Peripherals: Ink-jet printers and Daisy wheel printers

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Ink-jet printers

Like dot matrix printers, these create the shape of characters from a pattern of dots on the paper, but in this case the dots are created by squirting particles of ink from a fine jet. The quality is higher than that of dot matrix printers, almost as good as laser printers (see below), and being non-impact they are much quieter. Colour ink-jets are also available.

Ink-jets have recently come down in price, and they now compete directly with better quality dot matrix models. They are therefore likely to increase their share of the market in the future.

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Daisy wheel printers

The print head in this type of printer is a daisy wheel, a circular device with a diameter of 3 inches which resembles a daisy flower. The print characters are embossed on the tip of each 'stalk'. When printing, the wheel rotates to bring the required character uppermost, and a hammer strikes it against an ink or carbon ribbon and so produces the printed impression on the paper. The print quality is high, much better than that of dot matrix printers, and slightly superior to that of the current generation of desktop laser printers.

The cheaper daisy wheel printers cost about the same as the Epson FX-80 or equivalent dot matrix printers, but they are much slower, generally printing at 13 to 15 characters per second. A fast daisy wheel printer- that is, one printing at 40 or 50 characters per second - will cost several times this amount.

Because the print head is made up of preformed embossed characters, this type of printer is not as versatile as the dot matrix variety. It cannot print graphics, and if you wish to change the type style from e.g. normal to italics, you have to change daisy wheels.

clip_image003Laser printers

Laser-beam printers, commonly called laser printers, are page printers, meaning that they print an entire page at a time. In fact, they resemble photocopiers in size and appear­ ance (see Figure 3.3), and employ a similar technology. They are very fast, typical speeds being around 8 pages per minute, and virtually silent in operation. The print quality is good, almost equal to that of daisy wheel printers. The resolution of current models is 300 dots per inch (dpi), though some of the latest versions offer 600 dpi. Most laser printers can handle graphics as well as text.

They therefore offer the quality of the daisy wheel with the versatility of the dot matrix, while being faster and quieter than either. Their print quality is higher than that of ink-jet printers, but they are more expensive.

The print mechanism in a laser printer consists of a laser light, rollers, and ink, and works as follows. A sheet of

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Figure 3.3 The Centronics PP-8laser printer

paper is fed from a tray into the machine, and receives an electrostatic charge across its surface. The laser beam then rapidly and invisibly traces the computer's output (text or graphics) as a pattern of tiny dots on the paper, a process which removes the electrostatic charge from the points where the beam strikes the paper. The paper then receives a fine spray of ink across its surface, which adheres to the points with no charge but which is washed off the rest. After passing between rollers, the paper emerges, heated and dried, at the front of the machine.

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