How a laser printer works. How a laser printer works Printer structure diagram

In domestic conditions, laser and inkjet printers are popular. The principle of printing such devices is fundamentally different, which cannot but affect the operational features. In some cases it is best to use laser products, while in others it is best to use inkjet products. However, to make the final choice in favor of a particular device is possible only after considering the scheme of work.

Working principle of inkjet printer

Still, at home, it is most often used precisely jet printer. The principle of printing it is to form an image using liquid ink. They are transferred to the media through special nozzles located on the head. The number of such holes depends on the model of the printer. Usually their number ranges from 16-64 pieces.

Since an inkjet printer prints using liquid ink, it dries on the head nozzles if it is left idle for a long time. This requires cleaning of the printing element, which involves the additional consumption of colorants.

Such devices consist of the following components:

• supporting structure;
• power supply;
• print head;
• cleaning system;
• devices for supplying media;
• control node.

A color image is obtained by superimposing three primary colors on top of each other. Black ink is often added to them, so that it is possible to use devices for the usual printing of texts and black-and-white drawings, saving on color inks.

Core Inkjet Printing Technologies

Different models may have their own advantages and disadvantages. The principle of printing representatives of inkjet printers may also differ slightly depending on the technology used. The difference lies only in the way the ink is transferred to the solid media.

1. The piezoelectric method involves the formation of ink dots on paper using special devices that are connected to the diaphragm. The electric field has a direct effect on the piezoelectric element, and it expands the tube to fill the capillary system. The main advantage lies in the flexible control of the droplet dimensions, which makes it possible to obtain high-quality images with high resolution.
2. The gas bubble method implies the presence of heating elements directly in the nozzles. Electricity is passed through them. During the heating process, gas bubbles are formed, which push the right portion of liquid ink through the holes. After the heater cools down, a fresh portion of the coloring matter enters through the nozzles. High quality is noted for detailed drawing of lines, but when printing solid areas, there may be slightly blurry places.
3. The thermal jet method, as in the previous case, involves the use of a heating element. However, a special mechanism is used with it, which allows for faster injection of colorants. As a result, device performance increases. The color palette of the resulting image differs in contrast.

The inks used may vary. Water-based ink contains a soluble dye and certain additives to adjust the viscosity. Their advantage lies in their low cost. Pigment inks are UV and moisture resistant. The print quality in this case is less dependent on the media.

Using continuous ink supply

With the principle of printing an inkjet printer, everything became clear. Special cartridges are used to store dyes. However, there is a special system that allows you to continuously supply ink in order to save money. In this case, the capsule reservoirs are installed directly on the print head.

The system is a set of containers connected by a silicone cable, through which ink is supplied from donors to the main unit. Thanks to this device, the constant presence of the original dyes in the print head is achieved. Many large format office fixtures have a built-in ink system that cannot be seen from the outside.

The principle of operation of the laser device

A completely different branch of the development of printing devices is laser technology, which can be used to achieve high-quality deposition of colorants on paper. The formation of characters and images occurs due to the beam illumination of the device elements with photosensitivity. The resulting copies with text or graphic information are resistant to fading and abrasion.

Inkjet and laser printers have completely different printing principles. Toners act as colorants, which can be transferred to a solid carrier in three ways.

1. Using a two-component development system. The dye particles needed to be transferred to a special photosensitive drum cannot be fixed on a magnetic roller without a special magnetic carrier charged by agitation.
2. With the use of one-component toner without additional impurities. Particles of matter in this case are endowed with magnetic properties. In some devices, electrostatic application can be carried out. With this option, the toner does not require magnetization.
3. Using a two-component dye, mixed at the factory.

Unlike an inkjet printer, the principle of printing a laser analog is based on building an image using the photographic method. The laser beam hits a special shaft, the surface of which is electrified due to impact ionization of the internal air.

Design of laser devices

Laser printers succeed in obtaining high-quality printing due to technological features. They include the following elements.

