Ink-jet head and head unit

An ink-jet head includes a nozzle array including plural nozzles. The nozzle array has a first nozzle group arranged in the center thereof and second nozzle groups arranged further on outer sides than the first nozzle group. Inter-nozzle pitches of the second nozzle groups are larger than inter-nozzle pitches of the first nozzle group. A direction in which nozzles of the second nozzle group eject an ink and a direction in which nozzles of the first nozzle group eject the ink are different.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink-jet head and a head unit that eject an ink to a recording medium.

2. Description of the Related Art

For example, U.S. 2005/0122354A1 discloses an ink-jet head in which so-called end dot deflection is reduced. This ink-jet head has plural recording element substrates. Recording areas of the recording element substrates are arranged to overlap one another.

When ink droplets are ejected at high recording density, ink droplets ejected from nozzles located at both the ends of an ink-jet head deviate toward the center of the ink-jet head. This phenomenon is referred to as “end dot deflection”. In this ink-jet head, correction for adjusting the number of recording elements used for actual ejection is performed according to recording density. A stable image with a fixed quality is obtained according to this correction.

Further, U.S. 2005/0212854A1 discloses an ink-jet head that provides a time difference when ink droplets are landed on a recording medium. In this ink-jet head, plural head chips are arranged in a zigzag shape to function as one long ink-jet head as a whole. In forming dots on the recording medium in this ink-jet head, when dots adjacent to one another have to be formed, the dots are formed with a time difference equal to or longer than time in which an ink is absorbed by the recording medium. This prevents ink droplets from combining on the recording medium to damage a desirable dot shape.

However, in the invention disclosed in U.S. 2005/0122354A1, it is necessary to perform correction for adjusting recording elements actually used for ejection. Thus, it is likely that adjustment of the ink-jet head takes time. Further, since there are nozzles not used for ejection, the nozzles are wasted.

In the invention disclosed in U.S. 2005/0212854A1, there is no indication about end dot deflection. Thus, it is likely that, when end dot deflection occurs, it is impossible to cope with the end dot deflection.

It is an object of the invention to provide an ink-jet head that can cope with “end dot deflection” of an ink with a simple structure.

BRIEF SUMMARY OF THE INVENTION

In order to attain the object, an ink-jet head according to an aspect of the invention includes a nozzle array including plural nozzles. The nozzle array has a first nozzle group arranged in the center thereof and second nozzle groups arranged further on outer sides than the first nozzle group. Inter-nozzle pitches of the second nozzle groups are larger than inter-nozzle pitches of the first nozzle group.

In order to attain the object, an ink-jet head according to another aspect of the invention includes a nozzle array including plural nozzles. The nozzle array has a first nozzle group arranged in the center thereof and second nozzle groups arranged further on outer sides than the first nozzle group. Nozzles of the second nozzle groups eject an ink obliquely in directions of outer sides at both the ends of the nozzle array.

In order to attain the object, a head unit according to still another aspect of the invention includes a first ink-jet head that has a first nozzle array including plural nozzles and a second ink-jet head that has a second nozzle array including plural nozzles. The first nozzle array has a first nozzle group arranged in the center thereof and second nozzle groups arranged further on outer sides than the first nozzle group. Inter-nozzle pitches of the second nozzle groups are larger than inter-nozzle pitches of the first nozzle group. The inter-nozzle pitches of the second nozzle array are uniform.

In order to attain the object, a head unit according to still another aspect of the invention includes a first ink-jet head that has a first nozzle array including plural nozzles and a second ink-jet head that has a second nozzle array including plural nozzles. The first nozzle array has a first nozzle group arranged in the center thereof and second nozzle groups arranged further on outer sides than the first nozzle group. Nozzles of the second nozzle groups eject an ink obliquely in directions of outer sides at both the ends of the first nozzle array. Inter-nozzle pitches of the second nozzle array are uniform.

Objects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of an ink-jet recording apparatus will be hereinafter explained with reference toFIGS. 1 to 3. This ink-jet recording apparatus is mounted on an ink jet-recording apparatus and ejects ink droplets on a recording medium such as a sheet and forms characters, figures, signs, and images thereon.

