Method for detecting and compensating for defective printing nozzles in an inkjet printing machine for reducing unusable prints

Patent metadata

Field	Value
Publication number	US-11292269-B2
Application number	US-202117170999-A
Country	US
Kind code	B2
Filing date	Feb 9, 2021
Priority date	Feb 28, 2020
Publication date	Apr 5, 2022
Grant date	Apr 5, 2022

Abstract

A method for detecting and compensating for defective printing nozzles in an inkjet printing machine includes printing test sheets each including at least one printing nozzle test chart and at least one gray area for every color separation. The test sheets are recorded and digitized with subsequent pixel-nozzle mapping and amplitude/phase value determination by using a computer. Current measurements are taken at the printing nozzles in between test sheets and customer sheets while being printed. The computer is used for teaching in a SVM model with the results of the current measurement and pixel-nozzle mapping and amplitude/phase determination. The taught-in SVM model and the current measurements are applied to printed, recorded and digitized customer's images to detect defective printing nozzles during production printing on the inkjet printing machine and the detected defective printing nozzles are compensated for.

First claim

The invention claimed is:

1. A method for detecting and compensating for defective printing nozzles in an inkjet printing machine, the method comprising:
printing test sheets each including at least one printing nozzle test chart and at least one gray area for every respective color separation being used;
recording and digitizing the test sheets with subsequent pixel-nozzle mapping and amplitude/phase value determination carried out by a computer, and using the computer to examine the at least one gray area for potential print defects when detecting and digitalizing the test sheets;
taking current measurements at the printing nozzles in between the test sheets being printed;
teaching in a SVM model with results of the current measurement and pixel- nozzle mapping and amplitude/phase determination carried out by the computer;
applying the taught-in SVM model to printed, recorded and digitized customer's images to detect defective printing nozzles during production printing on the inkjet printing machine;
during production printing, searching for potential print defects in the customer's images having been produced and then identifying the printing nozzle having caused the potential print defect by using the taught-in SVM model; and
compensating for the detected defective printing nozzles.

2. The method according to claim 1 , which further comprises taking further current measurements in between individual print sheets being printed during production printing to be evaluated by the computer, for preventively deactivating and compensating for nozzles being conspicuous in terms of the current measurements.

3. The method according to claim 1 , which further comprises recording, digitizing and evaluating both the test sheets and the customer's images produced during production printing by using an inline image recording system, and using an image-processing computer of the inline image recording system as the computer.

4. The method according to claim 1 , which further comprises, excluding the results of current measurements and amplitude/phase value determination of nozzles in a defined environment of potential print defects from the teaching-in of the SVM model.

5. The method according to claim 4 , which further comprises, when the computer does not find any printing nozzles with at least one of deviating amplitude or deviating phase values in the specified environment of the potential print defects:
printing three further gray areas for a color separation in addition to a gray area without printing nozzle compensation for detecting defective printing nozzles and in addition to the printing nozzle test chart for amplitude/phase value determination;
the three gray areas including one gray area in which the printing nozzle having been identified by using pixel-nozzle mapping has been deactivated and compensated for, one gray area in which a neighboring printing nozzle to the left has been deactivated and compensated for, and one gray area in which a neighboring printing nozzle to the right has been deactivated and compensated for;
and using the computer to identify the printing nozzle causing the potential print defect by evaluating the three gray areas.

Assignees

• Heidelberger Druckmasch Ag

Inventors

• Trachanas Ilias
• Abosetta Mina Hakim Latif
• Fehlner Andreas

Classifications

• B41J29/393 Primary

  Devices for controlling or analysing the entire machine {; Controlling or analysing mechanical parameters involving printing of test patterns} · CPC title

• B41J2/12

  testing or correcting charge or deflection · CPC title

• G06T2207/30144

  Printing quality · CPC title

• B41J2025/008

  comprising a plurality of print heads placed around a drum · CPC title

• B41J2/07 Primary

  characterised by jet control (B41J2/205 takes precedence) · CPC title