Several classifications of printing devices, including the group of inkjet printers, have been previously developed. Different authors at different times proposed their own version of systematization of this type of printing devices (S.B. Shashkin, N.N. Shvedova, etc.). However, due to the rapid change of generations of these devices, as well as the emergence of new modifications of the inkjet printing method, there is a need to clarify it.
We divide the grounds for the proposed classification of inkjet printers into forensically significant (using the totality of which it is possible to establish the model of the printing device and the brand of ink) and optional (information that allows investigative and inquiry authorities to build versions of the capabilities of criminals who committed a crime related to the use of an inkjet printer).
Forensically significant grounds include:
- printing method;
- size of the dye drop;
- properties of dyes;
- properties of the paper-pulling mechanism;
- way to control the printing device.
Optional grounds include:
1) printing speed;
2) the cost of the printing device;
3) scope of application of the printing device.
Let us consider in more detail each of the bases of the proposed classification and reveal their content.
Printing method. Currently, two methods of inkjet printing are used: solid ink inkjet printers and liquid ink inkjet printers. Inkjet printers with solid ink (phase-change ink-jet) are in practice used less often than printers with liquid ink due to the high cost of a print.
Liquid ink inkjet printers can be divided into continuous and discrete devices. The latter, in turn, implement bubble technology with ink heating and technology based on the piezoelectric effect. Both technologies are described in the literature, including forensic literature.
The piezoelectric printing principle allows you to adjust the volume of a droplet emitted from the nozzle within 3-6 steps and does not require ink designed for high temperatures. Bubble inkjet printing technology is implemented as follows. A heating element is built into the nozzle wall. When an electrical pulse is applied, its temperature increases sharply. Then almost all the ink in contact with the heating element instantly evaporates.
The expansion of steam causes a shock wave. Under the influence of excess pressure, a drop of ink literally “shoots” out of the nozzle, after which the ink vapor condenses, the bubble bursts, and a zone of reduced pressure is formed in the nozzle, under the influence of which a new portion of ink is sucked into the nozzle.
An important design feature of such a printing device is the simple design of the nozzles, which ensures high reliability of each nozzle, reduces the size of the printing unit and increases print resolution.
Size of a drop of dye. Printer manufacturers, such as HP, Canon, etc., use technology to change the droplet size from 3 to 6 picalitres, which affects the quality of printed texts and images. The manufacturing company Epson offers a new type of multilayer piezoelectric head that eliminates satellites - splashes from a drop of ink, which increases the clarity of mostly monochrome images.
The key point of this technology is the return movement of the meniscus, which is designed to ensure the retraction of satellite droplets formed when the main drop leaves. This procedure, carried out using active meniscus control, is its main advantage and at the same time its technological role in printing. In other words, the purpose of the meniscus control, which eliminates the occurrence of harmful satellites or the formation of drops of irregular shape, is precisely to sharply retract the diaphragm immediately after the formation, separation and departure of the main drop from the nozzle.
Thanks to this, the vibration of the ink mass is stopped, including at the nozzle end of the print head, and excess spilled ink is drawn back into the nozzle. Therefore, the satellite drops simply do not have time to finally form and do not accompany the main ink drop in flight. Thanks to the technology described above, the following advantages are achieved when printing: the trajectory of the drop is not disturbed; positioning of a drop on paper becomes extremely accurate; the drop has a regular spherical shape; the dot on the paper has the correct shape; There is no “ink fog” in the image. Thus, droplet size can be a differentiating feature when establishing inkjet printing technology and printer model.
Currently, most inkjet printer models have a fixed print dot size. However, some models (for example, those produced by Canon and Epson) use a print head that has nozzles of two diameters, as a result of which the printed dot can have two fixed sizes. Shashkin S.B. Color inkjet printers with liquid ink as an object of identification research // Informatics in forensic examination: collection. works Saratov: SyuI MIA of Russia, 2003. Shashkin S.B., Soklakova N.A., Tyurina N.V. Some aspects of forensic research of texts printed on drop-jet printers. // Forensics in the 21st century: collection. scientific works M.: State Economic Center of the Ministry of Internal Affairs of the Russian Federation, 2001..
Technical progress in the field of color mark printing devices has led to the emergence of printers with liquid dye based on an alcohol-based binder. In this case, the formation of a full-color image is carried out in accordance with the principle of subtractive color synthesis. Four colors of ink are usually used as base inks: process inks (cyan, magenta, yellow) and black. Recently, the palette of colors used has expanded to six (Epson Stule Photo series printer cartridges, in addition to process ones, have pale cyan and pale magenta inks) Shashkin S.B., Vorobiev S.A. On the problem of identifying inkjet sign-forming devices // Expert practice. 2001. No. 50. or eight (for example, printer models HP PhotoSmart 8453 and Canon PIXMA iP8500).
Colorful dots are arranged in the form of parallel lines; in one place there can be from 2 to 16 drops of paints of 4 colors in various combinationsMedvedev A.S. A guide to types and methods of printing for ECP experts. M., 2003. Part 5. Some printing devices..
Properties of dyes. The range of properties of inkjet printer inks is quite wide, and this problem has not yet been reflected in the forensic literature. These properties can be studied using different methods. For example, microscopic examination of the morphology of strokes will make it possible to differentiate the relatively viscous ink of printers with a thermoelectric head from the ink of printers with a piezoelectric head.
All ink for inkjet printers are divided into two large categories: dye-based (liquid dye) and pigment based (solid or pigment dye).
Properties of the paper-pulling mechanism. They can be characterized by the size of the sheet of paper used, the size of the printing margins, the device's ability to print borderless, and the types of paper. Depending on the size of the sheet of paper used, printers of A4, A3, A2, A1, A0 formats are distinguished. Printers in A2, A1 and AO formats are commonly called plotters.
Currently, some printer models are equipped with the function of printing on the non-working surface of laser discs. For example, the PREDATOR - 845CD printer is designed for high-quality full-color direct printing on CDs using thermal inkjet technology with a resolution of up to 1200 dpi. The minimum drop volume is 5 picalitres. This technology allows you to produce a moisture-proof coating immediately after printing. To produce high-quality photo prints, HP printers use technology that allows up to 29 drops of color ink to be applied to one point of a photo image, which significantly expands the range of reproducible colors and reduces image graininess.
Method of controlling the printing device. Three groups of printing devices can be distinguished: those controlled by a personal computer, multifunctional printing devices (the ability to print without a personal computer - printer/scanner/copier) and devices with the ability to print from memory cards of other devices (cameras, flash cards, etc.) .).
Printing devices for computers can only operate in conjunction with a computer, using appropriate (mostly standard) software. They completely lack any original holder. Structurally, the range of printing devices for computers is extremely diverse - from miniature “pocket” devices for laptops to specialized ones, with a printed field width of up to 25 m.
Multifunctional duplicating devices occupy an intermediate position between direct copying devices and computer printing devices. As a rule, these are high-tech devices that make it possible to perform not only direct copying (original - copy), but also have a built-in microprocessor that allows you to connect to a computer through a standard interface. Therefore, images can be input not only from a document holder (or slide projector) through an optical system, but also in electronic (digital) form.
Multifunctional copying and duplicating devices also include devices in which the copying function is not the only one. It should be noted that copies made on devices with different design features, but implementing the same reproduction method, usually have the same set of characteristic features. Thus, in most cases, it is possible to determine the design features of a copying device only in a probabilistic form. Determination of the type of copying devices used in counterfeiting banknotes, securities and documents: methodological. recommendations / E.V. Starikov et al. M.: ECC of the Ministry of Internal Affairs of Russia, 1999..
Optional bases for classifying printers, such as printing speed, cost of the device and the scope of application of the printer, enable investigative and inquiry authorities to build versions of the identity of the criminal, namely, to assume what kind of money he might have, how much time the criminal might need to organize the crime and his implementation, etc.
In these types of printers, ink is directly transferred to the paper.
The operating principle of inkjet printers is similar to the operating principle of a cathode ray tube. In such printers, the paint is poured into a special vessel that has such a small hole in the bottom (this hole is called a nozzle) that under normal conditions the paint does not flow out of the vessel. However, when a potential difference is briefly applied between the nozzle and the paper, the paint begins to flow out in small drops, which are then accelerated in the electric field, deflected at a certain angle by a system of deflection plates and fall on the paper, leaving a mark on it. The image on a sheet of paper, like that of matrix printers, is formed from dots, but due to the fact that the dot of an inkjet printer is much smaller than that of a matrix printer, the image on a sheet of paper is of better quality.
The high printing speed of such printers is determined by the fact that there is no need to move bulky print heads.
