Printing devices types. Printing devices, principle of operation, basic parameters. Gas bubble method

In a modern office, almost all tasks related to the accumulation, storage and processing of a wide variety of information are performed using computers. However, whether we like it or not, it is still impossible to switch to a fully electronic document management due to a number of different reasons, and it is unlikely to succeed in the near future. That is why a modern office computer cannot be imagined without input-output devices.

Scanners

Scanners are the eyes of a computer that convert analog images (drawings, photographs, typewritten text, etc.) into one or another electronic format for subsequent storage and processing using various software tools.

Scanners are divided into several types depending on how the media is loaded. The most common at present are flatbed scanners: the document to be scanned is placed face down on a flat glass plate (usually it is closed on top with a special cover), under which there is a movable carriage with a light source, an optical system and a line of photosensitive elements. During scanning, the carriage moves along an axis parallel to the long side of the flatbed and reads the image line by line from the media placed on the flatbed.

The current popularity of flatbed scanners is fully justified, since they are the most versatile devices that allow you to scan individual sheets, pages of books and magazines without stitching, and with certain skills - even small volumetric objects. At the same time, they are easy to handle and do not require regular maintenance.

Sliding scanners are arranged somewhat differently: in them, the light source, the optical system and the line of photosensitive elements remain motionless during the scanning process, and the carrier is pulled through the scanning unit using a system of shafts and rollers. Currently, such devices are used mainly for scanning large format media - A3 and more. The main scope of their application is the input of various drawings, diagrams, maps and similar large-format documents for CAD and GIS systems.

Traverse scanners are not as versatile as flatbed scanners, because they allow you to work with media only in the form of rolls or individual sheets; however, there are restrictions on the maximum and minimum thickness of the carriers.

Previously, handheld and projection scanners were also common, but with the development of technology, the former were replaced by cheap flatbed models, and the latter gave way to more compact and convenient digital cameras. It is worth noting that after leaving the mass market, hand-held scanners have retained a rather specific niche: they are now quite widely used to read bar codes in automated point-of-sale terminals and other similar systems.

Consider the most important characteristics of scanners that you need to pay attention to when choosing the right model.

Resolution is measured in pixels per inch (ppi), and the larger this value, the more detail you can digitize the original images. Manufacturers usually indicate two resolution values: optical and interpolated (for example, 600 and 19,200 ppi), but in fact, it is the first parameter that characterizes the scanner's capabilities.

Another marketing ploy that is quite common among manufacturers is the indication of different optical resolutions for the vertical and horizontal axes, for example, 1200 × 600 ppi. However, one should not deceive oneself in this case, since the real value of the resolution corresponds to the smaller of the given values. Generally speaking, the pursuit of high resolution in the context of choosing an office scanner is hardly justified, since scanning opaque originals in reflected light with a resolution of more than 600 ppi is impractical. The fact is that, for a number of reasons, the detail of the resulting image will increase very slightly, but the file size will be very noticeable. Perhaps one of the few exceptions to this rule is the scanning of color printed originals: using a higher resolution will better cope with the characteristic moiré that inevitably occurs in this case.

As an example, here are the resolutions needed to perform some of the most typical office tasks:

optical text recognition - 300-400 ppi;
copying color and black and white documents - 200-600 ppi;
input of photos and drawings for posting on Web sites, in electronic documents and presentations - 75-150 ppi;
input of photographs and drawings for reproduction on monochrome and color printers - 200-400 ppi.

The number of shades reproduced during scanning is determined by the bit depth, measured in bits per color channel. For color scanners, the sum of the three color channels is often given. For example, the inscription "24 bits" means that for each of the three color channels - red, blue and green - the bit depth is 8 bits per color; the maximum possible number of shades is about 16.7 million. A typical value for this parameter is 8 bits per color channel (24 bits RGB), and many models of modern flatbed scanners allow you to digitize an image with a bit depth of 12, 14 and even 16 bits per color channel (respectively 36, 42 and 48 bit RGB). It must be said that for office applications, increasing the bit depth does not make practical sense, since office applications, as a rule, do not allow processing and placing images with a bit depth of more than 8 bits per color channel in documents. Some time ago, you could still find black and white scanners, but today the vast majority of models allow you to scan in color.

The maximum size of originals that can be scanned for flatbed scanners is determined by the size of the flatbed; the most typical value is 216x297mm (it can scan documents of the most common A4 size), although sometimes there are models with an extended flatbed (216x356mm). A3 flatbed scanners (297×420 mm) are quite expensive and usually belong to the professional class. As for draw models, the situation here is somewhat different: if the maximum media width is determined by the physical parameters of the device (the width of the feed path), then the limit on the allowable length is imposed by the driver and the software used.

With a heavy load on the scanner, its performance becomes very critical, which depends on the scanning speed. It is worth noting that this parameter even for the same model varies depending on the resolution: the higher the resolution specified in the settings, the slower the scanner works. In addition, the overall performance of the scanner is affected by the pre-scan speed and warm-up time. It should also be noted that when setting high resolution values, the bottleneck may not be the scanner itself, but the interface used to connect it.

For some flatbed scanner models, Auto Document Feeders (ADF) are available, which may be included as standard or sold separately. The use of such a device (which is usually installed instead of the standard tablet cover) allows you to increase the productivity of the scanner when entering a large number of originals of the same type on separate sheets, for example, ready-made forms (questionnaires, questionnaires), voluminous typewritten texts, etc.

Today, the most common interface for connecting scanners is USB 1.1. Recently, expensive models of flatbed scanners are equipped with higher-speed interfaces - USB 2.0 and IEEE-1394. Unlike USB 1.1, USB 2.0 and IEEE-1394 controllers are still rarely found as standard in office computers, so connecting scanners with these interfaces will most likely require the installation of an appropriate board.

