How does color laser work? Laser printing - basic principles of operation. The process of forming an impression on paper

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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 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.

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 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

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 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. 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.

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 the specified coordinates in the program. 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 an image formed) to be transferred to the sheet of paper.

Consolidation

The next step in laser printing is fixing the toner image 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.

Laser printers have become indispensable attributes of office equipment. This popularity is explained by the high speed and low cost of printing. To understand how this technique works, you should know the structure and operating principle of a laser printer. In fact, all the magic of the device can be explained by simple design solutions.

Back in 1938, Chester Carlson patented a technology that transferred images to paper using dry ink. The main engine of work was static electricity. Electrographic method(and this was exactly it) became widespread in 1949, when the Xerox Corporation took it as a basis for the operation of its very first device. However, it took another decade of work to achieve logical perfection and complete automation of the process - only after that the first Xerox appeared, which became the prototype of modern laser printing devices.

The first Xerox 9700 laser printer

The first laser printer itself appeared only in 1977 (it was the Xerox 9700 model). Back then printing was done at a speed of 120 pages per minute. This device was used exclusively in institutions and enterprises. But already in 1982, the Canon desktop unit was the first to come out. Since that time, numerous brands have been involved in the development, which to this day offer new versions of desktop laser printing assistants. Every person who decides to use such equipment will be interested in learning more about the internal structure and operating principle of such a unit.

What's inside

Despite the large assortment, the design of the laser printer of all models is similar. The work is based on photoelectric part of xerography, and the device itself is divided into the following blocks and units:

laser scanning unit;
node that transfers the image;
knot for fixing the image.

The first block is presented system of lenses and mirrors. This is where a semiconductor type of laser with a lens capable of focusing is located. Next are mirrors and groups that can rotate, thereby forming an image. Let's move on to the node responsible for transferring the image: it contains the toner cartridge and roller, carrying charge. Already in the cartridge there are three main image-forming elements: a photocylinder, a pre-charged shaft and a magnetic shaft (working together with the device drum). And here the ability of a photocylinder to change its conductivity under the influence of light falling on it becomes of great relevance. When a photocylinder is charged, it retains it for a long time, but when exposed to light, its resistance decreases, which leads to the fact that the charge begins to drain from its surface. This is how the impression we need appears.

In general, there are two ways to create a picture.

Getting into the unit, immediately before future contact with the photocylinder, the paper itself receives a corresponding charge. The image transfer roller helps her with this. After transfer, the static charge disappears with the help of a special neutralizer - this is how the paper stops being attracted to the photo cylinder.

How is the image captured? This happens due to the additives that are in the toner. They have a certain melting point. This “oven” presses molten toner powder into the paper, after which it quickly hardens and becomes durable.

Images printed on paper with a laser printer have excellent resistance to numerous external influences.

How the cartridge works

The determining element in the operation of a laser printer is the cartridge. It is a small bin with two compartments - for working toner and for already used material. There is also a photosensitive drum (photocylinder) and mechanical gears for turning it.

The toner itself is a finely dispersed powder, which consists of polymer balls - they are coated with a special layer of magnetic material. If we are talking about a color toner, then it also contains coloring agents.

It is important to know that each manufacturer produces its own original toners - they all have their own magnetism, dispersity and other properties.

That is why you should never refill cartridges with random toners - this may negatively affect its performance.

The process of creating an impression

The appearance of an image or text on paper will consist of the following successive stages:

drum charge;
exposure;
development;
transfer;
consolidation

How does photo charging work? It is formed on the photodrum (where, as is already clear, the future image itself is born). To begin with, a charge is supplied, which can be either negative or positive. This happens in one of the following ways.

Used coronator, that is, a tungsten filament coated with carbon, gold and platinum inclusions. When high voltage comes into play, a discharge is carried between this thread and the frame, which, accordingly, creates an electric field that transfers charge to the photodrum.
However, the use of filament led to problems with contamination and deterioration of the printed material over time. Works much better charge roller with similar functions. It itself looks like a metal shaft, which is covered with conductive rubber or foam rubber. There is contact with the photocylinder - at this moment the roller transfers the charge. The voltage here is much lower, but the parts wear out much faster.

