Abstract:
A printing device, in particular a printer or a copier, which includes a first electrographic printing unit for printing an image pattern on a sheet-type material in a first transfer printing transport path as well as a second electrographic printing unit for printing an image pattern on a sheet-type material in a second transfer printing transport path, and further including an input section via which the sheet-type material can be supplied individually one after the other to both the first and second electrographic printing units, and further having an output section via which the printed sheet-type material from either the first or second electrographic printing units is ejected individually one after the other.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device or, respectively, a system, in particular a printer or copier, with two electrographic printing units of substantially the same type, wherein each of the printing units prints an image pattern on a sheet-type material. The device includes an input section via which the sheet-type material can be supplied individually in successive fashion and an output section via which the printed sheet-type material is ejected individually in successive fashion. 
     2. Description of the Prior Art 
     Electrophotographic printers of this type are known, for example, from DE 34 16 252 A1, EP 0 104 022 A2, DE-PS 1,280,605, DE 34 07 847 A1 or WO 91/13386. With printers of this type, high printing performance can be achieved, even in duplex operation, as long as both printing units are working as they should. However, the devices specified in the cited publications have the disadvantage that, in the case of failure of one of the printing units, a drastic reduction in the performance of the duplex operation results. This is because a sheet that is to be printed on both sides in duplex operation must then be accelerated repeatedly in the opposite direction in order to enable it to be printed on both sides by the one remaining printing unit. 
     From U.S. Pat. No. 5,150,167, a printing unit is known that contains two printing units. One of the printing units has a priority status. As such, sheets that have been printed in the lower-order printing unit additionally can be printed in the priority printing unit. However, if the priority printing unit fails, double printing and, in particular, duplex printing is not possible. 
     From U.S. Pat. No. 5,208,640, a further print apparatus is known that contains several printing units. The printing units are connected with one another via a ring system, wherein a common turning apparatus with a shunt for all printing units is used. If the turning apparatus fails, e.g. due to a switching error in the shunt, duplex operation is no longer possible. 
     An object of the present invention, therefore, is to provide a device, in particular a printer or a copier, that has a high print performance or, respectively, copier performance, in particular in duplex operation. 
     SUMMARY OF THE INVENTION 
     This object is solved for the device, or system, named above in that a first printing unit and a substantially identical second printing unit are provided in the device, to which sheet-type material can be supplied via the common input section. The sheet-type material printed by the second printing unit is ejected via a common output section. The two transfer printing transport paths of the two printing units are respectively connected via connecting paths to form two ring systems. A shunt is respectively provided at each of the two rings by means of which the sheet-type material can be turned independent of the respective other shunt in the allocated ring. 
     In the device of the present invention, two printing units of substantially similar construction are used. The components for these printing units, e.g. the electronic control unit, the developer units, the toner supply and carry-off means, etc., can be retained almost unchanged. Each printing unit, therefore has in itself a very high operational reliability. Both printing units use a common input section via which the sheet-type material is supplied. Likewise, both printing units use in common an output section for carrying away the printed sheet-type material. The new device is thereby constructed very compactly and can be manufactured at a low expense. The print performance is increased significantly due to the two printing units. Also, by means of the inventive ring system, a sheet-type material printed by one of the two printing units can again be supplied to the same printing unit in the same direction as in the first print process. 
     According to an embodiment of the present invention, a first transfer printing transport path is provided for the first printing unit and a separate second transfer printing transport path is provided for the second printing unit. The transfer printing for both printing units takes place with the same speed. Since each printing unit has a separate transfer printing transport path, sheet-type material can be printed with one printing unit even upon failure of the other. 
     In addition, it is particularly advantageous if the two rings are connected via two three-way shunts. A multiplicity of transport paths arises by this arrangement. 
     An embodiment of the present invention provides that the input section contains a shunt that supplies sheet-type material either to the first transfer transport path or to the second transfer printing transport path. In this embodiment, the simplex printing operating mode is performed with one color; i.e., supplied sheet-type material (e.g., individual sheets of paper) are printed on one side by the first printing unit or by the second printing unit. In a further development, the shunt supplies sheet-type material alternately to the first transfer printing transport path and to the second transfer printing transport path. Since each printing unit prints the sheet-type material with the same transfer printing speed, and two printing units are arranged in parallel, the print performance in the device is doubled. Accordingly, individual sheets can be supplied and carried away with twice the print speed. 
     Another 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-type material can be conveyed in one or in both transport directions. By means of these measures, printed material can be supplied from the first printing unit to the second printing unit, and from the second printing unit to the first printing unit, in order to be printed. The connecting channel also creates a feedback that connects the two printing units with one another, thus enabling many print processes. 
