Patent Application
20070172270
The invention concerns a method and a device for printing of a recording medium in which a recording medium is printed with a first toner image in a first printing process by a printing device; the first toner image is fixed on the recording medium in a fixing device, whereby the recording medium shrinks along at least one main axis; and in which the same recording medium is subsequently printed with a second toner image in a second printing process.
There are numerous print operating modes in which a recording medium passes through a fixing process after the printing with a first toner image. In this fixing process, which generally occurs under pressure and relatively high temperature, the moisture in the recording medium (generally paper) is reduced, whereby a shrinking occurs in the longitudinal direction and/or width direction. The shrinking effect can be different in both of these directions, dependent on the fiber direction in the paper. The degree of the shrinkage likewise depends on the parameters of the fixing process. When a further toner image is subsequently applied on the same recording medium, given an otherwise identical printing process both print images are no longer in registration with one another, which leads to quality losses. The shrinking in the direction of a main axis can typically be up to 1%, meaning the shrinking in the longitudinal direction can be more than 2 mm given a sheet of the size DIN-A 4. The effect is even more distinct given even larger formats.
A method for operation of a printer with two printing groups in which various printing modules can be realized is known from WO 98/18054 by the same applicant. In a duplex printing operation, individual sheets are printed on both sides, whereby a fixing occurs between the respective printing process [sic]. Another operating mode is the two-color simplex printing, in which two image patterns of different color are printed on the front side of a single sheet. This operating mode is also known as highlight color printing. A further operating mode is two-color duplex printing, in which the front side and the back side of a single sheet are printed with image patterns of different color. Further reference is made again below to the cited printed document in connection with the specification of an exemplary embodiment. This printed document is herewith incorporated by reference into the disclosure content of the present patent application.
Printing systems and printing methods in which print images to be generated are corrected dependent on a shrinking of the carrier material are known from the documents DE 101 11 216 A1 and Jp 01-266568. Such a shrinking of the carrier material in particular arises due to heat effect on a recording medium on which the print image should be generated. From the document Ep 0 685 959 A2 it is known to analyze images stored in pixel form with the aid of raster cells that comprise 2×2 raster cells [sic] and to check whether color transitions from black to white raster cells are present. Also known from the document Ep 0 469 282 A2 is a printing method or a printing system in which the size of color extractions of a print image printed over one another on a carrier material [sic] of the paper shrinking of the [sic] occurring upon fixing of each color extraction [sic]
Furthermore, an electrographic printing device for printing of band-shaped recording media of different band widths is known from Ep 0 699 315 A1. A paper band is transported to and printed at a single printing group with a usable width of at least double the width of the paper band in a juxtaposition. An intermediate fixing of the first toner image occurs in the various printing operating modes, whereby a shrinking of the paper web occurs. The content of this document is discussed in detail in connection with the specification of exemplary embodiments. This document is hereby incorporated by reference into the disclosure content of the present patent application.
It is possible to reduce the shrinking effect in that the carrier material is brought to a low relative moisture via drying before the printing process. The shrinking effect is then reduced in the subsequent first fixing. However, such a measure is connected with a high expenditure. Another possibility is to climatically treat the carrier material after the first fixing process and to reproduce the original relative moisture prevailing in the first printing process. The shrinking process occurring in the fixing is thus reversed. This measure is also connected with a very high technical expenditure.
It is the object of the invention to specify a method and a device that allows or, respectively, allow a high print quality to be generated on the carrier material with relatively low technical effort.
This object is achieved via the features of the independent claims. Advantageous developments are specified in the dependent claims.
According to the invention concerning a method, the shrinking correction occurs via a software-technical intervention in the generation of the bitmap for the generation of the latent image for the first printing process or for the second printing process. The number of the image points to be taken into account in the printing is hereby changed corresponding to the expected shrinkage in the direction of the main axis. The main axis essentially runs in the line direction in which the LED line runs given an LED character generator. In the first printing process, in the generation of the bitmap the print image can be enlarged via insertion of additional image points in the line direction. The associated LEDs are hereby controlled such that they produce no image points to be inked at the appertaining image point positions. If the shrinking should be taken into account in the second printing process, the number of the image points to be taken into account in the printing is to be correspondingly reduced in the generation of the associated bitmap. Image points are accordingly omitted and the line length correspondingly shortened in the generation of the bitmap.
