U.S. patent application number 13/190084 was filed with the patent office on 2012-01-19 for continuous feed tablet coating system.
This patent application is currently assigned to O'Hara Technologies Inc.. Invention is credited to James Marjeram, David O'Hara.
Application Number | 20120015101 13/190084 |
Document ID | / |
Family ID | 37086569 |
Filed Date | 2012-01-19 |
United States Patent
Application |
20120015101 |
Kind Code |
A1 |
O'Hara; David ; et
al. |
January 19, 2012 |
CONTINUOUS FEED TABLET COATING SYSTEM
Abstract
A system for coating tablets and other small articles is
provided. The system is comprised of an elongate housing containing
a drum journalled for rotation about a horizontal axis. The drum
has two open ends that receive and discharge a supply of tablets
respectively. The drum is rotated about the axis by a drive means
to tumble the tablets and advance the tablets through the drum. The
system also includes a system for delivering a selected amount of
coating to the tablets while they are being tumbled and a feeder
for continually feeding tablets at a first end of the housing. The
system employs a weir plate for maintaining a depth of tablets
within the drum and for controlling the time that the tablets
remain in the drum. The system has a tablet discharge region for
receiving tablets for discharge.
Inventors: |
O'Hara; David; (Toronto,
CA) ; Marjeram; James; (Markham, CA) |
Assignee: |
O'Hara Technologies Inc.
Richmond Hill
CA
|
Family ID: |
37086569 |
Appl. No.: |
13/190084 |
Filed: |
July 25, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11911498 |
Oct 12, 2007 |
8015937 |
|
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PCT/CA2006/000552 |
Apr 12, 2006 |
|
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13190084 |
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60670271 |
Apr 12, 2005 |
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Current U.S.
Class: |
427/212 ; 118/19;
118/303 |
Current CPC
Class: |
B01J 2/006 20130101;
A23G 3/26 20130101; A23G 3/0095 20130101; A61J 3/005 20130101; B01J
2/12 20130101 |
Class at
Publication: |
427/212 ; 118/19;
118/303 |
International
Class: |
A23G 3/26 20060101
A23G003/26; B05D 7/00 20060101 B05D007/00; B05C 5/00 20060101
B05C005/00 |
Claims
1. A system for coating bulk articles comprising: a housing
comprising opposed first and second ends with an axis extending
therebetween; a pan mounted within the interior of the housing for
movement relative to the housing to tumble a bed of said articles
within said pan, said pan comprising a first end for receiving said
articles and an opposed second end for discharging said articles; a
coating dispenser for dispensing coating onto said articles within
said pan; a weir plate configured to partially obstruct the second
end of said pan and maintain a selected spillover height to retain
a bed of articles within the pan; and a mount for mounting the weir
plate to the housing to partially obstruct the pan, wherein the
weir plate remains static relative to the housing during movement
of the pan, said mount permitting selective adjustment of the
position of the weir plate to alter the effective spillover height
of the weir plate.
2. The system of claim 1, wherein said pan comprises a central axis
between said first and second ends and said weir plate mount
provides rotational movement of the weir plate about said axis to
permit said adjustment of position.
3. The system of claim 1, wherein said pan comprises a rotatable
drum having opposed open ends, said weir plate comprising an
arcuate lower edge conforming to the interior surface of said
drum.
4. The system of claim 3, wherein said weir plate is rotatably
mounted to the housing for adjustment about an axis of rotation
co-axial with the axis of rotation of said drum.
5. The system of claim 4, wherein said housing comprises opposing
first and second end walls at the respective ends thereof, and said
weir plate mount comprises a rotatable shaft journalled to the
second end wall and a radially-extending link arm connecting the
weir plate to the rotatable shaft wherein rotation of the rotatable
shaft adjusts the rotational position of the weir plate about an
axis of rotation defined by the rotatable shaft.
6. The system of claim 5, wherein said second end wall comprises a
port with a door covering said port for accessing the interior of
said drum, said shaft being mounted to said door, wherein opening
of the door pivots the weir plate outwardly from the housing.
7. The system of claim 1 further comprising a feeder for dispensing
a stream of bulk articles into a first end of the pan.
8. The system of claim 7 further comprising an actuator for
adjusting the position of the weir plate and a controller in
operative communication with said feeder and said actuator
configured to control the average dwell time of tablets within said
system by controlling the rate of introduction of said tablets into
said system and the spillover height of said weir plate.
9. A system for coating bulk articles comprising: a housing having
opposed first and second ends; a rotatable drum within said
housing, said drum having a central axis, a first end for receiving
said articles and an opposed second end for discharging said
articles; a coating dispenser for dispensing coating onto a bed of
said articles within said pan; a drive for rotating said drum
relative to said housing to tumble said articles within said drum;
a weir plate configured to partially obstruct the second end of
said drum and provide a selected spillover height to maintain a
selected depth of the bed of articles within the drum; and a weir
plate mount for mounting the weir plate to the housing to partially
obstruct the drum, wherein the weir plate remains static relative
to the housing during rotation of the drum, said mount permitting
adjustment of the rotational position of the weir plate about an
axis of rotation co-axial with the central axis of the drum to
alter the effective spillover height of the weir plate.
10. The system of claim 9 further comprising a feeder for
dispensing articles in bulk into said first end of said drum.
