Patent Application
20100045719
1. Field of the Invention
The present invention relates to an ink jet print head having a plurality of ejection openings to eject yellow, magenta and cyan inks, an ink jet printing apparatus using the print head, and an ink jet printing method.
2. Description of the Related Art
As personal computers, word processors and facsimiles have come into widespread use in offices and homes in recent years, a variety of types of printing apparatus have been commercialized as information output devices for these apparatus. Of these output devices an ink jet printing apparatus has many advantages, such as the capability to perform color printing relatively easily using a plurality of color inks, low printing noise, the capability to print on a variety of print media with high print quality and small printer size. Because of these advantages, an ink jet printing apparatus is suited for office use and for personal use at homes. Of the ink jet printing apparatus, a serial type that reciprocally moves the print head over a print medium for printing is very popular because of its ability to perform high quality, low cost printing.
In a serial type printing apparatus, bidirectional printing may be performed in which a print head mounted on a carriage (and capable of ejecting a plurality of inks) prints an image as the carriage moves forward and backward. In such a printer the order in which colored inks are ejected (the ink ejection order) is reversed for forward and backward movement of the print head. The reversal of the ink ejection order between the forward and backward movements of the carriage may cause bandlike grayscale level variations on a printed image (hereinafter referred to also as a “bidirectional color difference”).
A print head described in Japanese Patent Laid-Open No. 2004-001491, for example, has five ink ejection opening arrays, of which one is for yellow ink, two for cyan ink and the remaining two for magenta ink. The yellow ink ejection opening array is situated at the center of the five ejection opening arrays, with one cyan ink ejection opening array and one magenta ink ejection opening array on each side thereof. Two sets of the cyan ink ejection opening array and the magenta ink ejection opening array are arranged symmetrical with respect to the center yellow ink ejection opening array so that the ink ejection orders during the forward and backward movements are the same.
In such a print head, the yellow ink ejection opening array has only those ejection openings that eject large ink droplets while the cyan and magenta ink ejection opening arrays each have ejection openings that eject large and small ink droplets. This arrangement is made because the bright yellow ink hardly shows graininess of an image even if printed with only large ink droplets, whereas the cyan and magenta inks with low brightness levels tend to show graininess in printed areas with low grayscale levels unless the image is printed with small ink droplets. Therefore, small yellow ink droplets are not necessary to reduce graininess. So, only large ink droplet ejection openings are provided for yellow ink.
There has been a growing call for faster printing speeds in recent years and, among methods known to meet that demand, there is one method that reduces the number of scans (scan number). In printing images with the same grayscale levels, a reduction in the number of scans can increase ink ejection density in one scan.
In Japanese Patent Laid-Open No. 2004-001491, a yellow ink ejection opening array has large ink droplet ejection openings arrayed on each side of a corresponding ink supply port. The magenta and cyan ink ejection opening arrays each have large ink droplet ejection openings arrayed on one side of a corresponding ink supply port and small ink droplet ejection openings arrayed on the other side thereof. So, magenta and cyan large ink droplets are ejected from the openings situated on one side of the corresponding ink supply ports while yellow large ink droplets are ejected from openings situated on both sides of the corresponding ink supply port. Therefore, the print head has a high ejection density in a unit area for the large yellow ink droplets and, when an image of high grayscale level is printed, a strong air flow is produced near the yellow ink ejection opening array by the ejection of large yellow ink droplets. This raises a possibility of bandlike color variations being produced when an image of secondary color is printed by ink droplets ejected from the yellow ink ejection opening array and the adjoining magenta or cyan ink ejection opening array. That is, the air flow produced near the former ejection opening array may disturb landing positions of ink droplets ejected from the latter ejection opening array, causing bandlike color variations. Such bandlike color variations are called “air flow-based color variations”. Small ink droplets are affected particularly strongly by the air flows.
The present invention provides an ink jet print head that can be reduced in sized and still minimize the influence of air flows produced by ink droplets ejected from a smaller number of ejection opening arrays. This invention also provides an ink jet printing apparatus and an ink jet printing method to reduce bandlike color variations and thereby enabling the printing of high-quality images.
In the first aspect of the present invention, there is provided an ink jet print head having a plurality of ejection openings formed therein to eject yellow, magenta and cyan inks, the ink jet print head, the ink jet print head comprising: at least one of a first ejection opening array, along which the plurality of ejection openings for ejecting one of the yellow, magenta and cyan inks are arrayed; at least one of a second ejection opening array, along which the plurality of ejection openings for ejecting one of the remaining two inks are arrayed; and at least one of a third ejection opening array, along which the plurality of ejection openings for ejecting the remaining ink are arrayed, wherein the first, second and third ejection opening arrays are parallelly arranged to adjoin each other in a predetermined direction, wherein the number of the first ejection opening arrays is less than those of the second ejection opening arrays and the third ejection opening arrays, and wherein a fourth ejection opening array, along which a plurality of ejection openings for ejecting a fourth ink different from the yellow, magenta and cyan inks are arrayed, the fourth ejection opening array being disposed between the first ejection opening array and the second or third ejection opening array, the first ejection opening array and the second or third ejection opening array being arranged adjoining each other in the predetermined direction.