Among the oldest and cheapest scanners, you can still find models equipped with SCSI and even a parallel IEEE-1284 interface, however, in modern conditions, the acquisition of such devices can hardly be considered expedient.

Printer types

The undisputed leader among office printers today are A4 and A3 monochrome laser printers. They have high productivity, low cost of prints and are able to withstand heavy loads. Another advantage is the consistently high quality of prints, almost independent of the type of paper used.

Recently, there has been an increase in the popularity of color laser printers. A few years ago, these were very expensive and low-performance devices (due to the use of a four-pass process, the print speed in color mode was much lower than in monochrome), but today the prices for color laser models have dropped significantly, and many manufacturers have mastered the production of devices that allow print both monochrome and color images equally quickly.

In many ways, LED printers are similar to laser printers. Due to the use of a simplified (compared to laser) imaging technology, these devices are cheaper than laser ones; however, at the same time they are inferior to the latter in terms of the quality of the resulting prints and performance. Now many manufacturers produce both monochrome and color LED printers.

Currently, the market has a very wide range of models of laser and LED printers - from desktop personal to network corporate. As a rule, small desktop models have minimal configuration expansion options and are usually used in small departments for this reason. If we talk about laser and LED printers at the level of medium and large workgroups, then almost all of them are a kind of constructor: the required number of different functional modules (additional trays for supplying various media, sorters, booklet makers, finishers, etc.). In addition, there are opportunities to expand the configuration of the base device by installing additional components (memory modules, hard drives, font cartridges, network adapters and print servers, page description language interpreters, automatic two-sided printing modules, etc.). Thanks to this, it is quite easy to change the set of functionality of the printing device, depending on the needs of the department in which it is used.

Inkjet models are also quite widespread in offices, the vast majority of which are colored. Their use is justified in cases where there is a need for color documents, and the average monthly print volumes are small. It should be noted that if the cost of inkjet printers themselves is much lower than laser or LED, then the cost of consumables and, consequently, the cost of a copy is much higher. I would like to draw attention to the fact that three or four years ago, offices used mainly personal models of inkjet printers (since there were practically no others), and today a separate class of corporate inkjet printers specially oriented to office tasks has already emerged and is actively developing. . They are distinguished from personal models by higher productivity, the use of high-capacity cartridges, a long service life and the maximum allowable monthly load, as well as a lower dependence of the quality of the resulting images on the type of paper used.

Large-format inkjet printers stand somewhat apart, however, since they are used to solve quite specific tasks, we will not consider them in this article.

Despite the fact that today dot matrix printers have almost completely lost their positions in the market for personal printing devices, they are still produced and actively used in various organizations. Of course, matrix devices cannot boast of high performance and low noise levels, but thanks to a simple device, they are distinguished by very high reliability and extremely low cost of prints. But the secret of their longevity lies not in this, but in the fact that these are the only percussion printers that are widely used today (in addition to the dye dots, a relief mark remains on the paper), and the specifics of the activities of a number of companies require the use of just such printers when filling out official documents and forms. (for example, rail and air tickets).

It is impossible not to mention the rather exotic devices that are relatively rare in offices - thermal printers. The most famous representatives of thermal printers using solid dye thermal transfer technology are the devices of the American company ALPS and their OEM versions, also produced under the brands Citizen Printiva and OKI. These devices have a rather low printing speed and a very high cost of copies, but they also have a number of undeniable advantages: the use of a solid dye provides a very high resistance of prints to mechanical and chemical stress, and the resulting image is practically independent of the type and quality of the media coating. In addition, when using special media, printed images can be transferred to fabric and to the surface of various objects. It is also worth noting that cassettes with dyes of non-standard colors (for example, white, green, silver, bronze, gold, etc.) are produced for these printers. One of the most typical applications of thermal printers is the production of small runs of souvenir and representative (business cards, forms, invitations, etc.) products.

There are also specialized thermal printers designed for printing images on the surface of CDs. Examples include the Inscripta printers from Primera Technology Corporation and the Perfect Image Prism printers from Rimage Corporation. Such devices can be a good solution for departments whose activities are related to the distribution of various products and information materials on CD and DVD media.

Now that we have familiarized ourselves with the main types of printing devices common today, let's move on to reviewing the main characteristics of printers.

Main characteristics of printers

Resolution is measured in dots per inch (dpi). The larger this setting, the more accurately the printer can reproduce output images: when printing text and monochrome drawings, this means higher image detail, and for grayscale images, the ability to transfer more shades with the same lineature. A resolution of 300-600 dpi is sufficient for printing text documents, while a resolution of 720 dpi or more is required for high-quality output of grayscale and color images.

Currently, manufacturers use various technologies in their products to increase the number of reproduced halftones without increasing the resolution. In addition, it is worth noting that in practice, printers from different manufacturers with the same resolution do not always provide the same quality images.

Printer performance is determined by several parameters: warm-up time, screening speed, and the speed of the printing mechanism. The warm-up time depends on the printing technology used: if inkjet and dot matrix printers are ready for use almost immediately after being turned on, then laser and thermal printers take a certain time (from several seconds to several minutes) to enter the operating mode.

Depending on the design of a particular device, screening of the printed image can be performed both by the driver (which is typical for most inkjet and matrix devices, as well as entry-level laser printers), and by a specialized processor of the printer itself (this solution is usually used in medium and large laser and in some inkjet models). In the first case, the rasterization time is largely determined by the configuration of the computer from which the document is sent for printing. Other things being equal, the rasterization time depends on the resolution set in the print settings: doubling the resolution value will quadruple the size of the raster image of the page, which will significantly increase the time required to process the document and send it to the printer.

