Some of the discoveries or inventions that have long become familiar, over time, acquire a variety of beautiful myths and legends.
One of these stories tells about an employee of a small research laboratory that belonged to a large computer firm. After a sleepless night working on a capricious new design for some electronic contraption, this employee inadvertently placed a soldering iron next to a syringe filled with rosin (I would like to ascribe that it contained ink, but it is not). Naturally, as a result, overalls were spoiled, but most importantly, the idea of thermal inkjet printing arose. A stained white coat went to the dry cleaners, and inkjet technology, through the efforts of Canon, Hewlett-Packard, Epson, Lexmark and other companies, came to offices and homes, striking with its affordability and colorfulness.
Why an inkjet?
In the past few years, the computer industry has experienced a real ink boom. Inkjet printers for many users are the most affordable and versatile printing devices. The images obtained on them are in many cases superior in quality to printed copies, and the maximum print speed has already come close to the performance indicators of lower models of laser printers. Comparable to amateur photos from mini-labs, full-color photorealistic inkjet printing has become the main trump card of inkjet printer manufacturers in the fight to attract new customers.
In pursuit of the buyer and the envy of competitors, the droplet size is constantly decreasing and new technologies are being developed to improve color reproduction. From the new names and logos, the head is already spinning. Naturally, the most inquisitive question arises: are all the principles and ideas that each of the manufacturers is proud of so unique?
In proud loneliness
For quite a long time, two camps have formed in this sector of the market. In one, Epson single-handedly rules with piezoelectric technology, and in the other, a whole alliance of adherents of "boiling ink" gathered.
The piezoelectric printing method is based on the property of some crystalline substances to change their physical dimensions under the influence of an electric current. The most striking example is the quartz resonators used in many electronic devices. This phenomenon has been used to create a miniature pump in which a change in voltage causes a small volume of ink to compress in a narrow capillary channel and to be ejected instantly through a nozzle.
The printhead of a piezoelectric inkjet printer must be highly reliable, because, due to its rather high cost, it is almost always built into the printer and does not change when a new ink cartridge is installed, as is the case with thermal inkjet printing. This design of the piezoelectric head has certain advantages, but at the same time there is a constant risk of damage to the printer due to an air bubble in the ink supply system (which can happen when changing the cartridge) or ordinary downtime for several weeks. In this case, the nozzles become clogged, print quality deteriorates, and restoration of normal modes requires qualified service, which is often impossible to carry out outside the service center.
Stay away from the team
While Epson went its own way, periodically surprising the computer community with another breakthrough, other players in the inkjet printing market were no less successful in using a print head of a different design. Most of them consider their developments to be unique, although their essence is trivially simple, and the difference often lies only in the name.
So, Canon uses the term Bubble-Jet, which can be loosely translated as "bubble printing". The rest did not fence the garden and agreed with the more familiar phrase "thermal inkjet printing."
Thermal inkjet printers work like a geyser: inside the ink-limited chamber, a miniature heating element creates a bubble of steam that instantly expands, pushing a drop of ink onto the paper.
Using this technology, it is not difficult to obtain miniature printing elements located at a high density, which promises developers a potential increase in resolution with a solid margin for the future. However, thermal inkjet printing also has flip side. Due to the constant temperature difference, the print head is gradually destroyed, and as a result it has to be replaced along with the ink cartridge.
More names - loud and different!
Bubbles are bubbles, and simple pictures have not surprised anyone for a long time. So you have to fight for every picoliter in a drop, for every shade on paper. But there are really not so many ways to improve the quality of the final image. The most obvious and affordable option was to increase the number of ink colors. In addition to the four basic colors (black, blue, crimson and yellow), many manufacturers have added two more - light blue and light crimson. As a result, it became possible to reproduce lighter shades without reducing the density of dots applied to the paper, which made it possible to make the raster structure of the image in light areas, where it is especially well distinguishable, less noticeable. Canon called this technology PhotoRealism, Hewlett-Packard called PhotoREt, and Epson called Photo Reproduction Quality.
But progress, stimulated by competition, does not stand still. The next step towards the ideal was made by reducing and dynamically changing the size of the ink drop, and with it the end point on the paper. By controlling the amount of "portion" of ink applied to the paper, you can achieve lighter shades without increasing the distance between dots. This makes it possible to make the bitmap structure even less visible.
