In a printer based on laser printing technology, everything works through the use of static electricity. How does this work? The laser beam hits the photodrum in the cartridge and forms an image. At the next stage of image formation, the photodrum comes into contact with the toner and the toner sticks at the point of contact where the laser shone and changed the charge. Using the same principle, toner sticks to the paper from the photodrum and is then baked in the so-called “oven”. The paper comes out warm from the stove. Don't be afraid, it's already cooled down a little.

Learn more about the laser printing process

When the photosensitive drum rotates, a positive charge, which is applied to the photo roll using a laser beam. The positive charge attracts toner particles, which are negatively charged, and they stick to the surface of the drum.

The sheet of paper is positively charged and passes under a rotating photo roller during the printing process. The negatively charged toner particles are transferred from the drum to the sheet of paper, thus transferring the image onto the paper. Next, the toner, once on the paper, is fixed under the influence of heat.

Unlike printing on dot matrix and inkjet printers, where the image is transferred to paper line by line, when laser printing Text on an A4 sheet is formed in just 3 turns of the photodrum.

Laser printers are based on the printing system used in copiers. In copiers, a special lamp transfers the image from the sheet being copied to the photosensitive surface of the drum in the form of an electrostatic charge. The image drum converts the optical image created by light reflected from the copied image into its electrostatic equivalent, which attracts toner particles with the opposite charge to the surface of the drum.

However, a laser printer does not have an original image; instead, in its memory there is a matrix consisting of 1s and 0s that transmits the image. In the case of black and white printing, 1 transmits a signal to the microprocessor and directs the laser beam to the photodrum. When the beam touches the surface of the drum, a positive charge is formed at that location, and negatively charged toner particles will stick to the drum at that location. Accordingly, 0 does not transmit a signal and no charge appears on the surface of the drum, and later these areas will remain white on the paper. Read the article about how to get rid of white stripes when printing -

Laser printers are less demanding on paper than, for example, inkjet printers, and the cost of printing one page text document theirs is several times lower. At the same time, inexpensive models of laser and LED monochrome printers are already able to compete in 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 are aimed at corporate users.

Laser printers print on any thick paper (from 60 g/m2) 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 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 gradations of gray color, then to obtain high-quality graphic image A resolution of at least 600 dpi will be required. 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 option smart choice, since for modern personal laser printers the standard parameters are a resolution of 600 dpi and a print speed of 8...12 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 copiers it occurs using a lamp, and in laser printers, lamp light replaced the laser beam (Fig. 1).

Rice. 1. Device laser printer

The heart of a laser printer is a photoconductive cylinder (Organic Photo Conductor), which is often called a printing drum 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 in shape), 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:
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;
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?

CARTRIDGE DESIGN

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:
waste toner compartment and toner compartment.

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

1 – 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 – 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 – “Wiper”, 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 – 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).

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, inside of which there is a stationary magnetic core. The 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 – 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 – 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

In Fig. Figure 4 shows a sectional view 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 the laser beam is not turned on. Then the movement of the cartridge components stops - the printer enters the Ready state.

Rice. 4. Sectional view of the cartridge

After sending a document for printing, the following processes occur in the laser printer cartridge:
Charging the drum (Fig. 5). The Primary Charge Roller (PCR) uniformly transfers a 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 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.

Rice. 6. Exposure

Applying toner (Fig. 7). 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 on magnetic shaft.

Rice. 7. Applying toner

Transferring 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, negatively charged toner particles are attracted to the paper, which produces an image “sprinkled” with toner.

Rice. 8. Transferring toner to paper

Fixing the image (Fig. 9). A sheet of paper with a loose 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.

Rice. 9. Pin the image

Cleaning the drum (Fig. 10). 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.

Rice. 10. Cleaning the drum

“Erasing” the image (Fig. 11). 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.

Modern printers are mostly divided into laser and inkjet based on their operating technology. Moreover, thanks to progress, the latter are gradually leaving the “household office equipment” market, remaining specialized. In offices, homes, and even some printing centers, laser printers are most often found.

