Paper Thickness Detecting Circuit - Epson DLQ-3000 Service Manual

2.3.10 Paper Thickness Detecting Circuit

PG is detected by the paper thickness sensor which consists of the slit disc and the photo-
electric transfer element. See Table 2-19 and Figure 2-22 for the paper thickness sensor
specification and paper thickness sensor circuit block diagram, respectively.
Table 2-19. Paper Thickness Sensor Specification
Detecting method
Power supply voltage
Outputs
Minimum detecting thickness
Detecting range
Figure 2-22. Paper Thickness Sensor Circuit Block Diagram
To determine the paper thickness, the printer monitors the waveforms output from the PG
sensor, as shown in Figure 2-22. "T" output for PHD shows a period of time in which 2-
chanel pulses PENCA and PENCB change for 180°. The printer counts the different
numbers of pulses output while the printhead moves from PG home position to the platen
surface and surface of the loaded paper to determine the paper thickness which
corresponds to the difference between 2 values. The numbers of pulses are counted in the
following order:
1. After the printer power is turned on, the PG home position is detected.
2. Distance between the printhead and platen surface is measured
While the printhead is moving from the PG home position toward the platen surface,
the waveform stays at a constant level and when that status exceeds for specified
period of time, the printer assumes that the printhead has reached the platen. The
PG motor consequently stops rotating and the numbers of the pulses output during
this operation is counted and the value is fed back to the CPU.
3. The printhead returns to the stand-by position.
4. The distance between the PG home position and loaded paper surface is measured in
the same procedure.
Paper thickness is determined for each paper loaded. The last values for the platen position
and PG before power-off are stored in the EEPROM and are no lost if the printer power is
turned off.
Rev. A
Photo interrupt system
5 VDC 5%
In 2 channels, TTL level
0.008 mm
0 to 0.53 mm
Operating Principles
2-29