Depending on the mechanism used in the drop formation process, the technology can be categorized into four major methods: thermal, piezoelectric, electrostatic, and acoustic ink-jet. Most, if not all, of the drop-on-demand ink-jet printers on the market today are using either the thermal or piezoelectric principle. The thermal ink-jet method was not the first ink-jet method implemented in a product, but it is the most successful method on the market today.
Depending on its configuration, a thermal ink-jet can be a roof-shooter Fig. The roof-shooter design is used in the printheads from Hewlett-Packard, Lexmark, and Olivetti. The side-shooter design is implemented in the Canon and Xerox printheads. In the piezoelectric ink-jet, depending on the piezoceramic deformation mode Fig.
A squeeze-mode ink-jet can be designed with a thin tube of piezoceramic surrounding a glass nozzle as in a Gould's impulse ink-jet 25 or with a piezoceramic tube cast in plastic that encloses the ink channel as was implemented in a Seimens PT ink-jet printer. With a printhead array of twelve jets and an innovative maintenance station design, this product was fast and reliable enough to be the first truly successful ink-jet product for the office.
Subsequent efforts by the company to introduce a second-generation printhead with a jet array encountered difficulty in achieving jet-to-jet uniformity.
In a typical bend-mode design Fig. The printheads in Tektronix's Phaser and and Epson's Color Stylus , , and ink-jet printers are based on this design principle. In a push-mode design Fig. In theory, piezodrivers can directly contact and push against the ink. However, in practical implementation, a thin dia phragm between piezodrivers and ink is incorporated to prevent the undesirable interactions between ink and piezodriver materials. Successful implementation of the push-mode piezoelectric ink-jet is found in the printheads from companies such as Dataproducts, Trident, and Epson.
In both the bend- and push-mode designs, the electric field generated between the electrodes is in parallel with the polarization of the piezomaterial. In a shear-mode printhead, the electric field is designed to be perpendicular to the polarization of the piezodriver Fig. The shear action deforms the piezoplates against ink to eject the droplets.
In this case, the piezodriver becomes an active wall in the ink chamber. Interaction between ink and piezomaterial is one of the key parameters of a shear-mode printhead design. Companies such as Spectra 26 and Xaar 27,28 are pioneers in the shear-mode printhead design. Printhead Design and Fabrication Processes. Today the ink-jet technologies most active in laboratories and in the market are the thermal and piezoelectric drop-on-demand ink-jet methods.
In a basic configuration, a thermal ink-jet consists of an ink chamber having a heater with a nozzle nearby. With a current pulse of less than a few microseconds through the heater, heat is transferred from the surface of the heater to the ink. When the nucleation occurs, a water vapor bubble instantaneously expand to force the ink out of the nozzle. Once all the heat stored in the ink is used, the bubble begins to collapse on the surface of the heater.
Concurrently with the bubble collapse, the ink droplet breaks off and excels toward the paper. The ink then refills back into the chamber and the process is ready to begin again. This process is illustrated in Fig. Figure 11 reillustrates the same process by plotting the parameters including electrical pulse, temperature, pressure, and bubble volume against time. Figure Pressure, temperature, and bubble volume changes during a drop formation cycle of thermal ink-jet.
Figure 12 shows a scanning electron microscope SEM photograph of a Hewlett-Packard series thermal ink-jet channel with heater and ink barrier layer the aper ture plate was removed.
This jet was known to produce 32 pl ink droplets at the rate of drops per second. The ink channel in the SEM photograph is measured at about 0. However, the dimensional stability, accuracy, and uniformity of this channel are known to have great effects on jet performance such as drop frequency, volume, and velocity. All of these drop performances ultimately determine the quality and throughput of a printed image. The trends in the industry are in jetting smaller droplets for image quality, faster drop frequency, and a higher number of nozzles for print speed, while the cost of manufacture is.
These trends force further miniaturization of the ink-jet design. Consequently, the reliability issue becomes critical. In the latest generation of the Hewlett-Packard series, the company introduced a new nozzle tricolor printhead that can jet much smaller ink droplets 10 pl at the rate of 12, drops per second.
Figure 13 is a light microscopic photograph of an ink-jet channel from a Hewlett-Packard new tricolor printhead for the DeskJet C. The channel heater is measured about one mil square. Ink feeds from both sides of the heater chamber. This fluid architecture would significantly decrease the possibility of nozzle clogging that may result from particulates trapped in the printhead fabrication processes as well as in the process of making inks.
A row of small openings between the ink manifold and the heater chamber was also introduced in the new design, in order to improve the reliability of the new printhead. Another trend in the industry is market demand for lower cost per print. Printhead producers could pack in greater ink volume per cartridge to increase the print count or install a permanent or semipermanent thermal printhead to reduce the cost of new ink cartridges.
Again, this trend will demand even higher reliability for thermal ink-jet printheads. Canon is another major company that develops and produces thermal ink-jet printers. In the latest bubble-jet product BJC, Canon introduced a nozzle printhead. By far, this is the highest nozzle count for a single printhead module marketed to the home and small office color ink-jet printer market.
In the BJC implementation, the nozzle printhead consists of six colors with 80 nozzles per color. Other companies that develop and manufacture thermal ink-jet printheads are Lexmark, Olivetti, and Xerox. In the piezoelectric drop-on-demand ink-jet method Fig. This acoustic pressure wave overcomes the viscous pressure loss in a small nozzle and the surface tension force from ink meniscus so that an ink drop can begin to form at the nozzle.
When the drop is formed, the pressure must be sufficient to expel the droplet toward a recording media. The basic pressure requirement is showed in Fig. Table I. In general, the deformation of a piezoelectric driver is on the submicron scale. To have large enough ink volume displacement for drop formation, the physical size of a piezoelectric driver is often much larger than the ink orifice. Therefore, miniaturization of the piezoelectric ink-jet printhead has been a challenging issue for many years.
