JP2006044234A - Ejection head, image formation apparatus, and image formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ejection head, an image formation apparatus, and an image formation method for realizing preferable print quality by reducing unevenness generated in printing at turning positions of a head having nozzles disposed in a matrix. <P>SOLUTION: The print head 50 has a nozzle group 522 and a nozzle group 524 having a nozzle array 512 and a nozzle array 514 disposed in an inclined direction forming an angle θ (wherein 0°<θ°90°) to the main scanning direction. The nozzle group 522 and the nozzle group 524 are arranged with their phases shifted from each other in the main scanning direction so as complement the gaps of the projected nozzle arrays projected to arrange the nozzle arrays possessed by the nozzle groups in the main scanning direction. When the ink ejected from the print head 50 is to form a dot array continuously on one line in the main scanning direction, visibility of streak unevenness due to characteristics of interference of impacts caused at the turning positions A of the nozzle groups can be suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ejection head, an image forming apparatus, and an image forming method, and more particularly, to an ejection head structure and an ejection control technique for reducing the visibility of unevenness generated in a group of dots formed on an ejection medium (printing medium). .

  In recent years, ink jet recording apparatuses have become widespread as data output apparatuses for images and documents. An ink jet recording apparatus drives a recording element such as a nozzle provided in a recording head according to data, and forms data on a printing medium (recording medium) such as recording paper by ink ejected from the nozzle. it can.

  In an ink jet recording apparatus, a desired image is formed on a print medium by relatively moving a print head having a large number of nozzles and the print medium and ejecting ink droplets from the nozzles.

  The inkjet head used in the inkjet recording apparatus is a full-line head having one or more nozzle rows having a length corresponding to the full width of the print medium, or a short head having a length shorter than the full width of the print medium. There is a serial type head that scans in the width direction of the medium (main scanning direction) and forms dot rows in the main scanning direction. In the full-line type head, the head and the print medium are relatively moved in a direction (sub-scanning direction) substantially orthogonal to the width direction of the print medium, and the head scans the print medium once. Since printing can be performed over the entire printable area of the printing medium, high-speed printing is possible compared to a serial head.

  Here, FIG. 22 and FIG. 23 show the nozzle arrangement of a full-line type print head according to the prior art. FIG. 22A is a plan perspective view showing an example of the structure of the print head 500, and FIG. 22B is a plan perspective view showing another example of the structure of the print head 500.

  In order to increase the dot pitch printed on the recording paper surface in order to improve the print quality, it is necessary to increase the nozzle pitch in the print head 500, and the print head 500 shown in FIG. The nozzle 51 ejects ink droplets, and a plurality of ink chamber units 53 including a pressure chamber 52 and the like in which the planar shape is approximately square and the nozzle 51 and the supply port 54 are provided at both corners on a diagonal line are arranged in a matrix. In this way, an apparent high nozzle pitch density is achieved.

  Further, as shown in FIG. 22 (b), short two-dimensionally arranged heads 500 'may be arranged in a staggered manner and connected to form a length corresponding to the entire width of the printing medium.

  FIG. 23 shows details of the nozzle arrangement shown in FIG.

  According to FIG. 23, the nozzles 51 are arranged in a grid pattern in a fixed arrangement pattern along a row direction along the main scanning direction and an oblique column direction having a constant angle θ not orthogonal to the main scanning direction. It has become. With a structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along the direction of an angle θ ′ with respect to the main scanning direction, the pitch of the nozzles projected so as to be aligned in the main scanning direction (hereinafter referred to as the main scanning direction). Projection nozzle pitch) P0 is d × cos θ.

  That is, in the main scanning direction, each nozzle 51 can be handled equivalently as a linear array with a constant pitch P0. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  Here, as an example of general dimensions of the print head 500 shown in FIGS. 22 and 23, the size of the pressure chamber 52 is 700 μm × 700 μm, the size of the actuator 58 is 500 μm × 500 μm, and they are adjacent in the main scanning direction. The inter-nozzle pitch P1 (inter-nozzle pitch for ejecting droplets at the same timing) is 0.846 mm (corresponding to 30 npi (nozzles / inch)), and the inter-nozzle pitch is 1 mm. The ink viscosity normally used for 500 is 2 cp to 3 cp. In the print head having such a structure, various devices have been made for further increasing the nozzle density and improving the print quality.

