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

Patent metadata

Field	Value
Publication number	US-10214017-B2
Application number	US-201715836962-A
Country	US
Kind code	B2
Filing date	Dec 11, 2017
Priority date	Dec 14, 2016
Publication date	Feb 26, 2019
Grant date	Feb 26, 2019

Abstract

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.

First claim

The invention claimed is:

1. A method for detecting and compensating for failed printing nozzles in an inkjet printing machine by using a computer, the method comprising the following steps:
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 an entire print image height and dividing the added color values by a number of column pixels to obtain a column profile;
subtracting an optimized column profile without failed printing nozzles from an original column profile to provide a differential column profile;
setting a maximum value threshold defining a failed printing nozzle when exceeded;
applying the maximum value threshold to the differential column profile to obtain a resultant column profile having maximums each marking a failed printing nozzle; and
compensating for the marked printing nozzles in a subsequent printing operation.

2. The method according to claim 1 , which further comprises creating the optimized column profile without failed print nozzles by applying a median filter to the column profile, causing occurring maximum values and noise in the column profile to be filtered out.

3. The method according to claim 1 , which further comprises generating the optimized column profile without failed print nozzles by a previously created defect-free reference image column profile of the same print image.

4. The method according to claim 3 , which further comprises providing the defect-free reference image of the same print image as a printed, recorded and digitized print image having been declared defect-free by a user or created by the computer directly from prepress data of a current print job.

5. The method according to claim 3 , which further comprises using the computer to analyze the prepress image to determine image areas being covered to an optimum degree by respective process colors to be inspected, creating the column profile only for this area, and carrying out the subtraction of the previously created column profile of the defect-free reference image only in the determined image areas.

6. The method according to claim 3 , which further comprises using the computer to transform a prepress image into a camera color space by using a color space transformation aided by an ICC profile, and subsequently using the column profile of the transformed prepress image for the subtraction from the original column profile.

7. The method according to claim 3 , which further comprises using a respective color separation R or G or B of a prepress image in which a color to be evaluated has a greatest contrast relative to a selected color separation.

8. The method according to claim 1 , which further comprises printing a current print image with only one used process color, selecting from the digitized print image a color separation out of RGB that colorimetrically fits the printed process color or a gray value image out of RGB, and carrying out the method individually for every process color.

9. The method according to claim 1 , which further comprises providing the current print image as every print image printed in a course of a printing operation using all process colors and being examined in a continuous image inspection process, and selecting from the digitized print image a gray value image out of RGB from the digitized print image, the relevant color of the failed printing nozzle resulting from a combination of RGB color channels in question.

10. The method according to claim 1 , which further comprises providing the maximum value threshold defining a failed printing nozzle when exceeded as a fixed threshold or corresponding to a multiplied average or to a multiplied standard deviation.

11. The method according to claim 1 , which further comprises defining a location of the detected failed printing nozzles, before or after every detection process, by specifically deactivating individual printing nozzles at a defined distance and determining a position thereof in the detection process.

Assignees

• Heidelberger Druckmasch Ag

Inventors

• Geissler Wolfgang
• Mayer Martin
• Muth Frank
• Koehler Hans

Classifications

• B41J2/16579 Primary

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

• B41J2025/008

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

• B41J2/2142

  Detection of malfunctioning nozzles (generating single droplets or particles on demand by pressure, e.g. electromechanical transducers B41J2/045, B41J2/05; jet deflection sensors B41J2/125; for cleaning purposes B41J2/16579) · CPC title

• B41J2/2139 Primary

  Compensation for malfunctioning nozzles creating dot place or dot size errors (generating single droplets or particles on demand by pressure, e.g. electromechanical transducers B41J2/045) · CPC title

• B41J2/2146

  for line print heads · CPC title