Inkjet Nozzle Defect Detection Using Weighted Thresholds

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Solution Overview

Problem

Existing methods for detecting and compensating defective printing nozzles in inkjet machines rely on subjective human assessment and empirically set thresholds, which are inadequate for industrial contexts, leading to inefficiencies and quality issues due to false positives and false negatives, and do not account for substrate properties or ink variations.

Innovation Solution

A method using a computer to evaluate multi-row printing nozzle test charts and area coverage elements, calculating thresholds based on weighting factors to differentiate between alpha and beta defects, minimizing false positives and negatives, and adjusting compensation processes to optimize print quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If subjective human assessment is used to evaluate print quality, then print quality can be judged based on human expectations, but time consumption increases significantly making 100% assessment impossible in industrial context

Engineering Contradiction:

Improveprint quality assessment accuracyVSAvoidassessment time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent replaces the mechanical human assessment system with an automated image processing and evaluation system. The computer analyzes test prints using algorithms that objectively measure print quality parameters, substituting human visual inspection with automated digital analysis to eliminate time consumption while maintaining assessment capability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent creates a digital copy of the print quality assessment process through image processing. Instead of requiring human observers to physically examine each print, the system captures images of test prints and creates digital representations that can be analyzed computationally, enabling rapid evaluation without time loss

Inventive Principle:

Principle #26Copying

2Ease of manufacture

If empirically set thresholds are used for nozzle defect detection, then the detection process is simple to implement, but false positives and false negatives occur reducing detection accuracy

Engineering Contradiction:

Improvedetection system implementation simplicityVSAvoidnozzle defect detection accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent transforms fixed empirical thresholds into dynamic, adaptively determined thresholds based on actual print data analysis. The system adjusts detection parameters according to measured print characteristics and nozzle performance variations, changing the threshold values to match real-world conditions rather than relying on predetermined static values

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements a feedback mechanism where detection results and print quality measurements are continuously analyzed to refine threshold values. The system uses historical data and actual performance feedback to optimize detection thresholds, creating a closed-loop system that improves accuracy over time while maintaining implementation simplicity

Inventive Principle:

Principle #23Feedback

3Productivity

If fixed detection thresholds are applied without considering substrate properties or ink variations, then the detection process is consistent and simple, but detection accuracy decreases due to inability to adapt to different printing conditions

Engineering Contradiction:

Improvedetection process efficiencyVSAvoiddefect detection reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent transitions from static fixed thresholds to dynamic adaptive thresholds that automatically adjust based on detected substrate properties and ink characteristics. The system modifies detection parameters in real-time according to the specific printing conditions, enabling both efficient processing and reliable detection across varying substrates and ink types

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent applies different detection thresholds and parameters tailored to specific local conditions of each substrate and ink combination. Instead of using a universal fixed threshold, the system determines locally optimized thresholds based on the particular characteristics of the material being printed, improving reliability for each specific printing scenario

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS10549545B2Method for detecting and compensating for defective printing nozzles in an inkjet printing machine using a threshold calculation based on weighting factors

Publication Date: 2020.02.04 HEIDELBERGER DRUCKMASCHINEN AG

AI summary

A method for detecting and compensating defective printing nozzles in an inkjet printing machine includes periodically printing at least one printing nozzle test chart having horizontal rows of equidistant vertical lines underneath one another, with only nozzles contributing to the test chart in every row corresponding to horizontal rows, and printing an area coverage element geometrically associated with the test chart. Both elements are recorded by an image sensor and evaluated by a computer. The computer identifies print defects by evaluating the area coverage element and allocates the defects to defective nozzles. The computer evaluates the test chart based on thresholds to detect defective nozzles and compensate detected defective nozzles. The computer compares the detected defective nozzles from the area coverage element and the test chart to identify detected defective nozzles causing defects in only one element and calculates the thresholds based thereon to minimize the detected defective nozzles.