EP1008017A1

EP1008017A1 - Method to operate a printer with two printing units

Info

Publication number: EP1008017A1
Application number: EP97947019A
Authority: EP
Inventors: Georg BÖHMER; Joseph Dietl; Hans Hahn; Bernward Heller; Hubert Mugrauer; Otto Olbrich; Reinhold Rigauer; Otto Rotheimer; Rudolf Seeberger
Original assignee: Oce Printing Systems GmbH and Co KG
Current assignee: Canon Production Printing Germany GmbH and Co KG
Priority date: 1996-10-22
Filing date: 1997-10-22
Publication date: 2000-06-14
Anticipated expiration: 2017-10-22
Also published as: CA2269811A1; EP0957409A1; JP2001502815A; WO1998018054A1; US6101364A; DE59707176D1; EP1008017B1; CA2269811C; DE19781182D2; DE19781182B4; JP4253690B2

Abstract

Disclosed is a method enabling two similar printing units (D1, D2) to print sheetlike material in a printer. In case of failure of one of the printing units (D1, D2) limited printing can be maintained .

Description

description

Method for operating a printer with two printing units

The invention relates to a method for operating a printer or copier, in which a first electrographic printing unit, which prints an image pattern on a sheet material, is fed sheet material one after the other via an input section, and in which the printed material is fed individually via an output section is output one after the other.

In a known high-performance printer with only a single printing unit, the individual printer components are precisely matched to one another, so that a very reliable operating state with high printing performance is achieved. In order to further increase the printing performance, design changes must be made to these components, which leads to a high level of development effort and increases the probability of failure due to the redesign of the individual components.

A printer is known from US Pat. No. 4,587,532 which has three printing units arranged one above the other and which print individual sheets together or alternately. The paper feeder contains switches to feed the single sheets to the various printing units.

DE 34 22 942 AI describes a printing system that has two electrophotographic printing stations. If a fault occurs in one printing station, the printing station in question is switched off, the other printing station continuing to operate.

From WO 91/13386 a modular electrophotographic printing device is known, which two Contains printing modules. The printing modules can work in simplex mode, with both printing modules being fed single sheets via switches. Furthermore, duplex operation is possible, in which the single sheets are first fed to the one printing module for printing with a first printed image; a further printed image can then be applied by the second printing module. The print modules are designed as separate structural units for fastening in a single housing.

From DE 34 07 847 AI an image recording device with multiple functions is described. It is the functions, such as High-speed recording, two-sided recording and multiplex recording possible. The printer system contains two printing units that can be connected to each other via a paper guide system. The paper guide system also enables the cut sheets to be turned, so that duplex printing with printing on both sides is possible.

No. 4,972,236 also describes an image generation system with a plurality of printing units which are arranged vertically one above the other in order to save space. In one embodiment, the paper transports for both printing units are connected to one another by a connecting channel.

It is an object of the invention to provide a method for operating a printer or a copier that enables high printing performance or copying performance and works reliably.

This object is solved by the features of claim 1. Advantageous further developments are specified in the further claims. In the method according to the invention two essentially identical printing units are used. The components for these printing units, for example the electronic control, the developer units, the toner supply and discharge devices, etc., can be kept almost unchanged. Each printing unit on its own therefore has a very high level of operational reliability. Both printing units use a common input section through which the sheet material is fed. Likewise, both printing units jointly use an output section for discharging the printed sheet material. As a result, the new device is very compact and can be manufactured with little effort. Due to the two printing units, the printing performance is significantly increased.

According to the invention, the disturbed printing unit is switched off when the first printing unit or the second printing unit is disturbed, the first switch only feeding sheet-like material to the undisturbed printing unit. With the help of the undisturbed printing unit, a printing operation can still be maintained so that print jobs can be processed until the repair service arrives.

In so-called simplex operation, in which sheet-shaped material is fed to the input section at double transfer speed in undisturbed operation, feeding can only take place at half the speed of normal operation in the case of a faulty printing unit. Nevertheless, this variant of the invention has a considerable advantage since the user of the printing system can continue to work with reduced output.

Even in duplex mode, where the single sheets are printed on both sides, you can continue working if one of the printing units fails. The conveyor path in the printer is then set so that the undisturbed printing unit first has one page printed, then the single sheets are turned over and fed again to the same printing unit in order to print on the second side.

