Laser
printers are the very crescendo of printing technology! They stand second to
none but the 3-D printers. They are sleek, agile and cheap. Besides, they
eradicate the compulsive obsession of printing and cleaning regularly that
every inkjet printer’s user would have developed after being bogged down by a
quagmire or two! Optical physics has been a boon to humanity. The application
of LASERs (if you just felt that the caps were a typo that slipped in covertly,
let me clarify that it’s not the case! LASER stands for Light Amplification by
Stimulated Emission of Radiations.) has bought revolutions in Science,
Technology and medicine. The doctor of the 19th century standing
with a sharp scalpel would find himself clueless inside the 21st
century’s state-of-the-art operation theatres housing mysterious machineries!
In the field of computing lasers (from this instance on I’ll simply keep using
the lower case as it is an accepted industry standard. May be just to avoid the
awkward feeling of reading it in all capitals in a normal sentence!) have been
used to record and read optical media such as the CDs, DVDs and the Bluray
Discs apart from the printing technologies. However, our focus here is to study
the innards (or to simply put in, the internal working – as the very mention of
innards and viscera makes many people puke outright out of the psychological
feeling of filth associated. For now I’d rather like if you read on instead of
contemplating upon the bubble like transient nature of the physical form!) of a
laser printer and hence we will not dive into its myriads of other
applications; although it may sound unjust to readers who worship ‘LASER’ as
their sole deity!
Working principle of device:
The
ink cartridge is arguably the most important component in an inkjet printer. In
the same vein, for the part of a laser printer, the toner cartridge is
analogous to an ink cartridge. The toner cartridge contains the legendary photosensitive
drum (that is neither meant to be struck nor to produce any sound!), the toner
(the powdery substance that sticks to the paper) and the cleaning blade. The
driver and PCL (printer command language) /PS (post script) prepare the print
job into instructions per page that the printer can understand. Remember that
laser printers receive print jobs per page and not per character as the dot
matrix printers used to receive. This makes the printing snappy. These printers
have a Formatter board (used to format the print jobs), HVPS (high voltage
power supply), an LVPS (Low voltage power supply) and a halogen lamp that emits
the laser. Laser printers employ a process known as EP (electro-photographic)
print process. This process can be divided into 6 major steps which are
described below:
1.
Charging: The charging corona or
the primary corona draws power from the HVPS and applies a uniform voltage of
-600VDC to the drum.
2.
Writing: This step involves the
exposure of the drum to the laser beam. It is a curious phenomenon that when
the drum is exposed to a laser beam it loses its charge. The upshot is that the
regions of the drum where the laser is struck come down to -100VDC from
-600VDC. This laser emitted from a halogen lamp creates an image of that which
is to be printed on the drum making those regions relatively positive in
comparison to the rest of the drum.
3. Developing:
In this step toner is picked-up and bought near the drum. The toner possesses
excessive negative charge while the areas of drum that contain the image are
relatively positive. Thus when the toner approaches the drum, due to
electrostatic force of attraction it gets onto the drum which implies that the
image on the drum now carries the toner. The other parts of the drum which were
not exposed to the laser still remain at -600VDC and hence due to the
electrostatic force of repulsion between those regions of the drum and the
negatively charged toner, these regions remain free from any traces of toner.
4. Transferring:
The
toner on the drum somehow needs to be transferred to the paper. The various
rollers (that use friction feed mechanism – the roller rubs on the surface of
paper to pull it in or push it out. Also rubber pads are present below the
paper that prevent more than one paper from entering the printer) advance the
paper through the printer. At a certain stage the transfer corona roller (wire
in case of older printers) applies +600VDC to the surface of the paper from
HVPS. Thus when the paper passes past the drum again due to the electrostatic
force of attraction all the toner present on the drum get transferred to the
paper in the exactly same shape as it was on the drum. This creates the image
on the paper.
