EP0857322B1 - Method of operating an electrographic printer using different form lengths - Google Patents

Description

The invention relates to a method for operating a electrographic printer, in which a first and a second Web section of a web of an endless carrier material which can be folded in sheets with the specified form length at the Transfer location of an intermediate image carrier passed and can be printed at the same time.

The invention is concerned with a further development of a electrographic printing device for printing on band-shaped Recording media of different bandwidth WO 94/27193. The printing device described there has an electrographic intermediate carrier, for example a photoconductor drum, with a usable width accordingly the double width format of a standard form according to A4. The other units are also like that Fuser, developer station, cleaning station etc. designed for this usable width.

With this known printing device there are different operating modes possible. So in so-called simplex operation a recording medium with up to twice the width of a A4 sheets can be printed in conventional form. In one Parallel simplex operation can be arranged side by side narrow record carriers, e.g. with a width according to DIN A4, juxtaposed by the printing device led and printed.

In another operating mode, single-color duplex operation, becomes the path of the record carrier during transport turned by the printing device, so that two web sections result: The first line section is the Front of the web of the transfer location of a transfer station opposite, while in a second section of the track the back printed on the web at the same transfer location at the same time becomes. By using different colored color particles in different developer units of the printing unit two-color duplex operation is also possible.

In another operating mode, the two-tone simplex mode, becomes the web during transport in the printing facility offset in parallel by at least one track width, and the offset Path sections are put together in juxtaposition passed the transfer location. The first time you walk by The web at the transfer location becomes picture and text elements printed with a first color; on the second pass the web with offset becomes picture and text elements printed with the second color.

When printing on a single web, the parallel in the printer offset or offset in parallel and additionally turned Transfer point of the printing unit fed again and printed is to ensure that when printing at the same time the adjacent track sections of the track on the Transfer location the print locations on the web in a fixed predetermined Are related to each other. This firm relationship must be observed during the entire printing process, otherwise there is an undesirable shift in the printed image.

When using a continuous carrier sheet folded in sheets, which is also known as fan-fold carrier material the form length is in the transport direction through the Distance between two successive folds defined. The form lengths are worldwide in inches or fractions thereof defined - figures in metric units are unusual. in the the following are therefore, as in the field of printing technology common practice, form lengths are given in inches; on inch has a length of 25.4 mm. In practice, e.g. Form lengths from 12 inch, 12 1/2 inch, 12 1/6 inch, 12 2/6 inch etc. before.

In order to be able to reliably transport the web of the endless carrier material which can be folded in sheets, it contains transport holes at its edges which are at a distance of 3/6 inch from one another. Transport spikes of a transport device arranged near the photoconductor reach into these transport holes. These transport spikes are also 3/6 inch apart. The folds of the web are arranged between the transport holes, which reduces the risk of a sheet being torn out. The fold is preferably arranged centrally between two transport holes. If the web has a form length that is an integral multiple of 1/2 inch, all the folds are in the middle between two transport holes. However, if a form length is used that is not an integral multiple of 1/2 inch, the fold at the beginning of a sheet may still be halfway between two transport holes, but the fold at the end of the sheet has an off-center position. For form lengths F _L1 = (kx 1/2 + 1/6) inch or F _L2 = (kx 1/2 + 2/6) inch, with k a natural integer, two folds, the one, follow a centrally arranged fold have an off-center position between two transport holes. Such form lengths F _L1 and F _L2 are called eccentric form _lengths below.

The two web sections lying next to one another in the printer are guided past the transfer location of the photoconductor using a transport device. In the case of webs with off-center form lengths F _L1 or F _{L2 it} can now happen that two folds come to lie side by side, the position of which is different from one another between the transport holes. The folds of the adjacent web sections then do not align, with the result that sheets of the two web sections have different starting positions when viewed in the transport direction. In order for the correct print image to be reprinted sheet by sheet at the transfer point common to both web sections, measures must be taken to prevent an undesired shift in the print image.

