Brother MFC990CW Service Manual page 91

Ink spray function
The head employs drop-on-demand ink-jet printing.
Print commands to the drive circuit apply a bias voltage to the layer electrodes on the
piezoelectric ceramic surface stretching the elements perpendicular to that surface. Drive
signals removing this voltage for specific channel electrodes allow the piezoelectric elements to
return to their original shape, sucking ink into the corresponding channels*. Reapplying the bias
voltage stretches the elements once again, applying pressure to the ink, spraying it from the
head nozzle. The ink drop hits the paper on the platen, forming a dot.
* Pressure chambers for individual nozzles
Confidential
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