Laser printer message. How a laser printer works and works. Storing ink and applying it to the canvas

Laser printers provide higher quality than inkjet printers. The most famous firms - developers of laser printers are Hewlett-Packard, Lexmark.

The principle of operation of a laser printer is based on the method of dry electrostatic transfer of images, invented by C.F. Carlson in 1939 and also implemented in copiers. The functional diagram of the laser printer is shown in Fig. 5.6. The main structural element is rotating drum, which serves as an intermediate medium with which the image is transferred onto paper.

Rice. 5.6. Functional diagram of a laser printer

Drum is a cylinder covered with a thin film of a light-conducting semiconductor. Usually zinc oxide or selenium is used as such a semiconductor. Static charge is evenly distributed over the surface of the drum. This is done with a thin wire or mesh called a corona wire or corotron. A high voltage is applied to this wire, causing a glowing, ionized area called a corona around it.

Laser, controlled by a microcontroller, generates a thin beam of light reflected from a rotating mirror. The image is scanned in the same way as in a television kinescope: the movement of the beam along the line and frame. With the help of a rotating mirror, the beam glides along the cylinder, and its brightness changes abruptly: from full light to complete darkness, and the cylinder is also charged abruptly (pointwise). This ray, reaching the drum, changes it electric charge at the point of touch. The size of the charged area depends on the focusing of the laser beam. The beam is focused using a lens. Sharp edges and corners in the image are considered a sign of good focus. For some types of printers, in the process of recharging, the potential of the drum surface decreases from 900 to 200 V. Thus, a latent copy of the image appears in the form of an electrostatic relief on the drum, an intermediate carrier.

In the next step, the photosetting drum is applied toner- paint, which is the smallest particles. Under the action of a static charge, particles are easily attracted to the drum surface at the exposed points and form an image already in the form of a dye relief.

Paper is pulled out of the feeding tray and, using a system of rollers, is moved to the drum. Just before the drum, the corot-ron imparts a static charge to the paper. The paper then comes into contact with the drum and attracts, thanks to its charge, the toner particles previously applied to the drum.

To fix the toner, the paper is passed between two rollers with a temperature of about 180 "C. After the end of the printing process, the drum is completely discharged, it is cleared of adhering excess particles to carry out a new printing process. page by page, that is, it generates a full page for printing.

The process of a laser printer from the moment it receives a command from a computer to the output of a printed sheet can be divided into several interrelated stages, during which such functional components of the printer as the central processor are involved; scan processor; mirror motor control board; beam brightness amplifier; temperature control unit; sheet feed control unit; paper feed control board; interface board; power unit; control panel buttons and indication board; additional RAM expansion cards. Basically, the operation of a laser printer is like a computer: the same central processing unit on which the main communication and control functions are concentrated; RAM, where data and fonts are located, interface cards and a control panel board that communicate the printer with other devices, a print unit that issues information on a sheet of paper.

In everyday life, laser and inkjet printers are popular. The printing principle of such devices is fundamentally different, which cannot but affect the operational features. In some cases, it is best to use laser products, while in others, inkjet products. However, it is possible to make the final choice in favor of this or that device only after considering the scheme of work.

Working principle of inkjet printing device

Still, it is an inkjet printer that is most often used at home. The principle of its printing is to form an image using liquid ink. They are transferred to the media through special nozzles located on the head. The number of these holes depends on the printer model. Usually their number ranges from 16-64 pieces.

Since the principle of printing an inkjet printer assumes the use of liquid ink, with prolonged idle time, they dry out on the nozzles of the head. This requires cleaning the printing element, which implies additional consumption of dyes.

Such devices consist of the following components:

• supporting structure;
• power supply unit;
• print head;
• purification system;
• media feeding devices;
• control unit.

A color image is obtained by superimposing three base colors on top of each other. Black ink is often added to them so that it is possible to use devices for conventional printing of texts and black-and-white drawings, saving on color inks.

Basic inkjet technologies

Different models can have their own advantages and disadvantages. The printing principle of representatives of inkjet printers may also differ slightly depending on the technology used. The only difference is in the way the ink is transferred to solid media.