In the second aspect of the present invention, there is provided an ink jet printing apparatus for printing an image on a print medium by using an ink jet print head, wherein the ink jet print head has at least one of a first ejection opening array, at least one of a second ejection opening array, at least one of a third ejection opening array and at least one of a fourth ejection opening array arranged parallelly to adjoin each other in a predetermined direction, each of the ejection opening arrays having a plurality of ink ejection openings, wherein the number of the first ejection opening arrays is less than those of the second and third ejection opening arrays, wherein the fourth ejection opening array is disposed between the first ejection opening array and the second or third ejection opening array, the first ejection opening array and the second or third ejection opening array being arranged adjoining each other in the predetermined direction, and wherein the ink jet printing apparatus includes a unit that ejects one of yellow, magenta and cyan inks from the first ejection opening array, ejects one of the remaining two inks from the second ejection opening array, ejects the remaining ink from the third ejection opening array, and ejects a fourth ink, different from the yellow, magenta and cyan inks, from the fourth ejection opening array.
In the third aspect of the present invention, there is provided an ink jet printing method for printing an image on a print medium by using an ink jet print head, the method comprising: a providing step of providing the ink jet print head that has at least one of a first ejection opening array, at least one of a second ejection opening array, at least one of a third ejection opening array and at least one of a fourth ejection opening array arranged parallelly to adjoin each other in a predetermined direction, each of the ejection opening arrays having a plurality of ink ejection openings, wherein the number of the first ejection opening arrays is less than those of the second and third ejection opening arrays, wherein the fourth ejection opening array is disposed between the first ejection opening array and the second or third ejection opening array, the first ejection opening array and the second or third ejection opening array being arranged adjoining each other in the predetermined direction; and an ejecting step in which one of yellow, magenta and cyan inks is ejected from the first ejection opening array, one of the remaining two inks is ejected from the second ejection opening array, the remaining ink ejected from the third ejection opening array, and a fourth ink, different from the yellow, magenta and cyan inks, is ejected from the fourth ejection opening array.
According to the present invention, between a smaller number of first ejection opening arrays that eject one of three primary inks—cyan, magenta and yellow—and a greater number of second and third ejection opening arrays that eject the remaining two colors, there is a fourth ejection opening array that ejects a fourth ink different from the three primary inks. This arrangement can minimize the effect that the air flows, produced by the first ejection opening arrays ejecting ink droplets at high density, have on the ink droplets ejected from the second and third ejection opening arrays. As a result, the bandlike color variations can be alleviated, forming high-quality images. Further, since the air flow influences can be reduced without having to especially increase the intervals between a plurality of ejection opening arrays, the print head can be reduced in size.
The fourth ink, whatever it is, may be replaced with the three primary colors—cyan, magenta and yellow. For example, when ink is ejected from the first ejection opening array at a high density, higher than a predetermined level, the fourth ink may be replaced with three primary colors of cyan, magenta and yellow. When the ejection density of ink from the first ejection opening array is low, less than the predetermined level, the fourth ink may be used. As a result, when ink is ejected from the first ejection opening array at high density, the air flow-based color variations of ink ejected from the ejection opening array adjoining the first one can be avoided. Further, the use of the fourth ink can also improve the print quality of an image. Since the cyan, magenta and yellow inks are of the three primary colors, when an image is formed with colors made by mixing inks ejected from the first and fourth ejection opening arrays, it is possible to use the first and fourth ejection opening arrays at an ejection density that will not cause the “air flow-based color variations”.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Now embodiments of this invention will be described by referring to the accompanying drawings.
An ink jet print head 1 in this example includes an ink supply portion 2 and an ink ejection portion 3. The ink supply portion 2 has an ink tank holder 2A for holding an ink tank not shown and is connected to the ink ejection portion 3 for ink supply. The ink ejection portion 3 has a Bk chip 10 for ejecting pigment black ink a color chip 20 for ejecting a plurality of dye color inks.
The heaters, a bubble chamber enclosing the heater, ejection openings 22, 23 (that open on a plane of the bubble chamber facing the heater) and an ink path connecting the bubble chamber and the common liquid chambers 21 combine to form a nozzle (ink jet nozzle).
