JPS5867467A - Ink jet image recording device - Google Patents

Abstract

PURPOSE:To exceptionally improve the reproducibility for color tone and mean density as well as transient response characteristics, by a method wherein ink is jetted out from a nozzle by the static stress according to an impressed voltage. CONSTITUTION:Static stress is used to jet ink from a nozzle onto a recording medium, thereby an image is recorded. The static stress, in that case, is applied to the recording medium according to the voltage to be impressed between the ink pressed by the static pressure in the nozzle and the recording medium moving and scanning an image. Plurality of nozzles are arranged in the vertical direction along the vertical scanning direction for the recording medium so that the ink in the nozzle are pressed by different static pressure respectively and jetted alomost on the same position of the recording medium. Stringiness of ink is used effectively for this recording device, and the continuous change of the stringing flow is correctly followed by, which results in faithful reproducing the depth of the image. In addition, the device is made with low cost and with less noise.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized in that the ink is removed from all nozzles by electrostatic stress in accordance with the voltage applied between the ink that receives static pressure in the nozzle and the recording medium that moves and scans the screen. Regarding an inkjet image recording device that records an image* by ejecting it and depositing it on a recording medium, in particular, the gradation reproducibility of the recorded image is significantly improved, and the average density and transient response characteristics are also improved. This is how it was done.

In general, ink ejected from a nozzle by Coulomb force generated by applying a high voltage to ink with a high electric current rate adheres to the recording paper in the form of a thread-like pillar, or string T, as shown in Figure 181. nm by fully utilizing the stringiness of inkjet to form ink dots that are much finer than the nozzle diameter.
Conventionally, electric induction type inkjet recording apparatuses capable of recording gradation images*' with good quality have been widely used for image recording in facsimiles and the like. However, in this type of conventional image recording apparatus, the density dynamic range of the density image recorded is extremely narrow due to changes in the thread flow rate of the ink due to changes in the image signal level of the applied high voltage, resulting in poor fidelity. Due to these drawbacks, conventional methods have only been put to practical use in recording black-and-white λ-value images, but have not been put to practical use in recording general images with intermediate gradations.

The purpose of the present invention is to eliminate the above-mentioned conventional drawbacks, and to skillfully utilize the stringiness of the ink by jetting ink all around the nozzle with a simple configuration, without impairing the continuous change in the string flow rate. An object of the present invention is to provide an inkjet image recording device 1'i which is inexpensive, produces little noise, and is suitable for practical use, and is capable of faithfully reproducing the shading of an image.

That is, in the jet image recording apparatus of the present invention, the ink is moved to the surface by electrostatic stress according to the voltage applied between the ink that has received static pressure in the nozzle and the recording medium that moves and scans the screen tube. In an inkjet image recording device that records an image *Vr- by ejecting it from a nozzle and depositing it on the recording medium, the ink is arranged vertically along the vertical scanning direction of the screen, and the ink has a different static pressure 1.
The water is sprayed from multiple nozzles that receive the water.
The invention is characterized in that the ink is deposited on substantially the same position on the recording medium.

In the following, the invention will be described in detail by way of example embodiments with reference to the drawings.

As mentioned above, this type of inkjet image recording device is known for its nozzle diameter. . Although it has significant practical advantages, such as being able to record all the minute ink dots, and requiring no ink pressure mechanism or circulation system, it does have the serious disadvantage of lacking gradation reproducibility. Therefore, in order to achieve the above-mentioned object of the present invention, we will first conduct a detailed study on the essence of electrostatic attraction type inkjet recording, clarify the problems, and develop this type of image recording using various configurations. We attempted to solve the nine problems described above regarding the device.

Generally, inkjet recording apparatuses are broadly classified into two types.

(a) Apply low pressure to the ink and use electrostatic stress to generate a recording frequency of approximately KHz) 1-Low pressure electrostatic attraction type cb for recording > Apply medium pressure to the ink to cause vibrations in the inkjet, Recording frequency to KHz Medium pressure repetitive type that records dot rows at 8 degrees There is a non-on-demand type that is aimed at

(C) A high-pressure jetting type that applies high pressure to the ink and jets it at a recording frequency of about -00 KHz) 1-High-pressure jetting type that records However, for any type of inkjet recording device, in order to give a recorded image gradation, , the following means are generally used.

