Epson FX-870

Principles of Operation
Sensor Circuits
The FX-8’70/1170 printer has the following sensors: CRHOME, PE (FRONT), PE (REAR), PG
(platen gap), RELEASE LEVER(RL), and HEAD TEMPERATURE. All the sensors are mechanical
switches, except the rear PE sensor, which is a photo diode, and the HEAD TEMPERATURE
sensor, which is a thermistor.
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In addition to the sensor circuits, a +35 V monitor circuit and a Vref circuit are also provided. The
+35 V monitor circuit sets the pulse length of the head drive signal.
If the voltage of the +35 V line
drops below approximately +31 V, the printer stops printing for a while.
As soon as the voltage
recovers, the printer starts to print at halfspeed. (The PF motor also slows down.) The Vref circuit
supplies the reference voltage for the A/D convertor in the CPU.
The CPU constantly monitors the printhead temperature. If the printhead temperature exceeds
the maximum level, the printer stops printing until the temperature drops to a certain level. When
the printhead temperature cools down, the printer resumes printing automatically.
Figure 6-26 shows the sensor circuit block diagram.
CPU (1C)
P55
P52
P53
P34
P31
CRHOME
PE FRONT
PE REAR
PG
RELEASE
LEVER
P51P51
P50P50
VrefVref
Head TemperatureHead Temperature
+35 Voltage Monitor +35 Voltage Monitor
+35 v +35 v
VrefVref
ZDl
-.
Figure 6-26. Sensor Circuit Block Diagram
6-26
Epson FX-8700 170