264 of the ejection openings 22, 23 are arrayed at intervals of 600 dpi (about 42.3 μm) in each of the ejection opening arrays L. In the ejection opening arrays L on both sides of each of the common liquid chambers 21, the ejection openings 22 and the ejection openings 22, or the ejection openings 22 and the ejection openings 23, are arranged so as to be staggered. These ejection opening arrays L on both sides of each common liquid chamber 21 have a total of 528 ejection openings 22 and 22, or 22 and 23, at intervals of 1200 dpi (about 21.2 μm). The total of 528 ejection openings 22 and 22, or 22 and 23, in the ejection opening arrays L on both sides of each common liquid chamber 21, form a group of ejection opening arrays LG. In
In this embodiment, there are eight of the common liquid chambers 21 and the same number of the ejection opening array groups LG are also formed. Supplied to the eight common liquid chambers 21, from left to right in
Two gray ink (G) ejection opening array groups LG (G) are arranged one on each side of the yellow ink (Y) ejection opening array group LG (Y) so that they are symmetrical with respect to the ejection opening array group LG (Y). These two ejection opening array groups LG (G) are provided for the following purposes.
As for the black ink (Bk) ejection opening array group LG (Bk), only one is provided for the following purpose so that it is not symmetrical with respect to the central, yellow ink (Y) ejection opening array group LG (Y).
In this embodiment, a dye black ink (Bk) ejected from the color chip 20 is not used for printing on plain paper. For printing on plain paper a pigment black ink ejected from the Bk chip 10 is used.
Next, an ink ejection operation by the ink jet print head 1 will be described. In response to an electric signal from a drive portion (not shown) to the ink ejection portion 3, a drive current is selectively applied to the heater 24 of each nozzle. When each heater 24 is energized, ink near that heater is heated and boiled. A pressure generated by the boiling causes ink to be ejected from the ejection opening 22, 23 facing the heater 24. When all of the heaters 24 are energized at the same time, a large voltage drop will occur. Therefore, in each of the ejection opening arrays L one in every sixteen heaters 24 are grouped together, thus dividing the 264 heaters 24 into sixteen groups. Each group comprises 16 heaters 24. The sixteen groups of heaters 24 are operated on a time-division basis (on a 16-time-division basis) to minimize the voltage drop. A drive frequency for one heater 24 is 15 kHz.
16 heaters×16 (time-division)=256 heaters
It is noted that the actual number of heaters 24 in one array is 256, not 264, as described above. This is because there are eight dummy heaters (=264−256) not used for printing. The dummy heaters are used to discharge mixed inks at the end of the common liquid chambers 21 from ejection openings when ink mixing occurs in a common liquid chamber 21.
Next, the printer (ink jet printing apparatus) using the ink jet print head 1 of this embodiment will be described.
The printer of this example, as shown in
This printer has a carriage 5 that reciprocates in a main scan direction of arrow X, on which is mounted a print head 1. The print head 1 ejects ink as it moves with the carriage 5 in the direction of arrow X crossing the ejection opening arrays L (in this example, in a direction perpendicular to the ejection opening arrays L) to print an image on paper (print medium). This operation is called a printing scan. The paper is supplied from a paper tray within the printer and fed in a subscan direction crossing the main scan direction of arrow X (in this example, in a direction perpendicular to the main scan direction). On the upper part of the printer is provided a scanner 4 designed to take in an image to be printed. The scanner 4 is integrally formed with the upper cover of the printer.
Next, the printing operation will be explained. Image data read by the scanner 4 is stored in a buffer of the scanner 4, which performs image processing on the buffered image data. The processed image data is sent to a print buffer, from which it is further fed to a print image processing portion Then paper is supplied from the paper tray.
A print signal from one scan taken of the image is sent via wiring in the carriage 5 to the print head 1, which, based on the print signal, ejects ink as it moves forwards (in the direction of arrow X1) along with the carriage 5 (forward scan). This is followed by the paper being fed a distance of 128 dots of 600 dpi in the subscan direction. Then, the next print signal from another scan taken of the image is sent via the wiring of the carriage 5 to the print head 1, which, based on that print signal, ejects ink as it moves backwards (in the direction of arrow X2) along with the carriage 5 (backward scan). Each of the ejection opening arrays L has 256 ejection openings 22, 23 arrayed at intervals of 600 dpi. Of the 256 ejection openings, 128 ejection openings eject ink on the rasters that have been printed with ink dots in the preceding forward scan. Then, the paper is fed the distance of 128 dots of 600 dpi in the subscan direction.