     Another embodiment provides that the sheet-type material is turned during its transport from the first transfer printing transport path to the second transfer printing transport path. 
     In this way, each printing unit can print both the front side and the back side of an individual sheet. If developer stations with different colors are used for the two printing units, then two image patterns with two different colors can be printed on each side of the individual sheet; i.e., what is known as two-color duplex operation, or duplex color spot operation, can be performed. 
     According to another embodiment of the present invention, a printer system is specify in which two devices of the same type are connected by an interchange apparatus that supplies the sheet-type material printed by the first device to the second device of the same type. If each of these two devices contains differently colored printing units, then individual sheets can be printed on both sides with four colors. of course as well other variants are conceivable, e.g., one device prints two colors on one side and the other device prints two colors on the other side. 
     Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Preferred Embodiments and the Drawing. 
    
    
     DESCRIPTION OF THE DRAWING 
     FIG. 1 schematically shows the construction of a high-performance printer in accordance with the present invention; 
     FIG. 2 schematically shows the operating mode simplex printing with the lower printing unit; 
     FIG. 3 schematically shows the operating mode simplex printing with the upper printing unit; 
     FIG. 4 shows the operating mode alternating simplex printing; 
     FIG. 5 shows the operating mode duplex printing; 
     FIG. 6 shows the operating mode two-color simplex printing; 
     FIG. 7 schematically shows the operating mode two-color duplex printing; 
     FIG. 8 shows an arrangement with two high-performance printers that are connected with one another by an interchange apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a high-performance printer  10  that serves for the rapid printing of individual sheets of paper. The high-performance printer  10  contains a first, lower printing unit D 1 , as well as a second, upper printing unit D 2 . Both printing units D 1 , D 2  operate according to the known electrographic method with the same transfer printing speed. Fixing means, indicated schematically in FIG. 1 by two roller pairs  12 ,  14 , are connected downstream from the printing units D 1 , D 2 . A paper input  16 , containing several supply containers  18  to  24  with individual sheets as well as an external paper input channel  26  via which individual sheets can be supplied from the outside, is connected to the high-performance printer  10 . Individual sheets are supplied to an input section  28  via a transport channel. At the output side, a paper output  30  containing several output containers  32  to  36  is connected to the high-performance printer  10 . In addition, two output channels  38 ,  40  are provided via which individual sheets can be outputted to stations that carry out further processing. The high-performance printer  10  ejects the printed individual sheets via the output section  42 . 
     In the interior of the high-performance printer  10 , transport paths are arranged for the transport of the individual sheets, by means of which various operating modes of the high-performance printer are enabled. Transfer printing transport paths  44 ,  46  are respectively allocated to the printing units D 1 , D 2 , which are respectively set by means of drives in such a way that the supplied individual sheets at the printing units D 1 , D 2  have their transfer printing speed. Both transfer printing transport paths  44 ,  46  are connected with one another via a connecting channel  48 . The transport path about the first printing unit D 1  is supplemented to form a ring R 1  by a supply channel  50  via which individual sheets also can be supplied to the second transfer printing transport path  46  from the input section  28 . The transport path for the second printing unit D 2  is in a similar way supplemented by a carry-off channel  52  to form a ring R 2 , via which individual sheets printed by the printing unit D 1  can be supplied to the output section  42 . 
     A first shunt W 1  is arranged between the input section  28 , the first transfer printing transport path  44  and the supply channel  50 . The first shunt W 1  makes it possible for individual sheets to be supplied optionally to the first transfer printing transport path  44  or to the supply channel  50  from the input section  28 . A further variant is that individual sheets transported on the supply channel  50  in the direction of the shunt W 1  can be supplied to the first transfer printing transport path  44 . 
     In addition, a second shunt W 2  and a third shunt W 3  are arranged at the ends of the connecting channel  48  wherein they respectively connect the adjoining transport paths  44 ,  48 ,  52  or, respectively,  46 ,  48 ,  50 . A fourth shunt W 4  is located in the vicinity of the output section  42  wherein it connects the adjoining transport paths. The paper output  30  contains a fifth shunt W 5  that operates as a turning means. In addition, a modulation means  54  is provided, to which rejected individual sheets are supplied via a shunt W 6 . 
     By means of the arrangement specified in FIG. 1, various operating modes of the high-performance printer  10  can be enabled. In the following FIGS. 2 to  7 , the various operating modes are shown schematically. The respective conveying of the individual sheets is illustrated on the basis of arrows. 
