Laser printer device principle. How a laser printer works

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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 adheres to uncharged fragments under the influence of static electricity. This is called image development.

A special roller with a positive charge presses the 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 expands 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 you still did not get the most successful model of a laser printer and you did not use it much, then do not despair. KupimToner buys new printers from different brands, as well as components for them, offering a decent price.

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 is 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. The cartridge alone contains three main image-forming elements: a photocylinder, a pre-charged roller, and a magnetic roller (working in conjunction with the device’s 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 given charge, 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 ones. 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 sequentially transferring 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 print

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 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.

Laser printers provide higher quality than inkjet printers. The most famous companies developing laser printers are Hewlett-Packard and Lexmark.

The operating principle of a laser printer is based on the method of dry electrostatic image transfer, invented by C.F. Carlson in 1939 and also implemented in copying machines. The functional diagram of the laser printer is shown in Fig. 5.6. The main design element is rotating drum, serving as an intermediate medium with which the image is transferred to paper.

Rice. 5.6. Functional diagram of a laser printer

Drum is a cylinder coated with a thin film of light-conducting semiconductor. Typically, zinc oxide or selenium is used as such a semiconductor. The static charge is evenly distributed over the surface of the drum. This is achieved by a fine wire or mesh called a corona wire, or corotron. A high voltage is applied to this wire, causing a glowing ionized area called a corona to appear around it.

Laser, controlled by a microcontroller, generates a thin beam of light that is reflected from a rotating mirror. The image is scanned in the same way as in a television kinescope: by moving the beam along the line and frame. With the help of a rotating mirror, the beam slides along the cylinder, and its brightness changes abruptly: from complete light to complete darkness, and the cylinder is charged in the same abrupt manner (pointwise). This ray, reaching the drum, changes it electric charge at the point of contact. The size of the charged area depends on the focusing of the laser beam. The beam is focused using a lens. A sign of good focusing is the presence of clear edges and corners in the image. For some types of printers, during the charging process, the potential of the drum surface decreases from 900 to 200 V. Thus, a hidden copy of the image appears in the form of an electrostatic relief on the drum, the intermediate medium.

At the next stage, it is applied to the phototypesetting drum. toner- paint, which is the smallest particles. Under the influence of a static charge, particles are easily attracted to the surface of the drum at exposed points and form an image in the form of a dye relief.

Paper is pulled from the feed tray and moved to the drum using a roller system. Just before the drum, the corotone imparts a static charge to the paper. The paper then comes into contact with the drum and, thanks to its charge, attracts the toner particles previously applied to the drum.

To fix the toner, the paper is passed between two rollers at a temperature of about 180 "C. After the printing process is completed, the drum is completely discharged, cleaned of adhering excess particles to carry out a new printing process. A laser printer is page by page, i.e. it forms a full page for printing.

The process of operation of a laser printer, from the moment it receives a command from the computer to the output of the printed sheet, can be divided into several interconnected stages, during which such functional components of the printer as the central processor are involved; scan processor; mirror motor control board; beam brightness amplifier; temperature control unit; sheet feed control unit; paper feed control board; interface board; power unit; control panel buttons and indication board; additional RAM expansion cards. Essentially, a laser printer functions like a computer: the same central processing unit, which houses the main interconnection and control functions; RAM, where data and fonts are located, interface boards and a control panel board, which communicates the printer with other devices, a printing unit, which outputs information onto a sheet of paper.

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 the 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, it 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. You can even carry out this operation 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. In most cases, inkjet printer cartridges cannot be refilled, as this leads to a violation of their seal. 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 work 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 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.