In household use, the main difference between inkjet printers and laser printers is primarily the high efficiency of the latter. Ink consumption is almost minimal - one cartridge is enough for several thousand sheets with a fairly high ink density. In addition, laser printers operate very quickly and do not require special maintenance.

Contrary to popular belief, laser printers do not “burn” characters into paper. A special toner is used to apply the image. It is he who sticks to the paper sheet, leaving symbols or pictures. By the way, because of this feature of the technology, color laser printers are practically not found, unlike monochrome (black and white).

Main functional components of a laser printer

The design of any laser printer, regardless of specific model, manufacturer and capabilities includes several main functional units:

drum. It is on this that the toner is applied through electrostatic attraction and repulsion according to Coulomb's law;
squeegee. It is designed to clean the drum of any remaining toner before applying a new one;
coronator This device is designed to electrostatically charge the drum;
laser and mirror system. Being a source of coherent electromagnetic radiation, he discharges the drum pointwise;
magnetic shaft. The toner is fixed on it for subsequent transfer to the surface of the drum;
stove. It is designed to bake the toner remaining on the paper. Therefore, the sheets coming out of the laser printer have a fairly high temperature;
control model (controller)- a microprocessor system that controls all this equipment.

Both color and monochrome laser printers are based on these functional units. Only the system and capabilities change. For example, color laser printers have four drums - for each of the fundamental colors (red, yellow, blue and black) - and a so-called transfer ribbon, which is designed to transfer the image formed by the corresponding toners to the paper.

Operating principle of a laser printer

The principle of operation of a laser printer in an abbreviated description is quite simple. The complete thing differs from one model to another, but some fundamental elements are present in each case:

The drum is being cleaned. The squeegee blade removes toner from its surface that has adhered but was not used in the previous printing cycle;
The corona device charges the surface of the drum. Either positive ions appear on it, or the number of negative electrons increases. This is intended to generate Coulomb forces.
The laser, controlled by a rotating mirror, partially discharges the surface of the drum. The toner itself is negatively or positively charged. Therefore, it is repelled from the charged areas of the drum area and is attracted to the discharged ones. Again, this is due to the action of Coulomb forces.
The toner powder is transferred from the surface of the magnetic roller to the drum.
From the surface of the drum, the toner adhered to it is transferred to the paper sheet.
The paper is sent to the “oven,” which most often consists of a heating element in the form of a halogen lamp and a pressure roller. The toner is fixed by melting under the influence of high temperature and due to pressure from the shaft mounted on a spring.

If color laser printers have 4 separate drums and the same number of magnetic rollers, however, the toner is not applied to the paper itself directly, but to the transfer belt. All four shades are first applied to it. The transfer tape is then rolled over the paper and the multi-colored image ends up on the sheet. The toner is then baked and cured.

Fundamental non-technological differences between laser and inkjet printers

Laser printers have recently become more popular than inkjet printers. If we abstract from technological differences, then they have the following advantages:

efficiency. A laser printer cartridge can handle several thousand sheets of high-coverage paper.
possibility of refueling. Laser printer cartridges can be refilled with toner as needed without the risk of affecting their functionality. Conduct this operation You can even do it yourself, but you should be careful, since the coloring pigment is negatively or positively charged and, under the influence of Coulomb forces, quickly sticks to skin, clothing and other surfaces. Cartridges inkjet printer in most cases, refilling cannot be done, as this leads to a violation of their tightness. Some models of this type of equipment can use continuous ink systems, but this is considered an unauthorized modification and will void the warranty agreement.
high speed. Most laser printer models are capable of printing up to 10 pages of text per minute. Some are even faster.
no need for weekly printing. The toner used in laser printers does not dry out or clump. Therefore, there is no need to periodically “run the print” to prevent the head from clogging. Actually, there is no head in laser printers.
durability of prints. Images and text on paper obtained using such office equipment do not fade or disappear over time under the influence of high air humidity.
high image resolution. Color laser printers provide printing resolutions of up to 9600 X 1200 dpi.

