Automatic Image Density Sensor - Ricoh A219 Service Manual

OPTICS

3.5 AUTOMATIC IMAGE DENSITY SENSOR

The auto image density (ADS) sensor [A], a photodiode, is mounted on the
upper front frame. The sensor cover has a hole in it to allow light to fall
directly onto the sensor.
Sampling starts 6 millimeters from the leading edge of the original and
continues for 11.5 millimeters from the leading edge of original in full size
mode. These lengths "a" and "b" will vary depending on the selected
reproduction ratio. The lengths "a" and "b" for each reproduction ratio are
calculated as follows:
For every original in ADS mode, the photosensor circuit converts the light
intensity into a voltage. The detected voltage is amplified and sent to the
main board. If less light is reflected from the original (the image is darker), the
sensor outputs a lower voltage. The CPU compares the maximum ADS
output voltage with the standard ADS reference voltage and compensates
the copy image density by changing the development bias voltage in
accordance with the difference. The standard ADS reference voltage (2.5 ±
0.1 V) is generated by SP 56. Details about changes to the development bias
voltage are explained in "Development Bias for Image Density Control".
A219
CÓPIA NÃO CONTROLADA
A219D511.wmf
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CÓPIA NÃO CONTROLADA
[A]
A219D512.wmf
SM