By repeating such scans (forward scan and backward scan) and feeding the paper alternately, one page of paper is printed. In this embodiment, so-called, 2-pass printing is adopted, in which one raster is completed by two scans. Therefore, the print image processing portion uses a mask to divide print data for one and the same area into two scans.
Next, by referring to
First, small ink droplets of magenta ink begin to be ejected and the ejection ratio of small magenta ink droplets (small dot formation percentage) in a unit print area is increased progressively as the grayscale level increases. Once the ejection ratio of small ink droplets has reached a predetermined level, large ink droplets of magenta ink are started to be ejected as the grayscale level rises. This is intended to alleviate graininess of the printed image. If only large magenta ink droplets land on the print surface, the large-diameter ink droplets show heavy graininess. However, landing small ink droplets first followed by large ink droplets makes the large ink dots less noticeable, mixed with small ink dots.
Then, as the grayscale level rises, the ejection ratio of large ink droplets (large dot formation percentage) is gradually increased. When the ejection ratio between the small ink droplets and the large ink droplets reaches 1:1, a sufficiently high grayscale level is reached.
In this example, the 2-pass printing method is employed. So, in an area where the gradation reaches the highest level of grayscale, two ejection opening array groups LG (M) eject large ink droplet to form one large dot and small ink droplet to form one small dot on average in each of the forward scan and the backward scan. The two ejection opening array groups LG (M) are formed with a large enough distance between them so that, during the magenta color printing, no air flow-based color variations occur at whatever printing grayscale level.
(Printing a Gradation that Changes from Yellow to Red)
Next, by referring to
A gradation change is made from yellow to red as follows. Red is made by mixing yellow and magenta inks at a ratio of almost 1:1. So, yellow ink is ejected such that until yellow changes to red, three dots of yellow ink are formed in two scans at 600 dpi at all times.
When color changes from yellow to red, small magenta ink droplets are started to be ejected to progressively increase its ejection ratio (dot forming percentage). Then, once the small ink droplet ejection ratio has reached a predetermined level, large magenta ink droplets begin to be ejected. The ejection ratio of large magenta ink is gradually increased until the ejection ratio between the small magenta ink droplets and the large magenta ink droplets is 1:1, at which time the gradation becomes red at a sufficiently high grayscale level.
This example adopts the 2-pass printing method. So, in an area where the red color becomes darkest or has the highest grayscale level, two ejection opening array groups LG (M) eject large magenta ink droplet to form one large dot and small magenta ink droplet to form one small dot on average in each of the forward scan and the backward scan. In the area where the yellow color has the highest grayscale level, one ejection opening array group LG (Y) ejects large yellow ink droplets to form 1.5 dots on average in each of the forward scan and the backward scan. The ejection opening array groups LG (M) and the ejection opening array group LG (Y) do not adjoin and are spaced sufficiently part. Therefore, when the color changes from yellow to red during printing, no air flow-based color variations occur, regardless of the grayscale level of the printed image, assuring a high-quality printed image.
(Printing a Gradation that Changes from Cyan to Blue)
Next, by referring to
A gradation changes from cyan to blue as follows. Blue is made by mixing cyan ink and magenta ink at a ratio of almost 1:1. So, cyan ink is ejected such that until cyan changes to blue, two large dots of cyan large ink droplets and two small dots of cyan small ink droplets are formed in two scans at 600 dpi at all times.
When the color changes from cyan to blue, the magenta small ink droplets begin to be ejected and its ejection ratio is progressively increased. Then when the ejection ratio of the magenta small ink droplets has reached a predetermined ratio, magenta large ink droplets begin to be ejected. After this, the ejection ratio of magenta large ink droplets is progressively increased until the ejection ratio of the magenta small ink droplets and magenta large ink droplets is 1:1, at which time the color becomes blue with a sufficiently high grayscale level.
This example adopts the 2-pass printing method. So, in an area where the blue color becomes darkest or has the highest grayscale level, two ejection opening array groups LG (M) eject large magenta ink droplet to form one large dot and small magenta ink droplet to form one small dot on average in each of the forward scan and the backward scan. In the area where the cyan color has the highest grayscale level, two ejection opening array groups LG (C) eject large cyan ink droplet to form one large dot and small cyan ink droplet to form one small dot on average in each of the forward scan and the backward scan. The ejection opening array group LG (M) for magenta ink and the ejection opening array group LG (C) for cyan ink adjoin each other at a small interval. However, each of the ejection opening array groups LG (M) and LG (C) forms on average 0.5 dot with large ink droplet and 0.5 dot with small ink droplet and their ink ejection densities are sufficiently small so that there is no disturbance in the landing position of small ink droplets of either cyan ink or magenta ink. Therefore, as the color changes from cyan to blue during printing, no air flowbased color variations occur, whatever grayscale level the image being printed has, assuring a high-quality printed image.