This is the work of illumination, as a result of which part of the photocylinder becomes conductive and passes a charge through the metal base in the drum. And the exposed area becomes uncharged (or acquires a weak charge). At this stage, a still invisible image is formed.

Technically it works like this.

The laser beam falls on the surface of the mirror and is reflected onto the lens, which distributes it to the desired location on the drum.
This is how a system of lenses and mirrors forms a line along the photo cylinder - the laser is turned on and off, the charge either remains intact or is removed.
Has the line ended? The image drum will rotate and exposure will continue again.

Development

In this process it is of great importance cartridge magnetic shaft, similar to a metal tube containing a magnetic core inside. Part of the roller surface is placed in the refill toner hopper. The magnet attracts the powder to the shaft and it is carried out.

It is important to regulate the uniform distribution of the powder layer - for this there is a special dosing blade. It allows only a thin layer of toner to pass through, throwing the rest back. If the blade is not installed correctly, black streaks may appear on the paper.

After this, the toner moves to the area between the magnetic roller and the photo cylinder - here it will be attracted to the exposed areas and repelled from the charged areas. This way the image becomes more visible.

Transfer

In order for the image to appear on paper, it comes into play transfer roller, into the metal core of which a positive charge is attracted - it is transferred to the paper thanks to a special rubberized coating.

So, the particles come off the drum and begin to move onto the page. But they are held here so far only due to static tension. Figuratively speaking, the toner is simply poured where needed.

Dust and paper lint may get in with the toner, but they can be removed. viper(with a special plate) and are sent straight to the waste compartment on the hopper. After a full circle of the drum, the process is repeated.

To do this, the property of toner to melt at high temperatures is used. Structurally, the following two shafts help with this:

there is a heating element in the top;
at the bottom, melted toner is pressed into the paper.

Sometimes such a “stove” is thermal film– a special flexible and heat-resistant material with a heating component and a pressure roller. Its heating is controlled by a sensor. Just at the moment of passage between the film and the pressing part, the paper heats up to 200 degrees, which allows it to easily absorb the toner that has become liquid.

Further cooling occurs naturally - laser printers usually do not require the installation of an additional cooling system. However, here a special purifier passes through again - usually its role is played by felt roll.

Felt is usually impregnated with a special compound, which helps lubricate the coating. Therefore, another name for such a shaft is oil.

How is color laser printing done?

How does color printing happen? A laser device uses four such primary colors - black, magenta, yellow and cyan. The printing principle is the same as in black and white, but the printer will first split the image into monochrome for each color. Each cartridge begins to sequentially transfer its own color, and as a result of the overlay, the desired result is obtained.

The following color laser printing technologies are distinguished:

multi-pass;
monotreme.

At multi-pass version An intermediate medium comes into play - this is a roller or ribbon that carries the toner. It works like this: in 1 revolution, 1 color is applied, then another cartridge is fed to the right place, and the second one is placed on top of the first picture. Four passes are enough to form a full-fledged picture - it will be transferred to paper. But the device itself will work 4 times slower than its black and white counterpart.

How does a printer work with single pass technology? In this case, all four separate printing mechanisms have a common control - they are lined up in one line, each with its own laser unit with a portable roller. So the paper goes along the drum, sequentially collecting all four images of the cartridges. Only after this pass does the sheet go into the oven, where the picture is fixed.

The advantages of laser printers have made them favorites for working with documentation, both in the office and at home. And information about the internal components of their work will help any user to notice shortcomings in time and contact the service department for technical support for the operation of the device.

The history of laser printers began in 1938 with the development of dry ink printing technology. Chester Carlson, working on the invention of a new way to transfer images to paper, used static electricity. The method was called electrography and was first used by the Xerox corporation, which released the Model A copier in 1949. However, for this mechanism to work, certain operations had to be performed manually. Ten years later, the fully automatic Xerox 914 was created, which is considered the prototype of modern laser printers.

The idea of "drawing" what would later be printed directly onto the copy drum with a laser beam came from Gary Starkweather. Since 1969, the company has been developing and in 1977 released the Xerox 9700 serial laser printer, which printed at a speed of 120 pages per minute.

The device was very large, expensive, and intended exclusively for enterprises and institutions. And the first desktop printer was developed by Canon in 1982, a year later - the new model LBP-CX. HP, as a result of cooperation with Canon, began production of the Laser Jet series in 1984 and immediately took a leading position in the market of laser printers for home use.

