Canon CLBR 460ps Service Manual page 114

CHAPTER 2
b. Home position detection
The home position of the intermediate transfer belt is detected to transfer four color toners to
the intermediate transfer belt precisely and align the leading edge of print paper with the lead-
ing edge of the image.
There are four holes (home position detection holes) in the area outside the toner transfer
area on the intermediate transfer belt at equal intervals (see Fig.2-4-12). When the ITB home
position sensor (PS5) detects a home position detect hole while the intermediate transfer belt is
rotating, an ITB HOME POSITION DETECTION signal (/ITBHP) is sent to the DC controller.
Intermediate transfer belt
ITB home position sensor (PS5)
When it receives a PRINT signal (/PRNT), the D-CPU (IC1001) on the DC controller rotates the
intermediate transfer belt via the M-CPU (IC1009). When the PS5 detects the home position
detection hole, a /ITBHP signal is sent to the M-CPU via the developing PCB. The M-CPU deter-
mines the /ITBHP signal input first as the home position (HP1) and counts the home position
(HP2, HP3, HP4, .....) every time the same home position detection hole is detected. The M-CPU
controls the timing to drive various loads and detect various sensors based on the /ITBHP sig-
nal.
The M-CPU sends a /DTOP signal to the D-CPU via the gate array (IC1003) every time a
HOME POSITION signal is detected. When it receives the /DTOP signal, the D-CPU sends a TOP
OF PAGE signal (/TOP) to the video controller. When the video controller sends VIDEO signal
(/VDO 0 to 7) of an image, the D-CPU begins to form an image. For full-color printing, the D-
CPU sends the /TOP signal four times, and for mono-color printing once, to the video controller
to form an image (See Fig. 2-4-13).
When it does not detect a /ITBHP signal at constant intervals, the DC controller stops the
printer and notifies the video controller of the abnormality of the ITB unit.
Note: The number of holes in the ITB unit is different between the two makers; 2 holes and 4
holes. At power-ON or door close, the printer distinguish between the two. The printer
changes the value of high-voltage by detecting the maker of the ITB unit.
2 - 56
Toner transfer area
Home position detection holes
Figure 2-4-12