Detailed operating principle of a laser printer. How a laser printer works

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 is leading to growing interest in them from technical support services.

Principles of color printing

In printers, as in printing, 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 so called because to form any hue it is necessary to subtract from white“extra” components. 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 called CMY by the first letters of the primary colors.

In the subtractive model, when two or more colors are mixed, complementary colors are created by absorbing some light waves and reflecting others. Blue paint, for example, absorbs red and reflects green and blue; purple paint absorbs green and reflects red and blue; and yellow paint absorbs blue and reflects red and green. By mixing the main components of the subtractive model, different colors can be obtained, which are described below:

Blue + 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, but getting high-quality black in this way is almost impossible. The resulting color will not be black, but rather a dirty gray. To eliminate this drawback, one more color is added to the three main colors - black. This extended color model is called CMYK(C yan- M agenta- Y ellow-black K – cyan-magenta-yellow-black). The introduction of black color can significantly improve the quality of color rendering.

HP Color LaserJet 8500 Printer

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

Its main characteristics are:
- resolution: 600 DPI;
- print speed in “color” mode: 6 ppm;
- print speed in “black and white” mode: 24 ppm.

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

Image formation begins with residual potentials being removed (neutralized) from the surface of the photodrum. This is done so that the subsequent charge of the photodrum is more uniform, i.e. Before charging it is completely discharged. Removal of residual potentials is carried out by illuminating the entire surface of the drum with a special preliminary (conditioning) exposure lamp, which is a line of LEDs (Fig. 7).

Next, a high-voltage (up to -600V) negative potential is created on the surface of the photodrum. The drum is charged with a corotron in the form of a roller made of conductive rubber (Fig. 8). The corotron is fed AC voltage sinusoidal shape with a negative constant component. The alternating component (AC) ensures uniform distribution of charges on the surface, and the constant component (DC) charges the drum. The DC level can be adjusted by changing the print density (toner density), which is done using the printer driver or through adjustments through the control panel. An increase in negative potential leads to a decrease in density, i.e. to a lighter image, while decreasing the potential - on the contrary, to a denser (darker) image. The photodrum (its internal metal base) must be “grounded”.

After all this, a laser beam creates an image on the surface of the photodrum in the form of charged and uncharged areas. The laser light beam hitting the surface of the drum discharges this area. The laser illuminates those areas of the drum where the toner should be. Those areas that should be white are not illuminated by the laser, and a high negative potential remains on them. The laser beam moves across 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 black toner developing module is stationary and is in constant contact with the photodrum (Fig. 9).

The color developing module is a carousel mechanism with alternate supply of “color” cartridges to the surface of the drum (Fig. 10). Black toner powder is single-component magnetic, while colored toner powders are single-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 dosing squeegee. Due to the potential difference and the Coulomb interaction of charges, negatively charged toner particles are attracted to those areas of the photodrum 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. At any given time, only one color of toner is developed. During development, a bias voltage is applied to the developing roller, which causes toner to transfer from the developing roller to the drum. This voltage is a rectangular alternating voltage with a negative DC component. The DC level can be adjusted as the toner density changes. After the development process is completed, the image on the drum becomes visible and must be transferred to the transfer drum.

Therefore, the next step in creating an image 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 occurs due to an electrostatic potential difference, i.e. Negatively charged toner particles should be attracted to the positive potential on the surface of the transfer drum. To do this, a positive bias voltage is applied to the surface of the transfer drum. direct current from a special power source, as a result of which the entire surface of this drum has a positive potential. When printing full color, 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 voltage increases with each new color. This imaging stage is shown in Fig. 11.

During the transfer of toner to the transfer drum, some particles of toner may remain on the surface of the image drum and must be removed to avoid distorting the subsequent image. To remove residual toner, the printer has a drum cleaning unit (see Figure 17). This module contains a special shaft - a brush for removing the charge from the toner and the photodrum - this weakens the force of attraction of the toner to the photodrum. There is also a traditional cleaning squeegee that scrapes the toner into a special hopper where it is stored until the cleaning module is replaced or cleaned.