It is an object of the invention to provide a method for operating to specify an electrographic printer, which also at eccentric form lengths accurate sheet printing without Print offset is possible.

This task is accomplished through process steps according to the patent claims 1, 5 and 10 solved. Advantageous further training the invention are specified in the dependent claims.

According to a first aspect of the invention, the length L of the web is influenced from transfer location to transfer location to achieve the object. This length L is set in such a way that the integer residual value R = 0 when the ouotient n1 / 3 or n2 / 3 is formed, where nl or n2 are rounded-off integer numbers from L / F _L1 or L / F _L2 . As mentioned, the off-center form lengths F _L1 and F _{L2 are defined} in inch sizes: F L1 = (kx 1/2 + 1/6) inch and F L2 = (kx 1/2 + 2/6) inch, with k a natural integer.

These measures ensure that the folds of the side by side Path sections are aligned so that when transfer printing at the transfer printing point the beginning of the sheet Sheets of both web sections can be printed simultaneously can. The printed images can therefore be printed on the page Sheet foldable in duplex mode or in two-color Simplex operation can be transmitted.

In order to be able to set the web length in accordance with the relationships mentioned, the web runs through a web storage device during its transport from the transfer printing location to the transfer printing location, which is preferably preset to a minimum value L _DSMIN . If the number of sheets n1 or n2 from transfer point to transfer point, which results from the quotients L / F _L1 or L / F _L2 , can be divided exactly by 3 and the residual value R = 0, there are both in the middle between transport holes Folds as well as off-center folds in different web sections exactly opposite. When printing at the transfer location at the same time, there is therefore no offset in the print image in relation to the respective fold or to the beginning of the sheet.

According to a second aspect of the invention, when inserting of the two sections of the web that align themselves sheet by sheet leave the resulting small fold spacing in the transport direction. Rather, it acts on the generation of the toner images and this on the photoconductor, for example on the photoconductor drum, electronically generated toner image for one Web section by the fold distance from the toner image for moved the other section of the track. This print image offset around the fold distance is again determined from the residual value R, which results from the quotient n1 / 3 or n2 / 3 according to the relationships given above. Due to the print offset it is again possible that the individual leaves of the The web is printed on the right side starting with the beginning of the sheet become. Although the folds of the opposite Path sections are not exactly aligned with each other in duplex mode and in two-color simplex mode no print offset. With the measures according to the second Aspect of the invention is the length of the web from the transfer location minimal to transfer point.

According to a third aspect of the invention, the transport device to compensate for a possibly occurring Fold distance acted in the transport direction. The transport device is in a first transport unit for the first track section and a second transport unit for the second track section divided. Before printing begins, i.e. during insert operation, the two Transport units detached from each other, so that the folds of the adjacent track sections aligned with each other can be. Then both transport units again rotatably coupled to each other to the printing operation start. With this solution, neither the web store has to Recording a certain length of the web still the toner image generation be changed on the photoconductor.

Figur 1

eine Prinzipdarstellung eines Druckers, der im Duplexbetrieb arbeitet,

Figur 2

die Position des Falzes bei verschiedenen Formularlängen,

Figur 3

der Druckbildversatz der Tonerbilder für einen Restwert R = 1 gemäß einem Aspekt der Erfindung,

Figur 4

der Druckbildversatz für nebeneinanderliegende Tonerbilder für einen Restwert R = 2,

Figur 5

die Verstellung der voneinander gelösten Tranporteinheiten bei einem Restwert R = 1 gemäß einem weiteren Aspekt der Erfindung und

Figur 6

die Verstellung der voneinander gelösten Transporteinheiten zum Ausgleich des Falzabstandes bei einem Restwert R = 2.