The addition of image points for extension of the line or, respectively, the omission of the image points for shortening of the line advantageously occurs at the same image point positions for successive lines, such that overall print point columns are added or omitted in the bitmap. It is likewise possible to also apply the cited principle when the main axis runs in the transport direction of the recording medium, i.e. image point lines are added or omitted in a similar manner in order to compensate the shrinking.
According to a further aspect of the invention, a device is specified for printing of a recording medium. This device enables the compensation of the shrinking effect.
For a better understanding of the present invention, in the following reference is made to the preferred exemplary embodiments shown in the drawings, which preferred exemplary embodiments are described using specific terminology. However, it is noted that the protective scope of the invention should not thereby be limited since such variation and further modifications to the shown devices and/or the methods as well as such further applications of the invention as they are shown therein are viewed as typical present or future expertise of a competent average man skilled in the art. The Figures show exemplary embodiments of the invention, namely:
A high-capacity printer 10 in which the invention can be used is shown in
Transport paths for the transport of the single sheets are arranged inside the high-capacity printer 10, via which transport paths various operating modes of the high-capacity printer are realized. Transfer printing transport paths 44, 46 that are respectively adjusted by actuators are respectively associated with the printing groups D1, D2, such that the supplied single sheets have [sic] their transfer printing speed at the printing groups D1, D2. Both transfer printing transport paths 44,46 are connected with one another via a connection channel 48. The transport path around the first printing group D1 is expanded into a ring via a feed channel 50 via which single 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 group D2 is expanded in a similar manner into a ring via a discharge channel 52 via which printed single sheets can be fed from the printing group D1 to the output section 42.
A first shunt W1 is arranged between the input section 28, the first transfer printing transport path 44 and the feed channel 50, which first shunt W1 enables single sheets to be selectively supplied from the input section 28 to the first transfer printing transport path 44 or to the feed channel 50. A further variant exists in that single sheets transported on the feed channel 50 in the direction of the first shunt W1 can be supplied to the first transfer printing transport path 44.
Furthermore, a second shunt W2 and a third shunt W3 are arranged at the ends of the connection channel 48 and respectively connect the adjoining transport paths 44, 48, 52 or, respectively, 46, 48, 50. A fourth shunt W4 is located in proximity to the output section 42 and connects the adjoining transport paths. The paper output 30 contains a fifth shunt W5 that operates as a turnover device. A control device 54 is also to be indicated to which waste single sheets are fed via a shunt W6.
Various operating modes of the high-capacity printer 10 can be realized via the arrangement described in
A further operating mode is two-color simplex printing, also often designated as highlight color printing, in which the front side of a single sheet is printed with two image patterns of different colors. Both printing groups D1, D2 then print image patterns of different colors. In this operating mode, the single sheet is supplied to the printing group D1 via the shunt W1, printed, and fixed for the first time in the fixing station 12, whereby a shrinking occurs. The single sheet is subsequently supplied to the connection channel 48 via the shunt W2 without turnover and then to the printing group D2 via the shunt W3. The printing group D2 prints the shrunk front page with a color different from the color of the printing group D1. The single sheet is subsequently fixed a second time in the fixing station 14 and output to the paper output 30 via the shunt W4. A process workflow is also possible in which the printing group D2 prints first and the printing group D1 prints the second toner image after the fixing.
A further operating mode with intermediate fixing is two-color duplex printing, in which the front side and the back side of a single sheet are printed with image patterns of different colors. It is a requirement for this that the printing groups D1 and D2 print different-colored print images. As in the operating mode described above, two-color simplex printing proceeds for two-color printing of the front side. The single sheet is initially printed two-color on one side with the printing groups D1 and D2. The single sheet is subsequently resupplied to printing group D1 via the channel 48 and the shunts W1 and W6 for printing of the back side. The single sheet must be turned over on the transport path between the printing group D2 and the printing group D1 so that this back side is supplied to the printing group D1. This turnover can, for example, occur at the shunt W4, the shunt W2 or the shunt W3. The second color is then printed on the back side of the single sheet by the printing group D2. The single sheet can experience different shrinkages in the various fixing processes.
