EP1551640B1 - Device and method for guiding a continuous web by means of a pivotable apparatus - Google Patents

Abstract

Disclosed is a device for guiding a continuous web (10), said continuous web (10) being directed about a given angle of wrap via two rolls (24, 26). The shafts of said rolls (24, 26) lie parallel on one plane and are held by a frame (28) which can be swiveled about a first axis of rotation (30) so as to modify the position of the edge (11, 13) of the web (10) in the direction of the roll shafts. The frame can also be swiveled about a second axis of rotation (58), one component of which runs parallel to the direction of movement of the web (10) between the two rolls (24, 26).

Description

The invention relates to devices for guiding an endless web, as used for example in a printer or copier. Furthermore, the invention relates to methods for guiding an endless web.

When guiding a paper web through a printer, due to irregular mechanical web properties of the paper web or due to a not exactly parallel basic setting of the different guide rollers, there is a lateral distortion of the paper web and a wave formation and / or a unilateral sagging of the paper web despite stable running leading edge come. Such waves can be ironed at deflections with counter-pressure rollers, such as those required for transport, to wrinkles. Furthermore, a one-sided sagging of the web, for example, in the region of a non-contact fixing station disturbing because the sagging path section can come into contact with mechanical parts and the toner images are blurred or the sagging section is exposed to excessive energy load.

From the US-A-5,021,673 a device for guiding a paper web is known in which for guiding the web on both side edges rollers are arranged, which exert pressure with different force on the web. In this way, a lateral displacement of the web can be corrected.

In the US-A-5,323,944 a device for controlling the lateral position of a web is described in which the web is passed between a pressure roller and a counter-pressure roller. The pressure roller is pivotable and the force exerted along the axis on the counter-pressure roller can be varied to displace the side edge of the track. The Current position of the side edge of the web is detected by means of optoelectronic sensors.

The US-A-6,104,907 describes a device for guiding a paper web in a printer. To avoid vibrations and speed variations, the paper web is guided around rollers and clamped, whereby a lateral displacement of the web is counteracted. For example, a guide roller is used with pins to prevent the lateral displacement, which engage in corresponding holes of the web. Another variant provides to vary the force exerted by a roller along its axis on the paper web. In a further variant, the paper web is guided between pairs with upper and lower rollers. These upper and lower rolls wrap and clamp the web at an increased wrap angle, thus preventing speed variation of the web.

From the documents DE 689 07 466 T2 . DE-OS 14 24 318 . DE 195 20 637 and DE 199 60 649 A1 Web guiding devices are known for guiding an endless web. Further, from the documents DE 199 53 353 A1 and DE 44 35 077 A1 are pivotable extractors for paper webs known.

The DE 14 24 318 A describes a device for regulating a web of textile. This device can be pivoted about a first axis of rotation and about a second axis of rotation, substantially perpendicular to the first axis of rotation. The device works self-regulating, for which it is necessary that the textile web is guided around a wrap around a fixed tube, which is in frictional engagement with the textile web. If the tension on one side of the fixed tube is greater than on the other side, the entire device is pivoted about the two axes of rotation due to the force difference on the web sides, so that an off-center run of the textile web is corrected is that the textile web again takes a central course.

The DE 196 24 639 A1 describes a device for web guiding, in which a pivotable roller is arranged between two stationary rollers. This pivotable roller is pivoted relative to the stationary rollers. The three rollers exert no pulling force to pull off the conveyed through them web.

As further prior art is based on the documents US 3,600,551 A1 . DE 101 36 696 A . FR 2659426 A and JP 03-061248 A directed.

It is an object of the invention to provide devices and methods with which an accurate guidance of a continuous web is made possible and a one-sided sagging of the web is avoided.

This object is achieved for a device by the features of claim 1.

According to this solution, the endless web is guided over two rollers by a respective wrap angle. The axes of the rollers lie parallel in one plane and are held by a frame. The frame is pivotable about a first axis of rotation substantially perpendicular to this plane, to change the position of the edge of the web in the direction of the roll axes. In this way, a lateral displacement of the web can be corrected. Furthermore, the frame is pivotable in a second axis of rotation, a direction component in three-dimensional space runs parallel in the direction of movement of the web between the two rollers. In this way, the web tension can be changed on one side of the web, whereby a one-sided sagging of the web is avoided. The second axis of rotation can also run only parallel in the direction of movement of the web. The other components in three-dimensional space are then zero relative to the direction of movement. The then achievable effect of the web tension change is maximum. However, there are constructive advantages in oblique position of the axis of rotation to the direction of movement, with only one component must run parallel to the direction of movement.

In further aspects, the invention relates to methods of guiding an endless web having the features of claims 23 and 26, respectively, and to an apparatus having the features of claim 20.

Figur 1

eine schematische Darstellung des Papier- transports in einem Hochleistungsdrucker mit einem in zwei Drehachsen verstellba- ren Drehrahmen sowie eine verschwenkbare Abzugsvorrichtung,

Figur 2

den prinzipiellen Aufbau des Drehrahmens,

Figur 3

eine Einlaufwalze mit Bahnzugmessung,

Figur 4

eine schematische Darstellung zur Steue- rung des Bahntransports gemäß einer er- sten Variante,

Figur 5

die Darstellung einer Steuerung gemäß ei- ner zweiten Variante,

Figur 6

die schematische Darstellung einer Steue- rung gemäß einer dritten Variante,

Figur 7

den prinzipiellen Aufbau eines elektro- grafischen Druckers, bei dem eine Bahn- führung realisiert ist,

Figur 8

eine schematische Anordnung mit einem er- sten Sensor zum Erfassen der Seitenkante der Bahn,

Figur 9

ein Blockschaltbild des Regelkreises zum Regeln der Lage der Seitenkante,

Figur 10

einen schematischen Aufbau mit einem zu- sätzlichen zweiten Sensor im Zuführbe- reich der Bahn,

Figur 11

ein Blockschaltbild der Lageregelung mit zwei Sensoren,

Figur 12

den prinzipiellen Aufbau mit drei Senso- ren,

Figur 13

das Blockschaltbild der Lageregelung, bei der die Signale der drei Sensoren berück- sichtigt werden,

Figur 14

einen Drehrahmen mit einer einzigen ange- triebenen Walze und Gegendruckwalzen,

Figur 15

eine schematische Ansicht nach Figur 1 in Querschnitt,

Figur 16

ein Beispiel mit kleinem Umschlingungs- winkel,

Figur 17

Beispiele, bei denen die Drehachse des Rahmens senkrecht zur abgeführten Bahn steht,

Figur 18

Beispiele, bei denen die Drehachse paral- lel zur Bewegungsrichtung der abgeführten Bahn verläuft,

Figur 19

ein Beispiel einer Bahnführungsvorrich- tung,

Figur 20

ein Beispiel einer Bahn mit aufgebrachten Klebeetiketten,

Figur 21

das Rollverhalten der Gegenrolle mit ei- nem weichen Belag,

Figur 22

eine Bahn mit Etiketten, die auf der Sei- te der angetriebenen Walze aufgeklebt sind,

Figur 23

eine Anordnung mit weggeschwenkter Gegen- rollenvorrichtung, und

Figur 24

eine Bahnführungsvorrichtung mit einer ortsfest angeordneten angetriebenen Walze und einer Vielzahl von verdrehbaren Ge- genrollen.