Embodiments of the invention are explained below with reference to the drawings. In it show:

Figure 1

a schematic diagram of a printer that works in duplex mode,

Figure 2

the position of the fold with different form lengths,

Figure 3

the print image offset of the toner images for a residual value R = 1 according to one aspect of the invention,

Figure 4

the print image offset for adjacent toner images for a residual value R = 2,

Figure 5

the adjustment of the separated transport units with a residual value R = 1 according to a further aspect of the invention and

Figure 6

the adjustment of the transport units detached from each other to compensate for the folding distance with a residual value R = 2.

Details of the invention will now be described using a high performance printer operating in duplex printing mode, the web to be printed being a fan-fold paper web. FIG. 1 shows a schematic representation of the transport path of the web 10 through the printer. The folded web 10 with folds 12 is pulled off a stack 16. The distance between the folds 12 defines the form length F _{L of} a sheet. As mentioned, the form lengths F _L in the field of printer technology are usually given in "inches" and fractions thereof, for example 1/6 inch; one inch is 25.4 mm long.

A deflection unit 18 with a usable width at least equal to twice the width of the web 10 deflects it and guides them to a transport device, generally designated 20 to. This transport device 20 guides the web 10 with a first web section A at a transfer location 22 a printing unit 24 past.

The printer used here works on the principle of Electrophotography, with a photoconductor drum as the intermediate carrier 26 is used on the using a light source 28, for example a laser or an LED line, a latent charge image corresponding to the one to be printed Print image is applied. This charge image is made using a developer station 30 converted into a toner image, wherein this developer station 30 color particles of a desired Transfers color to the photoconductor drum 26. At the transfer location 22 becomes the toner image under the influence of a corona discharge transferred to the surface of the web section A, i.e. on the front of the web 10. The now smearable Toner image on the web section A is by a Fusing station 32 transported and there using pressure and temperature smudge-proof with the carrier material of the web 10 connected.

The web section A is then on a further deflection unit 34 deflected and reaches a turning station 36, in the the web 10 laterally offset by at least one web width and is turned so that now the back of the web 10th the transfer point 22 can be supplied. The section of the Web 10 after turning is referred to as web section B. The web section B is also printed at the transfer printing point 22 and then passed through the fuser 32. After passing through the fixing station 32 twice the web 10 arrives at an output roller 38 and from there an output stack 40 where they are folded in a sheet State is filed. Further details of the construction of the Printers are described in the aforementioned WO 94/27193, whose content corresponds to the present disclosure content of the Invention is attributable.

It should be mentioned that for two-color simplex operation Turning station 36 is replaced by a transfer station, which the web 10 without turning it by at least one web width transferred. The other processes agree with those for the duplex operation described here.

After the turning station 36, the web section B passes through a Web loop 41 of defined length. The web loop 41 forms a web storage and serves that the web section B fed to the transport device 20 free of tensile stresses becomes.

The transport device 20 comprises a first transport unit 20a for the first path section A and a second Transport unit 20b for the second web section B. Both Transport units 20a, 20b are during the printing operation coupled to one another in a rotationally fixed manner. This ensures that both track sections A, B at the same speed be transported forward, the one in the insert mode alignment of the two path sections A, B at any time is maintained. May be during insertion the rotary connection of the two in certain operating modes Transport units 20a, 20b are released, so that a rail transport of the second path section B even when it is at a standstill of the first path section A can take place. Different operating modes with coupled and decoupled transport units 20a, 20b are explained below.

The transport device 20 comprises caterpillar units (not shown) with transport spikes in transport holes on Intervene at the edge of the web 10. After inserting the web 10 flaps (not shown) are folded over their edges, which they with the transport holes firmly on the transport spikes hold. This type of transport mechanism for foldable Railways is well known and will not be discussed here explained.

