EP1668425A1

EP1668425A1 - Method and device for controlling the circulation speed of an endless belt and arrangement for generation of a braking force on an endless belt

Info

Publication number: EP1668425A1
Application number: EP04764556A
Authority: EP
Inventors: Markus LÖBEL
Original assignee: Oce Printing Systems GmbH and Co KG
Current assignee: Canon Production Printing Germany GmbH and Co KG
Priority date: 2003-09-29
Filing date: 2004-08-27
Publication date: 2006-06-14
Anticipated expiration: 2024-08-27
Also published as: WO2005040936A1; DE502004007079D1; DE10345149A1; US20070189806A1; EP1668425B1; US7643775B2; ATE394709T1

Abstract

The endless band (17) passes over at least two rollers (1) and is driven by at least one of the rollers at a preset first circulation speed. A braking force acting directly on the band is generated, with which the band is braked to a second circulation speed. The endless band can be a photoconductor band or a transfer band. An independent claim is also included for an arrangement for controlling the circulation speed of an endless band.

Description

Method and device for controlling the rotational speed of an endless belt and arrangement for generating a braking force on an endless belt

The invention relates to a method and a device for controlling the rotational speed of an endless belt, in which an endless belt is guided over at least two rollers. The belt is driven at a preset first rotational speed by at least one of the rollers.

In electrophotographic printers and copiers, a printed image is electrophotographically printed on a photoconductor, e.g. an OPC tape (Organic Photo Conductor photoconductor) by using a character generator to generate a charge image on the photoconductor and then developing it with toner. The toner image is then transferred to a ribbon-shaped intermediate carrier with defined electrical properties. The intermediate carrier can e.g. be a transfer ribbon.

The toner image located on the intermediate carrier is then transferred directly to a carrier material, for example a paper web, at a transfer printing point, or the toner image located on the intermediate carrier is again fed to the transfer printing area between the photoconductor and the intermediate carrier in order to add a further, in particular differently colored, toner image over the one already on to print the toner image located on the intermediate carrier. This method of overprinting toner images is also referred to as collecting the toner images in a collecting mode. The second toner image can, for example, have a toner color different from the first toner image or can contain a special toner, in particular a machine-readable micro-toner. This enables a two-color print with a basic color and an additional color to be created. Furthermore, printers and copiers are known in which three or four differently colored toner images are printed one above the other in order to thereby obtain a printed image in full color. While the toner images are being collected, the intermediate carrier is pivoted away from the carrier material, so that there is no contact between the intermediate carrier and the carrier material during the collecting process. Only when all the toner images on the intermediate carrier have been printed one on top of the other, is a mechanical contact made between the intermediate carrier and the carrier material in order to transfer the complete collected toner image onto the carrier material. The mechanical contact is preferably produced at the point in time at which the front edge of the toner image located on the intermediate carrier has reached the transfer printing point for transfer printing of the toner image from the intermediate carrier onto the carrier material. A cleaning station is then pivoted onto the carrier element when the point at which the front edge of the transferred toner image has been on the intermediate carrier has reached the cleaning station.

This results in corresponding load states due to the different operating phases, i.e. Load states of the intermediate carrier, through which the rotational speed of the intermediate carrier is changed. The operating phases and the resulting load conditions are explained in detail below in the figure descriptions for FIGS. 1 to 14b.

The different load conditions result in a slip on the drive roller that occurs depending on the load condition. Due to the different slip on the drive roller, the circulation speed and the circulation time of the intermediate carrier change. These changes in the revolution speed or revolution time cause a shift in the position of a plurality of toner images transferred one after the other on the intermediate carrier to one another, and that Compression of individual toner images or parts of the toner images in the conveying direction of the intermediate image carrier.

From international patent application WO 98/39691 and US Pat. No. 6,246,856 a printing and copying device for performance-adapted monochrome and colored printing on one and both sides of a recording medium is known. Several differently colored toner images are generated on a photoconductor belt and then transferred to a transfer belt on which the toner images are collected before they are all transferred together on a paper web. The collection and transfer takes place in the start-stop mode of the paper web. In continuous monochrome printing, the toner images are continuously produced one after the other on the photoconductor and transferred to the transfer belt, the transfer belt transferring a toner image directly onto the paper web in continuous operation. The contents of the international patent application and US Pat. No. 6,246,856 are hereby incorporated by reference into the present description.

In the prior art, a large number of attempts have been made to avoid the position shift and the length variation of toner images of the same nominal length. An attempt was made to keep the load change when restricting the transfer belt to a paper web as small as possible by reducing the speed difference between the paper web and the transfer web. However, depending on the paper properties of the paper web, a minimum speed difference is required, as a result of which when changing the paper type of the paper web to be printed and in particular the paper width and the paper thickness, the paper speed or the speed difference between the transfer belt and the paper web must be reset. From the German patent DE 199 42 116 C2 an arrangement for reducing the load with an activated cleaning unit is known. The content of the patent step DE 199 42 116 C2 and the patents or patent applications cited therein are hereby incorporated by reference into the present description. The arrangement known from this document reduces the forces acting on the transfer belt, which are caused by the cleaning unit. However, a load change remains when the cleaning unit is activated, which leads to the disadvantages already described.

There have also been approaches in the prior art that shift the print image by adjusting the writing speed by the imaging unit, i. to be compensated for by the character generator or the laser exposure device, in that the subsequent position shift and / or compression or stretching of the toner image is already taken into account when generating the latent printed image.

Alternatively, proposed solutions are known in which the speed-influencing swiveling movements take place before or after the toner image generation or after the transfer printing of the toner image onto the carrier material. However, this significantly reduces the overall print speed of the printer.

The object of the invention is to provide a method and a device for controlling the rotational speed of an endless belt, in which a constant rotational speed of the belt is ensured even under several different load conditions.

This object is achieved for a method for controlling the circulating speed of an endless belt with the features of claim 1. Advantageous further developments are specified in the dependent claims. The method for controlling the circulating speed of an endless belt according to claim 1 ensures that the endless belt can be braked to a second circulating speed, which is particularly advantageous if the belt is braked by the method according to the invention in a phase with low load and the belt is not or only slightly braked during phases of operation with a load of components of the printer or copier on the endless belt.

The direct effect of the braking force on the endless belt prevents inaccuracies and time delays when generating a braking effect.

