JPS6213357A - Ink jet printer - Google Patents

Abstract

PURPOSE:To obtain an ink jet printer capable of increasing the gradient, by providing a control circuit wherein the flying ink is varied in amount according to the variable pulse width of the voltage applied between recording electrodes and a counter electrode. CONSTITUTION:A printing control circuit sends a printing control signal varying the voltage to be applied between recording electrodes 9 and a counter electrode 5 according to an image signal. The pulse width (t) of the applied voltage is varied in 8 stages from t1 to t8, allowing an ink 8 flying out of tip ends 10 of the recording electrodes 9 to be varied in amount. Variation of the flying ink 8 in amount is proportional to the pulse width of the applied voltage. The printing control signal equivalent to the image signal is sent to switches from the printing control circuit to appropriately determine the size of the each dot to be formed on a recording paper 6. Namely, the dot of small diameter is formed on the portion to have low density and that of large diameter on the portion to have high density, resulting in the gradient produced in the image.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ink jet printer that forms images by selectively ejecting ink droplets using electrostatic means.

Prior Art Conventionally, ink droplets are selectively ejected by electrostatic means.
The flying ink is attached to the recording medium to form dots,
There are inkjet printers that form images by selectively aggregating these dots. Since the dot diameter of such a dot is uniform, it is not possible to impart gradation to the image using normal methods. Therefore, a dither method is used as a measure to give an image gradation.

This divides a pixel into multiple matrices and forms dots within the matrices. and.

When attempting to obtain a pixel with high density, the number of dots formed within that pixel is increased. Conversely, when trying to obtain pixels with low density, the number of dots is reduced.

In this way, it is possible to impart gradation to the nine images.

Problems to be Solved by the Invention On the other hand, in order to obtain natural image quality, it is necessary to increase the degree of gradation by one level. As a means to that end.

There is no other choice but to increase the number of matrices in one pixel.

This is because the dot diameter is uniform. However, when the number of matrices is increased, the density of each pixel in the entire image becomes rougher, and the natural image quality is impaired. Therefore, there is a limit to increasing the number of matrices, and there is a drawback that the degree of gradation cannot be increased.

The present invention has been made in view of the above points, and an object of the present invention is to provide an inkjet printer that can increase the degree of gradation.

Means for Solving the Problems In the present invention, ink is supplied to the tip and a conductive S electrode is formed, a counter electrode is provided to face the recording electrode through the recording body, and the counter electrode In a device in which an image is formed by electrostatically flying the ink at the tip of the recording electrode toward the recording medium by applying a voltage between the recording electrode and the recording electrode according to the image signal, the recording electrode and A control circuit was formed that changes the amount of flying ink by varying the pulse width of the voltage applied between the counter electrode and the counter electrode.

When a voltage is applied between the recording electrode and the counter electrode, the ink supplied to the tip of the recording electrode is electrostatically ejected and adheres to the recording medium to form a dot. Image formation is performed by this selective collection of dots.

On the other hand, when the pulse width of the applied voltage is varied, the amount of flying ink changes. This changes the diameter of the dots formed on the recording medium. Therefore, if the dot diameter is made smaller, the density in that area will appear to be lighter, and if the dot diameter is increased, the density in that area will appear to be higher. In this way, gradation occurs in the image. At this time, the predetermined dot density is constant regardless of changes in dot diameter, and by widening the degree of change in dot diameter, the degree of gradation can be increased without impairing natural image quality.

Embodiment of the Invention A first embodiment of the present invention will be described based on FIGS. 1 to 4. FIG. Inside the printer body 1, a rod-shaped guide shaft 2 is disposed horizontally at the end, and a carrier 3 is mounted on this guide shaft 2.
is installed so that it can reciprocate from side to side. A printer head 4 is placed on this carrier 3. A counter electrode 5 facing the printer head 4 is installed horizontally in the center of the printer main body 1. This counter electrode 5 is covered with a recording paper 6 as a recording medium that is guided along a predetermined path.

Next, the printer head 4 will be explained.

The outer shape of this printer head 4 is a housing-like case 7, and ink 8 is stored inside this case 7.

The physical properties of this ink 8 are as follows.