FIG. 2 shows the position of the folds 12 with different form lengths F _L. In the upper part of the picture, a web 10 is shown, of which four sheets or pages 1 to 4 are to be examined in more detail. The form length F _{L of} the web 10 is in this case F _L0 = kx 1/2 inch, with k an integer, for example F _{L0 is} 12 1/2 inch. The beginning of page 1 is formed by a fold 12, which coincides with a center line M between two successive transport holes 42 (for reasons of clarity, only one transport hole is provided with the reference symbol 42). The distance between two successive transport holes 42 is a = 3/6 inch when viewed in the transport direction. The fold 12 at the end of the side 1 also coincides with the center line M between two transport holes 42, ie the fold 12 of the following side 2 is arranged centrally between two transport holes 42 as in the case of page 1. Accordingly, the folds 12 for the following pages 3 and 4 are also arranged centrally between the transport holes 42 as seen in the transport direction.

In the middle part of FIG. 2, the web 10 is given for an off-center form length F _L1 = (kx 1/2 + 1/6) inch. A typical form length is F _L1 = 12 1/6 inch. The fold 12 at the beginning of page 1 coincides with the center line M. The fold 12 at the end of the page 1 is shifted to the right by 1/6 inch relative to the center line M, that is to say it is arranged off-center by 1/6 inch. The following page 2 is delimited at its end by a fold 12 which is shifted to the left by 1/6 inch with respect to the center line M. The fold 12 at the end of page 3 again coincides with the center line M. The following page 4 has fold layers like page 1. Thus, of three consecutive sides of the web 10, at least one side has a fold 12 at its beginning, which is arranged centrally between two transport holes 42.

A web 10 with an off-center form length F _L2 = (kx 1/2 + 2/6) inch is shown in the lower part of the figure. A typical form length is F _L2 = 12 2/6 inch. Again, the fold 12 is arranged at the beginning of the side 1 in the middle between two transport holes 42. Due to the form length F _L2 , the fold 12 at the end of page 1 is shifted 1/6 inch from the center line M to the left. The fold 12 at the end of the subsequent page 2 is arranged shifted 1/6 inch to the right outside the center line M. The fold at the end of the following page 3 again coincides with the center line M. The side 4 has a fold position like the side 1. It can be seen that in this example too the fold 12 is arranged at the beginning of at least one side of three successive sides in the middle between two transport holes 42 of the web 10. The fold layers are repeated at three-sided intervals; the local period is therefore three pages or three leaves.

If now in a printer in duplex mode or in two-color simplex mode, the web 10 is transported through the printer in such a way that it is offset and, if necessary, additionally turned, so that it passes with a first toner image on the transfer point 22 when it passes by for the first time and on the second time it passes the transfer point 22 is provided with a second toner image, it can happen with the off-center form lengths F _L1 and F _L2 that the folds 12 of the adjacent web sections A, B are not exactly aligned with one another. If no further measures were taken, the toner images, viewed in the transport direction, can differ from one another by ± 1/6 inch with respect to a sheet start or a start of web section A compared to those of web section B.

According to a first aspect of the invention, the length L of the web 10 is adjusted from the transfer location 22 to the transfer location 22 such that the folds 12 of the web 10 for the form lengths F _L1 and F _L2 are aligned with one another at the transfer location 12. The condition then has to be observed that the quotient of n1 / 3 or n2 / 3 results in a residual value R = 0, where nl is the rounded integer from L / F _L1 and n2 is the rounded integer from L / F _L2 .

Depending on the number of sheets or pages of the web 10 between the transfer point 22 and transfer point 22, according to the invention, so many additional pages with form length F _L1 or F _{L2 are to be} provided that the total number n1 or n2 of the pages from transfer point 22 to transfer point 22 without a remainder by 3 is divisible. The additional pages are recorded in the web memory 41. This web store 41 thus has a double function: on the one hand, it should serve for a certain compensation in the case of length tolerances of the form lengths F _{L of} the web 10 as a result of shrinkage or other length changes; on the other hand, it should accommodate a sufficient number of pages with off-center form lengths F _L1 and F _{L2 in} order to allow the folds 12 of the adjacent web sections A and B to be aligned at the transfer printing point 22.