By using two printing units in a single printing system or copying system, redundant operation can be set up. This redundancy operation considerably reduces the probability of failure of the entire printing system or copying system. According to the rules of stochastics, the function probability in redundant systems in which at least one of the two printing units is fully functional, regardless of which is defined as follows:

Pred. = Pl x (1-P2) x 2 + Pl x P2,

in which Pred. is the function probability of the entire printing system or copying system, Pl is the function probability of the first printing unit and P2 is the function probability of the second printing unit.

If one assumes a function probability of e.g. 90% for each printing unit, the function probability for redundant restricted operation increases to 99% according to this formula. As mentioned, the printing performance is reduced in the event of a printing unit failure, but the complete failure of the printing system or copying system is very likely to be avoided, which means a high level of security for the user in executing his jobs.

One embodiment of the invention provides that the input section contains a switch which supplies sheet material either to the first transfer printing path or to the second transfer printing path. In this embodiment, the simplex printing mode is realized with one color, ie supplied sheet-like material, eg single sheets of paper, are printed on one side by the first printing unit or by the second printing unit. In a further development, the switch leads sheet material alternately to the first transfer printing path and the second transfer printing path. Since each printing unit prints the sheet material with the same transfer printing speed and two printing units are arranged in parallel, the printing capacity in the device doubles overall. Accordingly, single sheets can be fed in and out again at twice the printing speed.

Another exemplary embodiment provides that the first transfer printing transport path and the second transfer printing transport path are connected by a connecting channel through which sheet material can be conveyed in one or in both transport directions. Through these measures, printed material can be fed from the first printing unit to the second printing unit and from the second printing unit to the first printing unit in order to print it. The connection channel thus creates a feedback link that connects the two printing units to one another, which enables a variety of printing processes.

A further embodiment provides that the sheet-like material is turned during transport from the first transfer printing path to the second transfer printing path. In this way, each printing unit can print on the front and also on the back of a single sheet. If developer stations with different colors are used for the two printing units, two image patterns with two different colors can be printed on each side of the single sheet, i.e. a so-called two-color duplex operation, also called duplex color spot operation, can be implemented.

Despite technical improvements to the printing units, damage and failures can never be completely ruled out, as before being partially caused by incorrect applications or operating errors. In order to shorten the downtime of such a printing system, the various device manufacturers for high-performance printers and copiers maintain a very quickly responding service operation with standby service. The effort for this service operation is very high. With the present invention, it is now possible to significantly reduce the overall failure probability of operating such devices.

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

FIG. 1 schematically shows the construction of a high-performance printer in which the invention is implemented,

FIG. 2 shows schematically the operating mode simplex printing with the lower printing unit,

FIG. 3 schematically, the operating mode simplex printing with the upper printing unit,

FIG. 4 the operating mode alternating simplex printing,

FIG. 5 the duplex printing mode,

Figure 6 shows the operating mode two-color simplex printing, and

Figure 7 shows schematically the operating mode two-color duplex printing.

FIG. 1 shows a high-performance printer 10 which is used for the rapid printing of single sheets of paper. The high performance printer 10 includes a first, lower one

Printing unit Dl and a second, upper printing unit D2. Both Printing units D1, D2 work according to the known electrographic method with the same transfer printing speed. The printing units D1, D2 are followed by fixing devices, which are indicated schematically in FIG. 1 by two pairs of rollers 12, 14. A paper input 16 is connected to the high-performance printer 10 and contains a plurality of storage containers 18 to 24 with single sheets as well as an external paper feed channel 26, via which single sheets can be fed from the outside. Single sheets are fed to an input section 28 via a transport channel. On the output side, a paper output 30, which contains a plurality of output containers 32 to 36, is connected to the high-performance printer 10. Furthermore, two output channels 38, 40 are provided, via which single sheets can be output to further processing stations. The high-performance printer 10 delivers the printed single sheets via the output section 42.

Transport paths for the transport of the single sheets are arranged in the interior of the high-performance printer 10, through which various operating modes of the high-performance printer are realized. The printing units D1, D2 are each assigned transfer printing transport paths 44, 46, which are each set by drives so that the single sheets fed to the printing units D1, D2 have their transfer printing speed. Both transfer printing transport paths 44, 46 are connected to one another via a connecting channel 48. The transport path around the first printing unit D1 is supplemented to form a ring by a feed channel 50, via which individual sheets can also be fed from the input section 28 to the second transfer printing transport path 46. The transport path for the second printing unit D2 is supplemented in a similar manner to form a ring by a discharge channel 52, via which individual sheets printed by the printing unit D1 can be fed to the output section 42.