A second aspect of the invention relates to an arrangement for controlling the circulating speed of an endless belt. This arrangement contains an endless belt that is guided over at least two rollers. A drive unit drives the belt over at least one of the rollers at a preset first rotational speed. A braking unit applies a braking force directly into the belt, by means of which the belt is braked to a second rotational speed.

This arrangement ensures that the endless belt is brought to the second rotational speed simply by braking.

A third aspect of the invention relates to an arrangement for generating a braking force on an endless belt. An electrically conductive surface is arranged substantially parallel to the endless belt. To generate a braking force, a voltage against the ground potential is provided on the surface. This arrangement ensures that the braking force acts directly on the endless belt, and the belt is therefore braked directly and without any time delays.

For a better understanding of the present invention, reference is made to the preferred exemplary embodiments illustrated in the drawings, which are described using specific terminology. However, it should be pointed out that the scope of protection of the invention is not to be limited thereby, since such changes and further modifications to the devices and the methods shown, as well as such further applications of the invention, as shown therein, are common current or future specialist knowledge responsible specialist. The "Figures show exemplary embodiments of the invention, namely:

FIG. 1 shows a schematic structure of a printing unit for producing a single-color toner image on a carrier material;

FIG. 2 shows the printing unit according to FIG. 1, a plurality of toner images being shown which are generated on a photoconductor belt and in some cases have already been transferred to a transfer belt;

FIG. 3 shows the printing unit according to FIGS. 1 and 2, a part of the toner images already being printed on the carrier material;

Figure 4 is a printing unit similar to the printing unit of Figures 1 to 3, with the help of the printing unit FIG. 4 two-color printed images can be generated;

5 shows the printing unit according to FIG. 4, whereby in contrast to FIG. generating print images in a first color, print images in a second color;

6 shows the printing unit according to FIGS. 5 and 6, the printed image of a second color being re-printed onto the transfer belt via the printed image of a first color;

FIG. 7 shows the printing unit according to FIGS. 4 to 6, the transfer belt being pivoted onto the carrier material in order to transfer a two-tone toner image;

8 shows the printing unit according to FIGS. 4 to 7, the transfer belt having been pivoted onto a cleaning unit after the two-tone toner image has started to be transferred;

FIG. 9 shows the printing unit according to FIGS. 4 to 8, the transfer ribbon being pivoted away from the carrier material again after the two-tone toner image has been transferred;

FIG. 10 shows the printing unit according to FIGS. 1 to 3, the printing unit being shown in a first operating phase; FIG. 11 shows the printing unit according to FIG. 10, the transfer belt being pivoted onto the cleaning unit;

FIG. 12 shows the printing unit according to FIGS. 4 to 9, the transfer belt being pivoted to the paper web and to the cleaning unit in the operating phase shown and an additional pressure roller being pivoted to the paper web at the pressure point;

FIG. 13 shows a round trip time-time diagram in which round trip times of different operating phases are shown;

Figure 14a to

14d changes in position of printed images due to different round-trip times;

Figure 15 shows an arrangement for braking the transfer belt according to a first embodiment of the invention;

Figure 16 shows an arrangement for braking the transfer belt according to a second embodiment of the invention;

FIG. 17 shows an arrangement for braking the transfer belt according to a third embodiment of the invention;

Figure 18 shows an arrangement for braking the transfer belt according to a fourth embodiment of the invention; Figure 19 shows an arrangement for braking the transfer belt according to a fifth embodiment of the invention;

FIG. 20 force-time diagrams, in which the braking forces occurring due to the load conditions during the operating phases of the printer, the braking forces acting on the transfer belt by the device for braking and the total braking forces acting on the transfer belt are shown;

FIG. 21 shows an arrangement for controlling the rotational speed of the transfer belt;

FIG. 22 shows an arrangement for regulating the rotational speed of the transfer belt;

Figures 23a to

23e the change in the rotational speed of the transfer belt at constant drive speed and different braking voltages according to the first embodiment of the invention according to the device according to FIG. 15; and

FIG. 24 shows a round-trip time / round-trip voltage diagram in which the change in the round-trip time and the round-trip speed is shown as a function of the applied voltage.

In FIG. 1, a printing unit is shown in which a load is generated with the aid of a character generator (not shown) is generated on a photoconductor tape 22, which is then colored with the aid of a developer unit 28 with colored toner material, preferably black toner material. This creates a toner image on the photoconductor belt 22. The photoconductor belt 22 is guided over deflection rollers 24 and 25 and over a drive roller 26. Deflection rods 27a, 27b, 27c are also provided for guiding the photoconductor belt 22.

The drive roller 26 is connected to a drive motor, not shown, and drives the photoconductor belt 22 in the direction of the arrow 23. Furthermore, the printing unit contains a belt drive for guiding a transfer belt 17. The belt drive has a drive roller 1 - as well as guide and deflection rollers 1, 5a, 5b, 7, 9, 11, 13, 16. The rollers 5a, 5b and 16 are stationary in the The tape drive is arranged, the guide and deflection rollers 7, 9, 11, 13 being connected to one another via a lever arrangement with levers 6, 8, 10, 12, 15 such that a pivoting movement of the transfer belt 17 against a paper web 19 and a cleaning unit 21 takes place with the belt tension of the transfer belt 17 remaining the same. Furthermore, two drive units, not shown, are provided for executing the pivoting movements. The transfer belt 17 is driven in the direction of arrow 18 with the aid of the drive roller 1, which is connected to a drive unit (not shown).

When driving the transfer belt 17 with the aid of the drive roller 1, a load-dependent slip occurs on the drive roller 1. The different load conditions occur, in particular, by pivoting the transfer belt 17 onto the paper web 19, pivoting the transfer belt 17 against the cleaning unit 21, activating the cleaning coronron 21c and pivoting a pressure roller 20 in the transfer area between the transfer belt 17 and paper web 19. The rollers 5a and 5b are arranged directly next to a transfer printing point between the photoconductor belt 22 and the transfer belt 17 and continuously press the transfer belt 17 against the photoconductor belt 22 guided by the deflection roller 24 at the transfer printing point.