With a minimal transport path L _UU from transfer location 22 to transfer location 22, it is proposed to set the capacity L _{DS of} the web store 42 as a function of the integer residual value R. The relationships apply: x1 = (L UU + L DSMIN ) / F L1 , x2 = (L UU + L DSMIN / F L2 , where x1, x2 are rounded integer values.
R is then determined from
x1 / 3 or x2 / 3

For R = 0, L _DS = L _DSMIN ,
R = 1 is L _DS = L _DSMIN + 2F _L1
or L _DS = L _DSMIN + 2F _L2 ,
and R = 2, L _DS = L _DSMIN + F _L1
or L _DS = L _DSMIN + F _L2 .

If these relationships are observed, the required web loop is minimal in the web store 41; the web store 41 can are designed to be correspondingly small in capacity.

In another exemplary embodiment of the invention, the small fold spacing of the adjacent web sections A and B, which are aligned sheet by sheet, is maintained at the transfer location 22 in the transport direction. As mentioned, the individual pages of the web sections A and B are printed sheet by sheet with toner images, the position of which relative to one another is precisely defined. For example, the toner images should have a defined position at the top of each page. Due to the fold spacing for off-center form lengths F _L1 and F _L2 , this positional relationship cannot be exactly maintained without additional measures. It is therefore provided according to the invention that the second toner image assigned to the second web section B is printed over the fold distance from the first toner image assigned to the first web section A. This fold distance is determined depending on the residual value R, which is for a form length F _L1 = (kx 1/2 + 1/6) inch or F _L2 = (kx 1/2 + 2/6) inch, with k a natural whole Number from which the quotient n1 / 3 or n2 / 3 results, in which nl is the rounded integer from L / F _L1 and n2 is the rounded integer from L / F _L2 and L is the length of the web 10 from transfer location 22 to transfer location 22 .

In FIG. 3, the fold distance resulting for the residual value R = 1, by which the toner images belonging to each side of the two web sections A and B are shifted, are for the form lengths L / F _L1 (left part of the image) and L / F _L2 (right part of the image) shown. In practice, the procedure is such that web section A is first inserted while web 10 is being inserted. A fold 12, which coincides with a center line M, then lies against a marking M _D which is assigned to the form length F _L1 or F _{L2 used} . The web section B is then inserted and guided past the transfer printing point 22. As can be seen in the left part of the figure in FIG. 3, with a residual value R = 1, a fold spacing of the opposing folds 12 of +1/6 inch is produced, based on the transport direction. According to the invention, the toner image for web section B is now also shifted by +1/6 inch and transferred sheet by sheet to web section B. The offset of the toner image by the fold distance generally takes place when the charge image is applied. The charge image for an entire side of the web section B is accordingly generated a time T earlier than for the web section A, for example by writing on the photosensitive surface of the photoconductor drum 26 by the laser beam or by the LED line. This time T is calculated from the fold distance divided by the peripheral speed of the photoconductor drum or the transport speed during printing.

In the right part of the picture, for a residual value R = 1 and the form length F _L2 , it can be seen that the fold spacing or the print image offset is -1/6 inch. The toner image for the sides of the web section B is therefore to be shifted by the fold distance -1/6 inch compared to that of the web section A in order to obtain correct printed images on the mutually associated sheets of the web sections A and B.

Figure 4 shows the fold spacing or the respective print image offset with a residual value R = 2 for the form lengths F _L1 and F _L2 . The fold spacing or the print image offset is -1/6 inch for the form length F _L1 in the transport direction; for F _{L2 it} is +1/6 inch.

With the residual value R = 0, the folds 12 of the neighboring ones are aligned Web sections A and B after insertion; the fold distance is 0, there is no print image offset of the toner images required.

