EP0508113B1 - Device for the rapid precise clamping and tensioning of printing plates on the forme cylinder of a printing press - Google Patents

Abstract

In order to be able to clamp and tension printing plates on the forme cylinder with a minimum of handling effort and in any angular position of said forme cylinder, the invention proposes to arrange the drive members, which bring about the clamping and tensioning of the printing plate, in the groove of the forme cylinder. The eccentric shafts (5.3, 6.3) of the front and of the rear tensioning rails (5, 6) are guided through appropriate openings (11) on both cylinder side walls and have actuating arms (12). Two adjusting rings (8, 9) are arranged rotatably in each case on a collar mounted upstream of the forme cylinder on both side walls thereof, said adjusting rings having recesses (13) in which the actuating arms engage. Turning the adjusting rings thus causes clamping or loosening of the corresponding tensioning rail. The adjusting rings are driven by appropriate spur wheels (17) which are guided out of the cylinder side walls and mesh with a tooth gearing (14) of the respective adjusting ring. Said spur wheels are driven in each case by a motor (20.a, 20.b) (compressed air motor) from the cylinder groove via a train of gears, consisting of a plurality of gearwheels, together with clutches. The tensioning is caused by one of the two motors provided, in that a further clutch is provided, by means of which a rotary spindle can be driven. By means of the latter, a pressure strip, assigned to the rear tensioning rail, can be displaced over a bridge. <IMAGE>

Description

The invention relates to a device for precise clamping and clamping of printing plates on the plate cylinder according to the preamble of the first claim.

A device according to the preamble of claim 1 is known from DE-PS 3 516 682 and enables, in a manner known per se, the clamping of the printing plate at the beginning and end of printing by rotating the eccentric shafts associated with the corresponding tensioning rails by means of a hand-operated tool. Likewise, the subsequent tensioning of the pressure plate is carried out manually using a tool in which the tensioning rail at the end of the print is displaced almost in the circumferential direction by a central actuating device and a pressure bar. The disadvantage here is that several manual manipulations on the cylinder channel are necessary, no re-tensioning is possible when the machine is running, and there is no automatic regulation or limitation of the clamping force exerted on the pressure plate. The latter is particularly disadvantageous in the case of large-format printing presses, since tolerances in the manufacture and assembly of the structural parts causing the tensioning of the printing plate mean that the rear split tensioning rail is not advanced exactly parallel to the front channel wall. An overload of the pressure plate - especially a one-sided one - cannot be excluded.

DE 3 843 433 A1 describes a device for Fast clamping of pressure plates, whereby the eccentric shafts that cause clamping and clamping are each provided with double roller levers on the cylinder side wall and can be rotated for clamping, unclamping, clamping, relaxing via a fixed actuator after a corresponding angular positioning of the plate cylinder.

EP 0 260 492 A2 also describes a technically similar route, in which the eccentric shafts carry simple lever arms on the cylinder side wall and can be rotated by means of tension or pressure via an actuating device on the frame.

DE 3 843 395 A1 shows another device for precise rapid clamping. Accordingly, the clamping and clamping device is assigned at least one common actuating device arranged on the machine frame and corresponding to the angular position of the plate cylinder at the time of clamping and clamping. Clamping and tensioning takes place via axially displaceable pull wedge gears, which can be moved by actuating devices arranged on both sides of the cylinder side walls.

A disadvantage of the three last-described solutions is that the clamping, but especially the clamping of the pressure plate can only take place in a certain position of the plate cylinder, i.e. re-tensioning while the machine is running and also an automatic regulation and limitation of the clamping force is not guaranteed. The quick release device according to DE 3 843 395 A1 also has the disadvantage that the forces for clamping and unclamping, tensioning and relaxing always act axially and these forces have to be absorbed by the bearings of the plate cylinder.

EP 0 396 220 A2 describes a device for quick clamping of printing plates, in which the clamping and clamping is effected by eccentric shafts which are led out on a cylinder side wall and each have a simple roller lever.

On the journal of the plate cylinder, this cylinder side wall is associated with a disk rotatably mounted so that it can be driven by a motor from the machine frame. In a certain angular range, a link is incorporated into this disk, which serves to hold the rollers of the roller levers. The backdrop is designed such that when the disk is rotated by the flanks of the backdrop, the roller lever is rotated by a certain angle. For example, when clamping a pressure plate, the disc is now rotated so that the roller lever of the pressure start clamping rail is rotated through the link to the clamping position, then the disc is rotated further, so that the roller lever of the printing end clamping rail is in turn turned into the clamping position through the link is rotated, lastly again by rotating the disc and through the backdrop, the roller lever causing the tensioning is turned into the tensioning position.