FIG. 2 shows the printing unit according to FIG. 1, wherein, as described in connection with FIG. 1, toner images are generated by coloring the charge images with toner material generated by a character generator by the developer unit 28 on the photoconductor belt 22, which are then transferred to the transfer belt 17 , In FIG. 2, two toner images 29c, 29d are arranged on the photoconductor belt 22, a first part of the toner image 29c having already been printed onto the transfer belt 17 and the developer unit 28 subsequently colors the latent printed image present as a charge image on the photoconductor belt 22 further to the toner image 29d , The toner images 29b and 29a previously colored by the developer unit 28 have already been transferred to the transfer belt 17 and are transported in the direction of the arrow 18 with the transfer belt 17 on its surface to a transfer location where they are then transferred from the transfer belt 17 to the paper web 19 are transmitted. In the operating phase shown in FIG. 2, the transfer belt 17 is pivoted onto a cleaning unit 21, so that the cleaning unit 21 is activated. The pivoting takes place with the aid of a drive unit, not shown, for moving the lever 8, as a result of which the levers 6 and 10 are also moved. The transfer belt 17 is pivoted onto the cleaning unit 21 by this lever movement. The belt tension of the transfer belt 17 always remains constant during the pivoting movement of the levers 6, 8, 10. The levers 6, 8, 10 involved in the pivoting movement are shown hatched in FIG. FIG. 3 shows the printing unit according to FIGS. 1 and 2, the transfer belt 17 being pivoted onto both the paper web 19 and the cleaning unit 21, so that the toner images 29b to 29f on the transfer belt 17 are transferred to the paper web 19. The paper web 19 is accelerated to the conveying speed shortly before the transfer belt 17 is pivoted and moved in the direction of the arrow 30. The swivel levers 6, 8, 10, 12 and 15 are guided with the aid of drive units in such a way that the transfer belt 17 contacts the paper web 19 in a transfer printing area between the rollers 11 and 20, with the transfer belt 17 swiveling onto the paper web 19 at the same time the pressure roller 20 is pivoted onto the paper web 19 from below. In FIG. 3 the levers 6, 8, 10, 12, 15 involved in the pivoting movements are shown with a hatched filling.

The swiveling lever mechanism is moved with the aid of a second drive unit such that the transfer belt 17 comes on in particular by guiding the roller 9. the cleaning unit 21 is pivoted after at least part 'of the toner image 29h first generated has been printed onto the paper web 19 and at least the point of the transfer belt 17 at which the front edge of the toner image 29h has been found reaches the cleaning area of the cleaning unit 21. The cleaning unit 21 contains an unloading corotron 21c, through the high-voltage corotron of which the toner residues located on the transfer belt are discharged.

Furthermore, the cleaning unit 21 contains a brush 21b, which brushes off the toner residues on the transfer belt 17, the direction of rotation of the cleaning brush 21b being opposite to the conveying direction of the transfer belt 17, so that a large brush effect and thus an efficient cleaning effect is achieved. The toner removed with the brush 21b Material is separated from it using a suitable device and fed back to the developer unit 28. Alternatively, the brush 21b can also be in the opposite direction, for example at a peripheral speed that is different from the rotational speed of the transfer belt 17. The removed toner material can alternatively be fed to a waste toner container.

FIG. 3 shows toner images 29a, 29b, 29c, 29d, 29e, 29f, 29g, 29h which have been colored one after the other with the aid of the developer unit 28, the toner image 29a being colored first and the toner image 29h being colored last. The toner image 29h has not yet been completely generated and is subsequently completed by coloring a charge image present on the ink conductor tape 22. The toner images 29a to 29h are as already described, stained successively with the aid of the developer unit 28 on the photoconductor belt 22, then from the latter to the - and subsequently transmitted ^'transfer belt 17 to the paper web 19th The generation of the toner images 29a to 29h is performed "continuously, 17, the photoconductor belt 22, the transfer belt 17 and the paper web 19 with substantially at the paper web 19 after the pivoting of the transfer ^tape" equal velocity are driven. To tighten the paper web 19, the drive speed of the transfer belt 17 is slightly higher than the drive speed of the paper web 19. As a result, the transfer belt 17 is braked substantially to the drive speed of the paper web 19 after pivoting onto the paper web 19. The pivoting of the paper web 19 thus causes a speed difference in the rotational speed of the transfer belt 17 due to the lower driving speed of the paper web. By braking the transfer belt 17 upon contact with the paper web 19 and the contact pressure of the pressure roller 20, a greater slip is generated on the drive roller 1 of the transfer belt drive. FIG. 4 shows a printing unit similar to the printing unit according to FIGS. 1 to 3, it being possible to use the printing unit according to FIG. 4 to produce a two-tone toner image on the paper web 19. The same elements have the same reference symbols. In Figure 4, four toner images 29a to 29d have been generated with the aid of the developer unit 28, the toner images being colored with black toner material. When the charge images generated by the character generator are colored with toner material, the developer unit 28 is activated and a developer unit 31 for developing toner images with red toner material is deactivated. In the operating phase shown in FIG. 4, the transfer belt 17 is pivoted away from the paper web 19 and pivoted onto the cleaning unit 21.

In Figure 5, the printing unit is shown in FIG 4, wherein the ^'' toner image 29d completely lereinheit using DER E twick- has been generated 28 and is almost completely transferred from the photoconductor belt 22 to the transfer belt 17th A further toner image 32a has subsequently been generated on the photoconductor belt 22 with the aid of the activated developer unit 31 with the developer unit 28 deactivated, the character generator having previously generated a corresponding charge image on the photoconductor belt 22. In the operating state shown in FIG. 5, only a first part of an entire toner image 32a is colored by the developer unit 31 with red toner material. The further printed image of the toner image 32a is already present as a charge image on the photoconductor belt 22 and is therefore present as a latent printed image, which is then colored with red toner material using the developer unit 31.

FIG. 6 shows the printing unit according to FIGS. 4 and 5, with the toner image 32a on the toner image 29a is printed, which is located on the transfer belt 17 and has been fed back to the transfer printing point between the photoconductor belt 22 and the transfer belt 17. The front edge of the toner image 29a coincides with the front edge of the toner image 32a, so that the toner images 29a and 32a are substantially congruent. In the operating state shown in FIG. 6, a further toner image 32b has been generated with the aid of the developer unit 31, the distance between the toner images 32a and 32b essentially being the distances between the toner images 29a and 29b; 29b and 29c; 29c and 29d corresponds. The printing unit according to FIG. 6 has thus generated a second red toner image 32a on the black toner image 29a.