Printer manufacturers in the technical specifications of their products usually indicate only two parameters: the maximum speed of the printing mechanism and the first page out time after sending the document to print. However, it should be borne in mind that, unlike laser and LED printers, the speed of operation of the printing mechanisms of inkjet, matrix and some thermal devices significantly depends on the set resolution and page coverage; thus, the actual figures for these printers may be significantly lower than those declared by the manufacturer.

Media requirements typically include a list of media types suitable for a particular device (plain paper, specialty papers, envelopes, postcards, labels, cards, transparencies, etc.) and the acceptable weight range, or specific gravity, for each type of media (usually indicated in grams per square meter, g/m 2; in addition, a limit on the maximum thickness of media is sometimes indicated). Please note that these settings may vary depending on the feeding method (manual or automatic) and the use of various options (auto duplex unit, booklet maker, etc.).

The capacity of the input and output trays is specified in the printer specifications. Most often, this parameter is calculated for sheets of plain paper with a density of 60 or 75 g / m 2.

Speaking about an office printer, one cannot fail to mention the integration of this device into a local network. Various solutions can be used for this, the most common of which is to install a special network adapter or print server in the printer. Naturally, when choosing a printing device, it is necessary to clarify whether the range of network adapters and print servers offered by the printer manufacturer has modules that are compatible with the projected or existing local network of the enterprise or division.

Optimizing Printer Usage

Any system administrator working in a more or less large office is well aware that the load on printers is extremely uneven - periods of temporary calm are suddenly replaced by spontaneous bursts of employee activity, and even high-performance network printers can not always cope with an avalanche of documents falling on them. Here is the most typical situation: one of the users sent a report of several hundred pages to print - as a result, other employees have to wait until their one-two-page letters and invoices are printed.

It is quite obvious that the purchase of additional printers is unlikely to effectively deal with such situations and, moreover, will entail additional financial costs. But it turns out that you can get by with the existing fleet of printers if you increase the efficiency of their use.

The essence of the solution is as follows: the printers available to this unit are combined into a cluster, the operation of which is controlled by a common print server. Using this scheme provides a number of advantages over the more traditional connection of individual network printers.

One of the most illustrative examples is the parallelization of printing when outputting large documents or a large number of copies. This is implemented as follows: when the minimum number of pages specified in the settings is exceeded, the document sent for printing is divided into several parts, which are printed in parallel on different cluster printers (the user who sent the task will receive a notification on which devices the parts of the document were printed on). This allows not only to reduce the time for obtaining a finished document, but also to evenly distribute the load between the devices included in the cluster. In addition, the cluster controller can redirect jobs in case of failures: for example, if any of the printers runs out of toner or paper jams, all jobs sent to it will be redirected to another device, and users will receive appropriate notifications.

It must be said that from the user's point of view, the printing procedure also becomes simpler: instead of several different printers, the menu remains one universal printing device, to which all tasks are sent, and the choice of the most suitable printer for printing a specific document is controlled by the cluster controller.

Examples of cluster printing solutions include JetCAPS ClusterQue (a joint development between Hewlett-Packard and LBM Systems) and Callisto (a Canon development).

Multifunction devices

it is false to say which of the developers first came up with the idea to combine the printer and scanner into a single device. Yes, it is, in general, and it does not matter. The benefits of such a symbiosis are obvious: the user receives one device that can perform the functions of three different devices at once - a scanner, a printer and a copier, and if you add a fax module, then four. Of course, this solution is cheaper than three or four separate devices and requires much less space. True, some disadvantage in this case is lower reliability: for example, if the power supply fails, you will simultaneously lose the ability to use all devices at once, and if you run out of toner or ink in the printing module, you will not be able to use not only the printer, but also the copier.

Be that as it may, for several years multifunctional devices have been in steady demand, and manufacturers regularly update the lineup of these office combines. Currently, there is a fairly clear division of multifunctional devices into two large groups: compact desktop devices and large corporate complexes.

Multifunctional desktop devices are distinguished by a variety of appearance and technical solutions. On sale you can find multifunctional devices built on the basis of both broaching and flatbed scanning modules. If we talk about the printer part, then it can be an inkjet (color or monochrome) and a laser (usually monochrome) printer. Typically, such devices provide the ability to connect to a computer via a bidirectional parallel interface IEEE-1284 and / or USB.

As for corporate multifunctional complexes, they are often high-performance digital copiers equipped with a computer interface. Typically, they are equipped with a laser printing mechanism (color or monochrome) and a flatbed (less often - traction) scanner module with an automatic document feeder. Similar to corporate laser printers, many multifunctional systems can be expanded by installing additional components and external functional modules.

ComputerPress 9 "2002

Dot matrix, petal, inkjet and laser printers are used in PCs.

Dot matrix printers are the most common. Printed characters are synthesized in dot matrix printers using a needle matrix (head) moving along each printed line along a special guide and hitting the ink ribbon. The most commonly used printers with 9- and 24-needle heads. These printers allow you to get print quality that is quite acceptable for most applications, including through multiple passes when printing one line with small offsets. However, this reduces the already low print speed. The disadvantage of dot-matrix printers should be considered a rather significant level of noise produced during printing.

When choosing a dot matrix printer, you should pay attention to the maximum width of the paper used ("narrow" or "wide" printer), the possibility of using roll paper, the number of needles in the matrix (head), the print speed indicated in the passport data. An important characteristic of a matrix printer, also indicated in its passport, is the number and types of built-in fonts and the ability to print Cyrillic. At the same time, most modern word processing software systems (Word, Word for Windows, Word Perfect, Lexicon, etc.) include special "downloadable" fonts (soft fonts).