(The particle diameter of the ink dots to be recorded? Dynamically changes depending on the image signal level.)

(2) The recording density is controlled until t, with the particle size of the ink dots being recorded constant.

When recording images using inkjet, consider the reproducibility of the recorded image, the recording speed, and the scale of the recording device configuration.
A means suitable for the purpose must be selected, but among the above-mentioned runner-type inkjet recording devices, (a) low-pressure electrostatic attraction type has the above-mentioned remarkable advantages, as well as the fact that the ink-jet mechanism is simple. Up1: Since it can be made into a small device, it is suitable for practical use as a facsimile recording device, but it seems that no attempt has been made to improve the gradation of recorded images with this inkjet recording device.

The present inventors have discovered that the series I! that natural paintings have! As a means of reproducing 2w1pi, we focused on the remarkable stringiness exhibited by inks using organic solvents, and we hope that such remarkable stringiness can significantly improve the gradation reproducibility of electrostatic attraction type inkjet image recording. We configured an inkjet F apparatus using the following methods, and examined in detail the printing results of images with intermediate gradations by changing the ink thread flow rate, that is, the thread volume, according to the image signal level, and at the beginning. Various problems arose, namely, the dynamic range of tone reproduction was insufficient, the recording density changed depending on the continuous recording length, the thread formation was accompanied by a hysteresis phenomenon, and the transient response of the ink was poor. Problem 11, such as sufficiency, etc., as detailed below, were solved and an inkjet image recording apparatus n having the desired performance 1 could be realized.

First, the physical configuration of the inkjet image recording apparatus according to the present invention used in the above study will be explained. Generally, as an image recording apparatus, (1) a pixel type (II) in which pixels are formed by a dot matrix; A character type (ill) in which a unit image part is formed in advance like a writer.A vector type screen that forms an image as a set of line segments each given a direction and length.For example, a V screen is created by scanning the screen in both vertical and horizontal directions. Picture l1K
- Although there are 4IS types of scanning type to form, an enlarged OV) scanning type was used as the inkjet image recording apparatus of the present invention, and it was basically configured as shown in FIG.

In the basic configuration shown in FIG. to perform sub-scanning intermittently. Through such rotation and movement, the drum that forms the entire screen/recording paper on top is formed, for example, in the shape of a disc with a central opening, and through nine signal electrodes, nozzles for ink jetting are placed facing each other, and the nozzles are filled in the reservoir 1. Supply ink with static pressure applied. The nozzle j has an inner diameter ψ1, for example.
The size is 300μ and the outer diameter is 1! It is constructed using a stainless steel injection needle with a diameter of 00μ, and its tip #ii' is cut at an elevation angle of 300 with respect to the center angle, so as to obtain the best threadability when ink is jetted. A nozzle shaped like that! The ink meniscus at the tip of, i.e.
For example, in order to form a semicircular convex (concave) liquid surface, static pressure corresponding to the high level of the ink liquid level in the reservoir 6 is used. As the ink, an oil-based or non-aqueous ink having a low conductivity and a high dielectric constant is used, which is prepared by dissolving an arbitrary dye that can be dissolved in an oil-based organic solvent such as kerosene in the oil-based organic solvent. Examples of such oil-based inks are shown in Table 1pJj.

Table 1 Also, the recording paper to which such oil-based ink is sprayed and adhered is loaded onto a drum L having an outer diameter of φo1r70 as, for example, and from the aspect of the drum /++a wind air W! a
t-separated, for example, center opening diameter l, outer diameter! Separated signal electrodes 4! − is placed, and from the signal electrode μ, further,
Air gap length λ = koJmvpr sky! The nozzle I mentioned above! Place the tip of the The oil-based ink in the nozzle j has the maximum density f of the recorded image! A DC bias voltage Vbf sufficient to obtain 1 is applied by the bias power supply 7, and the drum is grounded to serve as a reference potential.

On the other hand, a signal voltage vst representing the image tube to be recorded is applied to the signal electrode G, and the nozzle! A differential voltage vb-v is applied between the oil-based ink and the signal electrode in the television camera r.
2>' - A digital signal formed by supplying the image pickup output image signal from the controller via the controller, or by processing the 1liil & signal system in the microcomputer 11 which supplied the reproduced output image signal from the disk memory IO. The signal is supplied to the signal voltage source/3 through the Guishitaru analog converter, and the analog image signal and voltage sound in the voltage range necessary to record the required starvation range on the image are formed and connected to the signal electrodes. Supply to Hiroshi.

