to eject
the captured powder into receptacles, such as blister packages
as are commonly used in the art.
Positioned above rotatable member 50 is a hopper 54
having an elongate opening 56 (see Fig. 6). Operably mounted
zo frame 48 are a plurality of piezoelectric bending motors
58. Attached to each of piezoelectric bending motors 58 is a
-od 60. An exemplary piezoelectric bending motor is
commercially available from Piezo Systems, Inc., Cambridge,
Massachusetts. Such bending motors comprise two layers of a
oiezoceramic, each having an outer electrode. An electric
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field is applied across the two outer electrodes to cause one
layer to expand while the other contracts.
Rod 60 will preferably comprise a stainless steel
wire rod having a diameter in the range from about 0.005 inch
to about 0.10 inch, and more preferably from about 0.02 inch
to about 0.04 inch. However, it will be appreciated that
other materials and geometries may be used when constructing
rod 60. For example, a variety of rigid materials may be
employed, including other metals and alloys, a steel music
wire, a carbon fiber, plastics, and the like. The shape of
rod 60 may also be non-circular and/or non-uniform in cross
section, with an important feature being the ability to
agitate the powder near the distal end of the rod to fluidize
the powder. A perpendicular cross-member 62 (see Fig. 6) will
preferably be attached to the distal end of rod 60. One or
more cross-members may optionally be positioned above the
distal cross-member to help collapse any trenches created in
the powder bed during operation. When actuated, rods 60 will
preferably be vibrated at a frequency in the range from about
5 Hz to about 50,000 Hz, and more preferably in the range from
about 50 Hz to about 5,000 Hz, and most preferably in the
range from about 50 Hz to about 1,000 Hz.
Piezoelectric bending motors 58 are attached to
translation mechanism 64 which translates rods 60 along hopper
54. When translated, cross-member 62 will preferably be
vertically spaced above chambers 52 by a distance in the range
from about 0.01 mm to about 10 mm, and more preferably from
about 0.1 mm to about 0.5 mm. Translation mechanism 64
comprises a rotary drive pulley 66 which rotates a belt 68,
which in turn is attached to a platform 70. Piezoelectric
bending motors 58 are attached to platform 70 which is
translated over a shaft 72 when pulley 66 is actuated. In
this way, rods 60 may be translated back and forth within
hopper 54 so that rods 60 will be vibrated over each of the
chambers 52. Translation mechanism 64 may be employed to pass
rod 60 over chambers 52 as many times as desired when filling
chambers 52. Preferably, rod 60 will be translated at a speed
that is less than about 200cm/s, and more preferably less than
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about 100 cm/s. Rod 60 will preferably pass over each chamber
at least one time, with two passes being preferred.
In operation, hopper 54 is filled with fine powder
that is to be transferred into chambers 52. A vacuum is then
drawn through each of chambers 52 while they are aligned with
opening 56. At the same time, piezoelectric bending motors 58
are actuated to vibrate rods 60. Translation mechanism 64 is
actuated to translate rods 60 back and forth within hopper 54
while rods 60 are vibrating. Vibration of rods 60 agitates
the fine powder to assist in its transfer into chambers 52.
When chambers 52 are sufficiently filled, rotatable member 50
is rotated 180 to place chambers 52 in a downward position.
As rotatable member 50 is rotated, a blade at the bottom edge
of hopper 54 scrapes off any excess powder to ensure that each
chamber contains only a unit dose amount of fine powder.
When in the downward position, a compressed gas is
forced through each of chambers 52 to eject the fine powder
into receptacles (not shown). In this way, a convenient
method is provided for transferring fine powder from a hopper
into receptacles in a metered amount.
Referring now to Fig. 7, an alternative embodiment
of an apparatus 74 for transferring metered doses of fine
powder will be described. Apparatus 74 comprises a housing 76
and a piezo substrate 78 operably attached to housing 76.
piezo substrate 78 includes a plurality of holes 80 (or a
screen). Positioned above substrate 78 is a hopper 82 having
a bed of fine powder 84. Attached to substrate 78 is a pair
of electrical leads 86 for actuation of piezo substrate 78.