Next, the photodrum is charged again (after 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 correspond to 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 toner of one color, the image formation process is completely repeated with the only difference being that a developing unit of a different color is used. To use another developing unit, the carousel mechanism rotates at a given angle and brings the “new” developing shaft to the surface of the photodrum. Thus, when forming a full-color image consisting of four color components, the transfer drum is rotated four times, and at each rotation a toner of a different color is added to the existing toner. In this case, yellow powder is applied first, then purple, then blue, and black powder is applied last. As a result, a full-color visible image is created on the transfer drum, consisting of particles of four multi-colored toner powders.

After the toner powder lands on the surface of the transfer drum, it passes through the additional charge unit. This block (Fig. 12) is a wire coroton, to which a sinusoidal alternating voltage (AC) with a negative direct component (DC) is supplied. With this voltage, the toner powder is additionally charged, i.e. its negative potential becomes higher, which will contribute to more efficient transfer of toner to paper. In addition, the additional voltage reduces the positive potential of the transfer drum, which helps ensure that the toner is positioned correctly on the transfer drum and prevents the toner from moving. The result is accurate reproduction of color shades. The additional charge voltage is supplied to the transfer drum during the application of yellow toner, i.e. at the very beginning of the image formation process. When applying yellow toner powder, the additional charge voltage is set to a minimum value, and after applying each new color, this voltage increases. Maximum voltage additional charge is supplied while black toner is being applied.

Next, the full-color visible image from the transfer drum must be transferred to 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 moved onto 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 secondary transfer occurs only after four rotations of the transfer drum, the corotron transfer belt must feed the paper only when all colors have been applied, i.e. during the fourth revolution, and until this point in time, the belt should be in such a position that the paper does not touch the transfer drum.

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

During secondary transfer, a sheet of paper may be attracted to the surface of the transfer drum due to the difference in electrostatic potential. This may cause the sheet of paper to wrap around the drum, resulting in a paper jam. To prevent this phenomenon, the printer has a system for separating paper and removing static potential from it. The system is a corotron to which an alternating sinusoidal voltage with a positive constant component is supplied. The location of the corotron relative to the paper and transfer drum is shown in Fig. 15.

During the secondary transfer stage, some toner particles are not transferred to the paper, but remain on the surface of the drum. To prevent these particles from interfering with the creation of the next sheet and distorting the image, it is necessary to clean the transfer drum and remove any remaining toner. Cleaning the transfer drum is a fairly complex process. This procedure uses a special cleaning roller, image drum, and image drum cleaning unit. The transfer drum should not be cleaned continuously, but only after the secondary transfer, i.e. The cleaning system should be controlled similarly to the transfer corotron. While the image is being created, the cleaning system is not active, and when the toner begins to transfer to the paper, it turns on. The first cleaning step is to recharge the residual toner powder, i.e. its potential changes from negative to positive. For this purpose, a cleaning roller is used, which is supplied with an alternating sinusoidal voltage with a positive constant component. This roller is pressed against the surface of the drum during the cleaning period, and during image creation it is folded back. 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 image drum, which still has a negative bias voltage. And already from the surface of the photodrum, the toner is cleaned with a cleaning squeegee of the photodrum cleaning unit (Fig. 17).

The creation of a full-color image ends by fixing the toner on paper using temperature and pressure. A sheet of paper passes between two rollers of the fixing block (oven), is heated to a temperature of about 200 ºС, the toner is melted and pressed into the surface of the paper. To prevent toner from sticking to the fuser, a negative bias voltage is applied to the heating roller, causing the negative toner powder to remain on the paper rather than on the Teflon roller.

We examined the operating principle of only one printer from one company. Other manufacturers may use other principles of image formation and other technical solutions when constructing printers, however, all these solutions will be very close to those discussed earlier.

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IN article is being considered principle actions and device modern laser printers. She opens series articles, dedicated principles and problems laser boards.

The image obtained using modern laser printers (as well as matrix and inkjet printers) consists of dots. The smaller these dots and the more frequently they are located, the higher the image quality. The maximum number of dots that a printer can print separately on a 1-inch (25.4 mm) section is called resolution and is characterized in dots per inch, and the resolution can be 1200 dpi or more. The quality of text printed on a laser printer with a resolution of 300 dpi is approximately the same as typographical. However, if the page contains drawings containing shades of gray, then to obtain a high-quality graphic image you will need a resolution of at least 600 dpi. With a printer resolution of 1200 dpi, the print is almost photographic quality. If you need to print a large number of documents (for example, more than 40 sheets per day), a laser printer seems to be the only smart choice, since for modern personal laser printers standard parameters are a resolution of 600 dpi and a print speed of 8...1 2 pages per minute.