Specific resistance: 107~10"Ω・Surface tension at mouth: 20~30d
It is yn/am. Inside the case 7, a plurality of recording electrodes 9 are immersed in the ink 8 at their tip ends 1.
They are arranged in a vertical line with 0 exposed to the outside. Them! 2. The recording electrode 9 has electrical conductivity and ink-containing properties.

Thus, the recording electrode 9 and the counter electrode 5 are connected via a high-voltage power source 11 , 12 divided into two and a switch 13 . The middle point of the connection of the high voltage electricity g11.12 is connected to the ground 14. Moreover, the switch 13
The OFF side terminal of is also connected to ground 15. An image signal circuit (not shown) is connected to these switches 13 to send an image signal, and a print control circuit 16 is interposed in the middle. This print control circuit 16 generates a print control signal that varies the voltage applied to the recording electrode 9 and the counter electrode 5 in accordance with the image fI4 signal.

In such a configuration, when an image signal is emitted from the image signal circuit, the switch 13 is opened and a voltage is applied between the recording electrode 9 and the counter electrode 5.

At this time, the ink 8 in the case 7 permeates into the recording electrode 9 and is supplied to the tip 10. Therefore, the ink 8 supplied to the tip 10 receives electrostatic force, and the opposite electrode 5
The dots fly towards the recording paper 6 and form dots. An image is formed on the recording paper 6 by this selective collection of dots.

On the other hand, a print control signal is also sent to the switch 13 from the print control circuit 16 . This print control signal is a voltage applied between the recording electrode 9 and the counter electrode 5.

That is, the pulse width of the applied voltage is set to 8 from tl to t8.
Variable in stages. As a result, the tip 10 of the recording electrode 9
The amount of ink 8 that flies also changes. This is because the ink 8 flies in the form of a string, and this string state continues as long as the pulse of the applied voltage remains. Therefore, the amount of flying ink 8 increases or decreases in proportion to the pulse width of the applied voltage. Here, FIG. 3 shows an example of the flying state of the ink 8 when the pulse width is from tz to t5, and FIG. 4 shows the pulse waveform at that time. Therefore, if the flying amount of the ink 8 changes, the size of the dots formed on the recording paper 6 will naturally also change. That is, the shorter the pulse width of the applied voltage, the smaller the dot diameter, and the longer the pulse width, the larger the dot diameter.

Therefore, a print control signal corresponding to one image signal is sent from the print control circuit 16 to the switch 13, and the thickness of each dot formed on the recording paper 6 is set to an arbitrary size. That is, the dot diameter is formed small in a place where the density should be reduced, and the dot diameter is formed large in a place where the density should be increased, thereby causing gradation in the image. At this time, since the gradation is caused by the difference in the diameter of each dot, the degree of gradation is increased by increasing the difference between the maximum dot diameter and the minimum dot diameter.

Thus, the predetermined density of dots remains constant regardless of changes in dot diameter. therefore.

Even if the degree of gradation is increased, the density of dots will not become rough. Here, the degree of gradation can be increased without sacrificing natural image quality.

Next, a second embodiment of the present invention will be described based on FIGS. 5 to 7. Portions that are the same as or correspond to those in the first embodiment are designated by the same reference numerals and explanations are omitted (the same applies hereinafter). In this embodiment, the pulse width of the applied voltage is set to 4 by the print control circuit 16.
It can be changed in stages.

Printed dots 2o of four different sizes are formed. Then, the pixel 21 is divided into four matrices 22, and printing dots 2 of arbitrary size are placed in each matrix 22.
0 is now formed.

With such a configuration, pixels 21 are formed depending on whether or not print dots 20 are formed in each matrix 22, and the entire image is represented on the recording paper 6 by a set of pixels 21. Ru. And the one-tonality is
As the diameter of the printing dots 20 in each matrix 22 changes, the density of the entire image M21 changes, and this is caused by a difference in density between that pixel 21 and other pixels 21. Here, the diameter of the print dot 20 itself changes in four stages, but since the print dot 20 changes to any diameter within the four matrices 22, the density change of the entire pixel 21 is subdivided into various parts. . For example, if all the printed dots 20 in each matrix 22 have the same diameter, if the product of 2×2, the number of the matrix 22, and 4, the number of varying diameters of the printed dots 20, there is no printing. By adding 1, a total of 17 gradations are obtained. Some examples of such cases are shown in Figures 6(a) to d).
If each printed dot 20 in each matrix 22 has a different diameter, even more gradations can be obtained. An example of such a case is shown in FIG. 6(e). Therefore, in this embodiment, by simply changing the diameter of the print dots 20 in four steps using the printing control circuit 16, the degree of gradation can be increased, and natural gradation can also be obtained.

