EP1599343B1 - Printing system and method and computer program product comprising print data integrity monitoring - Google Patents

Description

The invention relates to a printing system, and more particularly to a method, a control device and a computer program product for monitoring printed data in a printing system. More particularly, the invention relates to a method of monitoring printed data in a high performance electrographic printing system.

In high-performance electrographic printing systems with a printing performance of more than 40 pages per minute, edge-punched, band-shaped paper as well as paper without edge perforation are used as the recording medium.

For high-performance printing systems, it is necessary for the print data and the printer itself to be synchronized page by page. For this purpose, a method is known in which at least two printed images are printed on each printed sheet, each printed image containing a bar code. These bar codes contain consecutive numbers. They can be read by a specific workstation, such as another printer or print engine, or a post-processing station. If deviations of the bar codes within an arc occur, then this is judged as an error.

In principle, the page numbers of the printed document can be used instead of the bar code. whereby it is possible to dispense with the printing of another control mark in the form of the bar code.

However, it is not always possible to use the page numbers, especially if a large print job consists of a large number of individual short documents, each with few pages, or if the documents do not contain page numbers. In addition, the automatic scanning of page numbers is much more complicated than that of a bar code.

A disadvantage of the previously known method is that the bar codes used in this case are very large and significantly affect the printed image of a printed page.

From the US 5,613,669 For example, a method for monitoring a high-performance production process for producing printed products is known. In this manufacturing process, the sheets to be printed are conveyed in a predetermined direction. In this case, a picture of the sheet or a section of the printed sheet is detected by means of a camera. The process synchronizes individual sections of the manufacturing process and calibrates the position of the sheets in the manufacturing process. Furthermore, this method comprises a control device with which an alarm can be triggered if, for example, the sheets are not merged correctly. This control function evaluates the image taken by the chamber, in which case a predetermined portion of the printed image or a code, such as a bar code, is read and evaluated.

From the US 3,458,688 a device for automatically identifying the line positions emerges. This device, besides being able to identify lines, also includes means for identifying different types of documents. Each document type is determined by means of a Identifies binary codes that may be printed as a bar code on the document.

The US 4,429,217 describes an apparatus and method for verifying credit cards, inserting credit cards into corresponding card cases, and stacking the card cases as appropriate for inserting the cards in envelopes. The cards are typically identified by specific information in the form of alphabetic, numeric or optical indicia (eg, 1-bar code or I-bar code) or information contained on magnetic stripes.

In the US 6,363,851 B1 For example, a method of making folded, bound printed products is described. Here, the initial product may be provided with individual printed markers so that each bound end product has at least one such mark. By means of this marking, for example, the page number or a sequence of further pages can be added. The mark can also represent the end of a particular sequence, which can then be used to monitor whether all necessary sub-products are present. The mark is preferably printed in a region which is cut off at the end of the production process.

The DE 10050 438 C1 discloses a method of synchronizing a plurality of paper-feeding channels of an inserter. Each sheet supplied by such a channel contains corresponding data or information identifying the membership of the sheet to a particular group, data identifying the sheet sequence within a group, and additional data indicating whether the sheet is a final or continuous one Sheet of a group. These data may be, for example, by means of a bar code, a 2 D code or other suitable coding on the sheets be upset. The group sequence number may consist of, for example, a six-digit number sequence and the sheet sequence number of a two-digit number sequence. The marking of an ongoing group or the group end can be in the form of a bit. In the case of an error, only one group is affected, which can be sorted out if necessary and supplemented by hand, for example.

Furthermore, it is usually necessary in so-called tandem printing systems to position the printed images of the two printing devices of the tandem printing system to the exact page. A tandem printing system is in the US-A-4,609,279 described. In the US-A-4,774,524 is for driving such a printing system provided to connect the main control devices of the two printers on the one hand via a host computer on a data control level and on the other hand via a second connection on a device control level. From the US B1-6,501,929 It is known to synchronize the printed page sequence in a tandem printing system via an electronic memory. From the US-A-5,488,458 a duplex printing system is known in which a control code is generated and printed for a page to be printed and the printed control code is evaluated. From the US-B1 6,246,856 is a printing device with two printing units for simultaneously printing the front and back of a web-shaped recording medium known. From the US-B1-. The above publications are hereby incorporated by reference into the present specification.

From the US 5,613,669 For example, a method for monitoring a high-performance production process for producing printed products is known. In this manufacturing process, the sheets to be printed are conveyed in a predetermined direction. In this case, a picture of the sheet or a section of the printed sheet is detected by means of a camera. The process synchronizes individual sections of the manufacturing process and the position of the Bends calibrated in the manufacturing process. Furthermore, this method comprises a control device with which an alarm can be triggered if, for example, the sheets are not merged correctly. This control function evaluates the image taken by the camera, in which case a predetermined portion of the printed image or a code, such as a bar code, is read and evaluated.

The US 5,265,008 relates to a system and a method for carrying out financial transactions by means of fax machines. A payment institution issues transaction vouchers to a particular customer, containing in the form of a bar code a series of alphanumeric random characters, each voucher printed with a different set of alphanumeric random characters. The party faxes this coupon to a central facility. The coupon will be read automatically and the set of alphanumeric characters will determine if this is an original coupon. Each coupon can only be used once. The individual vouchers of a customer must be used in a predetermined order.

From the JP 01 235658 A is a process to guard a printing process out. Each sheet of paper also prints a barcode that is a sequential number in the printing process. The barcode is automatically read after ordered workstations by means of a reader and compared with a serial number of the paper sheet. If the number of the barcode matches the serial number of the paper sheet, printing is OK.

The invention has for its object to provide a method for monitoring printed data in a printing system which is suitable for using smaller codes compared to conventional bar codes, and with which, nevertheless, the page-by-page synchronization of a large print job can be safely monitored. Furthermore, the invention has for its object to provide a printing system for performing the method.

The object is achieved by the invention specified in the independent claims. Advantageous embodiments of the invention are specified in the respective subclaims.

• Erzeugen eines Kontrollcodes für jeweils eine zu druckende Seite,
• Drucken des Kontrollcodes auf die jeweils entsprechende Seite eines zu bedruckenden Aufzeichnungsträgers,
• Automatisches Lesen und Auswerten der gedruckten Kontrollcodes.

According to a first aspect of the invention, a method of monitoring printed data in a printing system comprises the steps of:

• Generating a control code for each one page to be printed,
• Printing the control code on the respective corresponding side of a record carrier to be printed,
• Automatic reading and evaluation of the printed control codes.

According to this aspect, the invention is characterized in that control numbers are used as control codes which are not contained numerically in a checklist and that the checklist contains more control numbers than the number of counts contains control numbers. Individual control numbers are thus repeatedly included in the checklist. When evaluating the read control numbers, these can be compared in particular with the order of the control numbers of the checklist, with a deviation being assessed as an error.

It is also possible, if two or more control numbers are printed on one sheet, to carry out the evaluation by comparing the control numbers of the sheet, with a deviation being judged as an error.

According to a further advantageous embodiment of the invention, when evaluating the read control numbers their order compared with that of the control list.

Since the order of the control numbers in the control list deviates from a numerically ascending or numerically descending order, a very small number of sets can be used as the set of control numbers, such as a set of numbers consisting of a maximum of 64 numbers, and in particular a set of numbers consisting of a maximum of 16 Numbers, up to a number consisting of only eight, four or even two numbers, and yet it is possible to monitor a large number of pages. This is possible because, in contrast to conventional methods, in which each individual control number has a high information capacity, the information is transferred from the control numbers to the checklist in which this information is stored by the order of the individual control numbers. The larger the entropy in the numerical sense of the checklist, the greater the information contained in the checklist. In conventional methods, a decimal range of, for example, 0 to 99 is printed as a binary number in the form of a bar or bar code as a control mark. These binary numbers comprise seven digits and therefore form a correspondingly long bar or bar code.

The invention allows the use of one, two or three digit numbers. In extreme cases, the control number is a one-digit binary number, that is, each control number is either "0" or "1".

With the method according to the invention, the number of counts of the control numbers can thus be limited even to two numbers. With the invention, a number of numbers can be used which comprises not more than 32, in particular not more than 16, or not more than 8 numbers.

The checklist may be provided either as a stored data list or by a method (algorithm) for generating a consecutive sequence of control numbers. These methods are realized with typically pseudo-random number generators.

The period with which the control numbers repeat in the checklist is preferably greater than the typical print volume being executed on the printing system or greater than the maximum page number that may fail in a printing problem without being otherwise noted. If the typical print jobs only cover a few to a hundred pages, then a repetition period of 100 control numbers is sufficient. If the print jobs are considerably more extensive, it is expedient to provide correspondingly longer repetition periods. If, however, a few thousand pages are not printed in a large print job, this is also noticeable in other ways without the need for the monitoring system. Therefore, the repetition periods do not have to comprise more than a thousand or a few thousand control numbers. In the context of the invention, it is of course also possible to use longer repetition periods. In particular, if the checklists are generated by means of pseudo-random number generators, the repetition period can be significantly increased.

