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Printers

The printer is a peripheral that allows you to make a print-out (on paper) of computer data.

There are several printer technologies, the most common of which are:

• the daisy wheel printer
• the dot-matrix printer (also called impact matrix printer)
• the inkjet printer and the bubble jet printer
• the laser printer

Characteristics

The printer is generally characterised by the following elements:

• Print speed: expressed in pages per minute (ppm), print speed represents the printer's ability to print a large number of pages per minute. For colour printers, a distinction is generally made between monochrome and colour print speed.
• Resolution: expressed in dots per inch (abbreviated as dpi), resolution means the sharpness of printed text. Sometimes the resolution is different for a monochrome, colour or photo print-out.
• Warm-up time: the waiting time necessary before the first print-out. A printer cannot print when it is "cold". A certain temperature must be reached for the printer to run optimally.
• Onboard memory: the quantity of memory that allows the printer to store print jobs. The higher the amount of memory, the longer the printer queue can be.
• Paper format: depending on their size, printers are able to accept different sized documents, generally in A4 format (21 x 29.7 cm) or less frequently A3 (29.7 x 42 cm). Some printers allow you to print on other types of media, such as CDs or DVDs.
• Paper feed: the method of loading paper into the printer, characterising the way in which blank paper is stored. The paper feed can change depending on where the printer will be placed (rear loading is advised for printers that will be up against a wall).* The main paper feed modes are:
  • The feed tray, which uses an internal paper feed source. Its capacity is equal to the maximum number of sheets of paper that the tray can fit.
  • The sheet feeder is a manual feed method that allows you to insert sheets of paper in small quantities (of about 100). The sheet feeder in the back of the printer is either horizontal or vertical.
• Cartridges: cartridges are rarely standard and depend highly on the printer brand and model. Some manufacturers favour multicoloured cartridges whereas others offer separate ink cartridges. Separate ink cartridges are on the whole cheaper because often one colour is used more than others.

  It is interesting to examine the printing cost per sheet. The size of the ink drop is especially important. The smaller the drop of ink, the lower the printing cost will be and the better the image quality will be. Some printers produce drops that are 1 or 2 picolitres.

• Interface: how the printer is connected to the computer. The main interfaces are:
  • USB
  • Parallel
  • Network: this type of interface allows several computers to share one printer. There are also WiFi printers that are available through a wireless network

Daisy Wheel Printer

Daisy wheel printers are based on typewriters. A matrix in the shape of a daisy contains "petals" that each have one raised character. To print the text, a ribbon of ink is placed between the daisy and the sheet of paper. When the matrix hits the ribbon it leaves ink on paper in the shape of the character on the petal.

These printers are obsolete because they are extremely noisy and very slow.

Dot-Matrix Printer

The dot-matrix printer (sometimes called a matrix printer or an impact printer) allows you to print documents on paper thanks to the "back and forth" motion of a carriage housing a print head.

The head is made up of tiny metal pins, driven by electromagnets, which strike a carbon ribbon called an "inked ribbon", located between the head and the paper.

The carbon ribbon scrolls by so that there is always ink on it. At the end of each line, a roller makes the sheet advance.

The most recent dot-matrix printers are equipped with 24-needle printer heads, which allows them to print with a resolution of 216 dpi (dots per inch).

Inkjet Printer and Bubble Jet Printer

The inkjet printer technology was originally invented by Canon. It is based on the principle that a heated fluid produces bubbles.

The researcher who discovered this had accidentally brought a syringe filled with ink into contact with a soldering iron. This created a bubble in the syringe that made the ink in the syringe shoot out.

Today's printer heads are made up of several nozzles (up to 256), equivalent to several syringes, which are heated up to between 300 and 400°C several times per second.

Each nozzle produces a tiny bubble that ejects an extremely fine droplet. The vacuum caused by the decrease in pressure creates a new bubble.

Generally, we make a distinction between the two different technologies:

• Inkjet printers use nozzles that have their own built-in heating element. Thermal technology is used here.
• Bubble jet printers use nozzles that have piezoelectric technology. Each nozzle works with a piezoelectric crystal that changes shape when excited by its resonance frequency and ejects an ink bubble.

Laser Printer

The laser printer produce quality print-outs inexpensively at a high print speed. However, these printers are mostly used in professional and semi-professional settings because of their high cost.

Laser printers use a technology that is close to that used by photocopiers. A laser printer is mainly made up of an elecrostatically charge photosensitive drum that attracts the ink in order to make a shape that will be deposited on the sheet of paper.

How it works: a primary charge roller gives the sheets of paper a positive charge. The laser gives a positive charge to certain spots on the drum with a pivoting mirror. Then, negatively charged ink in powder form (toner) is deposited on the parts of the drum that were previously charged by the laser.

By turning, the drum deposits the ink on the paper. A heating wire (called a corona wire) finally attaches the ink to the paper.

Because laser printers do not have mechanical heads, they are quick and quiet.

There are two different types of laser printer technology: "carousel" (four passes) or "tandem" (single-pass).

• carousel: with carousel technology, the printer passes over the paper four times to print a document (one for each primary colour and one for black, which in theory makes printing in colour four times slower than in black).
• tandem: a laser printer using "tandem" technology deposits each colour in one single pass. The toners are deposited simultaneously Output is as fast when printing in colour as it is when printing in black. However, this technology is more expensive because the mechanics behind it are more complicated. Therefore it is used only by middle to top-of-the-line colour laser printers.

LED Printer

Another printer technology competes with laser printers: LED (Light Emitting Diode) technology. With this technology, an electroluminescent diode printhead polarises the drum with a very fine light ray, making very small dots. This technology is particularly well adapted for obtaining high resolutions (600, 1,200 or 2,400 dpi).

Given that each diode is makes one point, print speed hardly affects resolution. Moreover, this technology lacks moving parts, which translates into less-expensive and more solid and reliable printers.

Printer Command Language

Page description language is the standard language that computers use to communicate with printers. Indeed, a printer must be able to interpret the information that a computer is sending to it.

The two main page description languages are:

• Printer command language (PCL): a language made up of binary sequences. The characters are transmitted according to their ASCII code
• PostScript language: this language, originally used for Apple LaserWriters, has become the standard in page description languages. It is a language in its own right based on a set of instructions

Print Servers

There are control boxes called print servers that allow you to make a printer with a USB or parallel connection available to a whole network.

Last update on Thursday October 16, 2008 02:43:13 PM.