Method for controlling the rotor rotational speed of a rotor of a rotary tablet press, as well as a rotary tablet press

Abstract

A rotary tablet press comprises a rotor comprising a rotary drive configured to rotate the rotor and a die plate that rotates with the rotor and comprises a plurality of cavities and a plurality of upper and lower punches. A rotational speed governor is configured to drive the rotary drive of the rotor by comparing a measured rotor rotational speed with a target rotational speed value. A pilot control apparatus is configured to provide an additional target torque for driving the rotary drive. The additional target torque is based on values of a pressing force of at least one of the upper and lower punches input into the pilot control apparatus.

Claims

1. A method for controlling rotor rotational speed of a rotor of a rotary tablet press, the method comprising: rotating the rotor with a rotary drive; rotating a die plate with the rotor, the die plate comprising a plurality of cavities and a plurality of upper and lower punches; assigning the plurality of upper and lower punches in pairs to one of the plurality of cavities in the die plate for pressing a filling material in the one of the plurality of cavities into a pellet; providing top and bottom pressing rollers configured to exert a pressing force upon contacting the plurality of upper and lower punches; driving the rotary drive via a rotational speed governor configured to compare a measured rotor rotational speed with a target rotational speed value; determining, using a pilot control apparatus, an additional target torque for driving the rotary drive based on the pressing force of at least one of the plurality of upper and lower punches; preemptively applying the additional target torque before contact between the plurality of upper and lower punches with the upper and lower pressing rollers to maintain a constant rotational speed of the rotary drive upon contact between the upper and lower punches and the top and bottom pressing rollers; and controlling a rotational speed of the rotary drive after the upper and lower punches cease contact with the top and bottom pressing rollers such that the rotational speed does not increase above the target rotational speed value.

2. The method according to claim 1, further comprising determining the additional target torque during at least one complete rotation of the rotor.

3. The method according to claim 1, further comprising driving the rotary drive using a frequency converter as the rotational speed governor.

4. The method according to claim 3, further comprising: receiving the target rotational speed value as a first input variable and the additional target torque as a second input variable; and driving the rotary drive based on the target rotational speed value and the additional target torque.

5. The method according to claim 1, further comprising measuring the pressing force by at least one pressing force sensor that is arranged on at least one of the top and bottom pressing roller of the rotary tablet press that is configured to press the upper and lower punches to press the filling material into the cavities.

6. The method according to claim 1, further comprising, indirectly measuring the pressing force using a determination of torque of the rotary drive.

7. The method according to claim 1, further comprising rotating the rotor at a rotational speed that is less than 30 RPM.

8. A rotary tablet press comprising: a rotor comprising a rotary drive configured to rotate the rotor; a die plate that rotates with the rotor and comprises a plurality of cavities; a plurality of upper and lower punches and upper and lower pressing rollers, Wherein the plurality of upper and lower punches are assigned in pairs to one of the plurality of cavities in the die plate and are configured to press filling material in the cavity into a pellet; a rotational speed governor that is configured to drive the rotary drive of the rotor by comparing a measured rotor rotational speed with a target rotational speed value; and a pilot control apparatus configured to, measure pressure values for at least one of the plurality of upper punches and the plurality of lower punches during a pressing of filling material into at least one of the plurality of cavities, determine an anticipated load torque for the rotary drive when passing through the upper and lower pressing rollers, provide the anticipated load torque to the rotational speed governor before initial contact between the plurality of upper and lower punches with the upper and lower pressing rollers, wherein the rotational speed governor is configured to apply the anticipated load torque and a target torque needed to achieve a target rotational speed so that a rotational speed of the rotary drive does not drop upon the initial contact between the plurality of upper and lower punches and the upper and lower pressing rollers, wherein the rotational speed of the rotary drive does not increase beyond the target rotational speed when the upper and lower punches leave the upper and lower pressing rollers.

9. The rotary tablet press according to claim 8, wherein the pilot control apparatus is configured to determine the anticipated load torque during at least one complete rotation of the rotor.

10. The rotary tablet press according to claim 8, wherein the rotational speed governor is a frequency converter configured to drive the rotary drive.

11. The rotary tablet press according to claim 10, wherein a target rotational speed value is applied to the frequency converter as a first input variable and the anticipated load torque is applied as a second input variable to the frequency converter, wherein the frequency converter is configured to drive the rotary drive based on the target rotational speed value and the anticipated load torque.