The advantage of such printers is that by using several vessels with different inks, you can get a color image.
However, these printers are not widely used due to the fact that they use high voltage voltage. Nowadays such printers can only be found somewhere in production. They are used there mainly for printing the production date (a typical example is the distillery industry, where such printers apply the production date and other technical information directly to the drink bottles).
The next type of inkjet printers were inkjet printers (they are also often called inkjet printers) (see Figure 1). Such printers have a head, the lower part of which is located at a short distance (about 1 mm or even less) from the sheet of paper. At the bottom of the head, at a short distance from each other, there are several nozzles (sometimes up to several hundred or even thousands), combined into a rectangular matrix. Inside the housing, just above these injectors, there are microscopic resistors (each above a specific injector). The paint container, heating resistors and nozzles are often combined into one unit, which is called a cartridge.
Figure 1 – Inkjet printer
The paint flows onto the resistors and lingers under them because... cannot leak through small nozzles. When voltage is applied to a certain resistor, it heats up, the paint boils and splashes out through the nozzle under pressure. Because the distance between the nozzle and the paper is small, then a drop of paint falls into a strictly defined place on the sheet of paper. The print head is then moved a certain distance and the process is repeated.
The large number of nozzles is due to the fact that with a larger number of nozzles, a larger number of drops can be splashed onto the paper at the same time. This determines the printing speed of such printers. The printing speed of printers of this type can reach several tens of A4 pages per minute.
The resolution of such printers is up to 1200 dpi.
The advantages of this type of printer are:
high printing speed
possibility of color printing when using several vessels with different paints
high resolution printers, which allows you to obtain photographic quality prints
The disadvantages of these types of printers include:
high cost of consumables compared to dot matrix printers
low maintainability (after all, if the nozzle is clogged or the heating resistor is burned out, it will be easier to buy a new cartridge than to repair a broken one)
A. P. Andreev
expert criminalist
The author of the article, using a practical example, proved the fallacy of the hypothesis about the possibility of identifying an inkjet printing device by the location of discrete elements (microdrops of ink) on the printed image.
Keywords: inkjet printing; jet printer; inkjet printer identification; examination of documents; stochastic raster
A 65
BBK 67.52:32.973.2-044
UDC 343.983:681.327.2
GRNTI 10.85.31; 20.53.31
VAK code 12.00.12; 05.13.15
On the identification of an ink jet recording apparatus of the arrangement of discrete elements (microdroplets of ink) in the printed image
A. P. Andreev
expert criminalist
The author of the article on a practical example proved the fallacy of the hypothesis about the possibility of identification of an inkjet printing apparatus of the arrangement of discrete elements (microdroplets of ink) in the printed image.
Keywords: inkjet printing; inkjet printer; inkjet printer identification; examination of documents; stochastic raster.
_____________________________________
The possibility of identifying an inkjet printing device by the location of discrete elements (microdrops of ink) is based on the hypothesis put forward by S. B. Shashkin and a number of his co-authors about the individual location of these elements on printed images.
For example, in the training manual of the ECC of the Ministry of Internal Affairs of Russia, the authors evaluate the results of the experiment they conducted as follows: “The study of printouts was carried out by visual and microscopic comparisons of the relative positions of pixels on sections of documents comparable in content and graphic composition. The following results and conclusions from them were obtained.
Analysis of a series of printouts of the same electronic image of a document, made on printers from different companies, without replacing the print head, allows us to conclude that there is a high degree of similarity in the relative positions of the discrete elements that form the image, repeatedly obtained using the same printer. Here we cannot talk about complete identity, since some of the pixels, about five out of a hundred, allocated in any part of the image, disappear and appear again from print to print. This is explained by periodically occurring malfunctions in the operation of individual ink channels.
When printing the same electronic image of a document on different devices of the same model or when replacing cartridges on company printers Hewlett Packard under other identical conditions (identical software, maintaining the placement of the printed electronic image relative to the document boundaries), the relative position of the pixels changed significantly, which is explained by the combined action of the following production and operational factors: variations in the placement of nozzles on the print head that arise at the stage of its manufacture, individual deviations in the operation of its positioning mechanism, malfunction of individual ink channels. These factors determine the presence on a document prepared on an inkjet printer of particular characteristics of a particular PU or its print head. Thus, a feature that allows you to individualize a specific inkjet character-synthesizing device is the relative position of the discrete elements that form the image(italics A. A.) ".
In fact, the authors of the manual, referring to a series of their experiments, claim the possibility of identifying a specific inkjet printing device by comparing the location of ink microdroplets on printed images, the coincidence of which will indicate the execution of two documents with the same images using one printing device (as part of the software). hardware complex computer-printer-software), and their differences may indicate the use of a different printing device or printing on the same device, but with different settings. Thus, the authors of the hypothesis under consideration argue about the individuality of the location of the nozzles on a specific print head, which arises at the stage of its manufacture, which, together with the peculiarities of the functioning of the mechanisms of the printing device, makes it possible to identify it from the printed image.
Subsequently, the hypothesis under consideration was confirmed within the framework of a research work on the topic “Forensic study of documents produced using drip-jet printing devices,” completed in 2009 by the team of authors of the Saratov Law Institute of the Ministry of Internal Affairs of Russia: “The idea was also confirmed on a large amount of experimental material S.B. Shashkin about the possibility of solving the identification issue using images obtained using the same printer under the conditions of printing images from the same electronic original, the same software, under the same printing modes."
These ideas have found support not only in the scientific community, but also among individual practicing experts.
Thus, employee of the ECC of the Central Internal Affairs Directorate for the Altai Territory A.I. Khmyz in 2011, with reference to the work cited here by S. B. Shashkin, A. V. Gortinsky and A. V. Pakhomov, wrote that: “Comparison of comparable in content, graphic composition of image elements on counterfeit banknotes and images on sheets of paper (in this case, presented at the initiative of the expert) allows you to solve the identification task assigned to the expert. Thus, the coincidence in shape, size, color, location and relative position of the points with which the images were made (photo No. 6) gives grounds for the conclusion that the images were made using the same printing device, therefore, allows us to establish the fact of using a specific printing device in the manufacture of counterfeit banknotes, securities and documents.
Photo No. 6. Coincidence in the location and relative position of the dots (of the same color) that form the images on the banknote under study (left) and on the bill located on a sheet of paper (right) seized during a search from the suspect.
Establishing this fact is essential when proving a person’s guilt in committing crimes related to the production of counterfeit banknotes, forms of securities and documents.”
Employees of the ECC of the Ministry of Internal Affairs of Russia for the Ivanovo region S. A. Smotrov and I. S. Smotrov in their article give an example of an examination carried out as part of a criminal investigation, as a result of which “when examining images of watermarks on more than 3,000 counterfeit banknotes, set of locations of points of drops of coloring matter,” which made it possible “taking into account the previously established fact of printing the indicated images using one software and hardware complex using the same printing process settings ... to draw a conclusion about a single source of origin of watermark images on all studied objects.” In conclusion, the authors of the article write: “the application of the provisions of the research work carried out under the leadership of P. V. Bondarenko to the study of counterfeit Bank of Russia banknotes made it possible to establish the fact of printing halftone images on them, for example, watermark images, using one software hardware complex using the same printing process settings."
Thus, it can be stated that scientific and methodological sources contain absolutely clear data on the possibility of identifying inkjet printers by the location of ink microdroplets on printed images, on the basis of which separate examinations were carried out as part of the investigation of real criminal cases. Unfortunately, in all published works on this topic there is neither a detailed description of the progress and results of experiments, nor corresponding illustrative material, and there are also no specific methodological recommendations for conducting this type of research. These factors together may have influenced the fact that the approach under consideration has not found wide application in practice and generally causes skepticism. However, it seems easy to use and, if positive results are obtained from the test, it can serve as a fairly effective tool for solving such a difficult task today as identifying inkjet printing devices.
To study the possibility of identifying inkjet printing devices by the location of ink microdroplets on printed images, the author of this article conducted research work using inkjet printing devices of various brands and models, during which the following indicators were studied.
1. Stability of display and individual location of ink microdroplets on identical images printed with the same printing parameters on the same device.
2. Stability of display and individual arrangement of ink microdroplets on identical images printed with the same printing parameters using different devices of the same model (print heads of the same type).
3. Stability of display and individual arrangement of ink microdroplets on identical images printed with the same printing parameters using different devices of different models (different types of print heads).
4. The influence of changing printing parameters, as well as the use of different software and hardware systems (computers with different operating systems installed, different graphic editors) on the stability of the display and the individuality of the location of ink microdroplets on identical images made using one device.