     FIG. 2 schematically shows simplex printing with only one printing unit. In this simplex printing, only one side of an individual sheet is printed. The individual sheet moves via the input section  28  and the correspondingly switched shunt W 1  along the arrow P 1  to the first transfer printing transport path  44 . It is printed at the printing unit D 1 . Subsequently, the individual sheet is ejected (arrow P 3 ) into the paper output  30  along the carry-off channel  52  (arrow P 2 ) via the output section  42 . 
     FIG. 3 shows simplex printing with the upper, second printing unit D 2 . The transport of the individual sheet takes place via the supply channel  50  (arrow P 4 ), the second transfer printing transport path (arrow P 5 ) to the paper output  30  (arrow P 6 ). 
     In alternating simplex printing with increased print performance, individual sheets are supplied to the printing units D 1 , D 2  via the input unit  28  with at least twice the transfer printing speed. FIG. 4 schematically shows the transport of the individual sheets. The shunt W 1  alternately guides individual sheets to the supply channel  50  or, respectively, to the first transfer printing transport path  44  (arrows P 7 , P 8 ). The individual sheets are first braked to transfer printing speed on their transport up to the printing units D 1 , D 2 , are respectively printed there on the front side, and are subsequently further conveyed to the shunt W 4 . During this further conveying according to the arrows P 9 , P 10 , the individual sheets are accelerated to at least double the transfer printing speed so that at the common output section they are ejected via the shunt W 4  with a spacing from one another. Also, in the paper output  30 , they can be further transported one after the other according to the arrow P 11  with at least twice the transfer printing speed. 
     In the operating mode called “alternating simplex printing,” it is thus provided according to the present invention that in the paper input  16  the individual sheets at the input section  28  are supplied to the printing units D 1 , D 2  with at least twice the transfer printing speed. In the paper output  30  as well, the individual sheets are likewise further conveyed and deposited with at least double the speed. By means of these measures, the individual sheets arrive at the common input section  28  and at the common output section  42  without the possibility of the occurrence of a collision of individual sheets and, accordingly, a paper jam. Preferably, the transport paths for the individual sheets supplied to the first printing unit D 1  and the individual sheets supplied to the second printing unit D 2  are of symmetrical construction, or are at least equal in length so that on both transport paths the individual sheets can be braked and accelerated with the same speed profile. In this way, it is possible to construct the drives and apparatuses required for the transport in the same way. In addition, it is possible to use control units of the same type. 
     FIG. 5 schematically shows duplex print operation in which the individual sheets are printed on both sides. The individual sheets supplied to the input section  28  are supplied to the first transfer printing transport path  44  by means of the first shunt W 1  (arrow P 13 ). After printing by the first printing unit D 1 , the respective individual sheet is conveyed along a turning over path according to the arrow P 14  via the shunt W 2 . This turning over path is a part of the carrying-off channel  52 . Subsequently, the conveying direction is reversed according to arrow P 15 , and the shunt W 2  then guides the individual sheet into the connecting channel  48  according to the arrow P 16 . The individual sheet is then diverted to the second transfer printing transport path  46  in the direction of the arrow P 17  by the shunt W 3 . The not-yet-printed back of the individual sheet is thus supplied to the printing unit D 2  for printing. Subsequently, the individual sheets are supplied to the shunt W 4  according to the arrow P 18 , and are transported into the paper output  30  along the arrow P 19 . Since in this state the individual sheet is transported with its back side up, it still has to be turned over before being deposited into the compartments  32  to  36 . The shunt W 5  serves for this purpose. First, the individual sheet is guided by the shunt W 5  in the direction of the arrow P 20  for a predetermined turning over path. The transport direction according to the arrow P 21  is then reversed, and the shunt W 5  conveys the individual sheet in the direction of the arrow P 22 , whereupon it is deposited in side-correct fashion in the deposit compartments  32  to  36 . 
     As can be seen, the shunt W 2  operates as a turning over apparatus in order to supply the back of the individual sheet to the printing unit D 2 . Alternatively, the shunt W 3  also can be used for turning over the sheet. The individual sheet leaving the printing unit D 1  is then guided via the shunt W 2 , the connecting channel  48  of the shunt W 3 , and then, for a short turning over path, along the supply channel  50  in the direction of the shunt W 1 . Subsequently, the transport direction is reversed and the shunt W 3  guides the individual sheet in the direction of the printing unit D 2  with its back side facing up. 
     FIG. 6 schematically shows a further mode of operation, two-color simplex printing, in which the front of an individual sheet is printed with two image patterns of different colors. The two printing units D 1 , D 2  print image patterns of different colors. In the named operating mode, two-color simplex printing, the individual sheet is supplied to the printing unit D 1  via the shunt W 1  (arrow P 25 ). Subsequently, the individual sheet is supplied via the shunt W 2  to the connecting channel  48 , without turning over the sheet, and is then supplied to the printing unit D 2  via the shunt W 3  (arrows P 26 , P 27 ). The printing unit D 2  prints the front with a color different from the color of the printing unit D 1 . Subsequently, the individual sheet is ejected to the paper output  30  via the shunt W 4  (arrow P 28 ). 
