Abstract:
The present invention is directed to a method for transferring substrates by receiving a first substrate at a first substrate receiving station in a first transfer unit capable of holding at least two substrates, moving the first transfer unit containing only the first substrate along a conveying line to a second substrate receiving station, causing the first transfer unit to receive a second substrate at the second substrate receiving station; and transferring the first and second substrates simultaneously to a substrate transfer station.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a divisional application of and claims priority to U.S. patent application Ser. No. 10/393,609 filed Mar. 21, 2003, now U.S. Pat. No. 6,880,694, which is a continuation-in-part of U.S. patent application Ser. No. 09/967,414, filed on Sep. 28, 2001, now U.S. Pat. No. 6,742,646. 

   FIELD OF THE INVENTION 
   This invention relates generally to methods and apparatuses for transferring substrates, such as tablets, from one location to another. 
   BACKGROUND OF THE INVENTION 
   Double-sided tablet presses are commonly used in the pharmaceutical industry for making tablets. Their configuration is well known. Typically, they comprise a rotor having dies located along its periphery. The rotor rotates through first and second compression zones. In each compression zone, powder is fed to dies, optionally the powder is precompressed and then compressed within the dies, and finally finished tablets are ejected from the press. Because double-sided tablet presses contain two compression zones, with each revolution of the rotor two sets of tablets are made. The tablets are ejected from opposite sides of the press at first and second tablet ejection zones. The ejected tablets are conventionally transferred away in bulk by an ejection chute leading to a collection container such as a drum or hopper. 
   Commonly assigned, copending U.S. patent application Ser. No. 09/967,414, the disclosure of which is incorporated herein by reference, discloses a transfer device capable of handling substrates such as tablets having a high degree of friability and softness. It is a rotating device comprising a plurality of transfer units attached to a flexible conveying means, such as a belt. It is preferably used for transferring substrates within a continuous process from one operating unit to another, for example from a compression apparatus to a coating apparatus. The flexible conveying means follows a path from the first operating unit to the second operating unit. The velocity and positions of the transfer units are synchronized with the operating units to which it is coupled, so that substrates can be smoothly captured from the first operating unit and released to the second operating unit. The transfer units comprise retainers for holding the substrates. The retainers are preferably flexible and constructed from an elastomeric material. In a preferred embodiment, the retainers are circular and comprise segmented fingers of elastomeric material. 
   Applicants have now designed a transfer device having transfer units comprising inner and outer, side by side retainers that sequentially rather than simultaneously capture substrates. The device may be used to transfer tablets or other substrates, preferably from a rotary, double-sided tablet press to a second location. The transfer units are mounted on a flexible conveying means that travels along a path coincident with those portions of the tablet press where tablets are ejected. In one embodiment, the transfer units are adapted to receive first tablets at a first substrate receiving station of the apparatus located proximal to the first tablet ejection zone of the tablet press, and adapted to receive second tablets at a second substrate receiving station located proximal to the second tablet ejection zone of the tablet press. 
   SUMMARY OF THE INVENTION 
   The invention provides an apparatus for transferring substrates, comprising: a) a flexible conveying means; b) a plurality of transfer units mounted to said conveying means, each transfer unit adapted to hold first and second substrates; c) a cam track defining a path from a first substrate receiving station, passing through a second substrate receiving station, and then to a substrate transfer station; and d) means for driving said conveying means along said cam track. 
   The invention also provides an apparatus for transferring tablets from a double-sided tablet press comprising first and second tablet ejection zones to a second location, said apparatus comprising a plurality of transfer units mounted to a flexible conveying means, each transfer unit adapted to hold first and second tablets, a cam track defining a path from a first substrate receiving station located proximal to the first tablet ejection zone, passing through a second substrate receiving station located proximal to the second tablet ejection zone, and then to a substrate transfer station located at the second location; and means for driving said conveying means along said cam track. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts a conventional double-sided tablet press. 
       FIG. 2  depicts a transfer apparatus according to the invention coupled with the tablet press of  FIG. 1 . 
       FIG. 3  is a cross-sectional view of a transfer apparatus according to the invention. 
       FIGS. 4–8  illustrate a preferred embodiment of a transfer unit. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  depicts a conventional, double-sided tablet press  1 . The tablet press  1  comprises a rotor  2  having a plurality of dies  3  around its periphery.  FIG. 1  depicts 12 dies. Accordingly, each revolution of this tablet press produces 24 tablets. 
   Tablet press  1  comprises first and second powder feeders  4   a,    4   b,  first and second precompression rollers  5   a,    5   b  (which are optional), and first and second main compression rollers  6   a,    6   b.  First powder feeder  4   a  is located on the opposite side of rotor  2  from second powder feeder  4   b.  First precompression roller  5   a  is located on the opposite side of rotor  2  from second precompression roller  5   b.  Likewise, first main compression roller  6   a  is located on the opposite side of rotor  2  from second main compression roller  6   b.  A first compression zone  11   a  comprises first powder feeder  4   a,  first precompression roller  5   a  and first main compression roller  6   a.  A second compression zone  11   b  comprises second powder feeder  4   b,  second precompression roller  5   b  and second main compression roller  5   b.  Tablets  10   a,    10   b  are ejected from opposite sides of tablet press  1  at a first tablet ejection zone  7   a  and a second tablet ejection zone  7   b.    
