Abstract:
A fine powder is reliably dispensed from a hopper into containers on a moving conveyor belt with the assistance of a powder feed system. The hopper serves as a powder inlet that dispenses by gravity into a feed chamber that is form fitted to the sweep of a relatively slow rotating feed wheel with two spaced sets of pins. A relatively fast rotating agitator is located below the feed wheel which has a series of agitating blades that rotate between the span of the feed wheel pins, the blades in at least one embodiment resemble a J-shape. The agitator is located directly above a rotary trap chamber wheel, which has recesses that take doses of powder and dispense them into awaiting containers moving on a conveyor belt below.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority based on Provisional Application Ser. No. 60/877,683, filed Dec. 28, 2006, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to methods and apparatus for feeding powder to a powder dispensing device. The powder dispensing device may dispense controlled quantities of powder into cartridges or other containers. The powder can contain a drug, but the invention is not limited in this respect. 
     BACKGROUND OF THE INVENTION 
     Powders are used in a variety of applications, including medical applications. In one example, it has been proposed to deliver certain types of drugs to patients by inhalation of a powder as a delivery mechanism. One particular example uses diketopiperazine microparticles known as TECHNOSPHERE® microparticles. The TECHNOSPHERE microparticles have a platelet surface structure and can be loaded with a drug. One use of these microparticles is the delivery of insulin by inhalation. An inhaler having a replaceable cartridge or capsule containing the drug powder is used for drug delivery. 
     In the commercialization of drug delivery by inhalation, large numbers of cartridges containing the drug must be produced in an efficient and economical manner. In particular, the cartridges must be filled with precisely controlled quantities of the powder. While TECHNOSPHERE microparticles are highly effective for drug delivery by inhalation, the platelet surface structure causes TECHNOSPHERE powders to be cohesive and somewhat difficult to handle. 
     One prior art cartridge filling system includes a feed chamber which delivers powder to a dosing wheel. The dosing wheel, in turn, dispenses controlled quantities of powder into cartridges. The prior art system utilizes vibration and a large paddle wheel to facilitate the flow of powder from a hopper through the feed chamber to the dosing wheel. While the prior art system is generally functional, the energy imparted to the Technosphere microparticles causes the powder to compress and performance to be highly variable. The performance of the prior art system depends, at least in part, on the cohesiveness of the powder being handled, which may range from highly cohesive to free flowing. 
     Accordingly, there is a need for improved powder feeding methods and apparatus. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, a powder feed system comprises a housing that defines a feed chamber to hold powder, the feed chamber having a powder inlet and a powder outlet, at least one feed wheel in the feed chamber, the feed wheel rotating about a feed wheel axis, at least one agitator positioned in the feed chamber to move the powder from the feed wheel to the powder outlet of the feed chamber, the agitator rotating about an agitator axis, and a drive mechanism to rotate the feed wheel about the feed wheel axis and to rotate the agitator about the agitator axis. 
     The feed wheel can include a feed wheel hub and pins that extend radially from the feed wheel hub. The agitator can include an agitator hub and agitator elements, such as J-shaped pins, that extend from the agitator hub. The drive mechanism can include a feed wheel motor and an agitator motor. The feed chamber can be configured to limit dead space where powder can accumulate and become compacted. 
     According to a second aspect of the invention, a method for feeding powder comprises loading powder into a feed chamber having a powder outlet, rotating a feed wheel in the feed chamber, and rotating an agitator in the feed chamber, wherein the agitator is positioned to move powder from the feed wheel to the powder outlet. 