5. Individuality of the shape, size and location of nozzles on inkjet print heads.
Experimental work was carried out by printing the same color image on several printers of the same model or on one printer, but replacing the print head cartridges. The resulting images compared the location of microdroplets of ink of the same colors using a stereo microscope and the method of computer image overlay (experimental conditions are given in Appendix 1, illustrations of the results are in Appendixes 2, 3).
By comparing the obtained samples and studying the working surface of the print heads of inkjet printing devices, the following facts were established.
1. On identical images printed with the same printing output parameters on the same device, the relative position of ink microdroplets has a clearly repeating structure, in which there may be differences in the form of the absence of individual droplets, while no significant displacement of some droplets relative to others is observed ( Fig. 3-5, 7-9, 11-13, 15-17). Thus, in experimental images, the raster structure formed by individual microdroplets of ink is consistently repeated.
2. On identical images printed with the same printing parameters using different devices of the same model, a pattern corresponding to that described above is observed, characteristic of images printed on the same device - a steadily repeating raster structure (Fig. 6, 10, 14, 18 ).
The same picture is observed in images printed on the same device using cartridges of different models (Fig. 19, 20), the heads of which have significant differences in shape, size and location of the nozzles (Fig. 36).
3. On identical images printed with the same printing parameters using different devices of various models, there are significant differences in the presence and location of microdroplets (Fig. 21, 22).
4. On identical images made using the same device with different printing parameters, the following picture is observed:
a) when using different computers (including printing via network connections) and operating systems, but in one graphics program with the same settings, a stable repeating raster structure was observed in the images (Fig. 23, 24);
b) when using one graphics program, but with changing settings, significant differences in the raster structure were observed (Fig. 25, 26).
5. By comparing the structure of the working surfaces of the print heads of various inkjet printing devices, it was established that there are no significant differences in the shape, size and location of the nozzles on the print heads of the same model (device or cartridge of the same type) (Fig. 27-35, 37).
Summarizing the results of the experiment, we can state that the hypothesis about the individual arrangement of microdroplets of inkjet printing device ink on printed images for each printing device (print head) is currently erroneous. One of the reasons for this is the emphasis placed by the authors of these works on assessing the final result of the inkjet printing process - colorful images, while the location of discrete points was considered as a trace-image of a specific printing device, due to the features (variation) of the shape and placement of nozzles on the print heads that arise on stage of their production. The processes of forming an electronic image and printing it were not considered in detail.
The inkjet print head is only a performer in the chain of obtaining the final image. Rasterization of images during the printing process is carried out using the so-called “raster image processor”, which can be implemented in hardware (using rasterizing modules built into the printer) or software (through a printer driver or components of a graphic editor through which the image is printed). In relation to the topic under consideration, in inkjet printers for household use, rasterization processes are carried out in software and are controlled either by the printer driver or by components of the graphics editor. For example, “the electronics of budget-class Epson piezoelectric inkjet printers are not equipped with a raster processor and an Adobe PostScript language interpreter. The printer's control microcontroller performs the function of controlling the print head with line-by-line buffering of rasterized graphic data (coordinates of drops on the sheet) coming from the printer driver. The coordinates of the drops, information about their size and printer settings are transmitted to the microcontroller using a special low-level control language ESC.P2. In turn, the functions of the raster processor and color management system are performed by the printer application software installed on a personal computer.”
The above is confirmed by the results of the experiment: a stable coincidence of the placement of microdroplets in images printed with the same printing parameters using different devices or cartridges of the same model (using the same type of print heads), as well as in images printed using cartridges of different models (different type of print heads ) on one device, and the difference in their placement when changing print settings or printing from different graphics programs.
Thus, the results of the experiments clearly prove the impossibility of identifying an inkjet printing device by the location of discrete elements (microdroplets of ink) on the printed image.
Annex 1
HARDWARE, SOFTWARE AND IMAGE COMPARISON METHODS
1. Test pages for color printers were used as experimental images, containing color and monochrome halftone images, on which there are areas with a sparse raster structure that allows you to isolate and study the location of individual microdroplets of ink of different colors.
Taking into account the repeatability of the results on different images, the format and limited volume of the article, the experiment is illustrated using the example of a test page from Fotocommunity prints (original file http://printer-one.ru/wp-content/uploads/2015/05/test1.jpg).
2. Images were printed using color inkjet printers of the following models:
Models with a print head in a cartridge: Canon PIXMA IP2700 (original Canon PG-512+CL-513 cartridges); HP 5652 (original HP6657A+HPC6658A cartridges and three-color PScom cartridges compatible with HP6657A);
Model with built-in Epson L800 print head;
Model with replaceable Canon MG 5240 print head.
3. Comparison of the raster structure was carried out on identical areas of the images using the comparison method using a Leica M165 stereomicroscope, as well as the computer overlay method as follows:
a) printed images were scanned using an Epson Perfection 4870 Photo scanner with a resolution of 1200 dpi in TIFF format;
b) in the graphic editor Adobe Photoshop CS3, the loaded images were converted to CMYK mode and divided into separate channels for which comparison was carried out (for example, Fig. 3, 4);
c) channels of the same name were compared by creating a multilayer image and combining layers using the “Free Transform” tool (Ctrl+T): layer blending mode “Normal”, opacity of the top layer 50%, for clarity, one of the images was inverted (Ctrl+I) ( for example, Fig. 5).
As the experiment showed, the most effective comparison is along the yellow channel (Y), with the raster dots in the channel corresponding to microdroplets of yellow ink on the printed image (Fig. 1, 2).
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Rice. 1. Images of a fragment printed on a color inkjet printer. The image above was obtained using a microscope, below - scanned using a flatbed scanner (resolution 1200 dpi, TIFF format).
Rice. 2. At the top is the yellow channel (Y) of the image located below in Fig. 1. Below is the result of a computer overlay of this image (layer transparency 30%) and the image located at the top in Fig. 1: you can see the complete alignment of the arrangement of the raster elements of the yellow channel and microdroplets of yellow ink.
4. The conditions for printing samples and the results of comparing rasters were summarized in a table, with the help of which the final analysis of the obtained data was carried out (the header of the table is given below).
Appendix 2
RESULTS OF COMPARISON OF THE RASTER STRUCTURE OF EXPERIMENTAL IMAGES BY THE YELLOW CHANNEL (Y)
(for example, fragments of experimental images are given)
Rice. 3. Yellow channel (Y) of images printed on the first Epson L800 printer.
Rice. 4. Yellow channel (Y) of images printed on a second Epson L800 printer.
Rice. 5. Combination of images printed on one Epson L800 printer: on the left - located in Fig. 3 (first printer), on the right - located in Fig. 4 (second printer).
Rice. 6. Combination of images printed on different Epson L800 printers: located in Fig. 3 (right) and fig. 4 (right).
Rice. 7. Yellow channel (Y) of images printed on the first Canon MG 5240 MFP.
Rice. 8. Yellow channel (Y) of images printed on the second Canon MG 5240 MFP.
Rice. 9. Combination of images printed on one Canon MG 5240 MFP: on the left - located in Fig. 7 (first MFP), on the right - located in Fig. 8 (second MFP).
Rice. 10. Combination of images printed on different Canon MG 5240 MFPs: located in Fig. 7 (left) and fig. 8 (right).
Rice. 11. Yellow channel (Y) of images printed on an HP 5652 printer using the first original HP C6657A cartridge.
Rice. 12. Yellow channel (Y) of images printed on an HP 5652 printer using the second original HP C6657A cartridge.
Rice. 13. Combination of images printed on one HP 5652 printer using the same original HP C6657A cartridges: on the left - located in Fig. 11 (first cartridge), on the right - located in Fig. 12 (second cartridge).
Rice. 14. Combination of images printed on one HP 5652 printer using different original HP C6657A cartridges: located in Fig. 11 (left) and fig. 12 (left).
Rice. 15. Yellow channel (Y) of images printed on an HP 5652 printer using the first compatible PScom cartridge.
Rice. 16. Yellow channel (Y) of images printed on an HP 5652 printer using a second compatible PScom cartridge.
Rice. 17. Combination of images printed on one HP 5652 printer using identical compatible PScom cartridges: on the left - located in Fig. 15 (first cartridge), on the right - located in Fig. 16 (second cartridge).
Rice. 18. Combination of images printed on one HP 5652 printer using different compatible PScom cartridges: located in Fig. 15 (left) and fig. 16 (left).