The print quality provided by dot matrix printers is practically not inferior to the quality provided by a typewriter, but it is completely insufficient when working with graphics, as well as for making original layouts that could be used in printing.

Laser printers have a variety of printing options, provide high quality at a significant speed.

Laser printers have their own expandable memory unit. They allow scaling fonts, wide use of "downloadable" fonts. The "passport" print speed for various models of laser printers, as a rule, ranges from 4 to 16 pages per minute. However, this speed depends on the amount of the printer's own memory and can be noticeably reduced if it is insufficient for the specific information being printed.

Laser printers use only sheet paper (A4, A3, etc.), and therefore the capacity of the paper feed tray becomes essential, since the speed of the printer depends on it: the paper must be periodically put into the tray manually. The disadvantage of laser printers is rather stringent requirements for the quality of paper - it must be sufficiently dense (usually at least 80 g) and must not be loose, printing on plastic-coated paper, etc. is unacceptable.

Laser printers are especially effective in the production of original layouts for books and brochures, brochures, business letters and other materials that require high quality. They allow you to print graphics, drawings at high speed.

In recent years, a whole range of laser printers has appeared, providing not only black and white, but also multicolor color printing.

Even the simplest models of laser printers are five to ten times more expensive than the average models of dot matrix printers, and the price of color laser printers is more than a hundred times higher than the price of dot matrix printers. Very expensive and replaceable cartridges containing coloring powder. All this makes laser printers unsuitable for the production of large print runs, since printing one sheet is much more expensive than a photocopy.

In recent years, inkjet printers have become more and more widespread among PC users. This type of printer occupies an intermediate position between dot matrix and laser printers. Inkjet printers, being line-by-line printers like dot-matrix printers, provide print quality approaching the quality of laser printers. They are easy to use and operate almost silently. When working under the control of appropriate software, inkjet printers allow you to print graphic materials that are quite satisfactory in quality. At the same time, the print speed provided by inkjet printers is not much higher than the print speed of dot-matrix printers, and their cost is two to three times higher. Inkjet printers are used quite successfully in all cases where print speed and quality are not critical factors. Coloring liquid ("ink") for inkjet printers is placed in special compact cartridges. It is produced in several colors, so that by simply replacing the cartridge, you can print multi-color images. A number of models of inkjet printers allow simultaneous multi-color printing.

Graph plotters (plotters) are used to output graphic information to a PC. Plotters are much cheaper than laser printers, although their output speed is much slower. The advantage of plotters compared to laser printers is also the ability to use large-format paper and film for printing (up to AO format). Plotters are available in two types - roll and flatbed. In roll plotters, the paper sheet is moved by the transport roller in the vertical direction, and the writing unit - in the horizontal direction. Roll plotters produce good quality full color images. In flatbed plotters, a sheet of paper is fixed horizontally on a flat table, and the writing unit (one or several multi-colored pens) moves along guides in two directions - along the X and Y axes.

In this article I will talk about the types of printers and their differences. We will consider laser, inkjet, CSLF and other types. We will figure out which one to choose for home or office.

- This is a device designed to print information from a computer onto paper, or, as they say in "computer" language, onto a solid medium. In this case, the process of transferring information is called printing, and the resulting document is called printing.

Today there are already hundreds of printer names, and maybe thousands. They differ in the principle of operation, in the number of colors, in the type of ink and printed material, in purpose - in general, everything cannot be counted. And each of these types can still have their own characteristics and additional functions.

Today, the so-called multifunctional devices (MFPs), which combine a printer, a scanner, a copier, and even a telefax, are widely used.

Matrix printer

The dot matrix printer mechanism (the oldest type of printing device used today) was invented by the Japanese back in 1964.

The principle of its work, in general, is simple. The image on the sheet is created using a print head, consisting of a set of needles (matrix), which are driven by electromagnets.

The head moves line by line along a sheet of paper, and the needles hit it through the ink ribbon, leaving an imprint - a dot image.

In different devices, the print head can consist of 9, 12, 14, 18 or 24 needles. Of course, the quality is better where there are more needles: more dots - the image is clearer.

Dot-matrix printers, although already pushed out of the office by more modern devices, are still used in certain areas. So, the printing of sales receipts is based on this principle of work.

Low quality, akin to the operation of a typewriter, no longer allows the use of matrix devices in other areas. In addition, among the disadvantages of these printers are low print speed and noisy operation.

Although the rare device is not without advantages. For example, it can work in almost any conditions and with any paper size, and "needle" prints are not only resistant to friction and moisture, but also greatly complicate the forgery of documents.

Jet printer

The principle of operation of an inkjet printer is similar to the operation of a matrix printer: an image is created from dots. Only instead of heads with needles, they use a matrix (head) that prints with liquid dyes.

The print head can be built into the dye cartridge or fixed in the device itself (in this case, replaceable ink cartridges are used, and the head is not dismantled).

Printers with built-in matrix are produced by companies such as Epson and Canon. Hewlett-Packard, Lexmark use an approach in which the print head is built into the cartridge.

"Jeters" have their own classification according to many criteria. So, they differ in the type of ink used.

Ink can be:

water (used in most household and office devices);
oil (used for industrial marking);
pigmented (the best option for obtaining high quality images - photos, for example);
solvent (used for printing outdoor advertising, posters, stands, as they are resistant to water);
thermal transfer (with their help, an image is applied to clothes).

There is also alcohol ink, but they are not widely used because they dry very quickly on the head.