1. Photodrum, which is a cylinder made of aluminum. It is treated with a photosensitive material that tends to change electrical resistance in the presence of lighting.
2. The magnetic roller is used to transfer the toner from the reservoir directly to the drum or developing roller installed in some models of modern printers.
3. The doctor blade acts as a cleaning blade. With its help, excess coloring matter is removed from the screen roller. It can be made of plastic, steel or fiberglass.
4. The waste toner hopper is made in the form of a container. This compartment may be separate from the cartridge or together with it. The filling speed of such a tank depends on the quality of the toner.
5. The laser unit is designed to create an invisible image on the surface of the photoconductor by highlighting specific areas. The intensity of the beam can vary significantly.
6. The primary charge roller is made in the form of a metal rod covered with a layer of rubber. This element allows you to ensure the uniformity of the negative charge.
7. The transfer tape is necessary for applying an intermediate result from color cartridges.
8. The development unit allows you to transfer the toner directly onto the electrostatic image created on the surface of the photoconductive element.

Laser printing process

Not everyone fully understands the principle of printing laser printers from computer science courses. Inkjet devices operate according to a simplified scheme, so there are no special questions about them. How does the laser printing process work?

1. First, the photoconductive roller is charged. An electric charge is evenly distributed over its surface by rotating the roller. The rotating rod system reduces voltage and reduces the amount of ozone produced.
2. A laser scan is performed. At this moment, the charged surface of the shaft passes under the light beam. The laser hits only those places where the coloring matter will be applied in the future.
3. The toner is applied. A roller that has a negative charge transfers it to the toner. The dye from the hopper is attracted directly to the magnetic shaft, after which it comes into contact with the photoconductive element in those areas where the negative charge remains.
4. The transfer roller in contact with the solid carrier is no longer negatively charged but positively charged. Particles of the coloring matter fall on the surface of the paper due to electrostatic action.
5. The toner distributed over the carrier is fixed by heat and pressure. The thermal chamber consists of two shafts between which the paper moves. The temperature is controlled by a special sensor. The dye is melted and incorporated into the texture of the paper.

comparison table

It is suggested to look at the table to compare the properties of inkjet and laser printers, which print principle is very different.

Options	Printer type
	laser	Jet
Text printing
Obtaining color images in the form of diagrams and graphs
Printing photos
Performance
Number of pages printed after replacing ink cartridges

Having briefly considered the principle of printing an inkjet printer, one cannot fail to note the features of operation.

1. It is not recommended to use the device less than once a week to avoid ink drying out.
2. It is necessary to purchase high quality dyes, otherwise the head can quickly become clogged.
3. The correct paper should be used and should be marked as suitable for inkjet printing.
4. It is essential to keep the product clean, as dust wears out moving parts.

Features of working with laser devices

The main advantage of laser printers is the absence of the need for regular operation. It can even be used once a month. This will not affect the quality of work or wear of parts. However, you must use only original toner cartridges, otherwise there is a high risk of damage to the device. In addition, third-party supplies may simply not work.

Before purchasing a device with a lot of positive reviews, you need to find out additional information about the cost:

• Supplies;
• wear parts;
• one page printout.

Sometimes it turns out that it is easier to purchase a new device than to replace any parts.

Final part

Having briefly considered the principle of printing inkjet and laser printers, we can draw certain conclusions about the acquisition of certain devices. However, the final choice will depend on what goals are pursued during operation. For printing large volumes of text information, it is more profitable to buy laser devices. If you need to get high-quality photos, then it is better to give preference to inkjet counterparts.

Today it is already difficult to imagine life without printing devices. Transferring information to paper from time to time is simply necessary. Schoolchildren need to print reports, students - diplomas and term papers, office workers - documents and contracts.

There are several types of printers. They differ in the principle of printing, the size of the paper used, the type of printed materials and other features. Consider the principle of operation of two types of printing devices - laser and inkjet.

How an inkjet printer works

First of all, let's look at how an inkjet printer works. It is worth mentioning right away that in terms of print quality it is slightly behind the laser one. However, the cost of an inkjet printer is much lower. This type The printer is great for the home. It is easy to handle and easy to maintain.
If we talk about the principle of operation of laser and inkjet printers, then they are fundamentally different. The main difference is in the ink supply technology, as well as in the hardware design. Let's first discuss how an inkjet printer works.

The principle of operation of this printing device is as follows: the image is formed on a special matrix, after which it is printed on the canvas using liquid ink. There is another type of inkjet printers that have cartridges in their device. Cartridges are installed in a special block. In this design, the ink is transferred to the print matrix using the print head. After that, the matrix transfers the image to paper.

Storing ink and applying it to the canvas

There are several ways to apply ink to a canvas:

— method of gas bubbles;
— piezoelectric method;
- drop-on-demand method.

