This article aims to explain to the user how an inkjet printer works. The reader has the opportunity to learn about the history of the emergence and improvement of inkjet devices for printing, as well as get acquainted with the technology of drawing pictures on paper.
The content of the article:
A brief excursion into the history of the inkjet printer
Frenchman Felix Savart in 1833 he discovered an interesting phenomenon – droplets of liquid coming out through a very narrow hole have the same size and consistency. Only 45 years later, the Nobel laureate in physics lord Riley was able to explain this phenomenon based on the laws of nature.
Years passed, but this effect did not find application in practice. Only in 1951 the company’s employees Siemens in the laboratory were able to put into practice the phenomenon of providing the same consistency of liquid droplets in a voltage measuring device called a magnetograph. A decade later, scientists from Stanford developed a method for breaking droplets into equal and equidistant from one another with the possibility of supplying an electric charge to their stream or selected areas. Drops, having a certain color, fell on a solid surface, forming an image, and charged liquid particles returned back to the collector. This has been called continuous inkjet printing.
In the 70s, IBM was able to license the above technology and developed a line of devices for printing text on hard materials based on it. At the same time, Professor Hers from Sweden developed a technology for adjusting various flow parameters, achieving printing in grayscale, not just black. He was also able to adjust the density of the liquid applied to the surface.
Late 70s Canon developed the technology of thermal inkjet printing. Created the same and Hewlett-Packard independently of the first, and in 1984 released an inkjet printer available to a wide range of users.
The first liquid ink printer
Speaking about such a device as an inkjet printer, it is necessary to note one important point regarding the problem with the removal of excess drops back into the reservoir. It was solved in printers from Siemens and Silonics, released in 1980 and 1977, respectively. Independently of each other, the employees of the firms came up with a method called drop-on-demand, and began mass production of devices based on it. The essence of the drop-on-demand method is that the device releases drops on demand. These were the first printers to use the technology that became the prototype for piezoelectric printing.
In 1979, specialists from the company Canon developed a bubble printing method, according to which liquid droplets were released onto the surface of a heating element in close proximity to the nozzle. The heater, passing an electric current through itself, instantly heats up to several hundred degrees (about 500 ° C). During this process, microscopic air bubbles form in the liquid ink, pushing the liquid particles out of the nozzle onto the paper. This technology, which was presented at the 1981 Canon Electronics Grand Fair, was named Thermal Ink Jet.
Based on bubble printing, the world’s first Canon BJ-80 monochrome inkjet printer was released for business use.
Three years later, Canon’s first color inkjet printer appeared. It was called BJC-440 and supported printing on huge sheet sizes of the A2 standard with a resolution of up to 400 dpi.
Structure and working principle
Most business people use printers in their daily life, but only a few of them know and imagine how an inkjet printer works.
An inkjet cartridge is equipped with nozzles that hold the secret of its work. The number of nozzles can be up to several thousand, depending on the cartridge. A liquid called ink is heated in them, after which it is pushed out with enormous precision, unattainable for the optical system of the human eye, onto the carrier.
The appearance of the device is nothing special, but its internal structure is a very complex and well-organized mechanism.
The principle of printing is similar to the work of dot matrix printers in that the image is formed sequentially, line by line. Only instead of hitting the needles, in the case of a matrix, the image of an inkjet printer is formed by applying microscopic particles of ink emitted by nozzles. Paint is a mixture of water, a dye, and special chemicals that keep the ink from drying for a long period of time. They are divided into pigment and water-soluble. The first ones are applied to the surface of the paper, and the second ones impregnate it, making the image more durable and protected from the external environment.
Ink can be supplied to the printhead in two ways: from the cartridge, which has a built-in ink reservoir, and by continuous supply from a third-party reservoir. In the second case, as soon as a portion of ink is thrown onto the paper, the modulator immediately reports that their level has decreased and it is necessary to supply a certain amount of ink to fill the container with ink.
The printing process begins with the paper feed mechanism (some models use the automatic feeder located at a slight slope on the rear of the case) using rollers with rubber attachments picks up a sheet of paper from the tray. The system is controlled by one of the stepper motors located in the printer. A special roller pulls the sheet and advances further inside the printer to the print head. This head consists of several thousand microscopic nozzles that spray ink over the surface of the paper in a strictly specified order and mode.
By means of a drive belt made in the form of a cable, it is connected to a second stepping motor, which controls the movement of the rollers for picking up and feeding paper, providing the desired rate of feeding the sheets into the printer to the print head. The third motor controls the movement of the print head in one plane – back and forth, and the last one is responsible for the timely ejection of ink from the nozzles. These miniature electric motors power the printer and synchronize the print head, paper feed mechanism and the actual process of applying an image to the surface of a sheet of paper.