FIG. 7 shows the printing unit according to FIGS. 4 to 6, a first part of the toner images 29a and 32a printed one above the other having been transferred to the paper web 19 by means of the levers 10, 12 and 15 after the transfer belt 17 has been swung open. Simultaneously with the pivoting of the conveyor belt 17 onto the paper web 19, the pressure roller 20 is pivoted from below onto the paper web 19. Before the two pivoting operations, the paper web 19 has been accelerated to the conveying speed, as described in connection with FIGS. 1 to 3 for the printing unit shown there.

Further toner images 32a, 32c, 32d were produced with the aid of the developer unit 31 in a red toner color and are essentially congruent in their outer dimensions with the toner images previously colored black with the aid of the developer unit 28. The toner image 32d is superimposed on the toner image 29d, the toner image 32c on the toner image 29c and the toner image 32d on the toner image 29d. This overlaying of the toner images is also referred to as collecting. The generation of the superimposed toner images thus takes place in the collection mode. The transfer belt 17 is still in the operating state shown in FIG has not been pivoted to the cleaning unit 21, since the position at which the front edge of the toner images 29a and 32a has not yet reached the cleaning area in the cleaning unit 21.

In FIG. 7, a further toner image 33a has been produced by ^" coloring a charge image with the aid of the developer unit 28 with black toner material on the photoconductor belt 22.

FIG. 8 shows the printing unit according to FIGS. 4 to 7, a further part of the toner images 29a and 32a having been transferred to the paper web 19. The point at which the front edge of the toner images 29a and 32a was located has reached the cleaning area of the cleaning unit 21, the pivot levers 6, 8 and 10 in this way at the latest when the transfer belt 17 arrives in the cleaning area of the cleaning unit 21 ^{'are moved} with the aid of a drive unit (not shown) such that the transfer belt 17 is pivoted onto the cleaning unit 21, the positions of the pivot levers 12 and 15 not being changed when the transfer belt 17 is pivoted onto the cleaning unit 21. Furthermore, both "when pivoting the "Transfer belt 17 to the paper web 19 and the belt tension of the transfer belt 17 does not change when the transfer belt 17 is pivoted onto the cleaning unit 21.

From WO 98/39691 and US Pat. No. 6,246,856, a printer for performance-adapted monochrome and color printing on one and both sides of a recording medium is known, wherein in this patent application or in this patent the pivoting of the transfer belt on and off the record carrier is described in detail. The content of patent application WO 98/39691 and the content of US patent 6,246,856 are hereby incorporated by reference into the present description. FIG. 9 shows the printing unit according to FIGS. 4 to 8, the entire toner images shown in FIG. 8, ie printed one above the other, being transferred to the paper web 19. Finally, the rear edge of the printed images 29d / 32d was transferred to the paper web 19. After the rear edges of these toner images 29d / 32d have been transferred to the paper web 19, the transfer belt 17 has been pivoted away from the paper web 19 by means of the drive device (not shown) by moving the levers 10, 12 and 15. Both the unloading corotron 21c and the cleaning brush 21b are still activated, the transfer belt 17 still being pivoted to the cleaning unit 21. The cleaning brush 21b, the cleaning corotron 21c remain activated at least until the point on the transfer belt -17 at which. the trailing edges of the toner images 29d / 32d have been on the transfer belt 17, have completely passed through the cleaning area of the cleaning unit 21. Furthermore, the toner image 33a already generated in the operating status or operating state shown in FIG. 8 has been at least partially transferred from the photoconductor belt 21 to the transfer belt 17. Another toner image 33b is generated with the aid of the developer unit 28 on the photoconductor belt 22. Both the toner image 33a and the toner image 33b have been colored with toner material in the color black.

FIG. 10 shows the printing unit according to FIGS. 1 to 3, whereby, in contrast to the operating states shown in FIGS. 1 to 3, the printing unit is shown in an operating state in which print images 29a to 29d are transported on the photoconductor belt 22 and the transfer belt 17 are, wherein the transfer belt 17 is pivoted both from the cleaning unit 21 and from the paper web 19. A load state of the transfer belt 17 is thus similar to the load state according to FIG. 1 in FIG. 10 shown, in contrast to the load state according to Figure 1, toner images 29a to 29d are generated or transported. As a result, there is no braking effect due to the contact of the transfer belt 17 with the cleaning unit 21 and no braking effect due to the contact of the transfer belt 17 with the paper web 19 on the transfer belt 17. The toner images 29a, 29b and 29c transmitted from the photoconductor belt 22 to the transfer belt 17 have thus been transmitted at a higher first rotational speed Vi of the transfer belt 17 according to FIG. In the load state according to FIG. 2, in which the transfer belt 17 is pivoted onto the cleaning unit 21, at least the toner image 29c is transferred from the photoconductor belt 22 to the transfer belt 17 at a second average rotational speed v _{2 of} the transfer belt 17. The toner image 29c in FIG. 3 is transferred to the paper web 19 and to the cleaning unit 21 at least this toner image 29c at a third low rotational speed v _{3 of} the transfer belt 17 when the transfer belt 17 is pivoted ".

The rotational speed of the photoconductor belt 22 is constant regardless of the rotational speed of the transfer belt 17. As a result, the toner images are not compressed at the first circulation speed V of the transfer belt 17 at the transfer location between the photoconductor belt 22 and the transfer belt 17, ie the length of the toner images on the photoconductor belt 22 corresponds to the subsequent length of the same toner images on the transfer belt 17. If the toner images are removed from the photoconductor belt 22 transferred to the transfer belt 17 at an average rotational speed v ₂ , the toner image is compressed by a first amount during the transfer and is compressed by a second amount when the toner image is transferred at the third low rotational speed v _{3 of} the transfer belt 17.

The toner images are compressed in the range between one thousandth and several millimeters. This works also on the length of the print image subsequently produced on the paper web 19 and its position on the paper web 19. In the load state according to FIG. 10, the transfer belt 17 rotates at a first high rotational speed vi, which is additionally identified in FIG. 10 with the reference symbol 34. Furthermore, the speed v of the photoconductor band 22 is additionally identified by the reference number 35.