In addition, the synchronous motor λ, which rotates the drum l and performs main scanning, generates a pulse train generated by a pulse generator with a variable repetition rate, which is synchronously controlled by the synchronous component of the standstill signal from the microcoscipulator. , a step motor 3 which is supplied and driven via a phase shifter/driver/j' and which moves the drum/l in steps in the direction of the rotating shaft to perform sub-scanning. The image signal is supplied and driven through the synchronized public money, phase shifter /6 and driver /7f sequentially.

Note that the digital image signal formed by the microcomputer// corresponds approximately to seven fields of the television image signal. 2j6 X ujj pixels,
It is configured in the form of a digital image signal of r bits per pixel.

Using the sound of an inkjet recording device with the basic configuration described above, we investigated the characteristics of intermediate RJII tone reproduction in inkjet image recording, clarified the problems, and tried to solve the problems as detailed below. With this in mind, we have achieved the present invention.

Therefore, when considering the reproducibility of halftone images by modulating the flow rate of the string formed by jetting ink, that is, the volume of the string, there are two methods for producing gradations using a string of jetted ink. There are the following five types.

(a) Change the signal voltage v15 applied to the signal electrode≠ or the bias voltage vb applied to the ink in the nozzle.

(b) Spray ink onto the recording paper at approximately the same location overlappingly.

(C) Changing the static pressure applied to the ink within the nozzle.

(d) Appropriately switching and ejecting a plurality of Class 11I inks with different concentrations to deposit them on the recording paper.

(e) A plurality of nozzles with different diameters are appropriately switched and used for ink ejection.

However, the change in static pressure (C) is equal to the fluid pressure 1
1Avr, it is difficult to follow the change in thread volume, and (d
) The use of different density inks tends to cause changes in the ink chamber over time, and the degree of change differs depending on the trowel, making gradation reproducibility unstable. Each of them has drawbacks such as easy clogging of the nozzle, etc. Therefore, in the present invention, gradation is reproduced by (a) changing the ink ejection attraction voltage and (b) overlapping scanning with the ejected ink. did.

First, (a) When considering the gradation reproducibility due to changes in the ink ejection induced voltage, the aforementioned aperture φ = 300μ−
Kinematic viscosity coefficient ν=6 x 10− in the nozzle capillary of
6g”/s f) (y Ri(2) Flow velocity v, f O,
/ ta/B, the Raynozzle number Re = v4 #1/ν, which determines the type of fluid flow, is 2 g degrees and can be considered as laminar flow, so the thread flow rate W is determined by the pressure at both ends of the tube length. If the difference ΔP is the difference between ΔP and the fluid density is ρ, then W = πφ1・ΔP/128ν・ρ・L (1), and if the static pressure and surface tension of the nozzle tube population are constant, the electrostatic attraction force that determines the differential pressure Δpv , Therefore, the ink ejection induced voltage and the string flow rate W have a proportional relationship, and the string volume that determines the recording density for gradation reproduction is determined by the difference Vb- between the induced voltage, that is, the bias voltage vb and the signal voltage v8. It will change in proportion to Vs. On the other hand, in order to fully initiate the spray PA of the ejected ink, it is necessary to apply an induced voltage to the tip opening of the nozzle that is sufficient to make the convex (concave) liquid surface, that is, the meniscus, formed by the surface tension of the ink, unstable. Therefore, the voltage range of the induced differential voltage Vb-v required for gradation reproduction recording is measured as the static pressure H applied to the ink as /jms+mu. Voltage -, 0 KVS Also, the voltage at which transition to ink atomization, which constitutes the upper limit of continuous recording by stringing, starts was 4 KV. Therefore, the bias voltage Vbf corresponding to the maximum recording density is 2. j KV, and it is preferable to select a signal voltage in the range of vsfO to 600 V to obtain the differential voltage Vb-V8f.