• Erzeugen eines Kontrollcodes für eine jeweils ein zu druckendes Druckbild,
• Drucken von zumindest zwei Druckbildern mit jeweils einem Kontrollcode auf einen zu bedruckenden Bogen,
• automatisches Lesen und Auswerten der gedruckten Kontrollcode.

Further provided is a method of monitoring printed data in a printing system, comprising the steps of:

• Generating a control code for each print image to be printed,
• Print at least two print images, each with a control code on a sheet to be printed,
• automatic reading and evaluation of the printed control code.

This method is characterized in that are used as control codes control numbers that are included in a checklist not numerically ascending or descending sequentially, and in evaluating the read control numbers, the control numbers of each sheet are compared with each other, and in case of a deviation, this as a mistake is judged.

According to a preferred method of the invention, after detecting an error by means of the monitoring method according to the invention, a complete sequence of n read control numbers is determined and based on this sequence it is determined at which page number of the print job the error has occurred. The determination of the page number can be done by means of a decoding table in which all sequences of n-control numbers and the corresponding page numbers are stored. However, it is also possible to determine the page number such that the control numbers are sequentially generated with a certain control number until the complete sequence of read control numbers has been generated, the number of control numbers generated being a measure of the page number.

The term "page" also includes the terms "print image" and "print page". For example, if a sheet-shaped recording medium is used, a sheet can also be understood to mean a web section if a continuous sheet is used or web-shaped recording carrier (fanfold, continous or web-shaped recording carrier) is used, which is first printed in the web-like state and cut in a post-printing processing operation to a single sheet. In the latter procedure, an assignment to the finally generated sheet can already take place during the printing, if the corresponding post-processing operations are clearly defined.

The method and the device can be designed to monitor the exact page assignment of print data on the print material, the so-called data integrity. This is particularly important in printing devices or printing systems of importance, having a plurality of printing units and in which at least two printing units on the same recording medium and in particular print on a portion of the recording medium, which is associated with an output sheet. As part of the second printing process, the printed bit marks are detected, the reading result is compared with the originally assigned code, and thus the printing process is controlled.

To produce the output sheet, in particular a web-shaped recording medium can be cut in a later processing step along the area boundaries to the sheet shape.

According to another aspect of the invention, which may be seen in combination or independently of the aforementioned aspects of the invention, there is provided a method of monitoring area data integrity in transmitting print data from a data source to a data receiver, wherein the print data is transmitted are sequentially numbered according to an N-digit binary number, where N is a natural number. The serial number is used to read a one-digit control code from a checklist and to read the print data of the Transfer area. Within the checklist a specific sequence of N single-digit control codes is included only once. When receiving the print data, the associated single-digit control code is read in each case in regions and, based on a comparison of the read sequence of single-digit control codes with the code sequences available in the checklist, a decision about the data integrity is automatically made.

According to this aspect, the data integrity in the area-by-area transfer or printing of print data can be checked with a simple, minimal single-digit binary control code. The binary control code is not disturbing when transmitting the data because it has so little information content. On the other hand, in particular when printing, it allows a minimal print image in the form of a simple stroke, which in particular also corresponds to the area boundary, e.g. Page boundary of a document can be printed. Thus, in addition to data integrity checking, the printed bar code can still be used as a control mark for processes following the printing process, such as cutting, folding or punching of the recording medium.

According to an advantageous embodiment of the fourth aspect of the invention, upon receipt of the print data on the basis of N consecutive single-digit control codes, an N-digit read binary number associated with an area is formed and the consecutive numbering is reconstructed and checked therewith; this can be done by determining their position in the checklist and comparing the number associated with that position with the sequential number of the area generated during transmission.

In a further advantageous embodiment, the N-digit read binary number is assigned to an area whose read control code is contained in the N-digit read binary number and in particular the area whose read In a further advantageous embodiment, the N-digit read binary number is assigned to an area whose read control code is contained in the N-digit read binary number and, in particular, the area whose read control code is at the first or last digit of the N-digit read binary number. On the basis of the comparison result can then be decided automatically whether in the data transmission partially data has been lost.

If the numbering rules are the same when sending and receiving the print data, the result of the comparison can be used to automatically determine the number of areas where data has been lost.

For the fourth aspect, a computer or a controller, especially a printer, may be used as the data source. As a data receiver, a controller, a printing unit, each of which prints the single-digit binary control code as a bit mark on a region of the recording medium and / or in particular a recording medium as a carrier of the printed information including the control code. Furthermore, the printed bit marks can be read with a sensor and the reading result compared with the control code associated with the transmission and thus the printing process can be controlled. With the invention, it is thus possible to accomplish consistent integrity monitoring of the print data, from the generation of the data in a computer, especially the host computer, to the finished printed document. In this case, it is particularly advantageous that associated print data of a region (eg in form fields of forms or on the front and back of the document) produced by various individual printing processes with one or more printing units on the document be verifiable in terms of their data integrity or correct togetherness.

It is also advantageous to print the data of one area onto a common area of the record carrier. When the recording medium is cut into output sheets, it is advantageous if the printed control code associated with a portion of an output sheet lies on a lateral edge of the output sheet produced at the time of cutting.

The checklist may also be provided according to the fourth aspect as a stored data list or by means of a method (algorithm) for generating a successive sequence of control numbers, i. both the sending system (data source) and the receiving system (data receiver) may optionally be connected to the checklist as a stored list, e.g. Look-up-table (LUT) or calculate the control numbers of the checklist online with a computer processor.

Furthermore, the invention can be combined in particular with the methods or devices that are known from the publications mentioned above US-A-4,609,279 ; US-A-4,774,524 and US B1-6,501,929 are known.

The invention also provides devices, printing devices, controllers or computer software that can automatically effect a sequence according to the invention.

Figur 1

schematisch vereinfacht ein Drucksystem zum Ausführen des erfindungsgemäßen Verfahrens,

Figur 2

Steuersignale für einen Druckprozess,

Figur 3

schematisch ein Tandem-Drucksystem,

Figur 4

mögliche Darstellungsweisen von einstelligen Binärkontrollzahlen auf den bedruckten Bogen,

Figur 5

einen Teil des erfindungsgemäßen Verfahrens, mit welchen Kontrollzahlen erzeugt und gedruckt werden, schematisch vereinfacht in einem Flussdiagramm,

Figur 6

einen Teil des erfindungsgemäßen Verfahrens, mit welchem die gedruckten Kontrollzahlen überwacht und ausgewertet werden, schematisch vereinfacht in einem Flussdiagramm,

Figur 7

ein modifiziertes LFSR-Verfahren in einem Flussdiagramm,

Figur 8

eine Bedienfeldanzeige bei korrigierbaren Markenlesefehlern,

Figur 9

eine Bedienfeldanzeige mit einem nicht korrigierbaren Markenlesefehler,

Figur 10

eine weitere Bedienfeldanzeige bei einem korrigierbaren Markenlesefehler und

Figur 11

eine weitere Bedienfeldanzeige bei mehreren nicht korrigierbaren Markenlesefehlern.

The invention will be explained in more detail by way of example with reference to the drawings. In the drawings show:

FIG. 1

schematically simplifies a printing system for carrying out the method according to the invention,

FIG. 2

Control signals for a printing process,

FIG. 3

schematically a tandem printing system,

FIG. 4

possible representations of single-digit binary control numbers on the printed sheet,

FIG. 5

a part of the method according to the invention with which control numbers are generated and printed, schematically simplified in a flow chart,

FIG. 6

a part of the method according to the invention, with which the printed control numbers are monitored and evaluated, schematically simplified in a flow chart,

FIG. 7

a modified LFSR method in a flow chart,

FIG. 8

a control panel display for correctable brand reading errors,

FIG. 9

a control panel display with a non-correctable mark reading error,

FIG. 10

another control panel display in a correctable brand reading error and

FIG. 11

another control panel display for multiple non-correctable mark reading errors.

A printing system for carrying out the method according to the invention is schematically simplified in FIG FIG. 1 shown. This printing system has a printer 1, which is preferably a high-performance printer, for printing on a paper web 2. The printer 1 is connected via a data line 3 to a computer 4, from which the printer 1 via the data line 3, a print data stream receives. The computer 4 is either a server that merely caches or forwards the print data stream or a host to which the print job and the corresponding print data stream are generated. The print data stream used is the IPDS (Intelligent Printer Data Stream) print data stream typical for high-performance printers. Of course it is also possible to use print data streams in other formats, such as PCL (Print Command Language), PS (Post Script) or AFP (Advanced Function Presentation).

