Laser Printer
A laser printer is a common type of computer printer that rapidly produces high quality text and graphics on plain paper.
The main advantages of laser printers are speed, precision and economy. A laser can move very quickly, so it can "write" with much greater speed than an ink jet. And because the laser beam has an unvarying diameter, it can draw more precisely, without spilling any excess ink. Laser printers tend to be more expensive than inkjet printers, but it does not cost as much to keep them running -- toner powder is cheap and lasts a long time, while you can use up expensive ink cartridges very quickly.
Before a laser printer can do anything else, it needs to receive the page data and figure out how it's going to put everything on the paper. This is the job of the printer controller - the laser printer's main onboard computer.
The heart of a laser printer is a semiconductor material. This is usually a metal drum the width of a page coated with a plastic called Organic Photo Conductor (OPC). OPC removes charge from the areas exposed to light. This drum assembly is made out of highly photoconductive material that is discharged by light photons. Around the drum are organised three or four other rollers. One roller charges the photoconductor drum with a high voltage.
Initially, the drum is given a total positive charge by the charge corona wire, a wire with an electrical current running through it. (Some printers use a charged roller instead of a corona wire, but the principle is the same.) The drum rotates and is scanned with the image. The image is created using a laser, its a small infrared device pointed at a rotating mirror to give the scanning action.
The laser receives the page data -- the tiny dots that make up the text and images -- one horizontal line at a time. Each horizontal strip of dots across the page is known as a raster line or scan line. Creating the image to be printed is done by a Raster Image Processor (RIP), typically built into the laser printer.
As the beam moves across the drum, the laser emits a pulse of light across the surface to discharge every dot to be printed, and no pulse for every dot of empty space. The laser assembly moves in only one plane, horizontally. After each horizontal scan, the printer moves the photoreceptor drum up a notch so the laser assembly can draw the next line.
Now there are letters and images to be printed as a pattern of electrical charges on the drum's surface -- an electrostatic image. Rotating further the drum comes next to the developer, a roller carrying a coat of positively charged toner powder. Toner powder is made from fine particles of plastic. Since the toner has a positive charge, the toner is attracted to the negative discharged areas of the drum, but not to the positively charged "background." As it moves past the developer the drum becomes coated with the image that will print.
Next the drum moves over the paper which is being driven past it by the registration roller. Under the paper is the transfer roller. The transfer roller carries a charge that is stronger than the negative charge of the electrostatic image, so the paper can pull the toner powder away. Since it is moving at the same speed as the drum, the paper picks up the image pattern exactly.
To keep the paper from clinging to the drum, it is discharged by the detac corona wire immediately after picking up the toner. At this point, the only thing keeping the toner on the page is gravity -- if you were to blow on the page, you would completely lose the image.
After depositing toner on the paper, the drum surface passes the discharge lamp. This bright light exposes the entire photoreceptor surface, erasing the electrical image. The drum surface then passes the charge corona wire, which reapplies the positive charge. Most drums are about 2-3 inches in circumference so they turn 3 or 4 times to produce a page.
The image is now on the page but in dry toner powder. The toner needs sticking to the page and this job is done by the fuser, a pair of heated rollers. Fusers use the rollers and a combination of heat and pressure to do the job. The toner part-melts in the fuser to the point where it sticks to the paper. The fuser rolls normally coated with Teflon to prevent the toner from collecting on the fuser rolls.
The paper passes through the rollers so quickly that it does not get very hot. The fuser rolls the paper to the output tray, and you have your finished page. The parts all return to position ready for the next page.
Technological progress has been
*- increases in speed - typically up to 60 pages per minute (beyond this sheet fed paper gives difficulties)
*- increases in resolution - usually to 1200dpi (which needs finer toner, more memory and more processing power)
*- increasing the amount of memory a typical printer ships with which ranges from 2MB to 128MB on mono machines and 512MB with a maximum of a gigabyte on color devices
The other big advance has been the introduction of color. Color laser printers typically use four sets of imaging elements, each with a different colored toner (the CMYK process). This makes a rather complicated mechanism but since the demand is huge mass production (and the economics of cartridges) delivers affordable products. Essentially, color printers work the same way as monochrome printers, except they go through the entire printing process four times -- one pass each for cyan (blue), magenta (red), yellow and black. By combining these four colors of toner in varying proportions, you can generate the full spectrum of color.
Laser printers have complicated mechanisms but they can largely be modularised as cartridges. The HP / Canon design uses one print cartridge for the toner and the main imaging rollers in a mono machine. Other than the laser scanner and the HT power supplies the whole imaging subsystem is a cartridge. That means most faults can be identified by swapping the cartridge - and that's cheaper than the call-out charge for a technician. A color machine has four imaging subsystems, each in it's own cartridge. Having four cartridges does make life a bit more difficult but a rule of thumb is that if only one color has a fault its the cartridge and if all four have a fault its the transfer belt.
