Epson Stylus Pro XL Service Manual Page 29

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Principles of the Printing Operation
The printhead operates in one of two modes to eject ink from each nozzle:
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.
Ejecting state
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, the ink is
simultaneously supplied from the ink cartridge and ejected from the nozzle, according to the
change of volume in the cavity.
A thermistor is attached to the side of the color printhead drive board to monitor the temperature,
because the viscosity of the 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.
(The Tc pulse is shown in Section 2.3.2.5.)
Cavity
Nozzle
Vibration Plate
Normal
State
Piezo
Cavity
Nozzle
Ejecting
State
Ink Dot
Piezo
Figure 2-3. Principles of the Printing Operation
Stylus Pro XL Operating Principles
REV.-A 2-3
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