     According to a third aspect of the invention, a powder fill system comprises a powder feed system and a powder dispensing device. The powder feed system includes: a housing defining a feed chamber, a powder inlet and a powder outlet; a feed wheel and an agitator positioned in the feed chamber to move powder from the powder inlet to the powder outlet; and a drive mechanism to rotate the feed wheel and the agitator. The powder dispensing device is positioned below the powder outlet to dispense a controlled quantity of powder to a powder container. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, reference is made to the accompanying drawings, in which: 
         FIG. 1A  is a perspective view of a powder fill system in accordance with the first embodiment of the invention; 
         FIG. 1B  is a cross-sectional front elevation view of the powder fill system of  FIG. 1A ; 
         FIG. 2  is a cross-sectional top view of the powder feed system shown in  FIGS. 1A and 1B ; 
         FIG. 3  is a cross-sectional side elevation view of the powder feed system of  FIGS. 1A and 1B ; 
         FIG. 4  is a schematic front elevation view of the feed wheel; 
         FIG. 5  is a schematic cross-sectional view of the powder feed system; 
         FIG. 6  is a perspective view of a powder feed system in accordance with a second embodiment of the invention; and 
         FIG. 7  is a schematic cross-sectional view of a powder feed system in accordance with a third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     A powder fill system in accordance with a first embodiment of the invention is shown in  FIG. 1 . The powder fill system includes a powder feed system  10 , which supplies powder to a dispensing device, such as a dosing wheel  12 . Dosing wheel  12 , in turn, dispenses controlled quantities of powder to cartridges  22 . The powder feed system is shown in greater detail in  FIGS. 2-5 . 
     The dosing wheel  12  includes a series of dosing holes  20 , which can be spaced apart, for example, at 90° intervals and which retain powder by suction. As the dosing wheel  12  rotates, the powder is delivered to a cartridge  22  in a holder  24 . The powder dose delivered to each cartridge  22  from dosing hole  20  is typically in a range of 1 to 100 milligrams, but need not be limited to this range. In a practical system, multiple cartridges  22  in holders  24  move along a conveyor  26  and are filled by dosing wheel  12 . It will be understood that different powder dispensing devices can be used within the scope of the invention. In some embodiments, the powder dispensing device can comprise a dosing disk. Furthermore, retention of powder in the dosing hole by suction is not essential. In addition, the powder fill system can dispense powder to any type of powder container. 
     An embodiment of powder feed system  10  is described with reference to  FIGS. 1-5 , where like elements have the same reference numerals. The powder feed system of  FIGS. 1-5  includes a hopper  30 , a housing that defines a feed chamber  62 , a feed wheel  40 , and an agitator  42 . Feed wheel  40  and agitator  42  are located in feed chamber  62 . In the embodiment of  FIGS. 1-5 , housing components include a feed frame  32 , a flange plate  34  and chamber inserts  50  and  52 . 
     The hopper  30  provides a flared opening to feed frame  32  and permits powder to be easily loaded into the system. The feed chamber of the powder feeding system  10  is relatively narrow, and in the absence of hopper  30 , it would be difficult to load powder into the system without spillage. Hopper  30  defines a powder inlet  60 . 
     Feed chamber  62  extends from powder inlet  60  to a powder outlet  64 . Powder is supplied through powder outlet  64  to dosing wheel  12  or another dispensing device. In the embodiment of  FIGS. 1-5 , feed chamber  62  is partially enclosed by one or more components of the fill system to which the feed system is mounted. Thus, feed chamber  62  is defined by housing components including feed frame  32 , flange plate  34 , a housing plate  66  ( FIG. 5 ) and chamber inserts  50  and  52 . Housing plate  66  is a component of the powder fill system in this embodiment. It will be understood that the housing which defines feed chamber  62  may have different configurations within the scope of the invention. In the embodiment of  FIGS. 1-5 , feed chamber  62  has an internal thickness of 0.75 inch. It will be understood that the feed chamber thickness can be varied based on the physical characteristics of the powder being handled and the components of the powder feed system. 
     In the embodiment of  FIGS. 1-5 , flange plate  34  serves as a frame for mounting of components of the powder feed system  10 . Hopper  30 , feed frame  32 , feed wheel  40 , agitator  42  and chamber inserts  50  and  52  are mounted to the front side, or inboard side, of flange plate  34 . Drive motors for the feed wheel  40  and the agitator  42  can be mounted to the back side, or outside, of flange plate  34 . The flange plate  34  also functions as an adaptor plate for mounting of the powder feed system  10  to an existing powder fill system. The configuration of the flange plate  34  can be changed within the scope of the invention for mounting to other powder fill systems. For example, flange plate  34  can be replaced with a housing which encloses feed chamber  62 . 