In the printer 1, the data line 3 leads to a controller 5, in which the print data contained in the print data stream are processed for a subsequently arranged character generator. The character generator 6 generates control signals for driving a printing unit 19 with a photoconductor drum 7, with which the printing data are printed on the paper web 2. The character generator 6 and the photoconductive drum 7 constitute a printing unit 19. The controller 5 is further connected to a device controller, not shown, which drives the various units of the printing apparatus, e.g. The paper transport, the electrophotography unit, the fuser, etc. Furthermore, the controller 5 is connected to a control panel 20, displayed on the system information and can be made via the settings on the printer 1. It may include known means such as a screen (esp. Touch-screen), keyboard and / or mouse, etc. The paper web 2 is typically a continuous paper web for high-performance printers. However, there are now also known printers with very high performance, which print on single sheets, in which the application of the method according to the invention is also expedient.

In controller 5, control numbers are generated and inserted into the print data stream. This will be explained below. Downstream of the photoconductive drum 7, a sensor 8 for scanning the printed on the paper web 2 control numbers is provided adjacent to the paper web 2. If the control numbers are printed in the form of a bar or bar code, the sensor is a simple photo sensor which detects the brightness differences on the paper web. The sensor 8 is connected to a monitoring device 9, which in turn is coupled to a central pressure controller 10.

The paper web 2 is driven by a conveyor 13 in the conveying direction 14.

The data stream delivered via data line 3 contains additional information about the print job, such as a print job. Sheet or page numbers that are supplied via a further data line 11 to a monitoring device 9. Alternatively, this additional information can initially only be supplied to the controller 5, which then forwards it to the monitoring device 9 via a further data line 12. The data line 11 can then be omitted. It is also possible in this case that the controller 5 generates the additional information about the print job itself and delivers it to the monitoring device 9 if the computer 4 does not provide such information.

Inside the printer are two control signals (A) and (B) ( Fig. 2 ) for controlling the printing process. The control signal (A) is a central start / stop signal with which the beginning and the end of a printing process are marked. The control signal is usually generated by the character generator 6 as soon as it receives the information from the controller 5 that sufficient print data prepared for the printing process are available. The control signal (B) is a clock signal which predetermines a predetermined clock, which synchronizes all of the am Enabling the printing process and is constantly available. The individual devices of the printer 1 can determine on the basis of the start / stop signal (A) and the clock signal (B) when the individual pages or predetermined locations on the pages pass them. Usually there is a delay (C1) at the beginning of a printing process until the leading edge of the first page passes a predetermined location in the printer 1 and the cycle time (C2) of the further pages is usually constant.

With the aid of these control signals, both the imprint by means of the photoconductor drum 7 and the scanning of the control numbers by the sensor 8 are timed.

Hereinafter, the part of the method according to the invention, which is carried out in the controller 5, based on the flowchart from FIG. 5 explained in more detail.

This process starts with step S1. In step S2, the controller 5 reads the printing data coming from the computer 4 via the data line 3.

In the controller 5, a means for generating control numbers is provided, with which the control numbers are provided (step S3).

This facility can be a list of stored control numbers. However, this device can also be designed as a method. Such methods are, for example, pseudo-random number generators.

If the same means for generating control numbers as in the controller 5 is provided in the monitoring device 9, the controller 5 and the monitoring device 9 must synchronize their devices with each other, so that both devices in each case the same Provide a sequence of control numbers. Such a synchronization can take place by means of a synchronization command from the controller 5 via the data line 12 to the monitoring device 9. This synchronization takes place, for example, after an interruption of the printing process due to an error condition and after the error condition has been remedied. An error condition in this sense is also a detected by the monitoring unit 9 error in the printing process.

The sequence of control numbers should have as low a redundancy as possible, that is to say that sequences with a certain number of control numbers preferably occur only once in the entire list of control numbers. In other words, this means that the entropy should be as large as possible in the numerical order of the control number sequence.

The sequence of numbers 1, 0, 1, 0, 1, 0 ... has a very high degree of redundancy and a very low entropy, since this sequence repeats with the period two. It is expedient to provide significantly longer repetition periods. For printing systems intended for small print jobs, a repetition period of 100 may already be sufficient. More advantageously, however, larger repetition periods of at least 1000, 10000 or more are to be used.

The control numbers thus generated are inserted in the print data (step S4). In this case, a character is inserted in each page to be printed at a predetermined location in the print data, which reproduces the control number. Such a sign is also called a control mark.

The inventive method allows for the control numbers a small number of numbers with, for example, sixteen, eight, four or only two numbers corresponding to a few places, for example as a single-digit or two-digit Control numbers are displayed. Such control numbers can be printed with a smaller area brand than control numbers from a larger number of numbers.

In principle, it is possible to provide the control numbers in any number system, such as a hexadecimal, decimal or binary number system. However, preferred are control numbers in the binary system. The control numbers are preferably represented by bar or bar code, as these are easily detected automatically. In this case, either a thin or thick bar or an existing or a nonexistent bar is provided for each digit of the binary number. This is in FIG. 4 shown here, in each case the front and back of a sheet is shown, on which the corresponding control numbers are printed in the form of a bar code. The bar code is binary in this example, ie only one zero or one is coded. The zero can by no stroke (in the upper sides of the FIG. 4 shown) or by a relatively thin line (in the lower sides of the FIG. 4 shown). The one is then coded by a stroke (upper sides) or by a relatively thick stroke (lower sides). An advantage of using the variant with different line widths is that on each page to be printed in a given range, a single line can be printed, the downstream of the printing devices such as cutting sensory detected and as a trigger mark for certain actions such as cutting the Record carrier can be used on side transitions. The line can be printed in particular along the page boundary at the side transitions of a web-shaped recording medium, whereby it virtually completely disappears after a cutting operation and therefore can no longer be annoying. The barcode may also comprise a plurality of dashes and / or for the invention Control numbers of more than one bit represent information content.

After inserting the control numbers in the print data they are printed by the printing unit on the paper web 2 (step S5). This completes the process of generating and printing the control numbers (step S6).

At the monitoring device 9, a further part of the method according to the invention is carried out, which is described in more detail below with reference to the in FIG. 6 illustrated flowchart is explained.

This process starts with step S7. In step S8, the control marks or control numbers printed on the paper web 2 are scanned by means of the sensor 8. The sampling process is timed by the start / stop signal (A) and the clock signal (B) ( FIG. 2 ) controlled. As a result, exactly predetermined areas can be scanned on the respective printed pages.

The sensor 8 converts the sampled light signals into digital signals, namely into the control numbers and forwards them to the monitoring device 9. In the monitoring device, the read control number is compared with a corresponding check number of the checklist (step S9).

The checklist can in turn be stored in the form of a prestored data list in the monitoring device 9 or be generated by means of a predetermined method, such as a pseudo-random number generator. Regardless of how the sequence of control numbers is provided in the monitoring device 9, this sequence of control numbers must be synchronized with the sides to be monitored. This is done in the present embodiment in that the first Assigned control number in the checklist of the first by the start / stop signal (A) and the clock signal (B) side defined and the other control numbers of the list in the order in the checklist assigned to the pages following to the first page in this order with which they are also inserted by the controller 5 in the pages of the print data.

If it is determined in this comparison (step S9) that the read control number should not be the same as the corresponding check number of the checklist, this means that the sensor has scanned a check number which does not correspond to the page which is located at the corresponding position in the Sequence of pages of the printing process should be present. Such a deviation is thus assessed as an error. A corresponding error message is passed on to the print controller 10 (step S10).

The process then proceeds to step S11, in which it is checked whether another control number is to be sampled. If this is the case, the process flow returns to step S8, otherwise the process is terminated with step S12.

If the comparison in step S9 shows that the read control number is equal to the corresponding check number in the checklist, the method proceeds directly from step S9 to step S11.

This method can be modified such that not only is it determined whether the correct control number is read by the sensor 8, but it is also determined whether the control number passes exactly at the predetermined time at which it is to pass the sensor, and if there is a time difference, it can be measured, for example in units of the clock signal. By determining this time deviation, the deviation becomes the control number measured from the ideal position on the paper web. As a result, the registration accuracy of the imprint on the paper web can also be determined.

Since, according to the invention, the information contained in the order of the check numbers present in the checklist is used, the information contained in a check number can be very small. It is therefore even possible to use only a single-digit binary number as a control number. With the invention, the information contained in the control numbers is thus correlated with the information contained in the order of the control number.