1. The piezoelectric method involves the formation of ink dots on paper using special devices that have a connection with the diaphragm. The electric field has a direct effect on the piezoelectric element, and it expands the tube to fill the capillary system. The main advantage lies in the flexible control of the droplet size, which makes it possible to obtain high-quality images with high resolution.
2. The bubble method involves heating elements directly in the nozzles. An electric current is passed through them. In the process of heating, gas bubbles are formed, which push the required portion of liquid ink through the holes. After the heater has cooled down, a fresh portion of the coloring matter enters through the nozzles. High quality is noted when lines are drawn in detail, but when printing solid areas, there may be slightly fuzzy spots.
3. The thermal jet method, as in the previous case, involves the use of a heating element. However, together with it, a special mechanism is used that allows for a faster injection of dyes. In this regard, the performance of the devices increases. The color palette of the resulting image is distinguished by contrast.

The ink used can have a different composition. Water-based ink contains a soluble dye and certain additives to adjust the viscosity. Their advantage lies in their low cost. Pigment ink is UV and humid resistant. The print quality in this case is less dependent on the media.

Using continuous ink supply

With the principle of printing an inkjet printer, everything became clear. Special cartridges are used to store the dyes. However, there is a special system that allows you to provide a continuous supply of ink in order to save. In this case, the capsule tanks are installed directly on the printhead.

The system is a set of containers connected by a silicone loop through which ink is supplied from donors to the main unit. Thanks to such a device, the constant presence of the original dyes in the print head is achieved. Many large format office appliances have a built-in ink delivery system that cannot be seen from the outside.

How the laser device works

A completely different branch of the development of printing devices is laser technology, with the help of which it is possible to achieve high-quality application of dyes on paper. The formation of symbols and images occurs due to the illumination of the beam of the elements of the device with photosensitivity. The resulting copies with text or graphic information are resistant to fading and abrasion.

Inkjet and laser printers have completely different printing principles. The colorants are toners, which can be transferred to solid media in three ways.

1. Using a two-component development system. The dye particles required for transfer to a special photosensitive drum cannot be fixed on a magnetic shaft without a special magnetic carrier charged by stirring.
2. With the use of one-component toner without additional additives. Particles of matter in this case are endowed with magnetic properties. Some devices may carry out electrostatic deposition. With this option, the toner does not need to be magnetized.
3. Using a factory blended two-component colorant.

Unlike an inkjet printer, the principle of printing a laser analogue is based on the construction of an image using a photographic method. The laser beam hits a special shaft, the surface of which is electrified due to impact ionization of the internal air.

Construction of laser devices

Laser printers succeed in obtaining high-quality printing due to technological peculiarities. They include the following elements.

1. Photodrum, which is a cylinder made of aluminum. It is treated with a light-sensitive material that tends to change its electrical resistance in the presence of light.
2. A magnetic roller is used to transfer toner from the reservoir directly to the drum or developing roller found in some modern printers.
3. The squeegee knife acts as a cleaning blade. It removes excess dye from the raster roller. It can be made of plastic, steel or fiberglass.
4. Waste toner hopper is made in the form of a container. This compartment can be located separately from the cartridge or with it. The filling speed of such a reservoir depends on the quality of the toner.
5. The laser unit is designed to create an invisible image on the surface of the drum by illuminating specific areas. The beam intensity can vary significantly.
6. The primary charge roller is made in the form of a metal rod covered with a rubber layer. This element allows for the uniformity of the negative charge.
7. Transfer belt is required for applying intermediate results from color cartridges.
8. The development unit allows toner to be transferred directly onto an electrostatic image created on the surface of the photoconductive element.

Laser printing process

Not everyone fully understands the principle of printing laser printers from computer science courses. Inkjet devices work according to a simplified scheme, so there are no special questions about them. How does the laser printing process take place?

1. The photoconductive roller is charged first. An electric charge is evenly distributed over its surface by rotating the roller. The rotating rod system reduces stress and reduces the amount of ozone generated.
2. Laser scanning is in progress. At this moment, the charged surface of the shaft passes under the light beam. The laser hits only those places where the dye will be applied in the future.
3. Toner is being applied. The roller, which has a negative charge, transfers it to the toner. The dye from the hopper is attracted directly to the magnetic shaft, after which it comes into contact with the photoconductive element in those areas where a negative charge remains.
4. The transfer roller, in contact with the solid carrier, is no longer negatively charged, but a positive one. Dye particles are electrostatically applied to the surface of the paper.
5. The toner dispersed throughout the media is cured by heat and applied pressure. The thermal chamber consists of two shafts between which the paper moves. The temperature is controlled by a special sensor. The colorant is melted and incorporated into the texture of the paper.

comparison table

It is suggested to take a look at the table to compare the properties of inkjet and laser printers, the printing principle of which is very different.