For a better understanding of the present invention, reference will now be made to the preferred embodiments illustrated in the drawings, which are described in terms of specific terminology. It should be understood, however, that the scope of the invention should not be so limited since such changes and other modifications to the illustrated devices and / or methods, as well as such other uses of the invention as heretofore, will be expected to be present or future Expertise of a competent expert. The figures show embodiments of the invention, namely

FIG. 1

a schematic representation of the paper transport in a high-performance printer with an adjustable in two axes of rotation rotating frame and a swiveling extractor,

FIG. 2

the basic structure of the revolving frame,

FIG. 3

an infeed roller with web tension measurement,

FIG. 4

1 is a schematic representation of the control of the rail transport according to a first variant,

FIG. 5

The representation of a controller according to a second variant,

FIG. 6

1 is a schematic representation of a controller according to a third variant,

FIG. 7

the basic structure of an electrographic printer, in which a web guide is realized,

FIG. 8

a schematic arrangement with a first sensor for detecting the side edge of the web,

FIG. 9

a block diagram of the control loop for regulating the position of the side edge,

FIG. 10

a schematic structure with an additional second sensor in the feeding area of the web,

FIG. 11

a block diagram of the position control with two sensors,

FIG. 12

the basic structure with three sensors,

FIG. 13

the block diagram of the position control, in which the signals of the three sensors are taken into account,

FIG. 14

a rotating frame with a single driven roller and counter-pressure rollers,

FIG. 15

a schematic view after FIG. 1 in cross section,

FIG. 16

an example with a small wrap angle,

FIG. 17

Examples in which the axis of rotation of the frame is perpendicular to the removed path,

FIG. 18

Examples in which the axis of rotation runs parallel to the direction of movement of the discharged web,

FIG. 19

an example of a web guiding device,

FIG. 20

an example of a web with applied adhesive labels,

FIG. 21

the roll behavior of the counter roll with a soft coating,

FIG. 22

a web with labels adhered to the side of the driven roller,

FIG. 23

an arrangement with weggeschwenkter counter-roller device, and

FIG. 24

a web guiding device with a fixedly arranged driven roller and a plurality of rotatable counter-rollers.

FIG. 1 schematically shows the transport of an endless paper web 10 by a high-performance printer. In the upper half of the FIG. 1 is a schematic side view, shown in the lower half of a plan view. The web transport through the printer takes place in three zones Z1, Z2 and Z3. In the zone Z1, the paper web 10 is conveyed through a retraction device 12, which contains a roller 14 and a counterpressure roller 16. The retraction device 12 serves to act on the paper web 10, a predetermined web tension in the transport direction. The paper web 10 is then deflected at a guide roller 18 and fed to an inlet roller 20, which is seen in the transport direction a rotary frame 22 upstream. The infeed roller 20 comprises two sensors S1, S2 for measuring the web tension, as will be explained in more detail below. The rotary frame 22 includes two rollers 24, 26, whose axes are parallel and are held by a dashed line frame 28. The frame 28 is pivotable about an axis of rotation 30 in the direction of the rotary arrow 32. The web transport is monitored by two sensors S3, S4, which control the paper web 10 in the area between the rollers 24, 26 from above. Alternatively, the paper web can be controlled by appropriate sensors from below.

In the exit region of the rotary frame 22, an edge sensor 34 is fixed to the device, which determines the actual position of the side edge of the paper web 10. Depending on the actual position and the deviation of the edge from a desired position of the rotary frame 22 is pivoted on a frame about the axis 30 and thus adjusted the side edge to a predetermined desired position.

As seen in the transport direction of the paper web 10, a stabilizing roller 36, which serves to equalize the web tension in the paper web 10, is arranged after the rotating frame 22 in the zone Z2. The stabilizing roller 36 may be radially slightly resilient or compliant and thus causes a passive compensation for the paper web 10. In this zone Z2 further comprises a guide roller 38 and a drive roller 40 is arranged. The drive roller 40 acts on the paper web 10 with a tensile force and transports the paper web 10 against the resistance of a braking device 13, e.g. a vacuum brake, forward. The drive roller 40 determines the speed at which the paper web 10 is transported forward. Alternatively, the retraction device 12 can be used as a permanent brake.

In the zone Z3 takes place on transfer rollers 42, 44 a one-sided or two-sided printing of the paper web 10. Subsequently, the paper web 10 passes through a fixing station 46, in which the images placed on the paper web 10 toner images are fixed, for example by an infrared fixation. In the region of the fixing station 46 sensors S5, S6 are arranged, which monitor the paper web 10. At the end of the zone Z3 a take-off device 48 with rollers 49, 50 is arranged, which carries off the paper web 10 with a predetermined tensile force.

In the case of limited infrared fixation, the paper web 10 between the draw-off device 48 and the transfer rolls 42, 44 must not be in contact with mechanical parts in order to avoid blurring of the toner image. A one-sided sagging of the paper web is therefore to be prevented.

The removal device 48 is pivotable about a passing through the pivot 52 axis of rotation 54 in the direction of the double arrow 56. Thus, the tension along the two side edges 11, 13 of the paper web 10 can be varied in order to reduce or avoid a one-sided sagging of the paper web 10.

The rotary frame 22 is additionally pivotable in a second axis of rotation 58 in the direction of the rotary arrow 60. The axis 58 is substantially parallel or identical to the direction of movement of the paper web 10 between the two rollers 24, 26. In this way, the tension on one side of the paper web 10 can be increased or decreased and thus a one-sided sagging of the paper web 10 can be avoided.