Rice. 19. Yellow channel (Y) of images printed on an HP 5652 printer using different print heads: on the left - using the original HP C6657A cartridge (image in Fig. 11, left), on the right - using a compatible PScom cartridge (image in Fig. 16, right).
Rice. 20. Combination of images located in Fig. 19.
Rice. 21. Yellow channel (Y) of images printed on an Epson L800 printer (left) and a Canon MG 5240 MFP (right).
Rice. 22. Combination of images located in Fig. 21.
Rice. 23. Yellow channel (Y) of images printed through the Adobe Photoshop CS3 graphic editor on an Epson L800 printer using different computers and operating systems: on the left - Windows XP 32-bit, on the right - Windows 7 64-bit.
Rice. 24. Combination of images located in Fig. 23.
Rice. 25. Yellow channel (Y) of images printed through the Adobe Photoshop CS3 graphic editor on an Epson L800 printer with changing color management parameters: on the left - RGB mode with default parameters, on the right - RGB mode with changing parameters: brightness -50 / contrast +50.
Rice. 26. Combination of images located in Fig. 25.
Appendix 3
IMAGES OF INKJET PRINTHEADS USING A LEICA M165 MICROSCOPE WITH LEICA APPLICATION SUITE SOFTWARE AND ADOBE PHOTOSHOP CS3
Rice. 27. Enlarged images of a group of black ink nozzles of two print heads of the Canon MG 5240 MFP. At the top and in the center are the heads being compared, below is the result of a computer overlay of these images (the top layer is inverted): you can see the complete combination of the shape, size and location of the nozzles.
Rice. 28. Same as in fig. 27 at higher magnification.
Rice. 29. Enlarged images of a group of blue ink nozzles of two Canon MG 5240 MFP print heads. At the top and in the center are the heads being compared, below is the result of a computer overlay of these images (without inversion): you can see the complete combination of the shape, size and location of the nozzles.
Rice. 30. Enlarged images of the working surface of the print heads of two HP C6658A cartridges.
Rice. 31. Enlarged images of the groups of print head nozzles shown in Fig. 30. At the top and in the center are the compared cartridges, at the bottom is the result of a computer overlay of these images (the top layer is inverted): you can see the complete alignment of the shape, size and location of the nozzles.
Rice. 32. Same as in fig. 31 at higher magnification (showing groups of light magenta and light cyan ink nozzles).
Rice. 33. Enlarged images of groups of nozzles of two HP C6657A cartridges. At the top and in the center are the compared cartridges, at the bottom is the result of a computer overlay of these images (the top layer is inverted): you can see the complete alignment of the shape, size and location of the nozzles.
Rice. 34. Enlarged images of the working surface of the print heads of two PScom cartridges compatible with HP 6657A.
Rice. 35. Enlarged views of the magenta and yellow ink nozzle groups of the print heads shown in Fig. 34. At the top and in the center are the compared cartridges, at the bottom is the result of a computer overlay of these images (the top layer is inverted): you can see the complete alignment of the shape, size and location of the nozzles.
Rice. 36. The result of computer overlay of one-scale images of the working surfaces of the original HP 6657A cartridge (the top layer is inverted) (Fig. 33 in the center) and the compatible PScom cartridge (Fig. 35 in the center): the difference in the shape, size and location of the nozzles is visible.
Rice. 37. Enlarged images of a group of yellow ink nozzles of two Canon CL-513 cartridges. At the top and in the center are the compared cartridges, at the bottom is the result of a computer overlay of these images (the top layer is inverted): you can see the complete alignment of the shape, size and location of the nozzles.
Literature:
1. Shashkin S. B., Vorobyov S. A. On the problem of identifying inkjet character-synthesizing printing devices // Expert practice. - M. ECC of the Ministry of Internal Affairs of Russia, 2000. - Issue. 50.
2. Shashkin S. B. Theoretical and methodological foundations of forensic examination of documents made using printing and office equipment. Diss. ... Doctor of Law. Sci. - Saratov, 2003.
3. Shashkin S. B., Gortinsky A. V., Pakhomov A. V. Technical and forensic examination of documents produced using character-synthesizing printing devices: Textbook. - M.: ECC of the Ministry of Internal Affairs of Russia, 2004.
4. Forensic research of documents produced using drop-jet printing devices: Research report (supervisor P. V. Bondarenko). - Saratov: Saratov Law Institute of the Ministry of Internal Affairs of Russia, 2009.
5. Khmyz A. I. Identification of multifunctional printing devices using the principle of inkjet printing // Collection of materials of forensic readings. - Barnaul: Barnaul Law Institute of the Ministry of Internal Affairs of Russia, 2011. - Issue. 7.
6. Smotrov S. A., Smotrov I. S. Identification of the study of documents printed using drop-jet printing devices // Forensic science and forensic examination. - Kyiv: MJ of Ukraine, 2013. - Issue. 58. - Part 2.
7. Pshenichny D.V., Sysuev I.A. Optimization of color reproduction in piezoelectric inkjet printing // Omsk Scientific Bulletin. - Omsk: Omsk State Technical University, 2012. - Issue. 2 (110).
Rice. 2.2.10. Diagram of a printing device using solid ink. In the diagram: 1 - offset drum, 2 - print head, 3 - drum cleaning device, 4 - pressure roller, 5 - paper, 6 - paper heating device Rice. 2.2.11. Diagram of ink supply from the reservoir (a) and diagram of the print head in a solid-ink printer (b). In the diagram: 1 - reservoir, 2 - channels, 3 - distribution channel, 4 - input channel from the distribution channel to the drop emitters, 5 - pressure chamber, 6 - output channel, 7 - nozzle, 8 - piezo activator. Arrows - drip jets Rice. 2.2.19. HP printhead is 4.25 inches wide (top view). 5 crystals with four rows of nozzles are visible Rice. 2.2.14. Cross-section of a droplet emitter of a Memjet head with a suspended heater. In the diagram: 1 - pressure chamber, 2 - nozzle plate, 3 - inlet channel, 4 - spiral heating element, 5 - ink, 6 - steam bubble, 7 - drop Rice. 2.2.15. General view of the Memjet head droplet emitter with a suspended heater. In the diagram: 1 - nozzle hole, 2 - heater Rice. 2.3.1. Typical structure of photo papers for inkjet printing: a - glossy paper, b - paper with a chalky base, c - paper with an uncoated base Rice. 2.3.2. Scheme of photo paper with a hybrid ink-receptive coating: 1 - polymer layer, 2 - ink-holding layer, 3 - whiteness layer, 4 - polyethylene-coated base, 5 - hybrid particles, 6 - micropores
Inkjet printing consists of one stage - obtaining an image on the printed material. The image is formed by droplets of ink emitted from the print head. Ink - liquid paints with a viscosity of 1...30 cP. Printing is controlled by electrical signals sent to each droplet generator of the print head at each printing moment. The signal (voltage pulse) controls the flight of one drop.
In the vast majority of printers, the droplet generator ends with a nozzle - a calibrated hole with a diameter from several micrometers to several tens of micrometers. It is from the nozzles that droplet jets of ink fly out, drawing images on the printed material. However, there are inkjet printing methods where the print heads do not contain nozzles. One of them recently entered the inkjet market under the name "Tonejet".
Printheads typically contain multiple droplet jet generators (droplet emitters) arranged in rows along the length of the printhead at a density averaging 150-600 per inch. Usually there are 2 rows, and the jet sources (nozzles) in the rows are shifted relative to each other so that the sources of the second row are between the sources of the first row. Thus, the physical resolution of printing is doubled (300-1200 colorful dots per inch). The image recording control mechanism is located either in the computer (printer driver) or in the printer controller. Digital originals are converted into signals transmitted to the print head control board, and from there to the head chips that control the operation of droplet generators located on the surface of the chip (the number of chips can be different - from one to several pieces). An inkjet printer contains a mechanism for moving a head (or a block of heads) across a paper sheet and a mechanism for moving paper, as well as a system for supplying ink from an ink reservoir (cartridge). The vast majority of printers produce multicolor printing. Print heads for different inks are located one behind the other and move on the same carriage. If the head prints with several colors, then the rows of generators for different colors are placed parallel to each other.
The print head is the main element of an inkjet printing device. Inkjet printing is used in printers of various classes and formats and in digital printing machines. The use of inks of various natures allows you to print on a variety of materials.
Three types of inkjet printing have found practical application:
- Continuous inkjet printing. In this type of printing, a stream of ink continuously shoots out from each nozzle of the print head, breaking into tiny droplets. Drops are released from the jet and used to construct the image. Unused drops are sent to the drip tray.
