Canon CLBR 460ps Service Manual page 140

CHAPTER 2
c. OHT detection function
This printer has a function to distinguish OHT from plain paper.
The OHT detection is conducted by the OHT sensors (PS301, PS302) on the multi-purpose
tray PCB.
The light emitted from the PS301 passes through the paper path, reflected by the prism (45
degree reflective mirror), and received by the PS301. (See the figure below) When the plain
paper is picked up, the light emitted from the PS301 is interrupted by the paper and thus does
not return to the sensor. When the OHT is picked up, the light passes through the OHT, is
reflected by the prism, and returns to the sensor.
OHT sensor (left)
(PS301)
<When plain paper is fed.>
During printing, the DC controller monitors the media stopped at the registration position and
distinguishes between OHT and plain paper according to the light detection state of the PS301.
When the OHT is detected, the DC controller switches the printing mode to the OHT mode and
changes the feed speed after refeeding.
The Canon original OHT (OHT T-H1) cannot be used for this printer. (See note) When the
OHT T-H1 is picked up, the DC controller recognizes it as an unusable OHT by detecting the
marking on the OHT T-H1 with the PS301, reports it to the video controller, and stops the print-
er. Advise the user not to use the Canon original OHT (OHT T-H1).
The OHT with the marking for CLC cannot be used for this printer since it is detected as an
unusable OHT in the same way as the Canon original OHT (OHT T-H1).
Note: The Canon original OHT (OHT T-H1) is very thin and contains oil. Therefore, it tends to
cause roller wrapping jam in the fixing unit which has two fixing heaters and produces
large amount of heat.
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<Cross-sectional view of the OHT sensor>
Prism
Registration guide
Window
Multi-purpose tray PCB
Plain paper
No light received
Figure 2-5-6
OHT sensor (right)
(PS302)
OHT
Light received
<When OHT is fed.>
Paper feed space