In the lower part of the picture FIG. 1 is shown in a plan view of the transport of the paper web 10 through the high-performance printer. In one variant, the transport of the paper web 10 is effected so that a side edge has a fixed desired position, regardless of which width the paper web 10 has. In the present case, as seen in the transport direction, the left side edge 11 is fixed. This side edge 11 coincides with the second axis of rotation 58. In the present example, after FIG. 1 a pivoting of the entire rotating frame 22 about the axis of rotation 58 by the frame 28 about a support 62 which is located approximately below the extended axis of the axis of rotation 58, pivoted. On the opposite side of the support 62 for this purpose, a screw-nut combination 64 is arranged, with which the frame 28 can be pivoted about the axis of rotation 58. It should be noted that other definitions of the side edge 11 with respect to the axis of rotation 58 can be made. Likewise, other devices can be used for pivoting, which operate electrically, hydraulically or pneumatically. The screw-nut combination 64 shown only shows a particularly simple, also manually operated device.

The sensors S1, S2 are preferably designed as load cells and measure the forces that exert the paper web 10 on the axis of the inlet roller 20. Is on a page the paper web 10 reduces the force, the typical consequence is a sagging of the paper web 10 on this side. By adjusting the screw-nut combination 64, such a one-sided sagging can be compensated.

At the in FIG. 1 This asymmetry also leads to asymmetric forces occurring in the sensors S1, S2 as a result of different lever arms along the axis of the inlet roller 20 in the sensors S1, S2. The setpoints for any necessary correction are also asymmetrical here. They are determined, for example, by means of computer programs or by measuring and form the basis for correction data.

The sensors S3, S4 and S5, S6, monitor the edge regions with the side edges 11, 13 of the paper web 10 and can detect a one-sided sagging. For example, video cameras can be used as sensors. Another possibility is to detect the web tension in the region of the side edges 11, 13, for example by means of one or more force sensors. Another possibility is to determine the sagging of the respective side edge 11, 13 by means of displacement sensors which operate on an optical, inductive and / or, capacitive basis.

FIG. 2 schematically shows the rotating frame 22 with the two rollers 24, 26, whose axes 66 are parallel and held by the frame 28. By a rotation in the direction of the direction of rotation arrow 32 about the axis 30 with respect to stationary rollers W1, W2, the position of the side edges 11, 13 of the paper web 10 in the direction of the roll axes 66 can be changed. By pivoting in the direction of the direction of rotation arrow 60 about the axis 58, the web tension within the paper web 10 on the side of a web edge 11, 13 can be changed. The axis of rotation 58 is in the example of Figure 2 in the middle of the paper web 10. However, it can also on Edge of the paper web 10 as in the example after FIG. 1 or even outside of the paper web 10.

FIG. 3 shows an example of the measurement of the web tension of the paper web 10 by means of the feed roller 20 and the sensors S1 and S2, which are designed as a bending beam with strain gauges for force measurement. The feed roller 20 is mounted on both sides in receptacles 68. These receptacles 68 are by means of brackets (bending beam) 70, 72 with the printer housing (not shown) firmly connected. The strain gauges of the sensors S1, S2 measure the deflection of these brackets 70, 72 and thus the forces F1, F2 occurring on each side of the feed roller 20, the symmetrical arrangement of paper web 10 and feed rollers 20 approximately proportional to the respective web tension in the side edges 11, 13 of the paper web 10 are. The sensors S1, S2 emit electrical signals via the lines 74, 76. If the web tension in the region of a side edge 11, 13 of the paper web 10 is smaller than the desired value, then the respective force F1, F2 is smaller than the desired value, so that a sagging of this side edge 11, 13 of the web 10 can be concluded. In an asymmetrical arrangement of paper web 10 and feed roller 20, the lever arms for the respective sensors S1, S2 along the axis of the inlet roller 20 are taken into account, ie the desired forces are also asymmetric and correct the forces accordingly.

The shown measurement of the web tension of the paper web 10 on the feed roller 20 can of course also be applied to other rollers within the web transport by the printer, so that the sagging on one side of the paper web 10 are detected with a similar arrangement almost anywhere within the printer can.

The FIGS. 4 . 5 and 6 show three variants for controlling or regulating the web tension in the printer. In the variant according to FIG. 4, control or regulation of the web tension takes place with the aid of the sensors S3, S4 on the rotating frame 22 and with the aid of the sensors S5, S6 in the region of the fixing station 46. The signals of the sensors S3, S4 and S5, S6 are passed to a controller 80, which preferably this software in a control or Control algorithm processed. This controller 80 then generates control signals 82, 84 for driving respective drives for the rotary frame 22 and the extractor 48. The control algorithm processes predetermined setpoints 86; the controller 80 also generates information about operating conditions displayed on the display 88.

If it is determined in the region of the rotary frame 22 by means of the sensors S3, S4 that the paper web 10 sags along a side edge 11, 13, the rotary frame 22 is pivoted about the axis of rotation 58, for example by means of an electrically actuated screw-nut combination 64 or by other pivoting mechanisms. In this way, the paper web 10 is tightened in the sagging area. Similarly, a one-sided sagging in the region of the fixing station 46 by means of the sensors S5, S6 detected and counteracted by pivoting the trigger device 48 about the axis of rotation 52 along the double arrow 56 or completely compensated. In this way, a one-sided sagging is corrected in the field of fixation. In the described first variant, therefore, a one-sided sagging in the region of the rotary frame 22 and in the region of the fixing station 46 is corrected. This can be done with the help of control algorithms that are stored in the controller. However, it may also be a control such that the control setpoints are given, which are compared with actual values of the sensors S5, S6 and S3, S4, wherein a control deviation is compensated by deflecting the rotary frame 22 and the trigger device 48.

According to the second variant FIG. 5 , in which equal parts are designated the same, are used to correct the web tension the signals of the sensors S1, S2 in the region of the feed roller 20 and the sensors S5, S6 in the region of the fixing station 46 are evaluated. With the aid of the signals of the sensors S1, S2, a web tension which decreases along a web edge 11, 13 of the paper web 10 is detected, which is interpreted as a one-sided sagging of the paper web 10. The rotary frame 22 is then controlled to counteract this decrease in web tension on that side of the paper web 10. With the help of a control algorithm, the pivoting of the rotary frame 22 about the axis of rotation 58 so that predetermined forces for the sensors S1, S2 are achieved. The adjustment of the web tension by means of the sensors S5, S6 is carried out as in the variant FIG. 4 described. Also in this variant, a one-sided sagging of the paper web is corrected or avoided in the region of the rotary frame 22 and in the region of the fixing station 46.