This solution is disadvantageous that the roller lever can only be rotated by a fixed angle due to the backdrop. There is therefore no force limitation when clamping the pressure plate, but especially when tensioning the pressure plate. As with the quick release devices described, re-tensioning while the machine is running is also not possible and automatic regulation and limitation of the clamping force is not guaranteed.

DE 3 604 071 A1 and DE 3 604 073 A1 describe devices on plate cylinders in which the tensioning or clamping of the pressure plate is effected by actuators which become effective when pressure medium is applied. Working cylinders and locking mechanisms are integrated into the clamping or clamping devices. A disadvantage of these solutions is that the structure of the tensioning rails differs fundamentally from those which are customary in the manual quick-action clamping and tensioning devices (for example DE-PS 3 516 682). If a manufacturer wants both a manual and an automated plate clamping and Offer clamping device, this means increased manufacturing and storage costs.

From DE 3 731 642 A1 and DE 3 918 215 C1, plate locking devices are known in which the locking of the clamped printing plate is effected by drive means provided in the pit of the plate cylinder. These setting mechanisms driven in this way are, however, not suitable for precise quick clamping and clamping of pressure plates.

In the post-published German patent applications P 39 36 458.5 and P 39 36 459.3, it was proposed to regulate the tensioning force exerted on the pressure plate by means of tensioning levers pivotably mounted on the rear tensioning rail, each of these tensioning levers being associated with at least one spring supported by a cylinder. The rear tensioning rail is thus supported on the pressure bar via this tensioning lever. P 39 36 458.5 also describes a motor-driven adjusting spindle, which moves the pressure bar for tensioning via a spindle nut and a bridge.

The object of the invention is to expand the input specified device so that a clamping and tensioning of the printing plate can be carried out precisely with a minimum of handling effort, without the plate cylinder first having to be moved exactly into certain angular positions. An automatic regulation and limitation of the clamping force exerted on the printing plate should be ensured uniformly over the entire width, in particular in the case of large-format printing plates, and the constructional disadvantages mentioned in the prior art should also be avoided.

This object is achieved by a device according to the characterizing part of the first claim. Further developments result from the subclaims in connection with the description and the drawings.

The invention is explained in more detail below using an exemplary embodiment.

Fig. 1

eine Draufsicht auf einen Plattenzylinder nach der Erfindung,

Fig. 2a)

den Schnitt A-A nach Fig. 1,

Fig. 2b)

den Schnitt B-B nach Fig. 1,

Fig. 3a)

eine Draufsicht auf den linken Teil des Plattenzylinders,

Fig. 3b)

eine Draufsicht auf den rechten Teil des Plattenzylinders,

Fig. 3c)

den Schnitt C-C nach Fig. 3a),

Fig. 4a)

den Schnitt D-D nach Fig. 3a),

Fig. 4b)

den Schnitt E-E nach Fig. 3a),

Fig. 5

einen Spannhebel im Detail,

Fig. 6

die Anordnung der Spannhebel an der hinteren Spannschiene.

In the individual drawings:

Fig. 1

a plan view of a plate cylinder according to the invention,

Fig. 2a)

the section AA of FIG. 1,

Fig. 2b)

1 the section BB according to FIG. 1,

3a)

a plan view of the left part of the plate cylinder,

3b)

a plan view of the right part of the plate cylinder,

3c)

the section CC according to Fig. 3a),

4a)

the section DD according to Fig. 3a),

4b)

the section EE according to Fig. 3a),

Fig. 5

a clamping lever in detail,

Fig. 6

the arrangement of the clamping levers on the rear clamping rail.

The plate cylinder 1 is supported on both sides with its pin 2 in frame walls 3 of the printing press (FIG. 1). It has 4 means for clamping and tensioning printing plates in its cylinder channel. According to FIGS. 1, 2a), 2b), 3c), 4a), 4b), these means are, as is known from the prior art, as one of the Beginning of print DA and front and rear tensioning rails 5, 6 assigned to printing end DE, these being designed to be divided.