When electrical current is alternately supplied to leads 86,
substrate 78 is caused to expand and contract to produce a
vibration mode as illustrated by arrow 88. In turn, holes 80
are caused to vibrate to assist in agitating powder bed 84 to
more effectively allow the powder to fall through holes 80 and
into a chamber. A rotatable member having chambers in
communication with a vacuum source and a pressure source as
described in previous embodiments may also be used in
connection with apparatus 74 to assist in capturing the fine
powder and expelling the captured powder into receptacles.
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A further embodiment of an apparatus 100 for
transferring metered doses of fine powder is illustrated in
Fig. 8. Apparatus 100 operates similar to apparatus 10 as
previously described, except that the piezoelectric bending
5 motor has been replaced with a motor 102 having a crank 104
which drives a linkage shaft 106. As shaft 106 is
reciprocated, a rod 108 is vibrated within a hopper 110 that
is filled with powder 112. The agitated powder is then
captured in a chamber 114 in a manner similar to that
10 previously described. Further, rod 108 may be translated over
chamber 114 during vibration in a manner similar to that
previously described with other embodiments.
Another embodiment of an apparatus 120 for
transferring metered doses of fine powder is illustrated in
15 Fig. 9. Apparatus 120 comprises a motor 122 which rotates a
wire loop 124. As shown, wire loop 124 is disposed within a
bed of fine powder 126 just above a chamber 128. In this way,
when wire loop 124 is rotated, the powder will be fluidized
and drawn into chamber 128 in a manner similar to previous
20 embodiments. Further, loop 124 may be translated over chamber
128 during its rotation in a manner similar to that previously
described with other embodiments.
Referring now to Fig. 10, another embodiment of an
apparatus 200 for transporting fine powders will be described.
Apparatus 200 operates in a manner similar to the other
embodiments as previously described in that powder is
transferred from a hopper into metering chambers of a
rotatable member. From the rotatable member, the powder is
expelled into receptacles in unit dosage amounts.
Apparatus 200 comprises a frame 202 which holds a
rotatable member 204 such that rotatable member 204 may be
rotated by a motor (not shown) held on frame 202. Frame 202
also holds a trough or primary hopper 206 above rotatable
member 204. Positioned above hopper 206 is a vibrator 208.
As shown in Figs. 11 and 12, a vibratable element 210 is
coupled to vibrator 208. Vibrator 208 is coupled to an arm
212 by a clamp 214. Arm 212 in turn is coupled to a
translation stage 216. A screw motor 217 is employed to
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translate stage 216 back and forth relative to frame 202. In
this way, vibratable element 210 may be translated back and
forth within hopper 206.
Referring also now to Figs. 11 and 12, apparatus 200
further includes a secondary hopper 218 disposed above primary
hopper 206. Conveniently, hopper 218 includes wings 219 to
allow it to be removably coupled to frame 202 by inserting
wings 219 into slots 220. Hopper 218 comprises a housing 222
and a tubular section 224 for storing powder. A chute 226
extends from housing 222 and into hopper 206 when hopper 218
is attached to frame 202. Tubular section 224 includes an
opening 228 to allow powder to flow from tubular section 224
and down chute 226. A screen 230 is disposed over opening 228
to generally prevent the flow of powder down chute 226 until
housing 222 is shaken or vibrated.
Conveniently, a latch 232 is employed to secure
secondary hopper 218 to frame 202. To remove secondary hopper
218, latch 232 is disengaged from hopper 218 and hopper 218 is
lifted from slots 220. In this way, hopper 218 may be
conveniently removed for refilling, cleaning, replacement, or
the like.