• wobei x_n die im Berechnungsschritt n berechnete Pseudo-Zufallszahl ist. Die vorhergehende Pseudo-Zufallszahl x_n-1 ist gleichzeitig der "innere Zustand" des Pseudo-Zufallszahlen-Generators. Der Pseudo-Zufallszahlen-Generator wird initialisiert, indem x_n-1 auf einen definierten Wert gesetzt wird. Der Operator "mod" bezeichnet den ganzzahligen Rest einer Division. Die Koeffizienten a, b und m werden geeignet ausgewählt. Es können z.B. folgende Koeffizienten verwendet werden:
  • a = 1103515245
  • b = 12345
  • m = 2147483648 = 2³¹

As a pseudo-random number generator, a linearly congruent generator can be used with which the random numbers are generated with the following formula: $$x_n=\left(a\cdot x_{n-1}+b\right)\mathrm{mod}m.$$

• where x _{n is} the pseudorandom number calculated in calculation step n. The preceding pseudorandom number x _n-1 is also the "inner state" of the pseudorandom number generator. The pseudo-random number generator is initialized by setting x _n-1 to a defined value. The mod operator denotes the integer remainder of a division. The coefficients a , b and m are appropriately selected. For example, the following coefficients can be used:
  • a = 1103515245
  • b = 12345
  • m = 2147483648 = 2 ³¹

• wobei s_n die zusätzliche Information, z.B. eine Seiten- oder Blattnummer ist, die für jede Seite bzw. Blatt vom Server geliefert wird.

If additional information about the print job is to be included in the pseudo-random number generator, this can be realized with the following algorithm: $$x_n=\left(a\cdot \left(x_{n-1}+s_n\right)+b\right)\mathrm{mod}m.$$

• where s _{n is} the additional information, eg a page or sheet number, which is supplied by the server for each page or sheet.

• wobei y_n die im Berechnungsschritt n aus der Pseudo-Zufallszahl x_n berechnete Zufallszahl ist. Der Koeffizient c kann aus Gründen einer einfachen Berechnung eine Potenz von zwei sein. Der Koeffizient i ist der Informationsgehalt des Codes in Bits. i = 1 bedeutet ein Bit Informationsgehalt. Der Operator "div" bezeichnet die Ganzzahl-Division, also die Division mit Abschneiden der Nachkommastellen.

From a pseudo-random number can be calculated with the following formula a control number with only a few bits $$y_n=\left(\left(x_n\mathrm{mod}c\right)\mathrm{div}\frac{c}{2^i}\right)~k.$$

• where y _{n is} the random number calculated in the calculation step n from the pseudorandom number x _n . The coefficient c may be a power of two for ease of calculation. The coefficient i is the information content of the code in bits. i = 1 means one bit of information content. The operator "div" denotes the integer division, ie the division with truncation of the decimal places.

The coefficient k is used for inversion (variation) of the code values. The operator "~" denotes the bitwise exclusive-or-shortcut used to invert the calculated codes. It may be useful, for example, to use a sequence of control numbers for the front side and the corresponding sequence of inverted control numbers for the back side in the case of double-sided printing.

Example:

• c = 32768 = 2 ¹⁵
• i = 1
• k = 0 front side (no inversion)
• k = 1 back (inversion)

The method according to the invention can be used very advantageously in a tandem printing system. Such a tandem printing system comprises two printers 1a, 1b (FIG. Fig. 3 ) each having a controller 5a, 5b, a row generator 6a, 6b, printing units, each one a photoconductor drum 7abzw. 7b, a monitoring device 9a, 9b and a pressure control 10a, 10b. The two printers 1a, 1b print on a common paper web 2, wherein the paper web 2 is turned in the area between the two printers 1a, 1b by means of a turning device 15. It is thus printed by each printer 1a, 1b each have a side surface of the paper web, so that the paper web is printed on both side surfaces.

The two printers 1a and 1b receive the print data stream via a respective data line 3a and 3b from a computer 4. The data stream contains additional information about the print job, e.g. Sheet or page numbers, which are also supplied to the monitoring devices 9a and 9b via further data lines 11a and 11b. Alternatively, this additional information can initially be supplied only to the controllers 5a and 5b, which then pass them on to the monitoring devices 9a or 9b via further data lines 12a or 12b. The data lines 11a and 11b can then be omitted. It is also possible in this case that the controllers 5a and 5b generate the additional information about the print job itself and deliver it to the monitoring devices 9a or 9b if the computer 4 does not provide such information.

Within each printer are two control signals (A) and (B) ( Fig. 2 ) for controlling the printing process. The control signal (A) is a central start / stop signal with which the beginning and the end of a printing process are marked. The control signal is usually generated by the character generator 6a or 6b as soon as it receives the information from the controller 5a or 5b that the printing process can begin. This is the case in the printer 1a if sufficient print data prepared for the printing process are available in both printers 1a and 1b. In the printer 1b, this is the case when there there are enough print data available and additionally a sufficiently long paper web (supplied by printer 1a) is available for printing. The control signal (B) is a clock signal which predetermines a predetermined clock, which enables a temporal synchronization of all devices involved in the printing process and this is constantly available.
About the panels 20a, 20b, the two printers 1a, 1b each individually and in particular also jointly as a so-called. Single point of operation operated.

The printer 1a is arranged in the conveying direction (arrow 14) in front of the turning device 15 and similar to the printer 1 from FIG. 1 formed with a sensor 8a. The second printer 1b, which is arranged in the conveying direction after the turning device 15, has two sensors 8b, 8c, wherein the sensor 8a adjacent to one side of the paper web 2 and the sensor 8c at the same height adjacent to the other side of the paper web 2 is arranged so that both sides of the paper web are scanned by the sensors 8b, 8c.

In the printer 1a, the monitoring of the printing process is exactly as in the above-explained in FIG. 1 illustrated printing system. In the printer 1b, however, both sides of the paper web are monitored. Thus, on both sides of control numbers are printed, which have been created for example by means of the same control list, where on one side, the control numbers are not inverted and on the other hand, the control numbers are inverted. During monitoring, two control numbers are read out for each paper sheet, one for the front and one for the back. First, the inverted control number is inverted again, so that the two read control numbers can be compared with each other and with the corresponding control number of the control list. If one of these three control numbers deviates one, there is an error and is output accordingly.

The check list can in turn be provided by a predetermined list of control numbers, which is stored in the two controllers 5a, 5b. However, it can also be generated, for example, in the controller 5a by means of a suitable method and the control numbers can be forwarded via the data line 3 to the controller 5b of the printer 1b. Preferably, however, in the two controllers 5a, 5b, the control numbers are generated by a suitable method, such as a pseudo-random number generator. For this purpose, the random number generator is started with the same start parameters at a corresponding point in time.

As a corresponding point in time, for example, the start of a larger print job or, if a print job had to be interrupted by an error state, the continuation of this print process after the error state has been rectified. In a regular interruption of a printing operation, for example, when refilling toner or removing a paper stack, it is not necessary to restart the random number generators.

In the controllers 5a and 5b, the control numbers are passed on and processed by the page-by-side processing of the print data stream. In the monitoring devices, the control numbers are advanced by the page-by-page scanning of the control codes, which is enabled by the control signals (A) and (B) in synchronism with the printing operation.

The printed control numbers printed in the form of a bar code can furthermore be used to control other processes which are carried out on the web-shaped recording medium or on the paper web, for example cutting, folding, punching, stapling or adhesive processes. in the Example of FIG. 3 is in the paper feed direction behind the second printing device 1 b, a cutting device 16 is arranged, which has two sensors 17 a, 17 b on both sides of the paper web 2 to scan both turned and double-sided record carrier as well as unswept, printed on one side record carrier. One of the sensors 17a, 17b detects the printed bar code corresponding to the control code on the paper web 2. The scanning signal then controls the time at which the knife 18 of the cutting device cuts the paper web 2 into two parts. If the bar code consists of only one stroke, the blade 18 can be controlled so that it separates the paper web 2 exactly along the stroke. This makes it possible to achieve that the printed line is at the outermost edge of the cut paper or that the line is cut out or punched out and virtually no longer disturbs the paper sheet produced in the process.

The above embodiment shows how the printing process in two printers of a tandem printing system can be synchronized with one another by means of the method according to the invention. In the context of the invention, however, it is not only possible to synchronize printing processes, but it is also possible to synchronize a printing process with a post-processing process. Such post-processing processes are, for example, the cutting of paper webs, the punching or binding of the printed sheets. There are a variety of different finishing devices known. For synchronization with the printing system, a monitoring device with a corresponding sensor, as used in the above-explained printers, is to be provided in the post-processing device. In each case the checklist is provided in the monitoring device and read the control numbers of the sides to be monitored in order to be compared with the corresponding control numbers of the checklist.

The control numbers according to the invention can also be generated with the linear feedback shift register method, which is also referred to as LFSR method ("Linear Feedback Shift Register").

