Epson's Next-Generation Micro Piezo Print Head Boasts Macro Potential.
4 June 2007 - By capitalising on its semiconductor expertise, Epson has engineered an inkjet print head capable of producing 360 dots per inch–the industry's highest for a print head based on piezoelectric technology–doubling the density of its current print head. This ramp-up in ink placement will result in much speedier printers, usher in original compact designs for printers, and expand the range of inkjet printing applications.
Before describing the innovations that make the new Micro Piezo print head possible, first a recap of how piezoelectric technology works. The word "piezo" is derived from the Greek "piezein," meaning to squeeze or push. Essentially, when a voltage is applied to piezo material (e.g. ceramics or quartz) it causes the material to change dimension. By controlling the amount and type of movement, ink in a surrounding chamber can be jetted out through an orifice or nozzle in precisely measured droplets at great speeds.
Epson's current Micro Piezo head has a nozzle count of 180 per row, producing a print density of 180 dots-per-inch or dpi. The obvious way to increase print density and therefore speed, then, would be to increase the number of print nozzles in each row.
"But the present print head is engineered using machine tools and has reached the maximum density possible using this production method," says Tomoaki Takahashi, manager of the Epson group of researchers that developed the new version of the Micro Piezo print head.
Consequently, the researchers not only had to rethink the design of the print head but also needed to find a different way to manufacture it. The answer to the challenge was found in photolithography, the same production process used to create the infinitely small patterns that make up the circuits crammed into semiconductor chips.
Applying photolithographic techniques to a thin film of piezo material, Epson has created a microscopically small piezo element just 1 micron in thickness. Yet despite its minuteness, the new element has been designed to produce an even greater change of dimensions or distortion in the piezo material than the current print element. The greater the distortion produced in the material-and here Epson has achieved the industry's highest level-the greater the displacement of ink in the chamber, which in turn creates larger ink droplets.
The result is that with a piezo unit measuring almost half the effective area of the current unit, Epson has been able to double the number of nozzles on the print head, all while maintaining the same size of ink droplet. This advancement can be used either to accelerate print speed or to make smaller print heads for smaller printers that will deliver the same output as current models.
Despite the microscopic size of the elements, the next-generation Micro Piezo head retains all the advantages of the current print head, including the ability to produce variable sized droplets. "This is because we've designed the piezo unit to give us control over both the piezo vibration and the motion of the ink's surface," explains Takahashi. "Technically this is called meniscus control, and it differentiates our technology from that of our competitors."
Meniscus control helps to produce perfectly spherical dots and manages the degree of droplet impact. It also improves the speed of jetting. According to Takahashi, the Micro Piezo head can produce an astonishing 40,000 droplets a second. "This is something that our competitors using thermal inkjet printing cannot match outside of the laboratory," he says. "With the thermal approach, ink must be heated or boiled in order to jet it. This limits the printing speed and also makes for a less durable head."
Yet another advantage stemming from meniscus control is that it enables the Micro Piezo head to employ a range of inks, including dye and pigment types, solvent inks, and ultraviolet cure inks used in industry.
Epson is the leading company employing the piezoelectric approach in printing in the worldwide consumer market. At the same time, the flexibility of its Micro Piezo technology makes it suitable for use in commercial and industrial fields in such applications as photolab printing, textile printing, and the manufacture of color filters used in the production of liquid crystal displays.
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