JP2003136701A - Ink jet recorder and its image correcting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform correction appropriately when ejection of ink from a recording head is reduced or stopped due to various causes. SOLUTION: A plurality of shading patterns having different duties are recorded, a nozzle ejection of ink therefrom is reduced or stopped due to increase of channel resistance is judged from the difference of density distribution, and correction processing is performed differently depending on the state of the nozzle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a characteristic peculiar to each recording head in an ink jet recording method in which ink dots are formed on a recording medium by ejecting ink to form an image. The present invention relates to a correction method to be applied to a discharge failure.

[0002]

2. Description of the Related Art With the spread of copiers, word processors, information processing equipment such as computers, and communication equipment, an ink jet type recording head is used as one of image forming (recording) equipment of these equipment. Digital image recognition is rapidly becoming widespread. Also,
Along with the high quality and colorization of visual information in the above information equipment and communication equipment, there is an increasing demand for higher image quality and colorization in recording devices.

In such a recording apparatus, an ink ejection port and an ink ejection port are used as a recording head (hereinafter also referred to as a multi-head) in which a plurality of recording elements are arranged in an integrated manner in order to miniaturize pixels and increase the speed. It is common to use a plurality of liquid passages with a high density and to provide a plurality of multi-heads corresponding to each ink of cyan, magenta, yellow and black for further colorization. .

With this configuration, how to output a high-speed image at a high speed, a low cost, and a high quality image is one of the technological advances. Furthermore, in order to achieve higher speed,
A method in which the length of the multi-head is set to about the page width to be printed and high-speed output is performed in one pass is being implemented.

However, for example, when considering a page printer of A4 lateral feeding, the length of the multi-head becomes about 30 cm, which is 7000 in terms of 600 dpi.
The above nozzles are required. It is very difficult to manufacture a multi-head having a large number of nozzles without defects in terms of yield. Also, not all nozzles have the same performance due to the large number of nozzles. Further, there is a high possibility that some nozzles will stop ejecting ink during use.

Therefore, a head shading technique for correcting unevenness in the discharge amount of the nozzles and a density unevenness caused by a deviation (deviation) of the landing positions, and a complementary process for a non-ejection nozzle are performed so that the defect-free multi-head is not required. The technology of discharge failure complement which makes it possible to use has also been noted.

As a method of head shading, a predetermined pattern (for example, 50 dots arranged in a staggered pattern) is used.
% Duty pattern (hereinafter also referred to as a zigzag pattern) is printed, the density corresponding to each nozzle is measured, and the result is fed back to the input image data.

For example, when the ejection amount of a certain nozzle is small for some reason and the density of that portion is low, the gradation value of the portion corresponding to that nozzle in the input image is corrected so as to increase, The output image has a uniform image density.

Further, there is a technique for making an abnormal nozzle a nozzle having a smaller discharge amount than other nozzles, a nozzle having a large degree of deviation in the discharge direction, and a nozzle in a state in which discharge is impossible, and complementing this abnormal nozzle. Proposed. It should be noted that an abnormal nozzle may be simply called a non-ejection nozzle because it is treated as a nozzle that does not eject even if ejection is possible. Hereinafter, the technology for complementing the ejection failure nozzle to perform recording will be simply referred to as ejection failure complement.

[0010]

However, as described above, in the case of a long head having about 7,000 nozzles per head, for example, the flow path resistance of the ink flow path due to dust clogging or manufacturing failure may occur. In some cases, the refill characteristics may vary from nozzle to nozzle due to the increase in the nozzle.

If the actual recording conditions are lower than the refill characteristics of each nozzle, there is no particular problem, but if the refill characteristics of some nozzles are deteriorated and the characteristics are lower than the recording conditions, The amount of ink ejected from the nozzle may decrease, or in the worst case, no ink may be ejected from the nozzle. Hereinafter, this state will be referred to as "refill shortage failure discharge". However, the above-mentioned refill characteristics are difficult to discriminate from the nozzle check pattern for checking whether or not the nozzle is a non-ejection nozzle. Because this nozzle check pattern separates each nozzle from the surrounding nozzles and discharges independently, so when the flow path resistance due to dust increases, as schematically shown in FIG. Then, the ink is supplied from the surroundings of the dust, and it is indistinguishable from a normal nozzle.