A first switch W1 is located between the input section 28, the first transfer printing transport path 44 and the feed channel 50 arranged, which enables single sheets from the input section 28 to be optionally fed to the first transfer printing path 44 or the feed channel 50. Another variant consists in that single sheets transported in the direction of the switch W1 on the feed channel 50 can be fed to the first transfer printing path 44.

Furthermore, a second switch W2 and a third switch W3 are arranged at the ends of the connecting channel 48 and connect the adjacent transport paths 44, 48, 52 and 46, 48, 50, respectively. A fourth switch W4 is located in the vicinity of the delivery section 42 and connects the adjacent transport routes. The paper output 30 contains a fifth switch W5, which works as a turning device. Furthermore, it should also be pointed out to a control device 54 to which reject single sheets are fed via a switch W6.

Different operating modes of the high-performance printer 10 can be realized by the arrangement described in FIG. The various operating modes are shown schematically in the following FIGS. 2 to 7. The respective promotion of the single sheets is illustrated by arrows.

In Figure 2, the simplex printing is shown schematically with only one printing unit. With this simplex printing only one side of a single sheet is printed. The single sheet reaches the first transfer printing path 44 via the input section 28 and the appropriately switched switch W1 along the arrow P1 and is printed on the printing unit Dl. The single sheet is then output along the discharge channel 52 (arrow P2) via the output section 42 into the paper output 30 (arrow P3).

Figure 3 shows the simplex printing with the upper, second printing unit D2. The single sheet is transported via the Feed channel 50 (arrow P4), the second transfer printing path (arrow P5) to the paper output 30 (arrow Pβ).

In the case of alternating simplex printing with increased printing capacity, 28 single sheets are fed via the input section with at least twice the transfer printing speed of the printing units D1, D2. Figure 4 shows schematically the transport of the single sheets. The switch Wl alternately feeds the feed channel 50 or the first transfer printing path 44 single sheets (arrows P7, P8). The individual sheets are slowed down to the transfer speed on their transport to the printing units D1, D2, printed there on the front side and then conveyed further to the switch W4. In this further conveyance according to arrows P9, P10, the single sheets are accelerated to at least twice the transfer printing speed, so that they are output at a distance from one another at the common output section via switch W4 and successively in paper output 30 with at least twice the transfer printing speed according to arrow Pll can be transported further.

In the so-called "alternating simplex printing" mode of operation, it is therefore provided according to the invention that in the paper input 16 the single sheets to the input section 28 are fed to the printing units D1, D2 with at least twice the transfer printing speed. In the paper output 30, too, the single sheets are also conveyed and deposited at at least twice the speed. As a result of these measures, the single sheets arrive at the common input section 28 and at the common output section 42 without a collision of single sheets and consequently a paper jam occurring. The transport paths for the single sheets fed to the first printing unit D1 and the single sheets fed to the second printing unit D2 are preferably designed symmetrically, or at least the same length, so that the single sheets with the same speed profile can be slowed down and accelerated. This makes it possible to construct the drives and devices required for transport in the same way. It is also possible to use similar controls.

Figure 5 shows schematically the duplex printing mode, in which the single sheets are printed on both sides. The single sheets fed to the input section 28 are fed through the first switch W1 to the first transfer printing transport path 44 (arrow P13). After printing by the printing unit Dl, the respective single sheet is conveyed a turning distance according to the arrow P14 beyond the switch W2. This turning path is part of the discharge channel 52. The conveying direction is then reversed according to arrow P15, and the switch W2 then guides the single sheet according to the arrow P16 into the connecting channel 48. The single sheet is then moved from the switch W3 in the direction of the arrow P17 diverted to the second transfer printing transport path 46. The printing unit D2 is supplied with the not yet printed back of the single sheet for printing. The individual sheets are then fed to the switch W4 in accordance with the arrow P18 and transported to the paper output 30 along the arrow P19. As the single sheet is transported with its back upwards in this state, it must still be turned over in compartments 32 to 36. The W5 switch serves this purpose. The single sheet is first passed through the switch W5 in the direction of the arrow P20 for a predetermined turning distance. Then the transport direction is reversed according to arrow P21 and the switch W5 conveys the single sheet in the direction of arrow P22, whereupon it is deposited in the storage compartments 32 to 36 with the correct orientation.

