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. And here is the first prototype of the modern laser device was created in the mid-1950s. It should be added that the principle of operation of a laser printer is based on the process of the so-called. laser scanning. After the document is scanned, the ink is applied and transferred, as well as the finished image is fixed. A similar principle of laser printing allows you to print text and graphics on plain paper at a fairly high speed. You can learn more about how a laser printer prints below.

If we talk about what a laser printer device is, then it must be said that any model of such a device consists of a photoconductor, a laser unit, a transfer unit and a fixing unit. In addition, the cartridges, depending on the model, use a magnetic roller or a developing roller. Paper is fed to print using a special node 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, the toner is a substance consisting of very small particles of polymer 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, magnity, etc. For this reason, refilling a laser printer with any random powder paint is not worth it, because. this will degrade the print quality.

Office equipment of this type, as a monochrome printer / MFP, has found wide application for personal use, i.e. Houses. 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. All they need is 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 to print plain text or some black and white charts and diagrams where the presence of color does not play a big role. Other advantages of monochrome laser-type devices are low cost for consumables, withstanding 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 high print quality.

As for color laser printers, their advantages are good printing 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 insufficiently high quality color images. Those. such a device is not suitable for printing professional photos.

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

The first stage: the formation of a photodrum charge (photoshaft)

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 high photosensitivity. It is on it that at the first stage an image is formed, intended for further printing. To do 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 coronator (coronator) 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 way to give the photoshaft a certain charge using a coronator is that under the action of voltage between the frame and the wire (tungsten filament coated with platinum/gold/carbon), a discharge is formed. After that, an electric field is formed, which, in turn, transfers a static-type charge to the photoconductor.

The use of a coronator has a number of disadvantages, which are that the accumulation of ink / dust particles on its thread 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 surface of the photoconductor.

With regard to the second method, the charge roller, in contact with the drum, supplies its surface, which is characterized by high photosensitivity, with a certain charge. At the same time, 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 printer parts in this case wear out faster.

Stage two: exposure

The purpose of this stage is to form an invisible image of dots on the surface of a photodrum with increased photosensitivity, and without the use of a static charge. To do this, a thin laser beam shines on a four- or hexagonal mirror, after which it is reflected and hits the so-called. spreading lens. He sends it to a specific place on the surface of the drum. Next, a system consisting of several lenses and mirrors moves the laser beam along the photo shaft, resulting in the formation of a line. Because printing is carried out using dots, the laser is constantly turned on and off. The charge is also removed in a pointwise manner. After the line comes to an end, the photo roller starts to turn by means of a stepping motor and the exposure procedure continues.

Third stage: development

Another shaft in the laser printer cartridge is a metal tube, inside of which there is a magnetic core. A magnet inside the compartment attracts toner to the surface of the shaft and, rotating, takes it out. A special dosing blade allows you to adjust the thickness of the dye layer and thus prevent its uniform distribution.

After that, the ink gets between the photoconductor and the magnetic roller. In areas that have been exposed, the toner begins to be attracted to the surface of the phototube, and in charged areas it is repelled. The ink remaining on the magnetic roller usually travels further and passes through the hopper again. As for the toner that has moved to the surface of the drum, it makes the image on it visible, after which it follows on, i.e. to paper.

Fourth stage: transfer

A sheet of paper that was fed into the device passes under the photo roller. In this case, under the paper is the so-called. an image transfer roller that helps to bring the toner present on the surface of the drum onto the surface of the paper. A charge with a plus sign is applied to the core of the roller, made of metal, which is transferred to the paper through the rubber coating. The microscopic particles of toner transferred to the surface of the sheet adhere to it solely due to static attraction. All powder particles, paper fluff and dust remaining on the photoconductor are sent using a squeegee or wiper to a hopper specially designed for waste. As soon as the photoconductor completes the entire cycle, the charge roller / corotron again contributes to the restoration of charge on its surface and the whole work is repeated again.

Fifth stage: fixing

The toner used in laser printers must have the ability to melt at high temperatures. Only due 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 warms it up. Thanks 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 solidifies quickly enough, as a result of which the printed picture or text becomes quite stable.

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

The image obtained with the help of modern laser printers (as well as matrix and inkjet) consists of dots (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 separately print on a segment of 1 inch (25.4 mm) is called resolution and is characterized in dots per inch (dpi - dot per inch). A printer is considered good if its resolution is 300 dpi (sometimes the designation 300 x 300 dpi is used, which means 300 dpi horizontally and 300 dpi vertically).