Duty ratio j as signal voltage in this signal voltage range
Pulse response characteristics of inkjet recording when applying a λ value pulse voltage of 0% Total frequency f = 0.1 ~
In an example of a recorded image as a result of examination in the range of 6 KHz, line segment-shaped dots are almost well recorded up to the value of the pulse repetition frequency f of approximately 6 KHz, and the resolution F of this recorded image varies depending on the drum rotation. The number 'if J&Orpm is approximately 3 pixels/I1wL, but depending on the actual halftone image signal, continuous recording is performed by the thread of ejected ink and natural interpolation between pixels is performed, so the resolution in the main scanning direction is much improved compared to the example recorded image.

Note that the state of string formation of the jetted ink is easily affected by changes in the rotation speed of the recording drum, but when the rotation speed exceeds 4 rpm, the time delay in cutting the ink string becomes noticeable. This results in a decrease in resolution.

Next, FIG. 3 shows an example of a recorded image when a gray scale is recorded by threading the ejected ink while changing the signal voltage v8 with the ink static pressure H=/j wryam1 and the bias voltage vb constant. The figure shows the recording speed when the DC signal voltage v, '(ioo - zoov) is varied, and there is a tendency for density saturation to occur for signal voltages below 10OV. However, this density saturation seems to be mainly due to the penetration of the ink adhering to the recording paper.In other words, since the recording paper is an aggregate of cellulose fibers and has a porous structure, it is difficult to fill the gaps between the fibers. When the ink permeates and diffuses and the density increases, the recording density is averaged and the ink coverage increases.
#This is because it is no longer proportional to the amount. On the other hand, in the case of a recorded image with a signal voltage v8 in a region exceeding 5OOv, the electrostatic attraction of the ink jetting is too weak, so the jetted ink exhibits a tendency to become discrete and the recorded image becomes fine particles, and the lower limit of low density recording is arise. Incidentally, the frequency of such atomization was determined by the applied voltage value regardless of the frequency of the signal voltage, and was in the range of -00 to 7jOHz. On the other hand, in the recorded image when the pulse train signal voltage vs is changed with the repetition frequency f = i,r KHz constant, the lower limit of low density recording mentioned above increases by about -230V, and this tendency is reflected in the pulse train Repetition frequency f of signal voltage v8
This becomes noticeable as the number increases, and the continuous recording by the string and the above-mentioned atomized recording strangely coexist on the same scanning line, indicating that string formation by ink jetting is in an unstable state.

From the above study results, (a) the range of recording density that can be obtained by tone reproduction only by changing the ink ejection induced voltage, that is, by modulating only the string flow rate, is narrow, and the frequency of the signal voltage At the moment when the reproducible density range changes and the string flow rate changes (L), inkjet recording is performed at 11 different densities than in the steady state, so the actual halftone image*V will not be in good condition. It has become clear that modulation of the ink ejection induced voltage by an image signal alone is insufficient for recording.

Therefore, in the present invention, in order to improve the above-mentioned gradation reproducibility by using (b) redundant scanning using ejected ink, the following study was conducted regarding the effects of redundant recording performed by such redundant scanning. 9.

However, since the recording density resulting from overlapping recording of ejected ink is due to so-called subtractive color mixing, it is possible to increase the density through overlapping recording.
Assuming that the number of gradation levels to be reproduced by changing the level of is in, the number of gradation levels GL that can be expressed is given by the following combination (
2) is expressed by the formula, GL = n+m -10,m (
2) For example, multiplicity m-λ, required number of gradation levels n =
When j, the number of expressible gradation levels GL = f
becomes j. The recorded density g obtained by such two duplicate recordings is:
Let the recording density of each time be tl, fj (1, j = θ ~ l),
For simplicity, we use subtractive color mixture F)Cti, fj)2δ(f
l + fj), and if the inclusion coefficient δ is 0≦δ≦l in the same color mixture, then as t and f standards, to= aoFl , 12 = a2P1
.

fs-&sJ, f4 = a4f1 concentration coefficient a
If □-a4 is set, ao'' (7) becomes, and the values of the right diagonal components, for example, core a5 and a2+a4, are close to each other, and each element of the matrix has no equivalent pair, and the difference has a biased shift. Since it is difficult to select density coefficients that do not have a density coefficient, according to equation (3), GL < n + 111-10 m, and the number of expressible gradation levels GL is calculated from the above GL = /! Then, if the recording density is different by 1 each time in repeated recording, and βt - the number of feet, then (1 soil, βri) = δ
When (/+β)21, the overlap recording density Ill becomes only the left diagonal component, and the near iM between each matrix vX disappears, and the S degree range of the overlap recording is 0~δ(/+β) in equation (4) from θ~a4ft
Changes to a 4 t 1. Therefore, the gradation reproducibility can be improved by overlapping recording in which a density difference is given each time, and the decrease in recording speed due to an increase in the overlapping degree m can be avoided by using a plurality of nozzles in combination.