- Pulse inkjet printing (drop on demand). Here, the droplet flies out of the print head nozzle only when it receives an electrical impulse. Therefore, this type of inkjet printing is also called “drop on demand”.
- Tonejet. In this method, the ink is a dispersion of pigment particles in a non-polar liquid. The droplet generator (droplet jet source) is a pointed conductive protrusion on the body of the print head. The ink flows under pressure towards the source. When a voltage pulse is applied, the ink pigment particles are charged. They are moved by an electric field to the protrusion, where the concentration of paint is noticeably higher than the original one. The pointed end of the protrusion, due to the increased electric field strength, repels similarly charged pigment particles. They fly out, taking some of the liquid with them. Drops of concentrated paint are formed. These droplets fly onto the printed material, drawing an image. The print head contains multiple sources arranged in rows. The method is currently used in the packaging industry for printing on cans.
General information
Continuous inkjet printing consists of three processes:
- the formation of ink jets and their breaking into droplets;
- separation of drops into working drops, which go to image construction, and non-working drops, which fall into the drop catcher;
- separating working droplets from the drip jets and directing the working droplet jets onto the printed material; delivery of unused drops to the drip tray.
Currently, two methods of continuous inkjet printing have been brought to industrial use, in which the above processes occur differently.
In a long-standing and widely used method, drops are formed by applying high-frequency mechanical vibrations to the ink jet, forming a capillary wave. The separation of droplets into working and non-working ones is carried out by their selective charging, and the separation of droplet jets is done by deflecting the trajectory of charged droplets by an electric field, while uncharged droplets fly straight.
In Kodak's new Stream continuous inkjet printing process, thermal pulses are periodically applied to the ink jet leaving the nozzle to create a droplet jet, which changes the surface tension of the ink. Droplets form from cold areas of the jet. Droplets are divided into working and non-working by forming droplets of different sizes. The separation of working droplets from the jet is carried out by an air flow directed perpendicular to the jet trajectory. The air flow deflects small drops more strongly and they fall into the drip tray. Large drops continue to fly towards the printed material and are used to build the image.
In this method, electrically conductive ink is pressurized into the droplet generator of the print head. The jet flies out of the generator nozzle. Somewhere at the exit from the nozzle, for example, on the nozzle plate there is a piezoelectric stimulator that forms a droplet stream. A high-frequency electrical voltage is applied to the piezoelectric. Due to the deformation of the piezoelectric, mechanical vibrations arise, which are transmitted to the jet and cause the formation of droplets. As the jet passes through the charging zone, electrical voltage pulses are applied to the charging electrode. Selective charging of droplets is carried out. Next, the droplet stream is divided into two streams: charged and uncharged. One of them ends up on the printed material, the other goes into the droplet eliminator.
In Fig. 2.1.1 shows a schematic diagram of continuous inkjet printing with uncharged drops.
The jet generator contains an ink chamber 1 into which electrically conductive ink is supplied from the ink system through a tube 2. At the outlet of the ink chamber there is one or a series of calibrated holes called nozzles. Nozzles are electrically conductive, for example metal. Print heads can be single-nozzle or multi-nozzle. The diagram of a single-nozzle head is shown in Fig. 2.1.3. In Fig. Figure 2.1.1 shows a diagram of a jet generator of a multi-nozzle head, where the nozzles are made in the nozzle plate. Ink is released under pressure from each nozzle in a fine stream.
Near the nozzle, on the nozzle plate there is a piezoceramic element 3, to which a high-frequency alternating electrical voltage is applied. Mechanical vibrations of the same frequency occur in the piezoceramic element (inverse piezoelectric effect). The oscillatory disturbance from the piezoelectric is transmitted to the ink, and a capillary wave (a wave in which the surface tension of the liquid plays a large role) appears in the jets. Since the frequency of the superimposed oscillations corresponds to the resonance mode (it coincides with the natural frequency of the jet), the jet at a short distance from the nozzle breaks up into small drops of equal size.
The droplet jet separation system includes a charging electrode, a deflector and a droplet eliminator.
Charging electrode 5 is located near the nozzle. Charging is inductive. It occurs due to the fact that the jet of electrically conductive ink is grounded, and the layer of air between the jet and the charging electrode has dielectric properties. When an electrical voltage pulse is applied from the image generator to the charging electrode, a charge opposite in sign to the charge of the electrode appears in the grounded jet near the electrode. The jet enters the zone of action of the electrode at the moment preceding the separation of a droplet from it, so this droplet is charged. The supply of electrical impulses must be strictly synchronized with droplet formation.
Having left the zone of action of the charging electrode, the jet flies past the deflector 6, to which a high-voltage electric voltage is applied, the sign of which is the same as the sign of the droplet charge. Droplet eliminator 7 is grounded. The resulting electric field deflects charged drops into the drop catcher, and uncharged ones fly freely along a straight path onto the printed material. From the droplet eliminator, the ink enters the recycling system or into a special container and is then discarded (when using print heads with 1-2 nozzles per ink).
Image recording by charged droplets is used in continuous inkjet printing with multi-level jet deflection ( Multiple-deflection Continuous Inkjet, rice. 2.1.2 ). The droplets of the jet are charged in groups in such a way that the droplets of the group are given charges of a number of values. The deflector deflects droplets with different charges at different angles, creating a fan-shaped sweep of the droplet jet. This allows you to record a strip of an image containing several lines. Uncharged droplets fly along a straight path and fall into the droplet eliminator, and from there into the ink recycling device. When writing with charged drops, problems arise with the accuracy of positioning the drops on paper due to their interaction with each other. The method is widely used in marking printers intended for applying inscriptions, dates and barcodes to the surface of commercial and industrial products.
In the method with binary jet deflection (Fig. 2.1.1) there are two options. In the first, one-bit version, each image point is formed from the same amount of ink, for example, from one drop of 84 pl in size (picoliter - mark ">Iris Print, where at a resolution of 300 dpi an emulation of a resolution of 2400 dpi is obtained. The heads have 1-2 nozzles per paint.
The complexity of multibit recording is as follows. The maximum amount of ink falling on a micro-area (dot) of an inkjet print must correspond to the maximum optical density of the image. Too much ink will cause the tonal gradations in the shadows of the image to bleed and disappear. Too little ink will not produce highly saturated colors.
If this amount is provided by one drop per point, the drop must be large. If this task is performed by a group of 4 drops, the volume of each drop should be 4 times less; when using groups of 30 drops, the volume of one drop is 3-4 pl.
The volume of a drop depends on the diameter of the jet (nozzle) D and the wavelength formula" src="http://hi-edu.ru/e-books/xbook1004/files/130.gif" border="0" align="absmiddle" alt=".gif" border="0" align="absmiddle" alt="- jet speed in the Iris Print inkjet printer is 50 m/s, nozzle diameter is 10 microns. The frequency f represents the vibration frequency of the piezoelectric and the frequency of droplet formation, and the wavelength of the mark">Iris Print is 1000 kHz.
To stabilize the droplet formation process, the frequency of the superimposed oscillations must coincide in magnitude with the frequency of the jet’s natural oscillations. Then the oscillatory disturbance will be in resonance with the jet’s own oscillation. It is with this frequency that drops will form..gif" border="0" align="absmiddle" alt=".gif" alt="link to literature sources" onclick="showlitlist(new Array("L. Palm, L. Wallman, Nh. Laurell, J. Nilsson. Development and characterisation of silicon micromachined nozzle units for continuous ink jet printers. Journal of Imaging Science and Technology, v. 44, № 6, 2000, p. 544-551.",""));">].!}
The speed of inkjet printing depends on the number of nozzles in the print head (the width of the printed strip). The heads, which have a small number of nozzles per paint color, must shuttle across the direction of movement of the paper sheet. This slows down printing because the paper can only move a step after the color line of the image has been recorded. This affects printers with 1-2 nozzles per ink most strongly. In this case, despite the high speed of the droplet jet, the overall image recording speed is low (in the Iris 2 Print, an A2 format image is recorded in 13 minutes).
High-speed printing capabilities can be realized by using multi-nozzle wide-format print heads. In Fig. 2.1.4 shows a schematic diagram of the operation of a nine-nozzle head.
The print head has a distribution channel into which ink is supplied under pressure. If the exit from the channel is closed, ink flies out in streams through the nozzles (position 2 in Fig. 2.1.4).