11. The system of claim 9, wherein said housing comprises opposing
first and second end walls at the respective ends thereof, and said
weir plate mount comprises a rotatable shaft journalled to the
second end wall, and a radially-extending link arm connecting the
weir plate to the rotatable shaft wherein rotation of the shaft
adjusts the rotational position of the weir plate about an axis of
rotation defined by the rotatable shaft.
12. The system of claim 11, wherein said second end wall comprises
a port with a door covering said port located for accessing the
interior of said drum, said rotatable shaft being mounted to said
door, wherein opening of the door pivots the weir plate outwardly
from the housing.
13. The system of claim 9 further comprising an actuator for
adjusting the position of the weir plate and a controller in
operative communication with said feeder and said actuator
configured to control the average dwell time of tablets within said
system by controlling the rate of introduction of said tablets into
said system and the spillover height of said weir plate.
14. A continuous coating method for bulk articles comprising the
steps of providing a system comprising a moveable pan comprising
opposed first and second ends, a coating dispenser configured to
dispense coating onto a bed of articles within said pan, and a weir
plate at the second end of said pan; introducing articles into said
first end to form a continuous bed of said articles within said
pan; dispensing coating on said articles; providing a selected bed
depth within the pan by maintaining a selected spillover height of
said weir plate relative to the pan; determining the weight gain of
said articles indicative of the amount of coating thereon; and
controlling the average dwell time of articles within said pan to
obtain a selected coating dispensing exposure time and weight gain
of said articles by controlling the spillover height of the weir
plate relative to the pan, wherein said weir plate remains static
relative to the housing as the pan is moved.
15. The method of claim 14, wherein said pan comprises a rotatable
drum, said method comprising the steps of tumbling said articles
within said drum by rotation of the drum, and controlling the
spillover height of said weir plate by selectively adjusting the
rotational position of the weir about the elongate axis of the
drum.
16. The method of claim 14 comprising the step of further
controlling the rate of transit of said articles through the drum
by controlling the rate of introducing articles into said drum.
17. The method of claim 14, wherein said system is configured to
dispense said coating in either of a selected batch or continuous
coating mode, said method comprising the step of coating an initial
charge of articles in a batch mode, and subsequently transitioning
to a continuous coating mode by introducing a continuous stream of
articles into said pan, and adjusting the position of the weir to
permit continuous throughflow of said articles through the pan.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of application Ser. No.
11/911,498, filed on Oct. 12, 2007, the entire contents of which
are incorporated herein by reference. U.S. application Ser. No.
11/911,498 is the National Stage entry of PCT/CA2006/000552, filed
internationally on Apr. 12, 2006, the disclosure of which is hereby
incorporated by reference in its entirety. PCT International
Application No. PCT/CA2006/000552 claims priority to and the
benefit of U.S. Provisional Application Ser. No. 60/670,271, filed
of Apr. 12, 2005, the entire contents of which are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The invention relates to processes and equipment for
applying a coating in a bulk process onto articles such as
pharmaceutical tablets or other dosage forms, food articles, seeds
and other relatively small robust articles that can be processed in
bulk. More specifically, the invention relates to systems which
apply a spray-on coating onto a bed of articles within a horizontal
axis tumbler or pan.
BACKGROUND OF THE INVENTION
[0003] Coatings for articles such as tablets for human or animal
consumption (or other uses) may be applied in bulk with a system
consisting of a moveable pan, such as a rotating horizontal-axis
drum for tumbling the tablets while a coating substance is sprayed
on the tablet bed within the drum. Movement of the pan causes the
bed of articles to tumble, churn or be otherwise displaced to fully
expose the articles to an overhead sprayer. Typically, the pan is
perforated to permit a flow of heated air through the pan wall to
facilitate drying and to permit cleaning fluid to drain. Such
perforations may take on a variety of shapes and sizes suitable to
the desired application. Coating systems of this type can be are
used in a variety of other applications for applying a coating to
small articles capable of bulk processing, for example a range of
pharmaceutical dosage forms, candies and other food articles,
seeds, and other articles that can be subjected to the tumbling or
similar action of a coating system. As noted below, the terms
"tablets" and "articles" are used broadly herein to refer to any
such articles that are suitable for use in a coating system of this
type.
[0004] Tablets and other small coated articles are typically
produced in a wide range of shapes, sizes and densities.
Accordingly, any system for coating tablets or the like should be
capable of efficiently coating a wide variety of articles. A
typical coating system includes a housing, an overhead sprayer for
dispensing coating, a horizontal-axis pan for retaining the
articles during the coating stage, such as a perforated drum
journaled for rotation within the housing, and drive means to
impart motion to the pan to redistribute, tumble, or otherwise
place the articles in motion within the pan so as to fully expose
the article surfaces to the overhead sprayer. The system includes a
drive, such as a drive for rotating the drum comprising a variable
speed motor connected to the drum, for example by a belt or chain
drive. The system further includes means for introducing uncoated
articles into the pan and for removing the coated articles
following the coating process.
[0005] For pharmaceutical applications, such as coating tablets or
other dosage forms, a high level of precision in the coating
process is required in order to maintain a controlled thickness and
weight of coating. Preferably, the system includes a means for
introducing a flow of air through the pan wall, for example heated
air to facilitate the drying process. Finally, the system should
permit thorough washing of components which are in contact with the
tablets and spray liquid. Washing of the equipment may be provided
by means of fully or semi-automatic systems or a fully-manual
approach.
