US20240003064A1

US20240003064A1 - Autoleveller draw frame, method for operating an autoleveller draw frame, and method for converting an autoleveller draw frame

Info

Publication number: US20240003064A1
Application number: US18/344,910
Authority: US
Inventors: Dietmar Greis; Holm Goehler; Daniel Schmolke
Original assignee: Maschinenfabrik Rieter AG
Current assignee: Maschinenfabrik Rieter AG
Priority date: 2022-07-01
Filing date: 2023-06-30
Publication date: 2024-01-04
Also published as: CN117328177A; BR102023013267A2; DE102022116504A1; EP4299808A1

Abstract

An autoleveller draw frame includes a drafting system having a plurality of roller combinations. A drive unit configured with the plurality of roller combinations has a main motor that drives a first roller combination at a constant main rotational speed. A regulating motor regulates a rotational speed of a second roller combination wherein, due to the regulation, the rotational speed of the second roller combination is changeable from a basic rotational speed into an autolevelling speed. The basic rotational speed depends on the main rotational speed and the autolevelling speed is independent of the main rotational speed, wherein the drafting of the fibrous web is adjustable. The regulating motor is drive-independent of the main motor to drive the second roller combination at the autolevelling speed according to an electrical signal that is based on the main rotational speed.

Description

FIELD OF THE INVENTION

The present invention relates to an autoleveller draw frame having a drafting system, which includes multiple roller combinations situated one behind the other for drafting a fibrous web to be processed, and having a drive unit for driving the multiple roller combinations. The drive unit including: a main motor for the speed-constant driving of at least one first roller combination at a main rotational speed, and a regulating motor for regulating the rotational speed of at least one second roller combination, wherein, due to the regulation, the rotational speed of the second roller combination is changeable from a basic rotational speed, which depends on the main rotational speed, into an autolevelling speed, which is independent of the main rotational speed, and, in this way, the draft of the fibrous web is adjustable. The invention further relates to a method for operating an autoleveller draw frame and to a method for converting an autoleveller draw frame.

BACKGROUND

EP 2 149 628 A1 describes an autoleveller draw frame, which has a main motor for driving at least two roller combinations and a regulating motor for the superimposed driving of at least one of the roller combinations. A basic rotational speed of the main motor can be superimposed on by the regulating motor by means of a differential gear, which is connected on one side to the main motor and on the other side to the regulating motor. This has the disadvantage that the differential gear is highly maintenance-intensive and, in particular as the period of operation increases, is highly susceptible to failure. In addition, the maintenance and/or replacement of the main motor and/or regulating motor used here are/is very highly technically complex.

