Sensor Control Mode; Image Pixel Count Mode - Ricoh G147 Service Manual

Sensor Control Mode

In the sensor control mode, the amount of toner required to print the page is calculated by
the CPU. The CPU adds up the image data value of each pixel and converts the sum to a
value between 0 and 255. (255 would mean a completely black page.)
The machine must vary toner supply for each print in order to maintain the correct amount of
toner in the developer and to account for changes in drum reflectivity due to changes in
temperature and humidity. The CPU uses data from the TD sensor and ID sensor to
determine whether or not the toner supply motor should be switched on and to calculate how
long it should remain on in order to supply more toner to the mixture in the development unit.
TD Sensor
When new developer of standard toner concentration is installed, namely 20 g of toner per
500 g of developer (4.0% by weight), the TD sensor must be set to its initial setting of 4.0 V
with SP2801. This initial setting is used as the toner supply reference voltage or Vref. For
every print cycle, the TD sensor directly checks the toner density in the developer mixture,
and after 10 copies these 10 readings are averaged and this value becomes TD sensor
output voltage Vt (10).
The machine compares Vt (10) with Vref. If Vt (10) is greater than Vref, the toner
concentration in the development unit judged to be low. When Vt (10) is detected to be
greater than Vref 20 times, then this indicates that the toner concentration is consistently low,
Vref is incremented by 0.1 V, and the conditions are checked again. The result of this check
determines the value of K, the toner supply rate coefficient, which is one of the factors that is
used in the toner supply motor on-time calculation.
ID Sensor
In addition to comparing Vt(10) from the TD sensor and Vref after every 10 copies, the ID
sensor (located at the lower right area of the drum) checks both the reflectivity (Vsg) and the
pattern on the drum (Vsp) created by the laser diodes and charge roller. If the reflected light
is too strong, this indicates that toner is low and toner is added to the development unit. (The
frequency of these checks can be adjusted with SP2210.).

Image Pixel Count Mode

This mode should only be used only as a temporary measure while waiting for replacement
parts, such as a TD sensor. This mode controls the toner supply amount using the same
method for determining the toner bottle motor on time. However, the values that were in
effect when the toner density control mode was changed over to image pixel count mode
with SP2208-01 (Toner Supply Mode) remain in effect and cannot be changed.
SM 6-31 G147