Without additional tricks and significant change technological process only Epson could achieve a similar effect. The fact is that the principle of operation of the piezoelectric head allows you to control the size of the drop by changing the amount of control voltage applied to the piezoelectric element. This technology is called Variable Dot Size. Well, the adherents of bubble printing had to seriously work on changing the design of the nozzles. Each of them placed several heating elements of different power.
By turning them on one at a time or all at the same time, it is possible to obtain droplets of various sizes, as is the case in modern thermal inkjet printers. Canon dubbed its developments in this area Drop Modulation, while HP used a ready-made name with additional indices - PhotoREt II and PhotoREt III. In addition to the ability to control the size of the drop, there was also the possibility of successively applying several drops to the same point on the surface of a sheet of paper.
But the print quality depends not only on the technical perfection of the design of the printer itself, but also on other equally significant factors.
Behind the line of the jet front
With an increase in resolution and printing speed, it turned out that the pursuit of improving these characteristics in itself could not give a significant gain, if the image carrier, that is, paper, was not improved. It would seem, what could be simpler than paper? But it was not there! Any "cunning" technologies will be powerless if you put plain office paper in the printer tray.
A beautiful sheet of A4 format, from the sight and smell of which any laser printer begins to purr with pleasure, turns out to be completely unprepared for the streams of multi-colored ink erupted at it from hundreds of nozzles.
The surface of ordinary paper has a fibrous structure, which is due to the technology of its production. As a result, miniature, strictly sized drops begin to spread over the surface in the most unpredictable way. In this case, it does not matter at all what kind of printing is used - thermal or piezoelectric. One solution to this problem is the use of pigment ink, which is a suspension of dispersed particles in a colorless liquid carrier, since solid particles cannot penetrate into the inner layers and spread through the fibers of the paper.
Pigment-based inks make it possible to obtain bright and saturated shades, but they also have certain disadvantages, in particular, low resistance to external influences.
Inkjet printing technology is such that the best results can only be achieved using special paper. Photos on plain paper look faded and less clear. Specially coated paper and so-called photographic paper have several special layers, unlike regular paper. Prints on it are almost indistinguishable from photographs obtained by printing using a chemical photoprocess.
Plain budget paper for inkjet printing, as a rule, has a density of 90-105 g/m 2 , relatively thin thickness and excellent whiteness. Due to the special processing of the front or both sides, such paper is more resistant to the vagaries of ink and prevents them from spreading and penetrating deep into the sheet.
Special photo paper with a glossy or matte surface usually has a density of up to 200 g/m 2 and is a multi-layer product of modern technology. Each of the layers performs certain functions.
The bottom layer is the base that provides strength and rigidity to the document. The next layer acts as an optical reflector, giving the image brightness and whiteness. Next is the main bonding ceramic or plastic layer, constituting a set vertical channels without long fibrous formations along the surface of the sheet and providing the necessary ink density at the printed dot. The last, glossy or matte protective layer is applied to the absorbent, giving the surface strength and protecting it from external influences.
During the printing process, ceramic particles absorb ink, preventing it from spreading over the surface. As a result, the shape of the points and their orientation remain unchanged. In addition, you can not be afraid of accidental moisture ingress, since deep and strictly vertical microcapillaries minimize the likelihood of spreading.
Special paper for inkjet printers has become a panacea for many ills, but, unfortunately, quite expensive. I want to, of course, but ... And it's worth spending money to compare "heaven" and "earth" at least once.
ComputerPress 11 "2001
There are two main printing technologies on the market today for printing devices: piezoelectric and thermal inkjet.
Piezoelectric printing technology is developed on the ability of piezoelectric crystals to deform under the influence of electricity. Due to the use of this technology, it became possible to control printing, namely: to monitor the size of the drop, the speed of its exit from the nozzles, as well as the thickness of the jet, etc. One advantage of such a system is that the droplet size can be controlled. This ability allows you to get better images.
To date, experts have proven that the reliability of such systems is much higher than other inkjet printing systems.
When using this technology, the print quality is very high. Even universal and inexpensive models allow you to get images highest quality and high resolution. Also, the most important advantage of PU with a piezo system is high color rendering, which allows the image to look bright and saturated.
Epson technologies - time-tested quality
The printheads of EPSON inkjet printers are of high quality, and this is precisely what explains their high price. If you use a piezoelectric printing system, then you are guaranteed reliable operation of the printing device, and the print head does not dry out or clog due to the fact that it has minimal contact with air. The piezoelectric printing system was developed and implemented by EPSON, and only EPSON holds a patent for this system.
