Epson Stylus Color 640 Service Manual page 45

EPSON Stylus Color 440/640/740
2.1.1.1 Printing Mechanism
Basic principles of the print head which plays major role of printing
mechanism is the same as previous models; on demand type MACH
head method, but there is some difference in the resolution. (Refer to
figure1-1)
Also, unlike Stylus Color IIs, 820, 200 automatic correction type, in
order to fix the dispersion of mufti layer piezo electric element which is
used for driving each nozzles, it is necessary to input the VH value
written on the side of print head by using exclusive program when you
replace print head, control board, or the printer mechanism.(However,
there are no resistor array to decide the VH voltage on the main control
board.) Following explains print head.


PZT
PZT is an abbreviation of Piezo Electric Element. Print signal from
the PSB/PSE board is sent through the driver board on the print
head unit and to the PZT. Then, the PZT pushes the top cavity
which has ink stored, and make the ink discharge from each nozzle
located on the nozzle plate.


Cavity Set
Ink which is absorbed from ink cartridge go through the filter and will
be stored temporarily in this tank, which is called "cavity" until PZT is
driven.


Nozzle Plate
The board with nozzle holes on the printer head surface is called
Nozzle Plate.


Filter
When the ink cartridge is installed, if any dirt or dust around the
cartridge needles are absorbed into the head inside, there is a great
possibility of causing nozzle clog and disturbance of ink flow and
finally causing alignment failure and dot-missing. In order to prevent
this, filter is set at cartridge needle below and ink is once filtered
here.
Chapter 2 Operating Principles
I/C Sensor's actuator
Stylus Color 740
(Ink Cartridge)
PZT
Nozzle Plate
Figure 2-2. Print Head Sectional Drawing
Revision A
Nozzle Selector Board
I/C Sensor's actuator
Stylus Color 440,640
Needle
Filter
Cavity
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