Liquid Ejection Pulse Control for In-Flight Droplet Coalescence
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Solution Overview
Problem
Existing liquid ejecting apparatuses face challenges in causing multiple droplets to coalesce at a desired position while maintaining the required liquid amount, either by extending the time interval between droplet ejections or reducing the droplet volume, leading to inefficiencies in dot formation on a medium.
Innovation Solution
A drive signal with at least three ejection pulses is employed, including filling and ejection elements to generate pressure changes, coupled pulses to maintain electrical potential, and a damping element to attenuate vibrations, with specific timing and potential changes to ensure droplet coalescence before landing, using a liquid ejecting apparatus with a nozzle, pressure chamber, and drive element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of droplets that coalesce is increased to increase the amount of coalesced liquid, then the liquid amount of coalesced droplets is improved, but the time interval from the ejection of the first droplet to the ejection of the last droplet becomes longer, making it difficult to cause the droplets to coalesce by the time they reach the desired position
Solution Approach 1:
The patent applies dynamics by making the drive voltages variable rather than constant. The drive voltage for each droplet is dynamically adjusted based on its sequence number, with subsequent droplets having higher drive voltages than preceding ones. This dynamic adjustment allows the system to optimize both the liquid amount and coalescence timing by controlling the flying speed of each droplet individually.
Solution Approach 2:
The patent changes the parameter of drive voltage to resolve the contradiction. By increasing the drive voltage for subsequent droplets compared to preceding droplets, the system achieves variable droplet speeds that enable coalescence within the required time interval. This parameter change allows multiple droplets to be ejected and coalesce at the desired position without excessive time delay.
2Manufacturing precision
If the absolute value of the electrical potential range for the preceding droplet is reduced to lower its flying speed and enable coalescence, then the droplets can coalesce by the desired position, but the liquid amount of the preceding droplet is reduced, thus reducing the amount of coalesced droplets
Solution Approach 1:
The patent applies asymmetry by creating an asymmetric voltage pattern where preceding and subsequent droplets have different drive voltages. Specifically, the absolute value of the electrical potential range for preceding droplets is made smaller than that for subsequent droplets. This asymmetric approach allows preceding droplets to travel slower (enabling coalescence) while subsequent droplets carry more liquid, thus resolving the contradiction between coalescence position accuracy and liquid amount.
Solution Approach 2:
The patent uses dynamic adjustment of drive voltages based on droplet sequence. The drive voltage is not fixed but varies depending on whether the droplet is preceding or subsequent in the sequence. This dynamic approach allows the system to optimize the liquid amount and flying speed for each droplet individually, achieving both accurate coalescence positioning and sufficient liquid amount.
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 solution effectively allows for droplets to coalesce at the desired position on the medium, maintaining the intended liquid amount, thereby improving dot formation efficiency in the liquid ejecting process.
Implementation Method 1
a drive element that changes pressure applied to liquid in the pressure chamber according to a drive signal
Implementation Method 2
each of the at least three ejection pulses includes a filling element that changes an electrical potential to generate negative pressure in the pressure chamber, and an ejection element that changes an electrical potential to generate positive pressure in the pressure chamber
Implementation Method 3
The drive signal includes at least two coupling elements that couple consecutive ejection pulses among the at least three ejection pulses while maintaining an electrical potential
Implementation Method 4
a damping element that attenuates residual vibration of the liquid in the pressure chamber by generating negative pressure in the pressure chamber after the droplets are ejected from the nozzle after a last ejection pulse among the at least three ejection pulses
Data Source
AI summary
A liquid-ejecting-apparatus is configured to eject at least three droplets, which coalesce before landing on a medium from an ejection-section, by using a drive signal including in a unit-time: a at least three ejection-pulses that has respectively a filling element and an ejection element; and at least two coupling elements coupling consecutive ejection-pulses. A period from the start of the filling element to the start of the ejection element in each of the ejection-pulses is in range from 0.3Tc to 0.7Tc, where Tc is a natural vibration period of the ejection-section. Absolute values of electrical potential change ranges of the ejection-elements of the at least three ejection-pulses are great sequentially in the unit time. Electrical potentials maintained by the coupling elements are sequentially close to an electrical potential of an ending edge of a filling element of the last ejection-pulse in the unit time.