The image density sensor checks the density of the sensor pattern i m a g e once every 10 copy cycles. The CPU receives two voltage values directly from the sensor: the value for the bare drum (Vsg) and the value for the sensor pattern (Vsp). These two values are then compared to determine whether or not more toner should be added. High image density (no toner is added)
2. Vsp > 1/8 Vsg: Low image density (toner is added)
When the image density is too low, the CPU activates the toner supply clutch to add a selected amount of toner over the next 10 copy cycles. T h e amount added depends on the value of Vsp. If Vsp is between 0.5 and 0.6 volt, an amount of toner equivalent to a 30?40 black area copy image is added on each cycle. If Vsp is between 0.6 and 0.75 volt, the amount becomes 45%; and if Vsp is 0.75 volt or greater the amount becomes 60%. (These numbers apply only if Vsg is correctly adjusted to 4 volts.) The ID sensor can also initiate the toner end condition. If Vsp is 1.2 volts or greater 3 times in a row, the Add Toner indicator turns on. If Vsg goes below 2.5 volts or Vsp goes above 2.5 volts, the CPU judges that the ID sensor is malfunctioning. The CPU then stops reading the ID sensor voltage and shifts the copier to 7% fixed toner supply. At the same time either the Auto ID indicator or the selected manual ID level starts blinking. Test mode #3 is used to turn on the LED of the sensor manually; when it is on, VRI02 can be used to adjust the light intensity of the sensor LED.
