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

Patent metadata

Field	Value
Publication number	US-11198288-B2
Application number	US-202016742956-A
Country	US
Kind code	B2
Filing date	Jan 15, 2020
Priority date	Jan 17, 2019
Publication date	Dec 14, 2021
Grant date	Dec 14, 2021

Abstract

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 n th printing 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.

First claim

The invention claimed is:

1. A method for assessing the condition and improving the printing quality of printing nozzles in printheads of an inkjet printing machine, the method comprising the following steps:
printing at least one nozzle test chart formed of a specific number of horizontal rows of equidistant vertical lines printed periodically and disposed underneath one another, with only every n th printing nozzle in a width direction of a printhead contributing to the nozzle test chart in each respective row of the nozzle test chart and with n corresponding to a different number between one and the specific number of horizontal rows for every row;
using a computer to record and digitize the printed nozzle test chart and analyze the nozzle test chart in terms of a condition of contributing printing nozzles;
using the printing nozzles to additionally print horizontal lines between the horizontal rows, the horizontal lines complementing the equidistant printed vertical lines to form quadrangular objects being specifically used by the computer to analyze the condition of the contributing printing nozzles;
using the computer to employ the quadrangular objects to draw conclusions on the condition of the printing nozzles that contribute to the nozzle test chart by applying image processing algorithms to check:
whether all equidistant lines printed vertically exist by comparing the number of detected quadrangular objects to the number of expected equidistant lines printed vertically,
whether the quadrangular objects that have been formed are complete and do not have any gaps,
whether the equidistant lines printed vertically have been printed continuously and are not porous, and

whether the detected quadrangular objects have an expected regular size; and
then taking measures to improve the printing quality of the printing nozzles depending on the condition of the contributing printing nozzles.

2. The method according to claim 1 , which further comprises using an in-line image processing system to record the printed nozzle test chart, the computer corresponding to an image processor of the in-line image processing system.

3. The method according to claim 1 , which further comprises carrying out the measures to improve the printing quality of the printing nozzles by switching off printing nozzles having a condition not within desired printing quality parameters and compensating for those printing nozzles by using adjacent printing nozzles and, for printing nozzles having a print dot deviating in a printing direction, varying an instant in time at which printing takes place.

4. A method for assessing the condition and improving the printing quality of printing nozzles in printheads of an inkjet printing machine, the method comprising the following steps:
printing at least one nozzle test chart formed of a specific number of horizontal rows of equidistant vertical lines printed periodically and disposed underneath one another, with only every n th printing nozzle in a width direction of a printhead contributing to the nozzle test chart in each respective row of the nozzle test chart and with n corresponding to a different number between one and the specific number of horizontal rows for every row;
using a computer to record and digitize the printed nozzle test chart and analyze the nozzle test chart in terms of a condition of contributing printing nozzles;
using the printing nozzles to additionally print horizontal lines between the horizontal rows, the horizontal lines complementing the equidistant printed vertical lines to form quadrangular objects being specifically used by the computer to analyze the condition of the contributing printing nozzles;
printing the horizontal lines with a line thickness of multiple pixels and every contributing printing nozzle applying a larger ink drop volume than an ink drop volume applied for the vertical lines; and
then taking measures to improve the printing quality of the printing nozzles depending on the condition of the contributing printing nozzles.

5. A method for assessing the condition and improving the printing quality of printing nozzles in printheads of an inkjet printing machine, the method comprising the following steps:
printing at least one nozzle test chart formed of a specific number of horizontal rows of equidistant vertical lines printed periodically and disposed underneath one another, with only every n th printing nozzle in a width direction of a printhead contributing to the nozzle test chart in each respective row of the nozzle test chart and with n corresponding to a different number between one and the specific number of horizontal rows for every row;
using a computer to record and digitize the printed nozzle test chart and analyze the nozzle test chart in terms of a condition of contributing printing nozzles;
carrying out the step of recording the printed nozzle test chart by slightly overexposing the nozzle test chart to make porous equidistant vertical lines caused by weak nozzles more visible;
using the printing nozzles to additionally print horizontal lines between the horizontal rows, the horizontal lines complementing the equidistant printed vertical lines to form quadrangular objects being specifically used by the computer to analyze the condition of the contributing printing nozzles; and
then taking measures to improve the printing quality of the printing nozzles depending on the condition of the contributing printing nozzles.

6. A method for assessing the condition and improving the printing quality of printing nozzles in printheads of an inkjet printing machine, the method comprising the following steps:
printing at least one nozzle test chart formed of a specific number of horizontal rows of equidistant vertical lines printed periodically and disposed underneath one another, with only every n th printing nozzle in a width direction of a printhead contributing to the nozzle test chart in each respective row of the nozzle test chart and with n corresponding to a different number between one and the specific number of horizontal rows for every row;
using a computer to record and digitize the printed nozzle test chart and analyze the nozzle test chart in terms of a condition of contributing printing nozzles;
using the printing nozzles to additionally print horizontal lines between the horizontal rows, the horizontal lines complementing the equidistant printed vertical lines to form quadrangular objects being specifically used by the computer to analyze the condition of the contributing printing nozzles;
using the computer to binarize the recorded and digitized nozzle test chart for analysis by the computer in accordance with a dynamically detected threshold and using the computer to implement object recognition based on the thus obtained binarized nozzle test chart to detect the quadrangular objects; and
then taking measures to improve the printing quality of the printing nozzles depending on the condition of the contributing printing nozzles.

7. The method according to claim 6 , which further comprises determining the condition of the printing nozzles contributing to the nozzle test chart by analyzing the quadrangular objects, statistically determining an average size of the quadrangular objects, and using the computer to conclude from an existence of a regular quadrangle that a respective printing nozzle works correctly.

Assignees

• Heidelberger Druckmasch Ag

Inventors

• Fehlner Andreas
• Koehler Hans

Classifications

• B41J2/16579 Primary

  Detection means therefor, e.g. for nozzle clogging · CPC title

• B41J2/04536

  using history data · CPC title

• B41J2/04506

  aiming at correcting manufacturing tolerances · CPC title

• B41J2/2146 Primary

  for line print heads · CPC title

• B41J2/0451 Primary

  for detecting failure, e.g. clogging, malfunctioning actuator · CPC title