Impact printers, as the very name implies means that the printing mechanism touches the paper for creating an image. Impact printers were used in early 70s and 80s. In Dot Matrix printers a series of small pins is used to strike on a ribbon coated with ink to transfer the image on the paper.
Other Impact Printers like Character printers are basically computerized typewriters. They have a series of bars or a ball with actual characters on them, which strike on the ink ribbon to transfer the characters on the paper. At a time only one character can be printed. Daisy Wheel printers use a plastic or metal wheel. These types of printers have limited usage though because they are limited to printing only characters or one type of font and not the graphics.
There are Line printers where a chain of characters or pins, print an entire line, which makes them pretty fast, but the print quality is not so good. Thermal printers are nothing but printers used in calculators and fax machines. They are inexpensive to use. Thermal printers work by pushing heated pins against special heat sensitive paper.
More efficient and advanced printers have come out now which use new Non-impact Technology.
Non-impact printers are those where the printing mechanism does not come into the contact of paper at all. This makes them quieter in operation in comparison to the impact printers.
In mid 1980s Inkjet printers were introduced. These have been the most widely used and popular printers so far. Colour printing got revolutionized after inkjet printers were invented. An Inkjet printer's head has tiny nozzles, which place extremely tiny droplets of ink on the paper to create an image. These dots are so small that even the diameter of human hair is bigger. These dots are placed precisely and can be up to the resolution of 1440 x 720 per inch. Different combinations of ink cartridges can be used for these printers.
How an Inkjet printer works
The print head in this printer scans the page horizontally back and forth and another motor assembly rolls the paper vertically in strips and thus a strip is printed at a time. Only half a second is taken to print a strip. Inkjet printers were very popular because of their ability to colour print. Most inkjets use Thermal Technology. Plain copier paper can be used in these printers unlike thermal paper used for fax machines. Heat is used to fire ink onto the paper through the print head. Some print heads can have up to 300 nozzles. Heat resistant and water based ink is used for these printers.
The latest and fastest printers are Laser Printers. They use the principal of static electricity for printing it as in photocopiers. The principle of static electricity is that it can be built on an insulated object. Oppositely charged atoms of objects (positive and negative) are attracted to each other and cling together. For example, pieces of nylon material clinging to your body, or the static you get after brushing hair. A laser printer uses this same principle to glue ink on the paper.
How Laser Printer works:
Unlike the printers before, Laser printers use toner, static electricity and heat to create an image on the paper. Toner is dry ink. It contains colour and plastic particles. The toner passes through the fuser in the computer and the resulting heat binds it to any type of paper. Printing with laser printers is fast and non-smudge and the quality is excellent because of the high resolution that it can achieve with 300 dots per inch to almost 1200 dpi at the higher end.
Basic components of a laser printer are fuser, photoreceptor drum assembly, developer roller, laser scanning unit, toner hopper, corona wire and a discharge lamp. The laser beam creates an image on the drum and wherever it hits, it changes the electrical charge like positive or negative. The drum then is rolled on the toner. Toner is picked up by charged portion of the drum and gets transferred to the paper after passing through the fuser. Fuser heats up the paper to amalgamate ink and plastic in toner to create an image. Laser printers are called "page printers" because entire page is transferred to the drum before printing. Any type of paper can be used in these printers. Laser printers popularized DTP or Desk Top Publishing for it can print any number of fonts and any graphics..
This is how the computer and printer operate to print
When we want to print something we simply press the command "Print". This information is sent to either RAM of the printer or the RAM of the computer depending upon the type of printer we have. The process of printing then starts. While the printing is going on, our computer can still perform a variety of operations. Jobs are put in a buffer or a special area in RAM or Random Access Memory and the printer pulls them off at its own pace. We can also line up our printing jobs this way. This way of simultaneously performing functions is called spooling. Our computer and the printer are thus in constant communication.
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