Currently, monochrome and color printing devices are produced by many corporations. Each of them uses its own technologies, which can vary significantly, but the general principle of operation of a laser printer is typical for all devices, and the printing process can be divided into five main stages.

Drum charge

The print drum (Optical Photoconductor, OPC) is a metal cylinder coated with a photosensitive semiconductor on which an image is formed for subsequent printing. Initially, the OPC is supplied with a charge (positive or negative). This can be done in one of two ways using:

corotron (Corona Wire), or coronator;
charge roller (Primary Charge Roller, PCR), or charging shaft.

A corotron is a block of wire and a metal frame around it.

Corona wire is a tungsten filament coated with carbon, gold or platinum. Under the influence of high voltage, a discharge occurs between the wire and the frame, a luminous ionized area (corona), an electric field is created that transfers a static charge to the photodrum.

Usually a mechanism is built into the unit that cleans the wire, since its contamination greatly impairs the print quality. Using a corotron has certain disadvantages: scratches, accumulation of dust, toner particles on the filament or its bending can lead to an increase in the electric field in this place, a sharp decrease in the quality of printouts, and possibly damage to the surface of the drum.

In the second option, a flexible film made of special heat-resistant plastic wraps the supporting structure with a heating element inside. The technology is considered less reliable and is used in printers for small businesses and home use, where heavy equipment loads are not expected. To prevent the sheet from sticking to the stove and twisting it around the shaft, a strip with paper separators is provided.

Color printing

Four primary colors are used to form a color image:

black,
yellow,
purple,
blue.

Printing is carried out on the same principle as black and white, but first the printer splits the image that needs to be obtained into monochrome images for each color. During operation, color cartridges transfer their designs onto paper, and their superimposition on each other gives the final result. There are two color printing technologies.

Multipass

This method uses an intermediate carrier - a roller or toner transfer ribbon. In one revolution, one of the colors is applied to the tape, then another cartridge is fed to the desired location and the second is superimposed on top of the first image. In four passes, a complete image is formed on the intermediate medium and transferred to paper. The printing speed of color images in printers using this technology is four times slower than monochrome.

Single pass

The printer includes a complex of four separate printing mechanisms under common control. The color and black cartridges are lined up, each with a separate laser unit and transfer roller, and the paper runs under the photo drums, sequentially collecting all four monochrome images. Only after this does the sheet go into the oven, where the toner is fixed on the paper.

Have fun typing.

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

The most important element of a laser printer is the photoconductor. It is a cylinder coated 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 image drum and toner hopper are most often part of one solid cartridge, which in addition has many other important parts - charging and developing rollers, a cleaning blade and a waste toner hopper.

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

Printer operation steps

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

When the laser beam hits the drum, it removes the charge and uncharged zones remain on its surface. Each particle of toner is negatively charged and when in contact with the photodrum, the toner sticks 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 photodrum. 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 oven. Thanks to this, the toner is straightened and the image is securely fixed on the paper. Therefore, documents freshly printed on a laser printer are always warm.

At the last stage, the charge is removed from the photodrum and it is cleaned of the remaining toner, for which a cleaning blade and waste toner hopper are used.

This is how the printing process works. The laser paints a future image with charged particles. The photodrum catches and transfers the ink powder to the paper. The toner sticks to the paper due to static electricity and becomes fused to it.

Copiers work on the same principle.

Advantages of a laser printer

It is believed that the printing 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 cost per print, which is achieved due to the low consumption and price of toner. The cost of most laser printer models is also quite affordable.

For many years there has been controversy over whether laser printers are harmful to health. The particles of toner used in laser printing are so small that they easily penetrate the human body, settle and accumulate in the respiratory tract. With constant contact with toner for 15-20 years, headaches, asthma and other diseases may develop.

However, printer manufacturers assure that there is no harm from using the printer every day. Production technologies are constantly being improved, and cartridges are tested in laboratories.

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

The speed, service life and print quality of laser printers are truly excellent. 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, however, you did not receive the most successful model of a laser printer and you did not use it very much, then do not despair. KupimToner buys new printers from different brands, as well as components for them, offering a decent price.