OPERATING PRINCIPLE OF A LASER PRINTER

The laser printer was first introduced by Hewlett Packard. It used the electrographic principle of creating images - the same as in photocopiers. The difference was in the method of exposure: in photocopiers it occurs using a lamp, and in laser printers, lamp light replaced the laser beam.

With my heart laser printer is a photoconductive cylinder (Organic Photo Conductor), which is often called a printing photodrum or simply a drum. It is used to transfer images onto paper. The photodrum is a metal cylinder coated with a thin film of photosensitive semiconductor. The surface of such a cylinder can be provided with a positive or negative charge, which remains until the drum is illuminated. If any part of the drum is exposed, the coating becomes conductive and charge flows away from the illuminated area, creating an uncharged zone. This is a key point in understanding how a laser printer works.

Another important part of the printer is the laser and the optical-mechanical system of mirrors and lenses that moves the laser beam along the surface of the drum. The small-sized laser generates a very thin beam of light. Reflecting from rotating mirrors (usually tetrahedral or hexagonal), this beam illuminates the surface of the photodrum, removing its charge at the exposure point.

To obtain a spot image, the laser is turned on and off using a control microcontroller. The rotating mirror turns the beam into a line of latent image on the surface of the photodrum.

After forming the string, special stepper motor turns the drum to form the next one. This offset corresponds to the printer's vertical resolution and is typically 1/300 or 1/600 inch. The process of forming a latent image on a drum is reminiscent of the formation of a raster on a television monitor screen.

Two main methods of preliminary (primary) charging of the surface of the photocylinder are used:

Ø using a thin wire or mesh called “corona wire”. High voltage, applied to the wire, leads to the appearance of a luminous ionized area around it, which is called the corona, and gives the drum the necessary static charge;

Ø using a pre-charged rubber roller (PCR).

So, an invisible image in the form of statically discharged dots is formed on the drum. What's next?

DEVICECARTRIDGE

Before we talk about the process of transferring and fixing an image on paper, let’s look at the device of the cartridge for the Laser Jet 5L printer from Hewlett Packard. This typical cartridge has two main compartments: the waste toner compartment and the toner compartment.

Main structural elements of the waste toner compartment:

1 - Image drum(Organic Photo Conductor (OPC) Drum). It is an aluminum cylinder coated with an organic photosensitive and photoconductive material (usually zinc oxide) that is capable of retaining the image created by the laser beam;

2 - Shaft primary charge(Primary Charge Roller (PCR)). Provides a uniform negative charge to the drum. Made from a conductive rubber or foam base applied to a metal shaft;

3 - « Viper» , squeegee, cleaning blade(Wiper Blade, Cleaning Blade). Clears the drum of any remaining toner that has not been transferred to the paper. Structurally, it is made in the form of a metal frame (stamping) with a polyurethane plate (blade) at the end;

4 - Blade cleaning (Recovery Blade). Covers the area between the drum and waste toner box. Recovery Blade passes the toner remaining on the drum into the hopper and prevents it from spilling out in the opposite direction (from the hopper onto the paper).

Main structural elements of the toner compartment:

1 - Magnetic shaft(Magnetic Developer Roller, Mag Roller, Developer Roller). It is a metal tube, inside of which there is a stationary magnetic core. Toner is attracted to the magnetic shaft, which, before being supplied to the drum, acquires a negative charge under the influence of direct or alternating voltage;

2 - « Doctor» (Doctor Blade, Metering Blade). Provides uniform distribution of a thin layer of toner on the magnetic roller. Structurally, it is made in the form of a metal frame (stamping) with a flexible plate (blade) at the end;

3 - Sealing blade magnetic shaft(Mag Roller Sealing Blade). A thin plate similar in function to the Recovery Blade. Covers the area between the magnetic roller and the toner supply compartment. Mag Roller Sealing Blade allows toner remaining on the magnetic roller to flow into the compartment, preventing toner from leaking backwards;

4 - Bunker For toner (Toner Reservoir). Inside it is the “working” toner, which will be transferred to the paper during the printing process. In addition, a toner activator (Toner Agitator Bar) is built into the hopper - a wire frame designed for mixing toner;

5 - Seal, check (Seal). In a new (or regenerated) cartridge, the toner hopper is sealed with a special seal that prevents toner from spilling during transportation of the cartridge. This seal is removed before use.

