JPH06336015A - Ink jet recording method - Google Patents

Abstract

PURPOSE:To make a bad effect of a bidirectional positional shift of dots as inconspicuous as possible when it is inevitably generated in a two-way printing by waviness of a paper surface, numerous irregularities in driving, and a change in delivery speed. CONSTITUTION:In an ink jet recording method in which recording is being completed by conducting a plurality of times of bidirectional recording scan on the same image area using a multihead provided with arrangement of a plurality of ink delivery ports while paper is relatively and successively fed, pixel arrangement patterns used for every recording scan are compensated with each other, and two or more ones used for every recording scan at least in the same direction out of the pixel arrangement patterns are determined to be adjacent to each other in a recording scan direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording method, and more particularly to eliminating the harmful effects caused by dot misalignment during bidirectional printing.

[0002]

2. Description of the Related Art With the widespread use of copying machines, 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. Those that record digital images are rapidly spreading. In such a recording apparatus, in order to improve the recording speed, a recording head in which a plurality of recording elements are arranged in an array (hereinafter referred to as a multi-head) is formed by integrating a plurality of ink ejection ports and liquid paths. It is generally used and further provided with a plurality of the above-mentioned multi-heads for color correspondence.

FIG. 7 shows the construction of the printer section when printing on the paper surface by the above-mentioned multi-head. In this figure, reference numeral 701 is an ink cartridge. These are ink tanks filled with four color inks, black, cyan, magenta, and yellow, respectively,
702 multi-head. FIG. 8 shows a state of the multi-nozzles arranged on the multi-head from the z direction, and 81 is a multi-nozzle arranged on the multi-head 702. In this figure, the multi-nozzle 8
01 are arranged in parallel along the Y-axis, but they may have some inclination on the XY plane in the figure, for example. In this case, while the head moves in the traveling direction X, each nozzle performs printing while shifting the timing. Return to FIG. 7 again. A paper feed roller 703 rotates in the direction of the arrow in the figure while holding the print paper 707 together with the auxiliary roller of 704, and feeds the print paper 707 in the y direction at any time. Further, reference numeral 705 denotes a paper feed roller which feeds the printing paper and also plays a role of suppressing the printing paper 707 similarly to 703 and 704. Reference numeral 706 is a carriage that supports four ink cartridges and moves them with printing. This is when not printing
Alternatively, when performing a multi-head recovery operation or the like, the home position (h) at the position shown by the dotted line in the figure is waited.

Before the start of printing, the carriage (706) at the position shown in the figure (home position) moves in the x direction when the print start command arrives, and moves along the multi-head (702).
The upper n multi-nozzles (81) provide a width D on the paper.
Just print. When the data printing is completed up to the edge of the paper, the carriage returns to the original home position and x
Print in the direction. Or if it is double-sided printing, −
Printing is performed while moving in the x direction. From the end of the first printing to the start of the second printing, the paper feed roller (703) rotates in the arrow direction to feed the paper in the y direction by the width D. In this way, printing of only the multi-head width D and paper feeding are repeated for each scan of the carriage, whereby data printing on one paper surface is completed.

However, unlike a printer that prints only characters as a monochrome printer, various elements such as color developability, gradation, and uniformity are required to print a color image image. Particularly regarding uniformity, a slight variation in nozzle unit caused by a difference in multi-head manufacturing process affects the ink ejection amount and ejection direction of each nozzle when printing, and finally the printed image. This causes deterioration in image quality as uneven density.

A specific example will be described with reference to FIGS. In FIG. 9-a, reference numeral 91 is a multi-head, which is similar to that of FIG. 8, but for the sake of simplicity, it is assumed that it is composed of eight multi-nozzles (92). Reference numeral 93 is an ink droplet ejected from the multi-nozzle 92. Normally, it is ideal that ink is ejected in a uniform direction with a uniform discharge amount as shown in this figure. If such ejection is performed, dots of uniform size are landed on the paper surface as shown in FIG. 9-b, and a uniform image without density unevenness is obtained as a whole. (9-c). However, in reality, as described above, each nozzle has a variation, and if printing is performed in the same manner as above, as shown in FIG. The ejected ink drops vary in size and direction, and land on the paper surface as shown by 10-b. According to this figure
Area factor 1 periodically with respect to the head main scanning direction
There is a blank portion that cannot be filled with 00%, or conversely dots are overlapped more than necessary, or a white streak appears in the center of the figure. The collection of dots landed in such a state has the density distribution shown in FIG. 10-c in the nozzle arrangement direction, and as a result,
Normally, these phenomena are perceived as density unevenness as seen by human eyes.

