Abstract:
A rotary tablet press comprises a rotary system constituted by a turret and a drive shaft arranged in a housing for rotation of the turret. The turret includes a die table and a number of punches are guided in the turret. The turret is connectable to the drive shaft by a coupling including a first coupling part and a second coupling part which are interconnectable by clamping elements engageable between the coupling parts by at least one pneumatic actuator situated in the rotary system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   REFERENCE TO A MICROFICHE APPENDIX 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a rotary tablet press comprising a turret and a drive shaft arranged in the housing for rotation of the turret. 
   U.S. Pat. No. 5,004,413 discloses a rotary tablet press comprising a die table carried by bearings mounted on an intermediate axially extending portion of a spindle fixed stationary on the machine frame. The die table is driven through inter-engaging drive dogs by a pulley carried by bearings mounted on a lower, fixed end portion of the spindle. An upper end portion of the spindle is attached to a machine upper frame and comprises a fluid-operable piston which is downward displaceable axially in the spindle to engage an upper end face of the intermediate spindle portion in order to press a lower end face of this into engagement with an upper end face of the lower end portion of the spindle and thereby bring the drive dogs of the die table into engagement with the drive dogs of the pulley. The die table may be released from the machine frame by upward displacement of the piston in the upper end portion of the spindle and subsequently lifted out of engagement with the pulley by upward displacement of a fluid-operable piston arranged axially in the lower end portion of the spindle. However, due to the additional intermediate spindle portion with associated bearings carrying the die table, this design is rather complex and consequently costly. 
   BRIEF SUMMARY OF THE INVENTION 
   The object of the present invention is to provide a rotary tablet press of a simpler construction than known tablet presses. 
   The present invention relates to a rotary tablet press comprising a housing, a rotary system constituted by a turret and a drive shaft arranged in the housing for rotation of the turret, the turret comprising a die table, and a number of punches being guided in the turret, and at least a cam for cooperation with the punches in order to effect axial displacement of the punches by rotation of the turret, whereby the turret is connectable to the drive shaft by means of a coupling comprising a first coupling part and a second coupling part, said first and second coupling parts being interconnectable by means of clamping elements engageable between the coupling parts by means of at least one pneumatic actuator comprising an actuator piston displaceable in a cylinder arranged in the turret, whereby a pressure chamber delimited by the actuator piston in said cylinder is supplied with air through tubing releasably connected to an air supply 
   In this way, the clamping force may be applied directly between the turret and the drive shaft, without the need for mechanically transferring the clamping force from the stationary housing of the tablet press to the rotary system. 
   A rather large actuator may be accommodated in the turret, thereby ensuring the provision of sufficient clamping force for the coupling, and the employment of a pneumatic actuator minimizes the risk that harmful fluid leaks into areas containing product. 
   In a further embodiment, the first coupling part comprises a mandrel extending axially therefrom, and the clamping elements are arranged in a cavity in the second coupling part so that they are displaceable to grip around the mandrel. The interaction between the clamping elements and the mandrel ensures that the two coupling parts are aligned coaxially. 
   In a further embodiment simple to manufacture, the gripping operation of the clamping elements is activated by displacement of an actuator spindle, which is driven by means of the actuator piston. 
   In a further embodiment, the clamping elements are located around the actuator spindle in a bore in the second coupling part, and each clamping element has a first end with an inward projection arranged in a peripheral groove of the actuator spindle and a second end with an inward oblique face and an outward projection with an abutment, whereby, in a retracted position of the actuator spindle, the oblique face may abut a corresponding conical face of the mandrel and the abutment may abut a wall of the bore in the second coupling part so that the mandrel is fixed centrally in the second coupling part, and whereby, in an advanced position of the actuator spindle, the outward projection of the clamping element may be received in a recess in the wall of the bore so that the mandrel is released by the clamping elements. 
   The first end of the clamping elements may be provided with an outward groove in which an elastic ring, such as an annular spring, is located in order to maintain the inward projection of the first end of the clamping elements in the peripheral groove of the actuator spindle. 