There are several types of "stringers" and for their intended purpose. After all, if the application of the principles of the matrix printer today is limited to the banking sector, then inkjet printers are used in many areas. So, according to their purpose, they can be:

office (those that are in most offices - for printing on paper of small formats);
widescreen (used in the field of outdoor advertising);
interior (for printing posters, stands and other elements of interior design);
marking (from the name it is clear - for marking various kinds of parts);
photo printers (for photo printing);
souvenir (used for printing on small items - disks, phones, blanks of complex shape);
manicure (an innovation in beauty salons is an apparatus for applying a complex pattern to nails).

Most offices use, you guessed it, an office printer. It is quite suitable for domestic needs - outputting text or images to paper - and is produced by many companies: Epson, HP, Canon, Lexmark, etc.

Office printers, like photo printers, are equipped with one head per color and have very good color reproduction (especially with constant use). In addition, compared to matrix, office "inkjet" work quite quietly.

But the print quality can be high only if paper with a special coating is used - on a regular office, the edges of letters or a picture can “shake”.

The print speed surpassed dot matrix printers by only a few seconds. At the same time, prints are exposed to water, fade, smear (although much depends on the quality of the ink).

In addition, the device is rather capricious: uninterrupted operation is possible only if all cartridges are regularly printed (with a long stagnation, the ink on the head simply dries up).

But the main disadvantage is the high cost of maintenance. Cartridges run out of ink fairly quickly and need to be replaced periodically, which is expensive.

This problem was partly solved by CISS - a continuous ink supply system.

Continuous Ink Supply System

CISS is a system that successfully replaces cartridges. The essence of its work is simple - ink is supplied automatically through special tubes.

The print quality is greatly improved, and the money in your wallet is saved. You only need to periodically buy paint and pour it into special containers, which is much cheaper than changing cartridges. Yes, and the ink lasts for a long time.

Refueling of CISS can be carried out by the user himself - this does not require the help of a specialist.

If earlier it was possible to install such a system only on purpose (additionally), now there are already printers with a built-in CISS on sale.

The first models appeared in the fall of 2011, and they were Epson L100 and Epson L800.

Laser printer

Laser technology (and to be precise, electrographic technology) appeared as early as 1938. This printing method, first called electrography, then xerography, and today better known as laser printing, is characterized by speed, economy and high quality prints.

The main part of the device is the so-called photodrum, which stores an electric charge on the surface, and it is “own” at each point.

The laser beam, falling on the drum, "illuminates" individual points of the drum, removing the charge from them. By controlling the beam, you can "draw" on the drum with charged and uncharged areas.

Particles of a special composition (toner) wake up on the drum and stick only to charged dots, thereby forming an image. It is transferred to the paper, "melting" into it under the influence of high temperature and pressure.

This technology gives a very good result: the print speed is much higher than in an inkjet printer (even in a personal laser printer - 10-20 pages per minute).

The print quality is also very high, in addition, the print is resistant to friction and moisture and holds color well, which previous devices cannot boast of.

The advantage of a laser printer is its ability to print on almost any paper without losing print quality.

But, of course, this device is not perfect. Among the minuses are the high cost (although the issue is debatable: a laser printer is more expensive than an inkjet when buying, but much cheaper to maintain) and not always high-quality color reproduction.

As a drawback, edge distortions are also distinguished - a change in the shape of letters or a pattern along the edge of the sheet (for example, an oval dot). However, this problem is now solved with the help of specially shaped lenses.

Light-emitting diode printing (LED)

An offshoot of laser technology is LED printing. Their difference is in the light source. Instead of a single laser beam - a whole line of LEDs. Each point in the line has its own LED, so the light source does not move, unlike laser technology.

This is the first advantage: less mechanics - higher level of reliability. The second advantage is high speed (from 40 pages per minute). In addition, the print quality is better than that of a laser printer because there is no edge distortion.

However, the LED printer has one significant disadvantage - the high cost.

Other types of printers

There are many other technologies that have not taken root for some reason, or those that are used only in certain areas. So, sublimation printers as an alternative to inkjet, they are still not widely used in office printing, but are successfully used, for example, in printing. They have a very high level of color reproduction and picture quality.

drum printers also already out of use, although the speed of their work was and remains the highest among all existing printing devices.

It got its name thanks to the main element - a drum, equal to the width of the sheet, with a relief image of letters and numbers.

The drum rotated, and at the moment the desired character passed over the sheet, a special hammer hit the paper, imprinting a letter or number through the ink ribbon. Printouts from such a printer are recognizable: their font is similar to a typewriter font, with “jumping” letters.

Petal (or daisy) printers according to the principle of operation, they are similar to drum ones, only a set of letters was located on the flexible petals of a disk that rotated.

The desired petal was pressed against the ink ribbon and paper, leaving an imprint. It was possible to get a color print by putting a ribbon of a different color.

Over the history of its development, printers were not only drum and daisy, but also ball, caterpillar, chain. They differed in the principle of action, but, apparently, none of them became widespread. Their first places in the popularity rating today are occupied by more “smart” devices: inkjet and laser.

How to choose a printer

Choosing the right printer is, in general, a rather difficult task. But solvable. You just need to decide for what purpose you need a printing device.

Office or home?

In general, the difference between a “home” and an office printer is in print volumes.

Usually the user, even if he prints "a lot", is enough for 400-500 pages per month. In the office, this volume can be ten times more.

Therefore, "laser" (as well as LED, by the way) is more often chosen for the office, and "inkjet" - for the desktop at home. If you need a large amount of printing at home, a CISS is installed.

The purchase as a whole can be relatively inexpensive - from thirty to one hundred dollars.

Print Quality

In general, print quality is a rather ambiguous parameter. Often it is determined according to the principle "like it - do not like it", and, as you know, they do not argue about tastes. However, there is also an objective characteristic - resolution (dpi). It depends on him how clear the printout will turn out.