The piezoelectric method involves the creation of ink dots on the canvas using a piezoelectric element. The tube is unclenched and compressed again, preventing excess ink drops from falling. The gas bubble method is also known as the injected bubble method. They leave an imprint on the canvas due to high temperatures. The nozzle of each print matrix has a heating element. It takes a fraction of a second to heat up such an element. After heating, the resulting bubbles are transferred to the web through nozzles.

The drop-on-demand method also uses gas bubbles. However, this is already a more optimized method. Print speed and quality have improved significantly.

Ink is usually stored in an inkjet printer in two ways. The first method involves the presence of a separate tank from which ink is supplied to the print head. In the second method, a special cartridge is used to store ink, which is located in the print head. To replace the cartridge, you will have to change the print head itself.

Using inkjet printers

Inkjet printers have gained particular popularity due to the fact that these devices have the ability to print in color. An image in color printing is created by superimposing basic tones with different degrees of saturation on top of each other. The basic set of colors is also known by the acronym CMYK. It includes the following colors: black, cyan, magenta and yellow. Initially, a set of three colors was used. It included all the colors listed above, except for black. But even when overlaying cyan, yellow and magenta colors at 100% saturation, it was still not possible to achieve black, it turned out either gray or brown. For this reason, it was decided to add black ink to the main set.

Inkjet printer: features of work

Print speed, noise performance, durability, and print quality are commonly considered key performance indicators of a printer. Consider the performance of an inkjet printer.

The principle of operation of such a printer has already been discussed above. Ink is applied to paper through special printers. An inkjet printer operates very quietly, unlike, for example, needle-point printers, in which ink is applied by a mechanical shock process. You will not hear how the inkjet printer prints, you can only distinguish the noise of the mechanism that moves the print heads. If we talk about the noise characteristics of inkjet printers in quantitative terms, then during the operation of such a device, the noise level does not exceed 40 decibels.

Now let's talk about typing speed. An inkjet printer prints much faster than a needle printer. However, the quality of printing directly depends on such an indicator as speed. In this sense, the faster the print speed, the worse the quality. If you select the high quality print mode, the process will slow down significantly. The paint on the canvas will be applied carefully. Such a printer prints at an average speed of 3 to 5 pages per minute. In modern printers, this figure has been increased to 9 pages per minute. Color images will take a little longer to print.

One of the main advantages of an inkjet printer is the font. In terms of the quality of the font display, an inkjet printer can be compared, perhaps, only with a laser one. You can improve print quality by using good quality paper. The main thing is to choose paper that can quickly absorb moisture. High image quality can be achieved using paper weights between 60 and 135 g/m2. Xerox paper has proven itself well. Its density is 80 g/m2. To speed up the ink drying process, some printers have a paper warmer function. Despite the completely different principle of operation of an inkjet and laser printer, when using these devices, it is possible to achieve the same quality.

Paper for printing

An inkjet printer, unfortunately, is not suitable for printing on roll media. It is also not intended for making copies: you will have to use multiple printing.

Disadvantages of an inkjet printer

As mentioned earlier, inkjet printers print using a matrix. The image when printing on an inkjet printer is formed from dots. The most important and valuable element in the entire device is the print head. To reduce the size of the device, many companies embed the print head in the cartridge. An inkjet printer and a laser printer differ in how they print. The disadvantages of inkjet printers include the following points:

1. Low print speed;
2. Drying of ink during long periods of inactivity
3. High cost and short resource of consumables

Advantages of inkjet printers

1. Optimal price/quality ratio. When choosing a printing device, many users are most attracted by the price of this type of printers.
2. The printer has rather modest dimensions. This makes it possible to mark it even in a small office or office. It will not cause any inconvenience to the user.
3. Possibility of self-filling cartridges. You can just buy ink and read the user manual on how to properly refill.
4. Availability of continuous ink supply system. Such a system will significantly reduce the cost of printing at large volumes.
5. High quality print images and photos
6. Large selection of used print media

Laser printer

A laser printer today refers to a special type of printing equipment designed to print text or images on paper. This type of equipment has a very unusual history. The principle of operation of a laser printer began to be discussed only in 1969. Scientific research was carried out for several years.

To improve the principle of operation of this apparatus, many methods have been proposed. The world's first copier using a laser beam to create a print appeared in 1978. This device was huge, and the cost of it went through the roof. Some time later, this development was taken up by Canon.