  In the ink jet printer head described in Patent Document 1, the pressure chambers are formed in a substantially diamond shape or a substantially rectangular shape, and a large number of ink pressure chambers corresponding to multiple nozzles can be arranged in the ink jet printer head.

  In addition, the inkjet head described in Patent Document 2 is configured such that the planar shape of the surface on which the pressure plate of the chamber is arranged is defined as a substantially square or a roughly diamond shape, and the chambers are arranged in a high density.

  Further, in the head assembly method of the line type ink jet printer described in Patent Document 3, the matrix type heads are arranged in a staggered manner so as to avoid printing defects at the joints between the heads.

  In the ink jet recording apparatus described in Patent Document 4, the recording head driven by nozzle division is attached to the recording apparatus main body so that the boundaries for nozzle division driving do not overlap. The optical density distributions of the images are overlapped so that the density unevenness is alleviated and a high quality image can be obtained.

Further, in the inkjet printing apparatus and print head unit described in Patent Document 5, in a long inkjet print head configured by connecting a plurality of heater boards, the arrangement relationship of each heater board is set in one direction by a predetermined distance. The relationship is shifted, and the density unevenness that occurs at the portion corresponding to the boundary of the heater board is reduced.
JP 2002-166543 A JP 2001-334661 A JP 2002-337320 A JP-A-7-17034 JP-A-8-25635

  Next, the problems of the prior art will be described with reference to FIGS.

  FIG. 24 shows the relationship between the nozzle arrangement of the print head and the droplet ejection timing according to the prior art. The numbers shown in the circles representing the nozzles 51 indicate the droplet ejection timing. At timing t1, the nozzles 51-11, 51-21, ... indicated by 1 are ejected, and then at timing t2, 2 is ejected. The nozzles 51-12, 51-22,... Shown are ejected. In this way, at timing t3 to timing t6, the nozzles 51-13, 51-23,..., 51-16, 51-26,. In this way, droplet ejection from the nozzles shown in 1 to 6 is repeatedly performed in the order of timing t1 to timing t6, and thus one cycle of droplet ejection is performed sequentially from the nozzle shown in 1 to the nozzle shown in 6. One line of dot rows along the main scanning direction is formed on the recording paper 16 by droplet ejection.

  Further, P0 shown in FIG. 24 indicates a pitch between nozzles on which ink droplets forming adjacent dots in the main scanning direction are ejected, and P1 indicates a pitch between nozzles of nozzles adjacent in the main scanning direction (that is, the same timing). In FIG. 24, the pitch between nozzles at which droplet ejection is performed, for example, the pitch between the nozzles 51-16 and 51-26 in FIG. 24, is indicated, and P2 is the pitch between the folding positions (nozzle row connecting portions). (Interval between adjacent folding positions when projected so as to be aligned in the main scanning direction, pitch).

  The turn-back position A refers to a boundary (joint portion) of a nozzle row composed of six nozzles (for example, nozzle 51-11 to nozzle 51-16) arranged in an oblique direction. For example, in FIG. -16 and nozzle 51-21 or between nozzle 51-26 and nozzle 51-31, a nozzle that forms dots adjacent in the main scanning direction, and the pitch between nozzles in the sub-scanning direction is different from the others. Also refers to the part that is getting bigger.

  25A shows an ink droplet 501 ejected from the nozzle 51-11 at the timing t1 shown in FIG. 24 and an ink droplet 502 ejected from the nozzle 51-12 at the timing t2 shown in FIG. FIG. 25 (b) shows the cross-sectional shape (cross-sectional shape along the main scanning direction) of the droplet landed on the recording paper 16 shown in FIG. 25 (a). Yes. Note that reference numeral 511 shown in FIG. 25B indicates an ink droplet (dot) ejected from the nozzle 51-21 at the timing t1.

  As shown in FIG. 25 (a), since the ink droplet 501 ejected from the nozzle 51-11 at the timing t1 lands alone on the recording paper 16, other ink that has already landed on the recording paper 16 is used. Since it is not affected by the droplets, a dot of a size originally formed is formed at the landing position d1 where it originally landed. Further, when the ink droplet 502 ejected from the nozzle 51-12 at the timing t2 lands on the recording paper 16, the impact of the ink droplet 501 is caused by the landing interference (droplet interference) with the previously landed ink droplet 501. It is drawn in the direction (the direction of the arrow line K). As a result, a dot is formed at a position d2 ′ shifted to the ink droplet 501 side from the original landing position d2.

