Download Laser Printer Components:

LASER PRINTER
1.Definition of laser printer
2.Main parts of laser printer
3.Electrophotografic print proces
4.Color laser printer
5.Principle of laser
6.Work of laser beam in laser printers
7.Comparison between laser and inkjet printer
1.What is a laser printer?
A laser printer is a popular type of personal computer printer that uses a non-impact (keys don't
strike the paper), photocopier technology.
IBM introduced the first laser printer in 1975 for use with its mainframe computers. In 1984,
Hewlett-Packard revolutionized laser-printing technology with its first LaserJet, a compact, fast,
and reliable printer that personal computer users could afford. Since then, laser printers have
decreased further in price and increased in quality. Hewlett Packard continues to be the leading
manufacturer with competitors including Lexmark, Okidata, and Xerox.
2.Laser Printer Components:
A laser printer typically consists of 8 Field Replaceable:
1)Toner Cartridge
2)Laser Scanning Assembly
3)High Voltage Power Supply
4)DC Power Supply
5)Paper Transport Assembly
6)Transfer Corona Assembly
7)Fuser Assembly
8)Formatter Board
1) Toner Cartridge-A toner cartridge comprises of a toner, print drum, charge corona wire and the
cleaning blade. Toner consists of a carbon substance mixed with iron oxide and polyester resins.
2) Laser Scanning Assembly-A laser reflects off of a mirror onto the drum and discharges the
drum. Once the drum is discharged (to about -100 VDC), toner will stick to it.
3) High Voltage Power Supply (HVPS)-This converts the input AC voltage to DC and supplies
high voltages (-600 VDC) to the Charge corona wire and Transfer corona wire.
4) DC Power Supply (DCPS)-This applies +5 and -5 VDC to the formatter board and +24 VDC to
the paper transport motors.
5) Paper Transport Assembly-This is responsible for moving the paper through the printer. It
comprises of a motor and rollers. The pickup rollers pick up a single sheet of paper from the paper
tray, whereas the registration rollers synchronize the paper movement with the image on the print
drum.
6) Transfer Corona Assembly-This is either a wire or roller just beneath the printer cartridge,
which applies a high positive charge to the paper as it is pulled through the printer. The positively
charged paper attracts the negatively charged toner particles to form an image on the paper.
7) Fusing Assembly-The fuser contains 3 componentts, a halogen heating lamp, aTeflon coated
fusing roller and a pressure roller. The halogen lamp heats the fusing roller to 350 F before the toner
is melted onto the paper by the fuser unit.
8) Formatter Board
This is the main circuit board in the printer that is responsible for translating data received from the
computer into data that the printer can understand.
3.Electrophotographic (EP) Print Process
This is the process a laser printer uses to form an image onto the paper. The EP Print Process
consists of 6 stages:
1) Charging
2) Exposing
3) Developing
4) Transferring
5) Fusing
6) Cleaning
1) Charging-At the charging stage, the charge corona wire within the toner cartridge applies a
strong uniform negative charge (-600 VDC) to the toner drum's surface.
2) Exposing-The laser unit scans the drum from side to side, turning off according to the signals
received from the formatter board. The drums charge is reduced from -600VDc to -100VDc in those
areas that the laser beam touches. As the drum rotates around an image is built up on the toner
drums surface.
3) Developing-Toner is transferred to those areas of the drum with a slight negative charge
(-100VDc) at this stage. A developer roller inside the EP cartridge receives a charge of -600VDc.
The toner sticks to this roller because of the magnet inside and
the electrostatic charges.
When the toner comes between the developing roller and the photosensitive drum, the toner is
attracted to those areas on the drum that have been touched by the laser i.e. -100VDc. The drum
now has toner stuck to it where the laser has written.
4) Transfer-The formatter board signals to the registration rollers that the paper should be guided
through. The registration rollers move the paper underneath the drum and the image is transferred to
the paper. The Transfer corona wire applies a high positive charge (+600VDc) to the paper and the
negatively charged toner on the print drum's surface is attracted to the paper because opposites
attract. A static eliminator comb then removes any charge from the paper to prevent the paper
sticking to the toner cartridge, which would result in a printer jam.
5) Fusing-Up to this point the toner is only loosely attached to the paper. The fuser , a pair of
heated rollers, melts the toner onto the paper via a high temperature halogen lamp and a pressure
roller (at about 350 degrees Fahrenheit.).What keeps the paper from burning up? Mainly, speed that
the paper passes through the rollers so quickly that it doesn't get very hot.
6) Cleaning-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.
4.Color Printers
Initially, most commercial laser printers were limited to monochrome printing (black writing on
white paper). But in the last few years, more and more color laser printers have hit the market.
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.
Inside a color laser printer, there are several different ways of doing this. Some models have four
toner and developer units on a rotating wheel. The printer lays down the electrostatic image for
one color and puts that toner unit into position. It then applies this color to the paper and goes
through the process again for the next color.
