Canon i-SENSYS MF229dw Service Manual

22 2-192-19Technical Overview > Image Formation System > High-Voltage Control > Generating Transfer BiasTechnical Overview > Image Formation System > High-Voltage Control > Generating Transfer BiasHigh-Voltage Control■ OverviewThis circuit is comprised of the circuits that apply biases to the primary charging roller,developing cylinder, transfer roller, and the fixing control circuit. The CPU of the enginecontroller controls the high-voltage power supply circuit to generate these biases. The fixingcontrol circuit executes heater control of the fixing assembly according to the instruction bythe CPU of the engine controller.The following is the block diagram of this circuit.Transfer rollerCPU High-voltage power supplyPrimarycharginghigh-voltagegenerationcircuitDevelopinghigh-voltagegenerationcircuitTransferhigh-voltagegenerationcircuitprimary chargingrollerdeveloping cylinderEngine controllerPRIDEVTR■ Generating Primary Charging BiasThe primary charging bias (PRI) is a DC negative bias that is output to apply an evennegative potential to the surface of the photosensitive drum. The primary charging high-voltage generating circuit in the high-voltage power supply circuit generates this bias.The high-voltage power supply circuit applies the generated primary charging bias to theprimary charging roller at a specified timing.The primary charging bias varies in conjunction with the developing bias according to theinformation of image density sent from the main controller.F-2-26■ Generating Developing BiasThe developing bias is a DC negative bias that is output to affix toner to the static latentimages formed on the photosensitive drum. This bias is a development DC and ACsuperimposed bias and generated by the development high-voltage generating circuit in thehigh-voltage power supply circuit.The high-voltage power supply circuit applies the generated developing bias to the developingcylinder at a specified timing.The developing bias varies in conjunction with the primary charging bias according to theinformation of image density sent from the main controller.■ Generating Transfer BiasTransfer bias (TR) is a bias that is output to transfer toner to papers. There are two typesof bias; DC positive bias and DC negative bias, and generated by the transfer high-voltagegenerating circuit in the high-voltage power supply circuit. The DC positive bias is output atthe time of toner transfer, and the DC negative bias at the time of cleaning the photosensitivedrum.The high-voltage power supply circuit applies the generated transfer bias to the transfer rolleraccording to each print sequence.Each print sequence is described below.• Cleaning bias:The bias to move (clean) the toner attached to the transfer roller to the photosensitive drumat the time of warming up or last rotation sequence.The transfer negative bias is applied to the transfer roller.• Paper intervals bias:The bias to prevent the toner remained on the photosensitive drum from attaching to thetransfer roller at paper intervals during continuous printing. A minor transfer positive bias isapplied to the transfer roller.• Print bias:The bias to transfer the toner on the surface of the photosensitive drum to papers at thetime of print sequence. The transfer positive bias is applied to the transfer roller.