To transfer powder from hopper 218, an arm 234 is
placed into contact with housing 222 and is shaken or vibrated
to vibrate housing 222. A motor (not shown) is employed to
shake or vibrate arm 234. As shown in Fig. 12, housing 222
may optionally include an internal opening 236 containing a
block 238. As housing 222 is shaken, block 238 vibrates
within opening 236. As block 238 engages the walls of housing
222, it sends shock waves through housing 222 to assist in
transferring the powder from tubular section 224, through
opening 228, and through screen 230. The powder then slides
down chute 226 until it falls within hopper 206. Use of chute
226 is also advantageous in that it allows tubular section 224
to be laterally offset from vibrator 208 so that it will not
interfere with the motion of vibrator 208. One particular
advantage of including block 238 within opening 236 is that
any particulate generated as block 238 is vibrated will be
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maintained within opening 236 and will not contaminate any of
the powder.
Vibrator 208 is configured to vibrate element 210 in
an up and down or vertical motion. Vibrator 208 preferably
comprises any one of a variety of commercially available
ultrasonic horns, such as a Branson TWI ultrasonic horn.
Vibratable element 210 is preferably vibrated at a frequency
and range from about 1,000 Hz to about 180,000 Hz, and more
preferably from about 10,000 Hz to about 40,000 Hz, and most
preferably from about 15,000 Hz to about 25,000 Hz.
As best shown in Fig. 12, vibratable element 210
includes an end member 240 which is appropriately shaped to
optimize agitation of the fine powder during vibration of
element 210. As shown, end member 240 has an outer periphery
which is greater than that of element 210. Element 210 is
preferably cylindrical in geometry and preferably has a
diameter in the range from about 0.5 mm to about 10 mm. As
shown, end member 240 is also cylindrical in geometry and
preferably has a diameter in the range from about 1.0 mm to
about 10 mm. However, it will be appreciated that vibratable
element 210 and end member 240 may be constructed to have a
variety of shapes and sizes. For example, vibratable element
210 may be tapered. End member 240 may also have a reduced
profile to minimize the lateral movement of powder as vibrator
208 is translated through hopper 206. Preferably, end member
240 is vertically spaced above rotatable member 204 by a
distance in the range from about 0.01 mm to about 10 mm, and
more preferably from about 0.5 mm to about 3.0 mm.
Vibrator 208 is employed to assist in the transfer
of powder into metering chambers 242 of rotatable member 204
in a manner similar to that described with previous
embodiments. More specifically, motor 217 is employed to
translate stage 216 so that vibratable element 210 may be
translated laterally back and forth along hopper 206. At the
same time, vibratable element 210 is vibrated in an up and
down motion, i.e., radial to rotatable member 204, as it
passes over each of metering chambers 242. Preferably,
vibrator 208 is laterally translated along hopper 206 at a
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rate that is less than about 500 cm per second, and more
preferably less than about 100 cm per second.
As vibratable element 210 is moved laterally within
hopper 206, there may be a tendency for vibratable element 210
to push or plow some of the powder towards the ends of hopper
206. Such movement of the powder is mitigated by providing a
radiating surface or projecting member 244 on vibratable
element 210 just above an average powder depth within the
hopper. In this way, accumulated powder that is higher than
the average depth is preferentially mobilized and moved to
areas in the hopper having a smaller powder depth.
Preferably, projecting member 244 is spaced apart from end
member 240 by a distance in the range from about 2 mm to about
25 mm, and more preferably from about 5 mm to about 10 mm. As
an alternative, various plowing mechanisms, such as rakes, may
be attached to vibrator 208 (or be separately articulatable)
so that they will drag over the top of the powder to assist in
leveling the powder as vibrator 208 is translated along the
hopper. As another alternative, an elongate vibratory
element, such as a screen, may be disposed within the powder
bed to assist in levelling the powder.
As shown in Figs. 11 and 12, rotatable member 204 is
in a filling position where metering chambers 242 are aligned
with hopper 206. As with the other embodiments described
herein, once metering chambers 242 are filled, rotatable
member 204 is rotated 180 where the powder is ejected from
metering chambers 242 into receptacles. A Klockner packaging
machine is preferably employed to supply apparatus 200 with a
sheet containing the receptacles.