[0006] Coating systems are described in U.S. Pat. No. 4,725,446 to
Forster et al., which describes a rotateable horizontal axis drum
having a perforated wall. A supply of drying air flows through the
drum wall. Coating solution is sprayed onto the tumbling tablets
via a sprayer centrally positioned within the drum directed
generally downwardly towards the tumbling bed of pills within the
drum interior.
[0007] Certain prior art systems provide for batch processing of
tablets, which is relatively inefficient in comparison with a
continuous coating process. However, batch processing generally
requires simpler equipment, particularly in the pharmaceutical
processing context in which a high level of precision is required
in supplying a selected amount of coating for a given batch size of
tablets as well as tablet dwell time within the drum. Thus, it is
relatively simple to introduce a carefully measured batch size of
tablets into the drum and thereupon apply a measured amount of
coating to the tablets. Continuous processing, while more
efficient, has in the past encountered difficulties in terms of
consistency of the coating process.
[0008] Another aspect of coating systems, particularly in the
pharmaceutical industry, relates to rinsing and washing of coating
equipment, particularly those components which come into contact
with pharmaceutical product. A high standard of cleanliness applies
to the equipment, in particular when the machine is switched for
coating of one product to another. It is desirable to provide a
convenient system for spraying a cleaning solution throughout the
drum interior, with minimal worker contact with the equipment.
Cleaning of the spray assembly in a drum-type continuous coater can
be particularly difficult in that the spray assembly is housed
within the drum interior, where access is difficult. It is
desirable to provide a convenient means to retract the spray
assembly from the drum for cleaning, maintenance and other
purposes.
SUMMARY OF THE INVENTION
[0009] An object of the invention is to provide a system for
coating tablets and other small articles such as food articles,
seeds and other relatively small articles that are sufficiently
robust to withstand bulk processing steps such as tumbling, gravity
feed, and the like. For purposes of the present specification, such
small articles are usually referred to herein as "tablets" or
"articles". The present system is operable in a continuous
processing operation wherein tablets may be introduced and
discharged on a continuous basis. A further object is to provide a
system which optionally is operable in both batch and continuous
modes and able to switch seamlessly or with only minimal
interruption from one to the other mode. For example, upon system
startup the system may be operate in a batch mode, and then shifted
into continuous operation in order to minimize waste of coating
fluid. A further object is to provide an improved tablet coating
system having a horizontal-axis drum as the pan for retaining the
tablets or other articles, including improved means for washing the
tablet-coating drum and other components in contact with the
tablets.
[0010] In one aspect the invention includes a tablet coating system
including:
a) a housing comprising opposed first and second ends with an axis
extending therebetween; b) a pan mounted within the interior of the
housing for movement relative to the housing to tumble a bed of
said articles within said pan, said pan comprising a first end for
receiving said articles and an opposed second end for discharging
said articles; c) a coating dispenser for dispensing coating onto
said articles within said pan; d) a weir plate configured to
partially obstruct the second end of said pan and provide a
selected spillover height to maintain a selected depth of the bed
of articles within the pan; and e) a mount for mounting the weir
plate to the housing to partially obstruct the pan, wherein the
weir plate remains static relative to the housing during movement
of the pan, said mount permitting selective adjustment of the
position of the weir plate to alter the effective spillover height
of the weir plate.
[0011] The pan may comprise a drum journalled for rotation about a
horizontal axis extending between the housing ends, having a first
end for receiving tablets and an open second end for discharging
tablets, such that tablets received in the first end of the drum
are tumbled within the drum as the drum rotates while being coated
and optionally at least partially dried, and discharged from the
opposed end. The tablets are transited along the drum by the rotary
action of the drum as additional tablets are introduced into the
first end and discharged from the second end.
[0012] The tablets may be fed onto the pan with a feeder such as a
weigh-in feeder for dispensing a stream of bulk tablets on a
continuous basis into the first end of said housing. The tablets
may be dispensed at a selected rate, for example, by
weight/time.
[0013] The weir plate may be mounted to an end wall or door of the
housing such that its rotational position may be adjusted about a
circular path, the axis of which is co-axial with the elongate axis
of the pan or drum, in which the path corresponds with the pan or
drum wall. Repositioning of the weir plate by rotating it about the
elongate axis of the drum thus effectively changes its angular
position relative to the pan, thereby changing the effective
spillover height provided by the weir plate. The weir plate remains
static as the drum rotates except when its rotational position is
adjusted to change the effective spillover height.
[0014] In one aspect, a controller is operatively connected to the
weigh-in feeder and optionally the weir plate mount and drive means
for the pan to control operation of the system.
[0015] As the rotational position of the weir plate is adjusted,
the tablet bed depth is increased or decreased within the drum,
thereby increasing or decreasing the average dwell time of tablets
within the bed. Since the weir plate remains static as the drum is
rotated, the rotational position thereof defines its effective
spillover height relative to the lowermost portion of the drum.
[0016] The feeder may comprise a scale for weighing a stream of
tablets passing over said scale, with a conveyor belt or other
tablet transport system to carry tablets in bulk across said scale
while being weighed, and a controller/CPU which monitors total
tablet weight (or other unit of measurement) on a real time basis
as tablets are conveyed into the system. The controller is
operatively connected to said scale and feeder to monitor and
control operation of the system.
[0017] The system may be operated to process tablets in either of a
batch or continuous processing operation. Preferably the system is
controlled to operate with an initial batch process upon startup,
which then can be configured with no or minimal interruption for
operation in a continuous processing mode.
