Canon CLBR 460ps Service Manual page 132

CHAPTER 2
2. Density detection function
This function detects the density of the density pattern formed on the photosensitive drum with
the density sensor (PS14) during the image density adjustment control and the gradation
adjustment control. The PS14 is placed in the drum cartridge drawer unit and consists of an
density detection circuit, LED, photodiode 1 and 2. The light emitted from the LED is reflected
by the density detection pattern on the photosensitive drum and then received by the photodi-
ode 2. The photodiode 1 receives the light from LED directly.
Density detection pattern
Color toner and black toner have different characteristics toward the light. The density detec-
tion circuit switches the detection mode between the color toner and black toner with the
DETECTION MODE SWITCH signal (/DENSEL).
When it determines that the density detection is needed, the DC controller forms the density
detection pattern on the photosensitive drum at the specified timing. When the LED DRIVE sig-
nal (/DENB) input from the DC controller becomes "L", the density detection circuit emits the
light from the LED at the intensity determined by the LED INTENSITY SETTING signals (/D0 to
7). The photodiode 1 detects the light from the LED directly, and the density detection circuit
controls the LED to emit light at the specified intensity. The photodiode 2 detects the light
reflected by the density detection pattern on the photosensitive drum. The density detection cir-
cuit off sets the detected DENSITY signal by the TONER DENSITY DETECTION SETTING signal
(DLSHIFT) and sends it to the DC controller as TONER DENSITY DETECTION signal (DNS). The
DC controller converts the input DNS signal (analog) to the density value (digital) and stores it.
When the photodiode 1 and 2 cannot detect the light from the LED, the DC controller stops the
printer and notifies the video controller of a density sensor failure.
DC controller PCB
/D0 to 7
IC1001
/DENSEL
D-CPU
DLSHIFT
2 - 74
Photodiode 2
Density sensor
Figure 2-4-30
Density sensor
/DENB
Density
detection
circuit
DNS
Figure 2-4-31
Photosensitive drum
LED
Photodiode 1
(PS14)
(PS14)
LED
Photodiode 1
Photodiode 2
Photosensitive
drum