Referring now to Fig. 13, construction of rotatable
member 204 will be described in greater detail. Rotatable
member 204 comprises a drum 246 having a front end 248 and a
back end 250. Bearings 252 and 254 are insertable over ends
248 and 250 to allow drum 246 to rotate when attached to frame
202. Rotatable member 204 further includes a collar 256, a
rear slip ring 258 and a front slip ring 259 which are fitted
with gas tight seals. Air inlets 260 and 261 are provided in
collar 256. Air inlet 260 is in fluid communication with a
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pair 242a of metering chambers 242 while inlet 261 is in fluid
communication with a pair 242b of metering chambers 242. In
this way, pressurized air or a vacuum may be produced in
either pair of chambers 242a or 242b.
More specifically, air from inlet 260 passes through
slip ring 258, through a hole 264 in a gasket 270 and into a
hole 265 in a manifold 262. The air then passes through
manifold 262 and exits manifold 262 through a pair of holes
265a and 265b. Holes 265c and 265d in bracket 270 then route
the air into chambers 242a. In a similar manner, air from
inlet 261 passes through slip ring 259, through a hole 266 in
gasket 270 and into a hole (not shown) in manifold 262. The
air is routed through various holes in manifold 262 and gasket
270 in a manner similar to that previously described with
inlet 260 until passing through chambers 242b. In this
manner, two separate air circuits are provided.
Alternatively, it will be appreciated that one of the air
inlets could be eliminated so that a vacuum or pressurized gas
may be simultaneously provided to all of metering chambers
242.
Also disposed above manifold 262 is a change tool
274. Metering chambers 242 are formed in change tool 274, and
filters 276 are disposed between change tool 274 and air
bracket 272 to form a bottom end of metering chambers 242.
Air may be drawn into chambers 242 by attaching a vacuum to
air inlets 260 or 261. Similarly, a compressed gas may be
forced through metering chambers 242 by coupling a source of
compressed gas to air inlets 260 or 261. As with other
embodiments described herein, a vacuum is drawn through
metering chambers 242 to assist in drawing the powder into
metering chambers 242. After drum 246 is rotated 180 , a
compressed gas is forced through metering chambers 242 to
expel the powder from metering chambers 242.
Drum 246 includes an aperture 278 into which
manifold 262, gasket 270, air bracket 272 and change tool 274
are inserted. A cam 280 is also provided and is insertable
into aperture 278. Cam 280 is rotated within aperture 278 to
secure the various components within drum 246. When loosened,
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it is possible to slide change tool 274 from aperture 278. In
this way, change tool 274 may easily be replaced with another
change tool having different sized metering chambers. In this
manner, apparatus 200 may be provided with a wide assortment
5 of change tools which allows a user to easily change the size
of the metering chambers simply by inserting a new change tool
274.
Apparatus 200 further includes a mechanism for
doctoring any excess powder from metering chambers 242. Such
10 a doctoring mechanism 282 is illustrated in Figs. 14A and 14B
and is also referred to as a doctoring sheet. For convenience
of illustration, doctoring mechanism 282 has been omitted from
the drawings of Figs. 10-12. In Figs. 14A and 14B, rotatable
member 204 is shown in schematic view. Doctoring mechanism
15 282 comprises a thin plate 284 having apertures 286 which are
aligned with metering chambers 242 when rotatable member 204
is in the filling position. Apertures 286 preferably have a
diameter that is slightly larger than the diameter of metering
chambers 242. In this way, apertures 286 will not interfere
20 with the filling of metering chambers 242. Plate 284 is
preferably constructed of brass and has a diameter of
approximately 0.003 inches. Plate 284 is sprung against
rotatable member 204 so that it is generally flush against the
outer periphery. In this way, plate 284 is generally sealed
25 against rotatable member 204 to prevent excess powder from
escaping between plate 284 and rotatable member 204. Plate
284 is attached to frame 202 and remains stationary while
rotatable member 204 rotates. In this way, after powder has
been transferred to metering chambers 242, rotatable member
204 is rotated toward the dispensing position. During
rotation, the edges of apertures 286 scrape any excess powder
from metering chambers 242 so that only a unit dose amount
remains in metering chambers 242. Configuration of doctoring
mechanism 282 is advantageous in that it reduces the amount of
movable parts, thereby reducing the build up of static
electricity. Further, the removed powder remains within
hopper 206 where it will be available for transfer into
metering chambers 242 after they have been emptied.