FIG. 11 shows the printing unit according to FIG. 10, the print images 29a to 29d being generated in the same way as in FIG. 10. whereby the transfer belt 17 is pivoted at least when the toner image 29c is transferred from the photoconductor belt to the transfer belt 17 using the levers 6, 8 and 10 to the cleaning unit -21. By being swung cleaning unit 21 of the circulation ^'of the transfer belt 17 at the second intermediate rotational speed takes place v _2, wherein in Figure 11, the average peripheral speed v is in ₂ "in addition by the reference numeral 33rd

FIG. 12 shows the printing unit according to FIGS. 4 to 9, the transfer belt 17 being pivoted both to the cleaning unit 21 and to the paper web 19. Furthermore, the pressure roller 20 is pivoted from below onto the paper web 19. As a result, the transfer belt 17 rotates at a low third rotational speed v, which is additionally identified in FIG. 12 by reference number 35.

FIG. 13 shows a round-trip time-time diagram 40 as a screen printout of evaluation software for evaluating measured values determined on the printing unit according to one of the printing units shown in FIGS. 1 to 12. The current time is shown on the abscissa and the orbital time of a belt revolution of the transfer belt 17 is shown on the ordinate. In the slide 40, the rotational speeds vi, v ₂ and v _{3 of} the transfer belt 17 have been determined during the operating states shown in FIGS. 10 to 12. During the operating states 41a and 41b, the transfer belt 17 has neither mechanical contact with the cleaning unit 21 nor mechanical contact with the paper web 19. In these operating states, the transfer belt 17 has a round trip time of 1788.51 ms, which corresponds to the round trip speed i. During the operating state 42, the transfer belt 17 has mechanical contact to the activated cleaning unit 21, but no mechanical contact to the paper web 19. During the operating state 42, the transfer belt 17 has a round trip time of 1788.58 ms, which corresponds to a speed v ₂ .

During the operating state 43, the transfer belt 17 has both mechanical contact with the cleaning unit 21 and mechanical contact with the paper web 19. During the operating state 43, the transfer belt 17 has a round trip time of 1788.67 ms and thus a speed v ₃ . As a result, the rotational speed of the transfer belt 17 varies between the speeds vi to v ₃ . The rotational speed of the photoconductor belt 22 always remains constant during the operating phases 41a, 4b, 42 and -43. The orbital period of the transfer belt 17 results from the quotient of the length of the transfer belt 17 and the rotational speed of the transfer belt 17.

The relative speed deviation in the printing units according to FIGS. 1 to 12 is less than 2/1000 of the nominal rotational speed. However, in practice, especially in two and multi-color printing, it has visible effects. With the help of the printing units according to FIGS. 1 to 12, one or more pages with a total length of up to 1650 mm can be produced in an exemplary constructive embodiment of these printing units. After reducing the load-related Running speed of the transfer belt 17 after the transfer printing of a first toner image before the transfer printing of a second toner image by relatively 1/1000 of the transfer speed, the second toner image transferred from the photoconductor belt 22 to the transfer belt 17 is compressed by 1 ° a during this transfer relative to the first toner image, so that in ^"congruent top of both toner images the side end of the second toner image ends earlier than the side end of the first toner image.

With a writing length of the first color separation of 1650 mm, i.e. in the case of a toner image with a length of 1650 mm, in a first toner color, and when the second toner image subsequent to this first "toner image" is compressed in a second color, the second toner image is 1.65 mm shorter than the first toner image ( 1 V. of 1650 mm writing length of the first round).

In the same way, a second toner image transmitted at ^" a second revolution speed which is higher than a first revolution speed is stretched in relation to the first transmitted toner image. The relative speed deviation results from the quotient of the 'speed vxi at which the first" toner image is transmitted and the speed vx ₂ at which the second toner image is transferred, the quotient 1 being subtracted from this quotient. The absolute length error d1 results from the multiplication of the write length possible on the transfer belt 17 and the relative speed deviation.

In the present exemplary embodiment, the product of 1650 mm x 0.01 = 1.65 mm is thus obtained for calculating the length error, with a positive sign for a speed increase and a negative sign for the length error for a speed reduction. The human eye recognizes a line set with several printed images of different colors printed on top of each other very clearly and finds this disturbing, whereby this offset is generally referred to in printing technology as a color fringe. At the same time, an offset of 2/100 mm is clearly recognizable and is perceived as annoying. This means that with a possible length of a printed image of 1650 mm one on top of the other, the speed change may be a maximum of 0.012 SO, this value being calculated as follows:

Permissible speed change = 0.020 mm: 1650 mm x 1000 V. = 0.012 V.

FIGS. 14a to 14d show the effects of the upsetting of the printed images at the transfer printing location between the photoconductor belt 22 and the transfer belt 17 on the basis of schematically illustrated printed pages 48a to 48d. FIG. 14a shows five printed images of printed pages that are generated one after the other and transferred to the transfer belt 17, which are then reprinted onto an endless paper web 45. In contrast to this, the second color printout, which is labeled 48b in FIG. 14b, was transferred to the transfer belt 17 after the "pivoting" of the cleaning unit 21 at a rotational speed v of the transfer belt 17, the printed pages shown in FIG. 14b at least in the outer contours 14a, but the length of the printed pages is different due to the different rotational speeds vi, v _{2 of} the transfer belt 17, ie the difference between the speeds vi and v _2. The second toner image according to FIG 14a produces a different second toner color After the transfer belt 17 has pivoted onto the paper web 19, 45, the transfer belt 17 has an even lower rotational speed v ₃ . Subsequently, the transfer belt 17 is pivoted away both from the paper web 45 and from the cleaning unit 21, so that the transfer belt 17 again has a rotational speed vi. The print images generated thereafter are then transferred again from the photoconductor belt 22 to the transfer belt 17 without being compressed. The change in the total length of the five successive printed pages of 1650 mm when the speed of rotation of the transfer belt 17 changes from the speed of rotation vi to the speed of rotation v ₂ is indicated by the arrow 49a, the offset when the speed of rotation vi changes to the speed of rotation v ₃ is -with marked with arrow 49b and the offset when the rotational speed v changes to the rotational speed vi is marked with the arrow 49c.

With the help of the dimensions 46 the physical length of a page on the paper web 45 is indicated and with the ^" dimensions 47a to 47d the physical length of the toner image transferred to the transfer belt 17 is indicated, which after collecting the toner images is transferred to the transfer belt 17 onto the paper web 45. The physical side lengths are each indicated in FIGS. 14a to 14d ^" by vertical dashed lines.

