EP1445662B1 - Method for correcting the calibration of a registered printing process - Google Patents

Abstract

The method involves determining the influence of a toner field (1) applied to a transport belt for print sheets on the register maintenance accuracy of the printing process and printing it out in the form of at least one correction value or parameter suitable for the correction of calibration. The correction value is placed in a correction value table for access for registering sheets for printing processes.

Description

The invention relates to a method for correcting the calibration of the registration and / or register accurate printing process of an electrophotographically operating printing machine, preferably a color printing machine.

A method for calibrating the above-mentioned type is already in EP 1 156 384 been proposed.

It is known that, due to the printing material itself, registration errors, ie errors in precise overprinting of the color separations in color printing, can arise and in particular can affect the perimeter pass or the so-called intrack passer in printing process direction. Register errors, ie errors in the precise placement of a printed image on a printed sheet, can thus occur in particular in the circumferential register in the color or monochrome printing. In the following, the terms "register" or "register validity" in the broader sense are sometimes also used as a generic term including the passport. Conversely, the same is often true for the register as well as for the register.

In the printing material-related registration errors, ie errors that affect the registration of the color separations of a color printing relative to each other and each individually to the substrate, in particular the so-called gear-Passerfehler, the so-called creep Passerfehler and the so-called imprint-related magnification Passerfehler, not with a by Concurrency error caused by periodic magnification error is to be distinguished from each other.

The gear-registration error can be caused by the fact that a printing material through the narrow gap (nip) between the conveyor belt and a concomitantly driven, the print image on the substrate applying pressure member or transfer member (eg., A blanket cylinder), the speed of which (As for example, in a transmission by changing the gear ratio) changed, is forced.

The creep register error can be caused by the fact that in a deflection region or other curved path of the conveyor belt, the surface of the (so-called on twisting paths) printing material lies on a different radius to the deflection or curvature axis than the surface of the conveyor belt and therefore one has different web speed.

The printed material caused magnification registration error can be caused by the fact that a substrate through the narrow gap (nip) between the conveyor belt and a pressure image on the substrate applying pressure member or transmission member, the shape of which is changed in the pressure range is forced, resulting in a spread or enlargement of the printed image in the direction of the substrate can result.

In the foregoing, it is said in each case which cause could be responsible for the respective registration error, because the causes can be very complex and, ultimately, have not yet been clarified completely and confidently. For example, of course, temperature or humidity fluctuations may be responsible for registration errors. In particular, however, the registration errors fall on the basis of the printing material, eg. For example, depending on the format, thickness, coating, history and so on, the substrate of different sizes. Therefore, an online correction is particularly desirable. However, it is always important to correct the error, regardless of whether the cause of the error has been completely researched. The naming of the errors is therefore not a determination of a cause, but at best a kind of classification with regard to a disposal possibility of the respective error and serves more to facilitate communication between professionals.

From the publications mentioned above, methods can be taken which make it possible to determine corrective values or parameters for the print substrate-related registration errors which make it possible to correct the printing process with regard to register accuracy and thus to improve it. For this purpose, the correction values obtained by means of corresponding calibration runs can be stored, for example, in a correction table relating to the printing material, and it is possible to correct printing material sheets to be printed for the printing process by accessing this table.

However, it can also be provided to apply larger-area toner fields on a conveyor belt for the printing material, in particular in larger spaces between to be printed sheets of printing material would fit into a printing material, but for example, the currently running print job, for whatever reason, no printing material sheet is provided, so a corresponding gap remains. In the control of the printing process but, to put it another way, a window or frame for the introduction of a printing material sheet available. Such a window or such a gap is now used, preferably in the size of a printing material sheet, preferably in accordance with the size of a maximum large sheet of, for example, 470 mm by 343 mm, to apply a toner field to the extent so far free conveyor belt.

Namely, it is a known problem that in electrophotographic printing, when a toner image is fixed with a roller fixing device using fixing oil, oil can be carried up to the area of the imaging station by a subsequent reverse pressure, causing problems because it is a photoconductor, for example or a blanket soiled. By a large-area toner field application to the conveyor belt, for example, such oil residues can be safely bound in the toner and later removed and be prevented that the residual oil instead passes into the print image of the next to be printed substrate sheet and there impairs the printed image.

The object of the invention is to improve a method of the type mentioned, and it has been inventively recognized that such a toner field can lead to registration errors.

In solution of the problem is therefore proposed according to the invention that the influence of an applied on a conveyor belt for printing material toner field is determined on the register and / or register accuracy of the printing process and expressed in the form of at least one suitable for the correction of the calibration correction parameter or parameter.