On the other hand, if overlapping recording is performed without reducing the recording speed, the ink of the subsequent recording will not be able to adhere before the ink of the preceding recording dries, causing severe mutual interference other than simple density overlap. Therefore, it is difficult to quantify the concentration coefficient 5L□""a4.

In addition, in overlapping recording with such a density difference, only the ink solvent [the nozzles that eject normal ink are placed on the same scanning line and the overlapping recording by those nozzles is actively utilized; K can also be used to record ink dots of extremely low density. Such overlapping recording in which only solvent is ejected can be effectively used to solve the problem of changes over time in the relative density values between inks that occur when overlapping recording is performed by ejecting ink of multiple concentrations. The penetration of the recording paper mentioned above,
Since the recorded dots smear significantly due to diffusion, the resolution is degraded. However, the lower the density, the lower the visual sensitivity and the harder it becomes to discern the edges of the image, so there is no substantial deterioration in resolution.

Note that the overlapping time td expressed as the time interval of overlapping recording or delay time is the rotational speed Nr, In of the drum l, and the outer diameter φゎ, iIL? i6 recording frequency f,. Regarding the nozzle interval d, when a single nozzle is used, td=60/N, and when a plurality of nozzles are used in combination, the following equation (5) is obtained, as described later.

td (6o/Nπ) 5in-" d/φD (5) Therefore, this overlap time is calculated as td- for each value td mentioned above.
By varying it within the range of td±/2fmaX, various degrees of overlapping recording can be performed on the same recording dot, between recording dots, and in an intermediate state between them.

In the present invention, in connection with the recording density range obtained by the above-mentioned overlapping recording, the following study was further conducted regarding the effect of ink static pressure in inkjet recording.

Therefore, in electrostatic attraction type inkjet recording, the range of ink static pressure H in which the ejected ink becomes a string state is R=j
- Regarding Osm* system 9, as the ink static pressure is gradually lowered to H1, the atomized region of the recorded dots becomes narrower, and Q
In the range of <H<j>A9, the recording density can be reduced without causing any atomization of recording dots;
Therefore, it has become clear that there is a threshold value as the lower limit of the ejected ink stringing range, which becomes dangerous. That is, under the above-mentioned low static pressure state, it is possible to perform good continuous recording with the string over the entire signal voltage range from the starting point of flight due to electrostatic attraction to the area where conventionally atomized particles are formed. The reason for the disappearance of the recording dot atomization region is that in a weak attractive electric field, the electrostatic attraction force is not sufficient to sustain the entire string, and the meniscus, or ink liquid, at the nozzle opening cannot be obtained. Since the change in surface shape and the movement of charge to the ink tip have a time constant of 1, the ejected ink periodically flies intermittently and the recorded dots become fine particles, but the ink static pressure is extremely high. If it is low, the ink liquid level at the jet opening does not become a convex surface, so that the above-mentioned drawing-in phenomenon based on the time constant does not occur when an attractive voltage is applied, and it is recognized that recording dots do not become fine particles.

In view of the above-mentioned study results, the inkjet recording apparatus of the present invention can perform excellent continuous recording by strings over a wide signal voltage range by varying the ink static pressure in multiple nozzles that perform overlapping recording. It is now possible to record halftone images with different gradation characteristics. Examples of the configuration of such an apparatus of the present invention are shown in FIGS. 3(a) and 3(b), respectively. In the illustrated configuration example, for the sake of simplicity, duplicate records 1
Assuming that there are two nozzles t- and those two nozzles j-/
and J-coupler are arranged opposite to each other on the same scanning line on the drum with an interval d = 10 sis f, and are connected to the same ink laser, so that the ink in each nozzle has a different ink static pressure. It is intended to be received.

