6.5. Output devices − printers, plotters, projectors

Devices of output on a paper transmitter divide into printers, or print media, and plotters, or graphic devices. Consider that printers are intended mainly for the output of text (although can send to the printer graphic images), and plotters − for the output of graphic arts (it is although possible to print out texts also). Classification of devices of printing out on a paper carrier it is resulted in a table. 6.2.

The order of information output determines the volume of information, that is transmitted from buffer memory of peripheral unit for printing one memory access cycle.

The mechanical devices of output have shock operation principle − in the printers an image is recreated on a paper due to ink ribbon or paint which is coated on the surface of printing element. At the use of sensitive paper its color changes without carrier-paint.

Table 6.2. Classification of output devices on a paper carrier

Order of data output	A method of image registration at output	Principle of symbols forming on a transmitter	Working format	Design	Operation with a pan	Internal data output
Symbol	Mechanical	Character display	Mean-format	Uses a paper clamp and motion of pen	Roundabout is used	Vectorial
String	Unmechanical	Fullsymbol	Large-format	Drum	Roundabout is not used	Bit-mapped
Page			Small-format	Plane-table

In graphic devices for fixing of image use pencils, markers, ball point pens.

In unmechanical devices outputs the physical and chemical processes are used which arise up in the special transmitters at the action of different energy sources (light flow, magnetic-field, electrostatic voltage, laser ray). They are such types: electrosensitive, magnetic- (or ferro-) graphic, electrostatic, thermal and ink-jet.

The Fullsymbol devices of output have the limited set of symbols, that printed-in on a paper. The printing machines in which a character set is set once and for all during their making belong to such devices.

Character devices enable to print-out any images. To such output devices a plotters belong, and also mechanical printers of matrix type and all unmechanical printers.

After a working format – differ three types of output devices which have formats accordingly: А4 and A3; А2 and А1 and anymore А0.

The drum output devices are differed from previous design that a paper sheet is placed on a drum the rotation of which replaces the horizontal moving of sheet. In plane-table output devices a paper is immobile, and the output head moves in both directions.

Distribution of output devices by operation principle with pens is executed only for plotters. Plotters which use a roundabout, have the special storage for pens of different color, which is called roundabout and is placed one side from a paper sheet. If there is necessity of pen replacement, the output head moves to the roundabout, changes a pen and returns on previous a place for continuation of output. If a roundabout is not used and every pen is kept in the head, then the additional moving does not take place.

The vectorial output devices are used for presentation of output data, as a set of vectors in the system of coordinates X and Y.

The raster output devices are applied for presentation of images as a raster matrix, which during an output is scanned line after a line, that is why an image is consistently formed of points. The unmechanical output devices operate by such principle.

Most widespread are matrix and electrophotographic printers, ink-get and thermal devices of output on a paper transmitter.

Matrix printers. Operation principle of matrix printing devices is based on that a necessary image is recreated of a set of separate points which are coated on a paper by a corresponding method. So, in the coloured matrix printers a needles of output head "humer in" an ink from a ribbon straight in a paper (fig. 6.9).

Unlike usual monochrome devices, in last case use a multicoloured ribbon. Control system of these printers is charged with not only for a certain needle but also for the Fig. 6.9. Design of output colors of ribbon.

head of ninestylus printer:1 – stand - alone electrodrives for every needle; 2 − needles

Electrographic technology. The example of output device which uses еlectrographic technology is a laser printer, or plotter the chart of which is represented on fig. (6.10).

Basic parts of laser printer are a photoconductive drum 4, semiconductor laser 1 and precision optomechanical system 2, that moves the ray. A laser forms electronic image on light-sensitive photoreception coverage of drum consistently for every color toner (СМYК).

Before the acceptance of image line a drum is charged with the help of net which surrounds it. A net is under voltage, which results in appearance of ionized medium round a drum which charges it. A ray, getting on a drum, discharges some areas of drum. After forming of image line a step motor returns a drum for forming of next line.

If an image on a photosensitive layer is fully built, a sheet which is given is charged so that toner from a device 5 will get on a drum, and then attracted from a drum to the paper. After this image fastened on it due to heating of particles of toner to the melting temperature in a block 7. A toner contains a fusible matter − polymer or resin. At heating and increase of pressure powder is fused and united with a paper. The final fixing of image is carried out by the special rollers which press a molten toner to a paper.