SUMMARY OF THE INVENTION

A problem addressed by the present invention is that of eliminating the disadvantages known from the prior art. Additional objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
The problems are solved by an autoleveller draw frame, a method for operating an autoleveller draw frame, and a method for converting an autoleveller draw frame having the features described and claimed herein.
The invention provides an autoleveller draw frame having a drafting system, which includes multiple roller combinations situated one behind the other for drafting a fibrous web to be processed, and having a drive unit for driving the multiple roller combinations. Roller pairs made up of two rollers and/or arrangements made up of three rollers are usually used as the roller combinations. The drafting system usually has three roller combinations, wherein these roller combinations can be referred to as an input roller combination, a middle roller combination, and an output roller combination. A plurality of slivers usually enters the input roller combination, in which the fibrous web to be processed is formed by compressing the incoming slivers. Thereafter, the fibrous web is drafted in the drafting system, the input roller combination and the middle roller combination usually forming a pre-drafting field. The middle roller combination and the output roller combination usually form a main drafting field.
The drive unit includes a main motor for the speed-constant driving of at least one first roller combination at a main rotational speed. Moreover, the drive unit includes a regulating motor for regulating the rotational speed of at least one second roller combination, wherein, due to the regulation, the rotational speed of the second roller combination is changeable from a basic rotational speed, which depends on the main rotational speed, into an autolevelling speed, which is independent of the main rotational speed, and, in this way, the draft of the fibrous web is adjustable. Preferably, the main motor drives the output roller combination such that the output roller combination is operated at a constant rotational speed and at a constant delivery speed. The regulating motor preferably drives the input roller combination and/or the middle roller combination.
According to the invention, the regulating motor is drive-independent of the main motor and drives the second roller combination independently of the main motor at the autolevelling speed on the basis of an electrical signal, which depends on the main rotational speed. “Drive-independent” is to be understood to mean that the rotational movement of the regulating motor is mechanically independent of the main motor. The respective output elements of the regulating motor and of the main motor are independent of one another with respect to their rotational movement.
The basic rotational speed of the regulating motor depends directly on the main rotational speed of the main motor. The electrical signal, which depends on the main rotational speed, is transmitted directly or indirectly from the main motor to the regulating motor. The regulating motor is driven at the autolevelling speed on the basis of this electrical signal, wherein the autolevelling speed can differ from the basic rotational speed.
As described above, the main motor drives the at least one first roller combination at the constant main rotational speed. The basic rotational speed of the regulating motor is based on the main rotational speed of the main motor. If the regulating motor drives the at least one second roller arrangement at the basic rotational speed, the autoleveller draw frame is operated with a predefined draft. In order to change the draft in the drafting system, the basic rotational speed can therefore be replaced by a changeable autolevelling speed.
Due to the fact that the regulating motor drives the second roller arrangement on the basis of the electrical signal, which depends on the main rotational speed, a mechanical transmission of the rotational speed, for example by means of belt drives, is not necessary. A complicated drive unit having a differential gear can therefore be dispensed with. The electrical signal can also be very easily manipulated in order to adapt and/or change the autolevelling speed and/or the basic rotational speed.
It is advantageous when the drive unit includes a speed sensor for detecting the rotational speed of the at least one first roller combination and/or of the main motor. The speed sensor can therefore detect the main rotational speed of the first roller combination directly at the first roller combination and/or calculate this on the basis of the rotational speed of the main motor. As a result, the main rotational speed can be very easily and precisely determined. In addition, when converting an autoleveller draw frame having a mechanical differential gear, an existing speed sensor can be reused and/or the speed sensor can be easily retroactively installed.
It is also advantageous when the drive unit has at least one transmission unit for transforming the rotational speed detected by the speed sensor into the basic rotational speed of the second roller combination. The detected rotational speed can be the main rotational speed and/or the rotational speed of the main motor, as described above. The transmission unit transforms the detected rotational speed with a constant gear ratio such that the basic rotational speed formed therefrom depends directly on the main rotational speed. Alternatively, the transmission unit can be integrated in the speed sensor such that the speed sensor outputs the basic rotational speed as an electrical signal. The basic rotational speed of multiple second roller combinations, such as, for example, of an input roller combination and of an output roller combination, can differ from one another. Transmission elements and/or belt drives, for example, can be used to transform the rotational speeds.
It is advantageous when the autoleveller draw frame includes a pair of scanning rollers for detecting the thickness of at least one sliver entering the drafting system. The pair of scanning rollers is installed upstream from the input roller combination such that the thickness of the at least one incoming sliver can be determined before a fibrous web is formed from the sliver.
It is also advantageous when the autoleveller draw frame includes a specification unit, which is electrically operatively connected to the pair of scanning rollers and specifies a superimposition speed and/or determines a superimposition speed from the thickness of the at least one sliver. As described above, the draft of the drafting system is adjusted on the basis of the thickness of the incoming slivers. The superimposition speed can be ascertained by means of the specification unit from the thickness measured by the pair of scanning rollers, which superimposition speed is necessary in order to be superimposed on the basic rotational speed of the regulating motor in order to obtain a uniform draft or the desired draft of the fibrous web.
Moreover, it is advantageous when the drive unit includes a control unit for calculating the autolevelling speed and/or for controlling the regulating motor. The control unit preferably adds the basic rotational speed output by the transmission unit to the superimposition rotational speed output by the specification unit. Moreover, it is conceivable that the control unit is operatively connected to a quality sensor installed downstream from the drafting system such that the drafted sliver is checked for quality before being placed into the can. In this way, for example, the autolevelling speed can be adjusted on the basis of the quality of the drafted sliver.
It is also advantageous when the drive unit includes at least one transmission line for transmitting the electrical signal between the regulating motor, the main motor, the speed sensor, the transmission unit, the pair of scanning rollers, the specification unit and/or the control unit. The transmission line can be used for transmitting the electrical signal. It is also conceivable for the signal transmission to be carried out by means of a transceiver such that the electrical signal is transmitted wirelessly or by radio.