However, they also have some disadvantages compared to inkjet printers:

high cost. On average, a laser printer supplied “from the factory” - that is, with incomplete cartridges - costs several times more than a similar inkjet printer. For monochrome, this is a 2-3-fold increase in price, for color - 10-fold and higher.
high cost of cartridges and toner. Consumables for laser printers they cost 2-3 times more than for inkjet printers. However, it is worth considering that their usage limit is also 2-3 times higher.
bulkiness. Laser printers are usually several times larger than inkjet printers. This is also due to the complexity of the design. As a result, they require a separate installation space.
the need to warm up before work and the risk of overheating after prolonged printing. Despite the fact that the design of the “stove” includes a special thermoelement that does not allow the temperature to reach a critical level, in some cases it may fail or work inadequately. After this, the device overheats with the risk of system problems.
low environmental friendliness. When operating, such devices emit some harmful compounds, dust, and also emit infrared and ultraviolet radiation into the air.
high resource intensity. Due to the presence of current-hungry elements, laser printers consume more electricity. Moreover, the peak power can be so high that such office equipment will not work on household or office UPSs.
impossibility of stable repetition of full-color images due to the uncontrolled action of electromagnetic fields.

Thus, laser printers have both advantages and disadvantages compared to inkjet printers. However, in some use cases they prove to be significantly more optimal or useful than their analogues.

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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 pictures 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 reasonable choice, since for modern personal laser printers the standard parameters are a resolution of 600 dpi and a print speed of 8...12 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.

The heart of a laser printer is an Organic Photo Conductor, often called a print drum 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.

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 a line is formed, a special stepper motor rotates 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”. The high voltage applied to the wire creates a glowing ionized area around it, called a 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

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 the laser beam is not turned 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. With the help of 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.

How a laser printer works

The operating principle of all laser printers is quite similar to the operation of photocopiers. Initially, a magnetized area is created on the paper, to which the toner (printing powder) is then attracted. Then, the sheet of paper goes into what is called an oven, where the powder is melted. Once the process is complete, the powder cools and hardens. Strictly speaking, this is how the finished image is obtained on paper.

Despite the relatively high cost, in comparison with inkjet, even representatives of the entry-level price level will make it possible to obtain black and white images, but they will be obvious high quality. At the same time, the printing speed cannot be compared either. As for maintenance, it is quite simple and unpretentious; in particular, refilling laser printer cartridges is quick and, most importantly, inexpensive.

Main advantages of laser printers

Today, laser printers are the most popular and in-demand office equipment, due to a number of reasons:

high print quality, incomparable to inkjet counterparts;
reliability and long term operation;
resource efficiency:

refilling a laser printer is done several times less frequently than refilling/replacing cartridges in an inkjet printer;
If not used for a long time, toner for laser printers does not dry out and become unusable;

available pricing policy(despite the fact that laser printers are somewhat more expensive than inkjet printers, their quality of work and long service life will more than pay for all costs);
high printing speed;
relatively large print volumes;
resistance of printed copies to water and sunlight;
low noise level during operation;
low cost of printing (about 5 kopecks per 1 sheet);
environmental friendliness and safety for the environment and the human body.

Technical specifications or how to choose a laser printer?

When deciding to purchase a laser printer, most users do not know technical characteristics, often make the wrong choice.

Due to the fact that a laser printer is capable of completely forming the image that is to be printed on the selenium drum, it is extremely important to have a large amount of memory and a high-frequency digital processor. So, for a laser printer with black and white printing, the optimal memory size can be considered 4-8 MB, and for a color printer - from 32 MB. In modern printers, the memory capacity can be increased using additional modules.

Regarding optimal frequency processor, it varies from 25 to 150 MHz. In turn, the acceptable print resolution is from 600 to 1200 dpi.

The laser printer resources allow you to print about 8-12 thousand copies in one calendar month. Also, when choosing a model, you should pay attention to the cartridge resource, which means the number of copies that can be printed without refilling.