  In other words, the inter-dot pitch between the dots formed by the ink droplet 501 and the dot formed by the ink droplet 502 should be substantially the same as the inter-nozzle pitch P 0 between the nozzle 51-11 and the nozzle 51-12. ), The dot-to-dot pitch between the dot formed by the ink droplet 501 and the dot formed by the ink droplet 502 becomes P0 ′ smaller than P0.

  Further, the dots formed by the ink droplets 501 absorb the liquid of the ink droplets 502 to form dots larger than the original size, and the density of the dots formed by the ink droplets 501 is higher than the original density. Become. On the other hand, the dots formed by the ink droplets 502 are smaller than the original size, and the density of the dots formed by the ink droplets 502 is lower than the original density.

  Similarly, the ink droplets ejected at the timing t2 to the timing t5 are shifted toward the ink droplets that landed earlier than the original landing position due to the landing interference with the adjacent droplets that landed first. Dots are formed at the positions.

  On the other hand, as shown in FIGS. 26 (a) and 26 (b), the ink droplet 506 ejected from the nozzle 51-16 (nozzle at the return position) at the timing t6 is ejected from the nozzle 51-15 at the timing t5. The ink droplet 505 is landed between the ink droplet 505 and the ink droplet 511 ejected from the nozzle 51-21 at the timing t1, and is attracted to both the ink droplet 505 and the ink droplet 511.

  That is, the ink droplet 506 forms a dot at a position d6 ′ where the forces attracted from the ink droplet 505 and the ink droplet 511 are balanced. If the ink droplet 505 and the ink droplet 511 have substantially the same force for attracting the ink droplet 506, the ink droplet 506 forms a dot at the original landing point.

  When the ink droplet 506 forms a dot at an intermediate position between the ink droplet 505 and the ink droplet 511, the dot-to-dot pitch P 0 "between the dot formed by the ink droplet 506 and the dot formed by the ink droplet 505, and the dot and ink droplet formed by the ink droplet 506 The inter-dot pitch P0 "between the ink droplets 501 to 505 is the inter-dot pitch formed by the ink droplets 501 to 505 (the ink droplets 504 ejected at the timing t4 in FIGS. 26 (a) and (b)). The dot pitch between the dots due to the ink droplets 505 and the dots due to the ink droplets 505) is greater than P0 ′ (ie, P0 ′ <P0 ″).

  Therefore, in the nozzle arrangement shown in FIGS. 22 and 23, the inter-dot pitch varies in the printing at the turn-back position A shown in FIG. 24, and the inter-dot pitch variation causes high visibility along the sub-scanning direction. Unevenness may occur. Due to the influence of the specificity of landing interference occurring at the turn-back position A, the turn-back position becomes a singular point of landing interference, and stripe-like unevenness and density unevenness are likely to occur in the sub-scanning direction.

  Here, a visibility curve 600 is shown in FIG. The visibility curve 600 is a curve showing a boundary visually recognized as density unevenness when the horizontal axis is a spatial frequency and the vertical axis is a density difference (ΔD). The region above the visibility curve 600 is likely to be visually recognized as uneven density, and the region below the visibility curve 600 is difficult to be visually recognized as uneven density. Note that lp / mm (line pair / mm) represents the number of shades per unit length (one set of shades per unit length).

  According to the visibility curve 600, in particular, 30 npi to 50 npi (1.2 lp / mm to 2.0 lp / mm) has high visibility as uneven density, and becomes prominent in the intermediate density region when high-density image quality is improved. . According to the general dimensions of the print head 500 described above, the pitch P1 between the nozzles adjacent to each other in the main scanning direction is 0.846 mm, which corresponds to about 1.2 lp / mm when converted to a spatial frequency, The dots formed by the ink droplets ejected at intervals have high visibility of density unevenness. In particular, at the turn-back position A, it is difficult to raise the spatial frequency of density unevenness to a high-frequency region with low visibility due to its specificity.

  Further, the nozzle needs to have a hole diameter and position accuracy of about 1 μm with respect to the hole diameter φ30 μm. However, at the turn-back position A, the processing is likely to be discontinuous and the streak-like unevenness is likely to become more prominent. This is because the inter-nozzle pitch P02 of the nozzles on both sides of the folding position A shown in FIG. 24 is different from the inter-nozzle pitch P0 of other portions, or the nozzle diameters are discontinuously different. Furthermore, in order to further increase the density of the nozzle rows projected so as to be aligned in the main scanning direction, it is necessary to increase the number of nozzles aligned in the main scanning direction. There is a risk of lowering.