It is also advantageous when the control unit is electrically operatively connected to the specification unit, the transmission unit and/or the regulating motor such that the autolevelling speed is calculated from the superimposition speed and the basic rotational speed and/or is transmitted to the regulating motor as an electrical signal.
It is also advantageous when the main motor is formed as an induction motor and/or the regulating motor is formed as a reluctance motor. The main motor in the form of an induction motor has the advantage that this holds the rotational speed nearly constant. In addition, this has a very robust configuration and can be cost-effectively manufactured. The regulating motor in the form of a reluctance motor, in particular a synchronous reluctance motor, has the advantage that this has a simple and uncomplicated configuration and, thereby, can be operated reliably and in a cost-effective manner. The synchronous reluctance motor is preferably operated with a frequency inverter, which is arranged, for example, in the control unit. As a result, very high efficiency can be achieved.
Moreover, a method for operating an autoleveller draw frame is provided. In the method, a fibrous web to be processed is drafted using a drafting system, which includes multiple roller combinations situated one behind the other and the multiple roller combinations are driven by means of a drive unit. A main motor of the drive unit drives at least one first roller combination at a main rotational speed. A regulating motor of the drive unit regulates the rotational speed of at least one second roller combination, wherein, due to the regulation, the rotational speed of the second roller combination is changed from a basic rotational speed, which depends on the main rotational speed, into an autolevelling speed, which is independent of the main rotational speed, and, in this way, the draft of the fibrous web is adjustable.
According to the invention, the regulating motor drives the second roller combination drive-independently of the main motor at the autolevelling speed on the basis of an electrical signal, which depends on the main rotational speed.
Due to the fact that the regulating motor drives the second roller arrangement on the basis of the electrical signal, which depends on the main rotational speed, a mechanical transmission of the rotational speed is not necessary. As described above, a differential gear is no longer required in the drive unit. As a result, the mechanical transmission of the rotational speed from the main motor to the second roller combination is dispensed with. In addition, the electrical signal can be very easily manipulated in order to adapt and/or change the autolevelling speed and/or the basic rotational speed.
It is advantageous when the autoleveller draw frame is designed according to the preceding description and/or the following description, wherein the aforementioned features can be present individually or in any combination.
Moreover, a method for converting an autoleveller draw frame is provided. The autoleveller draw frame in this method for conversion includes a drafting system, which has multiple roller combinations situated one behind the other for drafting a fibrous web to be processed. In addition, the autoleveller draw frame includes a drive unit for driving the multiple roller combinations. The drive unit includes a main motor for the speed-constant driving of at least one first roller combination at a main rotational speed. The drive unit also includes a differential gear for transmitting the rotational speed of the main motor to at least one second roller combination such that a basic rotational speed of the second roller combination depends on the main rotational speed of the first roller combination. In addition, the drive unit includes a superimposition motor for superimposing a superimposition speed on the basic rotational speed by means of a differential gear such that, due to the superimposition, the rotational speed of the at least one second roller combination is changeable from the basic rotational speed into an autolevelling speed and, in this way, the draft of the fibrous web is adjustable.
The differential gear is preferably formed as a planetary gear that enables a three-shaft operation. The differential gear has a first drive element, which is driven by the main motor. A second drive element of the differential gear is driven by the superimposition motor. The at least one second roller combination can be driven by means of an output element of the differential gear.
According to the invention, the differential gear is removed from the drive unit and the superimposition motor is replaced by a regulating motor that is drive-independent of the main motor. After installation into the autoleveller draw frame, the regulating motor drives the second roller combination independently of the main motor at the autolevelling speed on the basis of an electrical signal, which depends on the main rotational speed.
Due to the above-described changes in the drive unit of the autoleveller draw frame, the mechanical differential gear, which is susceptible to failure, can be removed. Thereafter, the regulating motor mechanically drives the second roller combination independently of the main motor, and therefore a superimposition on the rotational speeds is no longer necessary. This results in a lower-maintenance operation of the autoleveller draw frame after the conversion.
It is advantageous when the autoleveller draw frame, after the conversion, is designed according to the preceding description, wherein the aforementioned features can be present individually or in any combination.
It is also advantageous when at least one drive element and/or output element of the differential gear are/is reused as a transmission element of the regulating motor. Drive elements are understood to be elements of the differential gear, which is removed during the conversion, at which the main motor and/or the superimposition motor drive(s) the differential gear. These types of drive elements can be, for example, drive shafts and/or driving pulleys. These types of drive elements are frequently connected to the superimposition motor and/or to the main motor by means of drive belts. An output element is understood to be an element that connects the differential gear to the second roller combination and drives the second roller combination. An additional belt drive for transforming the rotational speed can also be provided here.
In the mechanical differential gear, the at least one drive element and/or output element can be designed to set or adjust the ratio. Different sizes of the at least one drive element and/or output element can result in different rotational speeds of the second roller combination. This can be necessary for adjusting the main draft and/or the pre-draft, for example, when changing the material of the sliver or of the slivers. This adjustment of the main draft and/or of the pre-draft is independent of the autolevelling and, therefore, is a permanent change in the draft.
A transmission element of the regulating motor is to be understood to be an element that is slid directly onto the regulating motor or is arranged indirectly between the regulating motor and the at least one second roller combination such that the transmission element can transform the rotational speed toward the second roller combination. Due to the reuse of the at least one drive element and/or output element as a transmission element of the regulating motor, the permanent gear ratios, which are used in the autoleveller draw frame having the differential gear and the superimposition motor, can be very easily adapted to the autoleveller draw frame having an independent regulating motor.
It is also advantageous when a mechanical or electromagnetic brake or drive unit is removed. The brake is usually used to decelerate the superimposition motor so that the at least one second roller combination is operated at its basic rotational speed. Since the superimposition motor is removed, the brake is also no longer required and the rotational speed can be electrically controlled. For this purpose, the control unit is used to regulate the rotational speed. Therefore, with the brake, one further wearing device (in addition to the differential gear) can be saved.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the invention are described in the following exemplary embodiments, wherein:

