Abstract:
A method and a device controls a rotary tablet forming machine having a rotor. The rotor is capable of being rotated by a drive unit. The rotor includes at least one matrix with allocated upper punches and lower punches and a pressing force, to act on the press mass filled into the at least one matrix is determined. The determined pressing force (PK actual ) is compared with a pre-specifiable limit value (PK limit ) and, with a level going below the limit value (PK limit ). Then, required speed (n r ) of the rotor can be reduced to a speed below the rated speed (n r-rated ).

Description:
This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 03090036.9 filed in Europe on Feb. 10, 2003, the entire contents of which are hereby incorporated by reference. 
   FIELD OF THE INVENTION 
   The invention concerns a method and a device for the control of a rotary tablet forming machine where a rotor is capable of being rotated by means of a drive unit, the rotor including at least one matrix with allocated upper punches and lower punches and a pressing force, acting on the press mass filled into the one matrix at least, is determined. 
   DESCRIPTION OF THE BACKGROUND ART 
   Rotary tablet forming machines of the category-related type are known. A typical factor here is that, upon starting the drive unit, the rotor is brought from standstill position to its rated speed. By way of at least one filling shoe, the matrixes are filled with the press mass and, depending on the angular position of the rotor, the lower and the upper punches which are guided by guide curves are moved axially to the matrixes. The upper and lower punches are directed past at least one press station, normally a pre-press station and a main press station. At that location, the upper and lower punches are directed past stationary arranged press rollers, essentially tangential, so that a pressing force can be applied onto the press mass filled into the matrixes. 
   Setting and measuring the pressing force is known, for example from EP 0 698 481 B1. In this case, there is an essential correlation between the measured maximum pressing force and the mass of the press mass filled into the matrixes under the prerequisite of the same material properties of the press mass. There is, in this case, a direct correlation between the tablet weight and the pressing force required for the manufacture of the tablets. In dependence on the material to be pressed, a certain pressing force is allocated to each tablet weight with a tablet form pre-specified by the press tools and a set tablet height. If the filling volume, and subsequently the tablet weight, fluctuates at a constant tablet height, a pressing force change results therefrom in direct dependence. 
   If all matrixes in a rotary tablet forming machine are normally filled with press mass up to the press station (meaning, up to the pressure roller), pressure rollers and rotor during start-up are accelerated to the rated speed in the same time period. This is attributable to the fact that each punch, as a result of the rotational movement of the rotor, is drawn past under the pressure roller—touching this—and her via the rotation of the punches the acceleration of the pressure roller is effected so that the acceleration of the pressure roller is directly dependent on the rotational speed of the punches. 
   This correlation between acceleration of the rotor and acceleration of the pressure rollers is then disadvantageous if, upon rotation of the rotor, the matrixes arriving at the press station (pressure rollers) are not or are only partially filled with press mass. 
   This can be the case, for example, during the start-up of the rotary tablet forming machine after cleaning or in the event of an interruption of the material feed by way of the filling shoe(s) with press mass. 
   If the rotary tablet forming machine is now started up with non-filled or with only partially filled matrixes, the upper and lower punches in the press station do not touch or only partially touch the pressure rollers. By starting up the drive unit the rotor with the punch is, however, accelerated to its rated speed. If a first punch with a first orderly filled matrix now accesses the press station, the punch or the punch couple, corresponding to the rotor already accelerated to rated speed, hits the pressure roller which is not yet or only insufficiently accelerated. In this case, the punch has an abrupt impact on the pressure roller so that suddenly a high kinetic energy has to be absorbed by the pressure roller and the punches involved. This can lead to damage of the pressure rollers and/or the punches. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention is therefore based on the task assignment of creating a method and a device of the category-related type, by means of which such damage can be avoided. 
   Because of the fact that the determined pressing force is compared with a pre-specifiable limit value and, if a rate drops below the limit value, the required speed of the rotor is reduced to a speed below the rated speed, it is advantageously possible to synchronise the acceleration of the rotor and the acceleration of the pressure rollers in every operating situation to their rated speeds. In this way it is particularly avoided that the rotor is accelerated to its rated speed before the pressure rollers. Subsequently, an abrupt impact of the punches onto the pressure rollers is avoided and, with this, the damage possibilities existing with the state of the art of pressure rollers and/or punches are also avoided. 
   In a preferred embodiment of the invention, it is envisaged that the speed of the rotor is speed-controlled from its standstill position or its rated speed. In this way, the avoidance of the above-mentioned damage in every operating situation of the rotary tablet forming machine is possible. 
   Because of the fact that the rotary tablet forming machine includes a control device or similar for activating a drive unit of a rotor of the rotary tablet forming machine, a device for determining a pressing force as well as a means for comparing the determined pressing force with a pre-specifiable pressing force and at least one means for pre-specifying a required speed of the rotor in dependence of the comparison of the determined pressing force with the pre-specifiable pressing force, it is advantageously possible to implement in an uncomplicated manner. The control function in the rotary tablet forming machine which, depending on a filling degree of matrixes of the rotor, controls a required speed of the rotor. In this way a run-up, in particular, of the rotor adapted to the filling degree of the matrixes is made possible so that, in particular, mechanical loading/stressing/damage of pressure rollers and/or press punches can be avoided. 
   Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained as follows in greater detail with an embodiment as based on the relevant drawings, which are given by way of illustration only, and thus are not limitative of the present invention. The figures show the following: 
       FIG. 1 : a partially schematic illustration of a rotary tablet forming machine; 
       FIG. 2 : a block diagram of a device for the control of the rotary tablet forming machine, and 
       FIG. 3 : a control sequence. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Rotary tablet forming machines of the type referred to here are generally known. Within the framework of this description, therefore, more detailed attention is not given for the fundamental structural arrangement and basic functions. 
     FIG. 1  shows in a schematic partial view the configuration of a rotor  12  of a rotary tablet forming machine with an overall designation  10 . The rotor  12  has a large number of spaced matrixes  14  around its periphery. To each matrix  14  there is allocated a lower punch  16  and an upper punch  18  which are guided by guide curves  20  and  22 , respectively, indicated here. Rotor  12  and lower punch  16  as well as upper punch  18  here have a synchronous rotation around the rotating axis of the rotor  12 . The rotor  12  can be rotated by an electric drive unit  24  which is only indicated here. 
   A press mass  26 , which is only indicated here, is filled into the matrixes  14  by way of a filling facility, a so-called fill-in shoe. In the normal operating mode of the rotary tablet forming machine  10 , the press mass  26  is filled in over the entire height of the matrix  14 . The filling height can, for example, be defined by the height location of the lower punch  16  at a wiping station not shown here. In the example as illustrated, a non-normal filling is assumed. The press mass  26  is filled into the matrixes  14  only up to a partial height. It is also conceivable that absolutely no press mass  26  is filled into the matrixes  14 —for the non-normal case assumed here. Such circumstances could occur, for example, with a new startup of the rotary tablet forming machine  10  after a cleaning operation, maintenance or similar, or after an interruption of the stock feed of the press mass  26  by way of the filling facility. 
   In accordance with the course of the guide curves  20  and  22 , the lower punches  16  and the upper punches  18  plunge into the matrix  14  and press the press mass  26  to the required tablet or similar. 
   For this purpose, the lower punches  16  and the upper punches  18  are directed past at least one pressing station  28  which envelops fixed-positioned pressure rollers  30 . The pressure rollers  30  are individually trunnion-mounted around a rotating axis  32 . The spacing of the pressure rollers  30  to one another is defined and ultimately determines the height of the tablet to be pressed. A drive of the pressure rollers  30  in arrow direction  34 —the upper pressure roller  30  anti-clockwise, the lower pressure roller clockwise—is effected by a passing movement of the lower punches  16  and upper punches  18 , respectively, according to the movement direction  36  of the rotor  12 . The lower punches  16  and the upper punches  18 , respectively, come into a surface-to-surface contact with the peripheral surface  38  of the pressure rollers  30  and cause these rollers to rotate, practically carried along. The rotor  12  rotates here at a speed of n r  whereas the pressure rollers  30  rotate at a speed of n d . 
   As a result of the non-filled or only partially filled matrixes  14 , the press mass  26  to be pressed has only an inadequate counter force opposite the punches  16  and  18  in the pressing station  28  and/or in the area immediately before. The result here is that the punches  16  and  18  are accelerated to the rated speed of the rotor  12  due to the rotation of the rotor  12  but, however, as a result of inadequate surface-to-surface contact at the pressure rollers  30 , these are not accelerated to their rated speed. If, in this non-normal operating condition, a first punch couple—of the punches  16  and  18 —with a normally filled matrix  14  hits the pressure rollers  30 , there is a substantial difference between the momentary speeds of the rotor  12  and of the pressure rollers  30 , respectively. 
   Whereas the rotor  12  is already accelerated to its rated speed n r-rated , the pressure rollers  30  only have an actual speed n d-actual  that is far below their rated speed n r-rated . The result here is that the punches  16  and  18  have an impact on the peripheral surfaces  38  of the pressure rollers  30  with great acceleration so that, in consequence, considerable kinetic energy has to be absorbed. This can lead to mechanical damage both on the surfaces  38  of the pressure rollers  30  as well as on the punches  16  and  18 , respectively. 
   In order to prevent this mechanical stress, the following is envisaged: 
   The pressure rollers  30  are provided in the known manner with measuring data probes  40 , with which the momentary pressing force PK is measured. The invention is elucidated further with the schematic illustration in  FIG. 2 . 
     FIG. 2  shows the rotor  12  drivable by the electric drive unit  24  as well as the pressure rollers  30  allocated to the rotor  12 . The punches are not shown for reasons of clarity. A control unit  42  is allocated to the rotary tablet forming machine  10 , and this control unit can take over a large number of control and regulation functions. Finally, only the configuration and function of the control unit  42  as essential for the invention are described. 
