DIGITAL PRINT TECHNOLOGY: GROUPING OF PIEZOELECTRIC PRINTHEADS

Recall that in our previous editions when we began tyhis series, we brought to our knowledge that piezoelectric printheads can be grouped into one of the following types based on the way electrical current deforms the piezoceramic activator plate: shear mode, bend

mode, push-piston mode, and squeeze tube. Here is a continuation of our already published points:

“COUPLED” PIEZOELECTRIC CRYSTAL JET

The Calcomp Topaz CrystalJet printheads are a hybrid or “coupled” piezo technology, which combine shear mode with bend/normal technology to squeeze and push ink through its nozzles. Three PZT side walls and roof collapse in on the ink channel to eject its droplets. They use separated rather than shared walls and can generate a

number of different drop sizes per pixel for 12 gray levels to be expanded to 16. They consist of 256 nozzles per printhead with one printhead per color. This produces 180 dpi with one pass, 360 dpi with two passes and 720 dpi with 4 passes. These are relatively fast and robust printheads which can use a range of ink types. They have the

advantages of relatively fast processing speeds and the ability to produce variable droplet sizes and gray levels with higher viscosity inks than thermal inkjet. They own the disadvantage of a short track record.

PIEZOELECTRIC BEND MODE

Tektronix, Sharp, Epson, and On-Target Technologies print heads also employ piezoelectric bend mode, in which its electricity excited piezoceramic plate expands placing pressure on the ink forcing some through the nozzle thus forming ink droplets. The electrical field between its electrodes is in parallel with the piezoplate polarization.

The piezo transducer plates are bonded with the printhead diaphragm which isopposite the nozzle plate. Printers which use this form of piezo inkjet are Tektronix’s Phases 300 and 350 color phase change inkjets and the Epson Color Stylus 400, 600, 800, and 5000 inkjet printers. The Tektronix printheads and print system produce very good

saturated color which makes excellent overhead transparencies. Rather than printing directly to a print surface, they print to a transfer roll which in turn prints the surface. These systems are more complex and expensive than the Epson systems.

In 1997, Epson changed its multi-layer piezo design to bend mode technology for use on its Color Stylus 400, 600, and 800, 3000 and 5000 inkjet printers. Epson has combined its multi-layer vertically laminated piezoelectric disk technology with its Microweave

algorithm to eliminate banding and ultra-fine ink for uniform ink droplets and improved print quality.

Epson provides piezoelectric print heads to Original Equipment Manufacturers (OEM) Minaki Engineering, Raster Graphics, and Roland Digital Group for the manufacture of wide format color printers. These include the Mimaki’s JV-1800, Raster Graphics PiezoPrint 1000 and Roland’s CammJet series of printers.

Those printers which are capable of 1440 dpi, such as the 400, 600, 800, 5000, use Epson’s MicroPiezo refinement of its multi-layer technology. The advantages of these Epson heads are that they form very accurate circular droplets, and they are mass produced and low cost. Their disadvantage lies in their delicate multi-layer piezo louvers

which can only tolerate extremely low viscosity inks of about 1.6 to 3cP.

 

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