In the variant after FIG. 6 monitoring of the paper web 10 takes place only with the aid of the sensors S1, S2, which are arranged in the region of the feed roller 20. Assuming that the paper conveying conveyor rollers are in a parallel, basic setting on all axes, unilateral sagging of the paper web 10 can only result from the uneven mechanical web properties of the paper web 10. The signals from the sensors S1, S2 thus provide information about the paper web properties, for example, whether the paper web is curved, has a different density or has different stresses along the axes of its surface. With the aid of empirical values, which are determined from tests and calibration procedures, an associated deflection of the rotary frame 22 about the axis 58 and / or an associated deflection can be added to each value tuple of the sensors S1, S2, which also takes into account the web width and the paper type the take-off device 48 take place about the axis of rotation 52. Typically, such value tuples and the associated control parameters for the required deflection for the rotating frame and the extraction device 48 are stored in a memory as a table. In this variant, the cost of sensors is minimal, yet a high-quality paper web guide is achieved in the printer. Of course, the variant described after FIG. 6 combined with the variants after FIG. 4 or FIG. 5 , ie the signals from sensors S3, S4 and / or S5, S6 can be additionally used to control and regulate the web tension of the paper web 10.

According to a fourth variant, a monitoring of the web tension and a correction takes place only in the region of the fixing station 46 in order to avoid a damaging one-sided sagging of the paper web. With the aid of the signals of the sensors S5, S6 and the pivotable discharge device 48, a stable web guide for the relatively long distance of an infrared radiation-operated fixing station 46 is achieved.

In the FIGS. 7 to 13 According to a further aspect of the invention, examples are described which can also be combined with the examples described above. In FIG. 7 a high-performance printer is shown, in which the device and the method according to the invention is realized. The printer is divided into a printing unit 110 and a fusing station 112, each having independent housings 114, 116 connected together. A web 118 of continuous paper is passed through both housings 114, 116. In a web feed area 120 for the printing unit 110, a web retraction motor 122 is arranged which exerts a restraining force on the web 118 by means of a pair of rollers. Furthermore, a web brake 124 is provided which smoothes the web 118 and also exerts a restraining force on the web 118. The web brake 124 is realized for example by a felt which rests on the web 118. Another possibility is to use a vacuum brake. In this case, with the help of a variable negative pressure, the paper web on the underside is subjected to vacuum, that sucked, and it changes, consequently, the friction. In the railway catchment area of Retraction device 120, more specifically, seen in the normal transport direction shortly after the web brake 124, a second sensor 126 is arranged, which detects the actual position of the side edge of the web 118.

The web 118 is fed via a deflection roller 128 to a rotating frame 130, which serves as an actuator for adjusting the position of the side edge of the web 118. The rotating frame 130 performs rotational movements about an axis perpendicular to the track 118 and thereby displaces the side edge in a direction perpendicular to the plane of the paper FIG. 7 , In the outlet region of the rotating frame 130, a first sensor 132 is arranged, which detects the actual position of the side edge of the web 118. The web 118 is fed via two further deflection rollers 134, 136 to a web drive 138, which contains a pair of rollers. Web drive 138 advances web 118 in the transport direction against the restraining force of web brake 124.

On both sides of the web 118, an upper transfer printing station 140 and a lower transfer printing station 142 are arranged in the further course. Both transfer stations 140, 142 print the top and bottom of web 118 simultaneously with toner images. Both transfer stations 140, 142 are constructed substantially the same, which is why only the upper transfer station 140 will be explained in more detail below. The upper transfer station 140 comprises a character generator 144 which generates on a photoconductor belt 146 an electrostatic charge image corresponding to a printed image to be printed. An upper developer station 148 dyes the electrostatic charge image with toner material; the toner images are then transferred to a transfer belt 150. In the further course, the toner images located on the transfer belt 150 are then transferred to the transfer web 152 on the web 118, ie at the transfer printing station 152 toner images are simultaneously transferred from both transfer printing stations 140, 142.

As seen in the transport direction after the transfer printing point 152, a third sensor 154 is arranged, which also detects the actual position of the side edge of the web 118. The unfixed toner images on the web 118 are fed to the fuser 112 where they are fixed and cooled in infrared fixers 156, 158 and downstream blowers 160, 162 on both sides of the web. In the exit area of the fuser 112, there is a web take-off motor 164 which acts on a pair of rotary rollers and conveys the web 118 from the fuser 112.

The illustrated high-performance printer has various operating states, each of which has different tasks with respect to attitude control of the side edge of the web 118:

Operating state 1: Automatic web insertion

When reinserting a web 118 it is automatically transferred by means of a clip through the printing unit 110 and the fuser 112 and from there to the web outlet - transported. During the guidance of the path 118 by means of the bracket, the rotating frame 130 and the position control remain inactive. After completion of the insertion of the rotary frame 130 and the position control is activated.

Operating condition 2: Inserting a glued web

If a new web is glued to a previous web, the new web is passed through the printing unit 110 and the fixing station 112 at a transport speed which is significantly less than the normal printing speed in order not to load the bonded area too much. During the transport of the splice by the printer, a control adapted to the slow transport speed is active. Due to the splice between the old web and the new web, deviations in position may occur at the side edge. It is here rule task that the fastest possible settling on the target position of the side edge of the web 118 should take place. After the completion of the insertion, the normal position control is activated.

Operating Condition 3: Slow forward transport and reverse transport of the web

In order to position the web as accurately as possible when loading pre-printed paper (form paper), a slow forward and backward transport is required. During this positioning, the control and the rotating frame 130 are not active. After the completion of this fine positioning, the control and the rotating frame 130 is activated with the following paper movement and it should as quickly as possible the side edge of the web 118 are brought into the desired position (as in the operating condition 4 and 5 described below). What is important in this process is that as few print pages as possible are waste paper, i. Waste, accumulates.

Operating mode 4: Fast forward transport without printing operation

At the end of a print job, the web should be kept at the defined printing speed, but without printing operation, with respect to the side edge in the desired position, so that the last reprinted toner images can be fixed in the fuser 112. At the end of the forward movement of the web 118, a retraction movement is initiated, so that a restart of the operation can be carried out in a form-appropriate manner, ie the printed images must be printed in registration with a form on the web 118. In this forward and backward movement of the web, the control and the rotating frame 130 is active; It should be achieved that the desired position of the side edge of the web is reached as quickly as possible, which results in a few pages of waste paper.