Therefore, the following method has been devised as a countermeasure against this density unevenness. The method will be described with reference to FIGS. 11 and 12. According to this method, the multi-head 91 is scanned three times to complete the print area shown in FIGS. 9 and 10, but the half area of the 4-pixel unit is completed in two passes. In this case, the 8 nozzles of the multi-head are divided into a group of 4 upper nozzles and 4 lower nozzles,
The dots printed by one nozzle in one scan are defined image data thinned to about half according to a predetermined image data array. Then, at the time of the second scan, dots are embedded in the remaining half of the image data to complete the printing of the 4-pixel unit area. The recording method as described above is hereinafter referred to as a divided recording method. If such a divided recording method is carried out, FIG.
Even if the same recording head as that used in the above is used, the influence on the printed image peculiar to each nozzle is reduced by half, so the printed image looks like 11-b and the black as seen in 10-b. The streaks and white streaks become less noticeable. Therefore, density unevenness is 11
As shown in -c, it is considerably relaxed compared with the case of FIG.

When performing such recording, the first scan and the second scan
In the scan, the image data is divided according to a certain array so as to fill each other. Previously, this image data array (thinning pattern) is as shown in FIG.
It was most common to use a pixel that exactly forms a zigzag pattern for each vertical and horizontal pixel. Therefore, in the unit printing area (here, in units of 4 pixels), the printing is completed by the first scan for printing the zigzag lattice and the second scan for printing the inverse zigzag lattice. 12-a, 12 of FIG.
-B and 12-c show how the recording of a certain area is completed when using this zigzag and inverse zigzag pattern, respectively, using a multi-head having 8 nozzles, as in FIGS. It is the one explained. First, in the first scan, the staggered pattern ◯ is recorded using the lower 4 nozzles (12-a). Next, in the second scan, the paper is fed by 4 pixels (1/2 of the head length) and the reverse zigzag pattern is printed (12-b). Further, in the third scan, the paper is fed by 4 pixels (1/2 of the head length) again, and the staggered pattern is recorded again. (12-c) In this manner, the paper feed in units of 4 pixels and the recording in the staggered and reverse zigzag patterns are alternately performed in this manner, whereby the recording region in units of 4 pixels is completed for each scan. As described above, by completing printing with two different types of nozzles in the same area, it is possible to obtain a high-quality image without density unevenness.

Further, in this drawing, the structure in which the printing is completed in the same area by two scans has been described, but the effect of the divided printing method appears as the number of divisions increases.
Even in the printing apparatus described above, if the number of pixels printed by one scan is further halved and the width of the paper feed scan is set to 2 pixels (1/4 of the head length), four pixels are printed in the same scanning direction. Since the image is completed by the nozzles of different types, it is possible to obtain a smoother and better image.

However, in such divided recording, as the number of divisions is increased, the time cost for printing on one sheet is increased, and the throughput must be reduced. In such a case, a method of reciprocating print scanning of the carriage can be considered in order to perform printing in a shorter time. According to this, after the conventional one-scan recording is performed,
Since all the carriage scanning that has returned to the home position without performing any recording is omitted, the recording time per sheet can be virtually halved. In fact, there are not a few monochromatic printing methods that perform the above-mentioned reciprocal printing.

[0011]

However, the present inventors have confirmed that in the course of performing various recordings according to the above method, there is a new problem in the reciprocal printing. The problem will be described below with reference to the drawings.

FIG. 13A shows a state in which the head is moving at a constant speed V in the forward or backward direction and ejecting an ink drop at a constant speed v onto a smooth paper surface. When the paper surface is smooth as shown in the figure, the distance d between the paper surface and the head face surface is kept constant, and the dots printed on the forward path and the dots printed on the return path land at the same position on the paper surface as shown in the figure below. To be done. However, if the paper surface itself is lifted from the actual position like 13-b for some reason, the distance between the head face surface and the paper surface is reduced to d ′, and the ink drop arrives at the paper surface after the head ejects. Since the time until is shortened in both the forward and backward passes, the print dots are landed at different positions, which are different from the target positions, as shown in the figure below.

