EP0723858B1 - Method for drawing up a force-displacement-diagram of the punches of a rotary tablet press - Google Patents

Description

The invention relates to a method for creating a force-displacement diagram of the ram of a rotary tablet press according to the preamble of the claim 1.

As is well known, the rotor of a rotary tablet press equipped with a number of upper and lower stamps, whereby during a rotor revolution each punch at certain Positions of the circumference (pressing stations) of a vertical Movement and the associated force subject to. In addition to a pre-press station and a main press station an ejector station is considered here to draw.

Depending on the composition of the tablets to be compressed to maintain a predetermined pressing force. It is mostly with the help of stationary pressure rollers on the heads of the Press stamp applied.

EP 0 431 269 has disclosed such a Tableting machine the maximum pressing forces at the Monitor ram. Monitoring the pressing forces done to identify bugs and bad tablets to be able to sort out in time. The monitoring takes place also to provide evidence of the quality of the manufactured To be able to create tablets continuously. With the well-known The process is the one with the press rams Die plate in its position constantly via an angle pulse generator supervised. A computer coordinates the specified maximum impulses with the press force values. The Pressure rollers in the press stations are one example Load cell assigned. The centered position of a Die pair defined in the area of a pair of pressure rollers for example the zero point from which the pulses start of the angular pulse generator are counted, whereby accordingly the division of the die plate a certain number of Angular impulses the position of the next pair of dies centered to the pair of pressure rollers. In this way can be used for all pairs of press rams on a tablet press determine the maximum pressing force.

For many reasons, the compression characteristic is desirable of molding compounds. For this is above all, the force-displacement diagram of outstanding Importance. Physically speaking, the force-displacement diagram describes the quantitative energy curve during tableting. Leave with the help of the compression characteristic draw conclusions about the compressibility of certain Substances and the properties of the tablet. The compressibility is essentially determined by pressure holding time, Granulate state (moisture, particle size distribution), bulk volume, Lubricant, etc. To the tablet properties include tablet mass, disintegration time, drug release, Abrasion etc.

So far it was only in the galenics area with specially equipped Research presses possible using the Force-displacement diagram the compressibility of the to be pressed Assess substances. For this purpose, the research press with a force measuring device and one Stamp path measuring device equipped. This can be done of an eccentric press is relatively easy to accomplish. The Installation of distance measuring devices on rotary presses, as they are now used in development, is complex. The measured value transmission is only about Slip rings or contactless with an appropriate Transmission facility possible. For a production machine is such an effort is not justifiable.

While it is possible to move a press ram into one To determine the rotary press theoretically, as in "Press force and displacement-time characteristics of rotary presses", Inaugural dissertation by Ulrich Tenter. Because of various influencing factors of the machine give way the actual stamp paths are not insignificant of the theoretically calculable.

The invention is therefore based on the object of a method specify at which with a minimal measurement effort the compression characteristic under production conditions a rotary press can be determined.

This object is achieved through the features of the patent claim 1 solved.

In the method according to the invention, the course of the Pressing force of at least one ram in angular steps measured and stored in the computer. One turn of the For example, the rotor corresponds to 3,600 angular pulses. Each of these pulses (one pulse = 0.1 ° angle of rotation of the rotor) a force measurement is assigned and accordingly in Calculator saved. Furthermore, the theoretical Values for the path of the press ram saved. They can be calculated using appropriate geometric relationships will be discussed in more detail below becomes. The decisive factor for this theoretical value the diameter of the pressure roller, the shape of the stamp head and the relative position of these parts to each other.

Finally, one of the rotational angle positions is in the computer assigned correction table stored, which essential Influencing factors on the actual stamp path, such as the suspension of the tablet press and Hertzian Pressing taken into account. Both the suspension as well the Hertzian pressure are dependent on that of the Pressure roller on the press force applied. It force-dependent correction factors are thus determined, subtract from the theoretical values for the stamp path to determine the actual stamp path.

Since the stamp head only has a radius in the peripheral area size, but is flat in the middle is the size the Hertzian pressure also depends on the relative position the stamp head to the pressure roller. In one embodiment the invention therefore take into account the correction values Dependence of Hertzian pressure on the angular position of the ram.

It is conceivable that the correction values for Hertzian To calculate the compression and the spring deflection of the machine. On the other hand, it is preferable according to an embodiment of the invention the determination of the correction values in the correction table empirically by a selected pair of dies without intermediate molding compound for different Infeed values are moved towards each other and the associated press values can be measured.