Operating state 5: rail transport in printing operation

At the start of the printing operation, the web 118 is first brought at pivoted Umdruckstationen 140, 142 to the target speed corresponding to the printing speed. Subsequently, the transfer stations are pivoted with the transfer belts and there is the printing operation. At the end of a printing operation with forward movement of the web, a retraction transport of the web 118 is carried out at pivoted transfer printing stations, so that a restart of the printing operation can be carried out according to the form. In this operating state, the control and the rotating frame 130 is active. It should be done a quick swinging of the side edge to the desired position within the various transport speeds of the web 118.

FIG. 8 shows schematically the course of the web 118 within the devices 110, 112, as it is essential for the regulation of the position of the side edge on the basis of a first example with only one sensor 132. The web 118 is conveyed via the web feed-in region 120, symbolized by a pair of rollers, to the rotating frame 130, in the web exit of which the first sensor 132 is arranged. Thereafter, the web 118 is guided along the web drive 138, the transfer point 152 and the removal device 164.

FIG. 9 shows in a block diagram to the first embodiment, the position control. The actual signal S1 of the first sensor 132 is supplied to an adder 170 and the control deviation E is formed. A controller 172, eg a PID controller, generates a control signal R, which is fed to the rotary frame 130 as an actuator 130. The rotary frame 130 changes due to the control signal R its rotation angle and thus changes the lateral position of the side edge of the web 118. The actual position of this side edge is detected by the first sensor 132 as an actual signal S1, which is returned to the addition member 170 as mentioned. This control process takes so long until the control deviation E is equal to zero. The desired position and the desired signal S0 is set at the location of the first sensor 132 as an electrical signal.

The first sensor 132 determines measured values at predetermined path distances along the path 118. The actual signal S1 is an average value of these measured values. Preferably, the mean value used is a moving average or an exponential mean. At the moving average value, an average of n measured values is first formed. For each newly added measured value, a new mean value is calculated from the previous mean value and the new measured value. The setpoint S0 can be determined in a similar manner in a calibration process. Preferably, the mean value over a predetermined distance of the web is determined, generally an integer multiple of a standard format length of a printed page. Typically, the standard format length used is the 12-inch format, the multiple being preferably 3.

Due to the averaging, short-wave position deviations along the web edge do not lead to undesired deflections of the rotating frame. In addition, resonance-induced excessive positional deviations at the transfer printing point are avoided by averaging. Such resonance-related positional deviations can occur in paper webs with wavy cut side edges. By adjusting to the standard format length, ripples in the transport direction of the web within a form length do not occur along printed lines in print images.

In this first embodiment, it may be problematic that only at the location of the first sensor 132, ie in the vicinity of the rotating frame 130, the actual position coincides with the desired position of the side edge. At the transfer point 152, which is essential for the print quality, the side edge of the web 118 may again deviate from a desired position. by virtue of In addition, the averaging may be relatively slow in transient response. Furthermore, due to the averaging, a control deviation can remain permanent since maximum amplitudes are not compensated.

FIG. 10 shows a further embodiment in which two sensors are arranged. Same parts are the same. The second sensor 126 is arranged in the web feed-in area 120. The further arrangement agrees with the FIG. 8 match.

In FIG. 11 is a block diagram of the associated position control for the side edge of the web 118 shown. With the aid of the signal S2 of the second sensor 126, the controller 172 is acted upon, which outputs the controlled variable R to the rotating frame 130. In its signal S2, the second sensor 126 images the deviation of the position of the side edge of the web 118 in the web feed region 120, ie it determines the deviation of the actual position of the side edge from a desired position in the region of the web brake 124 (cf. FIG. 7 ). For this purpose, it is expedient that in the web feed region 120, a web feed device is arranged, which comprises a lateral stop (not shown) on which the relevant side edge of the web 118 is guided along. In this way, a stable starting situation for the side edge of the web is created in the catchment area of the track 118.

The second sensor 126 preferably includes a delay VZ. The delay time for the signal S2 corresponds to the time required for the web 118 to move from the location of the second sensor 126 to the location of the first sensor 132. In this way, the deviation of the side edge from a target value in the web feed region 120 can be compensated with a time delay. Thus, the deviation of the side edge from a reference value in the web-feed area is determined and, as the first alternative, the signal S2 is added to the desired value S0 (in FIG FIG. 11 dashed lines drawn). As a second alternative the signal S2 is fed directly to the controller 172, which forms the controlled variable R taking into account this signal S2. According to this embodiment FIG. 11 For the signal S1 of the first sensor 132, no averaging is carried out, because this would disturb the compensation with the aid of the signal S2.

The advantage of position control after FIG. 11 is that only the long-wave deviations of the mean actual position of the side edge of a desired position at the location of the first sensor 132 are compensated by the rotating frame 130. By taking into account a deviation of the side edge in the catchment area of the track 118, the transient response of the control loop is relatively fast. Also in this example FIG. 11 It should be noted that the control deviation at the location of the first sensor 132 may be minimal, but deviations from an optimal position of the side edge may occur at the location of the transfer point 152.

FIG. 12 schematically shows the structure with three sensors 126, 132 and 154. The second sensor 126 is optional, which is indicated by dashed lines. The third sensor 154 is arranged within a range of ± 100 mm relative to the transfer point 152 of the transfer printing stations 140, 142, since the transfer printing station 152 itself is difficult to access.

FIG. 13 shows the associated position control using the signals S1 of the first sensor, S3 of the third sensor and optionally the signal S2 of the second sensor. The position control contains, in addition to the addition element 170, the addition elements 174 and 176. The addition element 176 is supplied with the signal SU, which reproduces the desired position at the sensor 154, ie in the vicinity of the transfer printing point 152. The adder 176 performs a setpoint-actual value comparison between the signals SU and S3. The result is fed to the adder 174, the result of which is in turn supplied to the adder 170. At the adder 170, the actual value S1 of the considered first sensor 132 in the region of the rotary frame 130. The signal of the second sensor S2 can optionally as in the example of FIG. 5 as a delayed signal at the controller 172 or the addition element 170 (this variant is not shown) are taken into account. Optionally, the signal S2 can also be taken into account in the formation of the signal S3, ie the signal S2 acts on the third sensor 154.

With the help of the scheme FIG. 13 it is possible to take into account the positional deviation directly at the transfer printing point 152. The signal S3, possibly taking into account the signal S2, after the link in the adders 176 and 174, the target signal S0 for the control circuit containing the adder 170 forms. In order to keep the control system free of vibration, the signal S0 may only change slowly, for example by a factor of 110 slower than the signal S1. The advantage of the arrangement after FIG. 13 lies in the fact that even a deviation of the side edge in the region of the transfer printing point 152 is detected and corrected by the rotary frame 130.