In addition, at that time, the nozzle placed on the upper side! The configuration is such that the ink static pressure H within -/ is always maintained within the range of '<H<j wimAq. With respect to the inkjet recording mechanism having such a configuration and arrangement, in FIG. μ(a), the superimposed voltage of the bias voltage vb and the signal voltage Vs is determined for all prefecture nozzles j-1. '! In Figure Cb), a bias voltage vbt is applied to the ink lIr in the reservoir 6, and a signal voltage Vsf is applied to each nozzle! −
/and! -Signal electrodes arranged opposite to each other at λ-/
and is applied to λ. That is, Fig. μ(a)
, (b), the input digital image signal is converted into an analog-image signal by the digital-to-analog converter, and then the lower nozzle! -λ is directly supplied to the signal voltage generator /3 belonging to the upper nozzle! -/ to signal voltage generators /3-7 belonging to J-/, and adjust the respective voltages to appropriate voltage values. The signal voltage vst from - is supplied to the bias voltage generators 7-7 and 7-- to generate the above-mentioned induced voltages Vb-v, y for each nozzle 1/and! --Apply n to each ink at the gate,
In addition, in @+ figure (b), each signal voltage generator 13
- The signal voltages from / and 13-4 are applied to the aforementioned signal electrodes /)' - and /4 (-, respectively, and the bias voltage vb from bias voltage generator 7 is independently set.) Apply the ink in the reservoir,
The bias voltage vb is commonly applied to the ink in each nozzle 1t-i and 1t-x.

Therefore, when considering the advantages and disadvantages of the configuration examples shown in Figures (a) and (b) in terms of crosstalk between both recording dots, in the configuration example shown in Figure (a), each nozzle/! -/, /j-λ The currents corresponding to the differences based on the delay time tdK of the superimposed voltages applied to the inks respectively flow between them via the ink in the reservoir 6, so that the signal voltages v8 are connected to each other. The configuration example shown in FIG. 4B, in which the voltage is applied to the opposing electrodes and dark electrodes independently, is more advantageous. Furthermore, in the configuration example shown in (&) in the same figure, when the drum/recording paper on the drum rises above the drum surface, the induced voltage no longer corresponds faithfully to the signal voltage; There is an advantage that the potential gradient lt' between the nozzle and the signal electrode can be kept constant against floating of the recording paper.

Note that the delay time corresponding to the nozzle interval d in the configuration example shown in FIGS.
) When tl=IOm scales are used in the above-mentioned numerical sequence, td=7.6 mm.

According to the present invention, as described above, by overlapping printing using several nozzles with different static ink pressures, the relative gradation characteristics of printing density in inkjet printing can be significantly improved compared to conventional methods. As for the absolute value of recording density, there is generally a significant difference compared to other recording methods, as described below. Therefore, in the present invention, the following study was conducted regarding improvement of nine density bands including the absolute level of recording density by inkjet recording.

In general, for image signals such as television signals, interlaced scanning with an interlace ratio of λ:l is generally applied to improve the resolution and resolution characteristics.
However, even when recording image signals with this configuration based on ink frequently used in facsimile machines, interlaced scanning is not performed, and the image is recorded using image signals for 1 field. It is common to express this in rows.

Therefore, the visual absolute density of the recorded image is 1 of the ink itself.
It is not determined only by 11 degrees, but is determined by the average reflection density of the recorded area, blank area, and gold, and the area ratio of the recorded area in conventional inkjet recording is only about 0 slag λ.

Therefore, in order to improve the visual absolute density, that is, the density band characteristics of inkjet recording, it is extremely effective to perform interpolation in the sub-scanning direction of the facsimile image. Let me o
, r≠, the reflection density between the recorded area and the blank area increases significantly.

Therefore, a natural image with an intermediate level plt is represented by the brightness difference of neighboring m elements and an exponential characteristic whose histogram has a peak at zero, and the difference between the seventh-order entropy and the second-order entropy of density is small. , regarding interpolation in the next scanning direction targeting only adjacent pixels,
The linear seventh-order concentration prediction value f(1, j
) is generally expressed by the following equation (6).

Here, f(1,j) ” is the observed density value, Wk, z: correction coefficient, K/L: distance between images.On the other hand, as mentioned above, facsimile images are composed only of the / field, so There is no adjacent information in the scanning direction, so the above-mentioned property (6) cannot be applied as is to density prediction.

Therefore, in the present invention, the following two types of interpolation (mu) are used.
And try (B)9.

Interpolation (mu): Specifically, interpolation is performed in the p sub-scanning direction using the configuration shown in FIG. ' by the neighboring 6 pixels to the next (7
) expression.