   The tablet press operates as follows. Powder is fed from the first powder feeder  4   a  to dies  3  passing thereunder as rotor  2  rotates in the direction shown by arrows a. This powder is optionally precompressed by the first precompression roller  5   a,  and compressed by the first main compression roller  6   a  into tablets  10   a.  Tablets  10   a  are ejected from the dies  3  at first tablet ejection zone  7   a.  Empty dies  3  next pass underneath the second powder feeder  4   b  and new powder is fed to the dies  3 . The new powder is optionally precompressed by the second precompression roller  5   b,  and compressed by second main compression roller  6   b  into tablets  10   b.  Tablets  10   b  are ejected from the dies  3  at the second tablet ejection zone  7   b.    
   The apparatus for transferring substrates (also referred to herein as the transfer apparatus) may be coupled with a double-sided tablet press as described above, as shown for example in  FIG. 2 . In particular, the transfer apparatus may be used to retrieve tablets from a double-sided tablet press and transfer them to a second location for further processing, for example coating. Advantagously, the transfer apparatus transfers the tablets on a continuous basis. 
   Referring to  FIG. 2 , the transfer apparatus  12  comprises a flexible conveying means  13 , shown here as a belt, to which a plurality of transfer units  14  are attached. The flexible conveying means may be made of any suitable material, one example of which is a composite consisting of a polyurethane toothed belt with reinforcing cords of polyester or poly-paraphenylene terephthalamide (Kevlar®, E.I. duPont de Nemours and Company, Wilmington, Del.). Other flexible materials, such as chains, linked belts, metal belts, and the like can be used as the flexible conveying means. 
   The transfer apparatus can be driven by any suitable power source such as an electric motor. In one embodiment, the transfer apparatus is linked to the tablet press and driven by mechanical means through a gearbox (not shown) that is connected to a main drive motor (not shown). In this configuration the velocity and positions of the individual transfer units of the transfer apparatus can be synchronized with the dies of the tablet press. 
   In one embodiment of the invention, as shown in  FIG. 3 , the transfer apparatus includes a drive pulley  20  and an idler pulley  21 . A drive shaft  22  connects drive pulley  20  to a main drive train (not shown). Drive shaft  22  drives drive pulley  20  to rotate. Drive pulley  20  has teeth that engage teeth  23  disposed on the interior of flexible conveying means  13 , which in turn moves the transfer apparatus in the direction of arrows b shown in  FIG. 2 . Idler pulley  21  has teeth that engage flexible conveying means  13  as well, which causes the idler to rotate with flexible conveying means  13 . 
   The transfer apparatus further comprises a cam track  24  that precisely determines the path for the flexible conveying means  13 . The path of cam track  24 , the pitch distance between the transfer units  14 , the pitch of the flexible conveying means  13 , and the gear ratio between the driving means of the transfer apparatus and the driving means of the tablet press (as well as the driving means of other operating units to which the transfer apparatus is coupled) are all selected such that the transfer apparatus is precisely aligned with the tablet press and any other operating units linked to it. As each operating unit rotates, the transfer apparatus remains synchronized and phased with each, such that a precise and controlled transfer from one operating unit to another is achieved. 
   The velocity and positions of the transfer units  14  are matched to the velocity and positions of the dies  3  in the tablet press along two portions of the path defined by the cam track  24 . As shown in  FIG. 2 , the path travels through a first substrate receiving station  18   a,  a second substrate receiving station  18   b,  and a substrate transfer location  19 . Substrate transfer location  19  may be located for example at a second location remote from the tablet press, for instance proximal to another operating unit  17 . 
   First portion  16   a  of the path defined by the cam track is an arc coincident with tablet press rotor  2  when it passes through the first tablet ejection zone  7   a  of the tablet press. Second portion  16   b  of the path is an arc coincident with the tablet press rotor  2  when it passes through the second tablet ejection zone  7   b.  Substrates are received along these two arc lengths. 
   A preferred transfer unit  14  is depicted in  FIG. 4 . Each transfer unit is adapted to hold first and second substrates in a side-by-side fashion. Each transfer unit  14  generally includes a pair of plunger shafts  25 , one or preferably more than one cam follower  26 , a plurality of bearings  27  to retain the plunger shafts  25 , a spring  28 , a plate  29  that secures the plunger shafts  25  to cam follower  26  thereby controlling their movement, first retainer  30   a  and second retainer  30   b.  Preferably, each transfer unit  14  is attached to flexible conveying means  13  in a cantilever configuration so that retainers  30   a,    30   b  are cantilevered over the path of the substrates. 