The dash-dot lines drawn in between the printed images of FIGS. 14a and 14b illustrate the offset of the toner images produced or re-printed at the rotational speed vi in relation to the toner images produced or re-printed at the speed v ₂ , with the increasing inclination the initially vertical semicolon line at subsequent print image beginnings and print image ends shows the offset between the individual print images. FIG. 14b also shows that the third printed image is already printed on the paper web 45 in front of the physical page edge, which means that in a subsequent cutting process part of the toner image of this printed page is cut off. In the case of the fourth and fifth printed pages printed subsequently, larger parts of the printed page are then cut off, parts of the subsequent printed page being contained on the previous printed page after being cut.

In the solution of the problem according to the invention, the individual influences which lead to a speed reduction of the transfer belt 17 from the rotational speed vi to the rotational speed v ₃ are not avoided by complex measures as in the prior art, but the transfer belt 17 is also avoided under load conditions with higher rotational speeds v _x and v ₂ braked to speed v ₃ or- braked to a lower speed than speed v ₃ during all load conditions. ' ...

^"The rotational speed of the Trans-ferbands 17 are shown in Figures 15 specified to 22 Vorrichtungen- for reducing. In this case these devices is DIE finding that connected to a voltage source conductive surfaces on which a ^band-shaped" hereinafter material "insbesondere- an endless belt is passed, exerts a braking force on the belt due to the electrostatics generated and thus has a braking effect on the belt This knowledge is used in the devices according to FIGS. 15 to 22 to implement a braking arrangement by means of which the circulating speed of the transfer belt 17. The braking force of the brake arrangement is preferably changed depending on the load conditions, so that a constant rotational speed of the transfer belt 17 is generated in all load conditions.

In FIGS. 15 to 19 and 21 and 22, printing units are similar to the printing units according to FIGS. 1 to 12 shown. The same elements have the same reference symbols. Arranged on the inside of the transfer belt 17 is a rounded metal plate over which the transfer belt 17 is guided when the transfer belt 17 is driven by means of the drive roller 1. With the aid of a high-voltage source 56 with adjustable voltage, the metal plate 55 is supplied with a high voltage that can be set to the ground potential of the printer. Due to the high voltage, a braking force 58 is generated in the transfer belt 17, which acts directly on the transfer belt 17, whereby the transfer belt 17 is braked.

Furthermore, a diagram 57 is shown in FIG. 15, in which a graph shown with the aid of a dotted line shows the voltage curve of the high voltage and with a graph shown with a solid line the braking force generated by the high voltage with which the transfer belt 17 is braked. The course of the high voltage over time is controlled as a function of the different load states already described in such a way that a substantially constant rotational speed of the transfer belt 17 is brought about. In FIG. 15, the transfer belt 17 is pivoted away both from the paper web 19 and from the cleaning unit 21, so that the transfer belt 17 is braked to a constant, low rotational speed v ₄ with the maximum braking force required.

In contrast to FIG. 15, a high-voltage source with a constant high voltage is provided in FIG. 16, the high-voltage source 60 of FIG. 16 supplying the high voltage to the metal plate 55 in the form of voltage pulses of different pulse widths or pulse widths. Such a voltage is also referred to as a pulsed voltage. If a larger braking force is required, the pulse widths are increased and the pauses between the individual pulses are reduced. Conversely, a lower one If the braking effect is required, the pulse width of the individual pulses is reduced and the pauses between the pulses are increased. This dependency of the braking force on the pulse width is also shown in diagram 61, the voltage pulses being represented by hatched areas and the resulting braking force using a graph shown with a solid line.

In contrast to FIGS. 15 and 16, the printing unit shown in FIG. 17 does not have a metal plate 55, but rather a plurality of strip-shaped metal plates 65a to 65d which are arranged next to one another and insulated from one another in the conveying direction of the transfer belt 17, each of which is optionally available via a switch 66a to 66d a constant high voltage generated by a high voltage source 67 ^• is supplied. As a result, the area subjected to the high voltage is simply changed with the aid of the switches 66a to .66d, the braking force being dependent on the area which is effectively subjected to high voltage. The dependence of the braking force on the effective area is likewise in the force -Time diagram 68 shown, the metal plate 65a forming the surface segment AI, the metal plate 65b the surface segment A2, the metal plate 65c -the surface segment A3 and the metal plate 65d forming the surface segment A4, which then changes depending on the surface of the individual elements the transfer belt 17 acting total braking force, as shown in the diagram 68th using the footnotes of the surface segments that supplies the high-voltage surface segments are indicated. Thus, applied at the surface segment A _34, the metal plates 65c and 65d with high voltage by closing the switches 66c and 66d.

FIG. 18 shows the arrangement for braking the transfer belt 17 similar to the arrangement according to FIG. 17, with no high voltage of the high voltage source 67 being applied in a state in which the metal plates 65a to 65d leads but is supplied via a circuit arrangement ground potential. Floating potentials of this metal plate 65a to 65d are thereby avoided. The braking effect of this arrangement essentially corresponds to the braking effect of the arrangement according to FIG. 17, as is also shown in diagram 68.

FIG. 19 shows an arrangement for generating a braking force which acts directly on the transfer belt 17. The arrangement of the metal plates 65a to 65d essentially corresponds to the arrangement according to FIGS. 17 and 18. Via the switches 66a to 66d, which are implemented as changeover switches, the individual metal plates 65a to 65d can optionally be supplied with a first high voltage generated by a high voltage source 67 or a second high voltage generated by a high voltage source 71. As a result, a potential difference which differs from the ground potential can be generated between the individual metal plates 65a to 65d, in particular one of the high-voltage sources 67 and 71 being able to generate a high voltage which is negative to the ground potential. In the same way as shown in FIGS. 17 and 18, a braking force is generated by supplying the high voltage source 67 to the individual metal plates 65a to 65d, the area-dependent braking force being shown in diagram 68, which is shown in diagrams 68 according to FIGS 18 essentially coincides.

20 shows three diagrams 75, 76 and 77, diagram 75 showing the braking forces acting on the transfer belt 17 due to the different load conditions and diagram 76 showing the braking force generated by one of the braking devices according to FIGS Time is shown. FIG. 17 also shows a diagram 77 in which the sum of the braking forces from the diagrams 75 and 76 is shown, with the brake arrangement controlled as a function of the load. ne constant resulting braking force 78 is generated. In diagram 75, the braking force generated by the cleaning unit 21 is identified with F _Re ι, the braking force resulting from the pivoting of the transfer belt 17 onto the paper web 19 with Fp _a pi _er , the pivoting transfer band 17 against the paper web 19 and simultaneous pivoting of the transfer belt 17 to the cleaning unit 21 generated braking force with F _Re i _{+ ap} . Thus, the resulting braking force 78 can be kept constant over the entire time period, ie during the different operating phases with the different load conditions, as a result of the brake arrangements shown, as a result of which the transfer belt 17 has a constant rotational speed. "The different lengths of the toner images are thus effectively avoided. Toner images are produced with an exact preset length. Even with multi-color printing, exactly congruent toner images can be produced, thereby avoiding a color image border.

