Droplet Generator Frequency Inversion for Ink Consistency
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Solution Overview
Problem
Continuous inkjet printers face performance inconsistency due to manufacturing variations in resonant droplet generators, requiring inefficient tuning processes and being sensitive to ink type, especially when using acoustically soft materials or designs that account for ink resonance.
Innovation Solution
A droplet generator with a substantially rigid main body and a nozzle assembly, where the nozzle is vibrated by piezo-electric crystals, and a start/stop mechanism is decoupled from modulation to maintain consistent performance across different inks, with a resonant frequency significantly higher than the operating frequency, allowing for efficient operation with various inks without tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a resonant droplet generator is used to minimize power requirements, then energy efficiency is improved, but manufacturing variations cause resonance frequency shifts leading to performance inconsistency
Solution Approach 1:
Instead of designing the droplet generator to operate at its resonant frequency (conventional approach), the patent inverts the approach by operating at a frequency significantly below the resonant frequency. This eliminates sensitivity to manufacturing variations while maintaining energy efficiency through optimized actuator design.
Solution Approach 2:
The patent changes the operating frequency parameter from being close to resonant frequency to being significantly below resonant frequency (ratio of 1:5 or greater). This parameter change fundamentally alters the system's sensitivity characteristics, making performance consistent across manufacturing variations.
2Reliability
If acoustically soft materials are used to eliminate resonances, then resonance-related inconsistencies are resolved, but modulation control deteriorates and tooling costs increase
Solution Approach 1:
Rather than using acoustically soft materials to eliminate resonances, the patent uses rigid materials that maintain strong resonances but operates at a frequency far below resonance. This inverted approach preserves excellent modulation control and material durability while achieving resonance consistency.
Solution Approach 2:
The patent separates the resonance frequency from the operating frequency, creating a clear distinction between the system's natural resonance and its operational frequency. This segmentation allows the system to benefit from rigid materials without suffering from resonance-related inconsistencies.
3Use of energy by moving object
If the resonant frequency is close to the operating frequency, then power requirements are minimized, but the system becomes sensitive to ink type variations requiring tuning
Solution Approach 1:
The patent inverts the conventional frequency relationship by operating at a frequency much lower than resonance rather than at or near resonance. This eliminates ink-type sensitivity while maintaining reasonable power requirements through efficient actuator coupling.
Solution Approach 2:
By operating far below resonant frequency, the droplet generator becomes universal and compatible with multiple ink types without requiring tuning. The system gains multi-functionality across different ink formulations while maintaining energy efficiency.
4Reliability
If tuning is performed by changing nozzles to compensate for resonance variability, then performance consistency is improved, but productivity decreases due to nozzle discarding
Solution Approach 1:
Instead of tuning nozzles to match resonant frequency variations, the patent inverts the approach by making the system insensitive to resonance variations through low-frequency operation. This eliminates the need for nozzle changes and improves productivity.
Solution Approach 2:
The droplet generator design inherently compensates for manufacturing variations without requiring external tuning or nozzle replacement. The system is self-sufficient and maintains consistent performance across production batches, improving nozzle utilization.
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 ensures consistent droplet generation across a wide range of frequencies and ink types, reducing the need for frequent nozzle changes and minimizing acoustic energy applied to the ink, thus maintaining print quality and efficiency.
Implementation Method 1
an actuator to vibrate said nozzle with respect to said fluid chamber
Implementation Method 2
The mathematics of dividing an ink stream into droplets has been described by Rayleigh. The underlying mechanism of forming the stream into droplets, a process known as modulation, involves creating instability in the ink steam.
Implementation Method 3
Typically these generators have been designed and constructed as resonant systems to minimise power requirements and energy loss.
Data Source
AI summary
The present invention provides a droplet generator (10) of the velocity modulation type, the generator (10) being configured so that substantially all the modulation energy generated by piezo-electric crystals (60) is transformed into vibration of the nozzle (34). The generator preferably also includes an internal closure mechanism (70) which blocks off the nozzle (34) when the generator is not in operation, but which is de-coupled from the modulation process when the generator is operating.