By using an appropriate calculator it is possible, triggered by the angular impulses the complete To feel and store the force curve of all stamps. In the positions of the stamps can be determined in the same way, assign the angular impulses and the force values relate to a force-displacement calculation a rotary tablet press. With help The invention is therefore possible with the least Measuring effort on a rotary tablet press under production conditions production-specific compression characteristics for each pair of stamps and this with the values determined in the galenics compare and monitor. Since the total energy expenditure to produce a tablet from the spent Energies in the pre-printing station and the main printing station results in this method is also the calculation of energy use for the individual tablet during production feasible.

It is also individually selectable that only one or more Press stamps in succession or certain press stamps within one or more rotor revolutions for calculation and evaluation should be used. About that there is also the possibility to choose between measurements and evaluations for the main press and / or pre-press and / or Eject station to choose.

Fig. 1

zeigt schematisch eine Rundläuferpresse.

Fig. 2

zeigt ein Kraft-Weg-Diagramm für einen Stempel der Presse nach Fig. 1.

Fig. 3

zeigt ein Blockschaltbild zur Ermittlung des Kraft-Weg-Diagramms nach Fig. 2.

Fig. 4

zeigt verschiedene Horizontal- und Vertikalpositionen eines Preßstempels über einen bestimmten Drehwinkel des Rotors der Presse nach Fig. 1.

Fig. 5

zeigt die geometrischen Beziehungen zwischen einer Druckrolle und einem Preßstempel der Presse nach Fig. 1.

Fig. 6

zeigt schematisch die Draufsicht auf den Rotor der Presse nach Fig. 1 im Bereich einer Druckrolle.

Fig. 7

zeigt ein Kraft-Winkel-Diagramm für verschiedene Zustellwerte.

Fig. 8

zeigt ein aus dem Diagramm von Fig. 2 hergeleitetes Kraft-Korrektur-Weg-Diagramm.

Fig. 9

zeigt ein Kraft-Winkel-Diagramm ähnlich dem nach Fig. 7.

Fig. 10

zeigt ein aus dem Diagramm von Fig. 9 hergeleitetes Kraft-Korrektur-Weg-Diagramm.

The invention is explained in more detail with reference to drawings.

Fig. 1

shows schematically a rotary press.

Fig. 2

shows a force-displacement diagram for a stamp of the press of FIG. 1st

Fig. 3

shows a block diagram for determining the force-displacement diagram according to FIG. 2.

Fig. 4

shows different horizontal and vertical positions of a press ram over a certain angle of rotation of the rotor of the press of FIG. 1st

Fig. 5

shows the geometric relationships between a pressure roller and a press ram of the press of FIG. 1st

Fig. 6

shows schematically the top view of the rotor of the press of FIG. 1 in the region of a pressure roller.

Fig. 7

shows a force-angle diagram for different infeed values.

Fig. 8

shows a force correction path diagram derived from the diagram of FIG. 2.

Fig. 9

shows a force-angle diagram similar to that of FIG. 7th

Fig. 10

shows a force correction path diagram derived from the diagram of FIG. 9.

The rotor 12 of the tablet press 10 in FIG. 1 is included a die plate 14 indicated and a number of dies of the rotor 12 with a pair of dies an upper ram 16 and a lower ram 18 in the area of an upper pressure roller 20 or a lower one Pressure roller 22. The rotor 12 is supported by a shaft 24 driven by an electric motor 26, a drive belt 28 and a transmission 30. Also sits on the shaft 24 an angle pulse generator 32. The holder of the pressure rollers 20, 22 interacts with a load cell 34 or 36, with which the force is measured between the pressure roller and stamp acts when the stamp 16, 18 between the Drive pressure rollers 20, 22 along. As is well known here the preliminary or main pressing of a molding compound in the Die plate 14 for forming a tablet or the like.

2 is the force-displacement diagram of a pair of press rams, for example the ram 16 and 18, during the Movement between the pressure rollers 20 and 22 shown. With arrow 38 is the rising and with arrow 40 the falling Known branch of the diagram. Because of the compressibility the press material and the springback behavior the press material and the spring behavior of the press a hysteresis forms itself, as if through the surface indicated in the diagram.

In Fig. 3 it is indicated how the angle pulse generator 32 with the rotation of the rotor 12 generates an angular pulse chain, for example one pulse per 0.1 ° revolution. Moreover it generates an initial impulse through the central Position of a pair of dies with respect to a pair of pressure rollers is defined.

The pulses arrive at a pulse evaluation device 42 and from there to an analog-to-digital converter 44. In FIG. 3 is also shown how the force sensor 34 via a Measuring amplifier 46 also with the analog-digital converter 44 is connected. Its output goes to a machine computer 48. An operating computer is connected to the machine computer 48 50 connected, with the to be described later How the force-displacement diagram of Fig. 2 is created.