Such a toner field is thus also advantageously taken into account in the calibration or by a calibration, and the toner field is preferably treated like a printing material sheet from a special printing substrate. Errors occur through the toner field, probably by changing the frictional engagement between the conveyor belt and a concomitantly driven, the print image on the substrate applying pressure member or transfer member, as in place of the conveyor belt sections the toner field occurs with its other coefficient of friction. Likewise, a change in the frictional engagement or the delivery due to the continuous toner field between several moving intermediate carriers, for example between photoconductor and blanket cylinder, lead to such errors. Primarily, this can lead to a gear register error, possibly also to a magnification registration error. If these additional registration errors were not taken into account by toner fields, then the correction of printing material-related registration errors would become less and less reliable as the printing process progresses. The printing process would in this respect - figuratively speaking - so to speak "get out of hand".

It is preferably provided that the at least one correction parameter is similar to a correction value for the influence of a particular printing material in a Correction table is stored, which is accessible for a registration of substrate sheets for the printing process.

A development of the invention provides that at least one such toner field is applied to the conveyor belt for determining the influence of a toner field and for determining the at least one correction parameter for a calibration run and at least one register mark in front of the toner field and at least one register mark behind the toner field on the Transport belt is applied, wherein each of said register marks includes markers provided for the color printing process colors, and these register marks are detected by measuring.

It is therefore supplemented or corrected by its own corresponding calibration with at least one toner field, the printing material-related calibration.

"Color" is very broad in this context. It may thus be the usual colors of four-color printing, cyan, magenta, yellow and black, but also other or additional spot colors, colorless toners, lacquers or the like, which could be added to the print image in the manner of a color separation with a Bebilderungsstation.

Preferably, the invention provides that instead of at least one of said individual register marks, a plurality of register marks is used to average over the measurement results or the measurement results of their respective same color markings.

By the plurality of register marks more information can be achieved in a measuring run, are recognized by the reliable registration errors and eliminate, especially with regard to differently caused or to be corrected registration error, preferably not recognizable with individual register marks magnification registration error. On the other hand, the process works comparatively quickly by averaging information. It is suitable for an online application.

Furthermore, it can be provided that a plurality of mutually spaced toner fields along the transport direction is successively applied to the conveyor belt and that in each case in the space between two successive toner fields at least one register mark is applied to the conveyor belt, preferably via the measurement results in spaces between the toner fields register marks or their identically colored markings is averaged.

As already mentioned above can be provided according to the invention specifically that a so-called gear-Passerfehler is corrected, which is caused by a toner field through the narrow gap (nip) between the conveyor belt and thereby driven along, applying the print image on the substrate A printing member or transfer member, or between a transfer member and a Bebilderungsorgan whose speed is changed by, is forced and / or that a so-called magnification registration error is corrected, which is caused by a toner field through the narrow gap (nip) between the conveyor belt and a pressure member on the printing material applying pressure member or transfer member, or between a Bebilderungsorgan and a transfer member whose shape is changed thereby in the printing area is forced.

A development of the method according to the invention provides that of the existing plurality of toner fields and / or the register marks applied in spaces between the toner fields, only a selected, predetermined number is used.

In addition, a plurality of register marks are preferably applied to the conveyor belt successively in front of the entirety of the toner fields and / or behind the entirety of the toner fields, but in particular the register marks behind the toner fields could also be omitted.

With the exact number of the plurality of register marks and toner fields, an optimum should be found between the reliability of the determination of the errors and the time required for the necessary measurements.

The plurality of register marks in front of and / or behind the toner fields should each be approximately on the order of 20 to 60 register marks, wherein preferably the same number of register marks in front of and behind the toner fields is used.

The appropriate number of toner fields is one particular embodiment of an electrophotographic printing machine, by way of example only, such as 18 toner fields.

It may well be provided that not all existing register marks and / or toner fields are actually used for the measurement of parameters.

With the register mark scheme according to the invention and the associated calibration sequence, it is possible, in particular, to detect gear and magnification registration errors reliably and quickly and in only one or two measuring runs.

The number and the scheme of the register marks is not exactly defined, but can change according to needs and circumstances, as well as the calibration sequence.

An embodiment of a register mark scheme for carrying out the method according to the invention, from which further inventive features may result, to which the invention is not limited in scope, is shown in the single drawing figure and will be described in more detail below, but, as I said , merely by way of example, explained.

Shown in the drawing figure is an example of a register mark scheme according to the invention, the scale-scale by dash-dotted lines Lines broken and only partially shown in three sections. In the middle of the three sections, between the dot-dash lines, three toner fields 1 are indicated, which are applied to a conveyor belt, not shown, and are transported by this in the direction of an arrow 6. Registermark-like markings could also be provided on each of the toner fields 1 itself. Between the toner fields 1 register marks 3 are applied to the conveyor belt. As indicated in the drawing, the three drawn toner fields 1 preferably symbolize eighteen toner fields, which are applied one behind the other on the conveyor belt.