As can be seen, the switch W2 works as a turning device in order to feed the back of the single sheet to the printing unit D2. Alternatively, the turnout W3 can also be used. The single sheet leaving the printing unit DJ is then turned over the switch W2, the connecting channel 48 the switch W3 and then for a short turning distance along the feed channel 50 in the direction of the switch Wl. Then the transport direction is reversed and the switch W3 guides the single sheet in the direction of the printing unit D2 with its rear side up.

FIG. 6 schematically shows a further operating mode, two-color simplex printing, in which the front of a single sheet is printed with two image patterns of different colors. The two printing units D1, D2 print image samples of different colors. In the two-color simplex printing mode mentioned, the single sheet is fed to the printing unit Dl via the switch Wl (arrow P25). The single sheet is then fed via the switch W2 to the connecting channel 48 without turning and then via the switch W3 to the printing unit D2

(Arrows P26, P27). The printing unit D2 prints the front side with a different color from the printing unit Dl

Colour. The single sheet is then output to the paper output 30 via the switch W4 (arrow P28).

FIG. 7 schematically shows the transport path of a single sheet in the two-color duplex printing mode, in which the front and the back of a single sheet are printed with image patterns of different colors. The prerequisite for this is that the printing units D1 and D2 print different-colored print images. The two-color printing of the front is carried out as in the two-color simplex printing mode according to FIG. 6. The arrows P25, P26, P27 and P28 illustrate the transport route. The single sheet is then fed again to the printing unit Dl. The arrows P29 to P36 illustrate the transport path of the single sheet for printing on the back. So that this back is fed to the printing unit Dl, the single sheet must be turned on the transport path between the printing unit D2 and the printing unit Dl. This turning can take place, for example, on the switch W4, the switch W2 or the switch W3. In a preferred embodiment of the invention, the turning is carried out using the switch W4, ie the single sheet is first transported for a short turning distance in the direction of the switch W5, then the transport direction is reversed and the single sheet is conveyed further in the direction of the switch W2. After the transport into the paper output 30 according to the arrow P36, the turnout W5 is turned further and then the single sheet, which is printed on both sides with two color images, is deposited in the correct direction.

An alternative transport of the single sheet through the high-performance printer 10 to implement the two-color duplex printing mode can be carried out in the following manner. First of all, the single sheet is fed from the input section 28 via the switch W1 to the printing unit Dl, printed on its front side and then briefly directed via the switches W2 and W3 for turning in the direction of the switch Wl. After passing the switch W3, the transport direction is changed in the direction of the printing unit D2 and the single sheet is conveyed on the transfer printing transport path 46. The switch W3 thus serves as a turning station. The back of the single sheet is accordingly printed on the printing unit D2. Then the single sheet is fed again via the switches W4, W2, W3 and Wl to the first printing unit Dl in order to now print on the back. The single sheet must be turned over for this. This is done on switch W4, where it is briefly conveyed in the direction of switch W5, the transport direction is reversed and transported in the direction of switch W2 in the turned state. After printing on the back of the single sheet in the printing unit D1, the single sheet is fed to the printing unit D2 via the switches W2 and W3, whereby it is turned. Now the front is printed by the printing unit D2. The single sheet is then fed over the switch W4 to the storage compartments 32 to 36. Since it is now in the correct position, ie upside down in the tray 30 arrives, it does not have to be turned again through the switch W5.

As already mentioned above, the high-performance printer 10 can maintain a restricted printing operation even if one of the printing units D1 or D2 fails. In the operating mode simplex printing (Figure 2) e.g. If the printing unit D2 fails, the switch Wl can be set so that it feeds single sheets exclusively to the printing unit Dl. The printing unit D2 is switched off and the second transfer printing transport path 46 is not used. The single sheets printed by the printing unit D1 are output to the paper output 30 via the switches W2 and W4. In this operating state, the high-performance printer 10 only works at half the conveying speed of the single sheets compared to undisturbed operation.

In the event that the first printing unit D1 fails in the operating mode simplex printing, this is switched off. The switches W1 and W3 then feed single sheets via the feed channel 50 and the second transfer printing transport path 46 to the second printing unit D2. The printed single sheets are then output to the paper output 30 via the switch W4.

