DE102013224324A1 - Method for operating a web-processing machine with flying reel change - Google Patents

Abstract

The invention relates to a method for operating a web-processing machine for processing a web material, wherein the web-processing machine comprises a first and a second web roll, each driven by a first and a second motor, wherein a pressure roller is provided, with which of the second Web material running web material can be pressed against the first web roll, wherein a cutting device is provided for cutting the web material, which is arranged with respect to the course of the web material between the first and the second web roll, wherein at least one driven clamping point is provided for the web material, with respect the course of the web material after the first and the second web roll is arranged, wherein the first motor is associated with a first torque controller (63) whose actual value (MIst, 1) is proportional to the torque of the first motor, where in the first motor, a first speed controller (61) is assigned whose actual value (vIst, 1) is proportional to the rotational speed of the first motor. According to the invention, while the pressure roller (40) presses the web material (11) against the first web roll (20), a setpoint (MSoll, 1) of the first torque controller (63) is formed by a manipulated variable of the first speed controller (61) and an additive Torque setpoint (MSoll, add) is added, wherein the value (73) of the additive torque setpoint (MSoll, add) is different from zero.

Description

The invention relates to a method for operating a web processing machine for processing a web material according to the preamble of claim 1. The web material is, for example, a web of paper, plastic film, textile nonwoven or textile fabric. The processing preferably includes a printing process.

From the EP 1 693 323 B1 Such a method is known in which a flying role change is performed. In this case, the web material is initially unwound from a second web roll to process them in at least one driven nip. Even while the web material running from the second web roll is being processed, a full first web roll is inserted into the web processing machine, the outer coil end of which is provided with adhesive, for example in the form of an adhesive strip. The first web roll is rotated by a first motor so that its peripheral speed is equal to the speed of the web running from the second web roll. As soon as the web material of the second web roll is almost completely consumed, the web material draining from the second web roll is forced against the first web roll by means of a pressure roller. Shortly after the two web materials of the first and second web roll are glued, the web material running from the first web roll is cut by a cutter so that only the web material from the first web roll passes through the processing machine. It is important that the first motor and the second motor are controlled so that the web material does not tear, ideally causing almost no fluctuations in the tensile force acting in the web material.

Particularly critical here is the fact that the first motor before gluing must overcome only the frictional torque of the first web roll, and after the gluing and cutting, it must additionally apply the tensile force which acts in the web material. The corresponding torques act in the opposite direction, ie initially the first motor operates by motor, where he later works as a generator, which further complicates the engine control. To solve this problem proposes the DE 44 28 739 C1 To brake the first web roll with an additional motor before gluing, so that the first motor is already in the operating state before gluing, he must take after sticking.

To avoid this additional engine beats the DE 296 04 882 U1 To accelerate the first motor shortly before sticking to a speed slightly above the synchronous speed and decelerate this just before sticking. For this purpose, the setpoint of the speed control is changed accordingly. Since the braking torque is not exactly defined here, it comes to sticking to fluctuations in the tensile force in the web material. A torque control of the first motor is in the DE 296 04 882 U1 not mentioned

The aforementioned EP 1 693 323 B1 proposes to disable the tension control of the web material, which is done by means of a dancer roll, during the gluing. Next is in the EP 1 693 323 B1 described a torque control of the first motor.

The advantage of the present invention is that it can dispense with a complex brake drive for the first web material roll. Furthermore, the traction control for the web material may continue uninterrupted during adhesion. In addition, the tensile force in the web material remains almost constant during sticking and cutting. An optional dancer roll for adjusting the tensile force of the web material almost does not move.

According to the independent method claim, it is proposed that while the pressure roller presses the web material against the first web roll, a setpoint of the first torque controller is formed by adding a control variable of the first speed controller and an additive torque setpoint, the value of the additive torque setpoint being different from zero is. It is exploited that the torque controller of the first motor, which is preferably designed as a synchronous motor, works extremely fast. The proposed setpoint intervention thus causes the desired change in the drive torque in a very short time. This rapid torque change can only slowly follow the first web roll due to its high mass moment of inertia. Accordingly, there is almost no change in the rotational speed of the first web roll in that short time, which would be detrimental to the gluing process. Preferably, the proposed setpoint engagement is started as short as possible before sticking.

In the dependent claims advantageous refinements and improvements of the invention are given.