Standard resolutions (within office printing) are: 600, 1200, 2400 pixels per inch. The bigger, the better.

But still, you should not chase after this parameter - almost all modern models have a high resolution.

Printing cost

When choosing a printer, you should focus not only on the cost of the device itself, but also on the cost of its maintenance in the future.

If you plan to print a little, and at the same time want to save on paper and consumables, you can choose an inexpensive printer model with a small amount of possible load.

For those who plan to print a lot, a more reasonable option would be an expensive printer with a fairly large monthly load and expensive (but economical in operation) consumables.

In general, as practice shows, when choosing, there is one pattern: the more expensive the printer, the lower the cost of printing. But this is true only when it comes to the basic configuration, without the "bells and whistles".

The price can be "wound up" due to additional devices like memory, a duplex device, additional paper trays and other features, which, by the way, are not always really necessary and useful.

Significantly increases the price of the printer wireless connection method.

Of course, a multifunctional device (MFP) will cost more (and at times) more. However, if you set out to purchase a printer, scanner and photocopier in one, think carefully about whether you really need all three functions.

There is one more thing to be said about prices. Fortunately for the buyer, competition among manufacturers is quite high. And this means that they cannot afford to raise prices unreasonably.

And yet, the difference between printing devices of the same class from different manufacturers can vary between 10-15%. And these amounts are often nothing more than an overpayment for a name.

Rice. 7.3. Classification of printing devices

The type of printing device (its name) is determined by a number of classification features. The most widespread in professional PCs are small-sized character-synthesizing impact printers, as well as non-impact printers using inkjet, thermal contact, laser and other printing methods.

Impact printers. Such printing devices use printing mechanisms with an impact method for writing characters on a medium using an ink element (ribbon). In the process of imprinting, the impact elements (needles, hammers) or the type carrier are mechanically moved. The advantages of these printers include: the ability to obtain several copies simultaneously with the original, the use of conventional paper grades, and moderate cost. As disadvantages, we note: the complexity of manufacturing mechanical and electromechanical parts and assemblies, increased noise level, relatively low reliability due to a significant number of moving parts and assemblies. In character-synthesizing impact printing devices, the image of characters is formed by combining individual elements (points, segments, lines, etc.). The entire field of the printed character is divided into individual elements in the form of a matrix, called the decomposition matrix. The contours of the symbol are made up of the corresponding elements of this matrix and in appearance resemble a mosaic. Therefore, character-synthesizing printers are often also called matrix or mosaic printers. The printhead in a dot matrix printer contains a set of vertically arranged needle print elements that operate independently of each other when the corresponding control electromagnets are turned on (Fig. 7.4).

Distinguish between matrix impact printers of serial (character-by-character) and parallel (line-by-line) types. In sequential type devices, the print head slides along the rails parallel to the ink ribbon and sequentially, column by column, forms the corresponding character. The needles press the ink ribbon against the paper and form the required symbol configuration. In some cases, a special paper with a heat-sensitive coating is used instead of an ink ribbon, which darkens where the needles touch it. In sequential dot matrix printers, 9-needle printheads, which move along the length of the printed line, are most widely used. However, for high quality printing and high print speeds, sets with a large number of print needles, such as 12, 18 or 24, are often used.

In dot matrix printers of the parallel type, the elements (needles) of the print head are located along the entire length of the line. They allow you to print the characters of the entire line in parallel, so they are called bitmap. Despite the high printing speed (up to 1000 lines per minute), raster printers have large overall dimensions, weight, noise level, cost compared to serial devices, and are of limited use in PCs.

The print quality depends on the size of the decomposition matrix and increases with the increase in the number of dots in the matrix (partial overlap of printed dots is possible). The most commonly used matrices of the following sizes: 9x7, 9x9, 11x9 dots - for normal quality printing; 18x18 dots - for high quality printing; 35x16, 60x18 or more dots - for high quality printing. Sophisticated models of dot-matrix printers produce very high print quality, almost indistinguishable from typewriter print quality. Multi-pass forward and/or reverse printing is also used to improve quality. Since there is no permanent character carrier in matrix character-synthesizing percussion printers, its functions are performed by an electronic character generator. The number and nomenclature of printed characters are determined by the capacity of the character generator. A permanent set of printed characters (various national sets, fonts, graphics and other symbols) - a permanent character generator - is recorded in the ROM of the print control unit. Modern matrix printing devices are equipped with character generators downloaded from a PC, where the user can write down the characters he needs. In this case, the dot matrix printer provides direct addressing to the impact elements of the print head.

Matrix character-synthesizing devices, in addition to the output of alphanumeric information, as a rule, can also output graphic information. Element-by-element descriptions of graphic images are stored in the RAM of the print control unit.

The widespread use of color displays in recent years has led to the accelerated development and introduction of multicolor dot matrix impact printers. Usually an ink ribbon is used with four ink lanes: black and three primary colors - cyan, yellow and red. Two basic printing principles apply. In the first case, in one horizontal pass of the print head, only one color is printed, and then repeated passes with other colors. In the second, due to the movement of the ink ribbon in the process of one pass of the print head, all the required colors are printed. All this requires the complication of the printing device, and, consequently, increases its cost.

Thus, character-synthesizing impact printers of a sequential type are characterized by: low power consumption, small overall dimensions, the ability to change the set of symbols used and display graphic information over a wide range, and moderate cost. However, the print speed is relatively slow.