An inkjet printer cartridge consists of an ink reservoir and a print head.
The head is a huge number of reservoirs in which the ink is heated. They are called nozzles. These nozzles contain a microscopic heater, which, when voltage is applied to it, instantly heats a drop of paint to the boiling point. It immediately evaporates, expanding significantly in volume. This creates air bubbles that push the ink out of the nozzles. The whole process is based on the fact that the liquid occupies a smaller volume than the gas formed from it.
After turning off the heater, it instantly cools down and the next drop enters for evaporation. The procedure takes place at a tremendous speed – each nozzle manages to expel several thousand particles of the coloring liquid per second. But speed in this case is of secondary importance. The main thing is accuracy. Each droplet must be pushed out in the allotted time so that the necessary elements appear on the sheet of paper, and not disordered spots of paint. The particle diameter is no more than 0.02 mm, which is larger than the printing pitch. In this case, the drops are simply applied on top of each other.
In a similar way, a color image is applied to paper, only this is done by mixing ink from three or more multi-colored cartridges.
Thermoelectric print head
This technology was first proposed by a Canon engineer in the late 1970s. The structure of the thermoelectric head is quite simple. It consists of a large number of nozzles, a channel for supplying ink to them from a corresponding reservoir, conductors through which control is carried out, and a heating element in each nozzle.
At the moment the printer receives a print job, the nozzle is prepared for work. Ink is supplied to it, while the heating element is turned off. When the control signal is supplied through special conductors, the heater instantly heats up the liquid, it boils and evaporates. The process is accompanied by the loss of a certain amount of ink, reaching 1%. They are used to create steam. The created pressure immediately pushes a droplet of liquid from the nozzle onto the surface of the paper.
In order for the resulting liquid drop to obtain the speed necessary to reach the paper, the process of creating steam must be instantaneous in order for a high pressure to form. This is achieved due to the rapid heating of the heating element and the low boiling point of the solvent. After expelling a drop of liquid from the nozzle, the voltage on the heater drops and it cools down. At this moment, steam comes out and another portion of ink comes in. Print speed is largely dependent on the cooling rate of the nozzle.
The disadvantages of this technology include the need to calculate the composition of the ink, taking into account evaporation and the preservation of properties during an increase in temperature to hundreds of degrees. The second minor drawback is head wear due to the fact that heated bubbles constantly burst, sometimes causing microscopic cracks.
Piezoelectric printing or drop on demand
An inkjet printer with a piezoelectric print head is a device based on the so-called piezo effect – the ability of certain materials to change their physical shape when a voltage is applied to them. Piezo materials also have the opposite piezoelectric effect – a potential is formed on them during physical deformation. The work of such a print head is similar to a thermoelectric one. But in this case, the ejection of ink occurs due to a change in the size of the control crystal during the supply of potential to it.
The structure of the piezoelectric head depends on the type of material deformation: longitudinal or transverse. Piezoelectric printing technology has a significant advantage over the previous one – the ability to adjust the size of the ink droplet. This feature allows you to achieve high-quality printing of images in black tones. Also, this printing method does not consume ink for evaporation and does not generate thermal energy, thereby increasing the efficiency of the inkjet printer. This is why piezo head printers have become so popular in the last decade.
The piezoelectric head includes:
- piezoelectric element – the main component of the nozzle;
- nozzle – forms microscopic paint particles and ensures their accurate distribution;
- an elastic membrane that separates the piezo material from the ink container – it protects the conductors from the harmful effects of the substances that make up the paint;
- a chamber that supplies ink to the nozzle.
In view of the fact that the size of the piezoelectric crystal changes insignificantly, the chamber should have the minimum dimensions and provide as large an area of its contact with the ink through the membrane as possible.
The main difference between these heads is the variable or constant size of the formed ink droplets. Large particles cover the desired area faster, while smaller particles provide greater print accuracy and resolution. Variable droplet size heads are able to adjust this indicator on the fly, combining several ink particles of basic sizes.
Due to the huge range of modifications and materials for the manufacture of piezoelectric elements, printheads based on piezoelectric materials are very popular in various fields of human activity: printing text, documents, postage stamps, applying indexes and markers on fabrics, engraving, etc.
Advantages and Disadvantages of Liquid Ink Printers
- low speed of work, in comparison with laser printers, is not critical in case of home use;
- particles of paint in the nozzles can dry out, so you need to use the printer periodically so that you do not have to buy a new cartridge;
- high price for consumables for some printer models.
Positive aspects of using an inkjet printer:
- low cost of the device;
- very cheap consumables (cartridges and ink) for some models;
- the ability to print high quality color photographs;
- the cartridge can be refilled by yourself at home;
- the ability to connect a continuous ink supply system.