[0018] According to one aspect, the weir plate is generally
crescent or scimitar shaped, with an upper concave edge and a
substantially semi-circular lower edge which corresponds with the
inside surface of the pan. A scimitar shape provides that the upper
edge of the weir plate is asymmetric and comprises a generally flat
first region merging with a curved (hyperbolic) second region. The
weir plate is rotatably mounted so as to selectively vary the
obstruction of said drum so as to increase or decrease the depth of
tablets within said drum, and operatively connected to the
controller so as to control positioning of the weir plate. The weir
plate may be mounted to an end wall or door of the housing via a
horizontal shaft coaxial with the drum axis. A link extending
radially from the shaft connects the shaft to the weir plate, such
that rotation of the shaft causes the weir plate to travel in an
arcuate path aligned with the drum wall.
[0019] According to another aspect, the invention relates to a
coating dispenser for dispensing coating from a source onto a bed
of coatable articles within a pan. The dispenser comprises an
extendible member and a pair of opposing spray assemblies in end to
end linear relation overhead of said pan. Each of said assemblies
comprises an elongate nozzle support, an array of spray nozzles
mounted to the nozzle support for connection with a source of
pressurized coating fluid and optionally with a source of
compressed air, and an arm at an end of said nozzle support for
mounting the nozzle support to the extendible member. The
extendible member is extendible in length to permit retraction of
at least one of said spray assemblies away from said pan
independently of the other of said spray assemblies.
[0020] The extendible member may comprises two extendible segments,
which may be telescoping, to extend both respective ends thereof
outwardly in opposing directions for retracting both of said
assemblies away from the pan in opposing directions from each
other. A mounting bracket may be provided to mount the extendible
member to the system housing. The bracket extends from the
extendible member intermediate the ends thereof, with the
extendible segments being located on opposing ends of said bracket
for extending the respective ends of the extendible member on
opposing sides of the bracket.
[0021] The arms that support the sprayer assemblies may be
vertically oriented and extendible in length to vary the elevation
of the assemblies above the pan. The assemblies may be rotatably
mounted to respective ones of said arms for rotation about the
elongate axes thereof.
[0022] In the above coating dispenser, the pan may comprise a drum,
with the spray assemblies being configured for positioning within
the interior of said drum coaxially with the elongate axis of the
drum to dispense said fluid on a bed of articles located in the
base of said drum. The extendible member is external to said drum
with the respective arms being located at opposing ends of said
drum.
[0023] According to another aspect, the housing includes a lower
portion which is substantially sealed to permit cleaning liquid to
accumulate within the base of the housing, thereby effectively
forming a sealed sump or pan for retaining cleaning liquid during
the cleaning phase. A closable drain enters the housing, to permit
cleaning liquid to drain from the housing when opened. The drum is
positioned such that a lower portion of the drum extends into the
lowermost sealed portion of the housing, such that cleaning liquid
which accumulates within the lower base region of the housing may
be in contact with the drum, in order to permit a thorough cleaning
of the drum. The cleaning liquid is dispensed through nozzles on
the spray assemblies described above, which can be activated during
a cleaning cycle.
[0024] Heated air may be delivered into the housing, preferably via
an array of independently controlled plenums which form effective
zones within the housing with independently controlled temperature
and airflow levels. Discharge ducts permit the air to exit the
housing.
[0025] The invention also relates to a method of applying a coating
to tablets in bulk comprising the steps of providing a system as
defined above, feeding a supply of uncoated tablets and a supply of
coating liquid into said system, removing said tablets from said
system on a continuous basis, and controlling said system for
continuous deliver, coating and removal of tablets at a selected
rate comprising a selected weight of bulk tablets per selected unit
of time. Average dwell time for the tablets within the drum is
controlled by rotating the weir plate so as to control the
obstruction of the open second end of the drum so as to effectively
increase or decrease the depth of the tablet bed within the drum.
The dwell time is a function of the drum speed and other factors,
and may be selected in accordance with the desired coating process
parameters.
[0026] The method further comprises a start-up protocol wherein
tablets are dispensed into the pan on an initial batch basis. As
the tablets are initially dispensed, the spray zones are
sequentially activated to deliver coating fluid, commencing with
the zone adjacent the first end of the drum and sequentially moving
towards the second end in correspondence with the passage of the
initial tablet batch along the drum. Following the initial batch
process, the system may be then operated in a continuous processing
mode. The method comprises a shut-down protocol which is
essentially the reverse of the start-up protocol.
[0027] The term "tablets" as used in this patent specification is
not intended to be restricted to any particular type, size, shape
or form of articles that may be processed in the system described
and claimed herein. Rather, the term "tablets" is used to refer to
any small article suitable for coating within a tumbling apparatus,
including for example pills, lozenges, caplets and other sizes and
shapes of similar articles, as well as candies or other food
articles, seeds and any other small article that receives a coating
and which can be processed in a bulk processing system in which the
articles are tumbled and otherwise processed in bulk.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a side elevational view of a tablet coating system
according to an embodiment of the present invention.
[0029] FIG. 2 is a rear elevational view thereof.
[0030] FIG. 3 is a front elevational view thereof.
[0031] FIG. 4 is a perspective view of the tablet discharge region
of an embodiment of the system.
[0032] FIG. 5 is a plan view from above of the discharge
portion.
