Operation; Auto Exposure Control - Canon NP6251 Service Manual

2. Operation

a. Turning On and Off the Scanning Lamp
When LAON (scanning lamp activation signal) is '0', the output of the differential
amplification/phase control circuit goes '0', and the arc circuit remains off, depriving the
scanning lamp (LA1) of power.
When LAON is '1', on the other hand, the output of the differential
amplification/phase control circuit goes '1', and the arc circuit turns on, supplying the
scanning lamp (LA1) with power.
b. Controlling the Intensity of the Scanning Lamp
The intensity of the scanning lamp is controlled by controlling the voltage of power
supplied to the scanning lamp according to the intensity adjustment signal (LINT) from
the DC controller PCB.
LINT varies the pulse duty between 10% and 57.6% according to the setting of the
Copy Density key or the density of the original, sensitivity of the drum, and setting of the
intensity control VR so that the effective value of the voltage of power to the scanning
lamp will vary between 45 and 65 V (phase control).
c. Checking the Activation of the Scanning Lamp
While the scanning lamp remains on, the activation detection circuit generates the
activation detection signal (CVRON) at all times. CVRON is sent to the error detection
circuit on the DC controller PCB.
If the lamp activation signal (LAON) goes '0' and the scanning lamp turns on
because of a short in the activation circuit or the like, the DC controller PCB causes
PWOFF to go '0', thereby turning off the relay inside the power switch and, ultimately,
turning off the power switch (SW1); this condition deprives the lamp regulator of AC
power.

3. Auto Exposure Control

The machine is equipped with an auto exposure mechanism which automatically
controls the intensity of the scanning lamp to suit the density of the originals.
When copies are made in auto exposure (AE) mode, you can obtain fogging-free
copies without having to adjust the copy density manually. The intensity of the lamp
controlled by the AE mechanism is indicated on the control panel.
AE mode may be executed on the copier side or the RDF side, the latter of which is
used when originals are placed in the RDF. The copier's AE mode is used, however,
when manual feeding is selected.
COPYRIGHT © 1997 CANON INC.
Figure 4-106
CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 4 IMAGE FORMATION SYSTEM
Pulse duty: 10%
Pulse duty: 50%
4-7