     FIG. 7 schematically shows the transport path of an individual sheet in the operating mode two-color duplex printing, in which the front and the back of an individual sheet are printed with image patterns of different colors. A precondition of this is that the printing units D 1  and D 2  print multicolored images. For the two-color printing of the front, the procedure is the same as for the operating mode two-color simplex printing as described with reference to FIG.  6 . The arrows P 25 , P 26 , P 27  and P 28  illustrate the transport path. Subsequently, the individual sheet is again supplied to the printing unit D 1 . The arrows P 29  to P 36  illustrate the transport path of the individual sheet for the printing of the back. So that this back side is supplied to the printing unit D 1 , the individual sheet must be turned over on the transport path between the printing unit D 2  and the printing unit D 1 . This turning over can, for example, take place at the shunt W 4 , the shunt W 2  or the shunt W 3 . In a preferred embodiment of the present invention, the turning over takes place using the shunt W 4 , i.e., the individual sheet is first transported for a short turning over path in the direction of the shunt W 5  whereat the direction of transport is then reversed and the individual sheet is conveyed further in the direction of the shunt W 2 . After the transport into the paper output  30  according to the arrow P 36 , a further turning takes place by means of the shunt W 5 , and the side-correct depositing of the individual sheet, printed on both sides with, respectively, two color images, subsequently takes place. 
     An alternative transport of the individual sheet through the high-performance printer  10  for the realization of the operating mode two-color duplex printing can take place in the following manner. First, the individual sheet is supplied to the printing unit D 1  from the input section  28  via the shunt W 1 , its front is printed, and it is subsequently guided briefly in the direction of the shunt W 1  for turning, via the shunts W 2  and W 3 . After passing the shunt W 3 , the direction of transport is changed in the direction of the printing unit D 2 , and the individual sheet is conveyed on the transfer printing transport path  46 . The shunt W 3  thus serves as a turning over station. The back of the individual sheet is accordingly printed at the printing unit D 2 . Subsequently, the individual sheet is again supplied to the first printing unit D 1  via the shunts W 4 , W 2 , W 3  and W 1 , in order now to print the back. The individual sheet must be turned over for this purpose. This takes place at the shunt W 4 , where it is conveyed briefly in the direction of the shunt W 5 , the direction of transport is reversed, and it is transported in the direction of the shunt W 2  in the turned state. After the printing of the back of the individual sheet in the printing unit D 1 , the individual sheet is supplied to the printing unit D 2  via the shunts W 2  and W 3 , wherein it is turned. Now the front side is printed by the printing unit D 2 . Subsequently, the individual sheet is guided to the deposit compartments  32  to  36  via the shunt W 4 . Since it now moves in the correct position, i.e. with the upper side up, into the depository  30 , it does not need to be turned over again by the shunt W 5 . 
     FIG. 8 shows the arrangement of two high-performance printers  10  and  10 ′ to form a printing system  55 . The two high-performance printers  10  and  10 ′ are of identical construction so that the individual components do not need to be explained again. An interchange apparatus  56  is arranged between the ejection channel  38  of the first high-performance printer  10  and the external paper input channel  26  of the second high-performance printer  10 ′, which apparatus conveys individual sheets from the high-performance printer  10  to the high-performance printer  10 ′. Each high-performance printer  10 ,  10 ′ can operate in the already-described operating modes simplex printing, alternative simplex printing, two-color simplex printing, one-color simplex printing and two-color duplex printing. By combining the various operating modes, wherein a first operating mode is set in the high-performance printer  10 ′ and an agreeing or other operating mode is set in the high-performance printer  10 ′, new variants of operating modes are enabled. For example, both high-performance printers can operate in two-color simplex operation, wherein the first printer prints the front with two differently colored image patterns and the high-performance printer  10  prints the back with two differently colored image patterns. If respectively different colors are selected for a total of four different printing units, the printing system  55  can accomplish a four-color duplex printing; i.e., the front and the back respectively can be printed with four differently colored image patterns. 
     The printing system  55  further can be expanded in that at least one additional high-performance printer of the type of the high-performance printer  10  is connected to the high-performance printer  10 ′. In this way, with the use of all the technological possibilities of the high-performance printer, an n-color duplex printing is enabled in which an individual sheet is printed on the front and on the back with n different colors, where n is an arbitrary whole number. 
     Although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the spirit and scope of the invention as set forth in the hereafter appended claims.