With the LFSR method, a bit string can be generated which has the special property that any sequence of n consecutive bits within the entire sequence of N bits always occurs only once. The total length N of the bit sequence can be a maximum of 2 ⁿ .

• wobei a_k eine k-te Zufallszahl, a_k-1 die vorhergehende Zufallszahl, s ein Schlüssel, ^ eine bitweise UND-Verknüpfung und parity eine Funktion ist mit der die Anzahl der Bits des jeweiligen Wertes gezählt werden und die Bitzählung 0 für eine gerade Anzahl von Bits und 1 für ungerade Anzahl von Bits ergibt.

In the LFSR method, a sequence of values a _k ( k = 1 ... N ) is generated according to the following formula. The numbers a _k and s each comprise n bits: $$a_k=a_{k-1}\cdot \mathrm{parity}\left(a_{k-1}\wedge s\right).$$

• where a _{k is} a k-th random number, a _{k-1 is} the preceding random number, s is a key, ^ is a bitwise AND operation and parity is a function that counts the number of bits of each value and bit count 0 for even Number of bits and 1 for odd number of bits.

Multiplied by 2 of a _k-1 , the bits of a _{k-1 are} shifted to the left, cutting off the most significant bit.

For example, for n = 16, the decimal numbers 45462 or 46278 are appropriate keys. They provide a sequence of numbers of the maximum possible length without repetition, ie a repetition period of N = 2 ¹⁶ -1 = 65535. These keys are called "maximum keys".

To implement this method, there are special hardware solutions in the form of integrated circuits.

From each calculated number a _{k + 1} one bit is "extracted", eg the bit at the binary digit 0. These extracted bits form the bit sequence: $$B_k=a_k\wedge 1.$$

The parameters of the LFSR algorithm are the key values s and an initial value a, each with a length of n bits. Given a suitable choice of the key s, the LFSR method generates a bit sequence with a maximum length of N = 2 ⁿ -1 bits, after which the bit sequence is repeated.

• wenn: a_k = 0 so folgt: a_k+1 = 0

The state a _k = 0 leads to a "blockade" in the LFSR method explained above, since the subsequent state, independently of the key s, is also 0:

• if: a _k = 0 then follows: a _{k + 1} = 0

However, the state a _k = 0 is never reached when a maximum key and an initial value a ₁ ≠ 0 are used.

By an extension of the LFSR method, the "missing" state a _k = 0 can now be included in the sequence of numbers. The length of the sequence of numbers thus expands to N = 2 ⁿ .

• wenn: a_k = 2^(n-1) so folgt: a_k+1 = 1

It turns out that when using a maximum key, the following always applies:

• if: a _k = 2 ^(n-1) it follows that a _{k + 1} = 1

This transition from 2 ^(n-1) to 1 occurs for all maximum keys, because for all maximum keys the most significant bit is set at the binary digit n-1.

In this transition, the state "0" can be inserted at, since it occurs equally for all maximum keys.

The number sequence is extended by one state: ... → 2 ^(n-1) → 0 → 1 → ...

In order to avoid a "blockage" in the state 0, the LFSR method is extended as shown in the flowchart Fig. 7 is shown.

The property of the bit string that any sequence of n consecutive bits occurs only once within the entire sequence of N bits is now used for the determination of the page numbers. A sequence of n consecutive bits is understood as a coded page number. By a decoding method, the coded page number can then be converted into the normal, uncoded page number.

On each page the control number is printed, which does not form the complete, but only a part of a page number. That is, a page number is distributed to m consecutive pages each having a control number. Each control number consists of t bits, where t is a divisor of n. A sequence of m consecutive control numbers can then be reassembled into a complete page number.
It is true $$\mathrm{n}=\mathrm{t}\cdot \mathrm{m}$$

wobei $$\mathrm{N}={\mathrm{2}}^{\mathrm{n}}-\mathrm{1}\mathrm{order\; N}={\mathrm{2}}^{\mathrm{n}}$$

sein kann.The highest achievable page number Z is $$\mathrm{Z}=\frac{\mathrm{N}}{\gcd \left(\mathrm{N},\mathrm{t}\right)}\left[\gcd :\mathrm{greatest\; common\; divisor}\right]$$

in which $$\mathrm{N}={\mathrm{2}}^{\mathrm{n}}-\mathrm{1}\mathrm{order\; N}={\mathrm{2}}^{\mathrm{n}}$$

can be.

In the simplest case, t = 1, m = n and Z = N. That is, a page number consisting of n bits is distributed on n pages, and the control number of each page consists of only one bit.

Bits (1). Es wird nun ein möglichst großer Bereich für die Seitenzahlen 1 bis Z angestrebt. Gemäß der Formel (7) wird dies erreicht, wenn der Nenner ggt(N, t) möglichst klein wird. Im besten Fall ist der Nenner gleich 1, und damit gilt Z = N.The special case t> 1 should be examined here in more detail. Each control number consists of $\mathrm{m}=\frac{\mathrm{n}}{\mathrm{t}}$

Bits (1). It is now the largest possible area for the page numbers 1 to Z sought. According to the formula (7), this is achieved when the denominator ggt (N, t) becomes as small as possible. In the best case, the denominator is 1, and thus Z = N.

For N = 2 ⁿ -1 (8a) this is the case when t is even (or equal to 1).

For N = ²ⁿ (8b) this is the case when t is odd.

At t> 1, while the page numbers from 1 to Z are traversed, the N bits bit sequence of the LFSR method is iterated several times, at most t times.

Examples: a) t = 2; n = 16; m = 8; N = 2 ⁿ -1 = 65535

$$\mathrm{Z}=\frac{65535}{\mathrm{GGT}\left(65535;2\right)}=65535$$

The control numbers of eight consecutive pages give a complete page number. Each control number consists of two bits. The page numbers run from 1 to 65535. The bit sequence of N = 65535 bits is traversed twice. In the second pass, the bit positions are offset by one from the first pass, thereby making the second pass distinguishable from the first pass.

b) t = 3; n = 15; m = 5; N = 2 ⁿ = 32768

$$\mathrm{Z}=\frac{32768}{\mathrm{GGT}\left(32768;3\right)}=32768$$

The control numbers of five consecutive pages give a complete page number. Each control number consists of three bits. The page numbers run from 1 to 32768. The bit sequence of N = 32768 bits is traversed three times.

During the printing process, t-steps of the LFSR process are executed for each printed page (or printed sheet). In this case, t bits are supplied for each control number. This control number is printed on the paper according to the methods described above and detected by means of a monitoring device.

The page number of a page is determined by reading the control number from this page as well as the control numbers of the previous pages m-1. The total of m control numbers are then assembled into a coded page number (according to a predetermined order).

At the beginning of a print job, i. for pages 1 to m-1, the full number of previous pages or control numbers is not yet available. Here, the control numbers of the non-existent pages are replaced by defined replacement or initial values that correspond to the end sequence of the bit sequence generated by the LFSR method. With a suitable choice of the initial value a, the missing control numbers can always be set to 0.

Alternatively, the method can also be realized in such a way that the control numbers of the "searched" page and the following m-1 pages are assembled. However, then the determination of the page number for the last m-1 pages of a print job is problematic or not possible.

In the following example, let t = 1, n = m = 16, Z = N = 2 ⁿ = 65,536, a = 0, s = 46278

In this example, each page is printed with a control number consisting of one bit each. The first read control number is considered the most significant, the last one read as the least significant number. The missing control numbers on pages 1 to 15 are assumed to be "0". At page 65536, the end sequence of the sequence indicates that these control numbers actually take the value 0.

After the 65536th page there is an "overflow", the LFSR process starts all over again. The subsequent page counting starts quasi 1 again.

In order to obtain the regular, uncoded page number, a decoding method is used which supplies the uncoded page number z from the coded page number c. There are various variants available, whereby it is necessary to balance between memory requirements and computing time.

The variant with the shortest computing time, but the largest memory requirement uses a decoding table in which the associated uncoded page number is stored for each coded page number. At N = 65536, the table occupies 128 Kbytes: $$\mathrm{z}=\mathrm{DecodeTable}\left[\mathrm{c}\right]$$

The variant with the largest computation time and the smallest memory requirement uses the LFSR method, which is applied "backwards", ie opposite to the (encoding) LFSR method, which generated the control numbers.

The number of passes d required is then counted until the LFSR method reaches the initial state of the first coded page number C ₁ . In this case, in the trivial case of the decoding of the first page number, the number of passes d can also be 0.

The searched uncoded page number is then (since the first page is numbered "1"): $$\mathrm{z}=\mathrm{d}+\mathrm{1}$$

In another solution that compromises computation time and memory requirements, two tables are used. The first table is a listing of intermediate values evenly distributed over all coded page numbers. The second table contains the information as to whether a particular coded page number c is contained in the first table. The second table comprises N bits, that is one bit per possible value c.