Laser printers are less demanding on paper than, for example, inkjet printers, and the cost of printing one page of a text document is several times lower. At the same time, inexpensive models of laser and LED monochrome printers are already able to compete on price with high-quality color inkjet printers.

Most laser printers on the market are designed for black and white printing; color laser printers are quite expensive and designed for corporate users.

Laser printers print on any thick paper (from 60 g/m 2) at a speed of 6 to ... (this figure is constantly growing) sheets per minute (ppm - page per minutes), while the resolution can be 1200 dpi or more. The quality of the text printed on a laser printer with a resolution of 300 dpi is approximately the same as a typographic one. However, if the page contains graphics containing grayscale, then a resolution of at least 600 dpi is required to obtain a high-quality graphic image. With a printer resolution of 1200 dpi, the printout 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 reasonable choice, since 600 dpi resolution and a print speed of 8 ... 12 pages per minute are standard parameters for modern personal laser printers.

OPERATING PRINCIPLE OF A LASER PRINTER

The first laser printer was introduced by Hewlett Packard. It used the electrographic principle of creating images - the same as in copiers. The difference was in the method of exposure: in copiers it occurs with the help of a lamp, and in laser printers, the light of the lamp was replaced by a laser beam (Fig. 1).

Rice. 1. Laser printer device

The heart of a laser printer is a photoconductive cylinder (Organic Photo Conductor), which is often referred to as a print drum or simply a drum. It is used to transfer the image to paper. The photoconductor is a metal cylinder covered with a thin film of a photosensitive semiconductor. The surface of such a cylinder can be provided with a positive or negative charge, which is maintained as long as the drum is not illuminated. If any part of the drum is exposed, the coating becomes conductive and the charge flows from the illuminated area, forming 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 light beam. Reflected from rotating mirrors (usually tetrahedral or hexagonal in shape), this beam illuminates the surface of the photoconductor, removing its charge at the exposure point.

To obtain a dot image, the laser is turned on and off using a control microcontroller. The rotating mirror unfolds the beam as a line of latent image on the surface of the photoconductor.

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

Two main methods of preliminary (primary) charge of the photocylinder surface are used:
using a thin wire or mesh called "corona wire". The high voltage applied to the wire causes a glowing ionized area around it, called the corona, and gives the drum the necessary static charge;
using a pre-charged rubber roller (PCR).

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

CARTRIDGE DESIGN

Before we talk about the process of transferring and fixing an image on paper, let's look at the Hewlett Packard Laser Jet 5L printer cartridge. There are two main compartments in this typical cartridge:
waste toner box and toner drawer.

The main structural elements of the waste toner compartment (Fig. 2):

1 - Photodrum (Organic Photo Conductor (OPC) Drum). It is an aluminum cylinder coated with an organic light-sensitive and photoconductive material (usually zinc oxide), which is able to preserve the image applied by the laser beam;

2 - Primary Charge Roller (PCR) Provides uniform negative drum charge. It is made of a conductive rubber or foam base applied to a metal shaft;

3 - "Viper", squeegee, cleaning blade (Wiper Blade, Cleaning Blade). Cleans the drum of toner residue that has not been transferred to the paper. Structurally made in the form of a metal frame (stamping) with a polyurethane plate (blade) at the end;

4 - Cleaning blade (Recovery Blade). Covers the area between the drum and the waste toner box. The Recovery Blade lets the toner left on the drum into the hopper and prevents it from spilling out in the opposite direction (from the hopper to the paper).

The main structural elements of the toner compartment (see Fig. 3):

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

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

3 - Sealing blade of the 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 enter the compartment, preventing toner from leaking in the opposite direction;

4 - Toner Reservoir. Inside it is the "working" toner, which will be transferred to the paper during the printing process. In addition, the toner activator (Toner Agitator Bar) is built into the hopper - a wire frame designed to mix the 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 prior to use.

PRINCIPLE OF LASER PRINTING

On fig. 4 shows the cartridge in section. When the printer is turned on, all components of the cartridge begin to move: the cartridge is being prepared for printing. This process is similar to the printing process, but the laser beam does not turn on. Then the movement of the cartridge components stops - the printer enters the Ready state.

Rice. 4. Cartridge in section

After sending a document for printing, the following processes take place in the laser printer cartridge:
Charging the drum (Fig. 5). The primary charge roller (PCR) evenly transfers negative charge to the surface of the rotating drum.