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Illustrated in Fig. 14C is an alternative mechanism
for scraping or doctoring excess powder from metering chambers
242. The mechanism comprises a pair of doctoring blades 290
and 292 which are coupled to hopper 206, it being appreciated
that only one blade may be needed depending on the direction
of rotation of rotatable member 204. Blades 290 and 292 are
preferably constructed of a thin sheet material, such as 0.005
inch brass, and are sprung lightly against rotatable member
204. The edges of blades 290 and 292 coincide approximately
with the edges of the opening in hopper 206. After metering
chambers 242 are filled, rotatable member 204 is rotated, with
blades 290 or 292 (depending on the direction of rotation)
scraping any excess powder from metering chambers 242.
Referring back now to Figs. 10-12, operation of
apparatus 200 to fill receptacles with unit dosages of fine
powder will be described. Initially, the fine powder is
placed into tubular section 224 of secondary hopper 218.
Conveniently, hopper 218 may be removed from frame 202 during
filling. Housing 222 is then shaken or vibrated for a time
sufficient to transfer a desired amount of powder through
opening 228, through screen 230 and down chute 226 where it
falls into primary hopper 206. Rotatable member 204 is placed
in the filling position where metering chambers 242 are
aligned with hopper 206. A vacuum is then applied to air
inlets 260 and 261 (see Fig. 13) to draw air through metering
chambers 242. Under the influence of gravity, and with the
assistance of the vacuum, the powder tumbles into the metering
chambers 242 and generally fills metering chambers 242.
Vibrator 208 is then actuated to vibrate element 210. At the
same time, motor 217 is operated to translate vibratable
element 210 back and forth within chamber 206. As element 210
is vibrated, end member 240 creates a pattern of air flow at
the bottom of hopper 206 to agitate the powder. As end member
240 passes over each metering chamber 242, an aerosol cloud is
produced that is drawn into the metering chamber 242 by vacuum
and by gravity. As end member 242 passes over metering
chambers 242, ultrasonic energy radiates down into metering
chambers 242 to agitate the powder already inside the metering
*rB
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chamber. This in turn allows flow within the cavity to even
out any irregularities in density that may exist during
previous filling. Such a feature is particularly advantageous
in that agglomerates or chunks of powder which may create
voids in the metering chamber may be broken down to more
evenly fill the metering chamber.
After passing one or more times over each of the
metering chambers 242, rotatable member 204 is rotated 1800 to
a dispensing position where metering chambers 242 are aligned
with receptacles (not shown). As rotatable member 204
rotates, any excess powder is scraped from metering chambers
242 as previously described. When in the dispensing position,
a compressed gas is supplied through air inlets 260 and 261 to
expel unit dosages of powder from metering chambers 242 and
into the receptacles.
The invention also provides a way to adjust fill
weights by modulating the ultrasonic power supplied to
vibrator 210 as it passes over metering chambers 242. In this
way, fill weights for the various metering chambers may be
adjusted to compensate for powder weight discrepancies that
may periodically occur. As one example, if the fourth
metering chamber was consistently producing a dosage amount
that was too low in weight, the power to vibrator 208 could be
increased slightly each time it passed over the fourth
metering chamber. In conjunction with an automated (or
manual) weighing system and a controller, such an arrangement
may be used to make an automated (or manual) closed-loop
weight control system to adjust the power level of the
vibrator for each of the metering chambers to provide more
accurate fill weights.