  In the ink jet printer head described in Patent Document 1 and the ink jet head described in Patent Document 2, since the practical pressure chamber size is about 300 μm to 500 μm, the nozzle density is 30 npi to 50 npi. In order to use as a line-type head, a matrix arrangement of 10 to 20 rows or more (300 npi to 1000 npi or more) is required. Thus, a large-sized head in which nozzles are arranged at high density is difficult to manufacture. Will go up.

  Further, in the image forming apparatus described in Patent Document 3, division adjustment for improving the yield and maintenance performance in integration is disclosed, but the division is performed in the main scanning direction, and the high density in the matrix arrangement is disclosed. An effective method for the conversion is not disclosed.

  In addition, in the inkjet recording apparatus described in Patent Document 4 and the inkjet printing apparatus and print head unit described in Patent Document 5, a configuration in which the connecting position is shifted for each color is disclosed. I can't expect it.

  The present invention has been made in view of such circumstances, and an ejection head, an image forming apparatus, and an image that reduce unevenness in printing at a turn-back position of a head having nozzles arranged in a matrix and realize preferable printing quality. An object is to provide a forming method.

  In order to achieve the above object, an ejection head according to the present invention is an ejection head in which a plurality of ejection holes are arranged in an oblique direction having a predetermined angle θ (where 0 ° <θ <90 °) with respect to the main scanning direction. There are n ejection hole groups (n is an integer of 2 or more) in the sub-scanning direction in which the hole rows are arranged at predetermined intervals in the main scanning direction. In the projected discharge hole array in which the holes are projected so as to be aligned in the main scanning direction, between the adjacent discharge holes in the projected discharge hole array of one discharge hole group, the projection discharge hole array of the other discharge hole group The discharge hole groups adjacent in the sub-scanning direction are arranged so that the phase is changed in the main scanning direction so that the discharge holes are located.

  According to the present invention, in the ejection head according to the prior art, dot formation in the main scanning direction due to landing interference (droplet ejection interference) generated on the ejection target medium due to the peculiarity of the turn-back position that is a joint between the ejection hole arrays. The positional deviation is prevented, and streaky unevenness and density unevenness generated in the sub-scanning direction can be reduced.

  The entire discharge area of the discharge medium while relatively moving the discharge target medium and the full line type discharge head having a plurality of discharge holes arranged in a length corresponding to the entire printable width of the discharge medium In the case of discharging droplets, there is an aspect in which the main scanning direction is a direction substantially orthogonal to the relative conveyance direction between the discharge medium and the discharge head.

  On the other hand, the sub-scanning direction is a direction perpendicular to the main scanning direction, and there is an aspect in which the relative transport direction between the ejection target medium and the ejection head is the sub-scanning direction.

  The ejection head has a full line type ejection head in which ejection holes for ejecting liquid droplets are arranged over a length corresponding to the entire printable width of the ejection medium, and a length corresponding to the entire width of the ejection medium. There is a serial type (shuttle scan type) discharge head that discharges liquid droplets onto a discharge medium while scanning a short head in which discharge holes for discharging droplets are arranged over a short length in the width direction of the discharge medium. .

  The discharge hole arrangement of each discharge hole group may be the same or different. It is more preferable that the discharge hole groups have the same discharge hole arrangement because each discharge hole group can be shared. Each discharge hole group may be formed in the same discharge head, or a plurality of discharge heads including one or a plurality of discharge hole groups may be provided.

  A second aspect of the invention relates to an aspect of the ejection head according to the first aspect, wherein the ejection hole group includes an even number of ejection hole groups, and the ejection hole adjacent to the main scanning direction in the ejection hole array of the ejection hole group. When the position between the ejection holes, which is the boundary between the rows and the pitch between the ejection holes in the sub-scanning direction is larger than the other, is used as the folding position, the folding is performed when the folding position is projected so as to be aligned in the main scanning direction. The ejection hole groups are arranged with the phase changed in the main scanning direction so that the pitch between positions is uniform.