PRINCIPLE OF LASER PRINTING

The picture shows a cross-section of the cartridge. When the printer turns on, all components of the cartridge begin to move: the cartridge is prepared for printing. This process is similar to the printing process, but laser ray does not turn on. Then the movement of the cartridge components stops - the printer goes into a ready-to-print state.

After sending a document for printing, the following processes occur in the laser printer cartridge:

Charger drum. The Primary Charge Roller (PCR) uniformly transfers a negative charge to the surface of the rotating drum.

Exhibition. The negatively charged surface of the drum is exposed to the laser beam only in those places where the toner will be applied. When exposed to light, the photosensitive surface of the drum partially loses its negative charge. Thus, the laser exposes a latent image to the drum in the form of dots with a weakened negative charge.

Application toner. At this stage, the latent image on the drum is converted into a visible image with the help of toner, which will be transferred to paper. The toner located near the magnetic roller is attracted to its surface under the influence of the field of the permanent magnet from which the core of the roller is made. When the magnetic shaft rotates, the toner passes through a narrow slot formed by the “doctor” and the shaft. As a result, it acquires a negative charge and sticks to those areas of the drum that were exposed. “Doctor” ensures uniform application of toner onto the magnetic roller.

Transfer toner on paper. Continuing to rotate, the drum with the developed image comes into contact with the paper. On the reverse side, the paper is pressed against the Transfer Roller, which carries a positive charge. As a result, negatively charged toner particles are attracted to the paper, which produces an image “sprinkled” with toner.

Consolidation Images. A sheet of paper with an unfixed image is moved to a fixing mechanism, which consists of two contacting shafts, between which the paper is pulled. The Lower Pressure Roller presses it against the Upper Fuser Roller. The top roller is heated, and when it touches it, the toner particles melt and adhere to the paper.

Cleaning drum. Some toner does not transfer to the paper and remains on the drum, so it needs to be cleaned. This function is performed by the “viper”. All toner remaining on the drum is removed by a wiper into the waste toner bin. At the same time, the Recovery Blade covers the area between the drum and the hopper, preventing toner from spilling onto the paper.

"Erase" Images. At this stage, the latent image created by the laser beam is “erased” from the surface of the drum. Using the primary charge shaft, the surface of the photodrum is evenly “covered” with a negative charge, which is restored in those places where it was partially removed under the influence of light.

Many people have used laser printers, some have them at home, but does everyone know how a laser printer works? The reader will find the answer to this question in this article.

A laser printer is peripheral device, which quickly and efficiently prints text and graphic objects on regular office and specialty paper. The main advantages of these printers, such as low printing costs, high operating speed, high resource and resolution, resistance to moisture and fading, have made them the most frequently used not only among office workers, but also among ordinary users.

Creation and development of laser printers

The first image using dry ink and static electricity was made by Chester Carlson back in 1938. And only 8 years later he was able to find the manufacturer of the devices he invented. It was a company that everyone now knows as Xerox. And in the same 1946, the first copier entered the market. It was a huge and complex machine, requiring a number of manual operations. Only in the mid-1950s was the first fully automated mechanism created, which was the prototype of the modern laser printer.

Since the end of 1969, Xerox began work on the development of laser printers, adding a laser beam to existing samples at that time. But it cost a third of a million dollars by those standards and was enormous in size, which did not allow the use of such a device even in small enterprises, let alone in everyday life.

The result of cooperation between the current giants in the printing industry Canon and HP was the release of a series of LaserJet printers that are capable of printing up to 8 pages of text per minute. Such devices became more accessible after the first replaceable laser printer cartridge appeared.