The adverse effects of printing a 100% duty image in both directions using the thinning mask described above in such a state will be described below. FIG. 2 shows an example of a pixel array of each printing scan and a dot printing state at that time in a divided printing method in which an image is completed by four printing scans. The pixel array printed in each recording scan is from the first recording scan to the fourth
Up to the printing scan, there is a complementary pixel array, but at this time, the pixel array of the first printing scan and the pixel array of the third printing scan are printed by the forward scan of the head and the second printing scan and the second printing scan. The four recording scans are printed by the backward scan of the head. In the figure, the sum of the forward scan and the sum of the backward scan are shown, but here, each pixel array is set so that these sums draw a houndstooth check. When the dot misregistration as shown in FIG. 13 occurs in such a state, as shown in the lower part of FIG. 2, the dots in the forward printing and the dots in the backward printing largely overlap each other, and as shown in the figure, between the adjacent dots. The gap is open.

Although the dots are shown as being displaced by 1/4 pixel from the normal position in this figure, since adjacent dots are printed by reverse scanning in all the dots, one dot corresponds to each dot. That is, the gap is generated, and the overall concentration is low.

As described above, in order to simultaneously realize the divided recording and the bidirectional printing in order to realize the high image quality and the high speed, the image misalignment caused by the dot position deviation in the bidirectional printing described here occurs. It was dead.

[0016]

According to the present invention, a multi-head in which a plurality of ink ejection ports are arranged is used to perform bidirectional printing scanning a plurality of times on the same image area and relatively sequentially. In an inkjet printing apparatus that completes printing by feeding paper, the pixel arrays used for each printing scan are in a complementary relationship, and
At least a plurality of pixel arrays used in the same-direction recording scan among the pixel arrays are adjacent in the recording scan direction, which causes adverse effects of bidirectional dot position deviation that is caused by ups and downs of the paper surface, various driving unevenness, and changes in ejection speed. This makes it possible to obtain uniform and smooth high image quality.

[0017]

【Example】

(First Embodiment) The first embodiment will be described below. FIG. 1 is a diagram showing this embodiment by comparing with FIG. Also in this figure, as in the case of FIG. 2, there is shown a state in which the dot position deviation has occurred for ¼ pixel in bidirectional printing. However, in the completed dot landing state, it can be seen that the number of gaps in this embodiment is smaller than that in FIG.

The difference between this embodiment (FIG. 1) and FIG. 2 appears in the sum of the recording pixel arrays when printing in the same direction twice. In FIG. 2, the sum of the forward pass, the return pass, and each pixel array is a one-dot unit zigzag lattice, whereas in the present embodiment (FIG. 1), the forward pass sum and the return pass sum are always 2 pixels in the scanning direction. They are arranged in units of one. As described above, the pixel arrays for two same-direction scans are formed so as to be adjacent to each other, so that it is possible to prevent a low density.

The object of the present invention is to prevent the adverse effects of bidirectional dot position deviation, which is caused by ups and downs of the paper surface, various driving irregularities, and changes in the ejection speed in bidirectional printing.
It is to make it as inconspicuous as possible. Therefore, in general, what kind of arrangement of thinning masks can be used to realize these will be described below.

Misalignment during bidirectional printing always occurs under the same condition for any dot. Therefore, how much the gap as shown in FIG. 2 is reduced determines the effect of the present invention.

The number of gaps is equal to the number of spots where the dots landed on the outward path and the dots landed on the return path are adjacent to each other.
In FIG. 2, the forward printing and the backward printing are alternately arranged every other dot, so there is a gap next to all the dots, but in FIG. 1, the group of dots printed in the same direction is horizontal. Since two dots are continuously formed in the direction, no gap is generated in these two dots, and the number of gaps can be suppressed to once every two. That is, the number of dot deviation gaps in bidirectional printing is related to the number of continuous dots in the horizontal direction in the sum of the pixel arrays in the bidirectional printing.

As described above, in the present embodiment, the pixel array for each print scan is one pixel unit which is not adjacent to each other, but the pixel array as the sum of the forward direction and the backward direction is the head scanning direction. By forming a pixel array in which each two pixels are solidified, it is possible to make the gap that occurs when printing both lines inconspicuous.