Rice. 5. Charging the drum

Exposure (Fig. 6). The negatively charged surface of the drum is only exposed to the laser beam where the toner will be applied. Under the action of light, the photosensitive surface of the drum partially loses its negative charge. Thus, the laser exposes the latent image to the drum in the form of dots with a weakened negative charge.

Rice. 6. Exposure

Application of toner (Fig. 7). At this stage, the latent image on the drum is converted by toner into a visible image that will be transferred to paper. The toner located near the magnetic roller is attracted to its surface under the influence of the field of a 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 parts of the drum that have been exposed. "Doctor" ensures uniform application of toner on the magnetic roller.

Rice. 7. Applying toner

Transfer of toner to paper (Fig. 8). 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, the negatively charged toner particles are attracted to the paper, which produces an image "poured" with toner.

Rice. 8. Transferring toner to paper

Fixing the image (Fig. 9). A sheet of paper with an unfixed image moves to the fixing mechanism, which consists of two adjoining shafts, between which the paper is pulled. The lower shaft (Lower Pressure Roller) presses it against the upper shaft (Upper Fuser Roller). The top roller is heated, and upon contact with it, the toner particles are melted and fixed on the paper.

Rice. 9. Image pinning

Cleaning the drum (Fig. 10). Some of the 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. Any toner remaining on the drum is wiped off by the wiper into the waste toner box. At the same time, the Recovery Blade closes the area between the drum and the hopper, preventing toner from spilling onto the paper.

Rice. 10. Cleaning the drum

"Erasing" the image (Fig. 11). At this stage, the latent image applied by the laser beam is "erased" from the surface of the drum. With the help of the primary charge roller, the surface of the photoconductor is evenly “covered” with a negative charge, which is restored in those places where it was partially removed by the action of light.

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IN article considered principle actions and device contemporary laser printers. She opens series articles, dedicated principles and problems laser fees.

The image obtained with the help of modern laser printers (as well as matrix and inkjet) consists of dots (dots). The smaller these dots and the more frequently they are located, the higher the image quality. The maximum number of dots that the printer can separately print on a segment of 1 inch (25.4 mm) is called resolution and is characterized in dots per inch, while the resolution can be 1200 dpi or more. The quality of the text printed on a laser printer with a resolution of 300 dpi is approximately the same as a typographic one. However, if the page contains graphics containing grayscale, then a resolution of at least 600 dpi is required to obtain a high-quality graphic image. 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 reasonable choice, since 600 dpi resolution and a print speed of 8 ... 1 2 pages per minute are standard parameters for modern personal laser printers.

OPERATING PRINCIPLE OF A LASER PRINTER

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

The heart of a laser printer is a photoconductive cylinder (Organic Photo Conductor), which is often called a print drum or simply a drum. It is used to transfer the image to paper. The photoconductor is a metal cylinder covered with a thin film of a photosensitive semiconductor. The surface of such a cylinder can be provided with a positive or negative charge, which is maintained as long as the drum is not illuminated. If any part of the drum is exposed, the coating becomes conductive and the charge flows from the illuminated area, forming 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 light beam. Reflected from rotating mirrors (usually tetrahedral or hexagonal in shape), this beam illuminates the surface of the photoconductor, removing its charge at the exposure point.

To obtain a dot image, the laser is turned on and off using a control microcontroller. The rotating mirror unfolds the beam as a line of latent image on the surface of the photoconductor.

After the formation of the line, a special stepper motor turns the drum to form the next one. This offset corresponds to the vertical resolution of the printer and is usually 1/300 or 1/600 of an inch. The process of formation of the latent image on the drum resembles the formation of a raster on the screen of a television monitor.

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

Ø using a thin wire or mesh called "corona wire". A high voltage applied to the wire causes a glowing ionized area around it, called the corona, and gives the drum the necessary static charge;

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

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

DEVICECARTRIDGE

Before we talk about the process of transferring and fixing an image on paper, let's look at the design of the Hewlett Packard Laser Jet 5L printer cartridge. There are two main compartments in this typical cartridge: the waste toner compartment and the toner compartment.

