Dot matrix technology

    Today we present to your attention a detailed post on matrix printing technology.

    Matrix printing is perhaps the most respectable in age, but still enjoying well-deserved popularity. The essence of the technology is simple: to obtain an image on the paper, dots are applied, which are obtained when the needles of the print head hit through the ink ribbon on the paper. Needles are collected in vertically arranged rows. By the number of needles, two types of printers are distinguished - 9 needle printers (they have one row of 9 needles in the printheads) and 24-needle ones - they have 2 rows of 12 needles each. There are also printers with 18 needles in the print head. Such heads are used in high-speed printers. Needles are located in the head in the form of a rhombus. This arrangement provides fast printing with the same impact force on the central and outer needles. The print quality of such a printer is fully consistent with the print quality of a 9-needle printer. The "excess" needles are used to increase speed, but not quality.




    During operation, the print head moves along the carriage and the needle, sequentially flying out of it, put dots on the paper, thereby forming an image (usually letters and numbers, but printing in graphics is also possible). By the method of image formation, classical dot matrix printers are called SIDM devices (from Serial Impact Dot-Matrix - sequential shock dot-matrix technology). “Non-classical” matrix printers can be considered linear matrix printers. These are quite massive units, usually replacing malfunctioning ADCP modes in large organizations. The principle of image construction in them differs from that described above.


    The basis of a linear matrix printer is the so-called shuttle: an assembly consisting of a bed with a width of the entire width of the press, on which printing mallets are installed horizontally, along the entire bed. During operation, the part of the shuttle on which the mallets are mounted performs a reciprocating movement with a high frequency and amplitude equal to the distance between adjacent hammers (usually a few millimeters), set in motion by the shuttle crank mechanism. Depending on the speed of the printer, different types of frets with different numbers of hammers are used (the higher the speed, the more hammers in the fret).


    mallets are combined into modules called frets


    Shuttle


    When moving from one dead center to another, each hammer, if necessary, strikes through the tape on paper, which is why with each movement from edge to edge a full horizontal line of the future image is formed on the paper, after which the paper moves one step forward and the shuttle begins to move back side. Thus, an image line by line is formed on paper. Therefore, even the print speed of such a printer is measured not in signs per second, like a regular SIDM printer, but in lines per minute (when printing text) or in inches per minute if graphics are printed. When printing, the ribbon moves either one way or the other, rewinding from one bobbin to another (as in old typewriters). Regarding the bed with hammers, it is located at an angle, which makes it possible to wear it out fairly evenly. True, this makes it possible to unevenly wear the ribbon if printing is mainly carried out on narrow paper (A4 format), while only one half of the ribbon wears out (in the figure below, the upper part of the ribbon will wear out with the left side of the shuttle), and the second remains untouched. If such printing is really necessary, it is recommended from time to time to turn the bobbins, forcing one or the other half of the ink ribbon to work.



    There are two technologies that drive the needle or hammer of the dot matrix printer — ballistic technology and energy-efficient printing technology. Ballistic technology is based on electromagnets located on each of the needles. When the electromagnet is supplied with power, it attracts the heel of the needle (the implementation may vary depending on the manufacturer) and it is set in motion. The needle returns to its original position under the action of a spring. In the case of technology with stored energy, in the head on each of the needles there is a constantly curved spring held by a permanent magnet.


    ballistic technology


    energy storage printing technology


    A winding made on a permanent magnet, when applied to it, creates a small magnetic field that compensates for the magnetic force of the permanent magnet. This compensation is enough to ensure that the spring comes off the magnet and the needle attached to it starts to move. When removing power from the winding, the spring is again attracted to the permanent magnet, which returns the needle to its original state. Ballistic technology is older; stored-energy technology is newer. Its main advantages over ballistic is that the head heats up less during operation (after all, to compensate for the strength of the magnet, it is necessary to supply noticeably less power to the coil than when the electromagnet drives the needle), in addition, the force of impact of a needle in a head with stored energy depends only on the stiffness of a constantly bent spring, which means that it practically does not change with time and on heating. On the other hand, printheads made by ballistic technology are noticeably smaller in size, which saves energy on their movement along the carriage, as well as making them more powerful heat exchangers.

    Being the most venerable technology by age, today dot matrix printing has almost ceased to be interesting to home users. However, there are areas of application where it is not yet possible to replace it: printing of multiple copies of forms (customs or consignment notes); printing of PIN envelopes for SIM cards and bank cards; air ticket printing; printing on responsible forms and forms, where not only the printed information is important, but also the fact of applying it in an impact way.

    Sergey Lebedev OKI Marketing Director

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