Fig. 6.10. Laser printer: 1 − source of laser ray which is switched by a controlling microprocessor; 2 – six-sided mirror which sweeps a ray in a line; 3 − mirror of displaying; 4 − billow which gives from the special container coloring matter (toner) on drum; 5 − printing drum; 6 − cleaner of roll from a toner; 7 − block of image fixing.

Jetting technology presently is most widespread for realization of colour output devices. The simplified chart of jetting output device is represented on fig. 6.11.

Fig. 6.11. Chart of jet device

An ink comes in emitter under pressure from a nozzle. The block of acceleration electrifies and accelerates a drop thread. Thus each of drops receives a certain electric charge. In CB a flight path of drops changes by a help of deflection electrodes, and also there is turning on and off of stream. Thus the block of synchronization synchronizes operation of other devices.

The jet devices of output divide on the device of continuous and discrete action. The last, in turn, divide into two categories: with heating of ink ("bubble" technology) and with application of piezoeffect action.

Operation principle of device by technology of continuous action is based on that the stream of ink, which is constantly produced from the nozzle of printing head, gets or on a paper (for causing of image), or in the special transceiver, from where an ink again gets in a general reservoir. In a working chamber an ink is given by a micro-pump, and by element which predetermines its motion, usually there is piezosensor. However this operation principle is used presently in some of output devices.

For realization of discrete method with heating of ink there is a little element of heating in every nozzle of printing head, for example thin-film resistor. During passing of current through a resistor last for a few microseconds heated to the temperature about 500 °С and gives the distinguished heat directly to ink. An ink steam bladder, which appears in the process of the sharp heating, wants to push out a drop of liquid ink through the outlet of nozzle. As after breaking contact a resistor cools off quickly, then a steam bubble, decreasing in sizes, "sucks" through an nozzle inlet a new portion of ink, which takes seat of ejected drop (fig. 6.12).

Fig. 6.12. Chart of thermo-jet head:

1 − nozzle plate; 2 − card; 3 − corps; 4 − reservoir for ink; 5 − microresistor; 6 − the nozzle let

Another method for a nozzle controlling by discrete technology is based on the action of diaphragm, connected with a piezoelectric element. Piezoeffect consists in deformation of piezocrystal under the action of electric-field. Change of piezocrystal sizes, placed from one side of the nozzle outlet and constrained with diaphragm, predetermines throwing out of ink drop and lug of new ink portion

through inlet. Nozzles (channel lets) on the printing head of jet output devices, through which an ink is spraied, answer to the "shock" needles of matrix printers.

As a size of every nozzle considerably less, than diameter of needle, and an amount of nozzles can be more, then the got image in theory must be more clear. Unfortunately, in practice it is arrived at only in case of application of special link.

Thermal technology. Operation principle of output device with thermal transfer consists in that a thermoplastic coloring matter, deposited on the thin lining, gets on a paper exactly in a that place, where the proper temperature − about 70 ÷ 80 °С is ensured by the heating elements of printing head. Structurally such method of printing is simple enough, besides it provides almost noiseless operation. For causing of the coloured image it is needed three or four passage-ways: by once for primary colors and one time at the use of black that increases duration of printing accordingly. Surely, the special paper is needed for this purpose.

To thermal printers the printers of sublimations belong also, as for transference of image on the paper they use heating.

Sublimation of imager. At such method for a generation the imager is transfered from a ribbon by means of thermohead heating by a different temperature. Depending on a temperature there is transference of greater or less amount of transmitter, due to what the different tints of color appear. Such method of sublimation is the slowest. For printing use the special paper with coverage, in which imager accumulates.

Thermal wax transference. At thermal wax transference not such high temperature is used, as in a previous process, and only such, to melt a wax, covered on a ribbon. A wax flows down and hardens on a paper. Such method enables to print quickly, but this technology gives the best results on large areas which are covered by one color.

Thermal transference of dry resin (ТTDR). ТTDR analogical to the sublimation of imager. So, instead of that to carry one point from a ribbon on a paper, ТTDR-printers convert the special evaporated resin into a vapor. The purpose-made paper adsorbs fluid imager, due to what tints are created almost without a raster. Such printers use for printing of photo. This method of printing is mainly used in the printers АLРS, in which, however, use the sublimation of imager. Printers enable to print on different materials, using different imagers, in particular metallic.