5. Fusing:
It is a
common observation that when the fusing assembly of laser printer fails the
images on the paper smear when touched. The toner in the preceding step only
sticks to the paper due to that electrostatic force of attraction. But slowly
when the +600VDC charge of the paper bleeds away to the surrounding the toner
comes off it easily. To solve this issue fuser assembly uses heaters that work
at about 165℃ to melt the toner present on the paper. The melted toner cools
down on the paper and sticks to it permanently. Thus the fusing step makes the
image on the paper permanent.
6. Cleaning:
The drum has a cleaning blade fixed on its
side and often a pouch underneath it. The only function in life of the blade is
to remove any residual toner that has remained behind after the printing has
completed. A negligible amount of toner will more often than not remain on the
drum. If this toner is allowed to stay on the drum it will stick to the next
paper/print job in the queue. This would create what is known as ghosting in
the printer parlance. Don’t be petrified by the eerily sounding word! It only
suggests that a faint image of the previous print job appears on the current
one!
Looking
at the complexity of the printing process you may wonder that the printer
prints at all! But trust me, it indeed does and so fast that a wink of your eye
would be sufficient for a page to get printed!
Device
installation: The printers can be connected via the Parallel/Serial/USB/Ethernet
port or Wi-Fi. Appropriate drivers for the operating system used must be
installed before the printer is ready to blow all of its pristine bells and
whistles!
Manufacturer
of device, its models and prices:
1.
HP
- Hp M1136 Mfp Laserjet Allinone Copy (Rs. 11,499), Hp Color Laserjet Pro
Wireless Cp1025nw (Rs. 25,000), HP 1020Plus Monochrome (Rs. 7,900)
2.
Panasonic
– Panasonic KX-MB1500 Multi-Function Laser (Rs. 8,499), Panasonic KXMB2120 Monochrome Multi-Function (Rs. 15,090), Panasonic KX-MB1900 monochrome Multi-Function (Rs. 11,000) etc
3.
Canon
– Canon Lasershot Mono Mfc Printermf 4720 W (Rs. 12,699), Canon Image Class
Mf3010 Multifunction Laser (Rs. 15,000), Canon LBP-6230DN Monochrome (Rs. 12,000)
etc
4.
Samsung
- Samsung ML-2161 (Rs. 5,600), Samsung Scx3401xip Monochrome (Rs. 10,342), Samsung
SL-M2876ND/XIP Multifunction Laser (Rs. 13,749),
Standard
Configuration of device: They come in two variants; 1) black and white
printers and 2) color printers. They can have an NIC (network interface card)
built into it thereby facilitating it to connect directly to the wired/wireless
network. In case of network printers, the printer is usually the print server.
If the printer lacks the print server an external hardware print server can be
connected to the printer. Optional accessories include Hard Drives and small amount
of the DIMM (Dual In-Line Memory Module) DDR-X (Double Data Rate and where X
indicates the version of DDR used) RAM (Random Access Memory) chips. These are
desired as they reduce the load on the host and increase the speed of
processing the print job. Now-a-days multifunction devices are the trend du
jour! People want fast, efficient, compact and reliable devices that they can
lug around without any difficulties. These nifty features can incarnate only if
a multipurpose device is created to serve the insatiable desires of the
ever-demanding customers! The elite technicians reparteed with just such an
instrument that would blow their user’s minds away into marvel! Thus were born
multifunction printers that can print, photocopy and fax all from the same
device! It is said that necessity is the mother of invention. The need for
comfort paved the path for the introduction of devices such as feeders,
collaters and duplexers. These add-ons can store bunches of various kinds of
sheets, can collect, arrange and staple the print jobs and can print on the obverse
and the reverse without the need of human intervention respectively. Of course
our good old uncle Sammy has better to do than to sift through the mounds of
pages that can make his age go dizzy, thanks to the collaters!
Cost: As a rule of thumb color
printers are costlier than black and white printers and network printers are
pricier than their stand-alone counterparts. Average home-use printers can be
bought for about Rs. 4,000 while one needs to invest at least Rs. 15,000 in
professional printers.
Market share of
different models (Standard companies only):
l HP
l Panasonic
l Canon
l Samsung
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