The thermal inkjet printing principle is used in Canon, HP, Brother printers. By heating the ink, they are transferred to the paper. By means of an electric current, liquid ink is proportionally heated, which is the reason for the name of this printing method - thermal inkjet. An increase in temperature reproduces a heating element, which is located inside the thermal structure. With a strong increase in temperature, the main part of the paint evaporates, the pressure in the structure quickly rises, and a small drop of paint comes out of the heat chamber through a precision nozzle. This process is repeated repeatedly after one second.
The main disadvantage of the thermal inkjet method is that with such a printing technology, a sufficiently large amount of precipitation is formed in the print head of the printer, which over time can damage it. Also, this scale clogs the nozzles over time, which leads to a loss in quality and print speed of the printer.
Also, devices that use thermal inkjet printing, due to constant temperature fluctuations, the print heads deteriorate, as it corny burns out under the influence of enormous temperature. This is the main disadvantage of such devices. The period of operation of the Epson PG MFP is absolutely identical to the service life of the device itself. This was made possible thanks to the high-quality materials from which the print head was developed. Customers who use thermal inkjet printing will often need to change the print head, as the high temperature will often cause it to burn out, which will greatly increase financial costs. The quality of the print head will also make a huge difference if users are using remanufactured cartridges.
Using an Epson inkjet printer in conjunction with refillable cartridges is very beneficial, as it improves the quality of the printer and reduces the cost of each printed image.
The print head of EPSON printers is of great importance not only for stable operation printer. PG Quality allows you to increase print quality and print speed. Also, if the print head does not come into contact with air and dries out, the user will not have to change it, and therefore spend money in vain. Devices that use the thermal inkjet principle of operation can overheat greatly, and, accordingly, the print head can also overheat, which, if overheated, can simply burn out and get out of the standing.
As numerous checks and tests show, in order to print as economically as possible and at the same time be bright and effective, engineers recommend using EPSON printers with CISS. EPSON devices work much longer and more efficiently with the LF system than other similarly priced remote control units from other manufacturing companies.
Epson is a trusted manufacturer of quality products that make your job easier and more productive.
Inkjet technology appeared in the mid-1980s as a result of an attempt to get rid of the shortcomings of the two dominant printing methods at that time: dot matrix and laser (electrographic). Laser printing was unacceptably expensive, and color was not yet dreamed of (and even now, although color laser printers have become available, they have no chance to bypass inkjet printers in the field of photo prints). And inkjet printing originated as cheap alternative for printing office documents, devoid of the shortcomings of dot matrix printers - slow, noisy and giving low-quality prints.
The idea, which, apparently, almost simultaneously (around 1985) came to the minds of engineers from Hewlett-Packard and Canon, was to replace the needle that hits the paper in dot-matrix printers through the ink layer on the ribbon with a drop of liquid ink. The volume of the drop should be calculated so that it does not spread and creates a point of a certain diameter. real life this technology was obtained when they came up with a convenient way to form a dosed drop - thermal.
The thermal inkjet printing method is actually monopolized by Canon and Hewlett-Packard, which own most of the patents for this technology, the rest of the companies only license it, making their own small changes. While HP uses the term "thermal inkjet" (thermal ink-jet) printing method, and Canon prefers the term "bubble-jet" (bubble-jet).
Although there are differences between them, they are fundamentally identical.
On fig. 1 shows the process of thermal inkjet printing in the form of a conditional cinegram of the cycle of the nozzle (sometimes called ejectors). A miniature heating element is built into the chamber wall (highlighted in red in the top frame), which heats up very quickly to a high temperature (500 °C). The ink boils (second frame), a large vapor bubble forms in them (the next two frames) and the pressure rises sharply - up to 120 atmospheres, which causes the ink to be pushed out through the nozzle at a speed of more than 12 m / s in the form of a drop with a volume of about 2 picolitres (this is two thousandths from a billionth of a litre). The heating element is switched off by this moment, and the bubble collapses due to pressure drop (bottom frames). Everything happens very quickly - in a few microseconds. The ink is fed into the nozzle due to capillary forces (which is much slower), and after filling the nozzle with a new portion, the system is ready to work. The entire cycle takes approximately 100 ms, that is, the frequency of drops is 10 kHz, and in modern printers - twice as much.