Some printers add all four colors to a plate before placing the image on paper.
Some more expensive printers actually have a complete printer unit -- a laser assembly, a drum
and a toner system -- for each color. The paper simply moves past the different drum
heads, collecting all the colors in a sort of assembly line.
5.How a Laser Works
The word "laser" stands for "light amplification by stimulated emission of radiation." Lasers are
possible because of the way light interacts with electrons. Electrons exist at specific energy levels or
states characteristic of that particular atom or molecule. The energy levels can be imagined as rings
or orbits around a nucleus. Electrons in outer rings are at higher energy levels than those in inner
rings. Electrons can be bumped up to higher energy levels by the injection of energy-for example,
by a flash of light. When an electron drops from an outer to an inner level, "excess" energy is given
off as light. The wavelength or color of the emitted light is precisely related to the amount of energy
released. Depending on the particular lasing material being used, specific wavelengths of light are
absorbed (to energize or excite the electrons) and specific wavelengths are emitted (when the
electrons fall back to their initial level).
The ruby laser was the first laser invented in 1960. Ruby is an aluminum oxide crystal in which
some of the aluminum atoms have been replaced with chromium atoms. Chromium gives ruby its
characteristic red color and is responsible for the lasing behavior of the crystal. Chromium atoms
absorb green and blue light and emit or reflect only red light.
For a ruby laser, a crystal of ruby is formed into a cylinder. A fully reflecting mirror is placed on
one end and a partially reflecting mirror on the other. A high-intensity lamp is spiraled around the
ruby cylinder to provide a flash of white light that triggers the laser action. The green and blue
wavelengths in the flash excite electrons in the chromium atoms to a higher energy level. Upon
returning to their normal state, the electrons emit their characteristic ruby-red light. The mirrors
reflect some of this light back and forth inside the ruby crystal, stimulating other excited chromium
atoms to produce more red light, until the light pulse builds up to high power and drains the energy
stored in the crystal.
The laser flash that escapes through the partially reflecting mirror lasts for only about
300 millionths of a second-but very intense. Early lasers could produce peak powers of some ten
thousand watts. Modern lasers can produce pulses that are billions of times more powerful.
Another characteristic of laser light is that it is coherent. That is, the emitted light waves are in
phase with one another and are so nearly parallel that they can travel for long distances without
spreading. (In contrast, incoherent light from a light bulb diffuses in all directions.) Coherence
means that laser light can be focused with great precision.
Many different materials can be used as lasers. Some, like the ruby laser, emit short pulses of laser
light. Others, like helium-neon gas lasers or liquid dye lasers emit a continuous beam of light. Our
ICF lasers, like the ruby laser, are solid-state, pulsed lasers.
6.Work of laser beam in laser printers
The laser receives the page data -- the tiny dots that make up the text and images -- one horizontal
line at a time. As the beam moves across the drum, the laser emits a pulse of light for every dot to
be printed, and no pulse for every dot of empty space.The laser doesn't actually move the beam
itself. It bounces the beam off a movable mirror instead. As the mirror moves, it shines the
beam through a series of lenses. This system compensates for the image distortion caused by the
varying distance between the mirror and points along the drum.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. A small print-engine computer synchronizes
all this perfectly, even at dizzying speeds.
Here are some typical lasers and their emission wavelengths:
Argon fluoride (UV)193
Krypton Fluoride (UV)248
Nitrogen (UV)337
Argon (blue)488
Argon (green)514
Helium neon (green)543
Helium neon (red)633
Rhodamine 6G dye (tunable)570-650
Ruby (CrAlO3) (red)694
Nd: YAG (NIR)1064
Carbon Dioxide (FIR)10600
Some newer laser printers use a strip of light-emitting diodes (LEDs) to write the page image
instead of a single laser. Each dot position has its own dedicated light, which means the printer has
one set print resolution. These systems cost less to manufacture than true laser assemblies, but they
produce inferior results. Typically, you'll only find them in less expensive printers.
6.Comparison between laser and inkjet printer
Comparison
Inkjet
Laser
Speed (B&W)
Color printing
Cost
Resolution
Maintenance
# of pages
Application
4 - 12 ppm
Not available
$500 - $2000
great(600dpi, toner)
$100-$250 per cartridge
1500 - 2000 per toner
Business, large volume printing
4 - 6 ppm(draft mode)
1 - 2 ppm
$150 - 500 on the average
good(ink, 300-600 dpi)
$10-40 per cartridge
100 - 400 per cartridge
Home use, color printing
* ppm - pages per minute. dpi - dots per inch.
** Industrial color laser printer are available, but the price is out of reach for most consumers.
These printers start at $6000 and up.
Zdroj: www.bell.labs.com
www.members.aol.col/jimb3d/lasers
www.all-laser.com
www.laser-printer.com
www.pctechguide.com
www.howstuffworks.com
www.whatis.com
www.vista-net.com
www.sciam.com
www.isop.ucla.edu
www.llul.gov/nif./library