(Printing a Gradation that Changes from Yellow to Black)
Next, by referring to
A gradation is changed from yellow to black as follows. Black is a color made by mixing almost equal amounts of yellow ink, magenta ink and cyan ink. So, the yellow ink's ejection ratio is lowered progressively while the gradation changes from yellow to black. In a state in which only the yellow ink is ejected to form 3 dots in two scans at 600 dpi, small ink droplets of magenta and cyan inks begin to be ejected and their ejection ratio is slowly increased. Accordingly, the yellow ink's ejection ratio is progressively lowered. From when the yellow ink's ejection ratio has reached a predetermined level, where one dot of yellow ink is formed on average at 600 dpi, small ink droplets of gray ink begin to be ejected and the gray ink's ejection ratio is slowly increased.
The gray ink is made by mixing equal amounts of cyan ink, yellow ink and magenta ink and diluting the mixture to ¼.
Therefore, one dot of small gray ink droplet can be replaced with 0.25 dot of small magenta ink droplet, 0.25 dot of small cyan ink droplet and 0.125 dot of large yellow ink droplet. However, to get a black color the ejection ratios of magenta ink and cyan ink needs to be increased, so their ejection ratios both increase although the ejection ratios of magenta ink and cyan ink become more moderate as they are subtracted by the amount equal to what is replaced with gray ink.
As with the case of magenta ink in the aforementioned red color, from when the ejection ratio of the small gray ink droplets has reached a predetermined level, the ejection of gray ink shifts to the ejection of large gray ink droplets. In the mean time, the ejection ratio of yellow ink continues to decrease and the ejection ratios of magenta ink and cyan ink progressively increase.
From when the ejection ratio of large gray ink droplets has reached a predetermined level, a black ink begins to be ejected. Accordingly, the ejection ratios of yellow, magenta, cyan and gray ink are decreased. When the ejection ratio of black ink reaches a predetermined level, where 3 dots of black ink are formed in two scans at 600 dpi, the other ink ejections are stopped. This is when the color becomes black.
In this example, the 2-pass printing method is employed. So, in an area where the grayscale level of yellow is highest, the ejection opening array group LG (Y) ejects large yellow ink droplets to form 1.5 dots on average in each of the forward and backward scans. In an area where black is at the highest grayscale level, the black ink ejection opening array group LG (Bk) ejects large black ink droplets to form 1.5 dots on average in each of the forward and backward scans. When small gray ink droplets begin to be ejected, the yellow ink ejection opening array group LG (Y) adjoining the gray ink ejection opening array groups LG (G) ejects ink droplets to form one dot on average in each of the forward and backward scans. The magenta ink ejection opening array groups LG (M) eject small ink droplets to form 0.25 dot on average in each of the forward and backward scans. These ejection opening array groups LG (Y), LG (G), LG (M) adjoin each other at small intervals. However, as with the printing of blue color, since the ejection densities of ink droplets from these ejection opening array groups are sufficiently small, there are no disturbances in the landing positions of the ink droplets.
The distance between the black ink ejection opening array group LG (Bk) and the adjoining cyan ink ejection opening array group LG (C) is small. So, small cyan ink droplets are affected by the air flows as they land. However, since the black grayscale level is sufficiently high, the image quality is not impaired by the air flows. In this example, since the highest grayscale level of black color is accomplished by using only the black ink, small cyan ink droplets are affected by the air flows (air flow-based color variations). However, setting an ink parameter so that the highest grayscale level of black color is established by mixing cyan, magenta, yellow and gray ink with black ink, can prevent the small cyan ink droplets from being affected by air flows.
As described above, the image quality can be kept high even when printing a gradation that changes from yellow to black, regardless of the grayscale level of the printed image.
Next, a print head for comparison will be explained which has ejection opening array groups LG arranged as shown in
Using this comparison print head, the process of printing a gradation that changes from yellow to red will be discussed.
While yellow ink is ejected to form 3 dots in 2 scans at 600 dpi, small magenta ink droplets begin to be ejected in much the same way as the preceding embodiment. In this comparison example, the yellow ink ejection opening array group LG (Y) and the two ejection opening array groups LG (M) adjoin with a small distance in between. So, the landing positions of small magenta ink droplets may be disturbed by the air flows produced by the yellow ink droplets as they are ejected. Therefore, during the printing of a gradation that changes from yellow to red, air flow-based color variations may occur degrading the image quality.
Next, using this comparison print head, the process of printing a gradation that changes from yellow to black will be discussed.