In the following FIGS. 14 to 24 Examples of a rotating frame are shown according to another aspect of the invention. These examples can be combined with the examples described above. In FIG. 14 There is shown a web guiding apparatus comprising a single driven roller 210 mounted in a pivoting frame 212. The pivoting frame 212 can be pivoted about an axis of rotation 214 which is substantially perpendicular to the discharged path 216. Within the rotating frame 212 and counter rollers 218 are mounted, which press the web 216 with a predetermined force against the roller 210. The roller 210 is driven by means of a drive 220 and a gear 222. Due to the friction on the surface of the roller 210, the web 216 is conveyed in the direction of the arrow P21. The web 216 has a tendency to be conveyed away in the tangential direction from the lateral surface of the roller 210. By rotating the rotating frame 212 about the axis 214 according to the arrow P22 by an angle α and the transport direction of the web 216 is influenced, which is conveyed away by the roller 210. Accordingly, the location of the edge of the web 216 with respect to a reference position in the direction of the roll axis of the roller 210 can be changed.

For example, an electric drive 226 can be used to rotate the rotating frame 212, which deflects the rotating frame 212 by small angular amounts, typically by 1 ° in the clockwise or counterclockwise direction according to the arrow P22. The drive 226 includes a nut 228 in which a spindle 230 is reciprocated. To ensure defined positions in the deflection of the rotating frame 212, the inevitable in the drive between the nut 228 and the spindle 230 game due to tolerances by a tension spring 232 is prevented. This will cause the nut 228 to always bear on the same spindle flank upon forward and backward movement of the spindle 230.

The conveyed web 216 is acted upon by a rotational movement in the direction of arrow P22 only minimally with forces. However, it is also possible to arrange the rotation axis 214 eccentrically to the rotation frame 212. In the example below FIG. 14 the web 216 is guided centrally with respect to the roller 210. However, it is also possible to arrange the web 216 off-center.

Furthermore, the example is after FIG. 14 However, it is also possible to pass this web 216 on one side or on both sides of the roller 210, so that the width of the roller 210 is smaller than the width of the web 216.

FIG. 15 schematically shows the arrangement according to FIG. 14 in a cross section. The web 216 is in contact with the surface of the roller 210 by a predetermined wrap angle β. Typically, the angle range for the wrap angle between 3 ° and 80 °. The larger the wrap angle is, the higher the frictional engagement with the surface of the driven roller 210th

The wrap angle β defines the length of the contact zone 234 in which the web 216 makes contact with the surface of the roller 210. This contact zone 234 exerts a smoothing effect on the incoming web 216, thus reducing the effect of creasing of the web 216 upon rotation of the roller 210. The smoothing effect can be increased if the contact point of the counter-roller 218 with the web 216 in the running direction of the web 216 is at the end of the wrapping angle β.

The roller 210 has on its surface a friction lining, for example consisting of a closed-cell Pur material having a hardness of about 80 Sh-A hardness. The sprung counter rollers 218 cause a largely slip-free transmission of the driven roller 210 on the web 216. By setting the pressure forces of the counter rollers 218 on the driven roller 210, a denting or injury of the surface of the roller 210 is avoided and thus a constant surface speed of the web 216th ensured. The counter-rollers 218 have a coating of softer material than the roller 210. For example, the coating consists of foamed pure material having a hardness of about 50 Sh-A hardness.

FIG. 16 shows an example with a small wrap angle β. Even with such a wrap angle can still be achieved by rotating the rotary frame a positional shift of the web 216.

FIG. 17 shows an example in which the web 216 is fed from below. The axis of rotation 214 continues to be perpendicular to the conveyed away web 216, as can be seen from the examples a) and b). Examples c), d) and e) show web guide in plan view in example a) with different Twist angles α with respect to a normal position with 0 °.

FIG. 18 shows an example in which the rotation axis 214 is parallel to the transport direction of the conveyed away web 216. With a rotation about the rotation angle P12, a change in position of the web 216 in the direction of the axis 224 of the roller 210 likewise takes place. Examples a) and b) illustrate the arrangement with an axis of rotation 214 parallel to the transport direction of the web 216. Examples c), d) and e) show different deflections in the direction of the rotation angle P22 as seen in the direction of the rotation axis 214.

FIG. 19 shows a web guide device 240, which is arranged in the direction P10 of the web transport before the driven roller 210 shown in the preceding figures. The web guiding device 240 on the one hand serves for pre-setting a position of the web edge of the web 216 and on the other hand for establishing a predetermined web tension.

The web guide device 240 includes a guide sheet 242, such as a guide plate, in the form of a subcylinder jacket surface on which the web 216 slides. The guide blade 242 has flanges 244, 246 on each side of the web edge which guide the web 216 on both sides. The flanged wheels 244, 246 are adjustable in their distance from one another to the respective web width of the web 216.

In front of the guide blade 242 guide elements 248, 250, 252 are arranged, which can also wear flanged wheels, as shown for example in guide element 252 with flanged wheels 254, 256. This flange 254, 256 cause the withdrawn from a roll 258 web 216 already occupies a predetermined lateral position in the inlet region.

The guide elements 248, 250, 252 may be designed as a cylinder, over the respective lateral surface of the web 216 is guided by each predetermined wrap angle. The respective wrap angle can be adjusted by changing the position of the axes of the guide elements 248, 250, 252 relative to each other. This is important if the same web tension is required for different thicknesses of web material.

To further set the web tension defined, a braking device is provided which engages the guide sheet 242. For example, this braking device can be realized by a felt flap 260, which presses with a variable weight on the sliding over the guide sheet 242 track 216. Furthermore, facilities such as those in the patent application DE 44 01 906 same applicant for pre-centering and tensioning the web 216 are used.

FIG. 20 shows a web 216, which are provided with adhesive labels E. In such a web 216, which is used in practice, only the labels are to be printed in a printer or copier. This creates the problem that when hitting a label edge on the counter-roller 218 this is deflected by a stroke h, as in FIG. 19 is shown in dashed lines. The applied lifting work of the counter-roller 218 causes an abrupt torque change with concomitant load angle change on the drive motor 220 (see. FIG. 14 ). In operation, such an effect in a printer leads to an impairment in the printed image, especially when fine Grauraster be printed. The use of a soft covering for the counter-pressure roller 218, for example the use of foamed pure material, reduces this effect, since the lifting energy of the counter-roller 218 is absorbed by the elasticity of the lining.

