Canon MF4500 Series Service Manual

Canon MF4500 Series Service Manual Manual pdf 38 page image

22 2-132-13Technical Overview > Laser Exposure System > Laser Scanner Motor Control > OverviewTechnical Overview > Laser Exposure System > Laser Scanner Motor Control > OverviewLaser Control■ Auto Power Control (APC)This is the control to emit a constant level of laser diode.There are two types of APC; initial APC (note 1), and line space APC (note 2). The laserdriver executes the same procedure for both controls. The following is the details of thecontrol procedure.1) When the laser control signal enters LD1 forced ON mode (CNT0, CNT1, CNT2), the laserdriver emits LD1 forcibly.2) The emission level of LD1 is detected with photo diode (PD), converted from current outputto voltage, and compared with the standard voltage (voltage equivalent to the target laserlevel) with the comparator.3) The laser driver controls the laser current to achieve the voltage of LD1 target level.4) When the laser control signal enters LD forced OFF mode, the LD1 is forcibly turned off.The laser driver saves the adjusted laser intensity of the capacitor (C16).5) When the adjustment of LD1 laser intensity is completed, the laser control signal entersLD2 forced ON mode; the laser driver emits LD2 forcibly.The laser driver adjusts the LD2 laser intensity as in the case of LD1 and saves theadjusted laser intensity to the capacitor (C18).1. Initial APCAPC that is executed during initial rotation. APC adjusts laser intensity and detectsfaults in the laser.2. Line space APCAPC that is executed during printing. Laser intensity for one line is adjusted beforewriting one line.Laser Scanner Motor Control■ OverviewThis is the control to rotate the scanner motor at a constant speed to emit the laser beam onthe correct position on the photosensitive drum.The following is the control circuit of the scanner motor.Engine controller Motor driver PCBBD PCBOscillatorReferenceclockFrequencycomparatorLaser scanner unitIntegrationcircuitMScanner driver ICScanner motorACCDEC/BDIDrivecircuitCPU ASICX300+24VA +24VAThe engine controller creates standard clock based on oscillation frequency of the oscillator(X300); the cycles of the standard clock is compared with that of BD input signal (/BDI) with afrequency comparator and the rotations of the scanner motor is monitored.The engine controller sends the scanner motor acceleration signal (ACC) and scanner motordeceleration signal (DEC) to the scanner motor driver according to the detected rotationspeed to control the rotation speed.F-2-16