Having considered briefly the principle of printing an inkjet printer, one cannot fail to note the peculiarities of operation.

1. Using the device less than once a week is not recommended to avoid drying out the ink.
2. It is necessary to purchase high quality dyes, otherwise the head can quickly become clogged.
3. The paper should be suitable and marked for inkjet printing.
4. It is required to keep the product clean, as dust leads to wear of moving parts.

Features of working with laser devices

The main advantage of laser printers is that there is no need for regular use. It can even be used once a month. This will not affect the quality of work or wear of parts. However, only original toner cartridges should be used, otherwise there is a high risk of damage to the device. In addition, third-party consumables may simply not work.

Before purchasing a device with many positive reviews, you need to find out additional information about the cost:

• Supplies;
• wearing parts;
• printouts of one page.

Sometimes it turns out that it is easier to get a new device than to replace any parts.

Final part

Having considered briefly the principle of printing inkjet and laser printers, you can draw certain conclusions about the acquisition of certain devices. However, the final choice will depend on what goals are pursued during operation. For printing large volumes of text information, it is more profitable to buy laser devices. If it is necessary to obtain high-quality photographs, then it is better to give preference to inkjet analogs.

Color laser printers are beginning to actively conquer the printing market. If just a few years ago color laser printing was something unattainable for most organizations and even more so for individual citizens, now a very wide range of users can afford to buy a color laser printer. The rapidly growing fleet of color laser printers leads to an increasing interest in them from technical support services.

Principles of color printing

In printers, as in the printing industry, it is used to create color images subtractive color model, and not additive, as in monitors and scanners, in which any color and shade is obtained by mixing three primary colors - R(Red), G(green), B(blue). The subtractive color separation model is called so because for the formation of any shade it is necessary to subtract the “extra” components from the white color. In printing devices, to obtain any shade, the following are used as primary colors: Cyan(blue, turquoise), Magenta(purple), Yellow(yellow)... This color model is named CMY by the first letters of the primary colors.

In the subtractive model, when two or more colors are mixed, additional colors are obtained by absorbing some light waves and reflecting others. Blue ink, for example, absorbs red and reflects green and blue; magenta ink absorbs green and reflects red and blue; while yellow dye absorbs blue and reflects red and green. By mixing the main components of the subtractive model, you can get different colors, which are described below:

Cyan + Yellow = Green

Magenta + Yellow = Red

Magenta + Cyan = Blue

Magenta + Cyan + Yellow = Black

It is worth noting that to obtain black it is necessary to mix all three components, i.e. cyan, magenta and yellow, however, it is almost impossible to obtain high-quality blacks in this way. The resulting color will not be black, but rather a dirty gray. To eliminate this deficiency, one more color is added to the three primary colors - black. This extended color model is called CMYK(C yan- M agenta- Y ellow-blac K - cyan-magenta-yellow-black). The introduction of black can significantly improve the quality of color reproduction.

HP Color LaserJet 8500 Printer

After we have discussed the general principles of construction and operation of color laser printers, it is worth familiarizing yourself in more detail with their device, mechanisms, modules and blocks. This is best done using a printer as an example. Let's take a Hewlett-Packard Color LaserJet 8500 printer as such an example.

Its main characteristics are:
- resolution: 600 DPI;
- printing speed in "color" mode: 6 pages / min .;
- print speed in “black and white” mode: 24 p./min.

The main components of the printer and their relative positions are shown in Fig. 5.

Formation of the image begins with the removal (neutralization) of residual potentials from the surface of the drum. This is done so that the subsequent charge of the drum is more uniform, i.e. it is completely discharged before charging. Removal of residual potentials is carried out by illuminating the entire surface of the drum with a special lamp for preliminary (conditioning) exposure, which is a line of LEDs (Fig. 7).