As a result, in the low duty part,
Even if the effects of head shading and discharge failure complement can be sufficiently exerted, in a nozzle having poor refill characteristics, the effect cannot be exerted in the high duty portion. This is because even if an attempt is made to increase the density by performing head shading correction on a portion where the density is low because refill has not caught up (refill shortage failure), the number of recorded dots in that area is increased. The reason is that a substantially faster refill is required and, as a result, it has an adverse effect.

It is an object of the present invention to enable proper correction even if the flow path resistance of the ink flow path increases for some reason.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and uses a recording head in which a plurality of nozzles for ejecting ink are arranged to eject ink onto a recording medium. In an image correction method in an inkjet recording apparatus for recording an image, an output step of outputting at least two kinds of uniform patterns for measuring recording characteristics of a recording head, and a measurement step of measuring a density distribution of the output pattern And a calculation step of calculating, for each pattern type, data for performing correction for each of the plurality of nozzles based on the measurement result of the measurement step, and corresponding to each of the at least two types of patterns. Comparing the above-mentioned data, classifying the state of each of the plurality of nozzles into a plurality of types, and corresponding to each of the plurality of nozzles And a step of correcting the image according to the classified state type. The at least two types of patterns output by the output step are patterns having different recording duties. Different correction processing is performed.

Further, according to the present invention, the recording characteristics of the recording head are measured in an ink jet recording apparatus which records an image by ejecting ink onto a recording medium using a recording head in which a plurality of nozzles for ejecting ink are arranged. Pattern output means for outputting at least two types of uniform patterns, and data for performing correction corresponding to each of the plurality of nozzles based on the density distribution of the output pattern, the pattern type A calculation means for each of the patterns is compared with the data corresponding to each of the at least two types of patterns, the states of the plurality of nozzles are classified into a plurality of types, and the images corresponding to the plurality of nozzles are corrected. And at least two types of patterns output by the pattern output unit, respectively. A recording duty are different patterns patterns, the correction means is characterized by performing different correction processing depending on the classified state type.

As at least two types of shading patterns having different print duties, one is 50%.
The other is 50% or more, and is preferably set in consideration of the balance with the gradation value. Also, 2
It is also possible to use head shading patterns of three types and four types of print duty, such as 5%, 50%, 75%, and even 100%. As a result, more accurate information about the refill can be obtained.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The outline of the present invention is to record a plurality of shading patterns having different duties, and to judge the state of a nozzle that has decreased in ejection amount or has failed to eject from the difference in density distribution of each pattern. , To perform different correction processing depending on the state of the nozzle.

The reading of the head shading pattern is carried out by using an ordinary scanner, and it is desirable that the optical system has a resolution at least as high as the resolution of the recording head. This is because if the resolution of the reading optical system is too low, the read data becomes unnecessarily large and accurate feedback cannot be applied. The reading system may be installed in the printer online or offline, and is not particularly limited.

The value read by the scanner is converted into shading data for applying head shading, and head shading and discharge failure complement processing are performed based on this shading data. A difference between at least two types of shading data having different duties is calculated. If the shading data with the higher recording duty is larger than that with the lower recording duty (the shading data has the opposite sign to the density of the shading pattern), there is a possibility of insufficient refill discharge failure. If the difference is larger than a certain set value, it is determined that the nozzle is not refill insufficient and discharge failure. In addition, although the complete ejection failure nozzle determination is performed by setting a certain set value for the shading data, a separate nozzle check pattern is output,
The ejection failure nozzle may be specified.

In this way, at least three types of ejection failure nozzles, insufficient refill ejection failure nozzles, and normal nozzles are classified, and proper correction processing is applied to each. For normal nozzles, a coefficient for changing the gradation value of the input image is calculated based on the shading data, and correction is performed using this coefficient. Further, for the ejection failure nozzle, a correction method is determined from a table that is separately set according to the color and gradation value thereof and the number of consecutive ejection failure nozzles. For example, the discharge nozzle is independent,
When the gradation value is also low (bright), the correction is performed only by the nozzles on both sides, and when the ejection failure nozzles are continuous, the correction is also performed by using other colors. To do. Further, for the refill shortage / non-ejection nozzle, a gradation value that causes the refill shortage / non-ejection is set, and the processing is changed accordingly. If the gradation value is below the level at which insufficient refill occurs, the same correction processing as for normal nozzles is performed.
Above this, as in the case of the ejection failure nozzle correction, a table that is set separately is referenced to perform correction using another color. At this time, it is preferable to limit the gradation value to the nozzles that do not eject refill insufficiently so as not to exceed a certain limit value. By doing so, more of the original color can be used. In addition, by printing three or more types of shading patterns with different print duty and calculating the data, it is possible to know from which duty the refill insufficient ejection failure nozzle begins to occur, and it is possible to perform more detailed classification. Becomes

Embodiments of the present invention will be described in detail below with reference to the drawings.