Such an autonomously controlled nozzle is part of the print head, located on a carriage moving across the sheet, like a print unit dot matrix printer. With a nozzle diameter of 10 microns, the placement density is 2500 nozzles per inch; in one head there can be from several hundred to several thousand nozzles. In modern high-speed devices, fixed heads began to be used - in order to eliminate the slowest stage in the entire process of the transverse movement of the carriage. For example, HP produces high-performance photo kiosks in which the heads are arranged in blocks across the entire width of the sheet.
On Canon printers, the thermal element is located on the side of the camera (as in Fig. 1), while on HP (and Lexmark) it is on the back. Perhaps this difference is due to the original ideas: according to corporate legend, a Canon engineer dropped a soldering iron on a paint syringe (that is, the syringe heated up from the side), and HP researchers borrowed the principle from an electric kettle, which is heated from the end. Like it or not, the lateral arrangement allows Canon to mount two thermal elements per nozzle, which improves performance and manageable droplet size, but complicates and increases the cost of design.
Canon's more expensive "bubble" heads are reusable and built into the printer. HP heads are easier to manufacture, because they were traditionally built directly into the cartridge and thrown away with it. This is much more convenient, as it guarantees print quality (the head simply does not have time to work out the resource) and high reliability of the assembly. However, with this approach, improving the heads leads to a rise in the cost of cartridges, so many modern HP printers have separate heads, like Epson or Canon. For example, the Photosmart Pro B9180, today's flagship of HP's "home" photo printers, has replaceable individual heads, while its cheaper analogue, the Photosmart Pro B8353, has cartridge-integrated heads.
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Technology thermal inkjet printing based on the property of ink to expand in volume when heated. The heated ink, increasing in volume, pushes microscopic ink droplets into the nozzles of the print head of the printer, which form an image on paper. In general, the technology of thermal inkjet printing is presented below.
Thermal Inkjet Technology
Thermal inkjet printing is the most popular inkjet printing technology and is used in 75% of inkjet printers.
Share of printers using thermal inkjet printing technology
The largest contribution to the development of thermal inkjet printing technology was made by corporations Canon and HP, who independently developed two printing technologies in the 1970s: Bubble Jet (Canon) and Thermal Inkjet(H.P.).
Thermal Inkjet Technologies
Bubble Jet thermal inkjet technology was introduced to the public in 1981 at the Grand Fair. In 1985 using innovative technology The legendary Canon BJ-80 monochrome printer was released, in 1985 - the first Canon BJC-440 color printer.
Schematic representation of Bubble Jet inkjet printing technology
The essence of technology Inkjet Bubble Jet is as follows. A thermistor (heater) is built into each nozzle of the print head for instant heating of the ink, which at temperatures above 500 ° C, evaporating, form a bubble that pushes the ink drop out. Then the thermistor turns off, the ink cools and the bubble disappears, and the low pressure zone draws in a new portion of ink.
Interestingly, the ink heats up to a temperature of 500°C in just 3 microseconds, and drops fly out of the nozzle at a speed of 60 km/h. Every second in each nozzle of the print head, the ink heating and cooling cycle is repeated 18,000 times.
The second inkjet printing technology - Thermal Inkjet - began to be developed by HP in 1984, but the first ThinkJet printer based on this printing technology was introduced into mass production much later.
Schematic representation of Thermal Inkjet technology
Thermal Inkjet Technology is based on the same printing principle as Bubble Jet technology, with the only difference being that in printers using Bubble Jet technology, thermistors are located in the microscopic nozzles of the print head, while in printers using Thermal Inkjet technology, they are located directly behind the nozzle.
Thus, Bubble Jet and Thermal Inkjet technologies differ only in details.
The main advantages of thermal inkjet printing over piezo inkjet printing are the absence of moving mechanisms and stable operation. Along with this, thermal inkjet printing has one significant drawback: it does not allow you to control the size and shape of ink droplets. In addition, when ink drops fly out of the print head nozzle, satellite drops (satellites) that form when the ink boils escape with them. The appearance of such "satellites" can be triggered by the unstable vibration of the ink mass during its ejection from the nozzle. It is the satellite drops that cause the formation of an undesirable contour (“ink fog”) around the print and mixing colors in graphic files.