   In another embodiment, the first coupling part has a peripheral groove, and the second coupling part comprises a plurality of clamping elements, each clamping element being actuated by a separate pneumatic actuator and having a gripper adapted to engage the peripheral groove of the first coupling part. By providing the clamping elements at the periphery of the coupling, less clamping force has to be provided by each clamping element and consequently by each associated actuator in order to maintain the coupling parts connected during operation of the tablet press. 
   In still another embodiment, the coupling is constituted by a bayonet coupling, the clamping elements being integral parts of bayonet coupling parts. Thereby the coupling may be designed to be self-reinforcing so that the clamping force is increased automatically by rotation of the turret during operation of the tablet press. 
   In a further embodiment, the actuator is driven by means of pressurized air supplied from the housing via tubing comprising a rotary coupling. In this way, the connection between the air supply and the rotary system may be maintained during rotation of the turret, and no manual or automatic connection between the air supply and the rotary system has to be performed before the coupling may be operated in order to remove the turret from the drive shaft. 
   In a further embodiment, the first coupling part is provided on the drive shaft and the second coupling part is provided on the turret. 
   In a further embodiment, each coupling part is provided with a coaxially arranged toothed ring, said toothed rings being mutually engageable upon connection of the two coupling parts. The engagement between the toothed rings permits the transmission of sufficient torque from the drive shaft to the turret. 
   The present invention further relates to a method of mounting a turret of a rotary tablet press on a drive shaft of the press, the tablet press comprising a housing, a rotary system constituted by the turret and the drive shaft, the turret comprising a die table, and a number of punches being guided in the turret, and at least a cam for cooperation with the punches in order to effect axial displacement of the punches by rotation of the turret, whereby the turret is mounted on the drive shaft by means of a coupling comprising a first coupling part and a second coupling part. 
   The method according to the invention is characterized by interconnecting said first and second coupling parts by means of clamping elements and by engaging said clamping elements between the coupling parts by means of operating at least one pneumatic actuator, whereby an actuator piston comprised by the actuator is displaced in a cylinder arranged in the turret, whereby a pressure chamber delimited by the actuator piston in said cylinder is supplied with air from an air supply, and whereby the pressure chamber by means of tubing is connected releasably to the air supply before operating the actuator. Thereby the above-mentioned advantages are obtained. 
   In a further embodiment of the method according to the invention, the operation of the pneumatic actuator displaces an actuator spindle in a bore in the second coupling part from an advanced position to a retracted position, whereby the spindle displaces the clamping elements from a position, in which a mandrel extending axially from the first coupling part is releasable from the second coupling part, to a position, in which an oblique inward face of the clamping elements abuts a corresponding conical face of the mandrel and an outward abutment of the clamping elements abuts a wall of the bore in the second coupling part, whereby the mandrel is fixed centrally in the second coupling part. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The invention will be described in more detail below by means of examples of embodiments with reference to the schematic drawing, in which 
       FIG. 1  is a sectional view of part of the rotary system of a rotary tablet press according to the invention, 
       FIG. 2  is, on a larger scale, a sectional view of the coupling of the rotary system in  FIG. 1 , 
       FIG. 3  shows a detail of the coupling shown in  FIG. 2 , and 
       FIGS. 4 ,  5  and  6  are sectional views of different embodiments of the mounting of the lower cams. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a compression unit  1  and part of a drive shaft  2  of a rotary tablet press for compression of a feedstock in the form of powder or granular material into tablets, compacts or the like. The tablet press is of a type suitable for use in the pharmaceutical industry, but the press according to the invention may as well be a so-called industrial press employed in the production of a variety of different products, such as vitamins, pet food, detergents, explosives, ceramics, batteries, balls, bearings, nuclear fuels, etc. 
