Figure 2-3. Principles Of The Printing Operation - Epson Stylus 820 Service Manual

Stylus Color IIs / Stylus 820
Principles of the Printing Operation
The printhead operates in one of two modes to eject ink from each nozzle:
o Normal state
No electrical charge is applied to the MLP (Multi-Layer Piezoelectric) element attached to the back of
the cavity, and pressure inside the cavity is kept at a constant level.
o Ejecting state

Figure 2-3. Principles of the Printing Operation

The head data signal is applied to the specific nozzle control line to select the active nozzle for printing,
and the MLP element is gradually charged by the drive voltage. By charging the MLP element, the
vibration plate is bent to compress the cavity. Then, ink is ejected from the nozzle.
When the ink charge or printhead cleaning operation is performed, the ink in the cavity is vacuumed out with
the pump mechanism. During printing, on the other hand, ink is simultaneously supplied from the ink
cartridge and ejected from the nozzle, depending on the change in the volume of the cavity.
A thermistor is attached to the side of each printhead unit to monitor the temperature, because the viscosity of
ink varies, depending on the temperature. The detected temperature level is fed back to the printhead drive
voltage control circuit to change the timing of the Tc pulse.
Rev. A
Nozzle Plate
(Normal State)
(Ejecting State)
Operating Principles
Piezo
Cavity
Ink Course
Nozzle
2-3