Heidelberger Druckmaschinen Ag

Hans Koehler

Ralf Tita

Martin Mayer

Frank Muth

Johannes Muehl

Nikolaus Pfeiffer

Andreas Henn

Wolfgang Geissler

Steffen Neeb

Nicklas Raymond Norrick

Andreas Fehlner

Jan Krieger

Roland Stenzel

Christoph Michel

Annika Kamper

Mina Abosetta

Sepideh Samadzadegan

A method for assessing the condition and improving the printing quality of printing nozzles in printheads of an inkjet printing machine includes printing a nozzle test chart formed of a specific number of horizontal rows of equidistant vertical lines printed periodically underneath one another, with only every nprinting nozzle contributing to the test chart in every row of the test chart and n corresponding to a different number between one and the specific number of horizontal rows, recording and digitizing the test chart and analyzing the test chart regarding the condition of the contributing nozzles by using a computer. The nozzles printing horizontal lines between the horizontal rows complementing the equidistant vertical lines to form quadrangular objects used by the computer to analyze the condition of the contributing nozzles. Measures are taken to improve the printing quality of the nozzles depending on the condition of the contributing nozzles.

Method for assessing the condition and improving the printing quality of printing nozzles in printheads of an inkjet printing machine and improved printing nozzle test chart

A method compensates for position-dependent density fluctuations of print nozzles in an inkjet printing machine by use of a computer. The computer produces compensation profiles for the position-dependent density fluctuations over all the print heads for all print substrates used, calculates an mean profile from these, and applies the mean profile to compensate for the position-dependent density fluctuations in the inkjet printing machine. When one or more print heads of the inkjet printing machine are replaced, the computer calculates a new compensation profile for only one print substrate. The computer derives a new mean profile from this, and the computer calculates and applies the new mean profile using the old compensation profiles for the remaining print substrates.

Density fluctuation compensation during print head replacement

A method detects defective printing nozzles in an inkjet printing machine having a computer. The method includes printing a multi-row nozzle test chart for detection purposes, the test chart contains a number of horizontal rows of equidistant vertical lines printed periodically and disposed underneath one another. Wherein in every row of the nozzle test chart periodically only those respective printing nozzles of the print head contribute to the first element of the nozzle test chart that correspond to the specified number of the horizontal rows. An area coverage element geometrically associated with the nozzle test chart is printed. Both elements are recorded by an image sensor and both elements are evaluated by the computer. Defective printing nozzles are identified by evaluating the recorded nozzle test chart by the computer. Defects are allocated in the area coverage element to the printing nozzles in the nozzle test chart by the computer.

Determination of thresholds to detect missing printing nozzles

A method for detecting defective printing nozzles in an inkjet printing machine includes printing a multi-row printing nozzle test chart formed of horizontal rows of equidistant vertical lines periodically underneath one another, with only printing nozzles in a print head contributing to every row of the test chart corresponding to the horizontal rows. An area coverage element geometrically associated with the test chart is printed, both elements are recorded by an image sensor and analyzed by the computer. The computer analyzes the recorded area coverage element to detect print defects and allocates defects to a region of geometrically close printing nozzles. An analysis of the test chart in the region identifies nozzles causing the defect. Defective printing nozzles are detected based on thresholds, the detected printing nozzles are then compensated, and in the analysis of the recorded area coverage element, influences of the sensor are eliminated by shading correction.

Method for detecting defective printing nozzles in an inkjet printing machine

A method for detecting and compensating for failed printing nozzles in an inkjet printing machine by using a computer, includes printing a current print image, recording the printed print image by using an image sensor and digitizing the recorded print image by using the computer, adding digitized color values of the recorded print image of every column over the entire print image height and dividing the added-up color values by the number of pixels to obtain a column profile, subtracting an optimized column profile without failed printing nozzles from the original column profile to obtain a differential column profile, setting a maximum value threshold defining a failed printing nozzle when exceeded, applying that maximum value threshold to the differential column profile to obtain a resultant column profile every maximum of which marks a failed printing nozzle. The marked printing nozzles are compensated in a subsequent printing operation.

Method for detecting and compensating for failed printing nozzles in an inkjet printing machine

A method for compensating for failed printing nozzles in an inkjet printing machine uses a computer to provide an increased ink drop volume of adjacent nozzles. All existing printing nozzles are measured regarding print failure and deviation of a printed dot beyond a specific threshold, so that the printing nozzles are marked either as functioning, failed, or printing a dot deviating in a direction transverse to the printing direction, and the results are saved on the computer. The computer hides all functioning printing nozzles and marks all remaining isolated printing nozzles as failed nozzles. The computer groups adjacent remaining printing nozzles by marking nozzles printing a dot deviating in a direction transverse to the printing direction as functioning printing nozzles contributing to the compensation or as failed printing nozzles in accordance with a rule, and the computer compensates for all printing nozzles having been marked as failed.

Method for compensating for failed printing nozzles in an inkjet printing machine by using deviating nozzles

A method for automated detection of failed printing nozzles in an inkjet printing machine includes the following steps:

Method for detecting failed printing nozzles in inkjet printing systems and inkjet printing machine

A method for compensating failed printing nozzles in inkjet printing machines using a control computer, includes printing a test form for a material combination, evaluating the print and creating a look-up table having compensation probabilities for local surface density, detecting a failed nozzle, reading the size of the intended droplet to be compensated at the failed nozzle, calculating local surface density at the failed nozzle, reading a compensation probability from the table with the calculated local surface density, calculating a pseudo-random number for adjacent pixels right and left of the pixel to be compensated, increasing the droplet size for adjacent pixels if the pseudo-random number therefor is lower than the compensation probability from the table, calculating adjacent droplet sizes for all intended droplets at the failed nozzle and using the changed droplet sizes in printing data. The print job is carried out with changed printing data.

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Edingen-Neckarhausen, Germany

Hans Koehler