The additive torque command value may be equal to the product of an outer radius of the first web roll and a desired or actual tension of the web, adding at least one further term if desired. When the tensile force of the web material is adjusted with a dancer roll or with a tensile force control, the target tensile force is known. When using a draft control with a tensile load, the actual tensile force is known. From these values, the required driving torque can be calculated by multiplying by the outer radius of the first web roll. The said outer radius can be measured continuously. But it can also be always the same and known outer radius of a full web roll are recognized.

As a further term, the torque can be added, which is required to overcome the at least indirectly acting on the web material frictional forces. This ensures that the friction conditions changed by the gluing and the cutting off are also taken into account. In particular, the friction forces mentioned are the bearing friction of the rollers on which the web material passes. Next, the bearing friction of the first web roll is addressed.

The additive torque setpoint can be set to zero after sticking and trimming. This is to avoid that the additive torque setpoint disturbs the regulation or control of the tensile force of the web material as little as possible. This is preferably done as short as possible after sticking and trimming.

The transition of the additive torque command value from zero to the non-zero value and vice versa can be continuous or in several stages. This is to prevent mechanical or control-related resonances of the web processing machine being excited by the setpoint intervention according to the invention. For example, a steady transition can be achieved by filtering a sudden change in value through a PT1 element before it is used as an additive torque setpoint.

The additive torque command value may increase from zero to the nonzero value in a shorter time as it falls from zero to zero. The drop in the additive torque setpoint is compensated by a preferably existing draft control, so that such a change causes little disturbance. On the other hand, an excessively long time duration of the increase in the additive torque setpoint means that the web materials of the two web material rolls no longer run synchronously, at least for a short time. This interferes with the gluing process considerably. The above proposal accordingly stimulates few resonances of the web processing machine.

The first torque controller can react faster to a control deviation than the first speed controller. This is preferably achieved in that a proportional gain factor of the first torque controller is greater than a proportional gain factor of the first speed controller. Additionally or alternatively, it can be provided that an integral time constant of the first torque controller is smaller than an integral time constant of the first speed controller. In this case, preferably continuous linear regulators, in particular PI controllers, are used. As far as these controllers are calculated time-discretely, a cycle time of the first speed controller may be longer than that of the first torque controller. The first-mentioned cycle time is, for example, 125 μs or 250 μs, the second-mentioned cycle time being, for example, 62.5 μs. The proposed measure prevents the first speed controller from compensating for the torque intervention according to the invention before the sticking and the cutting off have taken place.

The second motor may be associated with a second torque controller and a second speed controller, wherein an actual value of the second torque controller is proportional to the torque of the second motor, wherein an actual value of the second speed controller is proportional to the rotational speed of the second motor, wherein a manipulated variable of the second speed controller is a setpoint of the second torque controller. The first and the second torque controller are preferably constructed the same and most preferably the same parameterized. The first and the second speed controller are preferably constructed the same and most preferably the same parameterized.

An actual value of the first and / or second speed controller can be determined by multiplying the speed of the associated motor by an outer radius of the associated web roll becomes. The speed of the motors can be determined much easier than the speed of the web material, which should be controlled primarily. The outer radius of the web material can be measured, for example, with a radius measuring device. But it can also be calculated from the known outer radius of a full web roll and the known speed of the web material and the elapsed time.

The web material may be guided around a dancer roller, which is displaceably mounted, wherein the position of the dancer roller can be measured with a position sensor, wherein a Tänzerlageregler is provided, the actual value is the position of the dancer roller, wherein the desired value of the first and / or the second Velocity controller is determined by a desired speed of the web material is added to a manipulated variable of the dancer position controller. It is known per se to adjust the tensile force of the web material with a dancer roller. Preferably, only a single dancer position controller is provided, the manipulated variable is the setpoint of the first and the second speed controller at the same time. A closed loop is then only for the web roll from which the web material is unrolled. The peripheral speed of each other web roll is equal to the speed of the web material. By means of this embodiment of the dancer control, it can be achieved that the dancer position controller is also active when the pressure roller presses the web material against the first web material roll.

There may be provided a tension regulator whose actual value is proportional to a tensile force of the web material immediately after the first or second web roll, wherein a manipulated variable of the draft regulator is the rotational speed of the first and second motors or the rotational speed of a said traction-influencing nip. The tension regulator replaces the dancer roller and the dancer position controller. Preferably, a single tension regulator is provided for both web rolls of material.