Sign-printing percussion printers with a chamomile-type petal type carrier provide higher print quality and higher reliability compared to character-synthesizing ones; they are usually used to display text information. The image of symbols in them is formed by a ziak-forming element (letter) that has an image of a symbol. The printing mechanism of such a device includes (Fig. 7.5): a thin steel disk with many petals (“chamomile”), each of which has embossed letters (letters, numbers, etc.); an impact lever (hammer) with an electromagnet, which can press the necessary letter to the paper through the ink ribbon, i.e. print this or that character; an electric motor that rotates the “chamomile” and brings the necessary petal to the desired percussion lever before imprinting.

The typical number of petals used is 50 ... 100. Due to the limited set of printable characters determined by the letter carrier, if a different set of characters is required, a change of the print head is required. The print speed is also low (20...80 characters/s). These circumstances led to the replacement of petal percussion printing devices in the PC with sign-synthesizing ones.

Both character-synthesizing and character-printing devices have fundamental disadvantages: speed close to the limit values, high noise level, complexity, and insufficient reliability. Therefore, intensive development of non-impact printing devices free from these shortcomings is underway.

Non-impact printing devices use non-contact printing methods or methods in which contact between the recording element and the paper carrier is negligible. As a rule, non-impact printers require special paper or ink media, they do not allow you to make copies of the document. In these devices, signs are formed by changing the properties of the substance on the carrier under the influence of thermal, chemical, electrical, electromagnetic, light or other effects, or by applying a recording substance in an inkjet or other way.

Impactless inkjet printers are characterized by low noise level, high print speed (up to 200 characters / s or up to 1 ppm), high resolution (up to 200 dots / cm) and print quality by converting a dot image on paper into more uniform (due to ink flow), the ability to display arbitrary graphics, as well as multi-color printing.

The recording body - the print head (Fig. 7.6) - contains several (usually 12) emitter capsules (injectors) with thin nozzles with a hole diameter of 0.01 ... 0.1 mm. Excessive pressure is created inside the capsule, and under the action of vibration (wave impulse) the recording body doses and ejects the ink jet through the nozzle towards the paper medium. Ink droplets are charged from a high-voltage source and, under the action of an accelerating electric prison, are directed to a roller that feeds paper and is one of the electrodes. The input signal modulates the flow of droplets in a manner similar to the modulation of an electron beam in a CRT. Small droplet diameter (0.03...0.2 mm) and high frequency of their generation provide high resolution and printing speed. The movement of the ink jet on the paper is controlled by deflecting plates. As a recording coloring liquid (ink), solutions of organic dyes are used, which have a high surface tension, high electrification and good absorption into paper.

There are two ways to apply drops to paper. The first is a continuous method, a continuous jet of drops flows out of the nozzle, passing through the electrostatic control system and falling either on paper or in a special collection

In the second method (pending), the capsules with the coloring matter give out a jet of ink only during the formation of the required character

Rice. 7.6. The principle of operation of the inkjet printer:

1 - paper moving roller; 2 - paper; 3 - deflecting plates; 4 - focusing electrode; 5 - control unit; 6 - nozzle; 7 - piezoelectric crystal; c - ultrasonic generator; 9 - pump; 10 - ink tank; collection of waste ink; 12 - formed symbol

Rice. 7.7. Color ink jet printer:

1 - cassette with three types of ink; 2 - tank for ink residues;
3 - ink receiver; 4 - needle regulators; 5 - bubble separator;
b - hose pump for ink; 7 - return of waste ink; 8 - cleaning switch block; 9 - central processor; 10 - drive control inkjet mechanism; 11 - secondary tank; 12 - transfer tank;
13 - drive control unit; 14 - wiper motor;
15 - protective cover; 16 - pulsating jet head

Standby ink jet printers are simpler in design (Figure 7.7) than continuous ink jet printers, use less ink, and are therefore cheaper. However, their performance is lower than continuous-flow ones. By increasing the number of nozzles in the print head and using ink of different colors, ink jet printers make it possible to obtain color images by combining primary colors.

The main factors hindering the widespread use of inkjet printers in PCs are:

constructive and technological complexity; the need to use special ink; the need to use special grades of paper that provide absorption acceptable for a given type of ink; low reliability of the print head (possibility of clogging of nozzles and capillaries, drying of ink); high cost, etc.

Thermal printers are low-speed printers (up to 30 characters per second sequentially) and are therefore not designed for use in high-volume systems. They are compact, low noise, provide satisfactory print quality, have a relatively simple design and low cost.

Thermal printing requires special heat-sensitive paper that changes color when exposed to heat generated when heated. The registering body in thermal printing devices is a thermal printing head (Fig. 7.8). The main part is a rod (usually glass), on which a matrix of point resistive heating elements, contact pads and conductors are formed using thin-film, semiconductor or thick-film technology. The thermal head may slide over the paper during operation. Symbols of height H and length L are formed in the form of a mosaic by exposing a specific point to a thermal pulse received from a point resistor heating element. Modern thermal printers with a resolution of up to 12 dots / mm, carry out sequential or line-by-line character synthesis of a printed line, allow you to get dry documents that do not emit odors characteristic of inkjet printing, since. they do not use liquid toxic dyes and dry toners.

Thermal transfer printers (thermowax) use rubber rollers coated with a layer of wax ink. The heat from the print head melts the wax and the print develops on paper, where it cools to fix the image. This technology gives the most juicy, multicolored and clear images.

The widespread use of such thermal printers in PCs is hampered by the use of special thermally sensitive paper (usually wax), which is more expensive than ordinary paper, and the fading of the record under the influence of direct sunlight and heat. These limitations are eliminated when using the thermal diffusion printing method, i.e. when transferring the composition of the ink ribbon to plain paper at the heating points (Fig. 7.9).