The main advantages of laser printers are speed, precision and economy. A laser can move very quickly, so it can "write" with much greater speed than an ink jet. And because the laser beam has an unvarying diameter, it can draw more precisely, without spilling any excess ink. Laser printers tend to be more expensive than inkjet printers, but it does not cost as much to keep them running -- toner powder is cheap and lasts a long time, while you can use up expensive ink cartridges very quickly.
Before a laser printer can do anything else, it needs to receive the page data and figure out how it's going to put everything on the paper. This is the job of the printer controller - the laser printer's main onboard computer.
The heart of a laser printer is a semiconductor material. This is usually a metal drum the width of a page coated with a plastic called Organic Photo Conductor (OPC). OPC removes charge from the areas exposed to light. This drum assembly is made out of highly photoconductive material that is discharged by light photons. Around the drum are organised three or four other rollers. One roller charges the photoconductor drum with a high voltage.
Initially, the drum is given a total positive charge by the charge corona wire, a wire with an electrical current running through it. (Some printers use a charged roller instead of a corona wire, but the principle is the same.) The drum rotates and is scanned with the image. The image is created using a laser, its a small infrared device pointed at a rotating mirror to give the scanning action.
The laser receives the page data -- the tiny dots that make up the text and images -- one horizontal line at a time. Each horizontal strip of dots across the page is known as a raster line or scan line. Creating the image to be printed is done by a Raster Image Processor (RIP), typically built into the laser printer.
As the beam moves across the drum, the laser emits a pulse of light across the surface to discharge every dot to be printed, and no pulse for every dot of empty space. The laser assembly moves in only one plane, horizontally. After each horizontal scan, the printer moves the photoreceptor drum up a notch so the laser assembly can draw the next line.
Now there are letters and images to be printed as a pattern of electrical charges on the drum's surface -- an electrostatic image. Rotating further the drum comes next to the developer, a roller carrying a coat of positively charged toner powder. Toner powder is made from fine particles of plastic. Since the toner has a positive charge, the toner is attracted to the negative discharged areas of the drum, but not to the positively charged "background." As it moves past the developer the drum becomes coated with the image that will print.
Next the drum moves over the paper which is being driven past it by the registration roller. Under the paper is the transfer roller. The transfer roller carries a charge that is stronger than the negative charge of the electrostatic image, so the paper can pull the toner powder away. Since it is moving at the same speed as the drum, the paper picks up the image pattern exactly.
To keep the paper from clinging to the drum, it is discharged by the detac corona wire immediately after picking up the toner. At this point, the only thing keeping the toner on the page is gravity -- if you were to blow on the page, you would completely lose the image.
After depositing toner on the paper, the drum surface passes the discharge lamp. This bright light exposes the entire photoreceptor surface, erasing the electrical image. The drum surface then passes the charge corona wire, which reapplies the positive charge. Most drums are about 2-3 inches in circumference so they turn 3 or 4 times to produce a page.
The image is now on the page but in dry toner powder. The toner needs sticking to the page and this job is done by the fuser, a pair of heated rollers. Fusers use the rollers and a combination of heat and pressure to do the job. The toner part-melts in the fuser to the point where it sticks to the paper. The fuser rolls normally coated with Teflon to prevent the toner from collecting on the fuser rolls.
The paper passes through the rollers so quickly that it does not get very hot. The fuser rolls the paper to the output tray, and you have your finished page. The parts all return to position ready for the next page.
Technological progress has been
*- increases in speed - typically up to 60 pages per minute (beyond this sheet fed paper gives difficulties)
*- increases in resolution - usually to 1200dpi (which needs finer toner, more memory and more processing power)
*- increasing the amount of memory a typical printer ships with which ranges from 2MB to 128MB on mono machines and 512MB with a maximum of a gigabyte on color devices
The other big advance has been the introduction of color. Color laser printers typically use four sets of imaging elements, each with a different colored toner (the CMYK process). This makes a rather complicated mechanism but since the demand is huge mass production (and the economics of cartridges) delivers affordable products. Essentially, color printers work the same way as monochrome printers, except they go through the entire printing process four times -- one pass each for cyan (blue), magenta (red), yellow and black. By combining these four colors of toner in varying proportions, you can generate the full spectrum of color.
Laser printers have complicated mechanisms but they can largely be modularised as cartridges. The HP / Canon design uses one print cartridge for the toner and the main imaging rollers in a mono machine. Other than the laser scanner and the HT power supplies the whole imaging subsystem is a cartridge. That means most faults can be identified by swapping the cartridge - and that's cheaper than the call-out charge for a technician. A color machine has four imaging subsystems, each in it's own cartridge. Having four cartridges does make life a bit more difficult but a rule of thumb is that if only one color has a fault its the cartridge and if all four have a fault its the transfer belt.
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