Epson EPL-N2700 Service Manual page 78

EPSON EPL-N2700 / N2750
The following illustrates an example where the letter "A" is written by the
laser beam and toner sticks onto the letter "A" on the surface of the PC
drum.
Sleeve Roller
PC Drum
Figure 2-24. Toner Image Production
The seal beneath the sleeve roller acts to discharge the negatively-
charged unused-toner on the sleeve roller. The discharged toner is fed
back to the toner feed roller for recycling it. Note that, during printing,
the seal voltage is the same as the sleeve roller voltage and discharge
is not made. However, before and after printing, the voltage of the seal
bias is set 100V higher than that of the sleeve roller to discharge the
unused toner for recycling.
Operating Principles
4108s036
Printer Mechanism Operating Principles
Operation of the Toner Empty Sensor:
o
The toner empty sensor detects the toner-empty status. The sensor is a
photo reflector mounted on the printer.
If low toner condition occurs, the light emitted from the LED of the photo
reflector passes the window of the toner hopper and reflected by the
mirror. The reflected light reaches the phototransistor of the photo
reflector and the phototransistor turns ON. Thus, the sensor output is
"L" when the toner is empty.
In actual fact, detection of the toner empty is a little more complicate.
Since toner in the hopper is agitated with the agitator blades, toner
empty cannot be detected like the ON/OFF status of a switch.
The rotating mirror/window blade cleans the mirror and window
repeatedly. Basically, the CPU on the main board judges that the toner
near empty occurred when a low toner condition has been detected by
a certain number of times while the mirror/window blade has been
rotated by a certain number of times. Next, the CPU judges that the
toner empty occurred when thus detected toner near empty has been
counted by a certain number of times. If toner empty is detected,
printing becomes impossible.
Revision B
79