Furthermore, a computer program, a storage medium and a web-processing machine are claimed, which realize the features described above.

The invention will be explained in more detail below with reference to the accompanying drawings. It shows:

1 a rough schematic representation of a web processing machine according to the invention;

2 a rough schematic representation of a control device according to the invention;

3 a signal flow plan of a method according to the invention;

4 a diagram showing a possible time course of the additive torque setpoint; and

5 a reel changer for a web-processing machine according to the invention.

1 shows a rough schematic representation of a web processing machine according to the invention 10 , Shown is a machine condition just before the sticking of the web material 11 that of the second web roll 30 expires, to the first web roll 20 , The winding end of the first web roll 20 is this with an adhesive strip 43 Mistake. Next is a pressure roller 40 provided on an associated, rotatable lever arm 41 is mounted rotatably. By pivoting the lever arm 41 becomes the pressure roller 40 and therefore the web material 11 against the first web roll 20 pressed. This will be the web material 11 from the first and second web roll 20 ; 30 on the adhesive strip 43 glued together. Shortly thereafter, that of the second web roll 30 running web material with the cutter 42 separated. The cutting device 42 For example, as a separating knife according to the DE 38 15 277 A1 be educated.

The first and the second web roll 20 ; 30 is in each case a first or a second radius measuring device 23 ; 33 assigned, with the current outer radius r _{Ist, 1} ; r _{is 2 of} the web roll concerned 20 ; 30 can be measured. The radius measuring devices 23 ; 33 For example, they can work by means of ultrasound or laser beams.

The first and second web roll 20 ; 30 each of a first and a second motor 21 . 31 driven, which are preferably designed as electric motors, in particular as synchronous or asynchronous motors. The motors 21 ; 31 are preferably coupled directly to the associated web roll, so without the interposition of a gear-driven gear. Both engines 21 ; 31 are each associated with an associated first and second speed sensor 22 . 32 provided, which can also be designed as a rotary position sensor, wherein the speeds n _{Ist, 1} ; n _{Ist, 2} then be calculated from the derivative of the measured rotational position after the time.

As manipulated variables y ₁ ; y ₂ become the engines 21 ; 31 Preferably, electrical alternating voltages supplied, wherein most preferably several, for example, three alternating voltages are used, which are out of phase with each other. As part of the controller calculation only the amplitude of these AC voltages is used as a manipulated variable. The said manipulated variable causes the motors a certain torque M _{Ist, 1} ; M _{is, 2} deliver. These torques could be measured with a torque sensor. However, it is easier to calculate these torques based on the alternating currents that are in the motors 21 ; 31 flow. These alternating currents are preferably measured, most preferably in the control device.

In web direction 16 after the first web roll 20 is a dancer roller 50 arranged, which on an associated, rotatable lever arm 52 is rotatably mounted. The web material 11 wraps around the dancer roller 50 for example, by 180 °, so that the weight 53 the dancer roller 50 in the web material 11 generates the desired tension. The desired tensile force can be adjusted for example with sliding counterweights or springs with adjustable biasing force. The position x _{actual, dancer of} the _dancer roller is measured, for example, by the lever arm 52 with a position generator 51 is provided in the form of a rotation angle sensor. But it can also be provided a linear displacement measurement.

In web direction 16 after the dancer roller 50 are preferably several driven clamping points 12 for the web material 11 arranged, in 1 only that clamping point is shown which the tensile force immediately after the first and the second web roll 20 ; 30 affected. At the terminal points 12 These can be printing units, infeed or extracting units, folding units, etc. For driving the clamping point 12 is in turn an associated third engine 13 provided, which is designed analogously to the first and the second motor.

2 shows a rough schematic representation of a control device according to the invention 14 , The control device 14 includes a storage medium 15 , For example, a flash memory in which a computer program is stored, which is set up for carrying out the method according to the invention. Furthermore, a computing unit (not shown) is provided, which executes the computer program. The control device 14 receives the following input variables, which are fed, for example, via a data bus which operates in particular according to the Ethernet standard: n _{is 1} Speed of the first motor n _{is, 2} Speed of the second motor M _{is, 1} Torque of the first motor M _{is, 2} Torque of the second motor x _{is, dancer} Actual value of the position of the dancer roller r _{is 1} Outer radius of the first web roll r _{is 2} Outer radius of the second web roll

For this purpose, the first and the second speed sensor, the first and the second radius measuring device and the position sensor are preferably also connected to the data bus. The first and second motors are preferably via dedicated power cables to the controller 14 connected.

