JPS60262663A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To prevent the resolution of picture elements from being deteriorated while securing a sufficient number of gradations, by a method wherein a repeated combination of m ink droplets out of droplets of i different inks are overlappingly jetted to a single point of a recording material in accordance with density information. CONSTITUTION:The recorder is provided with ink tanks 9 for i inks differing in ink concentration, piezoelectric elements 5 and nozzles, and m droplets out of the droplets of the inks are mixed on a recording paper, thereby expressing a multiplicity of gradations. To jet the m ink droplets to a single point on the recording paper, the volume of each of the ink droplets is set to be 1/m times of that in an ordinary system, and the diameter thereof is set to be 1/m<3/2> times of that in an ordinary system. Although the smaller ink droplets are used, the accuracy in positioning a dot may be the same as in a conventional system.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an inkjet recording device, and particularly to an inkjet recording device for expressing grayscale images and grayscale characters.

(Prior Art) An inkjet head of a conventional drop-on-demand type inkjet recording device will be described. FIG. 5 is a sectional view showing a basic example of the structure. One end of the ejection chamber 1 is open to the atmosphere through an orifice 2 for ejecting ink droplets, and the other end communicates with an ink supply hole 3.

Ink is supplied to the ejection chamber 1 from an ink tank (not shown) through an ink supply hole 3. A piezoelectric element 5 is attached to a flexible plate 4 forming a part of the wall of the injection chamber, forming a bimorph. Piezoelectric element 5
By applying an electric pulse to the flexible plate 4
is deflected in a direction that reduces the volume of the ejection chamber 1, and a pressure wave is generated inside, and the ink droplet 6 is ejected from the orifice 2 toward the recording paper 7 due to this pressure wave.

The inkjet head is manufactured by chemical etching using a mask, similar to semiconductor products such as ICs. For this reason, a large number of nozzles can be integrated and formed on a stainless steel or ceramic plate at the same time, making multi-nozzle formation extremely easy. Therefore, the inkjet head can demonstrate its true value in applications that use a large number of nozzles.

(Problems with the Prior Art) Conventionally, when displaying pseudo-gradation using the inkjet head, an area gradation method such as a dither method or a density bang method has been used. This is a method of expressing gradation by controlling the area covered by ink per unit area on the recording paper surface.

Specifically, it is expressed as a dot matrix of 1 pixel f j be. For example, the number becomes 1/2. Similarly, when the dot matrix is 4.times.4, for example, 17 gradations can be expressed as shown in FIG. 7, but the pixel resolution is as rough as 1/4. As described above, there is a trade-off relationship between the number of gradations that can be expressed and the pixel resolution, and if an attempt is made to obtain a sufficient number of gradations, there is a problem in that the image becomes rougher by that much.

(Objective of the Invention) An object of the present invention is to provide an inkjet recording device that prints a high-quality grayscale image while ensuring a sufficient number of gradations and preventing deterioration of pixel resolution.

(Structure of the Invention) According to the present invention, an inkjet recording apparatus reduces the volume of an ejection chamber by applying electric pulse gold to a piezoelectric element, and causes ink droplets to fly from the ejection chamber toward a recording medium through an orifice connected thereto. , one ink tank stores i types of ink each having a different concentration, i types of nozzles are supplied with ink from the ink tank and eject ink droplets toward the recording medium, and an i type of nozzle group receives input from the outside. There is obtained an inkjet recording apparatus characterized in that it includes a control unit that overprints m ink droplets including the i types of ink and the reciprocating ink droplets at one point on the recording medium in accordance with the density information.

(Operation/Principle of the Invention) The inkjet recording device according to the present invention prepares one type of ink having a different density, and further mixes m droplets of these inks on the recording paper surface to express a large number of densities. be. In the following explanation, this m will be referred to as multiplicity. In order to eject m drops to one point on the recording paper surface, the volume of the ink droplet needs to be 1/m 2 of the usual size, and the diameter of the ink droplet is 1/y'i'n. Although such reduction in ink droplet diameter can be achieved by making the orifice diameter of the nozzle finer and optimizing the pulse width of the electric pulse applied to the piezoelectric element, there is a limit to the magnitude of the multiplicity m. .

In our experiments, the practical multiplicity m was 2 or 3. In this case, the ink droplet volume is 1/2.1 of the normal volume.
/3. Ink droplet diameter is 79% of normal size.

It will be 69%. One of the excellent features of the present invention is that even if the ink droplets are made somewhat smaller than usual, the dot positioning accuracy remains the same as before.

Table 1 shows the number of densities expressed as recorded dots for multiplicity m of 2 to 3 and ink type i of 2 to 6.

As shown in Table 1, the inkjet recording apparatus according to the present invention can express recording dots with a greater number of densities than the ink type i, and can record high-quality grayscale images.

