Automatic Image Density Sensing - Ricoh FT4430 Service Manual

16 April '88

AUTOMATIC IMAGE DENSITY SENSING

Leading Edge of the Original
The input for the automatic image density circuit is via a fiber optic cable [A]
that is "mounted on the first scanner. Light from the exposure lamp [B] passes
through a small hole in the reflector, reflects from the original, and is collected
by the fiber optic cable. The sampled strip starts 31.5 millimeters from the
leading edge of the original and is 8 millimeters wide and 30 millimeters long.
The fiber optic cable conducts the light to a sensor (photodiode) on the lamp
regulator. The sensor circuit converts the light intensity to a voltage level. The
detected voltage is adjustable via a variable resistor on the lamp regulator
board. A peak hold circuit keeps the maximum voltage.
The lamp regulator sends the maximum voltage value to the main board. The
CPU then computes the correct image density and adjusts the development
bias accordingly. (See the section on image density control for more
information. )
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