According to a further aspect of the invention, the fold offset or the fold spacing in the transport direction can be compensated for eccentric form lengths F _L1 or F _L2 by moving the web sections A, B relative to one another before the start of the printing operation, so that the Folds 12 of the adjacent web sections A, B are aligned. To make this possible, the transport device 20 is divided into a first transport unit 20a for the first web section A and a second transport unit 20b for the second web section B (cf. FIG. 1). After the insertion of the web section A into the transport device 20, the web 10 is transported through the printer so that the web section B can be inserted into the transport unit 20b, whereby sheets of the web sections A and B lying side by side are aligned.

When using off-center form lengths F _L1 or F _L2 , a fold offset or a fold spacing can occur when viewed in the transport direction. If the fold distance differs from 0, the rotary connection of the two transport units 20a, 20b is released and the second web section B is transported by web relative to the first web section A by this fold distance, the web 10 of the web section A being stationary. After compensation of the fold spacing in such a way that the opposing folds 12 of the web sections A and B are aligned with one another, the transport units 20a, 20b are coupled to one another in a rotationally fixed manner for the printing operation. Since in practice only fold spacing of +1/6 inch and -1/6 inch occurs, the transport device 20 can be designed in such a way that the two transport units 20a, 20b can only be rotated by these values. This twisting can be done manually by an operator or automatically by the printer controller.

The rail transport of rail section B is determined depending on the residual value R. This residual value R is determined from the quotient of n1 / 3 or n2 / 3 for a form length F _L1 = (kx 1/2 + 1/6) inch or F _L2 = (kx 1/2 + 2/6) inch. In these relationships, n1 is the rounded integer from L / F _L1 and n2 is the rounded integer from L / F _L2 , with L the length of web 10 from transfer location 22 to transfer location 22.

5 shows states when the web sections A and B are inserted for the residual value R = 1. The state for the form length F _L1 after inserting the web section A and the web section B is shown in the upper left part of the picture. Viewed in the direction of transport, there is a fold spacing or fold offset of +1/6 inch. The rotary connection of the transport units 20a, 20b is now released and the transport unit 20b is adjusted by -1/6 inch with respect to the stationary transport device 20a. The result can be seen in the lower left part of the picture. The folds 12 of the adjacent web sections A and B are now aligned with one another, so that the toner images on both web sections A, B can be re-printed simultaneously with uniform alignment to the beginning of the page.

In the upper right part of FIG. 5, the fold spacing or the fold offset by -1/6 inch for the form length F _L2 after inserting the two web sections A and B is shown. There is an adjustment of the transport unit 20b by +1/6 inch so that the opposing folds 12 of the web section A and the web section B are aligned with one another (picture part on the bottom right). The two transport units 20a, 20b are then coupled in a rotationally fixed manner and the printing operation can begin.

In FIG. 6, states after the insertion of the web sections A, B and after the adjustment of the transport units 20a, 20b for eccentric form lengths F _L1 and F _L2 with a residual value R = 2 are shown in the manner of FIG. For the form length F _{L1 there} is a fold offset of -1/6 inch, and for the form length F _L2 a fold offset of +1/6 inch after inserting the web sections A, B. Accordingly, for the form length F _L1 a web transport by adjusting the transport units 20a, 20b against each other by +1/6 inch and with a form length F _L2 by -1/6 inch, so that the opposing folds 12 are aligned with one another. After the transport units 20a, 20b have been adjusted, they are connected to one another in a rotationally fixed manner and the printing operation is started.