Principle of operation

The basis for image formation is the dye contained in the toner. Under the influence of static electricity, it sticks and is literally imprinted into the paper. But how does this happen?

Any laser printer consists of three main functional blocks: printed circuit board, image transfer unit (cartridge) and printing unit. The paper feed unit supplies the paper for printing. They are designed in two designs - paper feeding from the lower tray and paper feeding from the upper tray.

Its structure is quite simple:

• roller – needed to pick up paper;
• unit for capturing and feeding one sheet;
• a roller that transfers a static charge to the paper.
• A laser printer cartridge consists of two parts - a toner and a drum or photocylinder.

Toner

The toner consists of microscopic polymer particles that are coated with dye, including magnetite and a charge regulator. Each company produces powder with unique characteristics for its own printers and multifunctional devices. All powders differ in magnetism, density, dispersion, grain size and others. physical indicators. Therefore, you should not refill cartridges with random toner. The advantages of toner over ink are the clarity of the printed image and moisture resistance, which is ensured by printing the powder into the paper. Among the disadvantages are the low color depth, saturation during color printing and the negative impact on the human body when interacting with the toner, for example, while charging the cartridge.

Structure and stages of image printing

The photodrum is made in the form of a longitudinal aluminum shaft, coated with a thin layer of material that is sensitive to light rays with certain parameters. The cylinder is covered with a protective layer. In addition to aluminum, drums are made from inorganic photosensitive substances. The main property of a photodrum is a change in conductivity (charge) under the influence of a laser beam. This means that if the cylinder is given a charge, it will store it for a significant period of time. But if you illuminate any area of ​​the shaft with light, they immediately lose their charge and become neutrally charged due to an increase in conductivity (that is, a decrease in electrical resistance) in these zones. The charge flows from the surface through the internal conductive layer.

When a document arrives for printing, the printed circuit board processes it and sends appropriate light pulses to the image transfer unit, where the digital image is converted into an image on paper. The photodrum rotates using a shaft and receives a primary negative or positive charge from a nearby roller. Its value is determined by the print settings reported by the printed circuit board.

After charging the cylinder, a horizontal laser beam scans it with enormous frequency. The exposed areas of the photocylinder, as mentioned above, become uncharged. These uncharged zones form the required pattern on the drum in mirror image. Next, in order for the image to appear on paper, the uncharged areas must be filled with toner. The laser scanning unit consists of a mirror, a semiconductor laser, several shaping lenses and one focusing lens.

The drum is in contact with a roller, made mainly of magnesium, and supplies toner to the photo cylinder from the cartridge tank. The roller, in which the permanent magnet is located, is made in the form of a hollow cylinder with a conductive layer. Under the influence of a magnetic field, the toner from the hopper is attracted to the roller under the force of the magnetized core.

Under the influence of electrostatic voltage, the toner from the roller will be transferred to the image formed by the laser beam on the surface of the photodrum, rotating close to the roller. The toner has nowhere to go, because its negatively charged particles are attracted to the positively charged areas of the photocylinder on which the desired image is formed. The drum's negative charge pushes unwanted toner back, filling the laser-scanned areas with it.

Let us note one nuance. There are two types of imaging. The most common is the use of toner with positive charge. Such powder remains on neutrally charged areas of the photocylinder. That is, the laser illuminates the areas where our future image will be. The drum is negatively charged. The second mechanism is less common and uses a toner with a negative charge. The laser beam “discharges” areas of the positively charged photocylinder where there should not be an image. This is worth remembering when choosing a laser printer, because in the first case there will be a more accurate transfer of details, and in the second - a more uniform and dense filling. The first printers are great for printing text documents That's why they became widespread.

Before the paper comes into contact with the cylinder, it receives static electric charge using a charge transfer roller. Under the influence of which the toner is attracted to the paper at the moment of its close contact with the drum. Immediately after this, the charge from the paper is removed by a static charge neutralizer. This eliminates the attraction of the sheet to the photocylinder. As the paper passes through the laser scanning unit, the formed image becomes noticeable on the sheet, which is easily destroyed by the slightest touch. For its durability, it is necessary to fix it by melting the additives included in the toner. This process occurs in the image fixation unit - this is the third key unit of the laser printer. It is also called a “stove”. In short, the substances contained in the toner melt. After they are pressed in and hardened, these polymers seem to cover the ink, protecting it from external influences. Now the reader will understand why the printed sheets coming out of the printer are so warm.

