Laser Printer Theory of Operation
September 19, 2005 page 2
Kestrel Systems, Inc.
MEMORANDUM
DATE: September 19, 2005
TO: All employees
FROM: John Doe
SUBJECT: Laser Printer Theory of Operation
INTRODUCTORY SUMMARY
All technical personnel need to know the theory of operation for a laser printer. This memorandum will explain the basic theory of operation of a generic laser printer. Laser printers consist of a paper feed section, a developing section, and a fusing section. This memorandum is not meant to be an all inclusive instruction nor a comprehensive technical resource.
Paper Feed
The paper feed section of the printer includes various rollers and sensors to carry the paper through the printer. The paper feed rollers start the paper along its path through the printer and properly aligns the paper with the drum prior to the image being transferred to the paper. Some larger printers have additional rollers or a transport belt that moves the paper to the fusing section. All along the paper path, various sensors detect the presence or absence of the paper for paper jam conditions.
Developing
The developing process is an on-going operation throughout the entire printing process. It has a cleaning stage, a charging stage, an exposure stage, a development stage, and a transfer stage. The following is a brief discussion of each.
Cleaning
The cleaning stage consists of two (2) parts, mechanical and electrical. A rubber blade shaves the excess toner from the surface of the drum accomplishing the mechanical cleaning. A row of lights across the entire width of the drum discharges any residual electrical charge accomplishing the electrical cleaning. The toner cartridge contains both cleaning devices.
Charging
The charge corona has a high negative electrical charge applied to it. This voltage induces an even charge on the surface of the drum. This charge prepares the surface of the drum for imaging during the exposure stage. The toner cartridge contains the charge corona.
Exposure
The printer has a sealed unit inside that contains the laser and a polygon mirror. The laser pulses on and off as required to produce the image. This light is reflected by the mirror to the drum and discharges the drum in the imaged areas. This unit should not require any service.
Development
The developer assembly in the toner cartridge contains the toner. Very fine plastic particles make up the toner. Mixed with the toner are negatively charged iron particles. This mixing action imparts a negative static charge to the toner. The difference of potential between the discharged areas of the drum and the charged toner particles attracts the toner to the surface of the drum.
Transfer
A transfer corona generally mounted in the printer makes up the transfer section. The toner is transferred to the paper when it is fed between the drum and transfer corona. The transfer corona has a high positive electrical charge applied to it, and this charge pulls the toner from the drum to the paper.
Fusing
The fuser has two (2) rollers in it. At least one of them is heated. A combination of heat and pressure fuses the toner into the paper as the paper travels between the rollers. Both the heat rising from the fuser and the warning labels on it allow you to recognize the fuser easily. Personnel should use caution when working near the fuser to prevent burns.
Conclusion
This description covers the basic theory of operation of the laser printer. Each printer is different. Please refer to manufacturer’s documentation for specific details regarding each printer. Any questions about this memorandum may be addressed to your immediate supervisor.