The following sizes become the control device 14 For example, via a (not shown) operating unit supplied, which is preferably equipped with a touch-sensitive screen: x _{Soll, dancer} Setpoint of the position of the dancer roller (middle position) v _{LA, sync} desired speed of the web material F Tensile force of the web material produced by the dancer roller

Based on these input variables, the control device calculates the following output variables: y1 Manipulated variable of the first torque controller y2 Control value of the second torque controller

3 shows a signal flow plan of a method according to the invention. The actual value x _{actual, dancer of} the dancer position controller 60 is the location of the dancer roller. The control difference is accordingly formed by the actual value of the position of the dancer roller x _{actual , dancer is} subtracted from the target value of the position of the dancer roller x _{target, dancer} . This control difference is preferably a PI controller 60 which is set slower than the other controllers 61 ; 62 ; 63 ; 64 , The manipulated variable of the dancer position controller v _{set, add} is the desired speed of the web material v _{LA, sync} added to the setpoint v _{setpoint of} the first and the second speed controller 61 ; 62 to obtain.

The actual value of the first speed controller 61 is the peripheral speed of the first web roll. Accordingly, the control deviation is formed by the corresponding actual value v _{ist, 1 is} subtracted from the corresponding desired value v _target . The mentioned actual value is calculated according to the formula v _{is, 1} = 2π × n _{Ist, 1} × r _{Ist, 1} calculated. The first speed controller 61 is preferably a PI controller that works faster than the dancer position controller 60 where it works slower than the first torque controller 63 , The manipulated variable of the first speed controller 61 the additive torque _setpoint M _{setpoint, add is} added to the setpoint M _{setpoint, 1 of} the first torque controller 63 to obtain.

The actual value of the first torque controller 63 is the torque of the first motor. Accordingly, the control difference is formed by the actual value M _{Ist , 1 is} subtracted from the setpoint M _{Soll, 1} . The actual value M _{ist, 1} is preferably calculated on the basis of the measured motor currents. The first torque controller 63 is preferably a PI controller that operates faster, most preferably significantly faster, than the dancer position controller 60 and the first speed controller 61 , It determines the first manipulated variable y _1, which has already been explained above.

The second speed controller 62 and the second torque controller 62 are analogous to the first speed controller 61 and to the first torque controller 63 trained, so that reference is made in this regard to the above statements. In the formula symbols, index 1 must be replaced by index 2. The only difference is that the setpoint M _{setpoint, 2 of} the second torque controller is equal to the control value of the second speed controller 62 is. The additive torque _setpoint M _{setpoint, add} is not added here.

4 shows a diagram showing a possible time course of the additive torque _setpoint M _{Soll, add} . Along the vertical axis, the additive torque _setpoint M _{Soll, add is} plotted. The time t is plotted along the horizontal axis. The period during which the gluing and cutting of the web material takes place is indicated by the reference numeral 70 characterized. During this period 70 the additive torque setpoint is constant and is preferably: M _{Soll, add} = M _Reib + F × r _{Ist, 1}

The symbol F designates the traction of the web material set by the dancer roller. The symbol M _friction denotes the friction torque which is required to overcome the frictional forces acting on the web material at least indirectly.

Before the period 70 increases the additive torque _setpoint M _{Soll, add} linearly from zero to the above-mentioned, non-zero value 73 at. After the period 70 falls the additive torque _setpoint M _{Soll, add} linearly back to zero. The rise 71 is preferably faster than the waste 72 , The rise 71 and / or the waste 72 Alternatively, they can also be stepped or according to an exponential function. Outside the periods 70 ; 71 ; 72 is the additive torque _setpoint M _{Soll, add} always zero.

5 shows a roll changer 80 for a web processing machine according to the invention. The reel changer 80 includes a frame 84 , which stands firmly on the ground. In the frame 84 are two swivel arms 81 concerning a fulcrum 83 rotatably mounted. The swivel arms 81 are on opposite sides of the first and second web roll 20 ; 30 arranged, the Web roll 20 ; 30 again at the two ends of the pivot arms 81 are rotatably mounted. The swivel arms 81 can with a fourth engine 82 be pivoted to the web rolls 20 ; 30 into the operating or loading / unloading position. The pivoting takes place either before or after the gluing and cutting of the web material.