Claims (17)

1. Method of operating an electrographic printer, in which a first web section (A) of a web (10) of an endless substrate material which can be folded into sheets is led, with a predefined forms length, past the transfer-printing location (22) of an intermediate image carrier (26), the web (10) is then transported through the printer and, in the process, is offset and, if necessary, additionally turned, so that an offset, second web section (B) is led past the transfer-printing location (22) of the intermediate image carrier (26) in one plane together with and in a position beside the first web section (A),

   each sheet of the web (10), when it first passes the intermediate image carrier (26), being printed with a first toner image and, when it runs past the transfer-printing location (22) again, being printed with a second toner image, which has a defined position in relation to the first toner image,

   and in which the transport of the first and of the second web section (A, B) is carried out by a transport device (20) which is arranged close to the intermediate image carrier (26) and has transport pins which are engaged in transport holes (42) in the web (10) and which move at the same speed,

   the transport pins (42) having, in the transport direction, a spacing of 3/6 x LE from one another, LE being a length unit which is typical of forms length, and the fold (12) of at least one sheet of three successive sheets being arranged centrally between two transport holes (42) in the web (10),

   characterized in that, for a forms length of F_L1 = (k x 1/2 + 1/6) x LE or F_L2 = (k x 1/2 + 2/6) x LE, where k is a natural whole number, the length L of the web (10) from transfer-printing location (22) to transfer-printing location (22) is set in such a way that the ratio of nl/3 or n2/3 results in a residual value of R = 0, where n1 is the rounded integer numerical value of L/F_L1, and n2 is the rounded integer numerical value of L/F_L2.
2. Method according to Claim 1, characterized in that, during its transport from transfer-printing location (22) to transfer-printing location (22), the web (10) passes through a web accumulator (41) whose capacity is at least 2F_L1 or 2F_L2.
3. Method according to Claim 2, characterized in that the web accumulator (41) is preset to a minimum value L_DSMIN.
4. Method according to Claim 3, characterized in that, for a transport path L_UU from transfer-printing location (22) to transfer-printing location (22), the capacity L_DS of the web accumulator (42) is set on the basis of the integer residual value R from the ratio xl/3 or x2/3, where x1 is the rounded integer numerical value of (L_UU + L_DSMIN)/F_L1, and x2 is the rounded integer numerical value of (L_UU + L_DSMIN)F_L2, where, for R = 0, the capacity is L_DS = L_DSMIN, for R = 1, the capacity is L_DS = L_DSMIN + 2F_L1 or L_DS = L_DSMIN + 2F_L2, and, for R = 2, the capacity is L_DS = L_DSMIN + F_L1 or L_DS = L_DSMIN + F_L2.
5. Method of operating an electrographic printer, in which a first web section (A) of a web (10) of an endless substrate material which can be folded into sheets is led, with a predefined forms length, past the transfer-printing location (22) of an intermediate image carrier (26), the web (10) is then transported through the printer and, in the process, is offset and, if necessary, additionally turned, so that an offset, second web section (B) is led past the transfer-printing location (22) of the intermediate image carrier (26) in one plane together with and in a position beside the first web section (A),

   the folds (12) in the sheets of the web sections (A, B) alongside each other being aligned with one another or having a small fold spacing from one another in the transport direction,

   and in which the transport of the first and of the second web section (A, B) is carried out by a transport device (20) which is arranged close to the intermediate image carrier (26) and has transport pins which are engaged in transport holes (42) in the web (10) and move at the same speed,

   the transport holes (42) having a spacing from one another of 3/6 x LE in the transport direction, LE being a length unit which is typical of forms lengths, the fold (12) of at least one sheet of three successive sheets being arranged centrally between two transport holes (42) in the web (10),

   and each sheet of the web (10), when it first passes the intermediate image carrier (26), being printed with a first toner image and, when it runs past the transfer-printing location (22) again, being printed with a second toner image which has a defined position in relation to the first toner image,