The operation of various piezoelectronic devices is based on piezoelectric effect , which was discovered in 1880 by the French scientists brothers P. Curie and J. Curie. The word "piezoelectricity" means "electricity from pressure". direct piezoelectric effect or simply piezo effect consists in the fact that under pressure on some crystalline bodies, called piezoelectrics, electric charges of equal magnitude, but different in sign, arise on opposite faces of these bodies. If you change the direction of deformation, i.e., do not compress, but stretch the piezoelectric, then the charges on the faces will change sign to the opposite.
Piezoelectrics include some natural or artificial crystals, such as quartz or Rochelle salt, as well as special piezoelectric materials, such as barium titanate. In addition to the direct piezoelectric effect, it is also used reverse piezo effect , which consists in the fact that under the influence of an electric field, the piezoelectric contracts or expands depending on the direction of the field strength vector. In crystalline piezoelectrics, the intensity of the direct and inverse piezoelectric effect depends on how the mechanical force or electric field strength is directed relative to the axes of the crystal.
For practical purposes, piezoelectrics of various shapes are used: rectangular or round plates, cylinders, rings. Such piezoelectric elements are cut out of crystals in a certain way, while maintaining orientation relative to the axes of the crystal. The piezoelectric element is placed between metal plates or metal films are applied to opposite faces of the piezoelectric element. Thus, a capacitor with a piezoelectric dielectric is obtained.
If we bring to such a piezoelectric element AC voltage, then the piezoelectric element, due to the inverse piezoelectric effect, will shrink and expand, i.e., perform mechanical vibrations. In this case, the energy of electrical vibrations is converted into the energy of mechanical vibrations with a frequency equal to the frequency of the applied alternating voltage. Since the piezoelectric element has a certain natural frequency, a resonance phenomenon can be observed. The greatest amplitude of oscillations of the plate of the piezoelectric element is obtained when the frequency of the external EMF coincides with the natural frequency of the oscillations of the plate. It should be noted that there are several resonant frequencies that correspond to different types of plate vibrations.
Under the influence of an external variable mechanical force, an alternating voltage of the same frequency arises on the piezoelectric element. In this case, mechanical energy is converted into electrical energy and the piezoelectric element becomes a variable EMF generator. We can say that the piezoelectric element is an oscillatory system in which electromechanical oscillations can occur. Each piezo element is equivalent to an oscillatory circuit. In a conventional oscillatory circuit, composed of a coil and a conder, the energy of the electric field concentrated in the conder is periodically transferred to the energy of the magnetic field of the coil and vice versa. In a piezoelectric element, mechanical energy is periodically converted into electrical energy. Let's look at the equivalent circuit of the piezoelectric element:
Rice. 1 - Equivalent circuit of the piezoelectric element
The inductance L reflects the inertial properties of the piezoelectric plate, the capacitance C characterizes the elastic properties of the plate, the active resistance R is the energy loss during vibrations. The capacitance C 0 is called static and is the usual capacitance between the plates of the piezoelectric element and is not associated with its oscillatory properties.
Piezoelectric inkjet heads for printers were developed in the seventies. In most piezoelectric inkjet printers, excess pressure in the ink chamber is created using a piezoelectric disk that changes its shape - bends when an electrical voltage is applied to it. Curving, the disk, which is one of the walls of the chamber with ink, reduces its volume. Under the action of excess pressure, liquid ink is emitted from the nozzle in the form of a drop. The pioneer of piezoelectric technology, Epson, was unable to successfully compete in sales volume with its competitors Canon and Hewlett-Packard due to the relatively high technological cost of piezoelectric printheads - they are more expensive and more complex than bubble printheads.
The main disadvantage of Epson inkjet printers is that the head costs the same as the printer. And if it dries up, then it is advisable to simply throw out the printer.
For other printers, the downside is the cost of consumables.
3. The principle of operation of laser printers. Laser and LED printers. Main characteristics, advantages and disadvantages.
The impetus for the creation of the first laser printers was the emergence of a new technology developed by Canon. Specialists of this company, specializing in the development of copiers, created the LBP-CX printing mechanism. Hewlett-Packard, in collaboration with Canon, began developing controllers that make the print engine compatible with PC and UNIX computer systems.
Initially competing with petal and dot matrix printers, the laser printer quickly gained popularity around the world. Other copier companies soon followed Canon's lead and began research into laser printers. Another important development was the emergence color laser printers. XEROX and Hewlett-Packard introduced a new generation of printers that used the PostScript Level 2 page description language, which supports color representation of the image and allows you to increase print performance, and color accuracy. Laser printers form an image by positioning dots on paper (raster method). Initially, the page is formed in the printer's memory and only then transferred to the printing engine. Raster representation of symbols and graphic images is produced under the control of the printer controller. Each image is formed by the appropriate arrangement of points in the cells of the grid or matrix.