[0033] FIG. 6 is a front elevational view of the discharge portion
with the door in the open position.
[0034] FIG. 7 is a perspective view of the drum support frame of
the system with associated components.
[0035] FIG. 8 is front view of the system with the drum removed to
show internal components.
[0036] FIG. 9 is a rear elevational view showing internal
components of an embodiment of the system.
[0037] FIG. 10 is a side elevational view of an embodiment of the
coating sprayer assembly.
[0038] FIG. 11 is a perspective view of the tablet discharge region
of an embodiment of the system.
[0039] FIG. 12 is a side elevational view of the discharge region
with the door open.
[0040] FIGS. 13A and 13 B depict a flow chart showing operation of
an embodiment of the present system.
DETAILED DESCRIPTION
[0041] The tablet coating system 10 described herein as one
embodiment of the invention comprises in general terms a weigh
in-feed conveyor 12, a housing 14, a tablet inlet chamber 16 and a
coated tablet discharge region 18 for discharging coated tablets
from the system. The housing 14 is supported by a frame 19,
including length-adjustable legs 20 for leveling the system.
Housing 14 fully encloses a horizontal-axis perforated rotatable
stainless steel drum 22, seen in detail in FIG. 7. Drum 22 is
open-ended at both opposed ends. Access to the interior of housing
14 is obtained by an array of doors 15 on both lateral sides of the
housing. As well, front and rear ports within the end walls,
covered by front and rear end doors 40 and 72 provide access from
the respective ends of housing 14. All doors of the housing are
sealed with inflatable seals. Housing 14 is generally elongate,
with a central axis extending between the opposed ends thereof.
[0042] In-feed conveyor 12 comprises a commercially-available unit,
such as that manufactured by Siemens AG.TM.. Conveyor 12 comprises
an inlet 28 to receive uncoated tablets, discharging onto a
motor-driven conveyor belt 30, which in turn discharges into a
hopper 32 for entry into inlet 16 through inlet conduit 33. Belt 30
passes across and bears on a scale 34 to detect the weight of the
tablets deposited onto the conveyor on a continuous basis. This
weight amount is calculated by subtracting the weight of the
conveyor and associated components from the total weight detected
by the scale. As discussed below, a system controller 36 extracts
from this tablet weight information the rate of tablet in-feed into
the system, in selected weight/time units.
[0043] In-feed conveyor 12 includes a controlled-flow dispenser to
dispense tablets at a selected rate of supply onto belt 30 in
response to a control signal from system controller 36. The
feedback signal from scale 34 permits a supply of tablets at a
constant rate in units of weight per unit of time (for example a
selected kg/min. rate of tablet supply).
[0044] As seen in FIG. 3, tablets received in inlet hopper 32 enter
via gravity through conduit 33 into tablet inlet chamber 16, which
constitutes a port into the interior of housing 14. Inlet chamber
16 comprises an annular flange 17 (see FIG. 1) which protrudes
outwardly from a first end of housing 14. Inlet 16 communicates
with the interior of housing 14. The proximal end of inlet chamber
16 comprises an openable door 40, which opens for access into the
interior of housing 14. Conduit 33 communicates with entryway 16
through an opening within flange 17. Inlet 16 comprises a chamber
aligned with drum 22 within the interior of the housing 14, such
that tablets entering chamber 16 are directed into the interior of
drum 22. Inlet 16 is partly obstructed by a plate 79 to retain a
tablet bed within the drum interior.
[0045] As seen in FIG. 7, drum 22 is housed within a cage
comprising a plurality of spaced-apart hoops supported by a frame.
The hoops include a central hoop 25 and first and second end hoops
27(a) and 27(b), all three of which have an outer contact surface
29 for contacting an array of drive and driven wheels 42. Central
hoop 25 also includes raised flanges 31 on either side thereof. The
flange have side edges for contact with a pair of
horizontally-oriented opposed centering wheels 35 to maintain the
fore-aft position of the drum. The frame is further comprised of an
array of stave-like rods 110 fastened to hoops 25 and 27. Drive
wheels 42(a) are mounted to a rotatable shaft 44 extending
lengthwise within housing 14. Shaft 44 is journaled for rotation
within a bearing hub 46 mounted within a corresponding end wall of
the housing. A first hub 46 supporting the drive axle includes a
drive shaft 48 extending outwardly from an end wall of the housing.
A pulley 50 is mounted to the drive shaft 48, which in turn is
driven by an electric motor 52 mounted to frame 18. The motor is
controlled by the control system, described below. The driven
wheels 42(b) are mounted to corresponding mounts within the
interior of the housing 12.
[0046] In one embodiment, constituting a representative example,
drum 22 is about 30 inches in diameter and comprises a perforated
stainless steel wall. In one version, the overall length of housing
14, including inlet and outlet chambers, is 206 inches, with the
housing interior length being about 187 inches. Drum 22 extends
substantially the full length of the housing interior.
[0047] As seen schematically in FIG. 9, within the interior of the
housing 14 and extending axially the length thereof is a stainless
steel baffle 60 which effectively divides the interior space within
the housing 14 exterior to drum 22, in order to channel the flow of
heated air through drum 22 and thus through the tablet bed. Baffle
60 is fastened to the floor of housing 14 and projects upwardly
with its upper edge contacting or approaching drum 22. The housing
interior is thus effectively divided between air inflow and air
outflow zones located on opposed lateral sides within housing 14,
with each zone extending the full length of housing 14.