As shown inFIG. 1, an ink-jet recording apparatus11has a head unit12and an ink tank25that supplies an ink to first to third ink-jet heads21,22, and23of the head unit12.

The head unit12has the first ink-jet head21, the second ink-jet head22, the third ink-jet head23, and a plate24for attaching the first to the third ink-jet heads21,22, and23. The first ink-jet head21has a first nozzle array31. The second ink-jet head22has a second nozzle array32. The third ink-jet head23has a third nozzle array33.

The ink tank25has a first tank25A for supplying the ink to the first ink-jet head21, a second tank25B for supplying the ink to the second ink-jet head22, and a third tank25C for supplying the ink to the third ink-jet head23.

The first ink-jet head21and the first tank25A are connected by a first tube26A. The second ink-jet head22and the second tank25B are connected by a second tube26B. The third ink-jet head23and the third tank25C are connected by a third tube26C.

As shown inFIG. 2, the first ink-jet head21and the second ink-jet head22of the head unit12are arranged in zigzag to partially overlap each other in a direction in which the first and the second nozzle arrays31and32extend. The second ink-jet head22and the third ink-jet head23are arranged in zigzag to partially overlap each other in a direction in which the second and the third nozzle arrays32and33extend. The first to the third ink-jet heads21,22, and23have the same structure. Therefore, the first ink-jet head21will be explained below.

As shown inFIGS. 2 and 3, in the first nozzle array31, for example, one hundred nozzles27in total from #1 to #100 are provided on a nozzle plate27A. The first nozzle array31has a first nozzle group31A arranged in the center thereof and second nozzle groups31B arranged further on outer sides than the first nozzle group31A. The second nozzle groups31B are provided as a pair on both the outer sides of the first nozzle group31A.

Inter-nozzle pitches of the first nozzle group31A refer to distances among the nozzles27adjacent to one another. The inter-nozzle pitches of the first nozzle group31A are uniform and are, for example, 40 μm.

Inter-nozzle pitches of the second nozzle groups31B are larger than the inter-nozzle pitches of the first nozzle group31A. In other words, the inter-nozzle pitches of the second nozzle groups31B are equal to or larger than 40 μm. More specifically, the inter-nozzle pitches of the second nozzle groups31B increase toward both the ends of the first nozzle array31.

The second ink-jet head22has a first nozzle group32A and second nozzle groups32B that are the same as those in the first ink-jet head21. The third ink-jet head23has a first nozzle group33A and second nozzle groups33B that are the same as those in the first ink-jet head21.

An example of ejection of ink droplets will be explained with reference toFIG. 4. In the example, ink droplets are ejected on a recording medium, which is assumed to be 2 mm apart from the surface of the nozzle plate27A, using an ink-jet head that has a nozzle array with uniform inter-nozzle pitches. When ejection of ink droplets is performed at high recording density using nozzles arranged at uniform pitches, a phenomenon called “end dot deflection” is observed at both the ends of the nozzle array. A cause of “end dot deflection” is not clear. As shown inFIG. 4, because of this phenomenon, ink droplets ejected from nozzles at both the ends of the nozzle array land on a recording medium deviating to the center of the ink-jet head. Therefore, pitches among dots adjacent to one another landed on the recording medium decrease toward both the ends of the nozzle array. It is confirmed that numerical values of the pitches fluctuate according to a clearance of recording media.

InFIG. 5, arrangements of the nozzles27of the first to the third ink-jet heads21,22, and23according to this embodiment are indicated by a solid line and dots. Values obtained by adding the inter-nozzle pitches 40 μm of the first nozzle group31A and a distance of movement of ink droplets by “end dot deflection” are indicated by a broken line and circles. The inventor has found that, when the inter-nozzle pitches of the second nozzle groups31B are set to numerical values indicated by the broken line and the circles, end dot deflection does not occur depending on conditions. Therefore, in this embodiment, the inter-nozzle pitches of the second nozzle groups31B are set to a value smaller than the numerical values indicated by the broken line. This value is found experimentally and set as appropriate according to distances between the first to the third ink-jet heads21,22, and23and a recording medium.