Even in duplex printing mode with printing on the front and back of the single sheets, restricted duplex printing can be maintained in the event of failure of a printing unit D1 or D2. If, for example in a duplex operation (cf. FIG. 5), the upper, second printing unit D2 fails, then this is switched off. The single sheets are still fed to the printing unit Dl via the switch Wl. The single sheets are then transported via the second switch W2 towards the fourth switch W4 (arrow P14). After passing the second switch W2, the transport direction (arrow P15) is reversed, and the single sheets are fed again to the first printing unit D1 via the third switch W3 and the first switch Wl. Due to the turning process by the transport direction reversal on the switch W2, the back is now printed by the first printing unit Dl. The sheet-like material is then output again via the second switch W2 and the fourth switch W4.

If the first printing unit D1 is faulty and the second printing unit D2 is still fully functional, duplex operation with the second printing unit D2 can still be maintained via the transport lines 46, 52 and 48. The single sheets are fed to the second printing unit D2 via the switches W1 and W3. The printed single sheets are led over the switch W4 for a short section in the direction of the switch W5. The transport direction is reversed and the respective single sheet is guided in the direction of the switch W2. By reversing the transport direction on the switch W4, the single sheet is turned. The single sheet is then fed again to the printing unit D2 via the connecting channel 48 and the switch W3 and the back is now printed. The single sheet printed on both sides is then output via the switch W4 and, if necessary, turned over on the switch W5 and then placed in one of the output containers 32 to 36.

The described redundancy operation with a faulty and a fully functional printing unit increases the probability of operation for the operation of the entire high-performance printer. In practice, the user of the high-performance printer can continue to process his order despite a faulty printing unit, until the repair service called up brings both printing units back into a functional state.

Claims

claims

1. method for operating a printer or copier,

in which a first electrographic printing unit (DI), which prints an image pattern on a sheet material, is fed sheet material one after the other via an input section,

the printed material is output one after the other via an output section (42),

wherein sheet-like material is fed to an essentially similar second printing unit (D2) via the same input section (28),

the sheet-like material printed by the second printing unit (D2) is output via the common output section (42),

and the between

a) a simplex mode with increased throughput of sheet material, in which the two printing units (Dl, D2) alternately via a switch

(Wl) sheet material is fed in the input section (28),

b) a duplex mode in which sheet material is fed from the input section and the first printing unit and the material from the first transfer printing path (44) via a connecting channel (48) to the second transfer printing path (46) of the second printer (D2) for printing on Back of the material is fed and c) an emergency operating mode in which, in the event of a faulty first printing unit (Dl) or in the event of a faulty second printing unit (D2), the faulty printing unit (Dl, D2) is switched off and the switch (Wl) is only sheet-like material to the undisturbed printing unit (Dl, D2 ) feeds

is switched.

2. The method according to claim 1, characterized in that in fast simplex operation, the first printing unit (Dl) sheet material only via the first transfer printing path (44) and the second printing unit (D2), the sheet material only via the separate second transfer printing -Transportweg (46) is fed.

3. The method according to any one of claims 1 or 2, characterized in that in the state with a faulty printing unit (Dl, D2) the sheet material is only fed at half the conveying speed compared to normal operation.

4. The method according to any one of claims 1 or 3, characterized in that the first Umdruc transport path (44) and the second transfer printing transport path (46) are connected by a connecting channel (48) through which sheet-shaped material in one or both Transport directions is promoted.

5. The method according to any one of claims 1 to 4, characterized in that the first transfer printing path (44) and the second transfer printing path (46) are connected by the connecting channel (48) through which sheet-shaped material in one or is promoted in both transport directions.

6. The method according to claim 5, characterized in that when transporting sheet material from the first transfer printing path (44) to the second transfer printing path (46) and vice versa, the sheet material is turned by a turning device (W2, W3, W4).

7. The method according to any preceding claim, characterized in that one or two turning devices (W2, W3) are arranged at one or at both ends of the connecting channel (48).

8. The method according to any one of the preceding claims, characterized in that the turning device contains a switch (W2, W3, W4), that the sheet material for turning first at the switch (W2, W3, W4) on a first transport route in one Transport direction is transported in a turning section, that the transport direction is then reversed, and that the switch (W2, W3, W4) conveys the sheet material to a second transport path in the other transport direction.