As long as a page number c is not included in the first table (the second table provides information about it), the reverse LFSR method is applied to c. This is done so many times until a state c * is reached, which is included in the first table. The number of passes d is counted. (In the trivial case d = 0 and c = c *). The reached state c * is then searched within the first table. Based on the position of c * within the first table and the counted passes d, the searched page number z can be determined. The distance between the intermediate values is v. $$\mathrm{z}=\mathrm{pos}\left(\mathrm{c}*.\mathrm{table}\mathrm{1}\right)\cdot \mathrm{v}+\mathrm{d}$$

[pos (c *, table): position of c * in Table 1] Example:

At n = m = 16 and N = 65536, each 64th value is stored as an intermediate value in the first table (v = 64). The first table then contains 1024 values or 2048 bytes. The second table claims 65536 bits or 8 kbytes. The number of passes d is always in the range of 0 to 63, and within the first table a maximum of 1024 search steps are necessary.

For the case t> 1 [and ggt (N, t) = 1, see formula (7)], i. If there are several bits per control number, then another calculation step must be performed.

Here, the LFSR bit sequence (1 to N) is traversed several times during a run of the page numbers (1 to Z). The page numbers are virtually "blended" into each other. The actual (uncoded) page number x is calculated from the page number z obtained in the first decoding step as follows: $$\mathrm{x}=\left(\left(\mathrm{z}-\mathrm{1}\right)\mathrm{mod\; t}\right)\cdot \left(\mathrm{N\; div\; t}+\mathrm{1}\right)+\left(\left(\mathrm{z}-\mathrm{1}\right)\mathrm{<figure-callout\; id="1"\; label="div\; t\; +"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">div\; t\; </figure-callout>}\right)+\mathrm{1}$$

Example:

With the methods described above, the number of pages at which an error has occurred can thus be determined from the sequence of read control numbers.

The LFSR method thus represents a preferred pseudo-random number generator, since the resulting sequence of control numbers is suitable for the subsequent determination of the page numbers.

Instead of a pseudo-random number generator, other random number generators can be used. For example, random number generators are known that use the thermal noise of a diode to generate the random numbers. Corresponding hardware components are commercially available. However, if no pseudo-random number generators but "true random number" generators are used, the relevant sequences of the random numbers must be recorded in the printing system and the monitoring devices made available.

In connection with the determination of the page number, further analysis of the error is expedient since the exact page number at which the error occurred can not always be specified. Rather, a page number can be specified in which the error occurred as early as possible, or a page area in which the error has occurred. To specify this page range, you must trace back the previous pages, each with the same control number.

It is therefore appropriate during the monitoring that the control numbers of at least n previous pages are stored in order to be able to indicate the earliest possible faulty page number in the event of an error. If the control numbers of the previous pages are not saved, to avoid erroneous printouts, all n previous pages must always be discarded and reprinted in the event of an error.

1. a) Sind die aktuell gelesene Kontrollzahl und die Kontrollzahl der vorherigen Seite nicht gleich, muss davon ausgegangen werden, dass mindestens eine Seite nicht gedruckt wurde. Der Bereich der vorherigen Seiten, die jeweils die selbe Kontrollzahl aufweisen, kann als fehlerhafter Bereich ausgegeben werden.
2. b) Sind die aktuell gelesene Kontrollzahl und die Kontrollzahl der vorherigen Seite gleich, muss davon ausgegangen werden, dass entweder mindestens eine Seite nicht gedruckt wurde, oder dass mindestens eine Seite mehrfach gedruckt wurde.

In case of an error two cases can be distinguished. For this, the currently read control number and the control number of the previous page are compared:

1. a) If the currently read control number and the control number of the previous page are not equal, it must be assumed that at least one page was not printed. The area of the previous pages, each having the same control number, can be output as a defective area.
2. b) If the currently read control number and the control number on the previous page are the same, it must be assumed that either at least one page was not printed, or that at least one page was printed multiple times.

Example 1:

The sequence A is the reference sequence (= checklist) of control numbers. The sequence B is the sequence of control numbers read from the printed pages.

At page No. 27, a deviation is detected. The control number on the previous page 26 ("0") differs from the Currently read control number of page 27 ("1"). It will therefore be further investigated according to case a).

Now, starting from the previous page 26, the pages which have the same control number are traced back. The page 26 has the control number "0", the preceding pages up to and including page 21 also have the control number "0" on. An error can therefore already have occurred at the earliest on page 21 or pages 21 to 27 can be specified as an area in which an error must have occurred.

It must be assumed that at least one of the pages from no. 21 was not printed. Printing must be stopped, sheets from # 21 must be discarded, and printing must be repeated from sheet # 21.

Example 2:

At page 31, a deviation is detected. Starting from page 30, the pages that have the same control number are traced back. As a defective area, therefore, pages 28 to 31 can be specified.

In this case, the control numbers of the previous page 30 and the current page 31 are the same, i. H. it will be further investigated according to case b).

• die Seite 31 nicht gedruckt wurde, oder
• mindestens eine der Seiten 28 bis 30 doppelt oder mehrfach gedruckt wurde.

It must be assumed that the error possibilities

• Page 31 was not printed, or
• at least one of pages 28 to 30 has been printed twice or more times.

The leaves from No. 28 are therefore discarded. Printing is repeated from sheet no. 28. It is questionable here, if sheet 28 really has to be reprinted. Namely, if the page or sheet 28 has been double-printed, the first copy of the sheet 28 can be maintained. However, since there is no guarantee that the page or sheet was printed correctly, it is safer to discard the sheet and reprint it.

It may happen that a control mark is not detected correctly by the sensor, and thus an incorrect control number is delivered. The method according to the invention can be modified such that a single read error is tolerated if thereafter the check numbers of at least following pages match again, where i is equal to or greater than 10.

In the case of an actual error in the printing process, however, at least one further deviation would occur within the following pages, whereby the error would be detected.
In the monitoring function, the memory for the control numbers of the past pages must then include at least 2i numbers to indicate the range of a possible error.

If the printing process is not stopped immediately after a detected error, but at least n-1 pages continue to run, additional information can be obtained from the additionally read control numbers of the pages following the error.

This is possible if it is a "singular" error, ie one or more consecutive pages are missing or individual pages are duplicated. For a complex error, eg. In the absence of multiple non-consecutive pages, may provide further information but not or not always won over the error.

If at least n-1 further control numbers are read after a faulty page, a page number can be decoded from this. This can be compared with a page number which is obtained, for example, by counting the printed sheets or is obtained by assigning to each check number of the checklist a page number which can then be correspondingly read out. From this comparison can be z. For example, you can see if and how many pages are missing in the printout or are duplicated. This is important for identifying and remedying possible causes of errors.

Example 3: Decoded page numbers:

reference read (A (B) 28 28 29 29 30 30 31 21713 32 10525 33 13196 34 51763 35 25627 36 1950 37 24396 38 24397 39 24398 40 43762 41 43763 42 43764 43 43765 44 16141 45 16142 46 47 47 48 48 49

This example continues Example 2 above. This list shows the decoded page numbers after an error. The page numbers in column A result from the reference sequence, the page numbers in column B result from the read control numbers. It turns out that the page numbers of column B over 15 pages are irregular and quasi disturbed, since in the expression one page and thus one bit of the associated page numbers was missing. From the reference page number 46, the page numbers of column B are again regular, and the difference between column B and column A indicates that exactly one page was missing. The assumption mentioned in Example 2 that pages could have been printed several times can thus be excluded. On page 31, where the error is first detected, this information is not yet apparent.

The data integrity monitoring in the in FIGS. 1 and 3 illustrated printing systems used for logical control and monitoring of the printing process. Corresponding data integrity monitoring can also take place in other printing systems, for example in a printing system which has two printing units in a common housing for simultaneously printing the front side and the back side of a web-shaped or sheet-like recording medium, as is known from US Pat US B1-6,246,856 is known.

For data integrity control and monitoring of the printing process, bar codes are printed as so-called bit marks on each printed page. The bit marks each contain one bit of information, represented e.g. B. by a thin or thick line. Whether a "0" or a "1" is printed as a bit mark is determined by the controller on the basis of the LFSR algorithm already explained above, which is run through for each printed page.

The LFSR algorithm is based on an N-bit key and generates a unique bit sequence of length 2 ^N bits. In each case N consecutive bits within the bit sequence are again unique and can therefore be understood as an "encrypted page number".