Despite the offensive inkjet printers, the dominance of laser devices in workplaces in the office is now unquestioned. There are many reasons behind the popularity of laser printers. They use a proven technology that has proven to be highly reliable: printing is fast, silent and quite affordable, its quality in most cases is close to printing. Manufacturers of laser printers have not stood still either, continuing to increase print speed and quality while pushing prices down. In 1994, a typical laser printer had a nominal speed of 4 ppm, a resolution of 300 dpi, and a price of $800. In 1995, we saw an increase in the number of products that print at 6 ppm at 600 dpi and have a real retail price of $350.
Every two to three years, manufacturers increase print speeds by 1 or 2 ppm, and by the end of the decade, personal laser printers had reached speeds of 12-15 ppm. In addition, they decrease dimensions of laser printers- thus, manufacturers achieve a reduction in price and the possibility of installing their products on a cramped desktop. One of the consequences of this is often limited means for handling paper compared to large-sized models. Input containers usually hold no more than 100 sheets, and the paper pocket is often designed for manual feeding of sheets at the same time - for this you must first remove a stack of paper from it. The capacity of output trays is also limited - if the printer is equipped with such a device at all. Some printers have a paper path that is so convoluted that vendors do not recommend using sticky label machines.
The most widely used laser printers use photocopying technology, also called electrophotography, which consists in precisely positioning a dot on a page by changing the electrical charge on a special film made of a photoconductive semiconductor. A similar printing technology is used in copiers.
The most important structural element of a laser printer is a rotating photoconductor, which transfers the image to paper. The photoconductor is a metal cylinder coated with a thin film of a photoconductive semiconductor (usually zinc oxide). A static charge is evenly distributed over the surface of the drum. With the help of a thin wire or mesh, called a corona wire, a high voltage is applied to this wire, causing a glowing ionized region, called a corona, to appear around it. A microcontroller-controlled laser generates a thin beam of light that reflects off a rotating mirror. This beam, falling on the photodrum, illuminates elementary areas (points) on it, and as a result of the photoelectric effect, the electric charge changes at these points.
For some types of printers, the drum surface potential decreases from -900 to -200 V. Thus, a copy of the image appears on the photoconductor in the form of a potential relief.
In the next working step, with the help of another drum, called the developer (developer), on the photoconductor is applied toner- the smallest coloring dust. Under the action of a static charge, small particles of toner are easily attracted to the surface of the drum at the points exposed, and form an image on it.
A sheet of paper from the input tray is moved by a roller system to the drum. Then the sheet is given a static charge, opposite in sign to the charge of the illuminated dots on the drum. When the paper contacts the drum, toner particles from the drum are transferred (attracted) to the paper. To fix the toner on paper, the sheet is charged again and it is passed between two rollers, which heat it up to a temperature of about 180° - 200°C. After the actual printing process, the drum is completely discharged, cleaned of adhering toner particles and ready for a new printing cycle.
The described sequence of actions is very fast and provides high quality printing. When printing on color laser printer two technologies are used. In accordance with the first, widely used until recently, a corresponding image was formed on the drum for each individual color (Cyan, Magenta, Yellow, Black), and the sheet was printed in four passes, which naturally affected the speed and quality of printing. In modern models, as a result of four successive passes, toner of each of the four colors is applied to the drum unit. Then, when the paper comes into contact with the drum, all four colors are transferred to it at the same time, forming the desired color combinations on the print. The result is smoother color reproduction, almost the same as thermal transfer color printers.
Printers of this class are equipped with a large amount of memory, a processor and, as a rule, their own hard drive. The hard drive contains a variety of fonts and special programs that manage the work, control the status and optimize printer performance. Color laser printers are quite large and heavy. The technology of the color laser printing process is very complex and the price of color laser printers is still very high.
LED printer: principle of operation, similarities with laser printers and differences from it
LED and laser digital printing technology have in common the use in both cases of the electrographic process to obtain the final print. In fact, these are devices of the same class: in both cases, the light source, controlled by the printer's processor, forms a surface charge on the photosensitive drum that corresponds to the desired image.