In FIG. 21 is indicated that the stroke h is reduced when using a corresponding elastic coating.

FIG. 22 shows an arrangement of the web 216, in which the labels are arranged on the driven roller 210 side facing. Due to the wedging action of the web 216 on the label edge, a kind of run-on slope is formed, whereby the lifting work for the counter-roller 218 is not abruptly applied. The arrangement after FIG. 22 Of course, with the after FIG. 21 be combined.

FIG. 23 illustrates that the counter-rollers 218 can be pivoted away from the driven roller 210 together, whereby a sufficiently large gap SP for performing a dashed line 216 is released. In this way, the insertion of a new web 216 can be facilitated.

FIG. 24 shows another example. The driven roller 210 is stationary, ie its axis does not change. The counter roll device 270 includes a plurality of rollers 272 which urge the web 216 to the roller 210. The plurality of rollers 272 and the roller 210 are held by a rotating frame. Each roller 272 is pivotable about an axis of rotation 274 alike. By a rod 276 which acts on a lever end for each roller 272, the angle of rotation of the respective rotary roller 272 can be adjusted. Again, the web 216 has a tendency to be conveyed away in a tangential direction to the surface of the respective roller 272, whereby the position of the edge of the web 216 can be changed in the direction of the roll axis. The variants described further above, for example with regard to the linings for the driven roller 210 and the linings for the rollers 272 can also be used here.

There are many variants possible. The in FIG. 14 described rotating frame can be part of a control loop, for example. The actual position of the edge of the web 216 is determined by means of a sensor with respect to a desired position. Depending on the signal from the sensor, the frame is adjusted stepwise or continuously in its rotation angle P12 in such a way that a control deviation between the actual position and the desired position of the edge is reduced.

With respect to the embodiment according to FIG. 24 For example, all the counter-pressure rollers 272 are controlled simultaneously by means of the rod 276 and a drive. This drive can be part of a control loop. With the aid of a sensor, the actual position of the edge is determined with respect to a desired position. Depending on the signal from the sensor, the angle of rotation for each counter roller 272 is adjusted so that a control deviation between the actual position and the desired position of the edge is reduced or becomes zero.

The illustrated examples of the various aspects of the invention can be advantageously combined with each other, with other variants arise. So can the in the Figures 14 and 24 described rotating frame in the example of the FIGS. 1 and 7 be used. The regulation of the side edge of the railway after the FIGS. 7 to 13 can in the examples after the FIGS. 1 to 7 and FIGS. 14 to 24 be used.

Although preferred embodiments have been shown and described in detail in the drawings and foregoing description, this should be considered as illustrative and not restrictive of the invention. It should be understood that only the preferred embodiments are shown and described and all changes and modifications that are presently and in the future within the scope of the invention should be protected.

LIST OF REFERENCE NUMBERS

10

paper web

Z1, Z2, Z3

zones

11, 13

side edges

12

retraction device

14

roller

16

Backing roll

18

deflecting

20

inlet roller

22

rotating frame

S1, S2

Web tension sensors

24.26

roll

28

frame

30

Rotary axis of the frame

32

rotation arrow

S3, S4

sensors

34

Edge sensor

36

stabilizing roll

38

deflecting

40

drive roller

42, 44

transfer printing

46

fuser

S5, S6

sensors

48

off device

49, 50

roll

52

pivot point

54

axis of rotation

56

double arrow

58

second axis of rotation

60

rotation arrow

62

In stock

64

Screw-nut combination

68

Recordings

70, 72

brackets

F1, F2

personnel

74, 76

cables

80

control

82, 84

control signals

86

setpoints

88

display

W1, W2

stationary rollers

110

printing unit

112

fuser

114

casing

116

casing

118

train

120

Web-up area

122

Train pullback motor

124

web brake

126

second sensor

128

idler pulley

130

rotating frame

132

first sensor

134.136

guide rollers

138

web drive

140

upper transfer station

142

lower transfer station

144

character generator

146

Photoconductor belt

148

developer station

150

transfer tape

152

transfer printing

154

third sensor

156.158

fixation

160.162

fan

164

off device

170

adder

172

regulator

174

adder

176

adder

S1

Signal of the first sensor

S2

Signal of the second sensor

S3

Signal of the third sensor

S0

setpoint

e

deviation

R

control signal

SU

setpoint

VZ

Delay Time

210

driven roller

212

rotating frame

214

axis of rotation

216

train

218

against rolling

220

drive

222

transmission

P21

arrow

P22

arrow

226

electric drive

228

mother

230

spindle

α

angle of rotation

β

Wrap angle

234

contact zone

240

Web guiding device

242

leader sheet

244, 246

flanged wheels

248, 250, 252

guide elements

254, 256

flanged wheels

258

role

260

of felt

e

adhesive labels

270

Against roller device

272

roll

274

rotational axes

276

pole

Claims (28)