In the embodiment described below, as a method of complementing ejection failure, for example, when a nozzle with cyan is not ejected, the dots to be ejected from that nozzle are replaced with the ejection from the nozzles on both sides. One of the methods is to use a method, or a method of compensating and supplementing data with ink dots of another color such as black in the portion corresponding to the cyan ejection failure nozzle.

In the present embodiment, a gradation image is output using a side shooter type thermal ink jet recording head in which a heater is arranged inside the nozzle and heat is generated by the heater to eject ink from the nozzle. The resolution (nozzle density) of this recording head is 600 dpi (dots).
per inch), the discharge amount is configured to be about 8 pl, and the number of nozzles arranged is 69.
12 and has a length (recording width) of about 293 mm. Cyan C Magenta M
A printer having a total of four units of yellow Y and black K was prototyped and an image was output. Also, the resolution of the output image is
This printer has a size of 600 × 600 dpi, and is a printer that performs so-called one-pass printing, in which a printing medium is conveyed to pass through a printing head fixed to the apparatus and printing is performed.

The C, M, Y and K inks used have physical properties such as a viscosity of 1.8 cps and a surface tension of 39 dy.
Various additives are adjusted to be approximately equal to n / cm, and the driving condition of the head is that the frequency is 8 kHz.
z, voltage 10 V, and applied pulse width 0.8 μs. By this drive, an ink droplet of about 8 pl is ejected at a speed of about 15 m / s.

FIG. 1 is a diagram showing the flow of data processing in the present embodiment. In FIG.
This is a portion for color-converting bit input image data into 8-bit CMYK 4-color image data, and processing such as γ conversion and enlargement / reduction is performed as necessary. A correction processing unit 2 embodying the present invention performs various corrections based on the shading data. Reference numeral 3 is a nozzle information holding unit in which shading data necessary for the correction processing of 2 is accumulated. An image processing unit 4 performs processing such as binarization. This bitmap data is sent to the head driver 5 and the head is driven according to the data to output an image.

In outputting the image, first, FIG.
The following three types of head shading patterns were output. These shading patterns 10 to 12 are
The patterns are recorded with a recording duty of 25%, 50%, and 100%, respectively, and the size thereof is 6912.
There are 256 pixels. In addition, a marker 13 is provided to correspond to the nozzle. This pattern was read by a scanner with an optical resolution of 1200 dpi to create shading data. The specific method of creating shading data is shown below. The 13 markers are provided to specify the nozzle number, and 28 markers are provided for every 256 nozzles. The image data read by the scanner is first divided for each color and converted into a gray scale that reflects the color density. In order to read the marker position from this grayscale data and convert it into data associated with the nozzle position, appropriate rotation and enlargement / reduction processing is performed. The density data associated with each nozzle is obtained by averaging 256 pixels for one nozzle (see FIG.
(A): d [i]), and an average value of three pixels including pixels on both sides is calculated (FIG. 3 (b): D [i] = {d [i-
1] + d [i] + d [i + 1]} / 3). Shading data (S [i] = {Ave-D) is obtained by dividing the difference between this value and the average density of the whole by this average value and multiplying by 100.
[i]} ÷ Ave × 100) (FIG. 3 (c)). In this way, the shading data S ₂₅ , S ₅₀ , and S ₁₀₀ of 25%, 50%, and 100% were obtained and stored in the nozzle information holding unit of 3. In this embodiment, this work is performed separately from the printer, but it is also possible to perform it online using a printer having a scanner function.

Next, the contents of the second correction processing section will be described. Prior to the correction process, three types of shading data are read for each nozzle, and it is determined whether the nozzle is a normal nozzle, an ejection failure nozzle, or a refill insufficient ejection failure nozzle (FIG. 4). This judgment method is shown below. First, recording duty 25
Based on the shading data of%, it is determined whether or not the nozzle is a discharge failure nozzle. This determination is made here by the discriminant of S ₂₅ [i]> 20, and if this is true, the ejection failure nozzle (Nozzle [i]
= 1). Next, the shading data with a print duty of 50% is used to determine the refill insufficient ejection failure nozzle. This is performed by the discriminant equation of S ₅₀ [i] −S ₂₅ [i]> 10. If this value is true, it is determined that the refill insufficient ejection failure nozzle at 50% (Nozzle [i] = 2). Similarly, from 100% shading data, S ₁₀₀ [i]
-S ₂₅ [i]> 10 is used to determine the refill insufficient ejection nozzle (Nozzle [i] = 3) in 100% recording. In this way, for all nozzles, the nozzle state is normal nozzle (Nozzle [i] = 0), non-ejection nozzle, 50% refill shortage non-ejection nozzle, or 100% refill shortage non-ejection nozzle. Is determined, and the correction process is performed using this result. FIG. 5 shows this correction processing, and the processing for cyan will be described with reference to this drawing. First, the image data is read, and the corresponding nozzle state determination result is referred to. According to this result, the following processes (1) to (4) are performed.