Further, a high-voltage (up to -600V) negative potential is created on the surface of the drum. The drum is charged by a corotron in the form of a roller made of conductive rubber (Fig. 8). The corotron is supplied with a sinusoidal AC voltage with a negative DC component. The variable component (AC) ensures an even distribution of charges on the surface, while the constant component (DC) charges the drum. The DC level can be adjusted by changing the print density (toner density) using the printer driver or by adjusting the control panel. An increase in the negative potential leads to a decrease in density, i.e. to a lighter image, while reducing the potential - on the contrary, to a denser (darker) image. The imaging drum (its inner metal base) must be grounded.

After all this, an image is created on the surface of the drum by a laser beam in the form of charged and uncharged areas. The laser light beam, hitting the surface of the drum, discharges this area. The laser illuminates the areas of the drum that should contain toner. Those areas that should be white are not illuminated by the laser, and a high negative potential remains on them. The laser beam moves along the surface of the drum using a rotating hexagonal mirror located in the laser assembly. The image on the drum is called a latent electrographic image, because it is represented as invisible electrostatic potentials.

The latent electrographic image becomes visible after passing through the developing unit. The developing module for black toner is stationary and is in constant contact with the drum unit (Fig. 9).

The color developing module is a carousel mechanism with alternate supply of “color” cartridges to the drum surface (Fig. 10). Black toner powder is magnetic one-component, and colored powders are one-component, but non-magnetic. Any toner powder is charged to a negative potential due to friction against the surface of the developing roller and the dosage squeegee. Due to the potential difference and the Coulomb interaction of charges, negatively charged toner particles are attracted to those areas of the drum that are discharged by the laser and are repelled from areas with a high negative potential, i.e. from those that were not illuminated by the laser. Only one color is developed with toner at a time. At the time of development, a bias voltage is applied to the developing roller, which causes the toner to be transferred from the developing roller to the drum. This voltage is a rectangular AC voltage with a negative DC component. The DC level can be adjusted by changing the toner density. Once the development process is complete, the image on the drum becomes visible and must be transferred to the transfer drum.

Therefore, the next step in image creation is to transfer the developed image to the transfer drum. This stage is called the primary transfer stage. The transfer of toner from one drum to another is due to an electrostatic potential difference, i.e. the negatively charged toner particles should be attracted by the positive potential on the surface of the transfer drum. To do this, a positive DC bias voltage is applied to the surface of the transfer drum from a special power source, as a result of which the entire surface of this transfer drum has a positive potential. In full color printing, the bias voltage on the transfer drum must constantly increase because after each pass, the amount of negatively charged toner on the drum increases. And in order for the toner to transfer and lay on top of the existing toner, the transfer stress increases with each new color. This stage of imaging is shown in Figure 11.

During the transfer of toner to the transfer drum, some toner particles may remain on the surface of the drum, and they must be removed in order not to distort the subsequent image. The printer has a drum cleaning unit to remove the remaining toner (see Figure 17). This module contains a special roller - a brush for removing the charge from the toner and the drum unit - this weakens the force of attraction of the toner to the drum unit. There is also a traditional cleaning squeegee that scrapes the toner into a hopper where it is stored until the cleaning module is replaced or cleaned out.

Then the drum is charged again (after a preliminary discharge), and the process is repeated until the image of the corresponding color is completely formed on the transfer drum. Therefore, the size of the transfer drum must fully match the print format, i.e. in this printer model, the circumference of this drum corresponds to the length of an A3 sheet (420 mm). After applying the toner of one color, the process of forming the image is completely repeated with the only difference that a developing unit of a different color is used. To use a different developing unit, the carousel mechanism rotates through a predetermined angle and brings the “new” developing roller to the surface of the drum. Thus, in the formation of a full-color image consisting of four color components, the transfer drum is rotated four times, and toner of a different color is added to the existing toner on each revolution. In this case, yellow powder is applied first, then purple, then blue, and the last is black powder. As a result, a full-color visible image is created on the transfer drum, consisting of particles of four different-colored toner powders.