The tensioning rails 5, 6 each consist of an upper and lower clamping device 5.1, 5.2, 6.1, 6.2 which can be actuated by rotating eccentric shafts 5.3, 6.3 (Fig. 3c), 4a), 4b)). The eccentric shafts 5.3, 6.3 are divided like the tensioning rails 5, 6, so that half the format width of the printing plate can be clamped. The front and rear tensioning rails 5, 6 are guided in the cylinder channel 4 by means known per se and not shown, so that they can carry out the corresponding movements when tensioning the pressure plate. The clamping rails 5, 6 are also arranged to be displaceable parallel to the axis of the plate cylinder 1 by means not shown (e.g. screws). (Correction of page register)

The front tensioning rail 5 is supported by tensioning screws 5.4 directly on the front wall of the cylinder channel, spring means (not shown) pressing the front tensioning rail 5 against this wall (FIGS. 1, 3c), 4a, 4b)).

As shown in FIG. 1, the plate cylinder 1 has two adjoining adjusting rings 8, 9 on each of the two cylinder side walls 7, which are rotatably supported independently of one another on a collar 10 in front of the cylinder journal 2. The eccentric shafts 5.3, 6.3 of the front and rear tensioning rails 5, 6 are led out through corresponding openings 11 on both cylinder side walls 7 of the plate cylinder 1 (FIG. 1) and have actuating arms 12 at their ends (FIG. 2a) and 2b)). The openings 11 are dimensioned in such a way that the adjustability of the tensioning rails 5, 6 is ensured. (Circumferential register)
The adjusting rings 8, 9 each have a recess 13 in the form of a gap on their outer circumference (FIG. 2a), 2b)). The eccentric shafts 5.3, 6.3 of the respective half of the plate cylinder 1 are in corresponding length in this case led out of the cylinder side wall 7 so that the actuating arm 12 of the eccentric shaft 5.3 dips into the recess 13 of the outer adjusting ring 8 and the actuating arm 12 of the eccentric shaft 6.3 dips into the recess 13 of the adjusting ring 9 (FIG. 1). Rotation of the adjusting rings 8, 9 thus causes the actuating arms 12 of the eccentric shafts 5.3, 6.3 to pivot, in which, depending on the direction of rotation of the adjusting rings 8, 9, press the flanks of the recesses 13 onto the actuating arms 12. According to FIG. 2a), rotating the adjusting ring 8 in the clockwise direction causes the tensioning rail 5 assigned to the start of pressure DA to be clamped. According to FIG. 2b), turning the adjusting ring 9 counterclockwise causes the clamping rail 6 assigned to the printing end DE to be clamped. The conditions on the left side of the plate cylinder 1 according to FIG. 1 have been described. The ends of the actuating arms 12 can, as indicated in FIGS. 2a) and 2b), be of spherical design.

The adjusting rings 8 and 9 on the two cylinder side walls 7 each have a toothing 14, in particular a straight toothing, in an arc region of their inner diameter. This toothing 14 is, as indicated in FIGS. 2a) and 2b), also incorporated in a recess 15 in the adjusting rings 8 and 9, respectively. A spur gear 16 or 17 is in engagement with the toothing 14 of the adjusting ring 8 or 9. The spur gears 16 and 17 are each on a shaft 16.1 or 17.1, which are led out on both cylinder side walls 7 from the plate cylinder 1 with a corresponding length such that the spur gear 16, adjusting ring 8 and spur gear 17, adjusting ring 9 can rotate ( Fig. 3a)). As indicated in FIG. 2 b), the adjusting ring 9, which is respectively directly assigned to the cylinder side wall 7, has a recess 18 in part of its inner circumference, which ensures that the shaft 16.1 does not hinder the turning ability of the adjusting ring 9.