FIG. 1 shows a schematic view of an autoleveller draw frame according to the prior art, and

FIG. 2 shows a schematic view of an autoleveller draw frame according to the invention.

DETAILED DESCRIPTION

In the following description of the alternative exemplary embodiments represented in the figures, the same reference signs are utilized for features that are identical or at least comparable in terms of their configuration and/or mode of operation. Provided the features are not described in detail again, their design and/or mode of operation correspond/corresponds to the design and mode of operation of the above-described features. For the sake of greater clarity, reference signs for previously described components have not been individually included in the figures.
FIG. 1 shows a schematic view of an autoleveller draw frame 1 according to the prior art. In the autoleveller draw frame 1, one or multiple supplied sliver(s) 2 is/are evened out and drafted and, thereafter, deposited in a can (not shown here), in a known way. The slivers 2 are supplied to a drafting system 4 via a pair of scanning rollers 3. It is also possible that the slivers 2, before being supplied to the pair of scanning rollers 3, are condensed to form one sliver 2 by means of a condenser (not shown here). The drafting system 4 includes multiple roller combinations 6, 6′, 6″, which are situated one behind the other. The roller combinations 6, 6′, 6″ are designed to draft a fibrous web 7, which is formed from the at least one sliver 2.
The roller combinations 6, 6′, 6″ can be formed as roller pairs having two rollers or as a roller combination having three rollers. In the exemplary embodiment shown, three roller combinations 6, 6′, 6″ are present in the form of an input roller combination 6, a middle roller combination 6′ and an output roller combination 6″.
The input roller combination 6 and the middle roller combination 6′ form a pre-drafting field. The middle roller combination 6′ and the output roller combination 6″ form a main drafting field. All roller combinations 6, 6′, 6″ are driven by a drive unit 8.
The output roller combination 6″ in the exemplary embodiment shown is driven as the first roller combination 6″ at a constant rotational speed by means of a main motor 9 of the drive unit 8. The output roller combination 6″ rotates at a constant main rotational speed. The input roller combination 6 and the middle roller combination 6′ are formed as a second roller combination 6, 6′, respectively, and are regulated.
As described above, the exemplary embodiment from FIG. 1 is the autoleveller draw frame 1 according to the prior art, in which a differential gear 10 transmits the rotational speed of the output roller combination 6″ to the input roller combination 6 and to the middle roller combination 6′ such that a basic rotational speed of the input roller combination 6 and of the middle roller combination 6′ depends on the main rotational speed of the output roller combination 6″. The differential gear 10 can be formed, for example, as a planetary gear.
The differential gear 10 includes a first drive element 11, a second drive element 12 and an output element 13. A constant rotational speed is introduced by the main motor 9 by means of the first drive element 11. By means of this constant rotational speed, the input roller combination 6 and the middle roller combination 6′ can be driven at the basic rotational speed. A superimposition speed can be introduced by a superimposition motor 14 by means of the second drive element 12. Due to the superimposition speed being superimposed on the basic rotational speed, the input roller combination 6 and the middle roller combination 6′ can be driven at an autolevelling speed. The autolevelling speed is thus essentially the sum of the basic rotational speed and the superimposition speed. For this purpose, the input roller combination 6 and the middle roller combination 6′ are connected to the output element 13.
Different rotational speeds can be achieved by means of different drive shafts of the roller combinations 6, 6′, 6″, as a result of which the basic rotational speed and/or the autolevelling speed of the regulated roller combinations 6, 6′ can differ from one another. Additional gear stages and/or belt drives can also lead to the individual roller combinations 6, 6′, 6″, as a result of which the rotational speeds can differ.
Changing the superimposition speed and, as a result, the levelling speed, allows the draft of the fibrous web 7 to be adjustable and changeable. Changing the autolevelling speed therefore results, in particular, in a change in the main draft from the middle roller combination 6′ to the output roller combination 6″. The thickness of the incoming slivers 2 is detected by the pair of scanning rollers 3. The pair of scanning rollers 3 is electrically operatively connected to a specification unit 15, which specifies the superimposition speed for the superimposition motor 14 and/or determines this from the thickness of the sliver 2. The specification unit 15 is also electrically operatively connected to the superimposition motor 14.