The main structural elements of the waste toner compartment:

1 - photoconductor(Organic Photo Conductor (OPC) Drum). It is an aluminum cylinder coated with an organic light-sensitive and photoconductive material (usually zinc oxide), which is able to preserve the image applied by the laser beam;

2 - Shaft primary charge(Primary Charge Roller (PCR)). Provides uniform negative drum charge. It is made of a conductive rubber or foam base applied to a metal shaft;

3 - « Viper» , squeegee, cleaning blade(Wiper Blade, Cleaning Blade). Cleans the drum of toner residue that has not been transferred to the paper. Structurally 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 the waste toner box. The Recovery Blade lets the toner left on the drum into the hopper and prevents it from spilling out in the opposite direction (from the hopper to the paper).

The main structural elements of the toner compartment:

1 - Magnetic shaft(Magnetic Developer Roller, Mag Roller, Developer Roller). It is a metal tube with a non-moving magnetic core inside. Toner is attracted to the magnetic shaft, which, before being fed to the drum, acquires a negative charge under the action of a constant or alternating voltage;

2 - « Doctor» (Doctor Blade, Metering Blade). Provides even distribution of a thin layer of toner on the magnetic roller. Structurally 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 enter the compartment, preventing toner from leaking in the opposite direction;

4 - Bunker for toner (toner Reservoir). Inside it is the "working" toner, which will be transferred to the paper during the printing process. Besides, the toner activator (Toner Agitator Bar) - the wire frame intended for hashing of a toner is built in the bunker;

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 prior to use.

PRINCIPLE OF LASER PRINTING

The figure shows the cartridge in section. When the printer is turned on, all components of the cartridge begin to move: the cartridge is being prepared for printing. This process is similar to the printing process, but the laser beam does not turn on. Then the movement of the cartridge components stops - the printer enters the ready-to-print state.

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

Charger drum. The primary charge roller (PCR) evenly transfers negative charge to the surface of the rotating drum.

Exposure. The negatively charged surface of the drum is only exposed to the laser beam where the toner will be applied. Under the action of light, the photosensitive surface of the drum partially loses its negative charge. Thus, the laser exposes the 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 by toner into a visible image that will be transferred to paper. The toner located near the magnetic roller is attracted to its surface under the influence of the field of a 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 parts of the drum that have been exposed. "Doctor" ensures uniform application of toner on the magnetic roller.

Transfer toner on the 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, the negatively charged toner particles are attracted to the paper, which produces an image "poured" with toner.

Anchoring Images. A sheet of paper with an unfixed image moves to the fixing mechanism, which consists of two contiguous shafts, between which the paper is pulled. The lower shaft (Lower Pressure Roller) presses it against the upper shaft (Upper Fuser Roller). The top roller is heated, and upon contact with it, the toner particles are melted and fixed on the paper.

cleaning drum. Some of the 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. Any toner remaining on the drum is wiped off by the wiper into the waste toner box. At the same time, the Recovery Blade closes the area between the drum and the hopper, preventing toner from spilling onto the paper.

"Erasing" Images. At this stage, the latent image applied by the laser beam is "erased" from the surface of the drum. With the help of the primary charge roller, the surface of the photoconductor is evenly “covered” with a negative charge, which is restored in those places where it was partially removed by the action of light.

Today I want to talk about device and principle of operation of a laser printer. Everyone is familiar with this device, but few people know about the principle of its operation and the causes of its malfunctions. In this article I will try to clearly talk about the principle of operation of "laser printers", and in subsequent articles about malfunctions of laser printers, about the reason for their appearance, and about how to eliminate them.

Laser printer device

At the heart of any modern laser printer is a photoelectricprinciple xerography. Based on this method, all laser printers structurally consist of three main parts (assemblies):

- Laser sanitizing unit.

- Image transfer unit.

- Node for fixing the image.

The image transfer unit usually refers to the laser printer cartridge and charge transfer roller (Transferroller) in the printer itself. We will talk about the device of the “laser” cartridge later in more detail, and in this article we will consider only the principle of operation. It should also be noted that instead of laser scanning in some printers (mainly from OKІ» ) LED scanning is applied. It performs the functionseHowever, only the role of the laser is performed by LEDs.

For example, consider laser printer HP LaserJet 1200 (Fig. 1.). The model is quite successful and well-proven for its long service life, convenience and reliability.

We print on any material (mainly paper), and the paper feed unit is responsible for sending it to the “mouth” of the printer. As a rule, it is divided into two types that are structurally different from each other. Lower Tray Feeder, is called - Tray 1, and feeding mechanism from the top(bypass) - Tray 2. Despite the structural differences in their composition, they have (see Fig. 3):

- Pickup Roller- needed to pull paper into the printer,

- Block brake pad and separator needed to separate and pick up only one sheet of paper.