   The compression unit  1  is detachably arranged in a not shown housing of the tablet press and comprises a stationary casing  3 , in which is arranged a rotary turret  4 . The turret  4  comprises a die table  5 , in which a number of dies  6  are arranged circumferentially. Each die  6  is associated with an upper punch  7  and a lower punch  8  guided in the turret  4  in order to compress material in the die  6 . The turret  4  is arranged rotatably in the casing  3  and by means of bearings  10  it supports stationary cams  11  cooperating with upper so-called mushroom heads  12  of the upper punches  7  in order to displace the punches  7  axially by rotation of the turret  4 . The lower punches  8  are provided with similar mushroom heads  13  arranged in corresponding lower cams  14 , which are not shown in  FIG. 1 , but are arranged in the housing of the tablet press, which will be described in greater detail below. The compression unit  1  comprises a not shown powder inlet releasably connected to a powder supply arranged in the tablet press housing as well as a not shown tablet outlet possibly releasably connected to a tablet chute arranged in the tablet press housing. Further, the compression unit possibly comprises other not shown releasable connections for dust extraction and die lubrication, among others. 
   The vertical drive shaft  2  is arranged rotatably in the tablet press housing by means of bearings  15  and is driven by means of a not shown drive motor in order to rotate the rotary turret  4 . The turret  4  is releasably connected drivingly to the drive shaft  2  by means of a coupling  16  comprising a first coupling part  17  provided at an upper end of the drive shaft  2  and a second coupling part  18  provided in the rotary turret  4 . 
     FIG. 2  shows the coupling  16  on a larger scale. The first coupling part  17  comprises a mandrel  19  fixed axially in the upper end of the drive shaft  2  by means of threads  20  so that it extends from the upper end of the drive shaft  2 . 
   The second coupling part  18  comprises a pneumatic actuator  21  having a piston  22  arranged displaceably in a cylinder  23  arranged coaxially in the rotary turret  4 . The piston  22  has an outer peripheral wall  24  sealed against the cylinder  23  by means of an O-ring  25  and a top wall  26  that together with the cylinder  23  delimits a pressured chamber  27 . In a top wall  28  of the cylinder  23  is mounted a rotary coupling  29  through which compressed air may be supplied from a supply tube  30  to the pressure chamber  27  in order to operate the actuator  21 . The actuator piston  22  is spring-loaded towards an upper position shown in the part of  FIG. 2  situated on the right side of the actuator centre line by means of a number of disc springs  31  arranged in a pile inside the outer wall  24  of the piston  22 . A lower position of the actuator piston  22 , which is reached when operating the actuator  21  by means of compressed air, is shown in the part of  FIG. 2  situated on the left side of the actuator centre line. An actuator spindle  32  is arranged coaxially in and connected rigidly to the actuator piston  22  in order to displace a number of clamping elements  33  arranged around the actuator spindle  32  in a bore  34  of the second coupling part  18 . The clamping elements  33  may be employed in a number of three, four or more. 
   A cylindrical stop  61  projects up from the centre of the top wall  26  of the actuator piston  22  in order to limit the upper position of the piston  22 . The cylindrical stop  61  is provided with a diametrical recess  62  so that the air supply through the rotary coupling  29  will not be covered by the stop  61 . 
   In the above-described embodiment the actuator  21  is operated by means of compressed air, but it may also be operated by means of hydraulic oil or by means of any suitable fluid, such as gas, liquid or any mixture of these. 
     FIG. 3  shows the clamping elements  33  of the second coupling part  18  in greater detail. Each clamping element  33  has a first end  35  provided with a projection  36  directed inwards in relation to the centre axis of the coupling and having an inward oblique face  37 . The projection  36  is maintained in a peripheral groove  38  in the actuator spindle  32  by means of an annular spring  39  passing through an outward groove  40  of the first end of each clamping element  33 . In the upper position of the actuator piston  22 , in which the actuator spindle  32  is in a retracted position, as shown on the right side of  FIGS. 2 and 3 , an inward oblique face  41  of a second end  42  of each clamping element  33  abuts a corresponding conical surface  43  of the mandrel  19  and an abutment  44  of an outward projection  45  of the second end  42  of each clamping element  33  abuts a wall  46  of the bore  34  in the second coupling part  18 , whereby the mandrel  19  is fixed centred in the second coupling part  18 . 