+f(1+1,j-1)10F(soil+1.j+1))/
4 Using the above equation (7), for example, for an actual image as described later with reference to FIG. 7, the average error power ε2− is
.

The correction coefficient Wt that minimizes IC((f(1,ko>-r(1,j)2)k) is calculated, the average error ε2, the signal-to-noise ratio s/Mt-, and the results are shown in Table 2 (a ).

Interpolation (B): Specifically, interpolation is performed in the sub-scanning direction using the configuration shown in Figure 1), and the predicted density value f(1,j) at point (i,j) is The following equation (8) is used to solve the problem using the number of pixels.

f (i, j) = r -9 (8) The above equation (Table 2 shows the values obtained in the same manner as described above for interpolation (A) using 8).

wJ 2 @ (a) In addition, images * (mu) and (B) in Table 2 (a) and (b) are facsimile test charts and Ko value iii images made by natural self-indulgence as shown in Figure 97. This is a very different weather map, and both images are KiI prime numbers 2j6X and 2jA.

In addition, in the above-mentioned interpolation (A), the 1iji vote density in the sub-scanning direction is doubled, and the pixel interval ratio in the horizontal direction/diagonal direction is '/(K). (B)
In this case, the interpolation pixel is shifted by a half-picture interval to the 11th place, but since the number of reference pixels is smaller than in interpolation (mu), some deterioration of S/N is observed. Furthermore, in both interpolation (MU) and (B), the prediction residuals associated with linear prediction were significant. As a countermeasure, it may be possible to divide the image gR frame into small regions so that the variance of the local correlation coefficient is small, and to obtain the correction coefficient V value for each small region, but this would be extremely complicated.

Considering all of the above, in interpolation (B), a meandering scan is applied in which a single nozzle is used and two scanning lines are processed at once by applying an electric field deflection t to the thread of the ejected ink. Interpolation (B)
' It is suitable to adopt it.

Furthermore, in the present invention, in addition to improving the P characteristics and density band characteristics in inkjet recording as described above, the following studies were conducted regarding improvement of transient response characteristics.

In the inkjet image recording apparatus of the present invention,
When recording a facsimile image using the configuration shown in a) and (b), an original image is captured, an analog image signal is formed by photoelectric conversion, and a digital WJgI is generated by performing analog-to-digital conversion. Inkjet recording in the manner described above is performed using signal processing mtmL nine appropriate signal processing signals as input image signals of the recording apparatus of the present invention. The density information possessed by the printer is not reproduced line-by-line accurately in the facsimile recorded image. Therefore, in an inkjet recording system within the scope of the present invention, when considering compensation for the deterioration of the transient response characteristics of the recording device due to the continuity of fluid due to the string of ejected ink, it is found that There is a delay in response, and the recording density may follow sudden changes in signal level at edge portions of the image, reducing the sharpness of the image contour. Now, the pixel density f(X, t)1 at position X in the main scanning direction and time tK is given by t(x+0
), and 2(”+
), then the following relationship in equation (9) holds true.

r(x, o) = r(x, 仝)−η・仝−V”−r(
x, 仝) (9) Here, 1η is a positive number.

Depending on the sign of the value of this equation (10), the record j! expressed by equation (9)! Since the density change characteristics of jS are fixed, it is possible to effectively modify the transient response characteristics of the inkjet recording system.

On the other hand, in the thread volume modulation of ejected ink, when the density changes from the black level to the white level, the density change from the white level to the black level that crosses the thread lower limit critical point is due to the density change due to the hysteresis phenomenon. Since a delay occurs, if compensation by overshoot is performed in such a case, the deviation in density change will further increase, and it is also necessary to prevent the recorded density after compensation from exceeding a permissible range.

Taking all the above into consideration, the limiting condition to be attached to the compensation for the deterioration of the transient response characteristic of yarn volume modulation is X11f
It is preferable to write the soil as K, and then install the power as shown in the diagram.

(1) (f(1-1, 仝)<θf)n(r(i,Q+
>a')n(f(i-1,Q-f<1.仝))〈θf)
When o: V2f□(,仝) = O(1)(f, x
Cold, -η・仝−v″x′(X,仝〈θ〇)
'(X, 0)=01 Also, 1.1 open U, j58-674e7(1o:+(P(X,
-η・Rei・V” y △t′x tx, t)ma
When x: f(x, O) = ”max (ill) (f(1-1, Q, ≦θy) n(t, ,
, , 仝,≦θy) Nod S: "x'(X, 仝, =.