     Feed wheel  40  includes a feed wheel hub  70  that rotates about a feed wheel axis  72 . Feed wheel pins  74 , or spokes, extend radially from feed wheel hub  70 . In the embodiment of  FIGS. 1-5 , feed wheel  40  includes twelve pins  74  that are straight and that have lengths of 2.5 inches. In one example, feed wheel hub  70  is a stainless steel disk having a diameter of 1.25 inches and a thickness of 0.75 inch. The overall diameter of feed wheel  40  can extend from the top of feed frame  32  and 0.375 inch into the tip radius of agitator  42 . 
     As shown in  FIG. 4 , the configuration of feed wheel pins  74  can include a first pin set  80  of six pins and a second pin set  82  of six pins. The pin sets  80  and  82  are axially spaced apart along feed wheel axis  72 . The first pin set  80  can be positioned on one side of feed wheel hub  70 , with the six pins spaced 60° apart. The second pin set  82  can be positioned on the other side of feed wheel hub  70 , with the six pins spaced 60° apart. The pin sets  80  and  82  can be offset by 30° in a circumferential direction to provide an equal spacing of the twelve pins around feed wheel hub  70 . Volumes  80   a  and  82   a  through which respective pin sets  80  and  82  travel are shown in  FIG. 5 . 
     The feed wheel  40  and the agitator  42  can rotate in the same direction so that powder is transferred from the feed wheel  40  to the agitator  42 . The number, size, shape, location on the hub and diameter of the pins  74  can be varied to optimize the configuration for powders with different physical characteristics. The rotational speed of the feed wheel  40  can also be varied depending on the flow characteristics of the powder. The agitator  42  can interact with the feed wheel  40  so that powder is conveyed from one to the other. The feed wheel  40  provides a continuous supply of powder to the agitator  42 , so that the agitator is not deprived of powder. The feed wheel prevents the creation of a void in the powder bed over the powder outlet  64 . The feed wheel  40  removes the pressure that would otherwise be imparted to the powder near the agitator  42  by an uninterrupted, relatively high powder bed height. 
     Agitator  42  can include an agitator hub  90  that rotates about an agitator axis  92 , and agitator elements  94  affixed to agitator hub  90 . Agitator axis  92  can be parallel to feed wheel axis  72 . In the embodiment of  FIGS. 1-5 , agitator  42  includes three agitator elements  94  equally spaced around agitator hub  90 . Each of the agitator elements  94  can be a J-shaped pin, as best shown in  FIG. 5 . The J-shaped agitator elements  94  are positioned between first pin set  80  and second pin set  82  of feed wheel  40 . This configuration permits the agitator  42  to capture powder and convey it to a position over powder outlet  64 . The J-shape of the agitator elements allows a small amount of powder to be plowed into position above powder outlet  64 . 
     In one embodiment, agitator  42  includes a stainless steel disk having a diameter of 1.25 inches and three J-shaped stainless steel agitator elements  94 . In some embodiments, the J-shaped agitator elements  94  include intersecting straight sections  94   a ,  94   b  and  94   c , as shown in  FIG. 5 . The J-shaped agitator elements can be dimensioned so that a straight section  94   b  at the base of the J-shaped agitator element pushes powder into powder outlet  64 . The agitator elements are mounted 120° apart and move directly over the powder outlet  64  in a continuous motion, thereby filling the outlet with powder. The agitator hub  90  of agitator  42  fits into a hole in flange plate  34 , and the hole can be sealed with a PTFE seal, for example. 
     The agitator  42  rotates in the opposite direction with respect to dosing wheel  12  in this embodiment. In other embodiments using different dispensing devices, the rotation can be reversed, if necessary. The number, size, shape, location on the hub and diameter of the agitator elements  94  can be varied to optimize the configuration for powders with different physical properties. The rotational speed of agitator  42  can also be varied depending on the flow characteristics of the powder and the dispensing device being utilized. 