The size of large-format print heads is limited by the fact that high-frequency vibrations of the piezoelectric are transmitted not only to the jets, but also to the body of the print head. The head, in turn, transmits vibration to the ink jets. The oscillations received by the jet from the head body differ from the useful oscillations of the jet and disrupt droplet formation (droplets of different sizes are formed and the length of the continuous part of the jet may change, which will disrupt the charging of the droplets). These problems become worse as the width of the print head and the frequency of superimposed vibrations increase. Problems are solved in different ways. In Fig. Figure 2.1.5 shows a print head in which piezoelectric vibrations are transmitted only to the nozzle plate. This head, which is 7.5 cm wide, operates at an oscillating frequency of 200 kHz.
Kodak Versamark high-speed inkjet presses use print heads up to 9 inches (22.8 cm) wide with a nozzle density of 300...360 nozzles per inch. In multicolor printing, heads for different inks are placed one after the other. The machines allow printing at speeds of more than 100 m/min. Thus, the Kodak Versamark VX 5000 Plus model, available in 11 different configurations, allows printing at speeds of 228 m/min (3080 A4 pages per minute) and 152 m/min (2052 A4 pages per minute). At high speeds, print resolution and quality of reproduction of tone and line images deteriorate. The mode can be used for mailing and transactional printing.
Kodak has developed a method of continuous inkjet printing with thermal activation of droplet formation. Its principle is as follows. The jet escaping from the nozzle receives thermal pulses of a certain frequency from the microheater. The surface tension of ink depends on its temperature, so each thermal pulse causes a change in surface tension (decreases it). The surface of the liquid is brought out of equilibrium, and a capillary wave appears in the jet. When such oscillatory disturbances are superimposed on the natural vibrations of the ink, the jet breaks up into individual droplets.
As in the classic method of continuous inkjet printing, the new method creates a continuous droplet jet and ensures its division into working and non-working droplets.
The thermally activated droplet print head contains a plurality of nozzles equipped with heating elements. When an electrical voltage pulse is applied to the heater, a current passes through it, causing strong short-term heating. The thermal impulse is transferred to the ink jet. The surface tension of the heated section of the jet decreases. Since heating, which causes disturbance of the jet, occurs periodically, a capillary wave arises, and the jet breaks up into droplets at some distance from the nozzle. The droplet size depends on the frequency of thermal pulses. The rarer they are, the larger the drops (Fig. 2.1.6). The image is recorded in large drops.
When no image is being recorded, the pulse frequency is high. In Fig. 2.1.6 there are 5 of them during the period T. The resulting small drops fall into the droplet eliminator. If a drop should fall on the printed material, the pulse frequency is reduced (1 pulse per period). The volume of the drop increases, for example, 5 times.
Since the working and non-working droplets have different sizes, they can be forced to fly along different trajectories by the air flow.
In an inkjet print head, jets containing droplets of different sizes fly straight from top to bottom until they enter the zone of action of the gas deflector, where an air flow is supplied perpendicular to the direction of the jets (Fig. 2.1.7). Drops with a smaller volume and mass are displaced by the gas flow over a greater distance than large drops. Thus, the jets are divided into two. In principle, either large drops or small drops can be used for printing. In the diagram Fig. 2.1.7 shows printing with large drops. Small drops, deflected by the gas deflector to the greatest extent, fall into the droplet eliminator.
Based on Kodak Stream technology, 2 digital printing machines (DPMs) were created that print with water-based ink. The Kodak PROSPER 1000 Press is designed for single-color printing at speeds up to 200 m/min on roll paper with a density of 45-175 g/m2. Printing width up to 600 mm, resolution 600 dpi, drop size 6 or 9 pl. The machine contains two lines of print heads, each with 6 inkjet modules. The head batteries are placed across the roll and are stationary during printing. An IR drying device is installed after each line of heads.
The machine can print at a speed of 3600 A4 pages/min on one roll or on two rolls (front and back). It can be used for printing mailings and book products.
The second Kodak PROSPER 5000XL Press is designed for 4-color printing. The print device contains 4 wide-format heads (a line of 6 print heads). After each wide-format head there is a drying device; a fifth device is used for final drying.
Suitable paper with a density of 45-300 g/m2, coated and uncoated. When printing on uncoated papers, a device for applying an underlayer (primer) can be installed in line with the machine, which allows you to expand the range of printing materials, as well as post-printing equipment.
The machine is designed for printing books, mailings, catalogs and tabs.
Kodak Prosper S10 print heads, about 10 cm wide, are designed for hybrid printing. It imprints variable data into offset products.
In pulsed inkjet printing, a drop of ink is expelled from a nozzle when an electrical impulse is applied to the activator (actuator), which is responsible for the formation of the drops. The ink ejected from the nozzle goes entirely to creating an image on the printed material. A pulse inkjet print head contains a plurality of nozzles. The inkjet micromodule associated with each nozzle includes an ink chamber, a channel for ink entering the chamber from a reservoir (or distribution channel), and an output channel ending at the nozzle. On the wall of the output channel or on the wall (roof) of the ink chamber there is an activator that receives electrical voltage pulses from the microchip that controls the operation of the head. The jet micromodule is also called a droplet emitter or droplet generator. The method of pulse inkjet printing is determined by the type of activator used. There are the following types of pulse inkjet printing: piezoelectric (piezojet), thermoelectric (thermojet and thermomechanical).
A typical piezojet print head includes a line of droplet emitters, each of which ends in a calibrated hole - a nozzle. In general, each nozzle is connected by a channel to the ink chamber. The camera is connected through a narrow channel to an ink reservoir common to all nozzles that print with ink of the same color. On the upper wall of the ink chamber, or on the wall of the channel connected to the nozzle, there is a piezoelectric element, which, when an electrical impulse is transmitted, changes the internal volume of the emitter. A decrease in volume leads to a portion of ink being pushed out of the nozzle, which flies out in the form of a droplet of one size or another. The size of the droplets and their speed depend on the size of the nozzle, the design of the print head, its operating modes (including the shape of the electrical signal supplied to the piezoelectric element) and the ink. Drop emitters of piezojet heads can differ in design and in the nature of deformation of the piezoelectric element.
The reason for the deformation of piezoelectrics when an electric field is applied is the inverse piezoelectric effect, which is as follows. Under the influence of an electric field, piezoelectrics quickly and strongly polarize and therefore change their dimensions. When the field is removed, these materials return to their original state.
Some materials, such as piezoceramics, exhibit the ability to exhibit an inverse piezoelectric effect if they are pre-polarized. Piezoceramic activators based on zirconate - lead titanate are widely used in inkjet print heads, as they have high strength and stability of piezoelectric properties.
When an electric field is applied to a polarized piezoceramic plate, two types of deformation are possible.
If the direction of the electric field is parallel to the direction of the polarization vector, the piezoceramic plate changes its horizontal and vertical dimensions, maintaining its volume. Depending on whether the directions of the polarization vector and the field strength vector coincide or are opposite to each other, the plate becomes thinner and wider or thicker and narrower.
If the piezoceramic plate is rigidly fixed to the elastic wall of the chamber (Fig. 2.2.1), then when its dimensions change, the elastic wall bends. When it bends towards the camera, the volume of the chamber decreases and a drop of ink is squeezed out of the nozzle. By bending outward, the piezoceramic activator increases the volume of the chamber, and a portion of ink enters the chamber from the reservoir through the inlet channel. The specific deformation is extremely small, so it is more correct to talk about an acoustic wave arising inside the emitter, pushing the drop out of the nozzle. To increase the pressure on the ink, the piezo activator is made quite large. Thus, with a chamber width of 108 microns and its length of 400 microns, the piezo activator in Epson Micro Piezo print heads is made up of piezoceramic plates 1 mm long, giving the overall dimensions ">Fig. 2.2.2.
Deformation in shear mode is observed if the directions of the electric field and polarization of the piezoceramic element are perpendicular to each other. This type of deformation is called Shear Mode.
The type of deformation of the piezoelectric activator when operating in shear mode is shown in Fig. 2.2.3. Printheads for pulsed inkjet printing have two options: “Shear Mode” from Spectra and “Shear Mode/Shared Wall” from Haar. In the first case, the upper wall of the ink chambers is made of piezoceramics, and in the second, the channel walls are piezoceramic.
Let's consider the principle of operation of the emitters of Spectra inkjet print heads, the piezoelectrics of which operate in Shear Mode.
Spectra's piezoceramic heads feature a thin cover plate for the ink chambers. The piezoceramic plate is common, and the electrodes are individual for each chamber. When a voltage pulse is applied to the middle electrode (the electrodes on the right and left are grounded), shear deformation occurs in the areas of the piezoelectric located on both sides of the electrode. Since the electric fields to the right and left of the electrode have opposite directions, the deformation ensures the lifting of the section of the thin piezoceramic plate located under the middle electrode. The volume of the ink chamber increases and a portion of ink is sucked into it. At the end of the pulse, the plate returns to its previous position, and an ink drop is pushed out of the nozzle located opposite the middle electrode. When a drop is pushed out, deformation into the chamber is possible due to a change in the direction of the electric field. The nature of deformation and the kinetics of droplet formation and ejection are visible in Fig. 2.2.4.
