10-1
October 2000 © TOSHIBA TEC
MR-3011/3012 DESCRIPTION OF CIRCUITS
10. DESCRIPTION OF CIRCUITS
10.1 Input Circuits for Original Length Sensor, Read Sensor and Reverse
Sensor
Since original length sensor, read sensor and reverse sensor have almost the same circuit configurations (the
reference voltage of comparator for read sensor input circuit can be set by D/A output), the input circuits for the
read sensor and reverse sensor are not described. The following is the input circuit for the original length sensor.
This circuit is an input circuit for the original length sensor and consists of a voltage-current conversion circuit
which adjusts the amount of light of the infrared LED and the voltage comparison circuit which compares the
voltage output from a phototransistor (PTR) with a reference voltage and converts the output voltage into digital
signals.
The original length sensor is a mirror reflection sensor, and consists of a pair of emission elements (infrared
LEDs) and a light receiving element (PTR). Both elements have a light axis running in the same direction. There
is a mirror on the extended light axis of these elements. When there is no original between the elements and the
mirror, infrared light emitted from LED is reflected by PTR in high reflectance. If there is an original, light emis-
sion to the mirror and reflected light from the mirror are blocked by the original, and the reflected light entering
PTR becomes extremely small.
When a large amount of light is entering PTR (this means there is no original) the optical current flowing in the
PTR is increased, and the voltage of IC3-10pin becomes higher due to a drop in voltage caused by R44. IC3 is a
comparator which compares the reference voltage input to 11pin (non-reverse input terminal) with the signal
voltage of 10pin (reverse input terminal). If the voltage of 10pin is higher, the output level (IC3-10pin) is "L". On
the contrary, when the amount of the incoming light is small (this means there is an original), the voltage of IC3-
10pin is low and the level becomes "H". R16, C6 and C7 are noise filters. This circuit has an automatic sensitivity
adjustment function to control the unevenness of the sensor sensitivity. Uneven sensor sensitivity is corrected by
controlling the machine to have a constant PTR voltage when there is no original. The intensity of the infrared
light emitted from the LEDs is changed to adjust the PTR voltage.
When the sensor sensitivity adjustment mode is selected, the PTR output voltage (analog value) is measured by
the A/D input terminals of the CPU (scanner side). The D/A output voltage of the CPU is changed to keep the
PTR output voltage to a certain level, and the LED current is adjusted by a voltage-current conversion circuit
consisting of IC4, R29, Q5, etc. Each machine has a different D/A output voltage value, which is stored in the
volatile memory.
CN3.1
+5V
CN3.2
*LENGS
CN3.3
LENGSLED
2
1
3
K 1
A 2
2
1
C1
1
C
2
E
LED1
PT1
Original length sensor
LENGS
C 2
E 3
Q5
1
B
+
-
IC4.3
10
9
8
2
1
R29
1
R32
2
2
1
SGND
C11
R17
1
2
TP10
1
1
SGND
C6
2
R16
1
2
SGND
2
1
R44
SGND
C7
2
1
R41
SGND
2
1
IC3.3
13
-
11
+
10
R35
2
1
+5V
R38
1
2
R9
+5V
2
1
SIZEL_5
SIZEL_5_DA
SIZEL_5_AD
TP12
1
TP11
1
+5V
#Chapter_10.p65
10/3/00, 5:09 PM
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