Grayscale Inkjet Print Head Voltage Waveform for Satellite Drop Control
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Solution Overview
Problem
High-frequency inkjet printing systems face challenges in achieving reliable jetting performance and high printing speeds due to excess acoustic energy leading to satellite drops and varying droplet velocities, which deteriorate image quality and productivity.
Innovation Solution
Incorporating a specific idle time period between ejecting pulses in a voltage wave form for pigmented inkjet inks, allowing for reliable ejection of large droplets using only two sub-drops, thereby increasing print head frequency and maintaining image quality at three gray levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-frequency wave forms (60 kHz or more) are used to improve printing speed, then productivity increases, but jetting performance deteriorates due to excess acoustic energy causing satellite drops and velocity variations
Solution Approach 1:
The wave form is designed with periodic structure including first and second pulses with different amplitudes and durations, creating controlled acoustic pressure variations that eject droplets at high frequency while managing excess energy through structured periodic cycles
Solution Approach 2:
The invention changes multiple parameters of the wave form including amplitude ratios (A1/A3 between 0.50-0.80), pulse duration ratios (t1/t3 between 0.30-0.70), and introduces specific idle time periods between cycles, optimizing these parameters to achieve high frequency operation with controlled acoustic energy
2Speed
If larger amplitude pulses are used to eject fast droplets, then drop velocity increases, but satellite drops are generated due to uncontrolled excess acoustic energy
Solution Approach 1:
The wave form is segmented into multiple pulses (first pulse with amplitude A1, second pulse with amplitude A3) where each pulse contributes differently to droplet ejection, allowing control of main droplet velocity while minimizing satellite generation through distributed energy delivery
Solution Approach 2:
The invention converts the potentially harmful excess acoustic energy into a beneficial structured pressure wave pattern where the idle time period allows energy dissipation, and the multi-pulse structure uses what would be excess energy to ensure complete droplet ejection without satellites
3Manufacturing precision
If smaller ink droplets are used to improve image quality, then image quality improves, but printing frequency must increase which worsens pressure damping between drops
Solution Approach 1:
The structured periodic wave form with controlled idle time periods creates consistent pressure cycling that ensures complete damping before each droplet ejection cycle, allowing high frequency operation with smaller droplets while maintaining reliability
Solution Approach 2:
The idle time period in the wave form allows the ink chamber pressure to self-damp naturally before the next ejection cycle, eliminating the need for active pressure control mechanisms while ensuring reliable operation at high frequencies
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
This approach enables reliable high-frequency inkjet printing with minimal impact on image quality, improving productivity and reducing satellite issues and droplet velocity variations.
Implementation Method 1
Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of a voltage changes the shape of the piezoelectric ceramic transducer in the print head creating a void, which is then filled with ink. When the voltage is again removed, the ceramic expands to its original shape, creating a pressure wave which leads to the formation of a drop ejected from the nozzle of a print head.
Implementation Method 2
A wave form is a set of timed actuator movements used to propagate and control acoustic pressure waves within an ink chamber of a grayscale print head to eject an ink droplet through a nozzle.
Implementation Method 3
by including a specific idle time period between two ejecting pulses, large ink droplets of a specific inkjet ink could be ejected in a reliable manner... The higher the printing frequency, the more likely that the pressure in the ink chamber is not yet damped to zero when the next drop and pressure wave comes along
Data Source
AI summary
A grayscale inkjet printing method including the steps of: a) supplying a pigmented inkjet ink to a grayscale print head having nozzles with an outer nozzle surface area smaller than 500 μm2 and having an acoustic resonance period ARP of not more than 5.5 μs; and b) applying a voltage wave form for ejecting pigmented inkjet ink from a nozzle of the grayscale print head within one jetting cycle; wherein the pigmented inkjet ink has a viscosity of at least 3.8 mPa·s at jetting temperature and a shear rate of 1,000 s−1; wherein the voltage wave form for ejecting the largest ink droplet includes, in chronological order, a first ejecting pulse having an amplitude A1 and a second ejecting pulse having an amplitude A3 with the amplitude A1 complying with the relationship: 0.50×A3<A1<1.40×A3; and wherein a time period between the end time of the first ejecting pulse and the end time of the second ejecting pulse defines an idle time period including no other ejecting pulse, the time period having a duration between 1.5 to 2.5 times the acoustic resonance period ARP; and wherein any non-ejecting pulse having an amplitude A2 present during the idle time period complies with the relationship: A2≤0.15×A3. An inkjet printing system is also disclosed.