Threshold calculation with weight

Abstract

The invention relates to a method for detecting and compensating defective printing nozzles in an inkjet printer by means of a computer, which comprises: printing at least one multi-row printing nozzle test pattern and at least one surface covering element, wherein the two elements are detected by at least one image sensor and are analyzed and processed by the computer; allowing the computer to analyze and process the surface covering elements to obtain printing errors and distribute the printing errors to defective printing nozzles; then, allowing the computer to detect the defective print nozzles by analyzing and processing the printing nozzle test pattern according to a threshold value, and compensating the defective printing nozzles thus detected. The computer compares the defective printing nozzles detected by the surface covering elements with the defective printing nozzles detected by the printing nozzle test pattern, and determines those detected defective printing nozzles thatcause deviations only in one of the two elements, therefore the threshold value is calculated from these data in such a way that the number of detected defective printing nozzles is minimized.

Description

technical field [0001] The invention relates to a method for detecting and compensating for defective printing nozzles in an inkjet printer. [0002] The invention belongs to the technical field of digital printing. Background technique [0003] The quality of printed products is always ultimately evaluated by human observers. Such a human observer can be an end user (Endkunde) of a printed product: for example a buyer of hair dye and its packaging on a supermarket shelf, a client of a printed product or a printer / owner of a production of printed products). The end user can likewise be a product manager, a certification engineer, an installation quality manager or a service employee of a company that manufactures a printing press on which printed products are produced. Therefore, the quality of a printed product and the resulting "marketability" is always subjectively defined by deviations from subjective expectations or requirements placed on the printed product and the ...

AI Technical Summary

Problems solved by technology

The main problem with subjective (i.e. human) evaluation is that a 100% inspection of all printed products can only be carried out with great time expenditure and is therefore practically never realized in an industrial environment

Alternatives in the form of sampling (stichprobe) with subjective evaluation have the problem that the quality of the printing result can vary at high frequency and not all unmarketable printed products can be detected by means of sampling

[0011] The downside of this approach is that current methods always use the same roughly empirically set thresholds to activate or deactivate print nozzles

This either leads to rejects due to too wide a threshold limit, or in the case of too narrow a threshold the print nozzle may be switched off too quickly

Furthermore, known methods are used very infrequently (ie usually only once a day)

This leads to a lot of errors in the case of volatile inkjet printing processes, as changes in the quality of the printing nozzles are not detected

Both of which negatively impact quality and / or productivity

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