     In some embodiments, the agitator  42  and the feed wheel  40  interact so that powder is conveyed from one to the other and over the powder outlet  64 . In particular, the outer diameters of the feed wheel  40  and the agitator  42  can overlap, but the devices are configured to avoid physical contact. In the embodiment of  FIG. 5 , the agitator elements  94  can rotate between pin sets  80  and  82 , thus overlapping the rotation of feed wheel  40  and agitator  42  while avoiding physical contact. In the embodiment of  FIG. 5 , the outer diameters of feed wheel  40  and agitator  42  overlap by a distance D. 
     As shown in  FIGS. 1-3 , agitator  42  is positioned below and to the right of feed wheel axis  72 , in the case of counterclockwise rotation of these elements. Feed wheel  40  pushes powder along the sloping surface of insert  52  toward agitator  42 , which in turn pushes the powder into powder outlet  64 . In this embodiment, powder outlet  64  is a space, at the bottom of feed chamber  62 , between inserts  50  and  52 . 
     As shown in  FIG. 5 , a drive module  100  can include an enclosure  102  mounted to the back side of flange plate  34 . Enclosure  102  can enclose a feed wheel motor  110  and an agitator motor  112 . Feed wheel motor  110  is coupled to feed wheel  40  and produces rotation of feed wheel  40  about feed wheel axis  72 . Agitator motor  112  is coupled to agitator  42  and produces rotation of agitator  42  about agitator axis  92 . 
     In one embodiment, each of the motors  110  and  112  is a brushless DC gear motor. Other types of motors, such as AC motors, can be utilized within the scope of the invention. Furthermore, feed wheel motor  110  and agitator motor  112  can be replaced with a single motor and a gear assembly to drive feed wheel  40  and agitator  42  at the required rotational speeds. The gear assembly establishes a desired ratio of the feed wheel rotational speed to the agitator rotational speed. In general, any suitable drive mechanism can be utilized to drive feed wheel  40  and agitator  42  at the required rotational speeds. 
     The rotational speed of feed wheel  40  and the rotational speed of agitator  40  are selected to optimize powder feed performance for a given powder or a given range of powder characteristics. The rotational speeds of the feed wheel and the agitator and the ratio of rotational speeds can be based on the flow characteristics of the powder being processed. In some embodiments, the rotational speed of feed wheel  40  is in a range of 0.1 to 2 rpm and the rotational speed of agitator  42  is in a range of 30 to 40 rpm. However, the rotational speeds are not limited to these ranges and can be varied depending on the flow characteristics of the powder. 
     In some embodiments, the dosing wheel  12  rotates intermittently in 90° increments (for a dosing wheel having four dose holes spaced apart by 90°), with each 90° rotation being considered a fill cycle. The dosing wheel stops with dosing hole  20  positioned under powder outlet  64 . In other embodiments, the dosing wheel  12  can rotate continuously relative to powder outlet  64 . In each case, the rotation speed of agitator  42  can be set such that at least one of agitator elements  94  passes over dosing hole  20  when it is positioned under powder outlet  64 . 
     The drive module can be designed to bring the motor shafts into precise alignment with the agitator shaft and the feed wheel shaft. This allows the couplings on the motors to engage slots in the shafts, creating mechanical drive couplings. The motors are mounted in the drive module using spring-loaded hubs so that it is not necessary to align the slot in the shaft with the motor coupling. When the motors are started, the couplings engage as soon as they rotate into alignment with the slots in the respective shafts. 