The controller also sends the internal state of the running LFSR algorithm (an N-bit value) to the device controller. For each printed page a new value is transferred. The internal state is uniquely determined for 2 ^N printed pages, ie the state is repeated only after 2 ^N passes. For N = 12, there are 4096 different states, whereby the repetition rate for the page-by-page assignment of the control numbers (page numbers) in this case is 4096 pages. In the control list (or in the LFSR algorithm), each N-digit binary control number exists only once, so there is a one-to-one correspondence between all start and end positions of N-digit sections with their respective position numbers (page numbers) , In the device control software, the same LFSR algorithm is used as in the controller. In a first monitoring step, the device controller checks to see if the state values supplied by the controller match the values calculated using its own LFSR algorithm. An advantage of this first monitoring is that a deviation in the parallel algorithms can be noticed immediately. Deviation of the status values leads to the immediate abort of the printing process with an error message. However, this type of monitoring is purely "virtual", a review of the printed image has not yet taken place.

In a second monitoring step, the printed bit marks are scanned with brand sensors. The device control evaluates the signals of the brand sensors and decodes the Scanning signals back to individual bits. The read bits must match the bits supplied by the LFSR algorithm. Even possible reading errors of the brand sensors can or must be taken into account. It may happen that a bit mark is either not read or misinterpreted. It is advantageous that individual read errors are tolerated within certain limits (eg N pages). A deviation of two or more bits within N pages causes the printing process to be aborted with an error message.

In addition, the "encrypted" page number can be formed from N consecutively read bits and, in turn, a "real", consecutive page number can be decoded therefrom, as described above.

It is also advantageous if in the control panel (graphical user interface, GUI) 20, 20a and 20b of the printing system, the flow of the data integrity monitoring can be tracked. The FIGS. 8 to 11 illustrate a representation in which the generated control codes, the read control codes and any system messages that are generated based on the reading result and / or the comparison of the sequence of control codes and the read control codes are displayed. In this case, a display in tabular form is provided, which can be called up by the user (operator) at any time, and which is constantly updated during a running printing process.

For each printed page there is one line in the table. The first column in the table shows the sequence of the LFSR algorithm with the expected page number and the expected bit mark. In addition, a further column is displayed for each monitored printing unit or for each monitored printer. These columns show for each page the ("decrypted") page number decoded from the bit marks, the individual read bit marks, as well as the result of the Data Integrity monitoring. For the examples of FIGS. 8 to 11 N = 12. If a bit mark is not recognized, a warning message is issued. If a bit mark with an incorrect bit value is read, a warning message is also issued, whereby the two types of error mentioned are distinguished from each other and result in different evaluation sequences. Threshold values can be set for the evaluation, namely, how many errors of the first or second type may occur before the decision "data integrity error" is automatically made and the printing process is aborted. The error of the first kind may occur at most twice per 12 pages before the printing process is aborted, while the second type error may only occur a maximum of once per 12 pages before the printing process is aborted. If a first type error and a second type error occur within 12 pages, printing will continue.

Within 12 pages a maximum of 2 false or invalid brand values are accepted.

In the example of FIG. 8 In the 16 consecutive pages numbered 11 to 26, the bit marks of page No. 14 on the lower printing unit and page No. 22 of the upper printing unit are not recognized. Thus, only a few bit marks from the brand sensor are not recognized, because there is a maximum of one reading at each printing unit within 12 pages. The missing bit mark can then be replaced by the expected bit mark of the algorithm, so that the page numbers continue to be properly decoded and displayed. The individual read errors are tolerated. The unrecognized mark ("mark missing") is marked in the color representation on the control panel with a first color, eg with yellow.

In FIG. 9 On pages 11 to 26 at the lower printing unit, the bit marks on pages 14, 18 and 24 are not recognized, ie the bit marks are very often not recognized. This leads to aborting the printing process with an error message. The page that caused the error is highlighted in the colored control panel display with a second color, eg red.
This in FIG. 10 The example shown shows the procedure for a single misinterpreted bit mark. On page 15, a "0" is read instead of "1". The decoding of the page numbers for the upper printing unit is temporarily disturbed (over 12 pages). Due to the misread bit, the subsequent page numbers are also incorrectly decoded because each page number consists of N = 12 bits. The monitor waits for a new bit error to occur. Only after 12 pages, the error has regenerated, the page numbers from page No. 27 vote again. The page read incorrectly and the following 11 page numbers are again marked yellow in the colored display.

This in FIG. 11 The example shown shows the procedure for two or more incorrectly read bit marks. The monitoring announces from the second bit error on page no. 25 the cancellation of the printing process. However, it is initially the printing of N = 12 pages (or slightly more pages) wait until the decoding of the page numbers is again "unique". Since at least as many pages are printed after the occurrence of the second error as the N-digit binary number with which the page numbers are coded has bits (N = 12), it can be seen that one page was skipped in the upper printing unit because the correct page number can be decoded again after the 12th page (assuming there is not a third error within 12 pages after the second error). As for page # 32, the data source bitstream is (first column), starting at page 21 and ending at page 32: 111110111011. The lower print engine (right column) has all Data printed correctly and therefore between pages 21 and 32 the same bit string of printed bit marks. On the other hand, the bit marks printed correctly by the upper print engine end at page 19. At page 20, a serious bit error occurs: A 1 is read, although a zero would be expected. If you then follow the read bit values until the page number 32 is decoded, it turns out that the above-mentioned bit pattern 111110111011 for the page number 32 already occurs at a position at which the first bit from the (computational) page number 20 (the first error occurred). From this it can be clearly concluded that a page has been lost in the printed page sequence. In the displayed list according to FIG. 11 this is immediately apparent to the viewer, because in the middle column for the upper printing unit, the page numbers from page 31 are shifted upwards by one line compared to the corresponding page numbers of the left column of the data source.

The invention is described above with reference to examples which print a web-shaped recording medium, in particular a paper web, on one or both sides. However, it can also be used to synchronize differently colored printouts or to check the data integrity of printouts on cut sheets, especially when different data from different print engines are printed on a single cut sheet. Data integrity on a record carrier can be accomplished by comparing the control codes between the data source and the data receiver (such as in particular FIG. 8 described) or by comparison between the control codes of two data receivers, in particular, if the two data receivers are printing units or different areas (front / back) of a recording medium, which were printed with different printing units or in separate printing processes. For this, the control codes of the print data of both areas must be included the same number sequence or a number sequence transformation have been performed. Each sheet can print several print images on the front and back and / or in different colors. For full-color printing, for example, up to five (or more) individual color images are printed per sheet page.

For each print image, a separate control number can be generated and printed in the form of a control mark. The control marks of different print images should not overlap. The control numbers of the individual print images do not have to be the same, but can be varied according to a fixed scheme; for example, the control numbers of the back side can be inverted to those of the front side.

In a simple monitoring stage, only the control numbers of the individual printed images are read and compared with each other. It can be determined whether the individual printed images belong together, d. H. whether, for example, match the front and back together. However, it can not be determined whether a particular sheet to be printed is missing in the entire printout, or possibly printed multiple times.

In a further monitoring stage, the read control numbers are compared with a reference sequence of control numbers supplied by an electronic circuit, a stored table, a calculation method or a random number generator. A missing or multiple printed sheet is recognized. For this purpose, it is expedient that at least one control number is provided on each sheet to be printed. In principle, however, it is also possible to provide only every x-th arc with a check number, but here the "resolution" of the monitoring method is reduced.

• es fehlt ein Teil des Ausdrucks,
• der Ausdruck ist nicht richtig auf der Seite positioniert,
• zu einer Vorderseite wurde die fertige Rückseite gedruckt,
• in einem farbigen Ausdruck sind Farb-"Schichten" miteinander vertauscht, zum Beispiel gelb mit cyan, oder
• mangelhafte Passgenauigkeit, d.h. Vorder- und Rückseite sind zueinander verschoben oder die einzelnen Farben eines mehrseitigen Ausdrucks sind zueinander verschoben.

Examples of erroneous printouts that can be determined by the method according to the invention are:

• a part of the expression is missing,
• the printout is not properly positioned on the page,
• to one front the finished backside was printed,
• in a colored expression, color "layers" are interchanged, for example, yellow with cyan, or
• poor fit, ie front and back are shifted from each other or the individual colors of a multi-page expression are shifted from each other.

One aspect of the invention may be briefly summarized as follows:

The invention relates to a method for monitoring pre-printed data in a printing system. According to the invention control numbers are printed as control code, which are contained in a checklist. In the checklist, however, the control numbers are not sorted numerically in succession, but arranged in an arbitrary order with the highest possible entropy. The expression checks whether the control numbers have been printed in the same order as in the checklist. This makes it possible to use control numbers with few digits, in particular even single-digit binary numbers.

The control numbers can either be provided by stored checklists or the checklists can be generated by a corresponding method. A preferred method is the LFSR method, since control numbers are generated which are suitable for calculating the page numbers from the control numbers.

