The structure of a laser printer and the purpose of components. What is the printing principle of inkjet and laser printer? How does an inkjet printer print?

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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, dispersion 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.

Color laser printers are beginning to actively conquer the printing market. If just a few years ago color laser printing was something unattainable for most organizations, and even more so for individual citizens, now a very wide range of users can afford to buy a color laser printer. The rapidly growing fleet of color laser printers is leading to growing interest in them from technical support services.

Principles of color printing

In printers, as in printing, it is used to create color images. subtractive color model, and not additive, as in monitors and scanners, in which any color and shade is obtained by mixing three primary colors - R(red), G(green), B(blue). The subtractive color separation model is so called because in order to form any shade, it is necessary to subtract “extra” components from the white color. In printing devices, to obtain any shade, the following are used as primary colors: Cyan(blue, turquoise), Magenta(purple), Yellow(yellow). This color model is called CMY by the first letters of the primary colors.

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

Blue + Yellow = Green

Magenta + Yellow = Red

Magenta + Cyan = Blue

Magenta + Cyan + Yellow = Black

It is worth noting that to obtain black it is necessary to mix all three components, i.e. cyan, magenta and yellow, but getting high-quality black in this way is almost impossible. The resulting color will not be black, but rather a dirty gray. To eliminate this drawback, one more color is added to the three main colors - black. This extended color model is called CMYK(C yan- M agenta- Y ellow-black K – cyan-magenta-yellow-black). The introduction of black color can significantly improve the quality of color rendering.

HP Color LaserJet 8500 Printer

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

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

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

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

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

After all this, a laser beam creates an image on the surface of the photodrum in the form of charged and uncharged areas. The laser light beam, hitting the surface of the drum, discharges this area. The laser illuminates those areas of the drum where the toner should be. Those areas that should be white are not illuminated by the laser, and a high negative potential remains on them. The laser beam moves across the surface of the drum using a rotating hexagonal mirror located in the laser assembly. The image on the drum is called a latent electrographic image, because it is represented as invisible electrostatic potentials.

The latent electrographic image becomes visible after passing through the developing unit. The black toner developing module is stationary and is in constant contact with the photodrum (Fig. 9).

The color developing module is a carousel mechanism with alternate supply of “color” cartridges to the surface of the drum (Fig. 10). Black toner powder is single-component magnetic, while colored toner powders are single-component but non-magnetic. Any toner powder is charged to a negative potential due to friction against the surface of the developing roller and the dosing squeegee. Due to the potential difference and the Coulomb interaction of charges, negatively charged toner particles are attracted to those areas of the photodrum that are discharged by the laser and are repelled from areas with a high negative potential, i.e. from those that were not illuminated by the laser. At any given time, only one color of toner is developed. During development, a bias voltage is applied to the developing roller, which causes toner to transfer from the developing roller to the drum. This voltage is a rectangular alternating voltage with a negative DC component. The DC level can be adjusted as the toner density changes. After the development process is completed, the image on the drum becomes visible and must be transferred to the transfer drum.

Therefore, the next step in creating an image is to transfer the developed image to the transfer drum. This stage is called the primary transfer stage. The transfer of toner from one drum to another occurs due to an electrostatic potential difference, i.e. Negatively charged toner particles should be attracted to the positive potential on the surface of the transfer drum. To do this, a positive DC bias voltage is applied to the surface of the transfer drum from a special power source, resulting in the entire surface of this drum having a positive potential. When printing full color, the bias voltage on the transfer drum must constantly increase because After each pass, the amount of negatively charged toner on the drum increases. And in order for the toner to transfer and lay on top of the existing toner, the transfer voltage increases with each new color. This imaging stage is shown in Fig. 11.

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

Next, the photodrum is charged again (after preliminary discharge), and the process is repeated until the image of the corresponding color is completely formed on the transfer drum. Therefore, the size of the transfer drum must fully correspond to the print format, i.e. in this printer model, the circumference of this drum corresponds to the length of an A3 sheet (420 mm). After applying toner of one color, the image formation process is completely repeated with the only difference being that a developing unit of a different color is used. To use another developing unit, the carousel mechanism rotates at a given angle and brings the “new” developing shaft to the surface of the photodrum. Thus, when forming a full-color image consisting of four color components, the transfer drum is rotated four times, and at each rotation a toner of a different color is added to the existing toner. In this case, yellow powder is applied first, then purple, then blue, and black powder is applied last. As a result, a full-color visible image is created on the transfer drum, consisting of particles of four multi-colored toner powders.

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

Next, the full-color visible image from the transfer drum must be transferred to paper. This transfer process is called secondary transfer. Secondary transfer is carried out by another corotron, made in the form of a transport belt (Fig. 13). The toner is moved onto the paper by electrostatic forces, i.e. due to the potential difference between the toner powder (negative) and the secondary transfer corotron, to which a positive bias voltage is applied. Since secondary transfer occurs only after four rotations of the transfer drum, the corotron transfer belt must feed the paper only when all colors have been applied, i.e. during the fourth revolution, and until this point in time, the belt should be in such a position that the paper does not touch the transfer drum.