A diagram of Haar (and Toshiba) print heads operating on the Shear Mode/Shared Wall principle (that is, in the “shift/shared wall” mode) is shown in Fig. 2.2.5.
In this head, two piezoceramic layers are attached to the base plate; droplet emitter channels are made in them. They are filled with ink through a distribution chamber located under the cover plate, where there is a hole for communication with the ink cartridge. The upper and lower piezoceramic layers are polarized in opposite directions. There are electrodes on the walls of the channels. Electrodes attached to the walls of one channel are electrically connected to each other. A plate with nozzles is attached to the front of the head in such a way that each channel ends with a nozzle.
When a voltage pulse is applied to the electrodes located on both sides of the wall separating adjacent channels, an electric field is created in it. Since the electrodes of one channel are connected, the electric field and shear strain occurring in the channel walls are in the opposite direction. Since the upper and lower parts of the walls are attached to the plates, only their middle parts can move. The nature of channel deformation is visible in Fig. 2.2.5, b.
When a drop is formed, the channel first increases in volume, and then, due to a change in the direction of the electric fields, it narrows and a drop of ink is pushed out of the nozzle. The channel is then expanded again and filled with ink from the reservoir. In this type of head, only every third nozzle can operate at the same time. To increase hardware resolution exceeding 360 dpi, the print head is oriented so that the nozzle plates with nozzle lines make an angle with the direction of movement of the head block that is different from the formula" src="http://hi-edu.ru/e-books/xbook1004 /files/10v-12.gif" border="0" align="absmiddle" alt="l), it is about 20 microns. In modern inkjet equipment, the minimum droplet volume has decreased to 1.5...5 pl, which has led to nozzles measuring 10 microns or even smaller.
In traditional Epson print heads, with a small nozzle size (10-20 microns), the width of the ink chamber is 108 microns, and the width of the piezoelectric is 141 microns. This limits the nozzle density to 180 per inch. To increase the print resolution from 180 to 360 dpi, the nozzles are arranged in two rows with a shift.
A further increase in resolution (increasing the number of tones and colors of the image) is achieved by releasing droplets of several sizes.
The droplet size and head operating speed depend on the frequency, duration and shape of the electrical signal supplied to the piezoelectric activator.
The most efficient operation of the head is ensured by the operating frequency of droplet ejection, which corresponds to the natural frequency of oscillation of the liquid meniscus in the nozzle. If the natural frequency is 40 kHz, then the signal width (duration) should be about 25 μs.
The signal (voltage pulse) must consist of at least two parts, with a duration equal to half the wavelength. Half of the signal is responsible for pushing ink out of the nozzle, and half helps speed up the filling of the emitter with ink. The highest rate of droplet ejection is provided by the mode in which the pulse first draws the meniscus into the nozzle and the ink into the chamber. At the moment when the ink is ready to change direction, the second half of the pulse imparts momentum to the ink towards the nozzle. Both oscillations (natural and superimposed) are in the same phase, so they reinforce each other and the amplitude of the oscillations increases, ending in the ejection of a drop.
The pulse shape is complex, it controls the subsequent movements of the ink. Initially, the meniscus is slowly drawn into the nozzles before the droplets are ejected to obtain the same meniscus shape in all nozzles. At this time, a portion of ink enters the camera from the input channel. The pressure in the ink chambers then increases sharply as the chamber wall bends inward and the droplet is pushed out of the nozzle. Next, the meniscus is retracted to quickly suppress its oscillation after the drop is ejected.
In Fig. Figure 2.2.6 shows the release of droplets of large size (mode I) and small size (mode II). The signal period is counted from the beginning of the rise (the positive part of the meniscus filling pulse) through the decline from maximum to minimum (ink extrusion) to the rise to the zero level (the negative part of the meniscus filling pulse). Thus, a quarter of the signal width (decay) is intended for jet emission. For small drops (mode II), the ink collection time is reduced and the signal includes an additional small pulse that ends when the ink is extruded to the zero meniscus level.
Another way to obtain droplets of different sizes is to merge several droplets into one. Panasonic print heads use the resonance method, when one or more preliminary pulses are applied to the piezo activator to produce large droplets. As a result of the addition of the vibration amplitudes, the size of the ejected drop increases.
A common method is to eject a chain of different numbers of drops (up to 3 or 7) from a nozzle at one point of material. Droplets of different sizes form on the material. The method is used, for example, in Haar print heads. In these heads, the initial drop can have a volume of 1 or 6 pl, and a drop composed of seven drops can have a volume of 7 or 42 pl, respectively. Large drops are used to seal solid areas, and small drops are used to obtain fine details and smooth changes in tones.
It is clear that when using the variable drop size mode, printing is slower than in the binary mode, where all drops are the same.
Using light inks (light cyan, magenta, and gray inks) in the kit further increases the number of saturation levels for each ink color and the total number of colors.
In recent years, methods characteristic of microelectronics have begun to be used for the manufacture of print heads. MEMS (Micro-Electro-Mechanical Systems). The basis of any MEMS structure is a wafer, which is a silicon crystal. On one of the silicon wafers, head emitter structures are formed using MEMS methods (sputtering, photolithography, dry etching, laser ablation, etc.), and on the other, microcircuits (boards) that control the formation of droplets and, if necessary, channels for ink supply are formed. By gluing them together, they get a chip, which in MEMS heads is called a die. The print head includes several chips arranged with the outermost nozzles overlapping.
The use of MEMS equipment and technologies for the manufacture of print heads makes it possible to create dense rows of nozzles of micron and submicron sizes, with high repeatability of element sizes, element strength, and also makes it possible to reduce the cost of producing large-sized heads. MEMS technologies are used by many manufacturers of print heads and printers. As examples, consider new print heads from two companies: Epson and Dimatix (formed by Fuji and Spectra).
Epson's latest generation print head is called Micro Piezo TFP Printhead, TFP- abbreviation for “thin film piezo”. Micro Piezo TFP heads contain thin film piezo activators. If the piezoceramic activator plate in traditional heads had a thickness of 1 mm and a width of 141 microns, then the thickness of the new piezoelectric is 1 micron and its width is 71 microns. This was made possible through the use of a new material with increased specific deformation and MEMS technologies for deposition of thin films.
The new printheads can produce droplets the same size as traditional printheads with half the ink chamber volume. In them, nozzles of one row are located with a density of 360 per inch. Two rows of offset nozzles provide a physical print resolution of 720 dpi. The heads can produce droplets of different sizes, just like the previous generation of heads, allowing for significantly increased print resolution.
Since MEMS technologies make it possible to obtain strictly identical emitter structures, it has become possible to increase the size of the print heads. In Fig. 2.2.7 shows a 2.54 cm wide chip containing 8 rows of nozzles, with nozzles for paints of the same color located symmetrically about the center line, parallel to the lines of the nozzles. This allows you to obtain the same order of paint application when moving the head forward and backward. By placing 4 chips on a common base in two rows in a checkerboard pattern, we got a print head 30.8 cm wide.
All this allows you to significantly increase print speed while maintaining high resolution and high print quality. Thus, in B500DN office printers with 10.8 cm wide heads, the color printing speed in standard mode is 32 s/min.
The Screen True Press 520 Jet digital inkjet printing press uses Micro Piezo TFP heads placed on a common base to produce a head up to 520mm wide. Wide heads located one behind the other across the printed material provide a color printing speed with water-based ink of 63 m/min with a resolution of 720 highlights">Fig. 2.2.8.
Dimatix (formed by Spectra and Fuji) produces wide-format “M-class” heads (made using MEMS technology) under the same name (Fig. 2.2.9). The print head is made up of crystals (silicon chips) sized 45">b). The distance between the nozzles of one row corresponds to a resolution of 182 dpi. Ink supply channels run along the base of the crystal.
The structure of the droplet emitter of the new print head (Fig. 2.2.9, a) is different from that of the Spectra heads (Fig. 2.2.4, a). The ink is fed into the pressure chamber from below the base of the crystal through the end acoustic device 3. The presence of such a device increases, due to resonance, the amplitude of the acoustic wave that pushes the ink. This allows you to reduce the size of the piezo activator located in position 1 of the figure. From pressure chamber 2, ink flows through the output channel into the nozzle, from where ink drops fly out perpendicular to the plane of the crystal with a frequency of 100 kHz.
