Last Updated on June 2, 2023 by You Ling
There are two main ways ink is ejected from a printer. The first one is thermal technology, which uses a heater to heat the ink and form bubbles, causing the ink to be expelled. The other one is piezoelectric technology, which applies voltage to change the shape of a piezoelectric element, resulting in the mechanical movement of the element that ejects the ink. Piezoelectric printheads are highly durable because they don’t experience degradation of function caused by heat. They are even compatible with inks that undergo material property changes when heated. Printers using piezoelectric technology can use various types of ink, including dye and pigment inks.
1、How does a piezoelectric printhead work?
In a micro piezoelectric printhead, micro-sized piezoelectric elements, such as crystals and ceramics, are embedded behind the printing nozzles. When a charge is applied to these elements, they bend backward, precisely pushing a certain amount of ink onto the substrate. Since the charges can be turned on and off like switches, there is a great deal of control over the rate of ink ejected through the nozzles, allowing for the formation of perfectly spherical ink droplets in different sizes.
2、How does a thermal printhead work?
Contrary to electricity, thermal inkjet technology uses heat to propel ink from the printhead onto the substrate. Conceptually similar to the way bubbles form when water boils, thermal inkjet technology works by applying current to micro-resistors behind the printing nozzles, generating intense heat that evaporates the ink and forms bubbles. The bubbles expand rapidly, causing the ink to explode onto the paper. After the ink is ejected, the chamber quickly cools, allowing for more ink to refill the chamber, and the process is repeated.
3、What is a piezoelectric inkjet printer?
A piezoelectric inkjet printer is a type of inkjet printer that utilizes a printhead containing special crystals and applies an electric current to it. This causes the crystals to expand, pushing the ink onto the substrate. When the current is removed, the crystals shrink again, drawing ink into the printhead. Piezoelectric technology is commonly used in large character inkjet printers.
4、How does a piezoelectric inkjet printer work?
Piezoelectric inkjet printers use Drop-on-Demand (DOD) printing technology, which means that the printer delivers ink to chambers located in the printhead. This printing technology is also used in thermal inkjet printers.
To jet ink onto the surface, piezoelectric inkjet printers employ what’s called the piezoelectric effect. This effect involves generating voltage on the surface by deforming the piezoelectric material, such as a piezoelectric crystal. As a result, the printing nozzles deform instantly, applying high pressure to the ink, causing the printhead to eject ink droplets. Then, the polarity of the voltage is reversed to stop the flow of ink from the nozzles.
Piezoelectric inkjet printers have two ink coating modes: bending mode and shear mode. In the first case, ink is drawn and expelled from the nozzles through bidirectional expansion. The second mode achieves the same result but with the use of pressure waves, consuming less energy.
5、What are the advantages of piezoelectric inkjet printers?
Piezoelectric inkjet printers have several advantages, especially when compared to thermal inkjet printers. These advantages include:
They offer high-resolution print results.
They can better control the shape and size of ink release.
They produce excellent print quality.
They are user-friendly and easy to set up.
Their ink cartridges can be separated from the printhead and replaced when needed.
They are faster and have a longer lifespan compared to thermal inkjet printers.
They are compatible with a wider range of ink types compared to thermal inkjet printers.
Despite these advantages, piezoelectric inkjet printers are typically more expensive than thermal inkjet printers. Additionally, unlike continuous inkjet printers, they tend to use water-based inks instead of fast-drying solvent inks, which slows down the printing process.
6、Application of piezoelectric elements in Epson printers
Creating Epson’s micro piezoelectric printheads with all their advantages required overcoming several challenges. One challenge was devising an inkjet mechanism that utilizes piezoelectric elements. Generally, if the thickness is the same, smaller surface area piezoelectric elements have smaller displacements compared to larger surface area ones. Therefore, improving resolution means reducing the displacement of the piezoelectric elements, resulting in less ink being ejected per nozzle.
Increasing the displacement of the piezoelectric elements is essential for selectively ejecting ink droplets of different sizes.
Thinner piezoelectric elements exhibit larger displacements under the same applied voltage. However, thinner piezoelectric elements are more fragile, making them difficult to manufacture and handle. To address this issue, Epson adopted multi-layer piezoelectric actuators composed of a stack of thin piezoelectric elements. They then developed a Multi-Layer Actuator Head (MACH) printhead that ejects ink through the vertical vibration of the piezoelectric elements. This approach achieved high density and responsiveness, significantly enhancing inkjet printing performance.
Several technologies were crucial in realizing MACH technology. These include high-level manufacturing and fabrication of the actuators, ultra-precision assembly for constructing the printhead, and advanced control for extracting printhead performance. By combining all these technologies, Epson’s MACH micro piezoelectric printhead is capable of delivering inkjet printing with high image quality, precision, and speed. MACH technology not only plays a role in Epson printers today but is also adopted by customers worldwide who utilize it in a wide range of printing applications.
In summary, piezoelectric inkjet printers offer numerous advantages compared to thermal inkjet printers. They provide high-resolution print results, precise control over ink release shape and size, and excellent print quality. These printers are user-friendly, with easy setup and the ability to replace ink cartridges separately from the printhead. They also exhibit faster printing speeds and longer lifespans. Moreover, piezoelectric inkjet printers are compatible with a wider range of ink types. However, they are generally more expensive than thermal inkjet printers and tend to use water-based inks, which can slow down the printing process.
Epson printers have successfully implemented piezoelectric elements in their micro piezoelectric printheads, overcoming challenges such as displacement limitations. By utilizing multi-layer piezoelectric actuators in their MACH technology, Epson has achieved high-density and responsive inkjet printing, enhancing image quality, precision, and speed. The MACH technology is not only employed in Epson printers but also adopted globally for various printing applications. Overall, the advancements in piezoelectric inkjet printing have revolutionized the industry, offering improved performance and versatility for printing needs.