In addition, the drive unit 8 has a brake 16 in the area of the differential gear 10 or between the differential gear 10 and the superimposition motor 14, which can, in particular, completely decelerate the superimposition motor 14 and/or the second drive element 12. In this way, the current rotational speed of the input roller combination 6 and of the middle roller combination 6′ can be decelerated toward the basic rotational speed as quickly as possible.
It is also pointed out that the view of the drive unit 8 from FIG. 1 and also of the following FIG. 2 are highly simplified models. The belt drives or the drive elements, output elements and transmission elements are shown purely schematically at the main motor 9, at the superimposition motor 14, at the differential gear 10, at the pair of scanning rollers 3 and at the roller combinations 6, 6′, 6″.
FIG. 2 shows a schematic view of an autoleveller draw frame 1 according to the invention. In comparison to the exemplary embodiment from FIG. 1 according to the prior art, among other things, the differential gear 10 has been removed and the superimposition motor 14 has been replaced by a regulating motor 17, which is drive-independent of the main motor 9 such that the regulating motor 17 drives the input roller combination 6 and the middle roller combination 6′ independently of the main motor 9 at the autolevelling speed on the basis of an electrical signal 18, which depends on the main rotational speed. The regulating motor 17 is preferably in the form of a reluctance motor. The main motor 9 is preferably in the form of an induction motor, and so this is driven at a constant rotational speed.
A speed sensor 19 for detecting the rotational speed of the main motor 9 and/or of the output roller combination 6″ is arranged in the area of the main motor 9 and/or of the output roller combination 6″ of the autoleveller draw frame 1 according to the invention. The speed sensor 19 is electrically operatively connected, for example, by means of transmission lines, to a transmission unit 20, which converts the detected rotational speed into the basic rotational speed of the input roller combination 6 and/or of the middle roller combination 6′ or into the rotational speed of the regulating motor 17 required therefor.
In addition, the drive unit 8 of the autoleveller draw frame 1 according to the invention, in the exemplary embodiment shown in FIG. 2 , includes a control unit 21, which can calculate or control the autolevelling speed of the regulating motor 17. For this purpose, the control unit 21 is electrically operatively connected to the specification unit 15, to the transmission unit 20 and to the regulating motor 17. The control unit 21 calculates the autolevelling speed on the basis of the basic rotational speed from the transmission unit 20 and on the basis of the superimposition speed from the specification unit 15. The specification unit 15 is preferably reused from the autoleveller draw frame 1 according to the prior art.
When converting the autoleveller draw frame 1 according to the prior art (FIG. 1 ) into the autoleveller draw frame 1 according to the invention (FIG. 2 ), preferably at least one of the drive elements 11, 12 and/or one of the output elements 13 of the differential gear 10 is/are reused as the transmission element 22 of the regulating motor 17. The transmission element 22 transforms the rotational speed of the regulating motor 17 such that the input roller combination 6 and the middle roller combination 6′ are driven at the autolevelling speed. The autolevelling speed of the input roller combination 6 and of the middle roller combination 6′ can also differ from each other in the exemplary embodiment from FIG. 2 . In the present exemplary embodiment, the second drive element 12 of the differential gear 10 has been reused as the transmission element 22 of the regulating motor 17. Due to the reuse of the second drive element 12 as the transmission element 22 of the regulating motor 17, the permanent gear ratios (according to FIG. 1 ) used in the autoleveller draw frame 1 having the differential gear 10 and the superimposition motor 14 can be very easily adapted to the autoleveller draw frame 1 having the independent regulating motor 17.
The present invention is not limited to the represented and described exemplary embodiments. Modifications within the scope of the claims are also possible, as is any combination of the features, even if they are represented and described in different exemplary embodiments.