A list of piezoelectric drop-on-demand printhead producers is provided in Table I. Tektronix nozzle and Sharp 48 nozzle printheads are made with all stainless steel jet stacks. These jet stacks consist of multiple photochemical machined stainless steel plates bonded or brazed together at a high temperature. Figure 16 shows a cross section SEM photograph of a Tektronix jet stack. The thin Au intermetallic bonding layers are visible between the brazed plates. The intermetallic bond in ink-jet printhead application requires uniform thickness for design performance consistency and hermetic sealing to prevent inks from leaking externally or between two adjacent ink channels.
Similar bonding characteristics are found in a Sharp jet stack. Figure 17 shows a cross section SEM photograph of the Ni intermetallic bond between the stainless steel plates of the Sharp printhead. Besides using Au or Ni to bond metal plates together, solder and epoxy are also used to fabricate printheads. Figure 18 shows a cross section SEM photograph of a Spectra printhead where the electroformed nickel orifice plate is bonded to the jet stack by epoxy.
In the same photograph, the solder bonds between multiple steel plates are also noticed. However, due to ink compatibility issues, the selection of epoxy or solder composition must be carefully considered. Given the trends to increasing the number of nozzles, decreasing their physical size, and jetting many different fluids, bond integrity and stability of the printhead become increasingly critical issue.
Cross section SEM photographs of a bond line in a Sharp stainless steel jet pack. In , Epson introduced the Stylus piezoelectric ink-jet printer to compete directly with thermal ink-jet or bubble-jet technology in the low-end home and small office printer market. This product introduction was very significant in the sense that it was the first time a reliable low-cost piezoelectric ink-jet with a permanent printhead was successfully introduced in a low-end printer.
This Epson printhead is based on a push-mode design with a multilayer piezoactuator. Alternate electrodes are seen in both sides of each PZT layer.
In , Epson introduced Color Stylus , , and with a bend-mode design piezoelectric printhead. Color Stylus employs two printheads: nozzle for black and nozzle for color CMY.
The technological breakthrough in this new bend-mode piezo printhead introduction is in the unique fabrication method for the thick film PZT sintered on top of the zirconia diaphragm to make piezoelectric drivers. Note that, as compared to the push mode with a long PZT structure design, the new Epson thick film PZT bend-mode device has a planar structure.
The fabrication process for the new design is simple and less costly. Furthermore, with a small, flat and thin printhead structure, any addition of heaters to control the operating temperature of the printhead is much easier to design.
The trends here are to increase the number of nozzles and add more flexibility in ink formulations, as was potentially realized with Epson's new printhead technology. Nu-Kote nozzle and Topaz Technologies nozzle piezoelectric drop-on-demand printheads are the two newest additions to the ink-jet market. The Nu-Kote printhead is based on the development of a Xaar shear-mode shared wall design.
The technology is about 10 years old, but the field experience is new. A key challenge for the Nu-Kote printhead is its reliability in the market. The Topaz nozzle printhead is also new to the industry.
It is known to combine both the bend and shear modes to jet ink droplets at a relatively high-drop-ejection frequency. The technology was introduced in the Calcomp CrystalJet large-format ink-jet printer. The challenge, however, was to come up with a way to create an affordable inkjet printer that would reliably create high-quality printouts. Technical challenges The quality of the printed page depends largely on the relationship between the ink, the print head, and the paper.
Researchers had a hard time creating a controlled flow of ink from the print head onto the page, and preventing the print head from becoming clogged with dried ink. Once these challenges were met by Canon and Hewlett Packard in the late s, liquid inkjet printers began to come on the market.
Different styles Continuous inkjet printers were developed by IBM , and use electrically-charged droplets to coat the page with ink very quickly but also waste a lot of ink. This technology never caught on with consumers, but is used today in industrial settings, for labeling cartons and addressing direct mail.
The following printer supplier introduces several historical breakthroughs in inkjet printer technology breakthroughs. Inkjet printing technology was proposed as early as , but the first commercial inkjet printer was born at IBM after 16 years. The so-called continuous inkjet is to produce ink droplets in a continuous manner regardless of the printing or non-printing, and then recover or disperse the non-printing ink droplets. However, this technique uses ink to print ink on paper.
The effect is imaginable, so it has no practical value in reality. The printer was mass-produced in and became the world's first inkjet printer with commercial value.
Japanese researchers at Canon successfully developed Bubble Jet bubble jet technology. This technology uses a heating element to instantly heat the ink in the nozzle to generate air bubble formation pressure, so that the ink is ejected from the nozzle and then the physical properties of the ink are used to cool the hot spot Air bubbles fade, thereby achieving the dual purpose of controlling the dot in and out and size.
Here is a small story of the company. One day in July , Endo I of the 22nd Lab of Canon Product Technology Research Institute, Meguro-ku, Tokyo, accidentally put a heated soldering iron on the laboratory while conducting experiments in the laboratory. When the needle was attached, ink quickly flew out of the needle. Inspired by this, the bubble jet technology was invented 2 years later. At the same time, Hewlett-Packard also invented essentially the same technology.
HP and Canon both claimed to be the first researchers to invent the inkjet printing technology to establish their position in the inkjet printing field. The first inkjet printer was developed by Hewlett-Packard in However, inkjet printers do not gain popularity until the mids.
Siemens developed the first DOD drop-on-demand inkjet printer in The DOD printer sprays ink where it is needed on the piece of paper. Canon introduced the LBP, the first semiconductor laser beam printer and their first printer unit.
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