Printers-Dot Matrix Printer, Inkjet Printer, Laser Printer, Plotter

An external hardware device responsible for taking computer data and generating a hard copy of that data

v Impact Printers: Hammer hits ribbons, papers or print head. Dot-matrix and daisy-wheel printers are the example.

v  Non-impact Printers: They do not have the hammer and do not hit. An example is an ink-jet and laser printer.

1.    Dot Matrix Printer

• The dot matrix forms images one character at a time as the print head moves across the paper.
• Dot-Matrix printers are bit image impact type of printers.
• These printers form characters and images by placing pattern of dots on the paper by striking inked ribbon with a number of small pins.
• These printers use a print head that shuttles back and forth across the width of the paper and a number of thin print wires on the head act as hammers that strike the ribbon and squeeze ink from ribbon to paper.
• Most Dot-Matrix printer models are inexpensive, small, lightweight and very efficient at their job.
• As these are impact type of printer one main drawback of these printers is the noise generated by them, but compared to fully formed character type impact printers such as the Daisy-Wheel printer, these printers are less noisy.
• 9 to 24 vertical column pins are contained in a rectangular print head. When print head moves across the paper, pins are activated to form a dotted character image. These printers can produce carbon copies along with the originals.

2.    Inkjet Printer

An ink-jet printer creates an image directly on paper by spraying ink. Inkjet printing, like laser printing, is a non-impact process. Ink is emitted from nozzles while they pass over media. The operation of an inkjet printer is easy to visualize: liquid ink in various colors being squirted onto paper and other media, like plastic film and canvas, to build an image. A print head scans the page in horizontal strips, using the printer's motor assembly to move it from left to right and back again, while the paper is rolled up in vertical steps, again by the printer. A strip (or row) of the image is printed, then the paper moves on, ready for the next strip. To speed things up, the print head doesn’t print just a single row of pixels in each pass, but a vertical row of pixels at a time.

3.    Laser Printer

A type of printer that utilizes a laser beam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. This is also the way copy machines work.

The process of printing is broken down into 6 phases:
1. Cleaning: Excess toner is scraped from the photoelectric drum.

2. Conditioning: A uniform -600 volt charge is placed on the photoelectric drum by the primary corona.

3. Writing: Laser diodes write an invisible electric image on the photoelectric drum by causing the drum surface to be less negative wherever the laser beam hits.

4. Developing: This is where the transfer roller places the toner on the drum. The toner sticks to the areas that have had the electric charge lessened due to the laser beam.

5. Transfer: The secondary corona uses a positive charge to attract the toner from the drum to the paper. The paper gets charged by corona too.

6. Fusing: The toner is then melted into the paper.

4.    Plotter

A plotter is a special kind of output device that, like a printer, produces images on paper, but does so in a different way. Plotters are designed to produce large drawings or images, such as construction plans for buildings or blueprints for mechanical objects. A plotter can be connected to the port normally used by a printer.