LIST OF REFERENCE NUMBERS

1, 1a, 1b

printer

2

paper web

3

data line

4

computer

5, 5a, 5b

controller

6, 6a, 6b

character generator

7, 7a, 7b

Photoconductor drum

8, 8a, 8b, 8c

sensor

9, 9a, 9b

monitoring device

10, 10a, 10b

pressure control

11, 11a, 11b

data line

12, 12a, 12b

Data line between controller and monitoring device

13, 13a, 13b

Conveyor

14

Running direction of the paper web

15

turning device

16

cutter

17a, 17b

sampler

18a, 18b, 18c

control lines

19, 19a, 19b

printing unit

20, 20a, 20b

Control panel

Claims (46)

1. A method for monitoring printed data in a printing system including a printing device (1, 1a), comprising the following steps:

   - generating a control code for one page to be printed each,

   - printing the control code on the respective corresponding page of a recording medium to be printed,

   - automatic reading and evaluating of the printed control codes,

   wherein, as control codes, control numbers are used which are included in a control list in a non-numerical order, the control list including more control numbers as the used number set includes control numbers.
2. The method according to claim 1, characterized in that when evaluating the read control numbers these are compared to the order of the control numbers of the control list, a deviation being considered as an error.
3. The method according to claim 1 or 2, characterized in that at least two print images with one control code each are printed onto a sheet to be printed, and when evaluating the read control numbers, the control numbers of a sheet are compared to each other, and in the case of a deviation, this is considered as an error.
4. The method according to claim 3, characterized in that all control numbers of a sheet are identical.
5. The method according to claim 3, characterized in that the control numbers of the reverse side of the sheets are inverted relative to the control numbers of the front sides and the control numbers of the reverse sides are inverted before they are compared to the control numbers of the front side.
6. The method according to one of the claims 1 to 5, characterized in that on one side of a sheet several print images are printed and to each print image a control number is assigned and is printed on the sheet.
7. The method according to one of the claims 1 to 6, characterized in that the numbers of the control list are numbers with a maximum of three digits and preferably one-digit numbers.
8. The method according to one of the claims 1 to 7, characterized in that the control numbers are binary numbers.
9. The method according to one of the claims 1 to 8, characterized in that the control list is made available as a stored list.
10. The method according to one of the claims 1 to 8, characterized in that the control list is made available by means of a predetermined calculation method.
11. The method according to claim 10, characterized in that the calculation method for calculating the numbers of the control list is a pseudo-random number generator.
12. The method according to claim 11, characterized in that an LFSR method is used as a pseudo-random number generator.
13. The method according to one of the claims 1 to 12, characterized in that the numbers of the control list have a repetition period of at least 100, preferably 1000.
14. The method according to one of the claims 1 to 13, characterized in that the list comprises N numbers, wherein a random sequence of n numbers is always only present once in the list.
15. The method according to claim 14, characterized in that after an error has been determined, the last complete sequence of n read control numbers is determined, and based on this sequence the page number following the error is determined.
16. The method according to claim 15, characterized in that the determination of the page number takes place by means of a decoding table in which all sequences of n control numbers and the corresponding page numbers are stored.
17. The method according to claim 15, characterized in that for determining the page number the control numbers are generated by means of a predetermined method, starting out from a given control number until the complete sequence of n read control numbers has been generated, wherein the amount of generated control numbers is a measure of the page number.
18. The method according to one of the claims 14 to 17, characterized in that after an error has been determined and the corresponding page number has been determined, it is analysed by comparing the determined page number to a page number that is available by counting the printed sheets or by an assignment to the control numbers whether

    - one or more pages have been printed multiple times, and/or

    - one or more pages have not been printed.
19. The method according to one of the claims 1 to 18, characterized in that the control numbers are printed as a bar code.
20. The method according to claim 19, wherein the control numbers are binary numbers and as a bar code for a zero a bar with a first bar width is printed and for a one a bar with a second bar width different from the first is printed.
21. The method according to one of the claims 1 to 20, characterized in that the control numbers are printed as Arabic numerals.
22. The method according to one of the claims 1 to 21, characterized in that by means of this method print data printed on continuous paper are monitored.
23. The method according to one of the preceding claims, wherein the control numbers are printed as a bar code on the in particular web-shaped recording medium and the printed bar code is used for controlling a device (16) further processing the recording medium after printing.
24. The method according to claim 23, characterized in that the further processing device performs a process step directly on the bar code.
25. The method according to claim 23 or 24, characterized in that the further processing device (16) performs a cutting, folding, punching, stapling or bonding process step on the bar code.
26. The method according to one of the preceding claims, wherein at a display device (20, 20a, 20b) the control list at least in part and/or the read control codes are displayed.
27. A method for monitoring the area-wise data integrity during the transmission of print data from a data source to a data receiver, wherein

    - the print data, during sending, are numbered consecutively area-wise corresponding to an N-digit binary number,

    - based on the consecutive number a one-digit binary control code is read from a control list and is transmitted with the print data of the area,

    - within the control list, a specific sequence of N one-digit binary control codes is only included once,

    - upon receipt of the print data, the associated one-digit binary control code is read area-wise each time,

    - based on a comparison of the read sequence of one-digit binary control codes and the code sequences available in the control list, a decision on the data integrity is automatically passed and

    - wherein for N a natural number is used.
28. The method according to claim 27, wherein, upon receipt of the print data, an N-digit read binary number assigned to an area is formed based on N consecutive one-digit control codes and by means of it the consecutive numbering is reconstructed and checked in that its position in the control list is determined and the number assigned to this position is compared to the consecutive number of the area generated during sending.
29. The method according to claim 28, wherein the N-digit read binary number is assigned to an area, the read control code of which is included in the N-digit read binary number, and in particular the area, the read control code of which is at the first or last digit of the N-digit read binary number.
30. The method according to claim 28 or 29, wherein based on the comparison result it is automatically decided whether data have been lost area-wise during the data transmission.
31. The method according to one of the claims 27 to 30, wherein the numbering rules are identical during sending and receiving the print data, and based on the comparison result automatically a decision is passed on the number of areas with respect to which data have been lost.
32. The method according to one of the claims 27 to 31, wherein as a data source a computer (4) or a controller (5, 5a, 5b) is used and as a data receiver a controller (5, 5a, 5b), a printing unit (19, 19a, 19b) which respectively prints the one-digit binary control code as a binary mark on an area of the recording medium (2) and/or a recording medium (2), wherein further the printed binary marks are read with a sensor (8, 8a, 8b, 9'8c) and the reading result is compared to the control code assigned during sending and the printing process is thus controlled.
33. The method according to claim 32, wherein the print data are printed with a printing device (1, 1a, 1b) or a printing system (1a, 1b) on a recording medium (2) having several printing units (19a, 19b) and in which at least two printing units (19a, 19b) print on a common area of the recording medium (2).
34. The method according to one of the claims 1 to 26, comprising further steps according to one of the claims 27 to 33.
35. The method according to one of the claims 27 to 34, wherein the control code is calculated by a pseudo-random number generator.
36. The method according to claim 35, wherein as a pseudo-random number generator an LFSR method is used.
37. The method according to one of the claims 27 to 36, wherein the data of an area are printed on a common area of the recording medium (2).
38. The method according to claim 37, wherein the recording medium (2) is cut into output sheets such that the printed control code belonging to an area of an output sheet lies on the lateral margin of the output sheet generated in this way.
39. The method according to one of the claims 29 to 38, wherein the control codes generated at the data source, the read control codes and/or system messages that are generated due to the reading result and/or the comparison of the sequence of the control codes and the read control codes are displayed on a display device (20, 20a, 20b).
40. The method according to claim 39, wherein the display is in table form, the display can be activated at all times by a user and/or the display can be updated regularly during an ongoing data transmission operation.
41. A computer program product, which after loading into a computer and upon execution on this computer (4, 5, 5a, 5b) for controlling a printing device (1, 1a, 1b) or a printing system performs a method according to one of the claims 1 to 40.
42. A printing system, comprising
    a control device (5, 5a, 5b) for processing print data,
    a printing unit (6, 7, 6a, 7a, 6b, 7b) for printing the print data, which printing unit is connected to the control device (5, 5a, 5b) via a data line for transmitting the print data,
    wherein the control device (5, 5a, 5b) has a control code generating device with which control numbers are generated and which are inserted into the print data as corresponding signs at predetermined positions, characterized in that the control device is connected to a computer (4) loaded with the computer program product according to claim 41.
43. The printing system according to claim 42, characterized in that the control code generating device is a random number generator.
44. The printing system according to claim 42, characterized in that the control code generating device is a list of control numbers.
45. The printing system according to one of the claims 42 to 44, characterized in that the printing unit (19, 19a, 19b) is developed for printing continuous paper.
46. The printing system according to one of the claims 42 to 45, characterized in that the printing unit (19, 19a, 19b) is developed for printing single sheets.

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