   In the lower position of the actuator piston  22 , in which the actuator spindle  32  is in an advanced position, as shown on the left side of  FIGS. 2 and 3 , the clamping elements  33  are displaced to a position, in which the second end  42  of the clamping elements  33  are displaced outwards in the radial direction of the coupling  16 , sufficiently for the conical face  43  of the mandrel  19  to pass out between the clamping elements  33  and out of the second coupling part  18 . In said position, the abutment  44  of the clamping elements  33  abuts a recess  47  in the bore  34  of the second coupling part  18 . As may be seen in  FIG. 3 , in the retracted position of the actuator spindle  32 , the oblique face  37  of the first end  35  of the clamping elements  33  abuts the bottom of the groove  38  in the actuator spindle  32  at its lower edge only, whereas the oblique face  37  in the advanced position of the actuator spindle  32  abuts the bottom of the groove  38  over substantially its entire area. In other words, the clamping elements  33  are tilted between the closed and open positions by means of displacement of the actuator spindle  32 , assisted by the spring force of the annular spring  39 . 
   In order to transfer the torque from the drive shaft  2  to the rotary turret  4 , the first coupling part  17  is provided with a toothed ring  48  which may engage with a corresponding toothed ring  49  on the second coupling part  18 . 
   On the top of the compression unit on a cover  9  is provided a shaft  50  which may be moved by means of a manipulator arranged in the housing of the compression unit in order to lift the compression unit  1  up from the drive shaft  2  and horizontally out of the tablet press in order to clean or exchange the compression unit. Before removing the compression unit, the tubing  30  is released from the air supply in the housing. However, during operation of the tablet press, the tubing  30  may be maintained connected to the air supply due to the rotary coupling  29 . 
   Different embodiments of the coupling  16  are possible, it would for instance be possible to provide the second coupling part  18  on the drive shaft  2  and the first coupling part  17  on the rotary turret  4 , i.e. the actuator  21  would be situated in the drive shaft  2 . The clamping elements  33  may have a different configuration, they may for instance be arranged at the periphery of the drive shaft  2  and may possibly each be operated by means of a separate actuator. Obviously, the coupling  16  according to the invention may also be employed in tablet presses without an enclosed compression unit as shown in the figures. 
     FIGS. 4 ,  5  and  6  show how the lower cams  14  may be provided releasable in the housing of the tablet press in order to release the lower mushroom heads  13  of the lower punches  8  from the tablet press housing before removal of the compression unit  1  from the tablet press housing. 
     FIG. 4  shows a single-acting cam  14 , i.e. a cam which grips over the mushroom head  13  at only one side of the head. The cam  14  is composed of a first cam block  51  fixed in the tablet press housing and a second cam block  52  which is mounted on the first cam block  51  by means of a shoulder screw  53 . The shoulder screw  53  ensures accurate positioning of the second cam block  52  in relation to the first cam block  51  by means of its shoulder  54  which fits exactly into both a toleranced bore  55  of the first cam block  51  and a toleranced bore  56  of the second cam block  52 . The second cam block  52  is divided into a first part  57  and a second part  58  by means of an intermediate rubber layer  59  in order to take up small tolerances between the first and second parts  57 ,  58 . The second part  58  grips over one side of the mushroom head  13  of the lower punch  8 . The first part  57  may suitably be made of corrosion-resistant steel and the second part  58  may suitably be made of bronze. 
     FIG. 5  shows a double-acting cam that has a first cam block  51  gripping over the right side of the mushroom head  13  and a second cam block  52  gripping over the left side of the mushroom head  13 . The two cam blocks  51 ,  52  are interconnected releasably by means of a shoulder screw  53  in the same way as the single-acting cam shown in  FIG. 4 . The double-acting cam shown in  FIG. 5  does not comprise an intermediate rubber layer. The first cam block  51  is by means of vertical screws fixed to a frame part  60  of the tablet press housing. As it is known in the art, a double-acting cam is employed in such parts of the operating cycle where the punch head  13  is submitted to high vertical acceleration forces. 
     FIG. 6  shows a different configuration of the single-acting cam shown in  FIG. 4 . The releaseable mounting of the cam blocks  51 ,  52  by means of the shoulder screws  53  is in itself an invention which may, of course, be employed independently of the coupling  16  according to the invention.