Hard Copy Devices

Hard Copy Devices

Hard-copy devices for graphics workstations include standard printers and plotters, in addition to devices for producing slides, transparencies, and film output. Printing methods include dot matrix, laser, ink jet, electrostatic, and electro thermal. Plotter methods include pen plotting and combination printer-plotter devices.

The major factors which control the quality of a printer are individual dot size on the paper and the number of dots per inch. Printers produce output by either impact or nonimpact methods. Impact printer’s press formed character faces against an inked ribbon onto the paper. A line printer is an example of an impact device, with the typefaces mounted on bands, chains, drums, or wheels. Nonimpact printers and plotters use laser techniques, ink-jet sprays, xerographic processes (as used in photocopying machines), electrostatic methods, and electro thermal methods to get images onto paper.

In a laser device, a laser beam creates a charge distribution on a rotating drum coated with a photoelectric material, such as selenium. Toner is applied to the drum and then transferred to paper. Figure 2.10 shows examples of desktop laser printers with a resolution of 360 dots per inch.

Ink-jet methods produce output by squirting ink in horizontal rows across a roll of paper wrapped on a drum. The electrically charged ink stream is deflected by an electric field to produce dot-matrix patterns.