In the transport direction 6 located in front of the toner fields 1 section of the conveyor belt twenty register marks 4 are applied to the conveyor belt in the illustrated example, of which, however, only four register marks 4 are shown in the drawing for reasons of space. Likewise, it is provided in the illustrated example that behind the toner fields 1 twenty register marks 5 are applied to the conveyor belt, of which in turn only four register marks 5 are shown.

As already mentioned above, however, it is also possible, for example, for the register marks 5 to be dispensed with altogether or for another number of register marks 4, 5 to be provided as twenty.

In the following, it will be explained in more detail, specifically for the gear registration error, how this or the associated parameter is determined in each case.

The gear parameter for a toner surface is calculated for the given color as follows from the measured register mark data RegData (even if the toner surface is only printed in black, for example, all colors are affected in their registration!): $${\mathit{Gear}}_{\mathit{colour}}:=-\left({<{\mathit{RegData}}_{\mathit{colour}\mathit{.}\mathit{patch}}>}_{\mathit{EffBatch}}-\frac{\left({<{\mathit{RegData}}_{\mathit{colour}\mathit{.}\mathit{patch}}>}_{\mathit{PrePrintCal}}+{<{\mathit{RegData}}_{\mathit{colour}\mathit{.}\mathit{patch}}>}_{\mathit{PostPrintCal}}\right)}{2}\right)$$

In case the register marks 5 are omitted, the gear parameter is calculated as follows: $${\mathit{Gear}}_{\mathit{colour}}:=-\left({<{\mathit{RegData}}_{\mathit{colour}\mathit{.}\mathit{patch}}>}_{\mathit{EffBatch}}-{<{\mathit{RegData}}_{\mathit{colour}\mathit{.}\mathit{patch}}>}_{\mathit{PrePrintCal}}\right)$$

In this case, the square brackets <> indicate an averaging over the sequence called the index, in these cases via the register marks 3 ( EffBatch ) used for the measurement of the gear parameter, as well as the register marks 4 of the so-called preprint calibration ( PrePrintCal ) and Register marks 5 of the so-called postprint calibration ( PostPrintCal ), if the register marks 5 are not a priori, as described above.

The size EffBatch takes into account the fact that not all, for example, 18 marks of a sequence of toner fields are used for the calculation, but only 11 values, for example, as in the case of perimeter calibration for large sheets (A3, A3 +, tabloid etc.) Case is. This corresponds to a full occupancy of the conveyor belt with large toner areas, so that residual errors that are based on the specific position of the sheet on the conveyor belt, be averaged out.

The color variable can assume the values cyan, magenta, yellow, black of a normal four-color print or additionally or alternatively also additional colors, including possibly colorless toner, or varnish in the printing press.

The index patch indicates that it is data derived from marks printed on the conveyor belt.

Claims (8)

1. Method for the correction of the calibration of the precisely aligned and/or registered printing process of an electrophotographically operating printing machine having a transport belt for sheets of printing material, preferably a color printing machine,
   characterized in that,
   for determining the influence of a toner field (1) and at least one correction parameter for one calibration cycle, at least one such toner field is applied to the transport belt and that at least one register mark (4, 5) is applied to the transport belt upstream of the toner field and at least one register mark is applied to the transport belt downstream of the toner field, each of said register marks comprising marks of the colors intended for the color printing process, and that said register marks are detected by measuring means.
2. Method in accordance with Claim 1, characterized in that the at least one correction parameter - similar to a correction value - is recorded in a correction value table to represent the influence of a specific printing material, said table being accessible for a registration of sheets of printing material for the printing process.
3. Method in accordance with Claim 1, characterized in that, instead of at least one of said individual register marks, a plurality of register marks is used to determine the average of their measured results or of the measured results of their respective same-color marks.
4. Method in accordance with one of Claims 1 to 3, characterized in that a plurality of toner fields located at a distance from each other is successively applied to the transport belt in transport direction, and that in each intermediate space between two successive toner fields, at least one register mark is applied to the transport belt.
5. Method in accordance with Claim 4, characterized in that the average of the measured results for the register marks located in intermediate spaces between the toner fields or for their respective same-color marks is determined.
6. Method in accordance with one of Claims 3 to 5, characterized in that, from the available plurality of toner fields and / or register marks applied in intermediate spaces between the toner fields, only one selected, predetermined number is used.
7. Method in accordance with one of Claims 1 to 5, characterized in that a so-called gear-type registration error is also corrected, said error being caused in that a toner field is forced through the narrow gap (nip) between the transport belt and a consequently indirectly driven following printing member or transfer member applying the printing image to the printing material, or forced between a transfer member and an imaging member whose speed is changed as a result of this.
8. Method in accordance with one of Claims 1 to 6, characterized in that a so-called magnification-type registration error is also corrected, said error being caused in that a toner field is forced through the narrow gap (nip) between the transport belt and a printing member or transfer member applying the printing image to the printing material, or forced between an imaging member and a transfer member whose shape is changed in the printing region as a result of this.

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