The various operating modes are described in greater detail in the already-mentioned WO 98/18054. Reference is herewith made to the statements made there.
The various units for the electrophotographic process are grouped around the photoconductor drum 61. A charge device 62 in the form of a charge corotron for charging of the intermediate carrier 61, which is designed as a photoconductor drum; an LED character generator 63 with a light-emitting diode comb for character-dependent exposure of the intermediate carrier 61 that extends over the entire usable width of the intermediate carrier 61; a developer station 64 for inking of the character-dependent charge image on the intermediate carrier 61 with the aid of a one- or two-component developer mixture; a transfer printing station 65 that extends over the width of the intermediate carrier 61 and with which the toner images are transferred onto the recording medium 61 [sic]. For removal of the residual toner after the development and the transfer printing, a cleaning station 66 is provided with integrated cleaning brush with associated suction device as well as a discharge device 67. The intermediate carrier 61 is driven in an electromotive manner and moved in the arrow direction in the printing operation.
Furthermore, the printing device 58 contains a fixing station 68 downstream from the transfer printing station 65 in the transport direction of the recording medium, which fixing station 68 is designed as a thermoprinting fixing station with a heated fixing roller 69 with associated pressure roller 70, as well as with guidance rollers 71 downstream from the fixing station that, among other things, serve as output elements for a stacker 72 for the recording media 60. Other fixing stations are also possible instead of the shown fixing station, for example with a heated or unheated supply saddle. The band-shaped recording medium 60 is, for example, confectioned [sic] as a pre-folded continuous paper provided with border perforations and, starting from a reservoir region 73, is supplied to the transfer printing station via feed rollers 74. However, it is also possible to supply a recording medium without border perforations via a roller feed.
The transport of the recording medium 60 thereby advantageously occurs via a transport device 75 associated with the transfer printing station 65 in the form of transport bands provided with pins, which transport bands engage in the border perforations of the recording medium 60 as directed via drive shafts 77. For the case that a recording medium free of transport holes is used, an adapted transport device familiar to the average man skilled in the art is to be provided that transports the recording medium via, for example, friction, controlled by a control device scanning synchronization markers. Furthermore, a deflection device 78 via which the recording medium 60 is directed back from the fixing station 68 to the transfer printing station 65 is arranged in the housing region of the printing device between reservoir region 73 and the fixing station 68.
The electrographic printing device is suitable for printing of recording media of different band widths. For these purposes, the intermediate carrier 61 (photoconductor drum) exhibits a usable width that corresponds to the largest possible recording media width (for example, a format DIN A3 across). This width corresponds to double the DIN A4 width. It is therewith possible to arrange two recording medium widths DIN A4 next to one another lengthwise in the region of the transfer printing station 65. The fixing station 68 and the other electrophotographic units (such as developer station 64, character generator 63, cleaning station 66) are designed corresponding to this usable band width.
An adaptation of the width of the character generator 63 to different recording medium widths requires no mechanical alteration to the character generator when (as in this case) an LED character generator with a plurality of LEDs arranged in series is used. An adaptation to the recording medium width used occurs electronically via activation.
The deflection device 78 arranged in a return channel for narrow recording media from the fixing station to the transfer printing station has two tasks: it serves for the lateral offset of the recording medium web in the continuous operation and for front-back side rotation of the recording medium 60 in the turnover operation. It is designed to be switched over dependent on the operating mode.