  According to the second aspect of the invention, the phase in the main scanning direction of each discharge hole group is shifted so that the pitch between the folding positions projected so that the folding positions are arranged in the main scanning direction is equal. The spatial frequency of the stripe unevenness generated in the image (three-dimensional shape) formed on the ejection target medium due to the aggregation of the liquid due to the turn-back position that is a singular point of the landing time difference can be increased, and the stripe unevenness The interval becomes uniform and it becomes difficult to be visually recognized as uneven stripes.

  The turn-back position where the pitch between the ejection holes in the sub-scanning direction becomes larger than the other is the connecting position (connecting portion) between nozzle rows adjacent in the main scanning direction.

  In addition, when the flight time from the time when the ink is ejected until the ink reaches the ejection target medium is sufficiently smaller than the difference in the landing time between the plurality of ink droplets, the difference in the landing time is equivalent to the difference in the droplet ejection time.

  In addition, the image (three-dimensional shape) referred to here is a photographic image, a picture, a pattern, a character, a figure, or a patterned shape (for example, a wiring board) formed on the ejection medium by the liquid that has landed on the ejection medium. Wiring pattern etc.).

  A third aspect of the invention relates to an aspect of the ejection head according to the first or second aspect, wherein each of the plurality of ejection holes is a projection ejection hole in which the plurality of ejection holes are projected so as to be aligned in the main scanning direction. It is characterized by being arranged at different positions in the row.

  Furthermore, it is preferable that the discharge holes are arranged so that the pitches between the discharge holes of the projected discharge hole row are uniform.

  In order to achieve the above object, the image forming apparatus according to the present invention has a plurality of ejection holes arranged in an oblique direction having a predetermined angle θ (where 0 ° <θ <90 °) with respect to the main scanning direction. N discharge hole groups (n is an integer of 2 or more) in the sub-scanning direction, each of which is arranged in the main scanning direction at a predetermined interval. In the projected ejection hole array in which the ejection holes of the group are projected so as to be aligned in the main scanning direction, the projected ejection of the other ejection hole group is between adjacent ejection holes in the projected ejection hole array of one ejection hole group. An ejection head in which ejection hole groups adjacent to each other in the sub-scanning direction are arranged so that the phase is changed in the main scanning direction so that the ejection holes in the hole array are located, and the main scanning direction when the droplets land on the ejection target medium So that the existing droplets adjacent to each other are present on both sides or not on both sides. Liquid is ejected from the head, and one dot row (except for both ends of the dot row) is formed on the medium to be ejected along the main scanning direction by the droplet ejected from the ejection hole. And a droplet ejection control means for controlling in this manner.

  According to the present invention, when the area coverage of dots formed by droplets ejected on a medium to be ejected, such as a (full surface) solid image, is large, it is mainly at a landing position that does not interfere with other droplets. Since there are droplets to be ejected and droplets to be deposited at the landing positions where droplets that have already landed on both sides adjacent to the main scanning direction exist, dot formation in the main scanning direction caused by landing interference The positional deviation can be prevented, and streaky unevenness and density unevenness generated in an image formed on the ejection target medium can be reduced.

  The image forming apparatus includes an ink jet recording apparatus that forms a desired image by ejecting ink onto an ejection target medium (recording medium).

  According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the fourth aspect, wherein the discharge hole group includes an even number of discharge hole groups, and the discharge hole rows of the discharge hole group are adjacent to each other in the main scanning direction. When the position between the discharge holes, which is the boundary between the hole arrays and the pitch between the discharge holes in the sub-scanning direction is larger than the other, is set as the turn-back position, the turn-back position is projected so as to be aligned in the main scanning direction. The ejection hole groups are arranged with the phase changed in the main scanning direction so that the pitch between the folding positions is uniform.

  According to the fifth aspect of the invention, due to the peculiarity of the return position of the ejection hole array, the visibility of streak irregularities along the sub-scanning direction generated in the recorded image can be reduced, and deterioration of the image quality can be prevented. .

  A sixth aspect of the present invention relates to an aspect of the image forming apparatus according to the fourth or fifth aspect, wherein at least one of the ejection head and the ejection target medium is moved to move the ejection target with respect to the ejection head. A transport unit configured to relatively transport the discharge medium, wherein the droplet ejection control unit moves at least one of the discharge head and the discharge target medium from which the droplet is discharged from the discharge head in the sub-scanning direction. However, relative to the discharge head in the relative movement direction of the discharge medium as a reference, the discharge is sequentially performed from the discharge hole on the most upstream side to the discharge hole on the most downstream side. One dot row is formed.