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

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

During the secondary transfer stage, some toner particles are not transferred to the paper, but remain on the surface of the drum. To prevent these particles from interfering with the creation of the next sheet and distorting the image, it is necessary to clean the transfer drum and remove any remaining toner. Cleaning the transfer drum is a fairly complex process. This procedure uses a special cleaning roller, image drum, and image drum cleaning unit. The transfer drum should not be cleaned continuously, but only after the secondary transfer, i.e. The cleaning system should be controlled similarly to the transfer corotron. While the image is being created, the cleaning system is not active, and when the toner begins to transfer to the paper, it turns on. The first cleaning step is to recharge the residual toner powder, i.e. its potential changes from negative to positive. For this purpose, a cleaning roller is used, which is supplied with an alternating sinusoidal voltage with a positive constant component. This roller is pressed against the surface of the drum during cleaning, and is folded back during image creation. The roller is controlled by an eccentric cam, which in turn is driven by a solenoid (Fig. 16).

The positively charged toner is then transferred to the image drum, which still has a negative bias voltage. And already from the surface of the photodrum, the toner is cleaned with a cleaning squeegee of the photodrum cleaning unit (Fig. 17).

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

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

Useful both in the office and at home. To decide whether such a device is needed, you must first understand what this type of device is. “Laser” means that this type of printer prints with a laser, and it also works with dry ink.

The article will tell you in more detail about how these devices are designed, how they work, as well as their main advantages and main disadvantages. All this will help you make the right decision.

Internal structure and mechanics

The photoelectric part of xerography is the basis of how the device works. Both laser printers print using the same principle. The devices are also arranged identically. Except that color devices have more cartridges. The table below shows the main components of the laser device, as well as their components.

What does the device consist of?
Laser scanning unit	It is a system of lenses and mirrors. Comprises:
	A semiconductor type laser with a lens that focuses automatically.
	Mirrors and their groups that are capable of rotating to form an image.
Image transfer unit	Its components are a toner cartridge and a roller, which is responsible for transferring charge. The cartridge is equipped with three basic elements for image transfer:
	1. photocylinder;
	2. shaft with preliminary charge;
	3. a magnetic shaft that interacts with the printer drum.
	The ability of a photocylinder to change conductivity under the influence of light falling on it is especially important in this case. When a photocylinder is charged, it retains it for a long time; when exposed to light, its resistance decreases, as a result of which the charge begins to drain from the surface and the necessary print appears.
Node for attaching an image	Responsible for fixing the image on paper. Fixation occurs due to the ability of the toner to melt at high temperatures and the heating element, which facilitates this process.

How it works - 8 steps:

The heating element melts the toner;
Melted clumps of powder stick to the paper;
The scraper removes remaining toner from the drum;
The drum is treated with electrostatics and receives a charge (positive or negative);
Using mirrors, an image appears on the surface of the drum;
The drum moves along a magnetic shaft, and the toner applies an image to it;
The drum transfers the image onto the paper by rolling over it;
is rolled through the oven, thanks to which the image is fixed.

Toner

Toner is a consumable item. This is a dry powder (can be black or colored), which is ink for laser printers. As already described above, it works like this: with the help of static, it (the powder) is transferred to a charged photodrum, due to which a picture appears. It is subsequently transferred to paper.

Each manufacturer produces an original one. Only with a proprietary dye can the company guarantee stable operation of the device. Qualities such as magnetism and dispersibility are individual for coloring substances. Devices are manufactured to use a specific toner. By refilling a cartridge with an alternative powder of dubious quality, the user risks compromising the performance of the device. If the required toner is not available, you can select a compatible option with identical properties.

Attention! Attempting to use incompatible products may result in serious equipment malfunctions. You may also lose warranty service.

You should be aware that toner may be harmful to your health while it is in powder form. It must not be allowed to enter the respiratory tract.

When refilling or removing excess substance, it is extremely important to take the following precautions:

use latex gloves;
wear a respirator or medical mask on your face;
work with the substance only in a well-ventilated area;
It is recommended to use a special vacuum cleaner to remove excess toner.

It’s even better not to refill the cartridge yourself, but to entrust this task to a professional. By contacting a service center, you don’t have to worry that the toner will damage the printer or harm your health.

In a printer based on laser printing technology, everything works through the use of static electricity. How it works? 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 shined 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 is formed on its surface, 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 matrix and inkjet printers, where the image is transferred to paper line by line, with laser printing the text on an A4 sheet is formed in just 3 revolutions 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 -

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) segment is called resolution and is characterized in dots per inch (dpi - dot per inch). A printer is considered good if its resolution is 300 dpi (sometimes the designation 300 x 300 dpi is used, which means 300 dpi horizontally and 300 dpi vertically).

Laser printers are less demanding on paper than, for example, inkjet printers, and the cost of printing one page of a text document is several times lower. At the same time, inexpensive models of laser and LED monochrome printers are already able to compete 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 images containing grayscale, 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 copiers it occurs using a lamp, and in laser printers, lamp light replaced the laser beam (Fig. 1).

Rice. 1. Laser printer device

The heart of a laser printer is a photoconductive cylinder (Organic Photo Conductor), which is often 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), 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:
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;
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 roller, 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 onto the magnetic roller.

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.