(Example) Next, drawings illustrating embodiments of the present invention will be described.

(Example 1) The simplest example of the present invention will be shown. FIG. 1 is a schematic diagram of the head. The head is equipped with ink tanks 9 and nozzles for four types of ink each having a different ink density. The dye concentration of the ink is lower than that of dl, d2. d3
．． d4, and the multiplicity m is 2, there are 10 dye densities of the recorded dots as shown in Table 1.
2), Support (d1+d3).

2 -1 2 (d 2 + d 3 ), 7 (d 3 + d
3) - Support (d, +d4), pot (d2+d4).

-(ds+d4), ”(d4+d4)2 becomes.

Since the multiplicity is 2, for example, two dl ink droplets may be ejected at one point. Therefore, in this embodiment, it is necessary to scan twice to record one line.

(Example 2) An inkjet head in Example 2 is shown in FIG. Although it is basically the same as the first embodiment, in the second embodiment, the number of nozzles for each ink is two, and these are arranged in the main scanning direction. Therefore, the total number of nozzles is 2 in Example 1.
However, one scan is required to record one line, making it possible to achieve a recording speed twice that of the first embodiment.

This embodiment (d2) takes full advantage of the feature of the on-demand type inkjet recording apparatus that it can easily be made into a multi-nozzle system, and is much more practical than the first embodiment.

(Example 3) An inkjet head in Example 3 is shown in FIG.

In the third embodiment, three nozzles are arranged in the main scanning direction assuming a multiplicity of m=3i. As a result, one line can be recorded in one scan as in the second embodiment. However, the ink droplet diameter must be reduced to 87% compared to Example 2.

What is the dye concentration of the recording dot? From Table 1, multiplicity m == 3
, 20 types are possible from 4 types of ink. They look like this:

Blue (a1 + dl + al), blue (d2 + dl + dl), gate (d2 + d2 + dl) blue (d2 + d2 + d2), blue (d
, +d1+d1), blue (d3+d2+dl)1(d a
+d ,, +d 2), square (d3+a3+dx), blue (
d3+d3+d2) blue (d3+d3+d3), blue (d4
+d1+d1), +(d4+d2'+d1)-! −(
d4+d2+dz), -L(d4+d3+d1), Kichi(
a 4+d a+a 2) 3 1(d4+d3+da), -L(d4+d4+d1
), 4(d4+d4+d2)3 L(a4+d4+d3), d, , +d4+d4) In this way, when the multiplicity is m = 3, more concentrations can be expressed than when m = = 2.

(Example 4) An inkjet head in Example 4 is shown in FIG. Embodiment 4 is a version of Embodiment 2 that achieves even higher speed by using multiple nozzles. The density that can be expressed with the multiplicity m-2 and the ink type i = 4 is the same as in Example 1.2, but in this example, 8 lines can be recorded at the same time.
The recording speed is 1016 times as high as that of the example and 208 times as high as that of the example.

(Effects of the Invention) As is clear from the above description, the inkjet recording apparatus of the present invention has the effect of being able to obtain a large number of recorded dot densities even with a small number of ink types i.

[Brief explanation of the drawing]

1, 2, 3, and 4 are schematic diagrams of an inkjet head in an embodiment of the present invention, FIG. 5 is a sectional view of an inkjet head of a conventional inkjet recording apparatus, and FIGS. 6 and 7. The figure is a display diagram showing an example of IJ sock gradation expression using a conventional inkjet recording apparatus, each having 2 x 2°4, x 4 pixels. In the figure, 1... injection chamber, 2...- orifice, 3... ink, supply hole, 4...
-Flexible plate, 5...-Piezoelectric element, 6...
...Ink droplets, 7...-Recording paper, 8...
...Ink dot, 9...Ink tank. Agent Patent Attorney Uchihara Mochi ゛7th ward z' 2nd evil ζ 3rd figure 2' 4th flash

Claims (3)

[Claims] (1) An inkjet recording device that reduces the volume of an ejection chamber by applying electric pulses to a piezoelectric element and ejects ink droplets from the ejection chamber toward a recording medium through an orifice connected to the ejection chamber, each having a different density. 1
i ink tanks for storing different types of ink; a nozzle group of ls types for ejecting ink droplets from the ink tanks toward the recording medium; An inkjet recording apparatus comprising: a control section for overlapping m ink droplets, including overlapping ones, of i types of ink at one point on the recording medium. (2) The ink jet recording apparatus according to claim (1), wherein the ink concentration i and the number m of ink droplets ejected to the same point on the recording medium are integers of 2 or more. (3) The inkjet according to claim (2), characterized in that m nozzles that eject ink of the same density are arranged in the main scanning direction, and recording of one point is completed in one scan. Recording device.