For two-sided, one-color printing of a narrow recording medium (one-color duplex operation) as it is shown in
The printing device is also suitable for multicolor printing operation in the operating mode “two-color duplex printing”. For this purpose, the developer station 64 is designed such that it generates separate inkable developer zones E1 and E2 on the intermediate carrier 61. A corresponding developer zone E1 or, respectively, E2 on the intermediate carrier 61 is thereby associated with each position region of the narrow recording medium 60 upon passage through the transfer printing station 65. For generation of these separate inkable developer zones E1 and E2, two developer stations 64/1 and 64/2 arranged in series can be respectively associated with the developer zones. The developer station 64/1 thereby contains a toner mixture of a first color, for example red, and the developer station 64/2 contains a toner mixture in a second color, for example black. The developer stations 64/1 and 64/2 are designed such that they can be activated separately with regard to the developer zones E1 and E2.
In order to be able to print a narrow recording medium 60 on both sides with different colors corresponding to the representation of
A further operating mode is the “two-color simplex operation”, in which a narrow recording medium 60 (of, for example, the width A4) is printed with two colors on one side. A separate inkable developer zone E1, E2 is thereby associated with each recording medium position on [sic] the transfer printing station 65. The printing of a toner image in a first color (for example red) over the developer zone E2 thereby occurs in a first pass through the transfer printing station 65. The toner image of this first color is subsequently fixed in the fixing station 68, whereby a shrinking of the recording medium occurs, and the recording medium 60 is re-fed without turnover to the transfer printing station 65 with the associated developer zone E1. The deflection device 28 is thereby located in the pass position and the recording medium is only offset in terms of width under retention of the front side-back side association. In the second pass through the transfer printing station 65, a second toner image with the second color (for example black) is superimposed on the first fixed toner image with the first color (red), and a two-color overall image is thus generated. The superimposed toner image is then re-fixed in the fixing station 68 and the recording medium printed on one side is deposited in the stacker 72.
Further details with regard to the printing system according to
A further application for the present invention for shrinkage compensation is given with the arrangement of printers as a twin system. Two printers are hereby coupled with one another such that two printers effect two printing processes in succession with intermediate fixing. For example, a first printer prints the paper front side and the second printer prints the paper back side. The fixing occurs after the first printing process, whereby the shrinkage effect occurs. A turnover device or a pass-through device can be arranged between the first printer and the second printer. The already-described two-color simplex printing or the duplex printing can be realized in this manner with a twin printing system.
Using an example,
Both examples according to
The method shown in
Images can be adapted relatively simply via insertion and/or omission of columns and lines without a noticeable quality change being visible. The method according to
As a further method, it is possible for the object type image when the image is located in an unprocessed (undithered) state [sic]. It is then possible to generate the image to the desired image size during this process.
A further possibility given the object type image lies in the displacement of the image, whereby a change of the image content is completely avoided. The displacement conforms to the position of the image on the carrier material. If the image is on the edge, it is placed exactly at the new edge. If the image is located in the middle of the print region, it is re-placed according to the shrinkage. The separation from the other objects of the print side is thereby enlarged or reduced.
The shown methods can also be combined among one another. A compensation of the shrinkage in the paper feed direction can thus occur in which the line frequency of the character generator is changed corresponding to the expected shrinkage in the transport direction. To generate the second toner image in the compressed form, the line frequency is then increased relative to the line frequency in the first print process. Another variant lies in changing the transport speed of the recording medium. For example, in the second process the transport speed of the recording medium in the second printing device is reduced relative to the transport speed in the first print process to apply the toner image in a compressed form. Furthermore, the degree of the shrinkage of the recording medium can be empirically determined and the compensation measures effected dependent on the degree of the shrinkage. The shrinkage can, for example, be determined with the aid of tectors [sic] that, for example, establish the length difference of a single sheet before and after the first fixing process.
Although preferred exemplary embodiments are shown and described in detail in the drawings and in the preceding specification, this should be viewed as purely exemplary and not as limiting the invention. It is noted that only the preferred exemplary embodiments are shown and described, and all alterations a modifications that presently and in the future lie in the protective scope of the invention should be protected.
Reference character list
| Number | Date | Country | Kind |
|---|---|---|---|
| 103 44 238.3 | Sep 2003 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP04/10687 | 9/23/2004 | WO | 12/11/2006 |