   The control unit  42  is connected to the pressing force probes  40  by way of a signal line  44  and receives a signal pk actual  proportionate to the actual pressing force pk actual . 
   The control unit  42  is also connected to the electric drive unit  24  by way of a signal line  46 , by way of which the electric drive unit  24  receives a control signal n r  that corresponds to the required speed of the rotor  12  which is to be set. 
   The control unit  42  includes an arithmetic-logic unit  48 , to which the signal pk actual  and a signal pk required  from a memory facility  50  are sent, corresponding to the required pressing force pk required  at the pressure rollers  30 . 
   In accordance with the schematic illustrated in  FIG. 3 , the following signal processing is effected. 
   In a step  52 , the actual-signals pk actual  sent from the pressing force probes and the required-signal pk required  sent from the memory facility  50  are processed. In this case, the difference between the signal pk required  and the signal pk actual  is measured. This difference signal pk diff  is joined up with a signal pk limit  in a further step  54 . The signal pk limit  is also, for example, provided by the memory facility  50 . In this case, for example, it can be variably determined as to what extent the pressing force pk limit  corresponding to the signal pk limit  can deviate from the required pressing force pk required . This difference between the pressing force limit value and the pressing force required value can, for example, amount to 10% of the pressing force required value. 
   If it is now determined in step  54  that the difference between the pressing force actual value and the pressing force required value is greater than the difference between the pressing force required value and the pressing force limit value, meaning, the pressing force actual value drops below the pressing force limit value, a signal n r-required  is generated that corresponds to a required speed n r  of the rotor  12 . This required speed is less than the rated speed of the rotor  12  in normal operation. In step  56 , the signal n r-required  corresponding to the required speed is joined up with a signal n r-actual  corresponding to the actual speed of the rotor  12 . Corresponding to a deviation between actual speed and required speed of the rotor  12 , the speed signal n r  is generated and made available to the drive unit  24 . This then accelerates the rotor  12  to the pre-specified speed n r . 
   Based on the explanatory statements given above, it is clear that a speed control of the rotor  12  is effected in dependence of the pressing force. In this way it is achieved that, with an assumed lesser pressing force pk than the required pressing force pk required , the rotor does not rotate at its rated speed. Particularly in the case as explained here, that the matrixes  14  are not or are only partially filled with press mass  26 , the result is that the rotor  12  rotates at a pre-specifiable minimum speed n r . In this way it is avoided that, upon first impact of lower punch  16  and upper punch  18  of an orderly filled matrix  14 , these have an impact on the pressure rollers  30  with the rated speed of the rotor  12 . Subsequently, the mechanical stress at this point of time is considerably reduced. 
   If the punches  16  and  18  of an orderly filled matrix  14  hit the pressure rollers  30 , this leads automatically to an increase of the pressing force pk which is measured as actual-pressing force pk actual  via the pressing force probes  40 . In this way, the difference between the actual pressing force and the required pressing force is reduced so that, according to the schematic as illustrated in  FIG. 2  and  FIG. 3 , the speed of the rotor  12  is increased until this reaches its rated speed. 
   The solution according to the invention is also suitable for recognising with a rotor  12 , rotating at rated speed, if the filling degree of the matrixes  14  with the press mass declines. With a reduction of the filling degree with the press mass  26 , the pressing force pk drops at the pressure rollers  30  due to the direct correlations. According to the course as illustrated in  FIG. 3 , this lowering of the actual pressing force also leads to a reduction of the required speed n r  of the rotor  12 . In this case and in accordance with different embodiment variants, either an incremental or continuous reduction of the required speed n r  can be envisaged. In this way, for example, the required speed n r  can be reduced straight away to a pre-specifiable minimum speed n r-min  or in interim steps from the rated speed n r-rated  to the minimum speed n r-min . 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 
   REFERENCED PARTS LIST 
   
       
         10  Rotary tablet forming machine 
         12  Rotor 
         14  Matrix 
         16  Lower punch 
         18  Upper punch 
         20  Guide curve 
         22  Guide curve 
         24  Electric drive unit 
         26  Press mass 
         28  Press station 
         30  Pressure rollers 
         32  Rotary axis 
         34  Arrow direction 
         36  Movement direction 
         38  Peripheral surface 
         40  Measuring data probe 
         42  Signal line 
         44  Signal line 
         46  Signal line 
         48  Arithmetic-logic unit 
         50  Memory facility 
         52  Step 
         54  Step 
         56  Step 
       PK Pressing force 
       PK required  Required pressing force 
       PK actual Actual pressing force 
       PK limit  Pressing force—limit value 
       n d  Speed of the pressure rollers 
       n d-rated  Rated speed 
       n d-actual  Actual speed 
       n r  Speed of the rotor 
       n r-min  Minimum speed 
       n r-rated  Rated speed 
       pk actual  Proportionate signal 
       pk required  Required signal 
       n r  Control signal 
       n r-required  Signal 
       n r-actual  Signal 
       pk diff  Difference signal