Instead of the roll changer shown, any other roll changer can be used. Alternative embodiments are in the DE 43 34 582 A1 , of the DE 40 00 746 C2 and the DE 44 28 739 C1 shown.

LIST OF REFERENCE NUMBERS

10

Web processing machine

11

sheeting

12

nip

13

third engine

14

control device

15

storage medium

16

Web direction

20

first web roll

21

first engine

22

first speed sensor

23

first radius measuring device

30

second web roll

31

second engine

32

second tachometer

33

second radius measuring device

40

pressure roller

41

lever arm

42

cutting device

43

tape

50

dancer roll

51

position encoder

52

lever arm

53

weight force

60

Dancer position controller

61

first speed controller

62

second speed controller

63

first torque controller

64

second torque controller

70

Period in which sticking and trimming takes place

71

rise

72

waste

80

reelstands

81

swivel arm

82

fourth engine

83

pivot point

84

frame

t

Time

F

Traction of the web material

x _{Soll, dancer}

Setpoint of the position of the dancer roller (middle position)

x _{is, dancer}

Actual value of the position of the dancer roller

v _{LA, sync}

desired speed of the web material

M _{Soll, add}

additive torque setpoint

M _rub

Frictional torque of the first web roll

n _{is 1}

Speed of the first motor

n _{is, 2}

Speed of the second motor

M _{is, 1}

Actual torque of the first motor

M _{is, 2}

Actual torque of the second motor

M _{set, 1}

Target torque of the first motor

M _{Soll, 2}

Target torque of the second motor

r _{is 1}

Outer radius of the first web roll

r _{is 2}

Outer radius of the second web roll

y ₁

Manipulated variable of the first torque controller

y ₂

Control value of the second torque controller

v _{set, add}

Manipulated variable of the dancer position controller

v _target

Setpoint of the first and second speed controller

v _{is, 1}

Actual value of the first speed controller

v _{is, 2}

Actual value of the second speed controller

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1693323 B1 [0002, 0005, 0005]
• DE 4428739 C1 [0003, 0044]
• DE 29604882 U1 [0004, 0004]
• DE 3815277 A1 [0026]
• DE 4334582 A1 [0044]
• DE 4000746 C2 [0044]

Claims (16)