The first desktop laser printer appeared in 1979. This has led other companies to optimize and promote new models of laser printers. The principle of printing itself has not changed. Prints produced using a laser printer are of high quality. They are not afraid of fading or erasing, they are not afraid of moisture. The images produced by a laser printer are of high quality and durability.

The principle of operation of a laser printer

Let us briefly describe the principle of operation of a laser printer. When printing on a laser printer, the image is applied in several stages. First, under the influence of temperature, a special powder is melted - toner. It sticks to paper. After that, unused toner is removed from the drum with a special scraper and moved to the waste accumulator. The surface of the drum is polarized by the coronator. An image is formed on the surface of the drum. Then the drum moves along the surface of the magnetic roller, on which the toner is located. The toner sticks to the charged areas of the drum. After that, the drum comes into contact with the paper and leaves toner on it. The paper is then rolled through a special oven in which the powder melts under high temperature and adheres to the paper.

Color laser printer

The process of printing on a color printer differs from black and white by using several shades. By mixing these shades in a certain ratio, you can create primary colors. Typically, laser printers have their own compartment for each color. This is their main difference. Printing color images on such a printer takes place in several stages. First, the image is analyzed, after which the charge distribution is formed. Next, the same sequence of operations is carried out as in black and white printing: a sheet with toner is passed through an oven, where the powder is melted and seized with paper.

Advantages of laser printers

1. High speed printing
2. Endurance and durability of the image
3. Low cost
4. High quality

Disadvantages of laser printers

1. During operation, ozone is released. Only use the laser printer in a well-ventilated area
2. Bulky
3. High power consumption
4. High price

Conclusion

After analyzing the principle of operation and the main characteristics of inkjet and laser printers, we can say that for home use the first type of devices is more suitable. They are affordable and small in size. Laser printers are more suitable for an office where you need to print a large number of documents.

Most modern printers are divided into laser and inkjet printers. Moreover, thanks to progress, the latter are gradually leaving the market of "household office equipment", remaining specialized. In offices, homes, and even some print centers, laser printers are the most common.

In domestic use, the main difference between inkjet printers and laser printers lies primarily in the high cost-effectiveness of the latter. Ink consumption is practically minimal - one cartridge is enough for several thousand sheets with a fairly high density of ink. In addition, laser printers work very quickly and do not require special service 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 never found, unlike monochrome (black and white).

The main functional units 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 it that the toner is applied by means of electrostatic attraction and repulsion according to Coulomb's law;
• squeegee. It is designed to clean the drum of toner residue 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. Toner is fixed on it for subsequent transfer to the surface of the drum;
• stove. It is designed to bake the toner left on the paper. Therefore, the sheets that come 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 possibilities 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 belt, which is designed to transfer the image formed by the corresponding toners to paper.

The principle of operation of a laser printer

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

1. The drum is being cleaned. The doctor blade removes toner adhering to its surface, but not used in the previous printing cycle;
2. The coronator charges the surface of the drum. Either positive ions appear on it, or the number of negative electrons increases. This is intended to give rise to Coulomb forces.
3. A laser controlled by a rotating mirror partially discharges the surface of the drum. The toner itself is negatively or positively charged. Therefore, it repels 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.
4. Toner powder is transferred from the surface of the magnetic roller to the drum.
5. From the surface of the drum, the toner adhered to it is transferred to the paper sheet.
6. 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 action of high temperature and due to pressure from the shaft fixed on the spring.

If 4 separate drums and the same number of magnetic rollers are installed in color laser printers, however, the toner is not applied directly to the paper itself, but to the transfer ribbon. All four shades are first applied to it. The transfer ribbon is then rolled across the paper, and the multi-colored image is placed on the sheet. The toner is then baked and fixed.

Fundamental non-technological differences between laser and inkjet printers

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

• economy. A laser printer cartridge lasts for several thousand sheets of high coverage paper.
• refueling option. Laser printer cartridges can be refilled with toner as needed without the risk of compromising their functionality. You can even carry out this operation on your own, but you should be careful, because the coloring pigment is negatively or positively charged and quickly sticks to skin, clothes and other surfaces under the influence of Coulomb forces. Inkjet printer cartridges in most cases cannot be refilled, as this leads to a violation of their tightness. For some models of this type of equipment, continuous ink supply systems can be used, but this is considered an unauthorized modification and will void the warranty agreement.
• high speed. Most laser printers can print up to 10 text pages per minute. Some work even faster.
• no need for weekly printing. The toner used in laser printers does not dry out or stick together. Therefore, periodically "chasing the print" to prevent head clogging is not necessary. Actually, there is no head in laser printers.
• print durability. Images and text on paper obtained using such office equipment do not fade or disappear over time under the influence of high humidity.
• high image resolution. Color laser printers provide print resolutions up to 9600 x 1200 dpi.