On both cylinder side walls 7, the shafts 16.1, 17.1 in the cylinder channel 4 have a further spur gear 16.2, 17.2 (Fig. 3a) and, 3b)). The spur gears 16.2, 17.2 mesh with two further spur gears 16.3, 17.3. These spur gears 16.3, 17.3 are, as indicated in FIGS. 3a) and 3b), rotatably but axially immovable, ie parallel to the axis of the plate cylinder 1. Another spur gear 16.4 is arranged parallel to spur gear 16.3 and another spur gear 17.4 is arranged parallel to spur gear 17.3. Spur gears 16.4 or 17.4 mesh together with a spur gear 19.a or 19.b which is attached to the shaft of a motor 20.a or 20.b (FIGS. 3a) and 3b)). So that the drive energy from the motor 20.a or 20.b is not simultaneously transmitted to the spur gears 16.3 and 17.3 via the spur gears 16.4 and 17.4, the spur gears 16.3 and 16.4 and the spur gears 17.3 and 17.4 are each assigned a clutch 16.5, 17.5. The clutch mechanism of the clutches 16.5, 17.5 consists in a simple manner in that the spur gears 16.4 and 17.4 are axially displaceable on their axis of rotation and the mutually opposite flanks of the spur gears 16.3, 16.4 and 17.3 and 17.4 are designed to be positive, so that the spur gear is pressed on 16.4 or 17.4 on spur gear 16.3 or 17.3 results in a non-rotatable connection. The corresponding pressing or shifting of the spur gears 16.4 or 17.4 is effected in a simple and particularly advantageous manner by a single-acting working cylinder, which is effective when pressure medium is applied. The working cylinders of the clutches 16.5, 17.5 are designed in such a way that the spur gears 16.4 or 17.4 only move when pressure medium is applied. In pressure-free operation, the spur gears 16.4 or 17.4 are released from the spur gears 16.3 or 17.3 by spring elements integrated in the clutches 16.5, 17.5. Since a shifting of the spur gears 16.4 or 17.4 essentially represents the clutch mechanism, the spur gears 19.a, 19.b and the spur gears 16.4 and 17.4 have to be straight-toothed.

With spur gear 17.4, which is always in engagement with spur gear 19.a, another spur gear 21 meshes that forms the end of a shaft 22 (Fig. 3a)). Shaft 22 is guided into a clutch 23, which is also designed, for example, as a clutch to be actuated by pressure medium. In clutch 23, for example, an axially (shaft 22) displaceable sleeve can be arranged such that a non-rotatable connection is generated when pressure medium is applied. A spring under appropriate pretension can then disengage this sleeve when the clutch 23 is operating without pressure medium. On the output side, clutch 23 has a further shaft 24, at the other end of which a pulley 25 is arranged.

An adjusting spindle 26 is arranged parallel to the axis of the plate cylinder 1 in the cylinder channel 4, as can be seen in FIG. 3a). This is rotatable, but axially immovable in the cylinder channel 4. The bearings supporting the adjusting spindle 26 are embedded in walls firmly connected to the bottom of the cylinder channel 4. A further pulley 25 is arranged on adjusting spindle 26. A toothed belt 28 is tensioned around pulley 25 and 27, as in FIGS. 3a) and 4a). The adjusting spindle 26 is thus actuated in the embodiment described so far from the motor 20.a via the spur gear 19.a, 17.4, 21 and the shafts 22, 24, i.e. non-rotatably switched clutch 23 can be driven.

A spindle nut 29 which is part of a bridge 30 is seated on the adjusting spindle 26 (FIG. 3a). Bridge 30 dips into a recess 31 of the pressure bar 32 with little play. As known from the prior art, pressure bar 32 serves to move the rear tensioning rail 6 and is arranged between this and the rear channel wall of cylinder channel 4 (FIG. 6). It has, for example, four recesses 33 with an inclined plane over its entire length, which slide on partial surfaces of counterparts 34 which are fixed in a cylinder. A movement of the pressure bar 32 parallel to the channel wall thus causes a tensioning of the Pressure plate by a different from the rear channel wall clamping rail 6 (Fig. 3a), 3b), 5, 6).

If the adjusting spindle 26 is driven by the motor 20.a, the movement of the spindle nut 29 over the bridge 30 displaces the pressure bar parallel to the channel wall of the printing end. Since bridge 30 is inserted into a recess 31 of pressure bar 32 with little play, bridge 30 merely entrains pressure bar 32 in the direction of the axis of plate cylinder 1. Two guide bolts 35 are arranged on bridge 30 parallel to the axis of adjusting spindle 26 immerse in a guide bush 36 firmly connected to the bottom of cylinder channel 4. The guide bushings 36 can be, for example, so-called ball bushings. The guide bolts 35 are used in conjunction with the guide bushes 36 for the axial guidance of bridge 30, so that when the adjusting spindle 26 is driven, only axial forces act on it via the spindle nut 29.