A special four-layer resistive-thermal ink ribbon is used, consisting of a polymer base, an aluminum conductive layer and a fusible layer that seals the ink film. The thermal head has micro miniature electrodes through which energy is transferred to the ink ribbon. The printing mechanism presses the ink ribbon to the paper, electric charges are transferred from the electrodes through the polymer base to the aluminum foil, where local heating occurs, destroying the fusible layer. The result is a dot transfer of ink to paper. Multicolor ink ribbons can also be used. The noise level is much lower than that of dot matrix printers, and the quality of prints is higher. The disadvantage of such devices is the rapid wear of the ink ribbon.

Laser printers are a more serious alternative to traditional impact printers. Modern PC laser printers are characterized by excellent print quality and high resolution. when displaying graphic information (24 dots/mm or more), high performance (up to 14 ppm or more), small size, reliability. The principle of operation of laser printers is similar to the principle of operation of electrostatic copiers (Fig. 7.10).

Rice. 7.10. How a laser printer works:

1 - solid-state laser; 2 - multifaceted reflector (mirror);

3 - photosensitive drum; 4 - apparatus for the day of thermal fixing

toner; 5 - receiving and completing device; 6 - cassette with toner;

7 - paper storage

The central element of the laser printer system is a rotating drum covered with a photosensitive semiconductor layer several tens of micrometers thick. The semiconductor (selenium and its alloys in amorphous form) layer in the dark is a good insulator, so the surface of the drum can be charged, like a capacitor, with a beam of high-voltage ionizers located near the drum. When a specific point on the surface of a drum charged with an electric charge is illuminated, the semiconductor layer becomes conductive only at this point and a discharge occurs in it. The data coming from the PC and containing information (graphic or text) is converted in the printing device using a laser-optical scanning system into signals that modulate the laser beam. When a point on the surface of the drum is irradiated with a laser beam of variable intensity, the residual charge turns out to be proportional to the change in the intensity of the laser beam. Thus, an invisible electrostatic image of a line or page of information of a certain format is created on the surface of the drum. In the next step, the image is developed using an electrostatically charged dusty tint of plastic particles with a diameter of several micrometers. The ink sticks to the surface of the drum only where there is a static charge. Where the surface has been irradiated with a laser beam, the paint does not stick. When the drum rotates, the pattern developed by dry dusty ink touches the paper at the receiving point, and under the influence of an electrostatic field, the required pattern is formed on the surface of the paper, which is fixed by melting the ink with special lamps and bonding it to the paper.

There are line and page laser printers. Page laser printers require sufficiently large memory (up to several megabytes) to store images. A number of foreign firms have developed models of laser printers with extended functionality: raster digitalization of a copied document with recording in a disk archive, direct copying of documents. printing of information output from a PC with simultaneous partial copying, i.e., it is possible to prepare mixed printed and graphic materials for publishing activities.

The disadvantages of laser printers include: the high complexity of the optical scanning system containing many optical elements (mirror polyhedra for beam deflection; collimating and focusing lenses; cylindrical lenses used to correct errors in beam positioning, etc.); the need for frequent replacement of tinting powder; increased influence of high ambient temperature and humidity; large amount of required buffer memory; the need for special software; high price. However, there has been a definite trend towards a decrease in the cost of laser printers.

Requirements for printers and their main characteristics. The personal nature of the PC, the specifics of their areas of application determine a number of specific requirements for printing devices. PC printing devices should be cheap, have small dimensions, weight, low power consumption, and provide a low noise level during operation. They should also have advanced functionality, including the ability to display text and graphic information, print a variety of character sets, multi-color printing, and be convenient for printing. their operation by the PC user. For example, if a device is able to print in both directions, i.e. not only from left to right, but also vice versa, then this greatly increases the speed of printing. If, for example, the device has logical capabilities, then those lines where nothing needs to be written, the device can simply “jump”. The paper feed method, the ability to connect an automatic sheet feeder and sheet stacking device, the ease of ink ribbon cassettes, etc. are important. The consumer quality of printing devices is determined by the combination and interrelation of their technical characteristics and depends on the purpose of the PC. Therefore, not all types of printing devices used in data processing systems, in large or portable computers, are suitable for use in professional PCs.

For the user of a professional PC, the following characteristics of printing devices are important: speed, quality and color of alphanumeric and graphic printing; the format and quality of paper and ink ribbons, as well as their availability; simplicity (convenience) of maintenance and repair; software; encoding methods and character set; type of interfaces and memory capacity; noise level; power consumption; weight and size characteristics; external design, etc. The most important characteristics are the speed and quality of printing, usually provided by a specific design of the printing device.

The print speed of character (serial) devices is determined by the number of characters printed per second, and for parallel (line and page) devices, by the number of lines or pages printed per minute.

Print quality is determined by a number of parameters: the number of characters printed per line; character and line printing step, minimum line thickness and line tolerance, character sizes, print density, accuracy, etc., as well as the possibility of highlighting (“bold” printing obtained by double printing a character or a slight offset of the character outline), superscript and interline printing, underlining, graphics printing, multi-color printing, etc.

The set of printable characters determines the ability to print a variety of text and graphic documents. In modern printing devices, in addition to the main font, as a rule, it is possible to programmatically generate additional characters. Some printers also use another version of the font library extension. The point sets needed to form alternative fonts are stored in ROM chips contained inside special font cassettes. In the course of work, the user can change not only the type of font, but also the size of printed characters, which is especially important when printing tables.

Management of printing devices is mainly carried out using commands and codes standardized by Epson and IBM. Much of the most common printer commands, such as carriage return, tab, etc., as well as the characters that the printer perceives as codes, are borrowed from the ASCII code character set. Escape sequences begin with a special character abbreviated as ESC with an ASCII value of 27.