By design, the so-called “stove” consists of two shafts, one of which contains a heating element. The second, often the bottom one, is necessary to press the molten polymer into the paper. Heating elements are made in the form of thermistors made in the form of thermal films. When voltage is applied to them, these elements heat up to high temperatures (about 200 °C) in a fraction of a second. The pressure roller presses the sheet against the heater, which presses liquid microscopic toner particles into the paper's texture. There are separators at the exit from the fixing block so that the paper does not stick to the thermal film.

It's hard to imagine modern life without a printer. At schools they print out scripts, at the university - essays, at work - contracts, and even at home we sometimes urgently need to transfer this or that information to paper. There are several types of printers, they are classified by type of printing, by format, by size and even by type of printed materials. Let's look at the printing principle of an inkjet and laser printer.

How does an inkjet printer work?

We will try to briefly highlight the printing principle of an inkjet printer. Its print quality is slightly worse than laser. However, their cost is significantly lower than laser ones. The inkjet printer is ideal for use at home. It is easy to operate and easy to maintain. The printing principles of inkjet and laser printers are noticeably different. This is manifested in both ink supply technology and equipment design. Therefore, let's first talk about how an inkjet printer prints.

Its operating principle is as follows: an image is formed in a special matrix, and then this matrix prints the image on the canvas using liquid dyes. Another type of inkjet printer is equipped with cartridges that are installed in a special unit. In this case, with the help of the print head, ink is supplied to the print matrix, and it transfers the image to paper.

Methods for storing ink and applying it to paper

There are three ways to apply ink to canvas:

Piezoelectric method;
. gas bubble method;
. drop-on-demand method.

The first method, when printing, leaves an ink dot on the canvas due to the piezoelectric element. With its help, the tube compresses and unclenches, preventing excess ink from getting onto the paper.

Gas bubbles, also known as injection bubbles, leave an imprint on the canvas due to high temperatures. Each nozzle of the printing matrix is ​​equipped with which heats up in a fraction of a second. The resulting gas bubbles are pushed through the nozzle and transferred to the consumable.

The drop-on-demand method also uses gas bubbles during operation. But this is a more optimized technology that significantly increases the speed and quality of modern printing.

An inkjet printer stores ink in two ways. There is a separate removable reservoir from which ink is supplied to the print head. The second method for storing ink uses a special cartridge, which is also located in the print head. To replace the cartridge, you must also replace the head itself.

Let's talk about inkjet printers

Inkjet printers have gained particular popularity due to their ability. When printing, an image is formed by superimposing basic tones of different saturations on top of each other. The set of primary colors is abbreviated CMYK. These include: yellow, magenta, cyan and black.

Initially, a three-color set was offered, which included all of the above tones, except for the black tint. But when layering yellow, cyan and magenta at 100% saturation, it was not possible to achieve black. The result was brown or grey colour. Therefore, it was decided to add black ink.

Features of an inkjet printer

The main indicators of high-quality printer operation include noise, print speed, print quality and durability.

Printer performance properties:

• The printing principle is inkjet. The ink is fed through special nozzles and printed on the canvas. Unlike needle printers, where applying ink is a shock-mechanical process, inkjet printers operate very quietly. You can’t hear how the printer prints, you can only hear the noise of the motor that moves the print heads. does not exceed 40 dB.
• The printing speed of an inkjet printer is much higher than that of a pin printer. The print quality also depends on this indicator. Printer printing principle: the higher the speed, the worse the print. If you choose a high-quality print, the process slows down and the ink is applied more thoroughly. The average of such a printer is approximately 3-5 pages per minute. More modern models have increased this figure to 9 pages per minute. Color printing takes a little longer.
• Font is one of the main advantages of an inkjet printer. The quality of font display can only be compared with a laser printer. You can improve print quality by using good paper. It should have quickly absorbing properties. A good image is obtained on paper with a density of 60-135 g/m². Copier paper with a density of 80 g/m² also performed well. To quickly dry the ink, use the paper heating function. Despite the fact that the printing principles of inkjet and laser printers are completely different, high-quality equipment allows you to achieve a similar effect.
• Paper. Unfortunately, the inkjet printer is not suitable for printing on roll media. And to get multiple copies you will have to use multiple printing.