After the toner powder is on the surface of the transfer drum, it passes through the booster unit. This unit (Fig. 12) is a wire coroton, to which an alternating sinusoidal voltage (AC) with a negative constant component (DC) is supplied. With this voltage, the toner powder is additionally charged, i.e. its negative potential becomes higher, which will facilitate more efficient transfer of toner to paper. In addition, the additional voltage reduces the positive potential of the transfer drum, which promotes correct placement of the toner on the transfer drum and prevents the toner from shifting. This results in accurate reproduction of color shades. Boost charge voltage is applied to the transfer drum during the yellow toner application, i. E. at the very beginning of the imaging process. When the yellow toner powder is applied, the additional charge voltage is set to the minimum value, and after each new color is applied, this voltage increases. The maximum boost voltage is applied during black toner application.

Next, the full color visible image from the transfer drum must be transferred onto the paper. This transfer process is called secondary transfer. Secondary transfer is carried out by another corotron made in the form of a transport belt (Fig. 13). The toner is transferred to the paper by electrostatic forces, i.e. due to the potential difference between the toner powder (negative) and the secondary transfer corotron, to which a positive bias voltage is applied. Since the secondary transfer takes place only after four revolutions of the transfer drum, the corona transport belt should only feed the paper when all colors have been applied, i.e. during the fourth turn, and up to this point in time, the belt should be in such a position that the paper does not touch the transfer drum.

Thus, the transport belt is lowered down during the creation of the image, and does not come into contact with the transfer drum, but at the time of the secondary transfer is lifted up and touches this drum. The transport belt of the corona is moved by an eccentric cam, which is driven by an electric clutch on command from the microcontroller (Fig. 14).

During secondary transfer, the sheet of paper may be attracted to the surface of the transfer drum due to the difference in electrostatic potential. Doing so may cause the paper to curl around the drum, resulting in paper jams. To prevent this phenomenon, the printer has a system for separating paper and removing static potential from it. The system is a corotron, which is supplied with a sinusoidal AC voltage with a positive DC component. The location of the corotron in relation to the paper and transfer drum is shown in Figure 15.

During the secondary transfer phase, some of the toner particles are not transferred to the paper, but remain on the drum surface. To prevent these particles from interfering with the creation of the next sheet and not distorting the images, it is necessary to clean the transfer drum and remove the remaining toner. Cleaning the transfer drum is a complex process. This procedure uses a dedicated cleaning roller, drum unit, and drum cleaning unit. The cleaning of the transfer drum should not be carried out continuously, but only after the secondary transfer, i.e. the cleaning system should be controlled in the same way as the transfer corotron. While the image is being created, the cleaning system is inactive, and when the transfer of toner to paper begins, it turns on. The first step in cleaning is to recharge the residual toner powder, i.e. its potential changes from negative to positive. For this, a cleaning roller is used, to which an alternating sinusoidal voltage with a positive constant component is applied. This roller is pressed against the drum surface during the cleaning period, and it is tilted during the imaging process. The roller is controlled by an eccentric cam, which in turn is driven by a solenoid (Fig. 16).

The positively charged toner is then transferred to the drum unit, which still has a negative bias voltage. And already from the surface of the drum unit, the toner is cleaned off with a cleaning squeegee of the drum cleaning unit (Fig. 17).

Finishes creating a full color image by fixing the toner on the paper using temperature and pressure. A sheet of paper passes between two rollers of the fixing unit (fuser), heats up to a temperature of about 200 ºС, the toner melts and is pressed into the surface of the paper. To prevent toner from sticking to the fuser, a negative bias voltage is applied to the heat roller, leaving the negative toner powder on the paper instead of on the Teflon roller.

We have considered the principle of operation of only one printer from one company. Other manufacturers may apply other principles of image formation and other technical solutions when building printers, however, all these solutions will be very close to those discussed earlier.

Laser printers are in great demand for office needs. This technique is also used for home. Excellent consumer qualities are due to the principle of operation of a laser printer. This, as well as the design features of the device, its advantages and disadvantages will be discussed in this material.

The essence of laser printing technology

The printing process in a laser printer is based on the static-electricity dry ink technique invented in 1938. In the late 70s, a laser beam began to be used to automate the work in copying machines. After almost 20 years, technological improvements have made it possible to produce desktop laser devices.

In modern laser printers, as well as multifunction devices with a scanner and a copier, the image is formed by the method of photoelectric xerography and fixed by a special toner under the influence of heat, which is used to fill replaceable cartridges.

Structural elements of a laser printer

Regardless of the model, any laser printing machine has a modular design from the following parts:

• laser scanning module (printed circuit board);
• imaging unit (cartridge);
• paper feed unit;
• thermo unit.