FIG. 7 shows a modification in which the applied voltage is increased to make each print dot 20 in one pixel 21 have a large diameter, and the print dots 20 overlap each other. As a result, pure black is expressed in that pixel 21. Moreover, since each printed dot 20 overlaps, the image becomes clearer.

Next, a third embodiment of the present invention will be described based on FIGS. 8 and 9. In this embodiment, the printer head 4 is made movable with respect to the recording paper 6 while the ink 8 is being ejected from the recording electrode 9. This kind of thing is the printer head 4
A continuous straight line 630 can be drawn in the running direction. Therefore, the image formed on the recording paper 6 becomes clearer. An example of such an image is shown in FIG. Also, No. 91i
! I is a modified example in which the straight lines 30 are thick < L, and the lines that are in contact with BI overlap each other. The straight line 30 is made thicker by increasing the pulse width of the applied voltage. Something like this is next door! ! The gap between 30 and 30 mm is eliminated, and a clearer image is formed.

Next, a fourth embodiment of the present invention will be described based on FIGS. 1O to 12. This embodiment is an example of application to color printing. That is, there are three recording electrodes 9, and each tip 10 is coated with yellow (Y) and magenta (M).
- The printer head 4 was formed so that three color inks 40 of cyan (C) were supplied. Then, the scanning line 41 formed by moving the recording electrode 9 with respect to the recording paper 6 is divided into three scans! A plurality of pixels 42 including @41 are formed, and an image is formed by a collection of these pixels 42. Within the 0 pixel 42, yellow (Y), magenta (M), and cyan (C) are formed. Band-shaped irregularly shaped dots 43 of each color are formed.

With such a configuration, yellow (Y) is displayed within one pixel 42.
) - magenta (M) - cyan (C) irregularly shaped dots 43 of each color are formed to a predetermined length.

The length of each irregularly shaped dot 43 is set by varying the pulse width of the applied voltage based on a print control signal from the print control circuit 16. Figure 12 shows each color ink 4
The amounts y1, ml, and C1 of each color ink 40 are shown when the pulse width relative to 0 is Y1, M1, and C1. In this way, yellow (Y), magenta (M), cyan (C
) are formed as irregularly shaped dots 43 of a predetermined length within one pixel 42, whereby all colors are reproduced.

Such pixels 42 are assembled to form an image, and color printing is performed. Moreover, the degree of gradation is also high.

Next, a fifth embodiment of the present invention will be described based on FIGS. 13 to 16. This embodiment is basically the same as the fourth embodiment, but differs in that black printing is performed in the blank space within one pixel 42. That is, the printer head 4 is provided with recording electrodes 45 for black printing at portions corresponding to the recording electrodes 9 for color ink 40, respectively. These recording electrodes 45 form strip-shaped black dots 46 of a predetermined length in the margins of each scanning line 41 within the pixel 42.
Each part was configured to form a

In this configuration, the black dots 46 are yellow (
It represents the color when the three colors of Y), magenta (M), and cyan (C) overlap. That is, yellow (Y)
- When the three colors magenta (M) and cyan (C) overlap, the color becomes black. Therefore.

As an example shown in FIG. 15, when three colors overlap in nine pixels 42, an irregularly shaped dot 43 is not formed in one overlapping part by the color ink 40, and instead a black dot 46 of the same length as the overlapping part is formed. It is formed. In FIG. 15, the amount of color ink 40 in the overlapping portion is indicated by a broken line.

Note that FIG. 16 shows a modified example in which a large number of black dots 46 are formed in the blank space within the pixel 42. As a result, irregularly shaped dots 43 of the color ink 40 are formed within the 5 pixels 42.
You can obtain strong colors that cannot be obtained by using only one color. This is because, although a strong color cannot be obtained unless the irregularly shaped dot 43 of the colored ink 40 exists beyond the section of one pixel 42, the black dot 46 can represent the transcendental part outside the pixel 42.

