Inkjet Printhead Nozzle Defect Detection Using Coded Line Patterns
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Solution Overview
Problem
Existing methods for identifying defective nozzles in inkjet printheads are limited by speed, cost, scalability, and reliability, particularly in high-end commercial printers, and fail to detect malfunctions in realistic printing scenarios where neighboring nozzles are fired simultaneously.
Innovation Solution
A method involving coded line patterns printed by nozzles, using two coding schemes to encode nozzle and cell positions, allowing for simultaneous firing of neighboring nozzles, and decoding the imaged test pattern to identify defective nozzles, which is scalable and effective even at low imaging resolutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a sparse pattern with large blank spaces is used to detect dead nozzles, then the imaging area is reduced, but the detection efficiency and information density are worsened
Solution Approach 1:
The patent merges multiple nozzles' test patterns into overlapping regions. Each nozzle prints a test pattern, and adjacent nozzles' patterns overlap on the media, creating combined signal regions. This allows simultaneous testing of multiple nozzles in a compact area, increasing information density without requiring large blank spaces between test regions.
Solution Approach 2:
The patent transitions from spatial separation (1D linear arrangement with gaps) to temporal/sequential encoding (2D matrix code). Instead of spacing nozzles apart spatially, the invention encodes nozzle positions and states in a two-dimensional code structure that can be read by imaging devices, allowing compact arrangement while maintaining full detectability.
2Reliability
If nozzles are fired sequentially with large separations, then dead nozzles can be detected, but the detection method fails to identify defects in realistic simultaneous printing scenarios
Solution Approach 1:
The patent makes the test pattern dynamic by having nozzles fire in sequences that create different overlap patterns. Multiple firing sequences are used where each sequence produces a unique combined pattern. This dynamic approach allows the system to detect not only dead nozzles but also artifacts that only appear when nozzles fire simultaneously, matching realistic printing conditions.
Solution Approach 2:
The patent employs periodic firing sequences where groups of nozzles are activated in repeating cycles. Each cycle tests a different combination of nozzles, and by analyzing patterns across multiple cycles, the system can distinguish between permanent dead nozzles and transient printing artifacts, improving reliability while maintaining adaptability to realistic scenarios.
3Measurement precision
If conventional patterns with large separations between line segments are used, then nozzle detection is possible, but the method requires high imaging resolution and adds processing complexity
Solution Approach 1:
The patent creates a coded copy of nozzle position and state information in the form of a two-dimensional matrix code printed on the media. Instead of requiring high-resolution imaging to detect subtle variations in sparse patterns, the system encodes all necessary information (nozzle positions, firing states, group identifiers) into a compact code structure that can be reliably read at lower resolutions, reducing both imaging and processing requirements.
4Loss of information
If registration marks are added to identify defective nozzles, then nozzle identification becomes possible, but the overall processing time and complexity increase significantly
Solution Approach 1:
The patent makes the test pattern itself multi-functional by embedding multiple types of information within the same printed structure. The overlapping test patterns serve both as functional tests for nozzle operation and as encoded data containing position and identification information. This eliminates the need for separate registration marks, reducing processing time while maintaining complete nozzle identification capability.
Data Source
AI summary
A method of identifying defective nozzles of a printhead. The method includes the steps of: (i) instructing each nozzle in one ink plane of the printhead to print a respective coded line pattern, each coded line pattern being represented by a column of printed pixels and absent pixels, the coded line patterns being defined by first and second coding schemes encoding a position of each nozzle within its respective cell and a position of each cell within its respective ink plane; (ii) firing each nozzle of the ink plane to print a test pattern comprising a plurality of neighbouring coded line patterns; (iii) imaging an area of the test pattern to obtain an imaged test pattern; (iv) decoding the imaged test pattern using the first and second coding schemes; and (iv) identifying the defective nozzles using the decoded imaged test pattern.