Method for operating a web-processing machine ( 10 ) for processing a web material ( 11 ), wherein the web-processing machine ( 10 ) a first and a second web roll ( 20 ; 30 ), each of a first and a second motor ( 21 ; 31 ), wherein a pressure roller ( 40 ) is provided, with which the of the second web roll ( 30 ) running web material against the first web roll ( 20 ) can be pressed, wherein a cutting device ( 42 ) for cutting the web material ( 11 ) is provided, which with respect to the course of the web material ( 11 ) is disposed between the first and the second web roll, wherein at least one driven nip ( 12 ) is provided for the web material, which with respect to the course of the web material ( 11 ) after the first and the second web roll ( 20 ; 30 ), wherein the first motor ( 21 ) a first torque controller ( 63 ) whose actual value (M _{actual, 1} ) is proportional to the torque of the first motor ( 21 ), wherein the first motor ( 21 ) a first speed controller ( 61 ) whose actual value (v _{Ist, 1} ) is proportional to the rotational speed of the first motor ( 21 ), characterized in that, while the pressure roller ( 40 ) the web material ( 11 ) against the first web roll ( 20 ), a setpoint (M _{setpoint, 1} ) of the first torque controller ( 63 ) is formed by a manipulated variable of the first speed controller ( 61 ) and an additive torque _setpoint (M _{setpoint, add} ) is added, the value ( 73 ) of the additive torque _command value (M _{target, add} ) is different from zero. A method according to claim 1, characterized in that the additive torque _setpoint (M _{Soll, add} ) equal to the product of an outer radius (r _{actual, 1} ) of the first web roll ( 20 ) and a desired or actual tensile force (F) of the web material ( 11 ), wherein if desired at least one further term is added. A method according to claim 2, characterized in that as a further term the torque (M _rub ) is added, which to overcome the on the web material ( 11 ) at least indirectly acting frictional forces is required. Method according to one of the preceding claims, characterized in that the additive torque _setpoint (M _{Soll, add} ) is set to zero after the sticking and the trimming. Method according to one of the preceding claims, characterized in that the transition of the additive torque reference value (M _{Soll, add} ) from zero to the non-zero value ( 73 ) and vice versa is continuous or in several stages. A method according to claim 5, when dependent on claim 4, characterized in that the additive torque command value (M _{target, add} ) is reduced from zero to the non-zero value in a shorter time ( 73 ) increases as it is different from zero ( 73 ) drops to zero. Method according to one of the preceding claims, characterized in that the first torque controller ( 63 ) reacts faster to a control deviation than the first speed controller ( 61 ). Method according to one of the preceding claims, characterized in that the second motor ( 31 ) a second torque controller ( 64 ) and a second speed control ( 62 ), wherein an actual value (M _{Ist, 2} ) of the second torque controller ( 64 ) proportional to the torque of the second motor ( 31 ), wherein an actual value (v _{Ist, 2} ) of the second speed controller ( 62 ) proportional to the rotational speed of the second motor ( 31 ), wherein a manipulated variable of the second speed controller ( 62 ) a setpoint of the second torque controller ( 64 ). Method according to one of the preceding claims, characterized in that an actual value (v _{Ist, 1} ; v _{Ist, 2} ) of the first and / or the second speed controller ( 61 ; 62 ) is determined by determining the rotational speed of the associated motor (n _{actual, 1} ; n _{actual, 2} ) with an outer radius (r _{actual, 1} ; r _{actual, 2} ) of the associated web roll ( 20 ; 30 ) is multiplied. Method according to one of the preceding claims, characterized in that the web material ( 11 ) around a dancer roll ( 50 ) is guided, which is slidably mounted, wherein with a position sensor ( 51 ) the position (x _{actual, dancer} ) of the _dancer roller ( 50 ), whereby a dancer position controller ( 60 ) whose actual value is the position of the dancer roller ( 50 ), wherein the desired value (v _setpoint ) of the first and / or the second speed controller ( 61 ; 62 ) is determined by a desired speed of the web material (v _{LA, sync} ) a manipulated variable of the dancer position controller ( 60 ) is added. Method according to claim 10, characterized in that the dancer position controller ( 60 ) is active while the pressure roller ( 40 ) the web material ( 11 ) against the first web roll ( 20 ) presses. Method according to one of claims 1 to 9, characterized in that a draft regulator is provided, whose actual value is proportional to a tensile force (F) of the web material ( 11 ) immediately after the first or the second web roll ( 20 ; 30 ), wherein a manipulated variable of the draft regulator controls the rotational speed of the first and second motors ( 21 ; 31 ) or the rotational speed of a clamping point influencing said tensile force ( 12 ). Method according to one of the preceding claims, characterized in that first torque controllers ( 63 ) and / or the second torque controller ( 64 ) and or the first speed control ( 61 ) and / or the second speed controller ( 62 ) and / or the dancer position controller ( 60 ) and / or the tension controller are continuous, linear controllers, preferably PI controllers.  Computer program adapted to perform each step of a method according to any one of the preceding claims.  An electronic storage medium on which a computer program according to claim 14 is stored. Web processing machine ( 10 ) for processing a web material ( 11 ), wherein the web-processing machine ( 10 ) a first and a second web roll ( 20 ); 30 ), each of a first and second motor ( 21 ; 31 ), wherein a pressure roller ( 40 ) is provided, with which the of the second web roll ( 30 ) running web material against the first web roll ( 20 ) can be pressed, with respect to the course of the web material ( 11 ) between the first and the second web roll ( 20 ; 30 ) a cutting device ( 42 ) for the web material ( 11 ), wherein at least one driven clamping point ( 12 ) for the web material ( 11 ), wherein the first motor ( 21 ) a first torque controller ( 63 ) whose actual value (M _{actual, 1} ) is proportional to the torque of the first motor ( 21 ), wherein the first motor ( 21 ) a first speed controller ( 61 ) whose actual value (v _{Ist, 1} ) is proportional to the rotational speed of the first motor ( 21 ), characterized in that the first and the second motor ( 21 ; 31 ) to an electronic control device ( 14 ), which is adapted to carry out each step of a method according to one of claims 1 to 13, wherein the control device ( 14 ) preferably a computer program according to claim 14 and / or a storage medium ( 15 ) according to claim 15.

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