(IVI and other cases, follow formula 9).

Here, θyFi is the lower critical concentration of the thread, and θ
f represents the density gradient for completely canceling the above-mentioned running condition for the λ value image. An example of a concentration cross-section when the compensation for the transient response characteristic is applied to the central part of the above-mentioned image (m) is shown in FIGS. 6(a) and 6(b). The figure (a) shows the state before compensation, and the figure (b) shows the parameters η and 01, respectively. A and 3j, and a state M is shown in which compensation is applied by making mata and θW correspond to v8=too y. The incidence of the need to provide such compensation was 6.3% and 3% for each of the above-mentioned limiting conditions (1), (it), and (1), respectively.

No. 7513 shows an example of an inkjet recording of the above-mentioned image (A) using the configuration shown in No. 7 with various improvements according to the present invention described above (detailed).

As is clear from the above description, according to the present invention, various problems such as poor gradation characteristics in conventional inkjet recording, particularly poor reproduction in low density areas, insufficient density bands, poor transient response, and hysteresis phenomena, can be solved. By solving this problem, it is possible to significantly improve various characteristics of inkjet recorded images, including gradation characteristics, compared to conventional methods. The overlapping recording using multiple nozzles enables good continuous recording over a wide density range, and also increases the average density range and improves transient response characteristics. It is possible to achieve good surface inkjet recording performance.

[Brief explanation of drawings]

@ Figure 1 is a microscopic projection diagram showing an example of a spun string of ejected ink, Figure 2 is a block diagram showing the basic configuration of the inkjet image recording apparatus of the present invention, and jRJlglI is the image recorded by the gray scale DC signal voltage. Figures (a) and Φ) are block diagrams showing examples of the configuration of the inkjet recording system, and Figure 83 is a block diagram showing an example of the interpolation mode. FIG. 6 is a perspective view showing an example of the density cross section of the recorded image before and after the improvement of the transient response characteristic, and FIG. 7 is a photograph showing the oscilloscope waveform of the recorded image. l...Drum, K...Synchronous motor, 3...Step motor, ≠, See-7. N-2...Signal electrode, j, j
-/, j-2... Nozzle, 6... Reservoir, 7.7
-/, 7-co...bias power supply (bias voltage generator), l...television camera, r...controller, 10...disk memory, l/...microcomputer, 7.2 ...Digital-to-analog converter, /J, /J-/, lj-co...Signal voltage source (
signal voltage generator), / to... pulse generator, l
j... Phase shifter and driver, /6... Phase shifter, 17.
...Driver, /I...Ink. Fig. 3 1) Fig. 7r''4 Fig. 1i Fig. 5' ” c b

Claims (1)

[Claims] 1. The ink is ejected from the nozzle by electrostatic stress according to a voltage applied between the ink that receives static pressure in the nozzle and a recording medium that moves to scan the screen. In an inkjet image recording device that records a third image by depositing the ink on the recording medium, the ink is arranged vertically along the vertical scanning direction of the screen so that the ink receives different static pressures. An inkjet image recording apparatus characterized in that all of the ink ejected from a plurality of nozzles is deposited on substantially the same position on the recording medium. 2. In the image recording apparatus according to claim 1, a required DC voltage is applied to the ink with respect to a reference potential of the recording medium, and the nozzle and the front 1 sei
5. An image signal voltage representing the image 1r to be recorded is applied to a signal electrode placed between the recording medium and the recording medium.1
-Characteristic inkjet image recording device. 3. In the image recording apparatus according to claim wJ1, a weight voltage of a required DC voltage and an image signal voltage representing an image to be recorded is applied to the ink with respect to a reference potential of the recording medium. An inkjet image recording device that measures t-% of the amount of water that has been applied. 4. The image recording device according to claim 92 or 93, characterized in that interpolation of the image signal is performed in sub-scanning performed in a direction intersecting the vertical scanning direction of the screen. Inkjet image recording device. 5. The image recording device according to claim 2, 3, or 4, characterized in that the image signal is subjected to Labracian calculation processing in the vertical direction. Inkjet image recording device.