     The size and shape of the feed chamber  62  can be configured to enhance performance of the powder feed system. In particular, the feed chamber  62  can be configured to limit dead space where powder can accumulate and become compacted, so that powder moves through the feed chamber  62  in a short time and does not remain in feed chamber  62  for extended periods. In some embodiments, the feed chamber walls are configured to match or conform to the volumes through which feed wheel  40  and agitator  42  rotate. For example, the feed chamber  62  can have an inside wall that, adjacent to feed wheel  40 , is slightly larger in diameter than feed wheel  40  and, adjacent to agitator  42 , is slightly larger in diameter than agitator  42  to permit rotation of these components without contacting the chamber wall. In further embodiments, the walls of feed chamber  62  can have a shape, such as a linear ramp, that does not conform to the outer diameter of feed wheel  40  or agitator  42  but which guides powder toward powder outlet  64 . In some embodiments, the size and shape of feed chamber  62  is determined during the initial design of the powder feed system. In other embodiments, the size and shape of feed chamber  62  is determined by providing one or more chamber inserts, such as chamber inserts  50  and  52 , to modify an existing feed chamber. 
     The chamber inserts  50  and  52  limit the size of the feed chamber  62 , which in turn limits the amount of powder in the chamber at any given time, so that a controlled bed height over the power outlet  64  is maintained. This improves the powder filling consistency. Chamber insert  50  establishes the right side boundary of feed chamber  62  on the upstroke of feed wheel  40 , and chamber insert  52  establishes the left side boundary of feed chamber  62  on the downstroke of feed wheel  40 , as shown in  FIG. 1 . 
     The rotation of the feed wheel  40  moves powder toward an upstroke surface of upstroke chamber insert  50 . The upper section of insert  50  is concave in shape with a relatively steep rise and can have a radius of curvature that is slightly larger than the radius of the feed wheel  40 . This shape reduces dead space in the feed chamber  62  and allows powder that did not transfer to agitator  42  to recirculate. The lower portion of insert  50  is vertical or nearly vertical with a gradual inward curvature toward powder outlet  64  near the bottom. This shape insures that powder is directed down toward powder outlet  64 . The bottom of insert  50  can have a radius of curvature that is slightly larger than the radius of agitator  42 . While the lower section of insert  50  should be vertical or nearly vertical, the upper section can be modified to accommodate different feed wheel designs, but insert  50  should be generally vertical in overall shape and should limit dead space. The underside of insert  50  can be shaped to accommodate a scraper to prevent escape of powder from the feed chamber. 
     Downstroke chamber insert  52  also limits dead space in the feed chamber  62 . The rotation of feed wheel  40  moves powder away from insert  52  and into the agitator  42  In the embodiment of  FIGS. 1A-5 , chamber insert  52  has a downwardly sloping downstroke surface that defines a linear ramp. The chamber insert  52  has a relatively steep angle that permits the feed wheel  40  to clear insert  52  and provides a straight path for powder to be fed down into agitator  42 , which captures and pushes the powder over the powder outlet  64 . The angle of insert  52  can be varied to accommodate different feed wheel designs and powders with different physical characteristics. 
     In other embodiments, the housing that defines feed chamber  62  is designed to provide a feed chamber shape as described above, without the use of separate inserts. As noted, the feed chamber can be sized and shaped to thereby limit dead space where powder can accumulate and become compacted. The thickness of the feed chamber  62  can be selected to accommodate the axial dimensions of feed wheel  40  and agitator  42 , while avoiding dead space in the feed chamber. 
     In some embodiments, two or more sets of feed wheels  40  and agitators  42  are provided for increased powder feeding capacity. Each set including a feed wheel and an agitator forms a powder feed section of the powder feed system. The two or more sets of feed wheels and agitators can be mounted in one or more larger chambers or can be mounted in subchambers of the feed chamber. In some embodiments, the thickness of feed chamber  62  can be increased and subchambers can be defined by dividing walls spaced along the axis of rotation of the feed wheel. In further embodiments, two or more sets of feed wheels and agitators can be spaced circumferentially around the dosing wheel, as shown in  FIG. 7  and described below. One or more drive mechanisms can be used to drive the two or more sets of feed wheels and agitations. 