The motors 20.a, 20.b are advantageously compressed air motors, in particular in the form of lamellas. Compressed air motors of this type generate relatively large torques in a small installation space. Appropriate compressed air supply to the motors 20.a, 20.b makes it easy to avoid overstretching and tearing of the pressure plate during tensioning. The compressed air supply for the motors 20.a, 20.b for driving in both directions of rotation takes place in a manner not shown by means of one or two rotary transducers designed in a correspondingly multi-channel manner via one or both pins 2 of the plate cylinder 1 and the frame wall 3 which supports them The invention provides for the clutches 16.5, 17.5 and 23 to be designed as clutches which can be switched with compressed air. Accordingly, three further compressed air transmission channels are necessary.

Below the split rear tensioning rail 6, that is, below the lower clamping device 6.2, along the support surface is the Pressure bar 32 assigned to each tensioning screw 6.4 a tensioning lever 37 (FIGS. 5 and 6). In the case of a divided rear tensioning rail 6 with two tensioning screws 6.4 per format half, a total of 4 tensioning levers 37, which are advantageously arranged in mirror image to the center of the plate cylinder 1 (FIG. 6). The tensioning levers 37 are supported on the pressure bar 32 via a molded-on cam 38 with a force-intensifying lever transmission. One end of each of the clamping levers 37 is connected to the rear clamping rail 6, that is to say the lower clamping device 6.2, by means of a swivel joint 39. The other free end of the tensioning lever 37 is supported on a stop pin 41 under the action of a spring 40 (supporting wall 42) which is supported in a cylinder-fixed manner. This lies on the connecting line of the swivel joints 39 in the rear clamping rail 6. A gap a therefore arises between the pressure bar 32 and the clamping device 6.2 (FIG. 5).

If the pressure bar 32 is now displaced in the direction of the end-of-clamping clamping via the motor 20.a with the clutch 23 switched and via the adjusting spindle 26, the rear clamping rail 6 is first pressed forward via the cams 38 of the clamping lever 37. In the circumferential direction, uniform clamping forces are exerted on the printing plate over the width of the format, since if a certain clamping force is exceeded, depending on the preload and the identification of the springs 40, in addition to the lever ratio of the clamping levers 37, the free ends of the clamping levers 37 pivot away from their corresponding stop bolts 41. The clamping force exerted on the pressure plate can thus be limited across the entire width of the format. In the swiveled-out state (clamping lever 37, stop bolt 41), the clamping force is also retained. As a result of the fact that the rear tensioning rail 6 is supported on the pressure bar 32 via tensioning lever 37, it is thus ensured that the tensioning force acts uniformly over the width of the format on the pressure plate and is not destructively exceeded at any point. Another advantage of this arrangement is the subsequent actuation of the clamping screws 6.4, for example to carry out a register correction in the circumferential direction. The To bring them into operation, clamping screws 6.4 only have to be turned to the distance "a" (time advantage). The tensioning device, consisting of the tensioning screws 6.4 and the pressure bar 32, which belongs to the prior art, thus represents a series connection consisting of a pretensioning device (pressure bar 32, recess 33, counterpart 34) and the tensioning screws 6.4 for the final, adjusting tensioning.

A further advantageous embodiment of the invention provides that the springs, which are supported in a cylinder-fixed manner, can be influenced in their pretension by further adjusting elements, not shown in the figures. This can be achieved in that the cylinder-fixed support (support wall 42) of the spring 40 is arranged on the bottom of the cylinder channel 4 in the direction of extension of the spring 40 relative to the plate cylinder 1.

Reference list

1

Plate cylinder

2nd

Cones

3rd

Rack wall

4th

Cylinder channel

5

front tensioning rail

5.1

upper clamping device

5.2

lower clamping device

5.3

Eccentric shaft

5.4

Clamping screw

6

rear tensioning rail

6.1

upper clamping device

6.2

lower clamping device

6.3

Eccentric shaft

6.4

Clamping screw

7

Cylinder side wall

8th

Collar

9

Collar

10th

Collar (pin 2)

11

opening

12th

Operating arm

13

Recess (collar 8, 9)

14

Gearing

15

Recess (collar 8, 9)

16

Spur gear

16.1

wave

16.2

Spur gear

16.3

Spur gear

16.4

Spur gear

16.5

Clutch

17th

Spur gear

17.1

wave

17.2

Spur gear

17.3

Spur gear

April 17

Spur gear

17.5

Clutch

18th

Recess (collar 8, 9)

