Xerox 6250N Service Manual - Page 41
Overview of the Phaser 6250 Color Laser Printer Theory of Operation, Summary of the Printing Process - supplies
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Overview of the Phaser 6250 Color Laser Printer Theory of Operation Summary of the Printing Process The Phaser 6250 Color Laser Printer is a 'full-color laser printer', that utilizes electrophotographic recording principals to place a full color image onto the print media. The system, contains a drum and developing unit for each color (yellow, magenta, cyan and black (YMCK)), and places the toner image of each color onto print media producing full-color prints through three transfer units (primary transfer units IDT1 (2 ea) and secondary transfer unit IDT2 (1 ea)). A summary description of the printing process is presented in the following Steps, see the illustration on the following page as a reference: 1. Charging: The charge roller (RTC) is negatively charged by the high voltage power supply (HVPS) and is kept in contact with the drum surface to provide a uniform negative charge on the drum as it rotates at a constant speed. This occurs simultaneously for YMCK. The refresher is a conductive brush that is also negatively charged by the HVPS to pick off any toner particles left on the drum after image transfer to the IDT. 2. Exposure: The laser unit emits laser beams in response to image data from the Image Processor board. The laser beams are directed onto the drum surface through a system of mirrors and lenses. A rotating polygonal mirror causes the laser beams to scan the drum surface from end to end (axially) as it rotates. The beams are turned on to print a pixel and off when no printing is required. The negative charge on the drum surface is reduced at each point where the energized laser beam strikes, to form an invisible electrostatic latent image on the drum surface. This process is performed simultaneously for YMCK. 3. Development: Toner is electrostatically attached to the invisible latent image on the drum surface to form the visible image on the drum. Toner is fed into the developer using the agitator and auger. The toner and the carrier in the developer form a homogeneous layer on the magnet roller in the developer. The magnet roller turns against the surface of the drum and is kept at a constant negative potential. At areas on the drum surface where the negative charge has not been reduced by the impact of laser light, potential between the drum and the toner particles is lower than that between the magnet roller and the toner particles. At areas where the drum charge has been reduced, the potential between the particles and drum is higher than between the magnet roller and toner particles are attracted to the drum. A thin semiconductive sleeve on the magnet roller is vibrated by an AC voltage to encourage migration of the toner particles to the drum. When the toner particles attach to the drum, the negative charge of the particles reduces drum potential at that point, thus reducing the attraction of additional toner particles. This process is performed simultaneously for YMCK. 4. Primary Transfer (drum --> IDT1): The toner image formed on the individual drum surface is transferred onto the surface of the IDT1 (intermediate Drum Transfer 1: intermediate transfer roller 1). There are two IDT1's: one for yellow and magenta and one for cyan and black. IDT1 is conductive and receives a high positive charge from the HVPS. The negatively charged toner image on the drum 2-2 Phaser 6250 Color Laser Printer Service Manual
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