1. A device for guiding an endless web (10),
   in which the endless web (10) is guided in one direction of movement via a first roll (24) directly to an additional roll (26) with a predetermined wrap angle to each roll, the shafts (66) of said rolls lying parallel to one another in a plane and being held by a frame (28),
   the web (10) being fed to and led away from the rolls (24, 26) held by the frame (28) via a stationary first roll (W2) and an additional stationary roll (W1),
   the frame (28) being pivotable relative to the stationary rolls (W1, W2) about a first axis of rotation (30) essentially perpendicular to the plane, in order to modify the position of the edge (11, 13) of the web (10) in the direction of the roll shafts (66),
   and in which the frame (28) can be pivoted relative to the stationary rolls (W1, W2) about a second axis of rotation (58), the component of which running parallel to the direction of movement of the web (10) between the two rolls (24, 26).
2. The device according to claim 1, in which the frame (28) can be displaced in the second axis of rotation (58) with the aid of an adjustment device that can be actuated manually, electrically, hydraulically, and/or pneumatically.
3. The device according to one of the preceding claims 1 to 2, in which a screw-nut combination (64) is used for the displacement.
4. The device according to one of the preceding claims, in which along the web (10) there is situated at least one sensor (S1, S2, S3, S4, S5, S6) that acquires a sagging at one side of the web (10) and indicates it via a control device,
   and in which, dependent on the display, the second axis of rotation (58) is pivoted.
5. The device according to one of the preceding claims, in which along the web (10) there is situated at least one sensor (S1, S2, S3, S4, S5, S6) whose signal is dependent on the sagging of one side of the web,
   and in which the signal is supplied to a control circuit that pivots the frame (28) in the second axis of rotation (58) in such a way that the one-sided sagging of the web (10) is reduced or is controlled to the value zero.
6. The device according to claim 5, in which one sensor (S1, S2; S3, S4) each is situated in the vicinity of the frame (28) at both sides of the web (10).
7. The device according to one of the preceding claims, in which as a sensor (S1, S2) a force sensor is used that acquires the web tension.
8. The device according to claim 7, in which the sensor (S1, S2) acquires the force that is exerted at one side at the feed-in roll (20) via which the web (10) is fed into the frame (28).
9. The device according to one of the preceding claims, in which the distribution of the tension of the web (10) in the area between the two rolls (24, 26) of the frame (28) is acquired by sensors (S3, S4) as a one-sided sagging or as a wave.
10. The device according to one of the preceding claims, in which, seen in the direction of the web transport, a fixing station (46) that fixes a toner image is situated downstream of a transfer printing station.
11. The device according to claim 10, in which, seen in the direction of the web transport, downstream of the fixing station (46) there is situated a draw-off device (48) for the web (10) that can be pivoted in order to correct a one-sided sagging of the web (10).
12. The device according to one of the preceding claims 10 or 11, in which the web tension in the area of the fixing station (46) for fixing a toner image on the web (10) is acquired by at least one sensor (S5, S6), the pivoting of the draw-off device (48) taking place dependent on the signal of the sensor (S5, S6).
13. The device according to claim 12, in which the draw-off device (48) contains two rolls (49, 50) that can be pivoted about a further axis of rotation (52).
14. The device according to claim 13, in which the further axis of rotation (52) runs essentially perpendicular to the web (10).
15. The device according to claim 14, in which the sensors (S3, S4) on the rotating frame (22) as well as the sensors (S5, S6) in the area of the fixing station (46) monitor the web (10),
    and in which a control unit (80) pivots the rotating frame (22) about the second axis of rotation (58) dependent on the signals from the sensors (S3, S4),
    and in which the control unit (80) pivots the draw-off device (48) about the further axis of rotation (52) dependent on the signals from the sensors (S5, S6).
16. The device according to claim 14, in which the sensors (S1, S2) in the area of the draw-in roll (20) and the sensors (S5, S6) in the area of the fixing station (46) monitor the web (10),
    and in which a control unit (80) pivots the rotating frame (22) about the second axis of rotation (58) dependent on the signals from the sensors (S1, S2), and pivots the draw-off device (48) about the further axis of rotation (52) dependent on the signals from the sensors (S5, S6) .
17. The device according to claim 14, in which only the sensors (S1, S2) in the area of the draw-in roll (20) acquire the web (10),
    and in which a control unit (80) rotates the rotating frame (22) about the second axis of rotation (58) and rotates the draw-off device (48) about the further axis of rotation (52), dependent on the signals from the sensors (S1, S2).
18. The device according to one of the preceding claims, in which the endless web (10) is fashioned as a paper web without marginal perforation.
19. The device according to one of the preceding claims, characterized in that it is used in a printer or copier.
20. A device for guiding an endless web in a printer or copier,
    in which, after the application of a smudgeable toner image in a transfer printing station (38, 40), the endless web (10) is supplied to a fixing station (46) for the fixing of the toner images,
    in which after the fixing station (46), seen in the direction of transport of the web, there is situated a draw-off device (48) that draws off the web (10) from the transfer printing station in freely suspended fashion with a predetermined tensile force,
    in which the draw-off device (48) can be pivoted in order to correct a one-sided sagging of the web (10),
    in which the draw-off device (48) contains two rolls (49, 50) that can be pivoted about an axis of rotation (52),
    and in which the axis of rotation (52) runs essentially perpendicular to the web (10).
21. The device according to one of the preceding claims 11 to 20, in which the web tension in the area of the fixing station (46) is acquired by at least one sensor (S5, S6), the pivoting of the draw-off device (40) taking place dependent on the signal of the sensor (S5, S6).
22. The device according to one of the preceding claims 10 to 21, in which the fixing station (46) operates in contactless fashion, preferably by means of infrared radiation.
23. A method for guiding an endless web (10),
    in which the endless web (10) in one direction of movement is guided via a first roll (24) directly to an additional roll (26) with a predetermined angle of wrap to each roll, the shafts (26) of the rolls lying parallel to one another in a plane and being held by a frame (28),
    the web (10) being fed to and led away from the rolls (24, 26) held by the frame (28) via a stationary first roll (W2) and an additional stationary roll (W1),
    the frame (28) being pivoted relative to the stationary rolls (W1, W2) about a first axis of rotation (30) essentially perpendicular to the plane, in order to modify the position of the edge (11, 13) of the web (10) in the direction of the roll shafts (66),
    and in which the frame (28) is pivoted relative to the stationary rolls (W1, W2) about a second axis of rotation (58), the component of which running parallel to the direction of movement of the web (10) between the two rolls (24, 26).
24. The method according to claim 23, in which at least one sensor (S1, S2, S3, S4, S5, S6) is situated along the web (10), the signal of which is dependent on the sagging of one side of the web,
    and in which the signal is supplied to a control circuit that pivots the frame (28) in the second axis of rotation (58) in such a way that the one-sided sagging of the web (10) is reduced or is controlled to the value zero.
25. The method according to claim 23 or 24, in which, seen in the direction of the transport of the web, there is situated downstream of the fixing station (46) a draw-off device (48) for the web (10) that is pivoted in order to correct a one-sided sagging of the web (10).
26. A method for guiding an endless web in a printer or copier,
    in which after the application of a smudgeable toner image in a transfer printing station (38, 40), the endless web (10) is supplied to a fixing station (46) for the fixing of the toner images,
    in which, seen in direction of transport of the web, there is situated downstream of the fixing station (46) a draw-off device (40) that draws off the web (10) from the transfer printing station in freely suspended fashion with a predetermined tensile force,
    in which the draw-off device (48) is pivoted in order to correct a one-sided sagging of the web (10), wherein the draw-off device (48) contains two rolls that are pivoted about an axis of rotation (52) that runs essentially perpendicular to the web (10).
27. The method according to claim 26, in which the web tension in the area of the fixing station (46) is acquired by at least one sensor (S5, S6), the pivoting of the draw-off device (48) taking place dependent on the signal from the sensor (S5, S6).
28. The method according to one of the preceding claims 26 or 27, in which the fixing station (46) operates in contactless fashion, preferably by means of infrared radiation.

Images