     In operation, powder is loaded into the hopper  30  until the powder reaches the tips of the feed wheel pins  74 . The motors  110  and  112  are energized and the agitator rotates at a speed that allows filling of the powder outlet  64  by an agitator element  94  passing over the outlet at least once on each fill cycle and in the same direction as the surface of the dosing wheel  12 . The feed wheel  40  rotates in the same direction and at a slower speed to prevent compacting of the powder but keeping the agitator  42  supplied with powder. The feed wheel pins extend into the tip radius of the agitator pins to insure sufficient transfer of powder and at the same time moving excess powder over the agitator and maintaining a consistent pressure on the outlet area to maintain accurate dosing. By minimizing compression of the powder, it will deaggregate more reproducibly, for example in an inhaler, and give more consistent performance. 
     A second embodiment of a powder feed system is shown in  FIG. 6 . A powder feed system  200  includes a feed frame  232 , a flange plate  234 , a feed wheel  240 , an agitator  242 , an upstroke chamber insert  250  and a downstroke chamber insert  252 . Feed frame  232  is part of a housing which defines a feed chamber  262 . Powder feed system  200  can include a hopper (not shown in  FIG. 6 ) as described above. 
     Feed wheel  240  includes a feed wheel hub  270  that rotates about a feed wheel axis  272  and feed wheel pins  274  extend radially from feed wheel hub  270 . In the embodiment of  FIG. 6 , feed wheel  240  includes 16 pins  274 , including a first pin set  280  of 8 pins and a second pin set  282  of 8 pins. The pin sets  280  and  282  are axially spaced apart along feed wheel axis  272 . The pins of each pin set can be spaced apart at 45° intervals. In the embodiment of  FIG. 6 , the pins of pin sets  280  and  282  are circumferentially aligned. 
     Agitator  242  can include an agitator hub  290  that rotates about an agitator axis  292 , and agitator elements  294  affixed to agitator hub  290 . The agitator  242  can be configured as described above in connection with agitator  42 . 
     Upstroke chamber insert  250  can include a curved edge  330  having a curvature that is based on the diameter of agitator  242 . Downstroke chamber insert  252  can include a curved edge  332  that is based on the diameter of feed wheel  240  and a curved edge  340  having a curvature that is based on the diameter of agitator  242 . Together, curved edge  330  of chamber insert  250  and curved edge  340  of chamber insert  252  define a U-shaped volume of feed chamber  262  that contains agitator  242 . A gap between chamber inserts  250  and  252  defines an outlet  342  of feed chamber  262 . As in the first embodiment, the feed wheel  240  provides a continuous supply of powder to agitator  242 , so that the agitator is not deprived of powder. 
     Powder feed system  200  can further include auxiliary pins  350  and  352  which are affixed to upstroke chamber insert  250  and which extend upwardly at an angle above agitator  242  and between pin sets  280  and  282  of feed wheel  240 . Auxiliary pins  350  and  352  direct powder being moved by a feed wheel  240  downwardly toward agitator  242  and thereby enhance performance of the powder feed system. 
     A schematic diagram of a powder fill system in accordance with a third embodiment of the invention is shown in  FIG. 7 . The powder fill system includes a powder feed system  400  which supplies powder to a dosing wheel  412 . Dosing wheel  412 , in turn, dispenses controlled quantities of powder to containers  422 . The dosing wheel  412  includes a series of dosing holes  420  around its periphery. The dosing holes  420  retain powder by suction. 
     Powder feed system  400  includes a feed frame  432  for receiving a powder, and powder feed sections  434 ,  436  and  438 . Each of powder feed sections  434 ,  436  and  438  includes a feed wheel  440  and an agitator  442  positioned in a feed chamber  462 , and a drive mechanism (not shown) for rotating feed wheel  440  and agitator  442 . Each of the powder feed sections  434 ,  436  and  438  may be configured as described above. Feed sections  434 ,  436  and  438  include powder outlets for delivering powder to respective holes  420  on dosing wheel  412 . The powder feed system  400  of  FIG. 7  can provide increased throughput in comparison with powder feed systems having a single powder feed section. 
     Having thus described several aspects of several embodiments of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.