Toshiba 4580, Service Manual

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6570/5570 ADF 16 - 40 Mar. 1999 © TOSHIBA TEC
16.10 Description of Circuits
16.10.1 Aligning sensor, timing sensor and exit sensor circuit diagrams
This item describes the aligning sensor circuit. A description of the timing sensor and exit sensor circuits
is omitted in this item as the aligning sensor, timing sensor and exit sensor share the same circuit con-
figuration.
This aligning sensor circuit comprises two circuits, a voltage-current conversion circuit for adjusting the
intensity of light emitted from the infra-red LEDs, and a voltage comparison circuit for comparing the
output voltage of phototransistor (PTr) with the reference voltage and converting the output voltage to
digital signals.
The aligning sensor is a mirror reflection-type sensor, and comprises a light-emitting sensor (infra-red
LED) and light-receiving sensor (PTr) pair each having the same optical axis. A mirror is placed along an
imaginary line extending from the optical axis of these sensors. When there is no original between the
sensors and the mirror, the infra-red rays radiated from the LED are reflected into the PTr at high reflect-
ance. Alternatively, when there is an original, the light radiated on the mirror and the light reflected from
the mirror is broken by the original, markedly reducing the infra-red incident to the PTr.
When there is a large amount of light incident to the PTr (that is, there is no original), the photo-current
flowing through the PTr increases, and the voltage of pin 6 of IC5 rises at the voltage drop by R81. The
comparator on IC5 compares the signal voltage of pin 6 (reversal input terminal) with the reference
voltage input to pin 7 (no reversal input terminal). If the voltage of pin 6 is higher, output (pin 1 of IC5)
turns Low. Alternatively, if there is little amount of light incident to the PTr (that is, there is an original), the
voltage of pin 6 of IC5 becomes low, and as a result, pin 1 of IC5 turns High. R15, C30 and C31 (NF2) in
the circuit diagram are noise filters.
This circuit has an automatic sensitivity adjusting function for suppressing unevenness in sensor sensi-
tivity. This function keeps the PTr voltage when there is no original at a constant level in all sensors , and
absorbs unevenness in sensor sensitivity caused by the physical differences of the sensor elements.
The PTr voltage is adjusted by varying the intensity of the infra-red light radiated from the LED.
Automatic adjustment is executed when the sensor sensitivity adjustment is selected and when power is
turned ON. By this adjustment, the PTr output voltage (analog value) is measured on the A/D input
terminal of the CPU, and the output voltage of the D/A converter is varied to adjust the LED current in the
voltage-current conversion circuit comprising IC4, R16 and Q7 so that the output voltage of PTr is the
required voltage. The D/A output voltage values at this time are values unique to each of the sensor
elements, and are stored to non-volatile memory EEPROM (IC11).
CN6.1
PT1
2
1
1
1 1
12
C17
C31
13
24
IC4.4
IC5.2
1 1
1 1
1
1
1
1 2 1
1
REG
REG-AD
REGS-DA
1
2
2 7
6
2
2
2
2
1
2 3
2
2
2
2 2
1
1 1 2
C
+
_
+
_
E
Q7
C30
R81
R44
R43
R45
3
B
3
2
1
E
K
A
LED1
C
CN6.3
+5V
CN6.2 *REGS
REGLED
TP35
TP45
TP25
+5V
NF2
R15
R55
SGND
SGND
SGND
SGND
SGND
SGND
R16
R36
R84
+5V
+5V
Aligning sensor
1