The crystals can be used to produce a composite head of long length, including a page format. The crystals are placed on a common base containing a control board, in steps with an inclination (in the shape of a ladder). This ensures that the nozzles overlap in the direction of movement of the printed material web. The head is stationary during the printing process. These print heads are found in a sheetfed inkjet digital printing machine. Fujifilm Digital Inkjet J Press 720, printing with water-based ink at a speed of 180 pp..gif" border="0" align="absmiddle" alt="1200 dpi.
Solid ink contains polymer wax. At room temperature they are solid, but when heated they melt and turn into a liquid whose low viscosity allows the ink to be used for inkjet printing. The ink is currently used in the Xerox ColorQube 9200 series multifunction printer, such as the ColorQube 9203. Xerox has also developed a solid ink inkjet digital press. The Xerox Ci Press 500 roll press prints on a web up to 520 mm wide at a speed of up to 150 m/min]) in the form of solid briquettes of 4 colors, differing in shape.
In the head they heat up, melt and fall into the ink reservoir, and from there into the distribution channels of the print head. The head contains 4 distribution channels, one per ink color, and rows of nozzles for ink colors CMYK..gif" border="0" align="absmiddle" alt="When the ink hits the drum, it cools; it does not spread over the surface of the drum, but retains its plasticity. The dots and strokes obtained on the drum are in relief.
The ink image is delivered on a rotating drum to the paper transfer area..gif" border="0" align="absmiddle" alt="600 dpi. Print speed in standard mode is 60-70, and in photographic quality mode - 35-38 A4 pages/min.
In this method, when a print is fixed on a printed material, the phase state of the ink changes; no solvents are released from the ink. Therefore, neither drying nor absorption of ink into the printed material is required. In addition, waste paper can be easily removed from paint. The disadvantage of ink is the sensitivity of prints to elevated temperatures. Development of an ink that can be cured onto a print is underway.
Hewlett Packard and Lexmark, and the generation of droplets in channels is carried out by Canon, which calls its technology Bubble Jet (the companies are given as an example). Recently, printers with Memjet printing devices have appeared on the market; the print heads for them were developed by the Australian company Silverbrook. In the droplet emitters of these heads, the heater is located mainly inside the ink channel.
Let us consider the mechanism of droplet generation under the influence of local heating using the example of a droplet emitter used in Canon print heads (Fig. 2.2.12). The emitter consists of a narrow pressure chamber (channel) ending in a nozzle on one side and an inlet channel from the ink reservoir on the other. There is a strip of heating element on the channel wall. When current passes through the strip, it heats up to a high temperature, in turn heating up the ink nearby. Water, serving as an ink solvent, quickly reaches an overheating temperature (more than 200 emission ">Fig. 2.2.13 shows a diagram of a droplet emitter with a thermoelement on the “roof” of the ink chamber. A bubble is formed in this chamber, and a drop of ink is squeezed out through the outlet channel and nozzle. The difference between this version of the emitter and the Canon emitter is that here the thermoelement is not located near the nozzle, but is separated from the nozzle by an output channel.Otherwise, the droplet ejection mechanism is the same.
Thermal inkjet printing with large format heads is difficult because the heaters generate a large amount of heat. Part of the heat is transferred to the body of the droplet emitter, since the heater is located on its wall. The Australian company Silverbrook has developed a spiral suspended heater. Its cross section with the resulting steam bubble is shown in rice. 2.2.14 In thermal inkjet printing, it is impossible to change the size of the droplet by changing the shape of the electrical pulse. To increase color depth, the following methods are used to vary the amount of ink falling on each micro-section of the image. In Hewlett Packard photo printers, the number of tones is increased due to the fact that many drops of ink, including different colors, can hit each point. Initially, this amount reached 16 (Photo RET II), and currently up to 32 (Photo RET IV) drops measuring about 4 pl. The word RET is an abbreviation for Resolution Enhancement Technology(Resolution Enhancement Technology). Interpolated resolution is 2400mark">Canon
Photographic quality printing requires photo paper.
For print on office papers an underlayer for ink can be used. Clear underlayers are applied from a special print head before applying the main ink. It is the sublayers that have direct contact with the paper. The ink is applied to the underlayer. In this case, the absorption of ink into the thickness of the paper is reduced, the color saturation of the prints increases and the print resolution increases. Since the ink does not react directly with the paper, the paper requirements are reduced. HP uses the underlayer in the CM8060 multifunction printer and the HP T300 Inkjet Web Press.
New generation thermal inkjet printheads are manufactured using MEMS methods (Micro Electro-Mechanical Systems), traditionally used in microelectronics. This increases the geometric accuracy of nozzles and emitters of drops of different (including very small) sizes, ensures their repeatability and allows the use of “scaling” - composing print head modules of the required size (format) and thereby ensuring a given print width. In addition, the use of MEMS technologies will reduce the cost of print heads, especially large format heads.
Let's look at what print head drop emitters look like.
Rice. 2.2.16 illustrates the formation of droplets in the new generation Canon emitter used in the Canon i850 printer. In the diagram: a - the emitter is at rest, b and c - a bubble forms and squeezes out the ink in the nozzle channel from the nozzle, d - a drop has flown out and the emitter begins to fill with ink, e - the nozzle channel is filled and is ready to eject the next drop. In these droplet emitters, a strictly defined amount of ink is pushed out of the nozzles - located in the nozzle channel. The formation of droplets of different sizes occurs by using two rows of nozzles of different sizes. In the emitters of one row, drops of 5 pl are formed, and in the emitters of the second row, drops of 2 pl are formed.
In Fig. Figure 2.2.17 shows a diagram of the drop emitter of the HP print head. Its fundamental difference from the new generation Canon print head emitter is that the heater is not located on the wall of the nozzle channel, but on the wall of the ink chamber opposite the nozzle channel.
In Fig. Figure 2.2.18 shows an example of the structure of a droplet emitter obtained by MEMS methods. The figure shows an ink chamber with a nozzle channel and heater 1, which is a thin layer of tantalum alloy with aluminum. The heater has aluminum contacts 2 and a protective layer 3. The ink supply channel into the internal cavity of the emitter is not shown. The emitter structures are made on the surface of the silicon wafer. The second silicon wafer contains a control integrated circuit.
The printing production process includes four stages:
- 1. Photo process - the stage of obtaining photographic forms of a reproduced image.
- 2. Form processes - provide printing forms.
- 3. The printing process involves transferring ink from a printing plate to paper in a certain sequence.
- 4. Finishing processes - to give printed products a consumer form.
The following printing methods are used:
- 1. Letterpress (typographic).
- 2. Osphite printing.
- 3. Intaglio (squeegee) printing.
In the manufacture of forms for letterpress printing, zinc and copper plates (clichés) coated with a photosensitive layer were used. Recently, to obtain letterpress printing forms, materials based on liquid and solid photopolymers have been obtained, onto the surface of which I copy photoforms. Letterpress prints are characterized by the presence of two main features: traces of ink indentation on the edges of the printed characters and deformation of the backing (paper) in the places where the printed characters were applied.
Osfetanya printing came out on top in terms of the quality of transmitted images, less labor intensity and high circulation resistance. Its main advantage is:
- Reduced plate wear due to elastic surface
- · Significant increase in printing speed.
There are flat osphite printing and typo osphite printing. The transfer of ink to the paper occurs through an intermediate rubber sheet on the osphete cylinder.
In intaglio printing, the printing elements on the form are located below the white spaces, which distinguishes this printing from others. The different depths of the printing elements filled with paint determine the tone strength (saturation) of the areas of the reproduced image due to the different thickness of the ink layer. The printing process occurs due to high pressure on the form, while the paper is pressed into the recessed elements of the form, as a result of which the ink layer transfers from the recesses of the form to the paper.
Currently, screen printing is carried out using a stencil through which ink penetrates onto the printed material.
Printing methods:
- 1. flat osphete printing, in this way background grids, micropatterns, microtexts are printed on banknotes.
- 2. The typo-osphet printing method combines elements made by letterpress and flat osphite printing.
- 3. Oryol printing, its main feature is that when printing a multicolor line original, an absolutely exact match of the design elements printed with inks of different colors in one cycle is achieved.
- 4. metallographic printing is divided into deep squeegee and metallographic. For banknotes, a mellallographic printing method is used - this is printing from an engraving.
- 5. Series numbers and letters are printed on all banknotes using letterpress printing.
- 6. iris printing - printing occurs from one form, smooth color changes are observed when moving from one paint to another.
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