Directly involved in the formation of the image printer cartridge(Fig. 4) and laser scanning unit.

The cartridge for laser printers consists of three main elements (see Fig. 4):

Photocylinder,

precharge shaft,

magnetic shaft.

photo cylinder

photo cylinder(ORS- organicphotoconductivedrum), or also photoconductor, is an aluminum shaft coated with a thin layer of photosensitive material, which is additionally covered with a protective layer. Previously, photocylinders were made on the basis of selenium, so they were also called selenium shafts, are now made from photosensitive organic compounds, but their old name is still widely used.

Main property photocylinder– change the conductivity under the influence of light. What does it mean? If the photocylinder is given some kind of charge, it will remain charged for quite a long time, however, if its surface is illuminated, then in places of illumination the conductivity of the photo coating increases sharply (resistance decreases), the charge "flows" from the surface of the photocylinder through the conductive inner layer in this place a neutrally charged region will appear.

Rice. 2 HP 1200 Laser Printer with cover removed.

The numbers indicate: 1 - Cartridge; 2 - Image transfer unit; 3 - Node for fixing the image (stove).

Rice. 3 Paper feed unitTray 2 , rear view s.

1 - Paper pickup roller; 2 - Braking pad (blue stripe) with a separator (not visible in the photo); 3 - Charge transfer roller (transferroller), transmitting paper static charge.

Rice. 4 Disassembled laser printer cartridge.

1- Photocylinder; 2- Precharge shaft; 3- Magnetic shaft.

Image overlay process.

Photo cylinder with pre-charge shaft (PCR) receives an initial charge (positive or negative). The amount of charge itself is determined by the print settings of the printer. After the photocylinder is charged, the laser beam passes over the surface of the rotating photocylinder, and the places where the photocylinder is illuminated become neutrally charged. These neutral areas correspond to the desired image.

The laser scanning unit consists of:

semiconductor laser with focusing lens,
- Rotating mirror on the motor,
- Forming lens groups,
- Mirrors.

Rice. 5 Laser scanning unit with cover removed.

1,2 - Semiconductor laser with focusing lens; 3- rotating mirror; 4- Forming lens group; 5- Mirror.

The drum has direct contact magnetic shaft m (Magneticroller), which supplies toner from the cartridge hopper to the photo cylinder.

The magnetic shaft is a hollow cylinder with a conductive coating, inside which a permanent magnet rod is inserted. The toner located in the hopper in the hopper is attracted to the magnetic shaft under the influence of the magnetic field of the core and an additionally applied charge, the value of which is also determined by the print settings of the printer. This determines the density of future printing. From the magnetic shaft, under the action of electrostatics, the toner is transferred to the image formed by the laser on the surface of the photocylinder, since it has an initial charge, it is attracted to the neutral areas of the photocylinder and repelled from equally charged ones. This is the image we need.

There are two main mechanisms for creating an image. Most printers (HP,Canon, Xerox) a toner with a positive charge is used, remaining only on the neutral surfaces of the photocylinder, that is, the laser illuminates only those areas where the image should be. The photo cylinder in this case is negatively charged. The second mechanism (used in printersEpson, Kyocera, Brother) is to use a negatively charged tuner, and the laser discharges areas of the photocylinder that should not have toner. The photo cylinder initially receives a positive charge and the negatively charged toner is attracted to the positively charged areas of the photo cylinder. Thus, in the first case, a finer transfer of details is obtained, and in the second, a denser and more uniform fill. Knowing these features, you can more accurately select a printer for solving your problems (printing text or printing sketches).

Before contact with the photo cylinder, the paper also receives a static charge (positive or negative), via the charge transfer roller (Transferroller). Under the influence of this static charge, the toner transfers from the photo of the cylinder to the paper during contact. Immediately after this, the static charge remover removes this charge from the paper, which eliminates the attraction of the paper to the photo cylinder.

Toner

Now we need to say a few words about the toner. Toner is a finely dispersed powder consisting of polymer balls coated with a layer of magnetic material. The composition of the color tuner also includes dyes. Each company in its models of printers, MFPs and copiers uses original toners that differ in dispersion, a magnetnawn and physical properties. Therefore, in no case should you refill cartridges with random toners, otherwise you can ruin your printer or MFP very quickly (verified by experience).

If, after passing the paper through the laser scanning unit, remove the paper from the printer, we will see an image that has already been formed, which can be easily destroyed by touch.