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

• high cost. On average, a laser printer in a complete set "from the factory" - that is, with incomplete cartridges - costs several times more than a similar inkjet. 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 place for installation.
• the need to warm up before work and the risk of overheating after prolonged typing. 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 that, the device overheats with the risk of system problems.
• little environmental friendliness. During operation, such devices release into the air some harmful compounds, dust, and also emit infrared and ultraviolet radiation.
• high resource intensity. Due to the presence of "gluttonous" in relation to the current elements, laser printers consume more electricity. Moreover, peak power can be so high that such office equipment will not work from household or office UPSs.
• the 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 counterparts.

Laser printers have become indispensable attributes of office equipment. Such popularity is explained by the high speed and low cost of printing. To understand how this technique works, you should know the device and principle of operation 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 an image to paper using dry ink. The main engine of work was static electricity. Electrographic method(and it was he) became widespread in 1949, when the Xerox Corporation took it as the 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 did the first Xerox appear, which became the prototype of modern laser printing devices.

First Xerox 9700 Laser Printer

The very first laser printer appeared only in 1977 (it was the Xerox 9700 model). 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 first Canon desktop unit was released. Since that time, numerous brands have been involved in the development, which to this day offer more and more new options for desktop laser printing assistants. Each person who decides to use such a technique will be interested to learn more about the internal structure and principle of operation of such a unit.

What's inside

Despite the large assortment, the laser printer device 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 nodes:

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

The first block is presented lens and mirror system. It is here that a semiconductor type laser with a focusable lens is located. Next are mirrors and groups that can rotate, thereby forming an image. We pass to the node responsible for transferring the image: it contains the toner cartridge and roller carrying charge. Already in the cartridge alone, there are three main image-forming elements: a photo cylinder, a pre-charge roller and a magnetic roller (working in conjunction with the drum of the device). And here the possibility of a photocylinder to change its conductivity under the action of light that has fallen on it acquires great relevance. When the photo cylinder is charged, it retains it for a long time, but when illuminated, its resistance decreases, which leads to the fact that the charge begins to drain from its surface. This gives us the impression we need.

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

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

How is the image captured? This is due to those additives that are in the toner. They have a specific melting point. Such a "stove" presses the molten toner powder into the paper, after which it quickly hardens and becomes durable.

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

How the cartridge works

The defining link 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 light-sensitive drum (photocylinder) and mechanical gears for turning it.

The toner itself is a fine-dispenser powder, which consists of polymer balls - they are covered with a special layer of magnetic material. If we are talking about color toner, then it also contains dyes.

It is important to know that each manufacturer produces its own original toner - all of them have their own magneticness, dispersion and other properties.

That is why in no case should you refill cartridges with random toners - this can adversely affect its performance.

The process of making an impression

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

• drum charge;
• exposure;
• developing;
• transfer;
• fastening.

How does photocharge work? It is formed on the photodrum (where, as is already clear, the future image itself is born). To begin with, there is a supply of charge, which can be both negative and positive. This happens in one of the following ways.

1. used coronator, that is, a tungsten filament coated with carbon, gold and platinum inclusions. When a high voltage comes into play, a discharge is carried between this thread by a frame, which, accordingly, will create an electric field that transfers a charge to the photoconductor.
2. However, the use of filament led to problems with soiling and degradation of printed material over time. Works much better charge roller with similar features. He himself 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 photo cylinder becomes conductive and passes the 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.

1. 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.
2. So the system of lenses and mirrors forms a line along the photocylinder - the laser turns on and off, the charge either remains intact or is removed.
3. Line ended? The drum unit will rotate and the exposure will continue again.

development

In this process, it is important cartridge magnetic shaft, similar to a tube made of metal, inside of which there is a magnetic core. Part of the surface of the shaft 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 uniformity of the distribution of the powder layer - for this there is a special dosing blade. It passes only a thin layer of toner, throwing the rest back. If the blade is not installed correctly, black streaks may appear on the paper.