FIG. 21 shows a brake arrangement according to FIGS. 15 and 16, "the metal plate 5.5, in contrast to FIGS. 15 and 16, being supplied with a high voltage generated at a high voltage source 80. The high voltage source 80 can output an adjustable, variable high voltage, the level of the high voltage output being adjustable by means of a microprocessor 81 connected to a control input of the high voltage source 80.

The microprocessor 81 also controls drive motors 83a and 83b for executing the pivoting movements of the transfer belt 17 to the cleaning unit 21 and to the paper web 19 with the aid of the lever mechanism of the levers 6, 8, 10, 12, 15. The outputs of the microprocessor 81 for controlling the drive motors 83a and 83b are connected to power converters 82a, 82b which convert the control signals of the microprocessor 81 into motor control signals for driving the motors 83a and convert 83b, with motors 83a and 83b preferably being stepper motors. The motor 83a pivots the lever 6 and the motor 83b pivots the lever 10. As a result, the same microprocessor 81 controls the high voltage generating the braking effect and the swiveling movement of the transfer belt 17. The load changes generated by the swiveling movements can thus be very easily taken into account when determining the high voltage to be set and the braking force resulting therefrom, at the same time or, if necessary, before this time , for which a change in load occurs, a corresponding change in the braking force caused by the metal plate 55 - is generated in order to ensure the constant braking force 78 shown in FIG.

FIG. 22 shows the brake arrangement according to FIG. 21, the high-voltage source 80 being controlled by a microprocessor 84 to which a setpoint 86 of the speed of the transfer belt 17 is supplied and with the aid of a sensor 85 for detection. an actual value of the circulating speed is supplied to the circulating speed of the transfer belt 17. As an alternative to the speed sensor 85, the circulation time of the transfer belt 17 can also be detected with the aid of a suitable sensor arrangement, from which the circulation speed is then simply determined with the aid of the belt length of the endless belt. The microprocessor 84 carries out an actual value / setpoint comparison and, depending on the control deviation, generates an actuating signal that the microprocessor 84 supplies to the high-voltage source 80. The high voltage source 80 thus serves as an actuator of the control loop.

FIGS. 23a to 23e each show the round trip times of the transfer belt 17 as a function of the set DC voltage. The effective area of the metal plate 55 is 545 cm ² , the circulating speed vi at a high voltage of 0 kV is only 992 mm / s. The average round trip time is shown in FIGS. 23a to 23e in each case with the aid of a dash-dot line. As already mentioned in FIG. 23a, no high voltage is applied to the metal plate 55, but there is a ground potential or ^" a potential corresponding to the ground potential. The average orbital circulation time is 1790.94 ms. FIG. 23b shows a diagram in which the Orbital period of the transfer belt 17 occurs when a high voltage of 0.4 kV is applied to the metal plate 55. The average orbital period of the transfer belt 17 is also 1790.94 ms.

FIG. 23c shows the round trip time of the transfer belt 17 when the metal plate 55 is subjected to a high voltage of 0.80 kV. The round trip time of the transfer belt 17 is on average 1791.09 ms ^" . FIG. 23d shows the round trip time of the transfer belt 17 when a voltage of 1.2 kV is applied to the metal plate -55. The average round trip time is 1791.21 ms When a voltage of 1.6 kV is applied to the metal plate 55, the average round trip time of the transfer band 17 is 1791.35 ms, as shown in FIG. 23e.

FIG. 24 shows a round trip time / round speed voltage diagram, in which the change in the absolute round trip time and the change in the round trip time is shown as a function of the change in the voltage supplied. The graph shown with a dashed line indicates the change in the absolute round trip time and the graph shown with a solid line shows the change in the round trip time with increasing voltage. In the exemplary embodiments, the metal plate 55 or the metal plates 65a to 65d is arranged on the inside of the transfer belt 17. The braking effect on the transfer belt 17 may be due to the fact that an electrical field is generated between the metal plate 55 or the metal plates 65a to 65d and the components of the printer which have a potential different from the potential of the metal plate 55, 65a to 65d that the transfer belt 17 is passed through. The metal plate 55, 65a to 65d is thus a capacitor plate. The electric field causes a temporary shift of charges in the transfer belt 17. The shift results in an accumulation of charges opposed to the charge of the capacitor plate in the transfer belt 17 to the metal plate 55, 65a to 65d. As a result, the charges in the transfer belt 17 are attracted by the charge on the capacitor plate 55, 65a to 65 with a force in accordance with Coulomb's law. "The transfer belt 17- is pulled towards or against the metal plate 55, 65a to 65d (ie capacitor plate) by this force. pulled, whereby a contact between the metal plate -55, 6-5a to 65d and the transfer belt 17, depending on the size of this attractive force, generates a frictional force between the metal plate 55, 65a to 65d and the transfer belt 17, which reduces the conveying speed. As a result, a braking force is generated independently of the rollers of the tape drive, which acts directly on the transfer belt 17. Furthermore, on the side of the transfer belt 17 opposite the metal plate 55, 65a to 65d, a further metal plate can be arranged essentially parallel to the metal plate 55, 65a to 65d, preferably at a preset distance from the transfer belt. The further metal plate then has a potential different from the potential of the metal plate 55, 65a to 65d, preferably ground potential, for generating the braking force. In other exemplary embodiments, the metal plate 55, 65a to 65d can also be arranged on the outside of the transfer belt 17 at a distance from the transfer belt 17, so that a toner image 29 on the transfer belt 17 is not damaged by the metal plates 55, 65a to 65d. As an alternative to a direct voltage, the high voltage sources 56, 60, 67, 71 can also generate an alternating voltage with which the plates 55, 65a to 65d are acted upon. The braking force generated by the supply of the high voltage acts directly and without a time delay on the transfer belt 17. This enables a very exact and precise control of the braking force. The metal plates 65a to 65d, 55 preferably extend over the entire width of the transfer belt 17. Due to the brake arrangements according to the invention, the transfer belt 17 and the plates 55, 65a to 65d are subject to very little wear.