The printed circuit board is a module protected by a cover, consisting of the following elements: a semiconductor laser with a focusing lens, a mirror rotating by a motor, a group of lenses guiding the laser beam, and a mirror.

Important! The laser beam generated by the printed circuit board is directed into the imaging module - the cartridge.

Cartridge design feature

The design of a cartridge for a laser printer is a separate replaceable housing with elements inside, the purpose of which is not very clear for dummies. Among them:

• photosensitive drum;
• charging roller;
• squeegee for cleaning the photo layer from the remains of coloring particles;
• toner reservoir;
• magnetic shaft with a core;
• dosing powder dispenser, the so-called "Doctor";
• seal (removed when installed in the printer).

Unlike dot matrix and inkjet printers, in which the characters transmitted by the processor to the print head are reproduced on paper by means of an ink ribbon or ink drops, the printing process in a laser machine is multi-step. So, first there is a preliminary charge of the drum, then the exposure of the latent image with a laser, then the transfer of the print on paper, followed by its heat treatment.

Basic consumables

The main consumable material of laser printing equipment is a cartridge. After an important node has worn out, the user has three service options.

1. Buy new original copy for replacement, which is quite expensive.
2. Purchase Compatible a printed circuit board from a third-party manufacturer. This is an acceptable economy option.
3. Use the services of a service company specializing in the repair and maintenance of office equipment, the list of services of which includes restoration / refilling of cartridges... This is a super economical option. But after 3-4 fillings, the drum unit wears out, and you will have to use 1 or 2 options.

The process of forming a print on paper

When turned on, the machine is put into a state of readiness for the printing process. The internal elements of the printer start to move, the fuser heats up, which is accompanied by a sound characteristic of printing, but at this moment the laser beam does not turn on. Then the device dies down, and the indicator on its body lights up, signaling that it is ready for work. When the device receives a command to print a document, a multi-step process of forming a printed sheet is initiated.

On a note! Laser printing equipment for controlling the process of outputting an image on paper is supplied with a built-in processor. Also, many high-speed office models are equipped with built-in memory.

Drum charge

When the machine, ready for operation, receives a command to print, all the mechanisms responsible for this process are set in motion: a printed circuit board, a cartridge, paper feed. There is also a prepress preparation of the cartridge, during which photocharging is carried out - an electric charge is transmitted to the photosensitive elements of the drum when the rotating PCR roller touches. The latter gets recharged when the printer is turned on.

Depending on the manufacturer of the printing equipment and the toner it uses, the transferred charge can be negative or positive... Digital models of HP, Xerox, Canon, Ricoh, Samsung have a combination of toner and photocylinder charges - both are negative. Accordingly, Epson, Kyocera, Brother are both positive.

Exposure to a laser beam

In the second stage of image formation, a laser beam is switched on, through which exposure takes place. The focused laser beam is reflected from the mirror and hits the lens guide system, and then is sent to the desired location on the rotating photocylinder.

Important! The character line on the photosensitive layer is formed from illuminated individual dots, which are created by a sequentially redirected laser beam. Under its influence, the photo points lose their charge. Thus, the latent image of the page is formed from the neutral charged points.

Image development

The next stage is the application of toner, which consists of a dye with special charged additives. As a result of this procedure, an image is developed on the photosensitive layer. The process is as follows.

1. The magnetic roller, part of which is located in the filling compartment, attracts powder particles, and they are directed through the "Doctor" to the photosensitive drum in dosed portions.
2. From charged areas (not treated with a laser beam), particles are repelled and stick to the points that have lost their charge. This makes the latent image visible.

Printing on paper and fusing the image

When the drum comes in contact with paper that is being fed by the transfer roller with opposite electrical charge, the dye is attracted to the sheet forming an impression. Particles of paint are trapped by static electricity. The remaining toner grains in the drum are scrubbed with a squeegee into the waste bin.

The image is fixed by heating. The toner coated sheet is pulled between the pressure and heating elements. Under the influence of the oven, the coloring particles are fused into the structure of the paper... Once released, the ink solidifies quickly and the printed image is stable.

