Printhead Heater Bubble Detection via Impedance
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Solution Overview
Problem
Existing methods for detecting the condition of inkjet printhead nozzles, such as optical detection and impedance sensing, are costly and complex, and fail to accurately detect bubble formation in real-time due to delayed detection of bubble formation and collapse, which occurs after the ejection event.
Innovation Solution
A system and method that detect the formation of a bubble on a heater surface based on the change in electrical resistance and slope of the sampled drain voltage of a corresponding drive element, using a sampling circuit and slope detect circuit, allowing for immediate detection of bubble formation and subsequent control of the heater element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical detection methods are used to detect nozzle condition, then detection capability is improved, but device complexity and cost increase due to external light sources and sensors
Solution Approach 1:
The patent extracts the detection function from external devices and integrates it directly into the printhead structure. Impedance sensors are placed on the ejector chip itself, eliminating the need for external light sources and sensors, thereby reducing device complexity while maintaining detection capability
Solution Approach 2:
The ejector chip is designed to perform multiple functions: it serves as both the actuation element for ink ejection and the substrate for impedance sensors for nozzle condition detection. This multi-functionality eliminates the need for separate external detection devices
2Device complexity
If impedance sensors are placed on the ejector chip to eliminate external devices, then device complexity is reduced, but detection timing is delayed until 5μs or more after drop ejection
Solution Approach 1:
The patent performs preliminary detection by monitoring impedance changes that occur during the bubble formation process itself, rather than waiting for bubble collapse. The impedance change is detected in real-time during the ejection cycle, enabling earlier detection of nozzle conditions
Solution Approach 2:
The system implements real-time feedback by continuously monitoring impedance sensor signals during the ejection cycle. The controller processes these signals to detect nozzle conditions immediately, allowing for timely corrective actions rather than delayed detection after ejection
3Measurement precision
If calibration methods are used to provide adequate system performance, then measurement precision is improved, but ease of operation deteriorates due to required calibration procedures
Solution Approach 1:
The system performs self-calibration by using the known electrical characteristics of the heater element and the measured impedance values to automatically determine nozzle conditions. The controller compares impedance changes against predetermined thresholds to identify blocked, open, or weak nozzles without requiring manual calibration procedures
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables real-time detection of bubble formation on the heater surface, improving the accuracy and efficiency of nozzle condition assessment without the need for external devices, thereby enhancing printhead performance and print quality.
Implementation Method 1
detecting the formation of a bubble on a heater surface based on the change in electrical resistance of the heater
Implementation Method 2
detecting the formation of a bubble on a heater surface based on the change in slope of the sampled drain voltage of a corresponding drive element
Data Source
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AI summary
A fluid printhead (10) including a plurality of heating elements (104) that are driven to nucleate bubbles in fluid so that the fluid is ejected from the printhead (10) in the form of drops, a plurality of drive elements, each driving element (204) selectively driving a corresponding one of the plurality of heating elements (104) in accordance with a printer controller (216), and a drop detection system that includes a plurality of drop detection cells (200), each drop detection cell (200) detecting a change in electrical resistance of a corresponding one of the plurality of heating elements (104) that occurs upon drop formation.