[0048] Heated air is introduced into the air inflow zone via an
array of overhead intake plenums 66, which receive heated air from
a common source, which is not shown. Operating temperatures are
controlled to within about +/-1 degree C. by way of tandem packaged
boilers, not shown, with turndown rations of 10:1 operatively
connected to intake plenums 66. The interior of housing 14
effectively comprises four zones along the length of drum 22, with
the supply of heated air being effectively independently delivered
within each zone. Independently controlled iris valves, not shown,
within plenums 66 allow for independent delivery of hot air into
the housing to permit balancing and tuning of the hot air supply
within the effective zones within the housing. Thus, within each
zone the rate and temperature of heated air delivered into the drum
may be independently controlled.
[0049] Baffle 60 channels the heated air to flow through drum 22,
exiting the housing via an array of exit ducts 68, which channel
the exhaust air via a common manifold for discharge either into the
exterior environment or through a treatment system, not shown.
Baffle 60 is positioned so as to direct the stream of heated air
through the tablet bed within drum 22, such that all or most of the
air flows through the bed of tablets. During rotation of drum 22,
the tablet bed will be tilted in the direction of rotation of drum
22; in order to accommodate such tilt, the baffles are positioned
accordingly. For example, if the drum rotates clockwise, when
viewed from a first end, the tablet bed will be tilted such that
the exposed surface of the tablet bed tilts upwardly and to the
left, as seen in FIG. 9. The speed of drum rotation as well as
tablet depth will determine the tilt of the tablet bed.
[0050] Tablets within drum 22 exit via tablet discharge opening 18.
Opening 18 comprises a cylindrical opening within the end wall of
the housing, surrounded by a tubular flange 70 aligned with drum
22. The flange opening is fully covered by a rear door panel 72,
comprising a circular panel hinged to the flange 70. An inflatable
seal 74 provides a waterproof and airtight seal when the door is
closed. Panel 72 includes a window 76 for viewing the drum
interior.
[0051] A weir plate 80 is provided at the second end of drum 22 for
retaining within the drum a selected depth of tablets while
permitting the discharge of tablets which exceed this depth. Weir
plate 80 partially obstructs the discharge end of drum 22 and
forces the tablets to spill over the top thereof in order to exit
the drum. This maintains a bed of a selected depth within drum 22.
As will be discussed below, the effective spill-over height of weir
plate 80 can be adjusted by adjusting its rotational position about
the axis of drum 22. As will be discussed below, adjustment of the
rate of inflow of tablets dispensed by the in-feed conveyor, with
adjustment of the effective spillover height of weir plate 80,
permits a continuous coating operation of the system. As seen in
FIG. 1, the shape of weir plate 80 departs somewhat from a crescent
shape, in that the plate comprises an arcuate lower edge that
conforms to the circular cross-sectional shape of drum 22, and an
upper edge having a straight region 82 merging with a hyperbolic
curved region 84. The overall shape thus is similar in appearance
to a scimitar blade. The upper edge of weir plate 80 thus generally
corresponds with the shape assumed by the upper surface of a tablet
bed as the drum is rotated in a clockwise direction when viewed
from the first end of the housing.
[0052] Weir plate 80 is mounted to housing 14 in a fashion which
permits it to remain static while drum 22 rotates. For this
purpose, weir plate 80 is positioned such that its lower edge is
within or immediately adjacent to the interior surface of drum 22,
thereby obstructing the lower portion of drum 22 to prevent
articles from escaping from between drum 22 and weir plate 80, such
that all articles must spill over the upper edge of weir plate 80.
Weir plate 80 is mounted such that its rotational position can be
adjusted by a selected amount. This function permits weir plate 80
to partially obstruct the outlet of drum 22 in an adjustable
fashion, such that tablets must spill over the upper edge of weir
plate 80 for discharge from drum 22. Adjustment of the rotational
position of weir plate 80 effectively changes its spillover height,
thereby changing the bed depth within the interior of drum 22.
Although weir plate 80 can be mounted to housing 14 in a variety of
mounting configurations, in the described embodiment it is mounted
to project from the inside face of door panel 72. This permits weir
plate 80 to pivot outwardly from housing 14 when door 72 is opened,
for inspection, cleaning etc. The space defined between door panel
72 and weir plate 80 provides a discharge region for tablets
spilling over the weir plate.
[0053] As seen in FIGS. 4 to 6, 11 and 12, weir plate 80 is mounted
to door panel 72 by an offset mount comprising a horizontal shaft
86 which is fixedly mounted to weir plate 80, for example by bolts
88. Shaft 86 is co-axial with the central axis of drum 22. Shaft 86
in turn is mounted at its opposed end to a first end of a
radially-extending linkage arm 90. The opposed second end of the
linkage arm 90 is fixedly mounted to a horizontal rotateable shaft
92, which is offset from and parallel to shaft 86. Rotation of
shaft 92 about its central axis has the effect of swinging weir
plate 80 about an arc, whose radius is defined by the length of arm
90 and whose axis is the central axis of shaft 90. The positioning
and shape of the weir plate 80 and the associated mounting shafts
and arm are arranged such that the lower edge of the weir plate
describes a circular movement corresponding with the drum wall,
when rotated.
[0054] Shaft 92 extends through door panel 72, and is rotatably
journaled within a bearing mount 73 extending through door 72.