19.a

Spur gear

19.b

Spur gear

20.a

engine

20.b

engine

21

Spur gear

22

wave

23

Clutch

24th

wave

25th

Pulley

26

Adjusting spindle

27

Pulley

28

Timing belt

29

Spindle nut

30th

bridge

31

Recess (pressure bar 32)

32

Pressure bar

33

Recess (pressure bar 32)

34

Counterpart

35

Guide pin

36

Guide bushing

37

Tension lever

38

cam

39

Swivel

40

feather

41

Stop bolts

42

Retaining wall

THERE

Start of printing

DE

End of printing

Claims (5)

1. Device for positionally exact rapid clamping and tensioning of printing plates on the plate cylinder of printing presses, particularly sheet offset printing presses, with a divided front and a divided rear tensioning rail in the cylinder channel of the plate cylinder, wherein these in each case consist of an upper and a lower clamping device and are actuatable via eccentric shafts for clamping the print start and print end of the printing plate, wherein the front tensioning rail supports itself directly via tensioning bolts on the channel wall and the rear tensioning rail supports itself via tensioning bolts on a pressure bar running parallel to the rear channel wall, which has recesses with an inclined plane relative to which are arranged corresponding wedge surfaces of counterpieces installed on the rear channel wall, and the pressure bar is displaceable via a central actuation unit in the direction of the cylinder channel, whereby the rear tensioning rail is moved in the direction rapid tensioning, wherein the pressure bar (32) is movable by means of an adjusting spindle (26) arranged axially non-displaceably running in the axial direction between front and rear tensioning rail (5, 6) on which a spindle nut (29) is movable and for controlling and limiting the tensioning force exerted on the printing plate below the rear tensioning rail (6) along the pressure bar (32) for each tensioning bolt (6.4) a tensioning lever (37) is arranged, wherein the tensioning levers (37) are supported with a bead (38) formed thereon under force amplifying lever conditions on the pressure bar (32), one end of the tensioning lever (37) is swivellably connected with the rear tensioning rail (6) by means of a pivot (39), the free end of the tensioning lever (37) is supported under the action of a spring (40) supported fast with respect to the cylinder on a stop pin (41), which is fixed on the connection line of pivots (39) in the rear tensioning rail so that on shifting the pressure bar (32), the free ends of the tensioning levers (37) on exceeding a given tensioning force are swivellable about the respective pivot (39) away from the stop pins (41), characterised in that on both cylinder side walls (7) of the plate cylinder (1) on the trunnions (2) there are mounted in each case two adjusting rings (8, 9) rotatable independently from one another which have at one portion of their exterior periphery in each case a recess (13), that the eccentric shafts (5.3, 6.3) are led out at both cylinder side walls (7) through openings (11) of differing lengths and have at their ends actuation arms (12) so that the actuation arms (12) are movable by the eccentric shaft (5.3) through the recess (13) from the adjusting ring (8) and actuation arm (12) from the eccentric shaft (6.2) through the recess (13) of adjusting ring (9), that the adjusting rings (8, 9) on both sides of the plate cylinder (1) can be driven in each case from a motor (20.a, 20.b) arranged in the cylinder channel (4), to both of which motors (20.a, 20.b) is connected in each case a gearing (16 - 16.4, 17 - 17.4, 19.a, 19.b) together with in each case two switchable clutches (16.5), (17.5), wherein the spindle nut penetrates via a bridge with little play into a recess (31) of the pressure bar (32) and the adjusting spindle (26) can be driven by a motor (20.a) via a switchable clutch (23).
2. Device according to Claim 1, characterised in that the motors (20.a, 20.b) are constructed as compressed air motors of lamellar construction.
3. Device according to Claim 1 or 2, characterised in that the adjusting rings (8, 9) are mounted in each case on a collar (10) pre-mounted on to the cylinder side wall (7).
4. Device according to one of the preceding Claims, characterised in that the adjusting rings (8, 9) have at one portion of their interior diameter a recess (15) with toothing (14) which is engaged in each case with a spur gear (16, 17) and the spur gears (16, 17) are drivable via differingly long shafts (16.1, 17.1) via further spur gears (16.2 - 16.4, 17.2 - 17.4) via the switchable clutches (16.5, 17.5) from the spur gears (19.a, 19.b) of the respective motor (20.a, 20.b).
5. Device according to one of the preceding Claims, characterised in that the adjusting spindle (26) can be driven via two pulleys (25, 27) and a toothed belt (28) from the motor (20.a) via switchable clutch (23).

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