The color is changed from yellow to black as follows. In a state in which only yellow ink is being ejected to form 3 dots in 2 scans at 600 dpi, small gray ink droplets begin to be ejected and its ejection ratio is progressively increased. Then, as with the preceding embodiment, as the ejection ratio of gray ink is increased, the ejection ratio of yellow ink is lowered. When the ejection ratio of gray ink has reached a predetermined ratio, the black ink begins to be ejected.
In this comparison example, the yellow ink ejection opening array group LG (Y) and the gray ink ejection opening array groups LG (G) do not adjoin and their distances are long. The distance between the black ink ejection opening array group LG (Bk) and the adjoining gray ink ejection opening array group LG (G) is short. Under this condition, although the small gray ink droplets are disturbed by the air flows produced by the large black ink droplets, the image quality is not degraded because the grayscale level of black color has already become high enough. So, during the printing of the gradation that changes from yellow to black, the image quality remains good, whatever grayscale level the image being printed has.
(Comparison Between this Embodiment and Comparison Example)
In this embodiment since the image quality is good during the printing of both a yellow-to-red changing gradation and a yellow-to-black changing gradation, this embodiment is clearly advantageous.
Other means of avoiding the air flow-based color variations may include simply increasing the distance between the ejection opening arrays, lowering the ink ejection densities, slowing down the carriage travel speed and increasing the sizes of ink droplets ejected. However, simply increasing the distance between the ejection opening arrays also increases the size of the print head, resulting in an increase in the cost of the print head. Lowering the ejection densities or slowing the carriage travel speed can reduce the printing speed. Increasing the sizes of ink droplets can deteriorate the graininess of the printed image, degrading the image quality. Compared with these means for avoiding the air flow-based color variations, this embodiment has clear advantages.
In the above embodiment, the gray ink ejection opening array groups LG (G) are placed between the magenta ink ejection opening array groups LG (M) and the yellow ink ejection opening array group LG (Y). It is also possible to use the black ink ejection opening array groups LG (Bk) instead of the gray ink ejection opening array groups LG (G).
In that case, the black ink ejection opening array group LG (Bk) adjoining the cyan ink ejection opening array group LG (C) may be replaced with other ink ejection opening array group. Or, as shown in
Arranging two black ink ejection opening array groups LG (Bk) symmetrically, as shown in
When a gradation that changes from yellow to black is printed using the print head of
It is also possible to put red ink ejection opening array groups LG (R) between the magenta ink ejection opening array groups LG (M) and the yellow ink ejection opening array group LG (Y), as shown in
By making the red ink have a higher saturation than does a color created by a mixture of magenta ink and yellow ink, an image with a strong red color, such as one of a setting sun, can be printed with a sufficiently high saturation. This also applies to other inks than the red ink, such as green or blue ink. Making these inks also have higher saturations than do colors created by mixtures of two color inks can print images with these strong colors. In such an arrangement, too, when the yellow ink is used in large quantities, cyan ink and magenta ink may be used, rather than the red ink, green ink or blue ink, to prevent air flow-based color variations, thereby improving the image quality.
It is also possible to put light cyan ink ejection opening array groups between the magenta ink ejection opening array groups LG (M) and the yellow ink ejection opening array group LG (Y). The light cyan ink is an ink made by increasing the amount of a solvent component of the cyan ink to lower the grayscale level of cyan dye. The use of such a light cyan can smooth the gradation ranging from a highlighted portion of the cyan color to an intermediate portion. In this arrangement, too, when the yellow ink ejection density is high, the cyan ink may be used, rather than the light cyan ink, to prevent air flow-based color variations, thus improving the image quality. When a light magenta ink is used in place of the light cyan ink, the gradation ranging from a highlighted portion of the magenta color to an intermediate portion can be made smooth.
In this embodiment, the cyan ink ejection opening array groups LG (C) are situated outside the magenta ink ejection opening array groups LG (M) with respect to the yellow ink ejection opening array group LG (Y). It is also possible to replace the two cyan ink ejection opening array groups LG (C) with the two magenta ink ejection opening array groups LG (M).
In the preceding embodiments, two kinds of ejection openings 22, 23—large and small ejection openings are provided for ejecting each of cyan, magenta and gray ink. The number of kinds of ejection openings is not limited to two.
For example, as shown in
Each of these ejection opening array groups LG (C), LG (M), LG (G), as shown in
The yellow ink ejection opening array group LG (Y) and the black ink ejection opening array group LG (Bk) are formed in the same way as the preceding embodiments. That is, these ejection opening array groups, as shown in
Since the ejection opening array groups LG (C), LG (M), LG (G) each eject three sizes of ink droplets—large, medium and small—the gradation can be divided largely into three stages. That is, the first stage is one where only the small ink droplets are ejected. When the ejection ratio of the small ink droplets reaches a predetermined value, the medium ink droplets begin to be used, which is the second stage. The third stage is one where, when the ejection ratio of the medium ink droplets reaches a predetermined value, the large ink droplets begin to be used.