Effects of the Invention The present invention provides ink supply to the tip, a counter electrode facing the conductive recording electrode via the recording medium, and a voltage applied between the counter electrode and the recording electrode. In a device that forms an image by ejecting the ink at the tip of the recording electrode toward the recording medium, the amount of ink ejected can be controlled by varying the pulse width of the voltage applied between the recording electrode and the counter electrode. By forming a control circuit that changes the gradation level, it is possible to increase the level of gradation without sacrificing natural image quality. Therefore, it is possible to easily form high-quality images. In this case, the degree of gradation can be increased even if the number of variable steps of the applied voltage is reduced, and the relative relationship between the recording medium and the recording electrode on which the ink is still flying can be increased. When moving, it is possible to form a continuous straight line in the scanning direction, making it possible to draw a more faithful and clear straight line.Also, each scanning line of the recording electrode can be divided into the same length for each scanning. If pixels containing lines are formed and color ink is formed in independent strips for each color within these pixels, color printing with a high degree of N tonality can be performed. If you print black in the margins of , it is possible to substitute the part where each color ink overlaps and the color becomes black, and the color ink in that part can be omitted. 6 having an effect

[Brief explanation of the drawing]

FIG. 1 shows a first embodiment of the present invention, and is a longitudinal side view showing the arrangement position and connection state of a recording electrode and a counter electrode;
FIG. 2 is an overall perspective view, and FIG. 3 is a side view of a recording electrode showing an example of an ink flying state. Fig. 4 is a graph showing an example of the pulse waveform of the applied voltage, Fig. 5 is a graph showing the second embodiment of the present invention and is a graph showing the relationship between the pulse width of the applied voltage and the dot diameter, and Fig. 6 is a graph showing the relationship between the pulse width of the applied voltage and the dot diameter. (a
)(b)(c)(d)(e) are front views showing various aspects of the pixel, FIG. 7 is a front view showing a modification thereof, and FIG. 8 is a front view showing a third embodiment of the present invention. FIG. 9 is a front view of an example of a formed image; FIG. 9 is an enlarged front view of a portion of a modified example thereof; FIG. 10 is a front view of an example of a pixel showing a fourth embodiment of the present invention;
1 is a front view showing an example of a pixel set, FIG. 12 is a graph showing an example of distribution of each color ink, and FIG. 13 is a front view of a printer head showing a fifth embodiment of the present invention.
FIG. 4 is a front view of an example of a pixel, and FIG. 15 is a graph showing an example of distribution of each color ink. FIG. 16 is a front view of an example of a pixel showing a modification. 5... Counter electrode, 6... Recording paper (recording body), 8...
ink, 9... recording electrode, 10... tip, 16.
...Printing control circuit (control circuit) Applicant Tokyo Electric Co., Ltd. - Atsushi J Figure J) is Figure 36 J39 J JO Figure 3''R

Claims (1)

[Claims] 1. Ink is supplied to the tip and a conductive recording electrode is formed, and a counter electrode is provided that faces the recording electrode through the recording body, and the counter electrode and the recording electrode An image is formed by electrostatically flying ink at the tip of the recording electrode toward the recording medium by applying a voltage between the recording electrode and the recording electrode according to an image signal. An inkjet printer characterized in that a control circuit is formed that changes the amount of flying ink by varying the pulse width of a voltage applied between the counter electrode. 2. The inkjet printer according to claim 1, wherein one pixel is formed by a plurality of matrices. 3. The inkjet according to claim 1, characterized in that a continuous straight line is formed in the scanning direction by relatively moving the recording body and the recording electrode with the ink flying therethrough. printer. 4. Supply color ink of different colors to the tips of the recording electrodes, divide each scanning line of the recording electrode into the same length to form a plurality of pixels including each scanning line, and form a plurality of pixels including each scanning line. 2. The inkjet printer according to claim 1, wherein the color ink is formed into independent strips for each color to perform color printing. 5. The inkjet printer according to claim 4, wherein black printing is performed in the margins within the pixels.