Upon completion of the process of forming the image on the paper sheet, drum photocharging is recovered by means of a charging roller, and then, in a cyclical manner, work continues on the printing of the following pages

Color laser technology

The basic principle of forming and obtaining a print on paper in color is identical to monochrome laser printing. To reproduce a multi-color picture, 4 images of different shades used in color printing are created and superimposed on each other: black, cyan, magenta and yellow.

On a note! A full-color picture can be created in one of two ways: by multi-pass or single-pass technology.

Multi-pass printing principle

When forming a color impression on a multi-pass principle, the printer is equipped with a revolver with 4 toner tanks. The technology also involves the use of an auxiliary carrier (belt), onto which an image of the same color is transferred in each pass. After forming all 4 multi-colored sketches, a full-color image from the transfer belt is printed on paper, and then the resulting print is fixed under the influence of heat. Multi-pass technology pretty slow, and it is used in budget models of laser color printing machines.

Single pass imaging

In order for a full-color picture to be formed in one pass, the laser equipment is equipped with four color mechanisms working simultaneously in tandem version. Each of them has its own drum unit and toner tank with a dispenser. The paper is guided by a roller conveyor under each photosensitive element, where toner is transferred to it. The color picture formed in one pass is fixed when it is pulled along the heating element. One-pass printing cycle is equipped with high speed expensive models.

Pros and cons of laser printing

Laser office equipment is very popular, high-tech and efficient. Many users prefer it for such advantages:

• high productivity;
• great resource opportunities;
• low cost of printing;
• unpretentious maintenance;
• fast drying of the print;
• resistance of the sealed image to external influences (moisture, heat);
• low noise level during operation;
• long-term storage of toner, excluding ink drying;
• high printing speed, etc.

These are the main advantages of representatives of all price segments, thanks to which laser technology is in the lead in terms of demand.

However, the technical characteristics of laser output devices are not suitable for printing complex 3d graphics, photographs, gif files. Another disadvantage is the cost of the devices - the most affordable devices are 2-3 times more expensive than inkjets.

Briefly summarizing the above information, it should be noted that laser models of office equipment are in demand when you need to print a lot and quickly. However, this does not apply to photographic prints, since they are subject to increased requirements for color rendering, which laser devices cannot provide. More details about the technology of such printing can be found in the thematic video.

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Before answering the question of how a laser-type printer works, it should be noted that the first image obtained by C. Carlson using static electricity and dry ink dates back to 1938. But the first prototype of a modern laser device was created in the mid-50s of the last century. It should be added that the principle of operation of a laser printer is based on the so-called process. laser scanning. After the document is scanned, the coloring matter is applied and transferred, as well as the final image is fixed. This principle of laser printing allows you to print text and graphics on plain paper at a fairly high speed. You can find out more about how a laser printer prints below.

If we talk about what constitutes a laser printer device, then it must be said that any model of such a device consists of a drum unit, a laser unit, a transfer unit and a fixing unit. In addition, the cartridges use a magnetic roller or developer roller, depending on the model. Paper is fed for printing using a special unit responsible for this action.

To answer in more detail the question of how a laser-type printer works, it is also necessary to talk about the paint (toner) used in this office equipment. So, toner is a substance consisting of very small polymer particles coated with a dye, with the inclusion of magnetite. In addition, it includes the so-called. charge regulator. Depending on the manufacturer, all such powders differ in such indicators as density, dispersion, grain size, magenta, etc. For this reason, it is not worth refueling the laser printer with any random powder paint. this will degrade the print quality.

Office equipment such as a monochrome printer / mfp is widely used for personal use, i.e. at home. Its main advantage lies in its affordable cost, which is due to the fact that such devices do not need a large amount of software resources or memory. They only need a controller that will allow them to carry out the most basic function, which is to print all kinds of documents. In general, it can be used for printing plain text or some kind of black and white diagrams and schemes, where the presence of color does not matter much. Other advantages of monochrome laser-type devices are the low cost of consumables, withstand heavy loads and the ability to print a large number of pages. But such a printer device does not allow him to print color photographs and complex diagrams. In addition, such a device does not have a high print quality.

When it comes to color laser printers, the advantages are good print speed and the ability to print color schemes, images and photographs. But keep in mind that such a printing device is quite expensive, which, in turn, significantly narrows its availability. Its other disadvantages are low profitability due to the high cost of consumables, high power consumption and insufficient quality of color images. Those. such a device is not suitable for printing professional photographs.