In this embodiment, too, a good image quality can be obtained, as in the preceding embodiments. When, for example, a gradation that changes from yellow to black is printed, the image quality can be improved by starting ejecting the gray ink only when the ejection density of the yellow ink has sufficiently lowered, as with the preceding embodiments.
This embodiment has the following advantages. That is, since there are three dot sizes, the grayscale representation is sufficiently smooth in frequently used grayscale ranges of individual color spaces. Another advantage is that a black color at high grayscale level can be printed. Still another advantage is that the size of the ink ejection portion 3 (see
Because of the provision of three dot sizes, when a light cyan ink and a light magenta ink are also used, the grayscale ranges in which they are used overlap the grayscale ranges of the normal cyan ink and the normal magenta ink. If only one kind of ink can be used as a halftone representation ink, the gray ink is given a priority. It is noted, however, that if there is no limitation on the size of the ink ejection portion 3, the image quality can be made better by the additional use of the light cyan ink and the light magenta ink.
In the ejection opening array groups LG (Bk), LG (Y), LG (P), LG (Gr) for black ink (Bk), yellow ink (Y), red ink (R) and green ink (Gr), the ejection openings 22 are arrayed at 600-dpi intervals on both sides of the associated common liquid chamber 21. The ejection openings 22 have a diameter of about 16 μm and eject large ink droplets of about 5 pl.
In the ejection opening array groups LG (C), LG (M) for cyan ink (C) and magenta ink (M), the ejection openings 22, about 16 μm in diameter, to eject large ink droplets of about 5 pl are formed on one side of the associated common liquid chamber 21 and the ejection openings 23, about 12 μm in diameter, to eject small ink droplets of about 2 pl are formed on the other side. More specifically, the ejection opening array groups LG (C), LG (M) have the ejection openings 22 formed at 600-dpi intervals on a side of the associated common liquid chamber 21 which is near the yellow ink ejection opening array group LG (Y) and, on the far side, the ejection openings 23 formed at 600-dpi intervals.
The red ink is made by selecting colorants more saturated than a mixture of magenta ink and yellow ink. Similarly, the green ink is prepared by selecting colorants more saturated than a mixture of cyan ink and yellow ink. The red ink and the green ink are used to allow for printing highly saturated colors, as when printing vivid color photos of, for instance, setting sun and grassy field.
(Printing a Gradation that Changes from Yellow to Red)
Next, by referring to
The gradation is made to change from yellow to red as follows.
Since this example employs the 2-pass printing method, the yellow color is produced by forming three large dots of large yellow ink droplets at 600-dpi in two scans. In this state, small magenta ink droplets begin to be ejected to progressively increase their ejection ratio. When the ejection ratio of small magenta ink droplets has reached a predetermined value, the large magenta ink droplets begin to be ejected. This is followed by the large red ink droplets being started to be ejected, with their ejection ratio being progressively increased. As the red ink starts to be used, the volumes of yellow ink and magenta ink used are progressively reduced. When three large dots of large red ink droplets are formed at 600-dpi, the red color reaches a sufficiently high grayscale level.
This example prints the gradation in two passes. So, in areas where the red color reaches the highest level of grayscale, one ejection opening array group LG (R) ejects large red ink droplets to form 1.5 large dots on average in each of the forward scan and the backward scan. When red ink droplets begin to be ejected, large yellow ink droplets are ejected to form 1.5 large dots on average in each scan. At this time, large magenta ink droplets are also ejected to form about 0.25 large dot and small magenta ink droplets ejected to form about 0.5 small dot.
The magenta ink ejection opening array group LG (M) on the left side in
However, since the red ink droplets are larger they are not affected by the air flow produced by the yellow ink ejection. So, during the printing of a color that is changing from yellow to red, no air flow-based color variations occur, whatever grayscale level the image being printed has, assuring a high-quality printed image.
(Printing a Gradation that Changes from Yellow to Green)
When printing a gradation that changes from yellow to green, the same process occurs as when printing a gradation that changes from yellow to red, except that the magenta ink is replaced with the cyan ink.
In this case also, the green droplets are large and thus are not affected by the air flow produced by the yellow ink ejection. Therefore, also during the printing of a color that is changing from yellow to green, no air flow-based color variations occur, whatever grayscale level the image being printed has, assuring a high-quality printed image.