In Fig. 4 it can be seen that the stamp 16 covers a vertical path s during its horizontal movement relative to the stationary pressure roller 20. With the load cell 34, pressing force values are determined, which are assigned to individual angular steps by triggering the Ahalog digital converter 44 through angular steps of the angular pulse generator 32 and stored in the computer. The course of the force during the path s is indicated at 52 in FIG. 4. To create the force-displacement diagram, it is also necessary to determine the actual path of both stamps belonging to a press station during their vertical movement. The actual path is made up of the geometric value Y and the values Y ₂ and Y _{3 used} for the correction. Depending on the angle of rotation, the following formulas apply: s (α) = s 1 + s 2nd s (α) = s Y 1 - Y 2nd - Y 3rd where s is the angle-dependent vertical path of the punches 16 and 19 and α is the angle of rotation of the rotor 12 (see FIG. 6).

5, the geometric relationships of the pressure roller 20 and the head 54 of the upper press ram 16 can be seen more clearly; corresponding designations apply to the lower ram. The absolute value for both stamps (vertical path from the upper and lower stamp) is: Y 1 (α) = 2 (c - f) where sizes e and f result from FIG. 5. The sizes e, f and c form a triangle, so: e 2nd = c 2nd + f 2nd and f = e 2nd - c 2nd

Furthermore: e = d 2nd 2nd + r k and c = a - d 3rd 2nd where r _{k is} the die head radius, d _{2 is} the pressure roller diameter and d _{3 is} the diameter of the mirror surface.

By inserting you get: f = d 2nd 2nd + r k 2nd - a - d 3rd 2nd 2nd

The geometric variable a can be found in FIG. 6 again as a function of the pitch circle diameter d ₁ and the angle of rotation α. It is: sinα = a d 1/2 → a = d 1 2nd · Sinα

By inserting you get: f = d 2nd 2nd + r k 2nd - d 1 2nd · Sinα - d 3rd 2nd 2nd and Y 1 = 2 d 2nd 2nd + r k d 2nd 2nd + r k 2nd - d 1 2nd sinα - d 3rd 2nd 2nd

For each angle of rotation α, the vertical movement of a Stamp pair are calculated. In the present case the angles of rotation are preferably selected in 0.1 ° steps according to the pulse interval of the angular encoder 32. However, this overall theoretical path must be corrected the total suspension of the tablet press and around Hertzian surface pressure between stamp head 54 of each stamp and pressure roller 20 and between the stamp head of stamp 18 and the pressure wave 22.

When calculating the flattening of the stamp head and the pressure roller based on Hertzian pressure, two areas must be distinguished, namely the edge area, which has the radius r _{k in cross} section, and the flattened central area (playing surface) of the stamp head. The following general equation applies to the border area: Y 2 (1) = 1.23 3rd F 2nd · 1 / r E 2nd · 2 where F is the pressing force, 1 / r is the sum of the radii of curvature and E is the common modulus of elasticity of the materials involved. The sum 1 / r is determined as follows: 1 / r = 1 / r k + 1 / r m where r _{k describes} the spherical curvature of the outer area of the stamp head and r _{m describes} a circle in this area. r m = r a + r s 2nd 1 / r = 1 / r k + 1 r a + r s 2nd where r _{a represents} the outer diameter of the stamp head and r _{s represents} the inner diameter of the curved outer region of the stamp head (mirror surface).

The pressing force I is shown in angular pulses α = x. 1/3600 ° (0.1 ° increments).

Inside the stamp head 54 of the stamp 16 touches the pressure roller 20 with a mirror surface, which means a line contact. The same applies to stamp 18 and pressure roller 22. The flattening of both stamps is calculated for the flattened middle region (mirror surface) according to the following equation: y 2 (2) = 0.398 10th 4th * F 0.925 L eff. 0.85 · 2 where F is the pressing force and L eff. is the load-bearing length of the mirror surface.

The pressing force is shown as for the above range. The measure for L eff. is calculated from: L eff. = 2 (r s 2nd - a 2nd ) where r _{s is} the radius of the mirror surface. The following formula finally results for the flattening: y 2 (2) = 0.398 10th 4th * F 0.925 2nd r 2nd s - d 1 2nd sinα 2nd 0.85

• Stempel und Druckrollen sowie Druckrollenlagerung
• Gußgehäuse
• unterschiedliche Lagerspiele
• Maschinensäulen

The suspension of the machine is mainly caused by the following individual components: tension, pressure, bending and / or torsion:

• Stamps and pressure rollers as well as pressure roller storage
• Cast housing
• different camp games
• Machine columns

It is assumed that the spring deflection is linear down to the lowest range according to Hook's law. It is therefore: Y 3rd = f (F) and F = f (α) .