Further, the method of the present embodiment is an equally effective means in the case of black printing of a single color and the color printing of a plurality of colors. For example, in the case of a color ink jet recording apparatus, a thinning arrangement as shown in FIG.
Cyan, magenta, and yellow may be commonly used, or four types of pixel arrays for each color may be cycled for each scan. Even when using pixel arrays having completely different complementary relationships for each color, if the pixel arrays for the same-direction recording scan are adjacent to each other as described above, the same effect as above can be obtained. Will be done.

(Second Embodiment) A second embodiment will be described below.
3 and 5 show the effect of this embodiment by comparing with FIG. 4 and FIG. Here, the pixel array of FIG. 3 is used for cyan, magenta, and yellow, and the pixel array of FIG. 4 is used for black.

The difference of the present embodiment from the first embodiment is that the pixel arrangement in each recording scan is already made up of 1 × 4 dot groups, and the position of the gap is 1 in advance regardless of the recording order of each pixel arrangement. That is, it is suppressed to / 4.

Also in this embodiment, the effect of the present invention is shown in FIGS. In FIG. 4, the area where adjacent dots are printed by reverse scanning is once every four times in the main scanning direction, whereas in FIG. 3, the sum of forward scanning or the sum of backward scanning is 8 pixels in a row. Has become. Therefore, the number of places where the gap appears is reduced to once every eight pixels.

Further, in this embodiment, in order to print by emphasizing only the black ink, the pixel arrangement different from other colors as shown in FIG. 5 is applied to black. In this case, 4
In order to print a total of 200% duty in each scan, 50% is recorded in each scan. At this time, if 100% printing is completed in the first two scans as shown in FIG. 6, the sum of the forward print pixel array and the return print pixel array becomes equal to the single scan pixel array. Will end up. On the other hand, as shown in FIG. 5, if the same pixel is overprinted in the first two reciprocating scans, and the pixel array having a complementary relationship with this is overprinted in the subsequent two reciprocating scans, the printing in the forward pass and the return pass are performed. This means that 100% of the image is printed by each printing independently, and no gap is generated due to the dot misalignment between the two directions.

In such printing of 200% or more, if the sum of the forward scan and the sum of the backward scan are each 100%, as in the first embodiment, each print scan is performed. Even if the pixel arrangement is different for each pixel, the same effect as in the present embodiment can be obtained with respect to the dot shift in both directions. FIG. 15 shows an example of one-way printing for color and reciprocal printing for black. At this time, black is recorded in the same pixel at the same head position as in the forward path in the backward path. Basically, the present invention is effective even for black emphasis in one-way printing.

However, strictly speaking, dot misalignment is not a phenomenon that occurs only in bidirectional printing. When the printing duty is high as in the present situation, the deflection of the paper surface changes for each recording scan, and there is some driving unevenness for each recording scan. That is, such a factor appears as a dot shift even in one-way printing.

Therefore, it can be said that the use of 1 × 4 pixels as the basic dot group for each recording scan as in the present embodiment is effective for the dot deviation which may occur even in one-way printing.

The pixel array based on 1 × 4 used in this embodiment for color and black also has the effect of reducing the number of gaps as compared with the first embodiment. Besides, the following effects can be expected.

Basically, the divided recording method does not sufficiently exhibit its effect unless the recording pixels in the unit area are recorded in substantially the same number of scans of the number of divisions. In the examples described so far, 100% duty images are all recorded, so that in any case, the same number of pixels is always recorded in four passes. However, the image data that is actually sent as a signal is the one that is sent after the multi-valued data representing a certain gradation is binarized by a predetermined binarization method and is set in a predetermined pattern. Many. The present method is effective for the dither method which is used most often among them.

In a binarization method such as the normal dither method, 4 ×
In a square matrix such as 4, the pixel array corresponding to each duty is determined. This matrix is for realizing area gradation inside thereof, and if equal duty values are input, the same pixel arrangement is always output. Therefore, when equal duty values are input to all the matrices, such as when recording a uniform pattern, all 4 × 4 matrices arranged vertically and horizontally on the recorded image have the same pixel arrangement. The dots are recorded to form a uniform image.

In such a case, assuming that the 1 × 4 dot group of this embodiment is the basis of the pixel array, the main scanning direction of the matrix is synchronized with this 1 × 4 dot group, and adjacent matrixes are simultaneously formed. Will not be printed by the printing scan of. Therefore, the difference in the number of dots for each print scan does not appear in the main scan direction for image data of any duty, and it is possible to always print with four types of nozzles.