In this embodiment, the red ink ejection opening array group LG (R) and the green ink ejection opening array group LG (Cr) are interposed between the magenta ink ejection opening array groups LG (M) and the yellow ink ejection opening array group LG (Y). However, one of the ejection opening array groups LG (R), LG (Gr) may be an ink ejection opening array group LG for a blue ink with high level of saturation. In this case, too, the gradation that changes from yellow to blue can be printed with a similar effect to that of the printing of a gradation that changes from yellow to red or to green.
In place of the red ink and the green ink, a gray ink and a light gray ink may be used. In that case, an effect of smoothing the gradation in monochrome printing can be produced in addition to assuring a good print quality of red color.
Further, in place of the red ink and the green ink, a light cyan ink and a light magenta ink may be used. In that case, the gradations of halftone of cyan and magenta can be made smooth in addition to assuring a good print quality of red color.
The diameter of the ejection openings 22 for red ink and green ink may be set to 12 μm rather than 16 μm. This makes smooth the gradation in the red or green color space near magenta or cyan.
It is also possible to provide between the magenta and yellow ink ejection opening array groups LG (M), LG (Y) an ejection opening array group LG that ejects an ink of light color or saturated color made of one or more of cyan, magenta and yellow ink. In that case, the gradation of halftone can be made deep or smooth or a highly saturated color printed, which in turn prevents the air flow-based color variations even if the yellow ink ejection density is high, assuring a high quality of printed images.
Although the preceding embodiments have been described to eject ink by using a pressure of bubble in ink produced by a heater, the heater may be replaced with a piezoelectric element.
While in the preceding embodiments the ejection opening array groups LG have been described to have two or three ejection opening arrays L, they may be constructed to have only one ejection opening array L. In such a case, too, the air flow-based color variations can be prevented.
In either of the preceding embodiments, one ejection opening array group is arranged between the yellow ink ejection opening array group LG (Y) and the magenta ink ejection opening array groups LG (M). It is also possible to arrange two or more ejection opening array groups between the ejection opening array groups LG (Y) and LG (M), as shown in
The ink jet print head of this invention needs only to include ejection openings for yellow, magenta and cyan inks and an ejection opening for a fourth ink other than yellow, magenta and cyan. A plurality of ejection openings for ejecting one of yellow, magenta and cyan ink are lined along at least one of a first ejection opening array, a plurality of ejection openings for ejecting one of the remaining two inks are lined along at least one of a second ejection opening array, and a plurality of ejection openings for ejecting the remaining ink are lined along at least one of a third ejection opening array. The first, second and third ejection opening array are arranged parallelly to adjoin each other in a predetermined direction, with the number of the first ejection opening arrays being less than those of the second and third ejection opening arrays. A plurality of ejection openings to eject the fourth ink are arranged along a fourth ejection opening array between the first ejection opening arrays and the second or third ejection opening arrays, that are arranged to adjoin each other in the predetermined direction.
The first, second third and fourth ejection opening arrays may be placed on both sides, with respect to the predetermined direction, of the associated common liquid chamber, to which ink is supplied, to form the first, second, third and fourth ejection opening array groups. In that case, the number of first ejection opening array groups is smaller than those of the second ejection opening array groups and the third ejection opening array groups. The fourth ejection opening array group is disposed between the first ejection opening array groups and the second or third ejection opening array groups, which adjoin each other in the predetermined direction. Further, on the outer side of the third ejection opening array groups may be arranged a fifth ejection opening array group for ejecting a fifth ink, which is different from yellow, magenta, cyan and fourth inks.
By using the ink jet print head having the first, second, third and fourth ejection opening arrays formed parallelly to adjoin each other in the predetermined direction, an image can be printed on a print medium. Each of the first, second, third and fourth ejection opening array has a plurality of ink ejection openings arrayed, with the number of the first ejection opening arrays being less than those of the second ejection opening arrays and the third ejection opening arrays. The fourth ejection opening arrays are disposed between the first ejection opening arrays and the second or third ejection opening arrays, which are arranged adjoining each other in the predetermined direction. Printing an image by using such a print head involves ejecting one of the yellow, magenta and cyan inks from the first ejection opening arrays, ejecting one of the remaining two inks from the second ejection opening arrays, ejecting the remaining ink from the third ejection opening arrays, and then ejecting the fourth ink, different from the yellow, magenta and cyan ink, from the fourth ejection opening arrays.
The present invention is not limited to the serial type, bidirectional printing apparatus but can also be applied to a unidirectional printing apparatus that prints an image in only a forward or backward scan. Further, this invention is also applicable to a so-called full-line type printing apparatus, which prints an image continuously with a long print head extending widthwise of the print medium over an entire width of the print area, by continuously moving the print head and the print medium relative to each other in one direction
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2008-213028, filed Aug. 21, 2008, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-213028 | Aug 2008 | JP | national |