Disadvantages of Inkjet Printing

As it turned out above, inkjet printers printed with liquid dyes using a matrix. The image is formed from dots. The most expensive part in a printer is the print head; some companies have built the print head of the printer into the cartridge to reduce the overall dimensions of the device. The printing principles of inkjet and laser printers are significantly different from each other.

The disadvantages of this printer include:

• Low printing speed.
• If the printer has not been used for a long time, the ink may dry out.
• Consumables have high cost and low resource.

Benefits of Inkjet Printer Printing

• Attractive price, ideal price-performance ratio.
• The printer has very modest dimensions, which allows it to be placed in a small office without causing inconvenience to the user.
• The cartridges are easy to refill yourself, just buy the ink and read the instructions.
• Connectivity For large print volumes, this will significantly reduce costs.
• High quality photo printing.
• Wide selection of print media.

A little about the laser printer

A laser printer is a type of equipment designed to print text or images onto paper. The history of the creation of this type of equipment is quite unusual. And it has a marketing approach, unlike the inkjet printer, which was created using hundreds of scientific concepts.

It was only in 1969 that Xerox began to develop the printing principle of a laser printer. For several years scientific works, many methods have been used to improve the existing apparatus. In 1978, the world's first copier appeared that used a laser beam to create a print. The printer turned out to be huge in size, and the price did not allow anyone to purchase this unit. After some time, I became interested in the development Canon company, and the first desktop laser printer was released in 1979. Afterwards, many companies began optimizing copiers and releasing new models, but the printing principle of a laser printer has not changed.

How does a laser printer print?

Prints obtained in this way have high performance characteristics. They are not afraid of moisture, they are not afraid of abrasion and fading. Images obtained in this way are very high quality and durable.

The printing principle of a laser printer in brief:

• A laser printer applies an image to a canvas in several stages. The toner (special powder) melts under the influence of temperature and sticks to the paper.
• A squeegee (special scraper) removes unused toner from the drum into the waste storage tank.
• The caronator polarizes the surface of the drum and, through electrostatic forces, assigns a positive or negative charge to it.
• The image is formed on the surface of the drum using a rotating mirror, which directs it to the desired location.
• The drum moves along the surface of the magnetic shaft. There is toner on the shaft, which sticks to those parts of the drum where there is no charge.
• The drum then rolls over the paper, leaving toner on the canvas.
• At the final stage, the paper with toner sprayed on it is rolled through an oven, where the substance melts under the influence of high temperatures and reliably adheres to the paper.

The printing principle of a laser printer has much in common with the technology used in copiers.

Color laser printers and their main differences

The printing process on a color printer differs from black and white in the presence of several shades, which, when mixed in a certain proportion, can recreate all the colors known to us. Color laser printers use four separate compartments for each ink color. This is their main difference.

Printing on a color printer consists of the following stages: image analysis, its raster image, arrangement of colors and their corresponding toners. Then a charge distribution is formed. Afterwards the procedure is the same as for black and white printing. The ink sheet passes through an oven where the toners are melted and firmly bonded to the paper.

Their advantage is that the printing principle of a laser printer makes it possible to achieve very thin beams that discharge the desired areas. As a result, we get a very high-quality high-resolution image.

Advantages of modern laser printers

The advantages of laser printer printing include:

• High printing speed.
• Durability, clarity and durability of prints (they are not afraid of a humid microclimate).
• High image resolution.
• Low cost of printing.

Disadvantages of laser printer printing

The main disadvantages of laser printers:

• During operation of the equipment, ozone is released. This means you need to work with it in a well-ventilated area.
• High power consumption.
• Bulky.
• High cost of equipment

Based on all the pros and cons, we can conclude that inkjet printers are perfect for home use. They have affordable price and small dimensions, which is important for many users.

A laser printer is suitable for offices and other institutions where there are a lot of black and white printouts and speed of document processing is important.