Image fixation unit or "stove"

In order for an image to become durable, it must be fix. Image freeze occurs with the help of additives that are part of the toner, having a certain melting point. The third main element of the laser printer is responsible for fixing the image (Fig. 6) - image fixation unit or "stove". From a physical point of view, fixation is carried out by pressing the molten toner into the paper structure and its subsequent solidification, which gives the image durability and good resistance to external influences.

Rice. 6 Image fixation unit or stove. Top view assembled, bottom with paper separator bar removed.

1 - Thermal film; 2 - Pressure shaft; 3 - Paper separator bar.

Rice. 7 Heating element and thermal film.

Structurally, the "stove" - ​​can consist of two shafts: the upper one, inside which there is a heating element and the lower shaft, necessary for pressing the molten toner into the paper. In the HP 1200 printer under consideration, the “stove” consists of thermal films(Fig. 7) - a special flexible, heat-resistant material, inside of which there is a heating element, and a lower pressure roller, which presses the paper due to the support spring. Monitors the temperature of the thermal film temperature sensor(thermistor). Passing between the thermal film and the pressure roller, the paper heats up to approximately 200 ° C at the points of contact with the thermal film.˚ . At this temperature, the toner melts and in liquid form is pressed into the texture of the paper. So that the paper does not stick to the thermal film, there are paper separators at the exit from the oven.

Here's what we've looked at - How does a printer work. This knowledge will help us in the future to find out the causes of breakdowns and eliminate them. But in no case should you climb into the printer yourself if you are not sure that you can fix it, this will only make it worse. It is better not to save money, but to entrust this matter to professionals, because buying a new printer will cost you much more.

Many believe that the laser printer is so named because it burns images onto paper with a laser. However, one laser is not enough to get a quality print.

The most important element of a laser printer is the photoconductor. It is a cylinder covered with a photosensitive layer. Another necessary component of toner is coloring powder. Its particles are fused into a sheet of paper, leaving the desired image on it.

The imaging drum and toner hopper are most often part of the same one-piece cartridge, which in addition has many other important parts - the charge and developer rollers, the cleaning blade and the waste toner bin.

Now let's look at how this all happens in more detail.

Printer steps

An electronic document is sent for printing. At this point, the printed circuit board processes it, and the laser sends digital pulses to the cartridge. By charging the photoconductor with negative particles, the laser transfers an image or text to it that needs to be printed.

When the laser beam hits the drum, it removes the charge and uncharged zones remain on its surface. Each toner particle is negatively charged and in contact with the drum unit, the toner adheres to uncharged fragments under the influence of static electricity. This is called image development.

A special roller with a positive charge presses a sheet of paper against the photoconductor. Because oppositely charged particles attract, the toner sticks to the paper.

Next, the paper with toner is heated to a temperature of about 200 degrees using a thermal shaft of the so-called stove. Due to this, the toner expands and the image is firmly fixed on the paper. Therefore, documents freshly printed on a laser printer are always warm.

The last step is to charge the photoconductor and clean it of any remaining toner using a cleaning blade and a waste toner box.

This is how the printing process works. The laser paints the future image with charged particles. The photoconductor catches and transfers the ink powder to the paper. Toner adheres to paper due to static electricity and fuses to it.

The copier works on the same principle.

Benefits of a laser printer

It is believed that the print speed of a laser printer is higher than that of an inkjet printer. On average, this is 27-28 prints per minute. Therefore, they are used to print a large number of documents.

The device does not make much noise during operation. The print quality is very high at a low print cost, which is achieved due to the low consumption and price of the toner. The cost of most models of laser printers is also quite affordable.

For many years there has been a debate about whether a laser printer is harmful to health. The particles of toner used in laser printing are so small that they easily enter the human body, settle and accumulate in the respiratory tract. With constant contact with toner for 15-20 years, headaches, asthma and other diseases can develop.

However, printer manufacturers assure that there is no harm in daily use of the printer. Production technologies are constantly being improved, and cartridges are tested in laboratories.

Danger can arise only when you try to open and refill the cartridge yourself. Toner particles can get into the lungs and are very poorly excreted from the body, so it is better to entrust the refilling of the printer to specialists.

The speed, service life and print quality of laser printers are really on top. This device is indispensable in the work and everyday life of many users and is not as whimsical as capricious inkjet printers, who often have problems with printing when refilling.

If you still got not the most successful model of a laser printer and you did not use it much at all, then do not despair. KupimToner buys new printers from different brands, as well as accessories for them, offering a decent price.