Referring now to Fig. 15, an exemplary embodiment of
a system 300 for metering and transporting a fine powder will
be described. System 300 operates in a manner similar to
apparatus 200 but includes multiple vibrators and multiple
hoppers for simultaneously filling a plurality of receptacles
with unit dosages of fine powder. System 300 comprises a
frame 302 to which are rotatably coupled a plurality of
rotatable members 304. Rotatable members 304 may be
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constructed similar to rotatable member 204 and include a
plurality of metering chambers (not shown) for receiving
powder. The number of rotatable members and metering chambers
may be varied.according to the particular application.
Disposed above each rotatable member 304 is a primary hopper
306 which holds the powder above rotatable members 304. A
vibrator 308 is disposed above each hopper 306 and includes a
vibratable element 310 to agitate the powder within hopper 306
in a manner similar to that described in connection with
apparatus 200. Although not shown for convenience of
illustration, a secondary hopper which is similar to secondary
hopper 218 of apparatus 200 will be disposed above each of
primary hoppers 306 to transfer powder into hoppers 306 in a
manner similar to that described in connection with apparatus
200.
A motor 312 (only one being shown for convenience of
illustration) is coupled to each of rotatable members 304 to
rotate rotatable members 304 between a filling position and a
dispensing position similar to apparatus 200.
Each vibrator 308 is coupled to an arm 314 by a
clamp 316. Arms 314 are in turn coupled to a common stage 318
which having slides 319 which are translatable over tracks 321
by a screw 320 of a screw motor 322. In this way, the
vibratable elements 310 may simultaneously be moved back and
forth in hoppers 306 by operation of screw motor 322.
Alternatively, each of vibrators could be coupled to a
separate motor so that each vibrator may independently be
translated.
Frame 302 is coupled to a base 324 which includes a
plurality of elongate grooves 326. Grooves 326 are adapted to
receive bottom ends of a plurality of receptacles 328 which
are formed in a sheet 330. Sheet 330 is preferably supplied
from a blister maker, such as a commercially available Uhlmann
Packaging Machine, Model No. 1040. Rotatable members 304
preferably include a number of metering chambers that
correspond to the number of receptacles in each row of sheets
330. In this way, four rows of receptacles may be filled
during each cycle of operation. Once four of the rows are
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filled, the metering chambers are again refilled and sheet 330
is advanced to align four new rows of receptacles with hoppers
306.
One particular advantage of system 300 is that it
may be fully automated. For example, a controller may be
coupled to the packaging machine, vacuum and pressurized gas
sources, motors 312, motor 322 and vibrators 308. By use of
such a controller, sheet 330 may automatically be advanced to
the proper position whereupon motors 312 are actuated to align
the metering chambers with hoppers 306. A vacuum source is
then actuated to draw a vacuum through the metering chambers
while vibrators 308 are actuated and motor 322 is employed to
translate vibrators 308. Once the metering chambers are
filled, the controller is employed to actuate motors 312 to
rotate rotatable members 304 until they are aligned with
receptacles 328. The controller then sends a signal to send a
pressurized gas through the metering chambers to expel the
metered powder into receptacles 328. Once filled, the
controller causes the packaging machine to advance the sheet
330 and to repeat the cycle. When needed, the controller may
be employed to actuate motors (not shown) to vibrate the
secondary hoppers to transfer powder into primary hoppers 306
as previously described.
Although shown with vibrators which comprise
ultrasonic horns, it will be appreciated that other types of
vibrators and vibratable elements may be employed, including
those previously described herein. Further, it will be
appreciated that the number of vibrators and size of the
troughs may be varied according to the particular need.
Although the foregoing invention has been described
in some detail by way of illustration and example, for
purposes of clarity of understanding, it will be obvious that
certain changes and modifications may be practiced within the
scope of the appended claims.
