How a Laser Printer operates
Created | Updated Jan 28, 2002
If you have ever wondered how a laser printer operates then this is the article to look at. In this article I shall discus both the theoretical and operational aspects of a "modern" monochrome (black and white) laser printer.
Theory:
All modern laser printers operate on the xerographic process initally developed by Xerox in the 1970's. This consists of exposing a charged, light sensitive drum to a carefully controlled light beam. This can be done using a laser beam on the more expensive ones, or by several rows of laser emitting diodes (LEDs) on the less expensive units. The light affects the charge on the drum, which then attracts colored particles of iron oxide coated in plastic (also known as toner) to the drum. These particles are then transferred to a sheet of paper by another static charge. The paper is then passed a fixing or fusing unit that bonds the particles permanently to the paper through heat and pressure.
Practical:
When you print a document, several things happen at once.
1. The control panel indicates that it is printing, and the logic in the printer forms what is termed a raster image, which is fed to the laser or LED during the print process.
2. The fixing unit heats up to operating temperature, usually around 390 - 400 degrees Fahrenheit (or 200-205 Celsius). This can take a while, especially if the printer has been in power save mode for some time.
3. The motors in the unit start up and rotate the drum and give it a uniform charge, and clear any excess toner that may be on it. In addition, usually a fan turns on. In addition, the laser motor spins up to operating speed. (This is the "jet" noise you may hear) LED based printer do not have this type of noise, but you will still hear the noise from the drive motors and such.
The print process
1. The paper pick up rollers activate and feed a single sheet into the printer. The printer "knows" where the paper is by several sensors and a programmed idea of where the paper should be at any given time in the print cycle. the printer also starts putting an image on the drum at this point.
2. By the time that the paper reaches the drum, it already has part of the image on it, and begins to transfer the image to the paper.
3. By the time that the image is fully transferred on the paper, the leading edge of the paper is usually in the fusing unit, where the image is fused to the paper via a combination of heat and pressure.
4. By the time the trailing edge of the page has left the fuser, the leading edge is usually already out of the printer.
Problems:
1. Environment. The early models where somewhat sensitive to the relative humidity of the environment that it was in. It affects print quality somewhat. Modern printers generally do not have this problem, except for some of the color units, which are much more expensive then the black and white units.
2. Expense. Although the price for most of the parts has come down, they are still a bit expensive. Hence, you normally only see them in a business office environment.
3. Maintenance. Laser printers do require routine maintenance. They keep track of this via a page count, and the more expensive ones will let you know when they need it.
4. Messy. Sometimes the toner leaks out of the cartridge, and this can be very messy, and also expensive to repair if it damages the printer.
Popular brands:
These are brands that myself, as a printer technician, recommend to people. I will admit to being a bit biased toward the Hewlett - Packard printers, as I am certified on them and have worked on many of them.
Hewlett-Packard is the de facto standard for most businesses. They are widely available, relatively easy to fix (from a technician's point of view), and quite reliable.
Xerox. They are more known for their copy machines (which are based on the same process), but they do make a good printer.
Lexmark. A former division of IBM, they make good, solid printers, which are, for the most part, easy to work with.
Okidata. Known for their rugged dot matrix printers, they make a good, affordable laser printer based on LED technology. Instead of using a laser beam, they use two rows of densely placed laser emitting diode above the imaging drum. This makes the printers less expensive to make.
Theory:
All modern laser printers operate on the xerographic process initally developed by Xerox in the 1970's. This consists of exposing a charged, light sensitive drum to a carefully controlled light beam. This can be done using a laser beam on the more expensive ones, or by several rows of laser emitting diodes (LEDs) on the less expensive units. The light affects the charge on the drum, which then attracts colored particles of iron oxide coated in plastic (also known as toner) to the drum. These particles are then transferred to a sheet of paper by another static charge. The paper is then passed a fixing or fusing unit that bonds the particles permanently to the paper through heat and pressure.
Practical:
When you print a document, several things happen at once.
1. The control panel indicates that it is printing, and the logic in the printer forms what is termed a raster image, which is fed to the laser or LED during the print process.
2. The fixing unit heats up to operating temperature, usually around 390 - 400 degrees Fahrenheit (or 200-205 Celsius). This can take a while, especially if the printer has been in power save mode for some time.
3. The motors in the unit start up and rotate the drum and give it a uniform charge, and clear any excess toner that may be on it. In addition, usually a fan turns on. In addition, the laser motor spins up to operating speed. (This is the "jet" noise you may hear) LED based printer do not have this type of noise, but you will still hear the noise from the drive motors and such.
The print process
1. The paper pick up rollers activate and feed a single sheet into the printer. The printer "knows" where the paper is by several sensors and a programmed idea of where the paper should be at any given time in the print cycle. the printer also starts putting an image on the drum at this point.
2. By the time that the paper reaches the drum, it already has part of the image on it, and begins to transfer the image to the paper.
3. By the time that the image is fully transferred on the paper, the leading edge of the paper is usually in the fusing unit, where the image is fused to the paper via a combination of heat and pressure.
4. By the time the trailing edge of the page has left the fuser, the leading edge is usually already out of the printer.
Problems:
1. Environment. The early models where somewhat sensitive to the relative humidity of the environment that it was in. It affects print quality somewhat. Modern printers generally do not have this problem, except for some of the color units, which are much more expensive then the black and white units.
2. Expense. Although the price for most of the parts has come down, they are still a bit expensive. Hence, you normally only see them in a business office environment.
3. Maintenance. Laser printers do require routine maintenance. They keep track of this via a page count, and the more expensive ones will let you know when they need it.
4. Messy. Sometimes the toner leaks out of the cartridge, and this can be very messy, and also expensive to repair if it damages the printer.
Popular brands:
These are brands that myself, as a printer technician, recommend to people. I will admit to being a bit biased toward the Hewlett - Packard printers, as I am certified on them and have worked on many of them.
Hewlett-Packard is the de facto standard for most businesses. They are widely available, relatively easy to fix (from a technician's point of view), and quite reliable.
Xerox. They are more known for their copy machines (which are based on the same process), but they do make a good printer.
Lexmark. A former division of IBM, they make good, solid printers, which are, for the most part, easy to work with.
Okidata. Known for their rugged dot matrix printers, they make a good, affordable laser printer based on LED technology. Instead of using a laser beam, they use two rows of densely placed laser emitting diode above the imaging drum. This makes the printers less expensive to make.
