CHAPTER 6 FIXING SYSTEMCOPYRIGHT © 1999 CANON INC. CANON NP6317 REV.0 APR. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON) 6-1I. BASIC OPERATIONSA. OutlineThe upper and lower rollers of the fixing assembly are driven by the main motor (M1).The upper roller is heated by a single heater (H1: 900W). When the surface temperature of theroller rises, the resistance of the thermistors (TH1/TH2) falls, so the voltage of the signal FIXINGROLLER SURFACE TEMPERATURE signal (MAIN-TH/AUX-TH) also falls.Whether the voltage of TH1 (analog) is above or below a certain level at a given time deter-mines if the microprocessor of the DC controller causes the HEATER DRIVE command (HTRD)to go '1' or '0'.The copier is provided with the following three protection mechanisms:• The microprocessor monitors the voltage of TH1 and TH2 and indicates 'E000' or 'E001' inresponse to an error, i.e., ACOFF goes '0' to turn the relay (K100) OFF, thereby cutting theAC power to the fixing heater.• The fixing roller error detection circuit monitors the voltage of TH1 and TH2 and, when itdrops below 0.9V (equivalent of 215°C), turns HTRD OFF.• The microprocessor monitors the signal of HTON. When the HTON signal is ON while theHTRD signal is OFF, the microprocessor cuts the AC power.• The thermal switch (F1) goes OFF when the temperature of its inside rises to 230°C to cut offthe power to the fixing heater.Note:The thermal switch (TS1) cannot be used after its contact has opened: the contact will notreturn to its normal state at room temperature.