Print processing using the ink-jet recording apparatus11according to this embodiment will be explained. The ink-jet recording apparatus11applies printing to a recording medium at high recording density and applies, for example, coating processing to the entire surface of the recording medium.

The first to the third ink-jet heads21,22, and23of the head unit12apply print processing to the recording medium at high recording density using all the nozzles27. In applying the print processing, the first to the third tanks25A,25B, and25C supply an ink to the first to the third ink-jet heads21,22, and23.

Ink droplets ejected from the nozzles27included in the first nozzle group31A are linearly ejected on the recording medium. Ink droplets ejected from the nozzles27included in the second nozzle groups31B gather in the center of the first ink-jet head21because of “end dot deflection”. However, in this embodiment, the inter-nozzle pitches of the second nozzle groups31B increase toward both the ends of the first nozzle array31. Thus, the ink droplets land on correct positions on the recording medium. This makes pitches among the ink droplets landed on the recording medium uniform.

The first embodiment of the ink-jet recording apparatus is described above. According to the first embodiment, the inter-nozzle pitches of the second nozzle groups31B are larger than the inter-nozzle pitches of the first nozzle group31A. According to this constitution, since the inter-nozzle pitches of the second nozzle groups31B are larger than normal inter-nozzle pitches, it is possible to mitigate the phenomenon of “end dot deflection”.

In this case, the inter-nozzle pitches of the second nozzle groups31B increase toward both the ends of the first nozzle array31. According toFIG. 4, ink droplets ejected from the nozzles27located at both the ends of the first nozzle array31move by a great degree because of the “end dot deflection” phenomenon. However, ink droplets ejected from the nozzles27close to both the ends of the first nozzle array31move in a very small distance because of the “end dot deflection” phenomenon. According to this constitution, it is possible to arrange the nozzles27by shifting positions thereof from one another in association with the “end dot deflection” phenomenon in which an amount of movement of ink droplets increases toward both the ends of the first nozzle array31. This makes it possible to mitigate the “end dot deflection” phenomenon and land ink droplets in proper positions on recording media that are conveyed while keeping a clearance decided in advance.

In this case, the inter-nozzle pitches of the first nozzle group31A are uniform. According to this constitution, the inter-nozzle pitches of the second nozzle groups31B are smaller than a value obtained by adding the inter-nozzle pitches of the first nozzle group31A in the center of the first nozzle array31, in which the “end dot deflection” phenomenon is not observed, and the distance of the movement of the ink droplets due to end dot deflection. Usually, the “end dot deflection” phenomenon is observed when printing is performed at high recording density. When recording density falls, “end dot deflection” less easily occurs. Therefore, when the inter-nozzle pitches of the second nozzle groups31B are simply set to the value obtained by adding the inter-nozzle pitches of the first nozzle group31A and the distance of the movement of the ink droplets due to end dot deflection, “end dot deflection” does not occur in the second nozzle groups31B in which the inter-nozzle pitches are set large. As a result, the ink lands on the recording medium while keeping the large pitches. In this embodiment, since the inter-nozzle pitches of the second nozzle groups31B are set smaller than the value, it is possible to prevent the situation in which “end dot deflection” does not occur in the ink ejected from the second nozzle groups31B and pitches among ink droplets landed on the recording medium become inappropriate.

A second embodiment of an ink-jet recording apparatus41will be explained with reference toFIG. 6. The ink-jet recording apparatus41according to the second embodiment is different from the ink-jet recording apparatus11according to the first embodiment in a structure of a second ink-jet head42. However, the other components are the same as those in the first embodiment. Thus, the difference is mainly explained. The same components are denoted by the same reference numerals and signs and explanations of the components are omitted.

The ink-jet recording apparatus41has the head unit12and the ink tank25that supplies an ink to first to third ink-jet heads21,42, and23of the head unit12.

The head unit12has the first ink-jet head21, the second ink-jet head42, the third ink-jet head23, and the plate24for attaching the first to the third ink-jet heads23.

