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3. Operational descriptions
A. Sensor/detector input circuit
[a] Original feed sensor (DFD)
Original feed sensor
TLN119
B4B-PH-K-S
C
A
4
PH110M
+5V
3
K
VOUT
E
2
LE D
DFD
1
SGND
ERJ6GEY
100K
J104V
The original feed sensor is of the reflection type, and is composed of the LED and the photo transistor. Infrared light emitted from the LED is
reflected by the original to the photo transistor to increase the photo current in the photo transistor, detecting "original presence." This circuit is
provided with the automatic adjustment feature. The LED cathode is connected to the voltage-current conversion circuit which is composed of the
operation amplifier (IC5), Q2, and R135. It controls the current value by the D-A output (analog voltage output) of the CPU. That is, the CPU D-A
output value (66 pin) is always made equal to the input voltage of IC5 9 pin (the voltage drop of the LED current by R135). Therefore, by changing
the D-A output value, the current value is changed accordingly.
On the other hand, the photo current of the photo transistor is converted into a voltage by the emitter resistance in the sensor PWB, and is passed
through the noise filter composed of R29 and C43 to IC2 6 pin and CPU 59 pin. R106, R110, R113, and IC2 form the voltage comparator, which
compares the input voltage from the sensor and the threshold voltage (about 2V) generated by dividing +5V with R106 and R110. When the input
voltage from the sensor exceeds the threshold voltage, the IC2 1 pin output is driven to LOW and is inputted to the CPU 18 pin as the "original
present" signal. The CPU 59 pin is an A-D input pin which can convert an analog voltage into a digital value in the CPU.
On the extension of the sensor optical axis, there is the background plate which has lower reflection rate than the original has. This background
plate reflects the light to provide the emitter voltage of the photo transistor, which serves as the reference voltage of "original absent." Since there
are some variations in the sensor sensitivities, the voltage of "original absent" is used as the reference voltage for automatic adjustment of the
sensor sensitivity. That is, the sensor voltage of "original absent" is A-D inputted and the D-A output voltage is changed to change the LED current
(LED light quantity). Then the CPU controls the sensor voltage to the constant level. The D-A output value is unique to each element, and its value
is stored in the EEPROM (IC10).
[b] Reverse original sensor (RDD)
Reverse original sensor
B3B-PH-K-S
A
1
LE D
C
2
VOUT
C
RDD
A
SGND
3
SGND
K
E
GP2S40
The reverse original sensor is of the reflection type, and is integrated with the LED and the photo transistor. Infrared light emitted from the LED is
reflected by the mirror and passed to the photo transistor to increase the photo current in the photo transistor, detecting "original absent." When, on
the other hand, there is an original between the LED and the mirror, there is no reflection light from the mirror, no increase in the photo transistor
photo current, detecting "original present." This circuit is provided with the automatic adjustment feature.
The LED anode is connected to the voltage-current conversion circuit composed of the operation amplifier (IC5), Q3 and R131. The current value is
controlled by the CPU D-A output (analog voltage output). That is, the CPU D-A output value (67 pin) is always kept equal to the IC5 13 pin input
voltage (the voltage drop of the LED current by R131). Therefore, by changing the D-A output value, the current value can be changed accordingly.
On the other hand, the photo current of the photo transistor is converted into a voltage value by the load resistor R132, and passed through the
noise filter composed of R30 and C47 to IC2 4 pin and the CPU 60 pin. R107, R111, R115, and IC2 form the voltage comparator, which compares
the input voltage from the sensor and the threshold voltage (about 2V) generated by dividing +5V with R107 and R111. When the sensor input
voltage exceeds the threshold voltage, IC1 1 pin output is driven to LOW and passed to the CPU 19 pin as the "original present" signal. The CPU 60
pin is an A-D input pin, which converts an analog voltage into a digital value in the CPU.
Since there are some variations in the sensor sensitivities, the voltage of "original absent" is used as the reference voltage for automatic adjustment
of the sensor sensitivity. That is, the sensor voltage of "original absent" is A-D inputted and the D-A output voltage is changed to change the LED
current (LED light quantity). Then the CPU controls the sensor voltage to the constant level. The D-A output value is unique to each element, and its
value is stored in the EEPROM (IC10).
+5V
16
CN1 -16
+5 V
14
CN1 -14
DFDL ED
CN13-4
+5V
CN13-3
CN13-2
R109
CN13-1
15
CN1-15
DFD
13
CN1-13
SGND
Original feed sensor input circuit
1
CN2-1
RDDLED
+5V
CN3 2-1
CN3 2-2
R132
CN3 2-3
2
CN2-2
RDD
3
CN2-3
SGND
Reverse original sensor input circuit
+5V
+5 V
Q2
R113
R110
IC2-2
R91
7
+
1
R2 9
6
-
R106
C4 3
+5 V
C
Q3
R131
E
+5V
+5V
R115
R111
IC2-1
5
R50
+
2
R3 0
4
-
VCC-+5V
R107
C4 7
– 23 –
IC5-3
C
10
R8 4
+
B
8
9
-
E
R135
TP9
B
TP5
IC5-4
12
R8 7
+
14
13
-
C1 5
TP7
TP8
166
D-A2
C1 0
TP71
18
P61/INT2
59
P46/AN6
67
D-A1
TP6
19
P60/INT1
60
P45/AN5
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