Canon MF8100 Series Service Manual

Contents

Canon MF8100 Series Service Manual Manual pdf 51 page image

Chapter 22-15In full-color printing, as four toner layers in each colors are piled up on the ITB in primary transfer, the holding force of toner weakens as the transfer processprogresses for the 1st color, 2nd color... Therefore, after transferring the first color, the primary transfer DC (positive) bias is increased for the toner in the rest ofthe colors to gain the holding force of the toner.2.3.2.5 Secondary Transfer Bias Generation 0008-1698The secondary transfer bias is output to transfer a toner image on the ITB onto paper.Two kinds of the biases, DC positive bias and DC negative bias, are generated in the secondary transfer high-voltage generation circuit in the high-voltage powersupply circuit. The DC positive bias is output to the secondary transfer roller in toner transfer. The DC negative bias is output to it in cleaning.The high-voltage power supply circuit applies these secondary transfer biases to the secondary transfer roller according to a sequence.The following are the biases applied at each sequence:- Print bias (DC positive):This bias is applied to the secondary transfer roller to transfer a toner image on the ITB onto paper in a print sequence.- Cleaning bias (DC negative):This bias is applied to the secondary transfer roller to return residual toners adhered on the secondary transfer roller to the ITB in a warm-up or last rotationsequence.The values of the secondary transfer bias vary according to the DCNT Board.The DCNT Board changes the amperage of the secondary transfer bias according to the SECONDARY TRANSFER CURRENT FEEDBACK (TR2S) signal sentfrom the secondary transfer high-voltage generation circuit and performs rated current control.2.3.2.6 Auxiliary ITB Cleaning Bias Generation 0008-1699The Auxiliary ITB cleaning bias is output to prevent residual toners on the ITB from falling on a paper path.Two kinds of the biases, DC positive bias and DC negative bias, are generated in the auxiliary ITB cleaning high-voltage generation circuit in the sub high-voltagepower supply circuit.The DC positive bias is output to the auxiliary ITB cleaning roller to charge residual toners on the ITB positively. The DC negative bias is output to the auxiliaryITB cleaning roller to clean negatively charged residual toner on the roller.The Sub high-voltage power supply circuit applies these auxiliary ITB cleaning biases to the auxiliary ITB cleaning roller during the cleaning period with specifiedtiming.2.3.2.7 ITB Cleaning Bias Generation 0008-1700The ITB cleaning bias is output to clean the ITB.Three kinds of the biases, DC positive bias, DC negative bias, and AC bias, are generated in the ITB cleaning high-voltage generation circuit in the high-voltagepower supply circuit.The AC bias and DC positive bias are output to the ITB cleaning roller to clean positively charged residual toners on the ITB. The AC bias and DC negative biasare output to the ITB cleaning roller to clean negatively charged residual toners on the roller.The high-voltage power supply circuit applies these ITB cleaning biases to the ITB cleaning roller during the cleaning period with specified timing.2.3.2.8 Fixing Bias Generation 0011-6387The fixing bias is generated and used to prevent adhesion to the fixing sleeve of toner that is on print paper before fixing takes place.The fixing bias is a DC positive bias generated in the fixing height-voltage generation circuit of the high-voltage power supply PCB. It is applied to the pressureroller of the fixing assembly at such times as programmed in advance.2.3.3 Image Stabilizaton Control2.3.3.1 Outline 0008-1703This printer performs image stabilization control using the image density detection function (see note) in order to reduce image density variations caused by changesin environments, deterioration of the drum or toner, etc.Two kinds of the image stabilization controls, image density calibration (D-max) control and image halftone calibration (D-half) control, are executed as necessary.Specified conditions to perform image stabilization calibration control are listed in the following:- Power is turned on.- Cartridge is replaced.- After printing 800 images or more (mono color: 800 pages, full color: 200 pages)- After 12 hours in the absence of a print command- In response to a command for execution from the SCNT Board.Image density detection functionThis printer has functions of striking light to image density patterns in each color formed on the ITB and measuring the density of the patterns from the amount ofreflected light.The DCNT Board emits light from the density sensor and strikes the light to each detection pattern. Then the reflected light off the patterns is received at a lightreceiver and returned to the DCNT Board as the IMAGE DENSITY signals.The DCNT Board converts the input IMAGE DENSITY signals (analog values) to density values (digital values) and stores them.F-2-28The DCNT board resets the image density to the default setting and starts the engine in the event of the following: at time of image density detection, the light-receiving segment does not receive light at all, or the level detected by the density sensor does not match a specific value.Density sensorDetectionpatternITB