The second ink-jet head42includes a second nozzle array43. The second nozzle array43includes the plural nozzles27. In the second nozzle array43, for example, one hundred nozzles27in total from #1 to #100 are provided on the nozzle plate27A. Inter-nozzle pitches of the second nozzle array43are uniform and are, for example, 40 μm. The nozzles27of the second nozzle array43are opened in a direction orthogonal to a recording medium. In other words, the nozzles27of the second nozzle array43are opened in the vertical direction.

The first ink-jet head21includes the first nozzle array31. The first nozzle array31has, for example, one hundred nozzles27in total from #1 to #100. The first nozzle array31has the first nozzle group31A arranged in the center thereof and the second nozzle groups31B arranged further on outer sides than the first nozzle group31A. The second nozzle groups31B are provided as a pair on both the outer sides of the first nozzle group31A.

Inter-nozzle pitches of the first nozzle group31A refer to distances among the nozzles27adjacent to one another. The inter-nozzle pitches of the first nozzle group31A are uniform and are, for example, 40 μm.

Inter-nozzle pitches of the second nozzle groups31B are larger than the inter-nozzle pitches of the first nozzle group31A. The inter-nozzle pitches of the second nozzle groups31B increase toward both the ends of the first nozzle array31. The inter-nozzle pitches of the second nozzle group31B are smaller than a value obtained by adding the inter-nozzle pitches of the first nozzle group31A and a distance of movement of ink droplets due to end dot deflection.

Print processing using the ink-jet recording apparatus41according to the second embodiment will be explained. In this embodiment, an ink-jet head used for printing is switched according to recording density of the printing.

When printing is applied to the recording medium at high recording density, for example, using the nozzles27equal to or more than 50% of all the nozzles, the “end dot deflection” phenomenon occurs. Therefore, for the printing at high recording density, the first ink-jet head21and the third ink-jet head23, which cope with “end dot deflection”, are used. Consequently, ink droplets land in desirable positions on the recording medium.

On the other hand, when printing is applied to the recording medium at low recording density, for example, using the nozzles27equal to or less than 50% of all the nozzles, the “end dot deflection” phenomenon is hardly observed. Therefore, for the printing at low recording density, the second ink-jet head42having the normal inter-nozzle pitches is used. Consequently, ink droplets land in desirable positions on the recording medium.

The second embodiment of the ink-jet recording apparatus is described above. According to the second embodiment, the head unit12has the first and the third ink-jet heads21and23, which cope with the “end dot deflection” phenomenon, and the second ink-jet head42having the normal inter-nozzle pitches. Therefore, it is possible to switch an ink-jet head used for printing according to recording density of the printing. Consequently, when printing is performed at high recording density and when printing is performed at low recording density, it is possible to appropriately correct landing positions of ink droplets and improve a printing quality.

A third embodiment of an ink-jet recording apparatus will be explained with reference toFIGS. 7,8, and9. An ink-jet recording apparatus51according to the third embodiment is different from the ink-jet recording apparatus41according to the second embodiment in structures of a first ink-jet head52and a third ink-jet head53. However, the other components are the same as those in the second embodiment. Thus, the difference is mainly explained. The same components are denoted by the same reference numerals and signs and explanations of the components are omitted.

The ink-jet recording apparatus51has the head unit12and the ink tank25that supplies an ink to respective ink-jet heads of the head unit12.

The head unit12has a first ink-jet head52, the second ink-jet head42, a third ink-jet head53, and the plate24for attaching the first to the third ink-jet heads52,42, and53.

The second ink-jet head42includes the second nozzle array43. The second nozzle array43includes the plural nozzles27. Inter-nozzle pitches of the second nozzle array43are formed uniform. The nozzles27of the second nozzle array43are opened in a direction orthogonal to a recording medium55shown inFIG. 9. In other words, the nozzles27of the second nozzle array43are opened in a direction orthogonal to the surface of a nozzle plate27A shown inFIG. 8.

Since the first ink-jet head52and the third ink-jet head53have the same structure, the first ink-jet head52will be explained.