After that, the toner moves to the area between the magnetic roller and the photocylinder - here it will be attracted to the exposed areas, and repelled from the charged ones. So the image becomes more visible.

Transfer

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

So, the particles break away from the drum and begin to move onto the page. But they are kept here so far only because of static stress. Figuratively speaking, the toner is simply poured where it is needed.

Dust and paper lint can get in with the toner, but they can be removed viper(with a special plate) and 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 the toner to melt at high temperatures is used. Structurally, this is assisted by the following two shafts:

• at the top there is a heating element;
• 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 pressure part, the paper heats up to 200 degrees, which allows it to easily absorb the liquid toner.

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

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

How color laser printing works

But what about color printing? The laser device uses four of these basic colors - black, magenta, yellow and cyan. The principle of printing is the same as in the black and white case, however, the printer will first split the image into monochrome for each color. The successive transfer of each color by each cartridge begins, and as a result of the overlay, the desired result is obtained.

There are such technologies of color laser printing:

• multipass;
• single pass.

At multi-pass option an intermediate carrier comes into play - this is a shaft or tape that carries the toner. It works like this: 1 color is superimposed in 1 revolution, 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 complete picture - it will go to paper. But the device itself will work 4 times slower than its black and white counterpart.

How the printer works single pass technology? In this case, all four separately printing mechanisms have a common control - they are lined up in one line, each has 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 passage does the sheet go into the oven, where the picture is fixed.

The merits of laser printers have made them a favorite for document work, both in the office and at home. And information about the internal component of their work will help any user to notice shortcomings in time and contact the service department for technical support device operation.

Color laser printers are beginning to actively conquer the printing market. If a few years ago color laser printing was something inaccessible 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 fast-growing fleet of color laser printers means that interest in them from technical support services is also growing.

Principles of Color Printing

In printers, as well as in printing, to create color images, subtractive a color model, and not an additive one, 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 called so because in order to form any shade, it is necessary to subtract the “extra” components from the white color. In printing devices, to obtain any shade, the primary colors are used: 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 obtained by absorbing some light waves and reflecting others. Blue paint, for example, absorbs red and reflects green and blue; magenta absorbs green and reflects red and blue; and yellow paint absorbs blue and reflects red and green. When mixing the main components of the subtractive model, you can get different colors, which are described below:

Blue + Yellow = Green

Magenta + Yellow = Red

Magenta + Cyan = Blue

Magenta + Cyan + Yellow = Black

It should be noted that in order to obtain black color, it is necessary to mix all three components, i.e. cyan, magenta and yellow, however, it is almost impossible to obtain high-quality black in this way. The resulting color will not be black, but rather a dirty gray. To eliminate this drawback, one more color is added to the three primary 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 reproduction.

HP Color LaserJet 8500 Printer

After we have discussed the general principles of construction and operation of color laser printers, it is worth familiarizing yourself with their device, mechanisms, modules and blocks in more detail. This is best done on 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 position is shown in Fig.5.

Image formation begins with the fact that residual potentials are removed (neutralized) from the surface of the photoconductor. This is done so that the subsequent charge of the photoconductor is more uniform, i.e. before charging, it is completely discharged. The 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).

Further, a high-voltage (up to -600V) negative potential is created on the surface of the photoconductor. The drum is charged with a corotron in the form of a roller made of conductive rubber (Fig. 8). An alternating voltage of a sinusoidal shape with a negative constant component is applied to the corotron. The variable component (AC) provides a 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) by using the printer driver or by adjusting the control panel. An increase in the negative potential leads to a decrease in density, i.e. to a lighter image, while a decrease in the potential, on the contrary, to a denser (darker) image. The photoconductor (its internal metal base) must be “grounded” without fail.

After all this, an image is created on the surface of the photodrum by a laser beam in the form of charged and uncharged areas. The light beam of the laser, falling on the surface of the drum, discharges this area. The laser illuminates those parts 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 is moved across the surface of the drum by 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 development unit. The black toner developing module is stationary and is in constant contact with the photoconductor (Fig. 9).

