2.- Computer - Printer
4.- Dot Matrix
6.- Thermal Wax Transfer
7.- Thermal Discoloration
Printers are output devices used to print characters or graphics from a computer. There are a variety of different types of printer, each of them has a different way of getting the image onto the paper or even a different type of paper. Also, each printer has a different speed, level of noise and cost. The quality of the printed image is determined by the printer's resolution, the number of ink dots which is capable of printing in an inch.
Printers are formed by a large number of components, the most important of which is the print head, common in the majority of printers.
The main types of printers are: daisy-wheel, dot matrix, laser, inkjet, thermal discoloration, thermal wax transfer, plotters and chain printers.
Computer - Printer
The printed image has to come from a source; this source is the computer. Using different types of program, an image can be created or a text can be written. Later, using one of the computer's COM ports, a signal is sent through an interface cable to the printer.
So that all the process can be completed, the computer has to know in what “language” to send the signal and how to communicate with the printer. There are some files called drivers (normally included in disks with the printers), which hold information about the device.
Inkjet printers are probably the most common type of printers because of their great advantages and their low cost. A colour inkjet such as Hewlett Packard's DeskJet 660C costs around 60.000 PTAs.
Inkjet printers hold a print head filled up with black or colour ink. When an image is sent from the computer to the printer, the print head circuits heat the ink until it is ejected outside of it and to the paper. At the same time, the print head moves horizontally through the paper so that a line of ink dots is left. Each time a line is finished, the printer moves the paper automatically to the next line. This process is repeated several times until the image is printed. Normally, print charges only contain three or four different colours so they have to be combined to obtain a variety pigments.
Inkjets can offer different print qualities, depending on which their print speed may vary, but usually a full colour page can take over 8 minutes to print. Another advantage of inkjets, is that they are quite silent, in comparison with daisy-wheel or dot matrix printers.
Dot matrix printers were the most popular a few years ago before inkjets arrived. Their printing system is based in the pins which make the print head. These prints can be ejected forming a pattern. In front of the print head, there is an ink ribbon hanging.
One a character has to be printed, the pins are fired onto the paper in the desired pattern. They meet the ink ribbon on their way, and this ribbon is the part which really hits the paper leaving on it small ink dots, forming a character. This process each time for all the characters of a document. By this method, the printer is also capable of drawing images.
The disadvantages of these printers are their low printing speed and quality, and the high amount of noise they produce. The ink ribbon also needs to be changed periodically. The price of these printers isn't extremely expensive although nowadays they are difficult to find.
Laser / Electrostatic
The way laser printers work is very similar to that in an office paper copier machine, except for, that in the printer the image to copy has been sent directly from the computer. Once the transfer process has ended, a laser source, guided by a mirror or prism, charges a cylindrical drum. The electrostatic charge, contained by the drum, attracts toner particles that later will become stuck to the paper in a pattern forming images or characters. So that the toner particles stay on the paper, and to prevent them from smearing, a heater roller bonds the toner permanently on the paper.
Although laser printers offer high quality graphics, they are not very popular because of their high cost of operation and maintenance (a toner charge can cost up to 50.000 PTAs), and because it is quite difficult to find one able to print in colour. Another great advantage of laser printers is the speed, which is in some cases incredibly high. Laser printers use to have high sizes although some companies such as OKI or Hewlett Packard have started selling some compact ones, the size of an inkjet.
Thermal Wax Transfer
The way thermal wax transfer printers work is very similar to that in a dot matrix printer. In fact, the print head in both is nearly identical, with the difference that pins in the thermal wax transfer print head are able to heat themselves. Also, the printer's ribbon has no ink, but coloured wax.
When the print head pins are heated and impact the ribbon, dots of wax are melted and transferred by impact to the paper where they cool down.
One of the great disadvantages of these printers is the problems that temperature can cause to the printed image because of the wax fragility.
A thermal discoloration printer uses a printing system very similar to the one in dot matrix and thermal wax transfer printer. The print head contains a variable number of metal pins. These pins are heated in a pattern according to the image desired. They are later ejected so that they contact the paper. This paper is special and changes colour depending in the temperature. That's why once the hot pins contact the paper, they create a pattern of little colour dots, which form characters and images.
The great disadvantage of these printers is the paper which can be damaged very easily by heat or sunlight. Also, it isn't very easy to find it and it is much more expensive than normal paper. These printers don't need ink ribbons or any type of ink cartridges so in some way they are cheaper than other computers.
The thermal printing system is also widely used in fax machines.
Plotter printers use a radically different print system than that in other common printers. They have no print head but a moving needle with a pen on the edge.
The needle uses a mechanism to move vertically and horizontally though the surface of the paper, while drawing the image. Depending on the type of plotter, the paper may be on a roller and both the pen and the roller move, but normally the paper is stationary and only the pen moves. The print head is also capable of changing between different pens with a different colour or line size.
Plotters are very used by people who need precision graphics such as architects. One of the great disadvantages of these printers, is their great cost and their big size.
Chain printers are in some way similar to daisy-wheel printers in that the print head requires a hammer-like movement to contact the paper and print a character. They are also similar in that they cannot print images because the characters or fonts are carved on the print head.
In chain printers, the print head is formed by a rotating chain which rotates at very high speed. Characters are embossed on the chain.
When something has to be print, the chain rotates until the desired character is in front of the hammer. Then the hammer hits the character on the chain, which at the same time hits an ink ribbon. This ink ribbon contacts the paper and prints on it the desired character.
These printers make a huge amount of noise but don't use to cost much. Another disadvantage is that they can only print one type and size of font and cannot print images.
A daisy-wheel printer prints characters by impacting a round printer wheel, which has letters on radial spokes, into an ink ribbon. At the same time, the ink ribbon impacts the paper printing on it the desired character.
Daisy-wheel printers make a great amount of noise and can only print a type and size of font. Another disadvantage of these printers is that they cannot print images.
Heathcore, P.M. Computing, 3rd Edition. London (1998). Letts Educational. Pgs. 336-338
Microsoft Encarta 96 Encyclopaedia World English Edition
Microsoft Encarta 98 Encyclopaedia
French, C.S. Computer Studies, 4th Edition. London (1993). DP Publications Ltd Pg. 161-168
Pau Latorre, PRINTERS
Pau Latorre, PRINTERS
|Enviado por:||Pau Latorre Costa|