As an alternative to the embodiments shown, the surface which generates the braking force can also be subdivided transversely to the transfer belt 17 into segments which can be acted upon individually or in groups with high voltage of the same voltage level or different voltage levels. The metal plates 55, 65a to 65d can be simple metal plates, in particular metal plates which contain a stainless steel alloy, copper or a copper alloy or which contain an aluminum alloy or aluminum. Furthermore, the plates can be subjected to a surface treatment or provided with a coating. Alternatively, electrically conductive plastics can also be used as plate 55. The plates 55 are preferably provided with a smooth surface or with a suitable surface structure. Further variations of the control, for example the detection of the actual value of the circulation speed with the help of the circulation time, of a setpoint value control controlled by a further process are possible in order to implement applications according to the invention. The invention Brake arrangement was provided in the exemplary embodiments shown for braking the transfer belt 17. However, it is also possible to use such a brake arrangement for braking the photoconductor band 22 or another band-shaped carrier material, the endless carrier material not necessarily being an endless rotating one. Band must be. Rather, the band 17 to be braked can also be a paper web or single sheets with a relatively long length.

Although preferred exemplary embodiments of the invention have been shown and described in detail in the drawings and in the preceding description, they should only be regarded as purely exemplary and not restrictive of the invention. It should be noted that only the preferred embodiments are shown ^'and described, and all variations and modifications that presently and in the future lie within the scope of the "invention should be protected.

reference numeral

I, 26 drive roller 5a, 5b, 7, 9,

II, 13, 16, 24, 25 deflecting roller 27a, 27b, 27c deflecting rod 6, 8, 10, 12, 15 swivel lever 17 transfer belt 18, 23, 30 directional arrows

19 paper web

20 pressure roller

21 Cleaning unit 21b cleaning brush. 21c cleaning corotron

22 "Eotoconductor tape ^■ 28, 31 developer unit 29a to 29h, - ^■

32a to 32f,

33a, 33b toner images

33, 34, 35 orbital speeds

40, 57, 61, 68 diagrams

41a, 41b, 42, 43 operating phases

45 paper web

46 Dimensioning physical page length 47a to 47d Dimensioning actual print page length 48a to 48d print image

55, 65a to

65d metal plate

56, 60, 67, 71, 80 voltage sources 66a to 66d switches

70 Ground potential of the printer

81 microprocessor

82a, 82b motor control unit

83a, 83b stepper motors / servomotors

84 microprocessor 85 orbital speed sensor

86 setpoint adjuster

78 resulting braking force

Claims

Expectations

1. A method for controlling the circulating speed of an endless belt, in which an endless belt (17) is guided over at least two rollers (1, 11), the belt (17) having a preset first rotational speed (vi) through at least one of the rollers (1) is driven, and in which a braking force acting directly on the endless belt (17) is generated, by means of which the endless belt (17) is braked to a second rotational speed (v ₃ ).

2. The method according to claim 1, characterized in that the endless belt is a photoconductor belt (22) or a transfer belt. (17) is.

3. The method according to any one of the preceding claims, characterized in that different loading conditions act on the endless belt (17) in successive operating phases during a printing or copying process, by means of which the belt (17) is braked to different extents, whereby in particular a slip is generated on the drive roller (1), and the braking force is controlled in such a way that an essentially constant slip is generated on the drive roller (1) at least in the operating phases.

4. The method according to claim 3, characterized in that the operating phases in particular by pivoting and pivoting the endless belt (17) to a carrier material (19), the activation of a cleaning device (21) and / or the activation of loading devices (21c).

5. The method according to any one of the preceding claims, characterized in that the resulting circulation speed (v ₃ ) is the second circulation speed (v ₃ ), the second circulation speed (v ₃ ) being constant in all operating phases.

6. The method according to any one of the preceding claims, characterized in that the endless belt (17) is guided past an electrically conductive surface (55, 65a to 65d) oriented essentially parallel to the endless belt (17) and that the surface is supplied with a voltage becomes.

7. The method according to claim 6, characterized in that the applied voltage is a potential difference compared to a general ground potential.

8. The method according to any one of the preceding claims, characterized in that the surface of at least one roller (1) has ground potential.

9. The method according to any one of the preceding claims, characterized in that the endless belt contains at least one high-resistance conductive layer.

10. The method according to any one of claims 6 to 9, characterized in that the voltage has a value in the range between 200 and 3000 volts, preferably has a value in the range between 400 and 1200 volts.

11. The method according to any one of the preceding claims, characterized in that the braking force with the help a control loop for regulating the circulation speed is set.

12. The method according to any one of the preceding claims, characterized in that the braking force is controlled with the aid of the level of the applied voltage.

13. The method according to any one of the preceding claims, characterized in that the braking force is set using a pulsed voltage according to the principle of pulse width modulation.

14. The method according to any one of the preceding claims, characterized in that the braking force is controlled by changing the effective area applied with the voltage.

15. The method according to any one of the preceding claims, characterized in that a plurality of surfaces (65a to 65d) are provided which are arranged substantially parallel to the belt (17) and which are optionally acted upon by a potential different from a ground potential.

16. The method according to any one of the preceding claims, characterized in that the surfaces are arranged on the inside of the endless belt (17).

17. The method according to any one of the preceding claims, characterized in that the braking force is controlled as a function of the load on the endless belt (17) caused by operating conditions, the braking force being controlled as a function of control times.

18. Arrangement for controlling the circulating speed of an endless belt, with an endless belt (17) which is guided over at least two rollers (1, 11), with a drive unit which drives the belt (17) at a preset first rotational speed (vi) through at least one of the rollers (1), and with a braking unit that generates a braking force that acts directly on the belt, by means of which the endless belt (17) is braked to a second rotational speed (v ₃ ).

19. Arrangement for generating a braking force on an endless belt, in which an electrically conductive surface (55) is arranged essentially parallel to the endless belt (17), -. and in which the surface (55) for generating the braking force is applied to the surface.

20. The arrangement according to claim 19, characterized in that the endless belt (17) is guided past the surface (55) in the range between zero and five millimeters.

21. The arrangement according to claim 18 or 19, characterized in that the surface has substantially the same width as the endless belt.

22. The arrangement according to claim 19, 20 or 21, characterized in that the surface is a metallic surface (55) or a surface formed from electrically conductive plastic.