The color developing module is a carousel mechanism with sequential supply of “color” cartridges to the surface of the drum (Fig. 10). Black toner powder is a magnetic one-component, and color powders are one-component, but non-magnetic. Any toner powder is charged to a negative potential due to friction on the surface of the developing shaft 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 photoconductor that are discharged by the laser and repel from areas with a high negative potential, i.e. from those that were not illuminated by a laser. Only one color of toner is developed at a time. At the time of development, a bias voltage is applied to the developer roller, which causes the transfer of toner from the developer roller to the drum unit. This voltage is a square wave AC voltage with a negative DC component. The DC level can be adjusted by changing the density of the toner. After the development procedure is completed, the image on the photoconductor 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 the electrostatic potential difference, i.e. the negatively charged toner particles should be attracted by the positive potential on the surface of the transfer drum. To do this, a positive DC bias voltage from a special power source is applied to the surface of the transfer drum, as a result of which the entire surface of this drum has a positive potential. When printing in full color, the bias voltage on the transfer drum must be constantly increased, because. after each pass, the amount of negatively charged toner on the drum increases. And in order for the toner to be transferred and lay on top of the existing toner, the transfer voltage increases with each new color. This stage of imaging is shown in Figure 11.

During the process of transferring toner to the transfer drum, small particles of toner may remain on the surface of the drum unit, and they must be removed so as not to distort the subsequent image. To remove residual toner, the printer has a drum cleaning unit (see Figure 17). As part of this module, there is a special shaft - a brush for removing the charge from the toner and the photoconductor - this weakens the force of attraction of the toner to the photoconductor. 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 out.

The image drum is then charged again (after a pre-discharge) and the process is repeated until the appropriate color is fully formed on the transfer drum. Therefore, the size of the transfer drum must fully match 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 the 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 a different developer unit, the carousel mechanism rotates to a predetermined angle and brings the “new” developing roller to the surface of the photoconductor. Thus, when forming a full-color image consisting of four color components, the transfer drum is rotated four times, and toner of a different color is added to the already existing toner at each revolution. In this case, the yellow powder is applied first, then purple, then blue, and the black powder is applied last. As a result, a full-color visible image is created on the transfer drum, consisting of particles of four different-colored toner powders.

After the toner powder is on the surface of the transfer drum, it passes through the additional charge unit. This block (Fig. 12) is a wire coroton, which is supplied with a sinusoidal alternating voltage (AC) with a negative constant component (DC). With this voltage, the toner powder is additionally charged, i.e. its negative potential becomes higher, which will contribute to a more efficient transfer of the toner to the paper. In addition, the additional voltage decreases the positive potential value of the transfer drum, which helps to properly position the toner on the transfer drum and prevents the toner from shifting. The result is accurate color reproduction. The boost voltage is applied to the transfer drum during yellow toner application, i. at the very beginning of the imaging process. When yellow toner powder is applied, the boost voltage is set to the minimum value, and after each new color is applied, this voltage is increased. The maximum boost voltage is applied during black toner application.

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

Thus, the transfer belt is lowered down during image creation, and does not come into contact with the transfer drum, and at the time of the secondary transfer, it is raised up and touches this drum. The movement of the transport belt of the corotron is carried out by an eccentric cam, which is actuated by an electric clutch on 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 and cause 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, which is supplied with a sinusoidal alternating voltage with a positive constant component. The location of the corotron relative to the paper and transfer drum is shown in Figure 15.

During the secondary transfer stage, some particles of toner are not transferred to the paper, but remain on the surface of the drum. To ensure that these particles do not interfere with the creation of the next sheet and do not distort images, it is necessary to clean the transfer drum and remove any remaining toner. Cleaning the transfer drum is a rather complicated process. For this procedure, a special cleaning roller, an image drum and an image drum cleaning unit are used. The transfer drum should not be cleaned continuously, but only after a second 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 transfer of toner to the paper begins, it turns on. The first cleaning step is to recharge the residual toner powder, i. its potential changes from negative to positive. For this, a cleaning roller is used, to which an alternating sinusoidal voltage with a positive constant component is applied. This roller is pressed against the surface of the drum during the cleaning period, and during the imaging process, it reclines. 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 drum unit, 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 with the fixation of the toner on paper using temperature and pressure. A sheet of paper passes between two rollers of the fixing unit (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 instead of on the Teflon roller.

We considered the principle of operation of only one printer of one company. Other manufacturers may apply other principles of image formation and other technical solutions when building printers, however, all these solutions will be very close to those that were considered earlier.