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Types of printer
Line printersMultiple copies of each alphanumeric character are distributed along a long cylinder which rotates at high speed. Hammers drive the paper against an inked ribbon, and against the cylinder, thus printing onto the paper. A whole line of printing is done at once, with the cylinder rotating one full revolution for each line of print.
Daisy wheelThe characters are on fingers around the edge of a disk, again using a hammer and inked ribbon to print.
Golf ballThe characters are distributed around the surface of a sphere approximately 1.5" in diameter. Again, a form of hammer and an inked ribbon is used to print.
Dot matrixAvailable in both 9 pin and 24 pin versions. Again uses an inked ribbon, but in this case the pins are driven against the ribbon and paper to print. The characters produced by 9 pin printers are obviously made up of a matrix of dots. The characters produced by 24 pin printers are less obviously made up from dots, but rounded characters still show the matrix. Best results are obtained from a typeface designed for the printer concerned. These are the cheapest type of printer to buy, with prices from around £ 90 upwards. These tend to be very reliable, the only consummable item is the ribbon, which cost from £ 5 upwards, depending on type. Colour versions are available, where the ribbon, instead of being all black, has parallel stripes of colour - the ribbon is lifted and lowered so that the required colour stripe is adjacent to the pins. Dot matrix printers are rather noisy in operation. They are very suitable for tractor feed paper.
InkjetStill uses a matrix principle, but instead of the pins and the ribbon, tiny jets squirt out a fast drying ink onto the paper. There are two types
Although still a matrix system, high resolution is obtainable, up to 720 dots per inch. They are silent in operation, and only slightly more expensive than dot matrix printers. However consummables are expensive, ie, the whole ink cartridge ( which on some models also includes the jets ) has to be replaced. Although they are not particularily expensive, these cartridges have a fairly short life.
LaserSimilar in operation to a photocopier. A drum made of light sensitive material which is also an insulator is electrically charged. A laser beam which is switched on and off scans across the surface of the drum - where the surface is irradiated with light, it becomes more conductive, and charge can leak away at these points. This results in the surface of the drum having a "picture" formed from the areas which have retained charge and the areas which have lost the charge. Now a second drum is used in close proximity to the first drum to spread toner over the surface of the first drum - the toner only sticks to the first drum on the areas where charge has been retained. A sheet of paper is rolled over the drum, and the toner is transferred to it, in the same way as the "picture" on the drum. The paper then passes over heated rollers to set the toner into the paper, and make the image permanent. Because the image produced on paper derives from an image produced on the drum, resolution is much higher than from matrix based printers. The laser printer is now the de-facto type of printer used in the office environment for single sheet printing like letters and similar documents. Laser printers cost more than twice the other types, with prices ranging from £ 220 up to £ 1000. Consummable costs are a bit higher, with a typical life from a toner cartridge around 3000 copies. Cartridge costs are higher than ink jet - some laser cartridges also contain a replacement drum - these cartridges cost a significant proportion of the original cost of the printer. The fact that a laser works by downloading a whole page at a time from the computer means that they are most suitable for single sheet printing. The fact that laser printers work in a similar way to photocopiers means that it is now possible to purchase printers that also function as free standing photocopiers.
© 1998 Ron Turner Return to the index page
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