LIST OF REFERENCE SIGNS

- 1 autoleveller draw frame
- 2 sliver
- 3 pair of scanning rollers
- 4 drafting system
- 6, 6′, 6″ roller combinations
- 7 fibrous web
- 8 drive unit
- 9 main motor
- 10 differential gear
- 11 first drive element
- 12 second drive element
- 13 output element
- 14 superimposition motor
- 15 specification unit
- 16 brake
- 17 regulating motor
- 18 electrical signal
- 19 speed sensor
- 20 transmission unit
- 21 control unit
- 22 transmission element

Claims

1-13: (canceled)

14. An autoleveller draw frame, comprising:

a drafting system having a plurality of roller combinations situated one behind the other for drafting a fibrous web from one or more slivers;

a drive unit configured with the plurality of roller combinations, the drive unit comprising:

a main motor that drives a first of the roller combinations at a constant main rotational speed;

a regulating motor that regulates a rotational speed of a second of the roller combinations, wherein, due to the regulation, the rotational speed of the second roller combination is changeable from a basic rotational speed into an autolevelling speed, the basic rotational speed depending on the main rotational speed and the autolevelling speed being independent of the main rotational speed, wherein the drafting of the fibrous web is adjustable; and

the regulating motor being drive-independent of the main motor to drive the second roller combination independently of the main motor at the autolevelling speed according to an electrical signal that is based on the main rotational speed.

15. The autoleveller draw frame according to claim 14, wherein the drive unit comprises a speed sensor that detects the main rotational speed of the first roller combination or rotation of the main motor.

16. The autoleveller draw frame according to claim 15, wherein the drive unit comprises a transmission unit that transforms a signal from the speed sensor into a signal for the basic rotational speed of the second roller combination.

17. The autoleveller draw frame according to claim 14, further comprising a pair of scanning rollers that detect a thickness of the slivers entering the drafting system.

18. The autoleveller draw frame according to claim 17, further comprising a specification unit electrically connected to the pair of scanning rollers, the specification unit setting a superimposition speed for the basic rotational speed based on the thickness of the slivers.

19. The autoleveller draw frame according to claim 18, wherein the drive unit further comprises a control unit configured with the regulating motor, the control unit calculating the autolevelling speed from the superimposition speed and the basic rotational speed.

20. The autoleveller draw frame according to claim 19, wherein the autolevelling speed is transmitted to the regulating motor as an electrical signal.

21. The autoleveller draw frame according to claim 14, wherein the main motor comprises an induction motor and the regulating motor comprises a reluctance motor.

22. A method for operating an autoleveller draw frame, wherein the autoleveller draw frame includes:

the method comprising driving the regulating motor independent of the main motor to drive the second roller combination independently of the main motor at the autolevelling speed on the basis of an electrical signal that is based on the main rotational speed.

23. A method for converting an autoleveller draw frame from an initial configuration to a final configuration, the initial configuration including:

a drive unit configured with the plurality of roller combinations, the drive unit including:

a main motor for driving a first of the plurality of roller combinations at a constant main rotational speed;

a differential gear that transmits a rotational speed of the main motor to a second of the plurality of roller combinations such a basic rotational speed of the second roller combination depends on the main rotational speed of the first roller combination; and

a superimposition motor that superimposes a superimposition speed on the basic rotational speed by means of the differential gear such that, due to the superimposition, a rotational speed of the second roller combination is changeable from the basic rotational speed into an autolevelling speed;

the method comprising:

removing the differential gear from the drive unit;

replacing the superimposition motor with a regulating motor that is drive-independent of the main motor; and

wherein the regulating motor drives the second roller combination independently of the main motor at the autolevelling speed on the basis of an electrical signal that depends on the main rotational speed.

24. The method for converting an autoleveller draw frame according to claim 23, wherein at least one drive element or output element of the differential gear is reused as a transmission element of the regulating motor.

25. The method for converting an autoleveller draw frame according to claim 23, further comprising removing a mechanical or electromagnetic brake of the drive unit.