3. Controlling the Transfer Corona CurrentHow well the toner image on the drum is transferred to copy paper is affected bychanges in the environment (temperature, humidity).To ensure a specific density in the presence of changes in the environment, themachine is designed to vary the transfer current level in relation to the temperature andthe humidity measured by the environment sensor.Figure 4-112The transfer corona current output is turned on and off by the high-voltage DCremote signal (DCON). The output level of the transfer current, further, is controlled bythe transfer charging level control signal (HVTTC).When HVTTC is about 3 V or more and less than 11 V, the output of the transfercorona current turns on; it turns off when the signal is about 12 V or more.a. When the Transfer Corona Current Output is OFFHVTTC is about 12 V.DCON is ‘0’.Comparator circuit goes OFF.Variable width pulse oscillator goes OFF.Drive circuit goes OFF.Primary transformer goes OFF.Humidity (%)Transfer current (+)COPYRIGHT © 1997 CANON INC. CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)CHAPTER 4 IMAGE FORMATION SYSTEM4-13