(1) In case of normal nozzle (Nozzle [i] =
0) If the nozzle is normal, general shading correction processing is performed. In this embodiment, 25 is applied to all gradation values.
The shading correction was performed using the% shading data S ₂₅ [i], but referring to the gradation value of the image data, S ₂₅ [i], S ₅₀ [i], and S ₁₀₀ [i] are used properly. May be. The correction formula used here is C ′ [i] = {1 + S ₂₅ [i]
÷ 100} × C [i].

(2) In the case of a discharge failure nozzle (Nozzle [i] =
1) If it is a non-ejection nozzle, check whether the nozzles on both sides are also non-ejection nozzles. Therefore, the discharge failure complement table is selected to refer to whether the number of continuous discharge failure nozzles (BNC) is 1, 2, or 3, that is, single discharge failure, 2 continuous discharge failures, or 3 or more continuous discharge failures. The black discharge failure complement table for cyan used here is shown in FIG. According to this table, the data is added to the corresponding position of black (B '[i] = B [i] + C_K _BNC [C [i]]) and the cyan data is deleted (C [i] = 0). . However, this cyan data erasure is not indispensable because any data cannot be recorded from that nozzle.

(3) Insufficient discharge of 50% refill (No
zzle [i] = 2) In the case of 50% refill insufficient ejection failure, first, the continuity is evaluated as in the ejection failure nozzle. According to the value, the black complement table for the ejection failure nozzle is referred to, and the data is added to the corresponding position of black. However, the difference from the case of the discharge failure nozzle is a coefficient k ₅₀ as shown below.
Is the point that is hanging. B ′ [i] = B [i] + k ₅₀ × C_K _BNC [C [i]] k ₅₀ = 0: C [i] ÷ 255 <5 ÷ 100 (image data value: less than 25%) k ₅₀ = (C [i] ÷ 255-0.25) × 0.8 ÷ 0.25: 25 ÷ 100 ≦ C [i] ÷ 255 <50 ÷ 100 ( 25% or more and less than _{50%) k 50 = 0.8:} 50 ÷ 100 ≦ C [i] ÷ 255 (50% or more) This is because when the gradation value is 25% or less, black complement is not performed, but when it exceeds that, the phenomenon of insufficient refill ejection failure begins to occur. , The amount of black complement is increasing. For cyan data, shading correction is also performed using 25% of shading data S ₂₅ [i]. At that time, a limit is added when the cyan data exceeds 25%, The above cyan data does not exist. This prevents the phenomenon of insufficient refill discharge failure. The correction formula used here is shown below. C '[i] = {1 + S ₂₅ [i] ÷ 100} × C [i] C' [i] = 0.25 × 255: C '[i]> 0.25 × 255 (4) 100% refill insufficient ejection failure (Nozzle [i] ＝
3) In case of 100% refill shortage failure, basically 5
Similar to the case of 0% refill insufficient ejection failure, the coefficient k ₅₀ is changed to k ₁₀₀ and the limit value of shading correction for cyan is different as described below. B '[i] = B [ i] + k 100 × C_K BNC [C [i]] k 100 = 0: C [i] ÷ 255 <5 ÷ 100 ( image data value: less than 50%) k ₁₀₀ = (C [i] /255-0.50) x 0.8 / 0.5: 25/100 ≤ C [i] / 255 ≤ 50/100 (50% or more) This is when the gradation value is 50% or less, black complement is performed. However, it is thought that the phenomenon of insufficient refill ejection failure will begin to occur at a point beyond that, and the amount of black supplemented will be increased accordingly. For cyan data, shading correction is also performed by using 25% shading data S ₂₅ [i], but at that time, when the cyan data exceeds 50%, a limit is added, The above cyan data does not exist. This prevents the phenomenon of insufficient refill discharge failure. The correction formula used here is shown below. C ′ [i] = {1 + S ₂₅ [i] ÷ 100} × C [i] C ′ [i] = 0.50 × 255: C ′ [i]> 0.50 × 255 The above is the processing according to the determination result.