With F equal to the pressing force and α equal to the position of the stamp relative to the pressure roller. Therefore: y 3rd = x. F

The factor x can only be done experimentally because of the complex view for every type of machine and every possible tooling be determined.

The actual total stamp path for area 1 is hence the geometric value given above minus the flattening in area 1 minus the spring deflection. Corresponding applies to the die path in area 2 of the die head. The corresponding formulas for this are no longer listed.

In practice, however, those calculated above are used Correction values determined empirically. this happens in the following way.

A pair of measuring stamps is installed in the tablet press, that is moved directly onto one another without molding compound. With this pair of measuring stamps by adjusting the web height (for example in 0.1 mm steps) different Force-angle curves are generated, as shown in FIG. 7. In Fig. 7 means w the delivery of the pressure rollers. It understands that the maxima of the forces with increasing w are larger. Then the maxima are shown in a force-displacement correction diagram 8 entered. With the help of 8 can correct the theoretical calculated total can be taken. In the embodiment 3 this is done in the form of a Table of values. The theoretical are in the operating computer Press stamp paths stored, which result from the above Calculation result. In addition, are in the operating computer 50 the values for the correction table according to the diagram 8 stored so that at a predetermined Force a given correction value from the theoretical Stamp path is subtracted.

However, the correction described so far is still not sufficient, because it is for Hertzian pressure only correct in the area of the maximum. Rather, the Correction value of a further optimization described above be subjected. In the area of the maximum of the pressing force the pressure roller 20 touches the stamp head 54 in a line, which corresponds to the mirror diameter of the stamp head. Before and after this line is getting shorter and shorter and then turns into a point touch. Corresponding is also the elastic penetration depth of the pressure roller in the stamp head different. Therefore, with help of the computer not only the force maxima, but also the respective force values for the 0.1 ° steps for the different Infeed values recorded as shown in Fig. 9 is shown. It is then known for these forces the geometric shape of the pressure roller and stamp head for the individual angle steps the penetration depth over the Hertzian pressure determined. To the deviation of this Values from the maximum values then become the original Correction value corrected. These values are then in the Force-displacement correction diagram entered. 10 is to recognize this correction diagram. Depending on, at which angular step a correction must take place another of the curves shown in Fig. 10 is selected. It it is understood that the correction diagram of FIG. 10 in Operating computer 50 in turn only in the form of a correction value table is saved.

Claims (4)

1. A method for setting up a force-displacement diagram of the punch pair of a rotary tabletting press, in which the position of the punches in the circumferential direction, which are actuated in a pressing station by way of a press roller, are determined with an angle encoder and are converted with the help of a computer and are set into a relationship with the measured pressing force at the punch, characterised by the following method steps:

   with each angular step of the angle encoder the pressing force at the punches of at least one punch pair is measured and the pressing force values are stored in the computer

   for each angular step of the angle encoder from the geometry of the press roller, punch head and the relative position of both to one another, the respective theoretical vertical values of the displacement of the punch pair is computed and stored in the computer

   in the computer further a force-displacement correction table is stored which represents the influence of the Herzian surface pressing between the punch head and the press roller as well as of the resilience behaviour of the rotary press on the actual vertical displacement of the punch pair, in dependency on the force and

   the computer reduces the theoretical value of the punch pair displacement at the individual angular steps by the corresponding correction value from the correction table.
2. A method according to claim 1, characterised in that the correction values also represent the dependency of the Herzian pressing on the angular position of the punch.
3. A method according to claim 1 or 2, characterised in that the correction values of the correction table are empirically determined in that a selected punch pair without a pressing mass lying therebetween are driven onto one another for different feed values.
4. A measuring apparatus and computer for monitoring the tablets manufactured on a rotary press, characterised in that for setting up displacement-pressing force associations for the punches, at least for one punch pair, the following elements are present:

   a) an angle encoder for determining the running angular position of the rotary table and thus of the punch pair,

   b) a pressing force measuring unit with which the pressing force values at least of one punch pair are determined and per angular step a pressing force reading is transmitted to the computer,

   c) an algorithm in the computer which is set up on acount of the geometric relationships in the tabletting press and with the help of which from the angular positions of the rotary table the theoretical values of the displacement of the punch pair in the matrix can be calculated,

   d) a correction function fed into the computer for converting the theoretical displacement values of the punches into the actual displacement values taking into account the Herzian surface pressing between the stamp head and press roller as well as the resilience behaviour of the rotary press.

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