Abstract:
A system for coating tablets and other small articles is provided, comprising a housing, a drum or other pan within said housing for retaining a bed of coatable articles, and a coating dispenser for dispensing coating from a source onto the bed. The dispenser includes an extendible support member and opposing spray assemblies in end to end linear relation overhead of the pan. The spray assemblies include an elongate nozzle support, an array of spray nozzles mounted to the nozzle support for connection to a source of pressurized coating fluid and optionally to a source of compressed air, and an arm at an end of the nozzle support connecting the nozzle support to the extendible support member. The support member is extendible in length to permit retraction of at least one of the assemblies independently of the other assembly.

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 rotatable 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: 
         [0000]    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 13B  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™. 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 rotatable 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  102   a  and  102   b  supported by an overhead support  152  exterior to the housing. Sub-assemblies  102   a  and  b  are positioned in end-to end coaxial relationship, with their respective distal ends abutting. Together, assemblies  102   a  and  b  extend substantially the full length of drum  22 . Each sub-assembly  102   a  and  102   b  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  102   a  and  102   b  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™ 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  102   a  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 arms  158  at either end thereof to which the bearing mounts are engaged. Extension of sections  156  permits the respective assemblies  102   a  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  102   a  and  102   b . Assemblies  102   a  and  102   b  are separable from each other and may be retracted away from each other by expanding sections  156 . In order to retract assemblies  102   a  and  b , the system is shut down and the respective end doors  40  and  72  are opened. One or both of assemblies  102   a  and  102   b  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  102   a  and  102   b . Support  152  includes a pair of hangers  142  to support cable loops in a convenient fashion. 
         [0061]    As seen in  FIG. 10 , assemblies  102   a  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  102   a  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  102   a  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  120   a  and  120   b  for wash liquid (such as water) supported by the assemblies  102   a  and  102   b  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  164   a  and  b  which are operatively connected to conduits  120   a  and  120   b  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 ¼ to ⅓ 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.