   Retainers  30   a,    30   b  are preferably flexible and constructed from an elastomeric material. Retainers  30   a,    30   b  flex upward as shown in  FIGS. 6–8  to grasp substrates, shown as tablets  100 , therein. Substrates are ejected from the retainers  30   a,    30   b  by pushing down on them, thereby flexing the retainers. Once released, the retainers  30   a,    30   b  flex back to their original positions to receive farther substrates. In a preferred embodiment, the retainers  30   a,    30   b  are circular and include segmented fingers of elastomeric material as shown in  FIG. 5 , but need not be so constructed. The retainers  30   a,    30   b  need only be flexible enough to flex, hold a substrate, and release the substrate. 
   First and second retainers  30   a  and  30   b  are disposed side-by-side within each transfer unit. In one embodiment of the invention, each transfer unit is attached to the center of the flexible conveying means as shown in  FIG. 2 , such that the first and second retainers  30   a  and  30   b  are disposed on either side of the flexible conveying means. Viewed from the perspective of forward movement of the flexible conveying means along the path, the first retainer  30   a  is located on the outside of each transfer unit, while second retainer  30   b  is located on the inside of each transfer unit, i.e., closer to the center of the transfer apparatus. This inner/outer configuration, coupled with the path followed by the cam track, allows the transfer unit to pick up one substrate at a time, as described below. 
   Referring to  FIG. 4 , riding in cam track  24 , cam follower  26  is mounted so that it can move up and down as shown in  FIGS. 4–8 . Plate  29  is coupled to cam follower  26 . Spring  28  biases the plate  29  and cam follower  26  to an upper position. Plate  29  is also coupled to each plunger shaft  25 , so that movement of the plate  29  will cause movement of the plunger shafts  25 . Each plunger shaft  25  is mounted within a transfer unit  14  by a plurality of bearings  27  that permit vertical movement of the plunger shafts  25 . The plunger shafts  25  are mounted so that one end of each plunger shaft  25  can move into the respective space in which a substrate is retained to eject it from the associated retainer, as shown in  FIG. 8 . The plunger shafts  25  and bearings  27  may be made of any suitable material. 
   The transfer apparatus operates as follows. As shown in  FIG. 2 , flexible conveying means  13  is moved along the path defined by the cam track  24  and wheels  15   a,    15   b,    15   c  in the direction of arrows b. This directs each transfer unit  14  in series to the first substrate receiving station  16   a.  Here, a transfer unit  14  comes into proximity with a die  3  containing a first tablet in the first tablet ejection zone  7   a  of the tablet press. The first retainer  30   a  of the transfer unit  14  aligns with the die  3 . The first tablet is ejected from the die  3  by the punches of the tablet press and into the retainer  30   a  as shown in  FIGS. 6–8 . Retainer  30   b  remains empty. 
   Further rotation of the transfer apparatus by the drive pulley causes the flexible conveying means  13  and its attached transfer units  14  to travel farther along the path shown by arrows b. Retainer  30   a  continues to hold a first tablet therein. When the transfer unit  14  reaches the second substrate receiving station  16   b  it comes into proximity with a die  3  containing a second tablet in the second tablet ejection zone  7   b  of the tablet press. The second tablet is ejected from the die  3  and into retainer  30   b.  Now, retainers  30   a  and  30   b  contain first and second tablets, side-by-side in the transfer unit. 
   As each full transfer unit  14  reaches substrate transfer location  19 , cam track  24  pushes on the cam follower  26 , which pushes on plate  29 . Plate  29  moves the plunger shafts  25 , which in turn move down and contact the retained substrates. The substrates are pushed past the elastomeric collects and ejected from the retainers. Plunger shafts  25  return to their original upward position. 
   The transfer device may alternatively comprise rotatable transfer units, as described in commonly assigned, copending U.S. patent application Ser. No. 09/967,414, particularly as shown in  FIGS. 77–81  therein. This is useful for example with elongated dosage forms,.i.e., caplets that are compressed horizontally but then must be coated in a vertical position. As shown in  FIG. 80  of the &#39;027 application, each transfer unit  602  comprises of a dosage form holder  608  rotatably mounted in a housing. Each dosage form holder comprises two sets of flexible retainers  630 ,  630 B, one for entry of a substrate  630  and one for exit of a substrate  630 B. During transit along path defined by the cam track  606 , the dosage form holder rotates 90 degrees due to motion of a cam follower  626  within the cam track  606 . An ejector pin assembly  612  enters through holes  608 A in the dosage form holder  608  to eject the substrate. The dosage form holder  608  rotates 90 degrees again, returning to its horizontal position to begin the cycle over again. 
   The following non-limiting example further illustrates the claimed invention. 
   EXAMPLE 
   Acetaminophen-containing tablets are compressed in a double-sided tablet press, Fette model 3090. The press operates at 2000 tablets per minute per side, or 4000 tablets per minute total. The tablet press is coupled to a coating apparatus via a transfer device according to the invention. The transfer device, tablet press and coating apparatus are all driven by a common motor, and are synchronized. The transfer device comprises transfer units, each with first and second retainers, and receives acetaminophen tablets from both sides of the tablet press. The first retainer receives first tablets from one side of the tablet press, and the second retainer receives second tablets from the other side of the tablet press. The transfer units proceed to a coating apparatus, where they are ejected and coated with gelatin.