The first ink-jet head52shown inFIG. 7has a first nozzle array61. The first nozzle array61includes the plural nozzles27. The first nozzle array61has a first nozzle group61A arranged in the center thereof and second nozzle groups61B arranged further on the outer sides than the first nozzle group61A. In the first nozzle array61, for example, one hundred nozzles27in total from #1 to #100 are provided on the nozzle plate27A. Inter-nozzle pitches of the first nozzle array61are uniform.

The first nozzle array61has the first nozzle group61A arranged in the center thereof and the second nozzle groups61B arranged further on the outer sides than the first nozzle group61A. The second nozzle groups61B are provided as a pair on the outer sides of the first nozzle group61A.

As shown inFIG. 8, the nozzles27of the first nozzle group61A are opened in a direction orthogonal to the recording medium55shown inFIG. 9, i.e., the vertical direction. The nozzles27of the second nozzle group61B are opened obliquely to the direction in which the nozzles27of the first nozzle group61A are opened. In other words, the nozzles27of the second nozzle group61B incline obliquely in directions of both the ends of the first nozzle array61. An angle of inclination of the nozzles27increases toward both the ends of the first nozzle array61. Therefore, an angle formed by the direction in which the nozzles27of the second nozzle groups61B are opened and the direction in which the nozzles27of the first nozzle group61A are opened increases toward both the ends of the first nozzle array61.

The third ink-jet head53has a third nozzle array63having the same structure as the first ink-jet head52. In other words, the third nozzle array63has a first nozzle group63A and second nozzle groups63B.

Print processing using the ink-jet recording apparatus51according to the third embodiment will be explained. In this embodiment, an ink-jet head used for printing is switched according to recording density of the printing.

When printing is applied to the recording medium55at high recording density, for example, using the nozzles27equal to or more than 50% of all the nozzles, the “end dot deflection” phenomenon occurs. Therefore, for the printing at high recording density, the first ink-jet head52and the third ink-jet head53, which cope with “end dot deflection”, are used.FIG. 9shows the neighborhood of one end of the first nozzle array61of the first ink-jet head52. As shown inFIG. 9, ink droplets ejected from the end of the first nozzle array61are ejected obliquely to the recording medium55. However, the ink droplets land closer to the center of the first ink-jet head52because of the “end dot deflection” phenomenon. Consequently, ink droplets land in correct positions on the recording medium55.

On the other hand, when printing is applied to the recording medium55at low recording density, for example, using the nozzles27equal to or less than 50% of all the nozzles, the “end dot deflection” phenomenon is hardly observed. Therefore, for the printing at low recording density, the second ink-jet head22having the normal inter-nozzle pitches is used. Consequently, ink droplets land in correct positions on the recording medium55.

The third embodiment of the ink-jet recording apparatus is described above. According to the second embodiment, the head unit12has the first and the third ink-jet heads52and53, which cope with the “end dot deflection” phenomenon, and the second ink-jet head42having the normal inter-nozzle pitches. Therefore, it is possible to switch an ink-jet head used for printing according to recording density of the printing. Consequently, when printing is performed at high recording density and when printing is performed at low recording density, it is possible to correct landing positions of ink droplets and improve a printing quality. A correlation of the “end dot deflection” phenomenon for each recording density is calculated, a correction value is stored, and an ink-jet head used for printing is switched according to the recording density.

In the first and the third ink-jet heads52and53, the nozzles27of the second nozzle groups61B and63B are opened obliquely in the directions of both the ends of the first nozzle array61. According to this constitution, it is possible to mitigate the “end dot deflection” phenomenon without using the method of changing the inter-nozzle pitches of the second nozzle groups61B and63B.

An angle formed by the direction in which the nozzles27of the second nozzle groups61B are opened and the direction in which the nozzles27of the first nozzle group61A are opened increases toward both the ends of the first nozzle array61. According to this constitution, it is possible to incline an ejecting direction of the ink in association with the “end dot deflection” phenomenon in which an amount of movement of ink droplets increases toward both the ends of the first nozzle array61. This makes it possible to mitigate the “end dot deflection” phenomenon and land ink droplets in proper positions on recording media55.

Besides, it is possible to modify and carry out the ink-jet recording apparatuses11,41, and51in various ways without departing from the spirit of the invention.