As described above, in the present embodiment, the pixel array for each print scan is based on 1 × 4, but the pixel array as the sum of the forward and backward directions is in the head scanning direction. By making the pixel array solidified by eight pixels, it is possible to make the gaps that occur when printing both lines inconspicuous.

Also, in this embodiment, as in the first embodiment, the thinning-out arrangement may be such that four kinds of pixel arrangements for each color of black, cyan, magenta and yellow are circulated for each scanning.

Further, in the present embodiment, as an example of emphasizing only black, the black pixel array is different from the color. However, the present embodiment is carried out even when all colors are recorded by reciprocal printing as shown in FIGS. 5 and 15. The example is valid.

Up to this point, it has been described that the present embodiment is more effective than the first embodiment. However, the first embodiment may be more effective for OHP paper or the like having poor ink absorbency. . This is because, in the configuration of this embodiment in which ink drops are adjacently printed at the same time, adjacent dots may be attracted to each other, and a phenomenon may occur in which a large ink drop is solidified on the recording medium. In such a case, it can be said that the first embodiment in which the ink drops are independent of each other in each recording scan is more effective.

[0039]

As described above, according to the present invention,
Using a multi-head with multiple ink ejection ports arranged,
In an ink jet recording method that completes recording by performing bidirectional recording scanning a plurality of times on the same image area and relatively sequentially feeding paper, the pixel arrays used for each recording scanning have a complementary relationship. In addition, since at least a plurality of pixel arrays used in the same-direction recording scan among the pixel arrays are adjacent to each other in the recording scan direction, it is caused by ups and downs of the paper surface, various driving irregularities, and changes in ejection speed. This makes it possible to make the adverse effect of dot position deviation in both directions inconspicuous and obtain uniform and smooth high image quality.

In the above two embodiments, both have been described as four-division printing with equal print duty, but the effect of the present invention is not limited to this. For example, even if it is divided into three or eight, or even if the print duty of the pixel array is not equally divided for each print scan, the sum of the pixel arrays of the forward path and the backward path is configured such that the pixel arrays of each scan are adjacent to each other. If it has been used, its effect can be exhibited.

For example, FIG. 14 shows the second recording scan and the fourth recording scan of FIG.
The print scan is combined as the second print scan, and 25%, 50
%, 25% is an example in which recording is completed in all three divisions. Even in such a case, the number itself of the gaps between dots does not change, and the first embodiment is performed against the problem to be solved by the present invention. The same effect as the example can be obtained.

[Brief description of drawings]

FIG. 1 is a pixel array according to a first embodiment of the present invention.

FIG. 2 is a comparison diagram of FIG.

FIG. 3 is a pixel array according to a second embodiment of the present invention.

FIG. 4 is a comparison diagram of FIG.

FIG. 5 is a black pixel array according to a second embodiment of the present invention.

FIG. 6 is a comparison diagram of FIG.

FIG. 7 is a diagram of a printing unit of an inkjet printer used in the present invention.

FIG. 8 is a diagram of a multi-head used in the present invention.

FIG. 9 is a diagram showing an ideal printing state of an inkjet printer.

FIG. 10 is a diagram showing a printing state of an inkjet printer having uneven density.

FIG. 11 is a diagram showing division printing used in the present invention.

FIG. 12 is a diagram showing division printing used in the present invention.

FIG. 13 is an explanatory diagram of dot misalignment

FIG. 14 shows a second print scan and a fourth print scan of FIG.
FIG. 6 is a diagram showing an example of combining as a print scan and printing in three divisions.

FIG. 15 is a diagram showing an example of unidirectional printing for color and bidirectional printing for black.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B41J 2/51 B41J 3/04 103 B 3/10 101 G

Claims (2)

[Claims] 1. A printing is completed by using a multi-head in which a plurality of ink ejection openings are arranged, performing bidirectional printing scanning a plurality of times on the same image area, and relatively sequentially feeding the paper. In the inkjet recording method, the pixel arrays used for each recording scan have a complementary relationship, and at least a plurality of pixel arrays used in the same-direction recording scan among the pixel arrays are adjacent to each other in the recording scan direction. Inkjet recording method. 2. The ink jet recording method according to claim 1, wherein a plurality of droplets of the same color are recorded in the same pixel in an overlapping manner.