Includes seven sequential operations to create a given image on a sheet of paper. This is a very interesting and technological process that can be divided into two main stages: applying the image and fixing it. The first stage is associated with the operation of the cartridge, the second takes place in the fusing unit (oven). As a result, in a matter of seconds we get the image we are interested in on a white sheet of paper.

So, what happens in such a short period of time in the printer? Let's figure this out.

Charge

Let us remember that toner is a finely dispersed substance (5-30 microns), and its particles very easily accept any electrical charge.

In the cartridge, the charge roller ensures uniform transfer of negative charge to the photodrum. This happens when the charge roller is pressed against the photodrum, and rotating in one direction (while uniformly imparting a negative static charge to the photodrum), causes it to rotate in the other.

Thus, the surface of the photodrum has a negative charge evenly distributed over the area.

Exhibition

In the next process, the future image is exposed on a photodrum.

This happens thanks to a laser. When a laser beam hits the surface of the photodrum, it removes the negative charge in this place (the point becomes neutrally charged). Thus, the laser beam forms the future image according to given coordinates in a programme. Exclusively in those places where it is necessary.

This way we get the exposed part of the image in the form of negatively charged dots on the surface of the photodrum.

Development

Next, toner is applied to the exposed image on the surface of the photodrum in an even thin layer using a developing roller. The toner particles take on a negative charge and form a future image on the surface of the drum.

Transfer

The next step is to transfer the negatively charged toner image from the drum to a blank sheet of paper.

This occurs when the transfer roller comes into contact with a sheet of paper (the sheet passes between the transfer roller and the image drum). The transfer roller has a high positive potential, causing all the negatively charged toner particles (in the form of a formed image) to be transferred to the sheet of paper.

Consolidation

The next step in laser printing is to fix an image from a toner onto a sheet of paper in a fusing unit (in the oven).

At its core, this is the process of “baking” onto paper. A sheet of toner, passing between a thermal roller and a pressure roller, is subjected to thermo-baric (temperature and pressure) treatment, as a result of which the toner is fixed on the sheet and becomes resistant to external mechanical influences.

In our picture you see a thermal shaft and a pressure roller. Thermal roll is used in a number of laser printing devices. A halogen lamp is used inside the thermal shaft, which provides heating (heating element).

There are other models of laser printing devices, where thermal film is used instead of a thermal roller (as a heating element). The difference between them is that the halogen heater takes longer to operate. It is worth noting the fact that devices with thermal film are very susceptible to mechanical influences from foreign objects (paper clips, staples from a stapler) on a sheet of paper. This is fraught with failure of the thermal film itself. She is very sensitive to damage.

Cleaning

Since during this whole process a small amount of toner remains on the surface of the photodrum, a squeegee (cleaning blade) is installed in the cartridge to clean residual microparticles of toner from the photodrum shaft.

As it rotates, the shaft is cleaned. The residual powder ends up in the waste toner bin.

Removing charge

During the last stage, the photodrum shaft comes into contact with the charge roller. This leads to the fact that the “map” of negative charge is again aligned on the surface of the drum (up to this point, both negatively charged places and neutrally charged ones remained on the surface - they were the projection of the image).

Thus, the charge roller again imparts a uniformly distributed negative potential to the surface of the photodrum.

This ends the cycle of printing one sheet.

Conclusion

Thus, laser printing technology includes seven successive stages of transferring and fixing an image on paper. On modern devices, this process of printing one image on A4 paper takes only a matter of seconds.

When worn out internal parts, such as the photodrum, charge roller or magnetic shaft, are replaced. These components are located inside the cartridge, and you can see them in the picture above. Due to wear of these elements, print quality deteriorates significantly.

A little about the history of laser printing

And finally, a little about the development of laser printing technology. Surprisingly, laser printing technology appeared earlier, for example, the same matrix printing technology. Chester Carlson invented a printing method called electrography in 1938. It was used in photocopiers of that time (60-70s of the last century).

The very development and creation of the first laser printer was directed by Gary Starkweather. He was an employee of Xerox. His idea was to use copier technology to create a printer.

First appeared in 1971 first laser printer Xerox company. It was called the Xerox 9700 Electronic Printing System. Serial production was launched later - in 1977.