  The one-cycle discharge operation referred to here is a minimum unit discharge operation that forms one dot row in the main scanning direction, and all the nozzles of the discharge hole rows arranged in an oblique direction with respect to the main scanning direction are set in a predetermined manner. There is a mode of driving in order (timing). Of course, some of the ejection holes in the ejection hole array may be turned off at a predetermined timing.

  A seventh aspect of the present invention relates to an aspect of the image forming apparatus according to the fourth, fifth, or sixth aspect, wherein the ejection head is configured to eject ink droplets that form dots adjacent in the main scanning direction. The phase of the ejection hole group is changed in the main scanning direction so that the relationship between the maximum value δTmax1 of the adjacent landing time difference and the maximum value δTmax2 of the landing time difference between the ejection holes in the head satisfies the following formula δTmax1 <δTmax2. It is characterized by arranging.

  According to the seventh aspect of the present invention, the maximum value δTmax1 of the adjacent landing time difference of the discharge holes forming the dots adjacent in the main scanning direction is not the same as the maximum value δTmax2 of the landing time difference of the discharge holes of the discharge head. As described above, since the ejection hole groups are arranged with a phase shift in the main scanning direction, it is possible to suppress unevenness in the image caused by aggregation of ink droplets that have landed on the ejection target medium.

  The invention according to an eighth aspect relates to an aspect of the image forming apparatus according to the fourth, fifth, or sixth aspect, wherein the ejection head is disposed between ejection holes that eject ink droplets that form dots adjacent in the main scanning direction. The ejection hole groups are arranged with the phase changed in the main scanning direction so that the relationship between the minimum value δTmin1 of the adjacent landing time difference and the maximum value δTmax1 of the adjacent landing time difference satisfies the following formula δTmin1 / δTmax1 ≧ 0.5 It is characterized by that.

  According to the eighth aspect of the invention, the ratio of the minimum value of the adjacent landing time difference to the maximum value of the adjacent landing time difference is predetermined so as to reduce the variation in the landing time difference of the ejection holes for forming the dots adjacent in the main scanning direction. By setting the ratio to less than or equal to, it is possible to suppress the unevenness of the lines caused by aggregation. More preferably, δTmin1 / δTmax1 ≧ 0.25.

  The relationship between the maximum value δTmax1 of the adjacent landing time difference described in claim 7 and the maximum value δTmax2 of the landing time difference between the ejection holes in the head, and the maximum value of the adjacent landing time difference described in claim 8 and the adjacent landing time difference The arrangement interval of each ejection hole group in the sub-scanning direction may be changed so as to satisfy the relationship with the minimum value.

  A ninth aspect of the invention relates to an aspect of the image forming apparatus according to any one of the fourth to eighth aspects, wherein the discharge head extends over a length corresponding to the full printable width of the discharge target medium. A full-line type discharge head including at least one row of a plurality of arranged discharge holes is included.

  In a full-line type ejection head, short heads having short ejection hole arrays that are less than the length corresponding to the entire printable width of the ejection medium are arranged in a zigzag pattern and joined together, It may be a length corresponding to the entire printable width.

  The present invention also provides a method invention for achieving the above object. That is, in the image forming method according to the tenth aspect of the present invention, an image is formed by ejecting liquid droplets onto an ejection target medium from an ejection head having ejection holes for ejecting liquid droplets. In the formation method, when the liquid droplets land on the medium to be ejected, the liquid droplets are ejected from the ejection head so that the existing liquid droplets adjacent in the main scanning direction exist on both sides or do not exist on both sides. Thus, one dot row (except for both end portions of the dot row) is formed on the medium to be ejected along the main scanning direction by the droplets ejected from the ejection holes.

  In particular, a large effect can be expected in the case where dots are densely formed on a medium to be ejected, such as a solid image.

  According to the present invention, an ejection hole array having a plurality of ejection holes in an oblique direction having a predetermined angle θ (0 ° <θ <90 °) that is not orthogonal to the main scanning direction is determined in the main scanning direction. The number of ejection hole groups arranged at intervals of n in the sub-scanning direction (where n is an even number), and between the ejection holes of the projected ejection hole rows projected so that the ejection hole rows of each ejection hole group are arranged in the main scanning direction Since the phase in the main scanning direction is changed so that the pitches are interpolated with each other, when the area coverage of the dots formed by the droplets ejected on the ejection medium, such as a (full surface) solid image, is large, Deviation of the dot formation position in the main scanning direction caused by landing interference can be prevented, and streak unevenness occurring in the sub-scanning direction can be reduced.