But all types of laser printers generally have the same operating principle. The differences lie only in their cost and functionality and parameters, for example, such as the resolution of a laser printer. As for the printing process itself, it can be divided into five key stages, described below.

The first stage: the formation of a charge of the drum (photo drum)

To answer the question of how a laser printer works and how it works, it should be said that one of its main devices is a print drum coated with a special semiconductor that has a high photosensitivity. It is on it, at the first stage, that the image is formed, intended for further printing. For this, this part is supplied with a charge with a plus or minus sign. This is done, as a rule, with the help of a corotron (corona wire) or a charging shaft (charge roller). The first is a block consisting of a wire around which there is a metal frame, the second is a metal shaft covered with foam rubber or conductive rubber.

The first method of imparting a certain charge to the photovale using a corona wire is that a discharge is generated under the action of a voltage between the frame and the wire (platinum / gold / carbon coated tungsten filament). After that, an electric field is formed, which, in turn, transfers a static-type charge to the drum unit.

The use of a corona wire has a number of disadvantages, which are that the accumulation of ink / dust particles on its filament or its bending can lead to a sharp decrease in print quality, an increase in the electric type field in a certain place, and even damage to the drum surface.

As for the second method, the charge roller, when it comes into contact with the drum, supplies it with a surface characterized by high photosensitivity with a certain charge. In this case, the voltage on the roller is an order of magnitude lower, which, in turn, solves the problem with the appearance of ozone. But in order to carry out the transfer of charge, contact is necessary. Consequently, the parts of the printer will wear out faster in this case.

Stage two: exposure

The purpose of this stage is to form an invisible image from dots on the surface of the photodrum with increased light sensitivity, and without the use of static charge. To do this, a thin laser beam shines on a four- or hexagonal-shaped mirror, after which it is reflected and hits the so-called. a distribution lens. He sends it to a specific place on the surface of the drum. Further, a system consisting of several lenses and mirrors moves the laser beam along the photogallery, as a result of which a line is formed. Because printing is carried out using dots, the laser is constantly turned on and off. In this case, the charge is also removed in a point manner. After the line comes to the end, the photo roll begins to rotate with the help of the step motor and the exposure procedure continues.

Stage three: development

Another shaft in a laser printer cartridge is a metal tube with a magnetic core inside. The magnet inside the compartment attracts the toner to the surface of the shaft and, rotating, carries it out. A special metering blade allows you to adjust the thickness of the dye layer and thus prevent it from being evenly distributed.

The ink then flows between the drum unit and the magnetic roller. In the areas that have passed the exposure, the toner begins to be attracted to the surface of the photogallery, and in the charged areas, it repels. The colorant remaining on the magnetic roller usually goes on and passes through the hopper again. As for the toner that has moved to the surface of the drum, it makes the image visible on it, and then follows on, i.e. to paper.

Stage four: transfer

The sheet of paper that was fed into the device passes under the photogallery. In this case, under the paper is located the so-called. transfer roller, which helps to ensure that toner on the drum surface hits the paper surface. A plus sign is applied to the metal core of the roller, which is transferred to the paper through a rubber coating. Microscopic particles of toner transferred to the surface of the sheet are adhered to it solely due to static attraction. Any remaining powder particles, paper lint and dust remaining on the drum unit are sent using a squeegee or wiper to a specially designed waste bin. Once the drum unit completes the entire cycle, the charge roller / corotron again helps to restore the charge on its surface and all the work is repeated again.

Fifth stage: consolidation

The toner used in laser printers must necessarily have the ability to melt at high temperatures. Only thanks to this property can it finally be fixed on the surface of the paper.

To do this, the sheet is pulled between two shafts, one of which presses it, and the other heats it up. Due to this, microscopic particles of the coloring matter are, as it were, fused into the structure of the page. After leaving the oven, the powder hardens quickly enough, as a result of which the printed picture or text becomes sufficiently stable.

It should also be added that the upper roller, which heats up the sheet of paper, is in the form of a thermal film or a Teflon roller. Moreover, the second option is considered more durable and reliable. However, it is expensive and is used most often in devices that have to withstand heavy loads. The first option is less reliable and is usually used for printers intended for small offices and home use.