Further, to put it simply, the rotating drum passes by the toner hopper, attracts particles of toner to the `illuminated` places and transfers the toner to the paper. Then the toner is fixed on the paper with a thermoelement (oven) and we get a finished print at the output. ¶Now let's go back and take a closer look at the design of the light source that illuminates the drum. It is in the type of light source used that the difference between a laser and LED printer lies: unlike a laser unit, in the latter case a line consisting of thousands of LEDs is used. Accordingly, the LEDs through the focusing lenses illuminate the surface of the photosensitive drum across its entire width.
4. The principle of operation of sublimation printers. Main characteristics, advantages and disadvantages.
Sublimation printers appeared about ten years ago. Then they were considered exotic, highly professional equipment. Inkjet printers were originally aimed at the mass user, which means that these two product groups did not compete with each other. The image quality of sublimation printers of a decade ago was incomparably superior to that which inkjet machines could provide. But the cost of printing on the latter was almost an order of magnitude lower.
A common drawback of all inkjet photo printers, caused by technological reasons, is the banding of the print, which manifests itself in different models to varying degrees. At best, it is imperceptible or barely noticeable, however, if part of the nozzles become clogged or the printer mechanics fail, the print becomes divided into unattractive horizontal stripes. Sublimation printers belonging to the class of thermal printers are completely free from this drawback.
Sublimation printing technology comes from the Latin word sublimare ("lift up") and represents the transition of a substance when heated from a solid state to a gaseous state, bypassing the liquid state.
The principle of operation of a sublimation printer is as follows: when a print job is received, the printer heats the film with the dye applied to it, as a result of which the dye evaporates from the film and is applied to special paper. As a result of the same heating, the pores of the paper open and the dye is clearly fixed on the print, after which the surface of the paper again becomes smooth and glossy. Printing is carried out in several passes, since the three main dyes must be transferred to the paper in the correct combinations: magenta, cyan and yellow.
Since pixelation and banding are completely absent in this case due to the printing technology itself, sublimation printers working with a seemingly modest resolution of 300x300 dpi are capable of producing photographs that are not inferior in quality to prints of inkjet models with a much higher resolution. The main disadvantages of sublimation models are the high cost of consumables and the lack of household models that work with A4 sheets.
A conventional inkjet printer prints on plain paper, while a sublimation printer requires special paper and a dye cartridge (ink ribbon), which are usually sold in a set. The cost of a set of 20 photos of a standard format 10 x 15 cm can be from $5 to $15. Thus, printing on a sublimation printer costs 3-4 times more than on an inkjet printer, and ten times more expensive than developing and printing conventional (analogue) films in the laboratory. This is clearly shown in the figure. 
5. The principle of operation of thermal printers. Main characteristics, advantages and disadvantages.
Color laser printers are not yet perfect. Thermal printers or, as they are also called, high-end color printers are used to obtain a color image with a quality close to photographic or to produce prepress color samples.
At present, three color thermal printing technologies have become widespread: inkjet transfer of molten dye (thermoplastic printing); contact transfer of molten dye (thermowax printing); thermal dye transfer (sublimation printing).
Common to the last two technologies is heating the dye and transferring it to paper (film) in the liquid or gaseous phase. The multicolor dye is usually applied to a thin lavsan film (5 µm thick). The film is moved by means of a tape transport mechanism, which is structurally similar to that of a needle printer. The matrix of heating elements forms a color image in 3-4 passes.
Thermal wax printers transfer the dye dissolved in the wax to the paper by heating a ribbon of colored wax. As a rule, paper with a special coating is required for such printers. Thermal wax printers are commonly used for business graphics and other non-photographic printing.
Sublimation printers are the best choice for printing an image almost indistinguishable from a photograph and making prepress samples. According to the principle of operation, they are similar to thermal wax, but only the dye (which does not have a wax base) is transferred from the tape to the paper.
Printers using inkjet transfer of molten ink are also called solid ink wax printers. When printed, colored wax blocks are melted and splattered onto the media, creating vibrant, saturated colors on any surface. The "photos" obtained in this way look slightly grainy, but satisfy all the criteria for photographic quality. This printer is not suitable for making transparencies because the wax drops are hemispherical after drying and create a spherical effect.
There are thermal printers that combine the technology of sublimation and thermal wax printing. Such printers allow you to print both draft and finishing prints on one device.
The print speed of thermal printers due to the inertia of thermal effects is low. For sublimation printers from 0.1 to 0.8 pages per minute, and for thermal wax printers - 0.5-4 pages per minute.