   characterized in that the first toner imager is transfer-printed so as to be displaced with respect to the second toner image by the fold spacing, which is determined on the basis of a residual value R, which, for a forms length F_L1 = (k x 1/2 + 1/6) x LE or F_L2 = (k x 1/2 + 2/6) x LE, where k is a natural whole number, is given by the ratios n1/3 or n2/3, where n1 is the rounded integer numerical value of L/F_L1, and n2 is the rounded integer numerical value of L/F_L2, and L is the length of the web (10) from transfer-printing location (22) to transfer-printing location (22).
6. Method according to Claim 5, characterized in that, for a residual value of R = 0, the fold spacing is 0.
7. Method according to Claim 5, characterized in that, for a residual value of R = 1, the fold spacing for the forms length F_L1 is equal to 1/6 x LE, and for the forms length F_L2 is equal to -1/6 x LE.
8. Method according to Claim 5, characterized in that, for a residual value of R = 2, the fold spacing for a forms length F_L1 is equal to -1/6 x LE, and for a forms length of F_L2 is equal to +1/6 x LE.
9. Method according to one of the preceding Claims 5 to 8, characterized in that the charge image on the intermediate image carrier (26) for producing a toner image on the second web section (B) is produced so as to be offset by a time T with respect to the charge image for the toner image of the first web section (A), the said time being given by the fold spacing divided by the transport speed during printing.
10. Method of operating an electrographic printer, in which a first web section (A) of a web (10) of an endless substrate material which can be folded into sheets is led, with a predefined forms length, past the transfer-printing location (22) of an intermediate image carrier (26), the web (10) is then transported through the printer and, in the process, is offset and, if necessary, additional turned, so that an offset second web section (B) is led past the transfer-printing location (22) of the intermediate image carrier in one plane together with and in a position beside the first web section (A), the folds (12) in the sheets of the web sections (A, B) alongside each other being aligned with one another or having a small fold spacing from one another in the transport direction, and in which the transport of the first and of the second web section (A, B) is carried out by a transport device (20) which is arranged close to the intermediate image carrier (26) and has transport pins which are engaged in transport holes (42) in the web (10) and move at the same speed,

    the transport holes (42) having a spacing from one another of 3/6 x LE in the transport direction, LE being a length unit which is typical of forms length, the fold (12) of at least one sheet of three successive sheets being arranged centrally between two transport holds (42) in the web (10),

    each sheet of the web (10), when it first passes the intermediate image carrier (26), being printed with a first toner image and, when it passes the transfer-printing location (22) again, being printed with a second toner image which has a defined position in relation to the first toner image,

    and the transport device (20) comprising a first transport unit (20a) for the first web section (A) and a second transport unit (20b) for the second web section (B),

    characterized in that the rotational connection between the two transport devices (20a, 20b) is released during the insertion operation, and the second web section (B) is transported by the fold spacing in relation to the first web section (A), and in that thereafter both transport units (20a, 20b) are coupled to each other so that they rotate together for printing operation with simultaneous printing on the web sections (A, B).
11. Method according to Claim 10, characterized in that the second web section (B) is transported while the first web section (A) is at a standstill.
12. Method according to one of the preceding Claims 10 or 11, characterized in that the web transport is brought about automatically by the printer control system.
13. Method according to one of the preceding Claims 10 or 11, characterized in that the web transport is determined on the basis of an integer residual value R, which is given for a forms length F_L1 = (k x 1/2 + 1/6) x LE or F_L2 = (k x 1/2 + 2/6) x LE, where k is a natural whole number, by the ratios n1/3 or n2/3, in which n1 is the rounded integer numerical value of L/F_L1, and n2 is the rounded integer numerical value of L/F_L2, and L is the length of the web (10) from the transfer-printing location (22) to the transfer-printing location (22).
14. Method according to Claim 13, characterized in that, for a residual value of R = 1, the fold spacing for the forms length F_L1 is equal to 1/6 x LE, and for the forms length F_L2 is equal to -1/6 x LE.
15. Method according to Claim 13, characterized in that, for a residual value of R = 2, the fold spacing for a forms length F_L1 is equal to -1/6 x LE, and for a forms length of F_L2 is equal to +1/6 x LE.
16. Method according to one of the preceding Claims 1 to 15, characterized in that the length unit LE is 25.4 mm (1 inch).
17. Method according to one of the preceding Claims 1 to 16, characterized in that a photoconductor (26) is used as the intermediate image carrier.

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