12. The rotary tablet press according to claim 11, further comprising at least one pressing force sensor configured to determine a pressing force, the at least one pressing force sensor is arranged on at least one of the upper and lower pressing rollers of the rotary tablet press that presses at least one of the upper and lower punches to press the filling material into the plurality of cavities.

13. The rotary tablet press according to claim 8, wherein the pilot control apparatus is configured to only become active when the rotational speed is less than 30 RPM.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of the invention is explained in greater detail below with reference to the figures.

(2) FIG. 1 illustrates a schematic representation of an embodiment of a rotary tablet press;

(3) FIG. 2 illustrates a partial cross-sectional view of an embodiment of a rotary tablet press; and

(4) FIG. 3 illustrates a perspective view of an embodiment of a rotary tablet press without the punches pressing rollers, and pressing force sensors.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring to FIGS. 1-3, the rotary tablet press has a machine housing 10 in which a rotor 12 of the rotary tablet press can be driven by means of a rotary drive 14 that is also arranged within the machine housing 10. In a manner known per se, the rotor has a die plate 11 that rotates with the rotor and has a plurality of cavities 13, as well as a plurality of upper and lower punches 15. 17 that also rotate with the rotor and which are assigned in pairs to a cavity in the die plate to press filling material in the cavity into a pellet, in particular a tablet. The filling material is also pressed in a manner known per se in compression stations that comprise pressing rollers. In FIG. 1, only two top pressing rollers 18 are shown for reasons of illustration. Of course, bottom pressing rollers that are arranged opposite the top pressing rollers 18 are generally also provided and are shown in FIG. 2. Moreover, a pressing force sensor 20 such as a force transducer 20 is assigned to each pressing roller 18 in the shown example. The pressing force sensors 20 measure the pressing forces of the upper, or respectively lower punches that are guided through by the pressing rollers 18. This is accomplished in a manner known per se on the pressing rollers 18. Of course, corresponding pressing force sensors can also be assigned to other provided pressing rollers, in particular bottom pressing rollers.

(6) The measured values of the pressing force sensors 20 are applied to a pilot control apparatus 22 as illustrated by the arrows 24. The pilot control apparatus 22 is arranged in a control housing 26 in which a frequency converter 28 forming a rotational speed governor is also arranged. In the shown example, the pilot control apparatus 22 dictates to the frequency converter 28 a target rotational speed value for the rotor rotational speed of the rotor 12 as illustrated by the arrow 30. The frequency converter 28 also receives the actual rotor rotational speed of the rotor 12 as a comparative measured value. From a comparison of the actual rotor rotational speed with the target rotational speed value, the frequency converter 28 determines a target torque value in the shown example for the frequency converter 28 to drive the rotary drive 14, as illustrated by the arrow 32, in order to adapt the actual rotor rotational speed to the target rotational speed value.

(7) Based on the pressing force values provided by the pressing force sensors 20, the pilot control apparatus 22 determines an additional target torque as a pilot control in order to compensate in advance the load torque to be anticipated during a rotation of the rotor 12 due to the interaction between the upper and lower punches and the pressing rollers 18. The additional target torque is also provided to the frequency converter 28 by the pilot control apparatus 22 as illustrated in the FIGURE by the arrow 34. The frequency converter 28 adds this additional target torque to the target torque that it determined for the rotational speed control. The rotational drive 14 is therefore driven based on the target torque value determined by the frequency converter 28 during the control of the rotational speed, and the additional target torque provided by the pilot control apparatus 22. In this manner, a constant rotor rotational speed can be ensured even at low rotational speeds of the rotor 12.

(8) In the portrayed example, the explained pilot control, in particular the determination of the additional target torque, only becomes active as of a threshold of, e.g., less than 30 RPM, preferably less than 20 RPM of the rotor 12. Below this threshold, the additional target torque is then permanently determined during the operation of the rotary tablet press by the pilot control apparatus 22. In particular, an additional target torque profile thereby results for the respective rotation of the rotor 12 that is correspondingly also taken into consideration during the rotational speed control which also runs permanently.

REFERENCE NUMBER LIST

(9) Machine housing Rotor Rotary drive Pressing rollers Pressing force sensors Pilot control apparatus Arrow Control housing Frequency converter Arrow Arrow Arrow