CHAPTER 4 IMAGE FORMATION SYSTEMCOPYRIGHT © 1999 CANON INC. CANON NP6512/6612/7120/7130/7130F REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)4-28B. Detecting the Level of Toner1. OutlineThe level of toner inside the developing assembly is monitored by the toner level antenna andthe toner level detection circuit.The toner level antenna is mounted inside the developing assembly, and an AC bias is appliedto the developing cylinder.The developing cylinder and the antenna are staticaly bonded, and the level of toner is detectedwith reference to the changes in the degree of the bond.2. OperationThe amount of static between the developing cylinder and the toner level antenna changesaccording to the level of toner inside the developing assembly. The AC bias occurring in relation tothe level of toner inside the developing assembly is checked by the toner level antenna, and theresult is sent to the toner level detection circuit. An AC bias of the same level as the bias applied tothe developing cylinder is also sent to the toner level detection circuit as a reference signal.The toner level detection circuit compares the signal (AC bias level) from the toner level an-tenna against the reference signal to find out the level of toner.In the absence of toner, the level of the signal from the toner level antenna will be lower thanthat of the reference signal.During copying operation, the DC controller PCB checks the toner signal every 0.25 msec,treating data collected of 100 checks (equivalent of one A4 copy) as a single block. If it finds thatthe data indicating levels suggesting the absence of toner is 90% or more, it will identify the blockin question as indicating the absence of toner.If six such blocks occur in succession, the absence of toner will be identified, and the ReplaceToner Cartridge message will be flashed on the control panel.The toner signal detected during copying operation is stored in memory on the DC controllerPCB, and the data will be retained for accumulation even when the power switch is turned off andon.All copying operations are prohibited while the Replace Toner Cartridge message is flashed. Ifthe absence of toner is detected during a continuous copying job, the ongoing operation will bestopped when as many as five copies have been made after the detection of the absence of toner.The Replace Toner Cartridge message will go out when the power switch is turned off and thenon, enabling copying operation once again. The level of toner is checked during last rotation ex-ecuted after copying operation once; if the absence of toner is detected, the message will be flashedonce again.As many as 100 copies may be made after the detection of the absence of toner; however,subsequent copying will be prohibited unless toner has been replenished.If the cumulative number of copies reaches 100 during a continuous copying job, copying willbe stopped thereafter.
