Sensor Circuits - Epson Stylus Photo Service Manual

EPSON Stylus Photo

2.2.2.2 Sensor Circuits

This printer has 3 photo diode sensors(ASF sensor, PE sensor and HP sensor), 2 mechanical switch
sensors (black/color ink cartridge sensor) and one thermistor sensor.
The following explains each sensor's function and principles of detection.

ASF Sensor:

PE Sensor:

HP Sensor:

Print Head Thermistor: Print Head Thermistor is located on the print head driver.

Ink Cartridge Sensors: This sensor is mounted on the each print head board and detects if
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ASF sensor is a photo-interrupter type sensor and is installed on the left
edge of the ASF and detects the home position of the ASF. Home position
means waiting mode and ASF is controlled to return to this home position
at the waiting mode after the power is turned on. The home position of
ASF is detected by ASF HP sensor wheel which is located in the left edge
of the LD roller axis. In the ASF HP sensor wheel, there is only one small
hole and it is detected as ASF home position when this small hole is
among the photo diode terminals. In the home position, since the space
among photo diode terminals is not cut in, Low signal is output to the CPU.
Therefore, when it is detected as out of home position, the photo diode
terminals is interrupted and then High signal is output to the CPU.
PE sensor is a photo-interrupter type sensor and is installed under the right
edge of the frame on the printer mechanism and detects if there is any
paper in the printer or not. When there is no paper, the PE sensor lever
interrupts sensor, outputting the High signal to the CPU. When there is any
paper, PE sensor lever is pushed up by the paper. This motility also pushes
the sensor lever out of the photo diode sensor terminals and Low signal is
output to the CPU.
HP sensor is a photo-interrupter type sensor and is installed on the right
edge of the frame on the printer mechanism and detects the carriage home
position. When the CR unit is in the home position, the sensor flag, which
is located back of the CR assembly, interrupts sensor, outputting the High
signal to the CPU. When the CR unit moves out of home position, Low
signal is output to the CPU.
By this thermistor, surrounding temperature of the head is monitored
and it is fed back to the analog port of CPU. By this sensor signal,
voltage of electric discharge is controlled according to temperature.
ink cartridge is there or not. When there is an ink cartridge, the sensor
board spring, which is pushed in at installing the ink cartridge to the
CR unit, connects two terminals on the print head board and outputs
Low signal to the CPU. If there is no ink cartridge, the sensor board
spring detaches from two terminals, blocking electric connection between
two terminals and outputs High signal to the CPU.
Figure 2-22. Sensor Circuit
Rev. A