as well as LED printers
rely on one and the same technology used at first in photocopying machines. This process is known as electrophotography
and was invented in 1938 and developed by Xerox
in the later 1980s.
Electrophotographic process in laser printers
, involves six basic steps:
) is uniformly charged
with static electricity by a corona discharge
. Then the charged photoconductor is exposed
to an optical image through light
to discharge it selectively and forms a latent
or invisible image
is done by spreading toner
, a fine powder, over the surface, which adheres only to the charged areas, thereby making the latent image visible. At the next step an electrostatic field transfers
the developed image from the photosensitive surface to a sheet of paper. Then the transferred image is fixed permanently to the paper, by fusing
the toner with pressure and heat. The last step is cleaning
of all excess toner and electrostatic charges from the photoconductor to make it ready for next cycle.
as well as LED printers
offer the best print quality
i.e. the highest resolution
. The unique difference is the method of exposition or formation of the latent image.
Laser printer scanning assembly:
Laser printers rely on a laser beam
and scanner assembly
to form a latent image on the photo-conductor
bit by bit. The scanning process
is similar to electron beam scanning used in CRT.
The laser beam modulated
by electrical signals from the printer's controller is directed through a collimator lens
onto a rotating polygon mirror
), which reflects the laser beam. Then reflected from the scanner laser beam pass through a scanning lens
system, which makes a number of corrections to it and scans on the photoconductor.
This technology is the major key for ensuring high precision in laser spot at the focal plane, accurate dot generation at a uniform pitch and therefore better printer's resolution.
Laser printer scanning process: the latent image creation
,developed by Oki
, use an array
of small L
evices to form the latent image, hence no scanner is required. Thus LED technology offers some potential advantages over laser one. However, several problems are related to this method. A main problem is the integration of the 2400
diodes (A4 format with 300 dpi) into a staggered or single row, along with lens arrays
for focusing the LED emission onto the photosensitive surface.
The image scanning process is similar to that in line dot matrix printers
as shown bellow.
The LED printer scanning process
Laser printers as well as LED printers are the right solutions for applications demanding high quality with high-speed output of images and text data, such as desktop publishing.