Liquid Ejection Head Circulation Layout for Stable Ink Ejection
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Solution Overview
Problem
Existing liquid ejection heads face issues with ink thickening at ejection nozzles due to evaporation, leading to variations in ejection amount and direction, resulting in poor image quality, and current circulation mechanisms are limited by pump size and frequency restrictions.
Innovation Solution
A liquid ejection head design featuring a circulation flow passage with two thermoelectric conversion elements disposed at different timings to enhance circulation efficiency, using a U-shaped configuration with alternating driving signals to manage flow resistance and prevent reboiling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the energy generating element for circulation is driven at high frequency to increase the flow rate, then the circulation efficiency is improved, but re-boiling is caused by local heating, a foaming failure is generated, and the flow rate decreases
Solution Approach 1:
The circulation flow passage is divided into multiple sections with separate thermoelectric conversion elements (first and second elements) positioned at different locations. This segmentation allows the circulation system to be controlled in stages, enabling high-frequency operation without causing re-boiling throughout the entire passage. The first element operates at higher frequency to generate strong circulation, while the second element operates at lower frequency to prevent local overheating and foaming failure.
Solution Approach 2:
The patent employs periodic driving of thermoelectric conversion elements at different frequencies and timings. The first thermoelectric conversion element is driven at a higher frequency than the second element, creating a periodic circulation pattern that prevents continuous local heating. This periodic action allows the ink to be circulated effectively while avoiding the re-boiling condition that would occur with continuous high-frequency operation of a single element.
2Measurement precision
If the density of ejection nozzles is increased, then the ejection resolution is improved, but the flow passage width narrows and pump size is restricted
Solution Approach 1:
The patent replaces the traditional mechanical pump with thermoelectric conversion elements that utilize thermal expansion and contraction of the ink to generate circulation flow. This substitution eliminates the need for a mechanical pump, allowing the system to achieve effective circulation in a much smaller volume. The thermoelectric elements can be integrated directly into the flow passage structure, enabling high nozzle density without requiring additional pump space.
3Stability of the object's composition
If ink is circulated continuously, then ink thickening is prevented, but circulation efficiency decreases due to flow resistance
Solution Approach 1:
The patent implements dynamic control of the thermoelectric conversion elements, adjusting their operating frequencies and duty cycles based on circulation requirements. The first thermoelectric conversion element operates at a higher frequency during periods when strong circulation is needed to overcome flow resistance, while the second element operates at a lower frequency to maintain steady flow. This dynamic adjustment optimizes circulation efficiency while continuously preventing ink thickening.
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
The design effectively circulates fresh ink to the nozzles, preventing thickening and improving image quality by maintaining consistent ejection performance.
Implementation Method 1
an energy generating element that generates energy to eject liquid inside the pressure chamber from the ejection nozzle
Implementation Method 2
a first thermoelectric conversion element which is disposed on the circulation flow passage and a second thermoelectric conversion element which are disposed on the circulation flow passage
Implementation Method 3
At an ejection nozzle where the ejection of ink has not been performed for a while, ink evaporates from the ejection nozzle, whereby ink thickens
Data Source
AI summary
Provided is a liquid ejection had including: a liquid ejection portion which includes a pressure chamber, an ejection nozzle for ejecting liquid from the pressure chamber, and an energy generating element that generates energy to eject liquid from the ejection nozzle; a circulation flow passage which includes an inflow port to which liquid flows in, and an outflow port from which liquid flows out, with the pressure chamber being disposed between the inflow port and the outflow port. The liquid ejection head further includes: a first thermoelectric conversion element which is disposed on the circulation flow passage on a side closer to the inflow port than the energy generating element; and a second thermoelectric conversion element which is disposed on the circulation flow passage, and which is disposed adjacent to the first thermoelectric conversion element. The first and second thermoelectric conversion elements are driven at timings different from each other.