Shaft 92 is rotatably driven by a drive means which may comprise
any suitable means to precisely impart rotational positioning, such
as an electro-pneumatic positioner 94, operatively connected to
shaft 92 via linkages 95, 96. If motor driven, control of the motor
is effected by the central control system, described below.
[0055] Tablets spilling over the top edge of the weir plate 80 exit
via a discharge hopper 98 which opens into the space between weir
plate 80 and door panel 72. The coated tablets exit the system
through hopper 98 and are then handled in a conventional
manner.
[0056] Weir plate 80 can be rotatably adjusted to essentially any
desired rotational position about the elongate axis of drum 22,
within a range from a fully obstructing position wherein its
effective spillover height is at a maximum, and a full
non-obstructing position wherein it does not block the exit of
tablets from drum 22. In the maximally obstructing position, weir
plate 80 is positioned such that a relatively larger portion of the
plate is located above the base of the drum, in the direction of
drum rotation. The shape of the upper edge of weir plate 80 is
configured such that it generally matches the contours of the
tablet bed as drum 22 rotates. Weir plate 80 thus can be precisely
located to provide a spillover surface which is matched in its
orientation to the surface of the tablet bed, which in turn is
tilted by an amount that depends on the drum rotational speed. The
effective height of the spillover surface of weir plate 80 is
determined by its angular position, and adjusting this position has
the effect of altering the tablet bed depth. This in turn affects
the average dwell time for tablets within the drum. As will be
seen, tablets deposited in a first end of the drum will move
towards the discharge end upon rotation of the drum, with the
continuous addition of tablets at one end and discharge at the
other end. Hence, the speed of drum rotation, rate of tablet
introduction and rotational position of weir plate 80 cooperate to
establish an average dwell time.
[0057] As well, when weir plate 80 is adjusted into the appropriate
rotational position for maximal bed depth, the system can then
operate as a batch processor if desired, for example at the start
of a production run. The weir plate 80 may then be rotated into an
intermediate position for continued processing on a continuous
basis.
[0058] A controlled supply of a coating substance such as a coating
liquid is dispensed onto the tablet bed via a spray assembly 100,
shown in detail in FIG. 10. Assembly 100 extends within the
interior of the drum parallel to the elongate axis thereof and
comprises two independently rotatable sub-assemblies 102a and 102b
supported by an overhead support 152 exterior to the housing.
Sub-assemblies 102a and b are positioned in end-to end coaxial
relationship, with their respective distal ends abutting. Together,
assemblies 102a and b extend substantially the full length of drum
22. Each sub-assembly 102a and 102b comprises a nozzle support,
consisting of two parallel pipes consisting of an upper pipe 130
and a lower pipe 132, which communicate with each other internally
via conduits 103. Pipes 130 and 132 are configured such that lower
pipe 132 is located within the interior of drum 22 during the
normal operation of the system, and upper pipe 130 is exterior of
drum 22. Effectively, the respective pipes and conduit 130, 132 and
103 form a C-shaped structure whose lower member inserts within the
interior of drum 22 for dispensing spray and the upper member
provides structural support and serves as a manifold for the spray
fluid.
[0059] Each of assemblies 102a and 102b are independently mounted
at their proximal ends to respective shafts 134, which are in turn
each rotatably journalled within bearing mounts 150 at respective
ends of housing 14. Shafts 134 are operatively connected to an
external drive, not shown, for rotation about the elongate axis
thereof. Pipe 130 supports an array of spray nozzles comprising
Schlick.TM. spray guns 106 to spray coating in atomized form onto
the tablets. It will be understood that other types of spray guns
may be used as is appropriate. The source and makeup of the
pressurized coating fluid will consist of any suitable coating
fluid, depending on the needs of coating operation and the
operating parameters imposed by nozzles 106 and other components of
the system. Pipes 130 are each independently fed coating liquid
from a pressurized source thereof by flexible supply lines, not
shown. Pressurized air is delivered from a source thereof to spray
guns 106 via hoses, not shown, connected through air fittings 140.
Assemblies 102a and b include inlets for the pressurized coating
fluid and compressed air.
[0060] Bearing mounts 150 are each mounted to support 152,
comprising a horizontal arm 154 extending the length of housing 14.
Arm 154 comprises telescoping sections 156 at either end thereof
and telescoping vertical aims 158 at either end thereof to which
the bearing mounts are engaged. Extension of sections 156 permits
the respective assemblies 102a and b to be independently retracted
horizontally outwardly from housing 14, away from drum 22, for
cleaning, maintenance or the like. Horizontal arm 154 is mounted
externally of housing 14, with vertical arms 158 overhanging the
ends of the housing and entering the respective chambers 16 and 18.
Vertical arms 158 fit within grooves 160 within flanges 16 and 18.
Each of the bearing mounts 150 is operatively connected to a drive,
for independently rotating the assemblies 102a and 102b. Assemblies
102a and 102b are separable from each other and may be retracted
away from each other by expanding sections 156. In order to retract
assemblies 102a and b, the system is shut down and the respective
end doors 40 and 72 are opened. One or both of assemblies 102a and
102b are then retracted, such that the corresponding telescoping
sections 156 are extended. Sections 156 provide sufficient
extension to permit the respective assemblies to be essentially
fully retracted from housing 14 for cleaning or maintenance. The
supply line includes sufficient slack to permit such movement of
the assemblies 102a and 102b. Support 152 includes a pair of
hangers 142 to support cable loops in a convenient fashion.