As described above, in this embodiment, a new table is not prepared for refill shortage failure discharge,
Although the ejection failure / non-complementation table for the ejection failure nozzles is used for the correction, it is of course preferable to create a dedicated table for the correction. Further, in the present embodiment, when the correction for magenta is performed, the complementary table using black is used similarly to cyan, and for the correction for black, the complementary table using three colors of cyan, magenta and yellow is used. On the other hand, the supplementary table was not used for yellow. It should be noted that these tables are preferably prepared depending on various conditions such as the medium used.

After the correction was performed in this manner, the image data of 4 was binarized by the error diffusion method to prepare bitmap data. An image was output from the data through the head driver. As a result, it was possible to make inconspicuous the image defect of insufficient refill and ejection failure due to the increase of the flow path resistance of the ink.

[0033]

As described above, according to the present invention,
By measuring the shading correction pattern recorded with at least two types of recording duty, and identifying the nozzle that is not refill insufficiently discharged from the difference and performing the correction, it is possible to reduce image defects that could not be corrected by the conventional method. It will be possible. Further, as a result, there is an effect that the yield of the head that can be practically used is also increased.

[Brief description of drawings]

FIG. 1 is a block diagram of data processing according to an embodiment of the present invention.

FIG. 2 is a pattern to be recorded in head shading.

FIG. 3 is a diagram illustrating processing of a read shading pattern.

FIG. 4 is a flowchart showing a discrimination process for each nozzle.

FIG. 5 is a flowchart illustrating a correction process.

FIG. 6 is a diagram showing a table for complementing discharge failure of cyan with black.

FIG. 7 is a schematic diagram of an ink flow path in a head.

[Explanation of symbols]

1 color converter 2 Correction processing section 3 Nozzle information holding unit 4 Image processing section 5 head driver 10 25% head shading pattern 11 50% head shading pattern 12 100% head shading pattern 13 markers 20 ink channels 21 nozzles 22 heater 23 nozzle filter

Continued front page    (72) Inventor Norifumi Koitabashi             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation (72) Inventor Hitoshi Tsuboi             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation (72) Inventor Yasunori Fujimoto             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation F-term (reference) 2C056 EA06 EB27 EB42 EC75 EC76                       EC79 FA03                 2C057 AF24 AF25 AF91 AF93 AG16                       AL36 AM28 AM40 AN05

Claims (4)

[Claims] 1. An image correction method in an ink jet recording apparatus for recording an image by ejecting ink onto a recording medium using a recording head in which a plurality of nozzles for ejecting ink are arranged, and the recording characteristic of the recording head is measured. For outputting at least two types of uniform patterns, a measuring step for measuring the density distribution of the output pattern, and a plurality of nozzles corresponding to the plurality of nozzles based on the measurement result of the measuring step. Data for correction,
The calculation step of calculating for each type of the pattern is compared with the data corresponding to each of the at least two types of patterns, the states of the plurality of nozzles are classified into a plurality of types, and the states of the plurality of nozzles are handled. And a step of correcting the image, wherein the at least two types of patterns output by the output step are patterns having different recording duties, and the step of correcting the image is performed according to the classified state type. An image correction method characterized by performing different correction processes according to the above. 2. The at least two types of patterns are 25%, 50%, 75%, 100% by the recording head.
The image correction method according to claim 1, wherein the pattern is any one of the patterns recorded with the duty of. 3. An inkjet recording apparatus for recording an image by ejecting ink onto a recording medium using a recording head in which a plurality of nozzles for ejecting ink are arranged, and at least 2 for measuring recording characteristics of the recording head. Pattern output means for outputting a pattern of uniform type and data for performing correction corresponding to each of the plurality of nozzles are calculated for each type of the pattern based on the density distribution of the output pattern. A calculation unit and a correction unit that compares the data corresponding to each of the at least two types of patterns, classifies the states of the plurality of nozzles into a plurality of types, and corrects an image corresponding to each of the plurality of nozzles; And at least 2 to be output by the pattern output means.
The type of pattern is a pattern pattern having a different print duty, and the correction unit performs a different correction process according to the classified state type. 4. The recording head applies heat to the ink to eject the ink from a nozzle.
The inkjet recording device according to item 1.