Epson Stylus Pro 7400 Service Manual page 162

EPSON Stylus Pro 7400/7800/9400/9800
The sensors used in the paper feeding mechanism are explained below.
P REAR sensor
This is a photo-reflective sensor located on the backside of the H Top Cover. It
detects paper absence by detecting the rear edge of the paper, and detects the
leading edge of paper when the paper is loaded to let the printer start the paper
setting operation such as attracting the paper to the paper guides.
Paper set lever, paper thickness detection (P THICK1, P THICK2)
P THICK1 Sensor: A transmissive photosensor located on the right side.
P THICK2 Sensor: A transmissive photosensor located on the left side.
In the paper feeding mechanism, there is a point where paper thickness threshold is
set to 0.3 to 0.4 mm (P THICK2 sensor) and a point where that is set to 0.6 to 0.7
mm (P THICK1 sensor). When the Paper Set Lever is set on those points, the two
sensors start to operate.
The paper thickness detection range for moving the Paper Set Lever is 0.34 to 2.05
mm (design value). By a combination of the two sensors, the printer can determine
to reduce the pressure of the Paper Set Lever according to the paper thickness.
"Thick paper state" occurs when the connections are open.
There is no error processing since this mechanism can not determine whether it
has broke down or not.
Since the mechanism is always in recognition of thick paper, printing on thin paper
is carry out with the platen gap kept large.
Table 2-5. Modes
Shield Plate
Paper Thickness
P THICK2
Below 0.3 mm Absent (Open)
0.4mm to 0.6mm Present (Closed)
0.7mm to 2.0mm Present (Closed)
Pressure release (Hi-Up) Absent (Open)
Connector not connected ---
Operating Principles
Sensor Output
P THICK1 P THICK2 P THICK1
Absent (Open) L
Absent (Open) H
Present (Closed) H
Present (Closed) L
--- H
Print Mechanism Components
Figure 2-13. Paper Feed Assembly (P Rear Sensor)
L
L
H
H
H
Revision B
P Rear Sensor
162