[0061] As seen in FIG. 10, assemblies 102a and b are releasably
coupled together by coupler 141, which transmits rotational force
from one assembly to the other when the assemblies are in contact
with each other.
[0062] Assemblies 102a and b can be rotated through 360 degrees,
with an operative range of rotation being about 90 degrees to
permit positioning of the spray guns 106, described below, such
that they are perpendicular to the surface of the tablet bed.
Further, telescoping vertical arms 158 can vary the vertical
position of the spray assembly 102 within a range of about 90-100
millimeters so as to vary the distance between the spray guns 106
and the tablet bed so as to vary the spray pattern striking the
tablet bed.
[0063] Nozzles 106 are arranged spatially to provide
independently-controlled spray zones along the length of the drum
22, directed generally downwardly towards the position of the
tablet bed within the drum.
[0064] Spray guns 106 are arranged on each of assemblies 102a and b
in three arrays of three guns each, for a total of 18 guns in six
independently controlled spray zones. Each array of guns 106 within
a given zone is independently controlled. The independently
controlled spray zones permit a controlled build-up of the sprayed
coating to permit accurate coating weight gain, particularly in the
transition time between the initial batch processing and the
subsequent continuous mode operation. In particular, the system
reduces losses incurred through undercoating or off-spec coating
while in the batch production mode.
[0065] A wash-in-place system is provided for cleaning of the
interior of the housing 14 and the drum 22. The system comprises a
pair of conduits 120a and 120b for wash liquid (such as water)
supported by the assemblies 102a and 102b respectively. Conduits
120 each receive a pressurized supply of liquid from a flexible
hose, not shown. Cleaning liquid is dispensed under pressure via
two nozzles 164a and b which are operatively connected to conduits
120a and 120b respectively. Nozzles 164 are each capable of 360
degree rotation to deliver cleaning liquid towards the interior
drum wall with full 360 degree coverage.
[0066] During the wash cycle, wash liquid collects within the base
of housing 14, filling the housing about 1/4 to 1/3 of its height
with solution to form an internal sump region. The components of
the system are designed to maintain the primary drive components
above the sump region while permitting immersion of the sump
region. In practice, sufficient liquid will be introduced such that
a portion of the drum will enter the collected wash liquid and
during drum rotation is thus effectively washed. Nozzles 164 also
direct a liquid spray towards the end walls, so as to effectively
wash the interior of the housing. The first and second doors are
sealed against leakage of liquid, by means of a highly watertight
seal formed by an inflatable gasket, fixedly mounted around the
perimeter of the respective doors. Each door is also provided with
a latch to tightly close the door.
[0067] Liquid used for cleaning of the system which collects within
the base of the housing may be drained, via one or more drains for
either disposal or re-use.
[0068] Operation of the system 10, including tablet in-feed rate,
drum rotation, coating spray delivery, heated air delivery, weir
plate position and the wash-in-place cleaning system, is controlled
via central controller 36, which is operatively linked to tablet
inlet 28, in-feed conveyor 26, drum drive motor 52, weir plate
positioner 94, and coating spray and liquid dispensing systems.
Controller 36 comprises any suitable electronic system capable of
receiving electronic signals from the various sensors incorporated
in the system, processing the signals according to a logic sequence
as described herein, and transmitting control signals. The
controller 36 includes a user interface to permit programming of
the system operation.
[0069] FIG. 13 comprises flow charts depicting one mode of
controlling and operating the present system. Controller 36 is
configured to operate the system initially in a start up mode,
wherein the system is readied for operation, as seen in the
"operating sequence--preparation" flow chart. The system is then
operated in an operational mode, as seen in the flowchart entitled
"Operating Sequence--Coating". In this sequence, tablets are
introduced into the rotating drum in an initial batch basis to
fully charge the drum with tablets. At this stage, weir plate 80 is
in its fully obstructing position and the system is operated in a
"batch processing" mode to fully coat the tablets within the
initial charge of tablets. System operation is then shifted into a
continuous processing mode. For this purpose, the weir is then
adjusted to a height selected to permit spillover, and tablets are
introduced on a continuous basis at the intake end of the drum. The
spray zones are sequentially activated, commencing at the first
zone adjacent the intake end. Sequential activation permits
transitioning of the system from the batch mode to a continuous
mode. Shut-down of the system comprises positioning the weir plate
in the closed (fully obstructing) position, and the spray zones are
activated sequentially in a manner similar to the start up
sequence, so as to fully coat all tablets present in the drum by an
equal amount. The weir plate is then fully opened, with the drum
activated to fully discharge the coated tablets.
[0070] In an alternative embodiment, some or all of the steps
described and illustrated herein can be controlled by manual
operation in place of the automatic operation by the
controller.
[0071] The controller is programmed with conventional programming
language and means to operate the system according to the steps and
flow chart shown above. Persons skilled in the relevant art will
appreciate the diverse means available to program the controller to
operate according the logic described herein. The controller
programming may comprise either a programmable software or may be
embedded within the structure of a chip.
[0072] Although the present invention has been described in part by
reference to one or more embodiments described in detail, it will
be understood that the invention is not limited in its scope to
these embodiments nor to any particular aspect of same. Rather, the
full scope of the invention is described by reference to this
patent specification as a whole including the claims.
* * * * *