9. The method according to any one of the preceding claims, characterized in that in the duplex printing operation, the sheet material is first fed to the first transfer printing path (44) and then to the second transfer printing path (46), that by the second printing unit (D2 ) printed sheet material is fed back to the first transfer printing path (44) under turning, and that finally the sheet material is fed to the second transfer printing path (46) without turning and then output.

10. The method according to any one of the preceding claims, characterized in that the first transfer printing transport path (44), the connecting channel (48) and a feed channel (50) form a closed transport path, wherein the feed channel can transport sheet material in both directions and feed sheet material to the second transfer printing path (46).

11. The method according to any one of the preceding claims, characterized in that the second transfer printing transport path (46), the connecting channel (48) and a discharge channel (52) for sheet material form a closed transport path, the discharge channel (52) sheet material in can promote both directions and connects the first transfer printing path to the output section.

12. The method according to any one of the preceding claims, characterized in that a turning device (W5) is arranged in the conveying direction of the sheet material after the output section (42), which turns the sheet material before depositing.

13. The method according to any one of the preceding claims, characterized in that seen in the conveying direction after the input section (28) a first switch (Wl) is arranged that at the connection point between the first transfer printing path (44) and the connecting channel (48) and a second switch (W2) is arranged in the discharge channel (52), that a third switch (W3) is arranged at the connection point between the connecting channel (48), the second transfer printing path (46) and the feed channel (50), and in that A fourth switch (W4) is arranged between the connection point between the second transfer printing transport path (46) and the discharge channel (52).

14. The method according to claim 13, characterized in that in the duplex printing mode with printing on both

Sides of the single sheets over the sheet material the input section (28) and the first switch (Wl) are fed to the first printing unit (Dl) and the first page is printed there,

that the sheet material is transported via the second switch (W2) and the third switch (W3) to the second printing unit (D2) and then the first page is printed there,

that for printing the second side the sheet material is transported to the fourth switch (W4), after passing the fourth switch (W4) the sheet material is transported into a turning section, the transport direction is reversed and changed in the direction of the second switch (W2), that the sheet material is fed via the third switch (W3) and the first switch (Wl) to the first printing unit (Dl) and the second side is printed,

that the sheet material via the second switch (W2) and the third switch (W3) is fed to the second printing unit (D2) and the second side is printed, and

that the sheet material is output via the fourth switch (W4).

15. The method according to claim 13, characterized in that in the duplex printing mode with printing on both sides of the single sheets, the sheet material via the input section (28) and the first switch (Wl) fed to the first printing unit (Dl) with the front and there the front is printed,

that the sheet material over the second switch (W2) and the third switch (W3) under turns to the second Printing unit (D2) transported and then the back is printed,

that the sheet-shaped material is fed with its back over the fourth switch (W4), the second switch (W2), the third switch (W3) and the first switch (Wl) to the first printing unit (Dl) and printed,

that the sheet material via the second switch (W2) and the third switch (W3) is fed to the second printing unit (D2) and the front is printed, and

that the sheet material is output via the fourth switch (W4).

16. The method according to any one of the preceding claims 14 or 15, characterized in that when the first printing unit (Dl) or the second printing unit (D2) is disturbed, the disturbed printing unit (Dl, D2) is switched off and the duplex operation is performed exclusively by the undisturbed printing unit ( Dl, D2) takes place.

17. The method according to claim 16, characterized in that in duplex operation with the second printing unit switched off

(D2) the sheet material is fed via the input section (28) and the first switch (Wl) to the first printing unit (Dl) and the first page is printed there,

that the sheet material is transported over the second switch (W2) towards the fourth switch (W4), after passing the second switch (W2) the sheet material is transported into a turning section (52), the transport direction is reversed and towards the third switch (W3) is changed that the sheet material over the third switch (W3) and the first switch (Wl) the first printing unit (Dl) fed again and the second page is printed, and

that the sheet material is output via the second switch (W2) and the fourth switch (W4).

18. The method according to claim 16, characterized in that in duplex mode with the first printing unit (Dl) switched off, the sheet material via the input section (28), the first switch (Wl) and the third switch (W3) fed to the second printing unit (D2) and there the first page is printed,

that the sheet-shaped material is transported to the fourth switch (W4) for printing on the second side, after passing through the fourth switch (W4) the sheet-shaped material is transported into a turning section, the transport direction is reversed and changed in the direction of the second switch (W2) is that the sheet material is fed via the third switch (W3) to the second printing unit (D2) and the second side is printed, and

that the sheet material is output via the fourth switch (W4).