  In particular, when the present invention is applied to the folding position where the pitch between the ejection holes in the sub-scanning direction is larger than the others, the specificity of landing interference at the folding position can be improved, and the unevenness of the stripes occurring at the folding position can be improved. Visibility can be improved.

  Furthermore, the present invention is also effective for the discontinuity of discharge hole processing at the turn-back position.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[Overall configuration of inkjet recording apparatus]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. As shown in the figure, the inkjet recording apparatus 10 includes a print unit 12 having a plurality of print heads 12K, 12C, 12M, and 12Y provided for each ink color, and each print head 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feeding unit 18 for supplying recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle of the printing unit 12 A suction belt transport unit 22 that is disposed to face a surface (ink ejection surface) and transports the recording paper 16 while maintaining the flatness of the recording paper 16, and a print detection unit 24 that reads a printing result by the printing unit 12, A paper discharge unit 26 that discharges printed recording paper (printed matter) to the outside.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When multiple types of recording paper are used, an information recording body such as a barcode or wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration that uses roll paper, a cutter (first cutter) 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least portions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 are horizontal ( Flat surface).

  The belt 33 has a width that is greater than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. Then, the suction chamber 34 is sucked by the fan 35 to be a negative pressure, whereby the recording paper 16 on the belt 33 is sucked and held.

  When the power of a motor (not shown in FIG. 1, not shown in FIG. 8) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, the belt 33 rotates in the clockwise direction in FIG. , And the recording paper 16 held on the belt 33 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although a mode using a roller / nip conveyance mechanism instead of the suction belt conveyance unit 22 is also conceivable, if the roller / nip conveyance is performed in the print area, the image easily spreads because the roller contacts the printing surface of the sheet immediately after printing. There is a problem. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print region is preferable.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  The printing unit 12 is a so-called full line type head in which line type heads having a length corresponding to the maximum paper width are arranged in a direction (main scanning direction) orthogonal to the paper feed direction (see FIG. 2). Although a detailed structural example will be described later (FIGS. 3 to 5), each of the print heads 12K, 12C, 12M, and 12Y is a recording paper of the maximum size targeted by the inkjet recording apparatus 10 as shown in FIG. The line head includes a plurality of ink discharge holes (nozzles) arranged over a length exceeding at least one side of 16.

  A print head 12K corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 16 (hereinafter referred to as the sub-scanning direction). , 12C, 12M, 12Y are arranged. A color image can be formed on the recording paper 16 by discharging the color inks from the print heads 12K, 12C, 12M, and 12Y while the recording paper 16 is conveyed.

  Thus, according to the printing unit 12 in which the full line head that covers the entire area of the paper width is provided for each ink color, the operation of relatively moving the recording paper 16 and the printing unit 12 in the sub-scanning direction is performed once. An image can be recorded on the entire surface of the recording paper 16 only by performing it (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the print head reciprocates in the main scanning direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink are added as necessary. May be. For example, it is possible to add a print head that discharges light ink such as light cyan and light magenta.

  As shown in FIG. 1, the ink storage / loading unit 14 has tanks that store inks of colors corresponding to the print heads 12K, 12C, 12M, and 12Y, and each tank is connected via a conduit (not shown). The print heads 12K, 12C, 12M, and 12Y communicate with each other. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  The print detection unit 24 includes an image sensor for imaging the droplet ejection result of the print unit 12, and functions as a means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor.

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than at least the ink ejection width (image recording width) by the print heads 12K, 12C, 12M, and 12Y. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor is composed of a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  The print detection unit 24 reads the test pattern printed by the print heads 12K, 12C, 12M, and 12Y for each color, and detects the ejection of each head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  A post-drying unit 42 is provided following the print detection unit 24. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by pressurizing the paper holes with pressure. There is an effect to.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined surface uneven shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) that switches the paper discharge path so as to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

  Next, the structure of the print head will be described. Since the structures of the print heads 12K, 12C, 12M, and 12Y provided for the respective ink colors are common, the print heads are represented by reference numeral 50 in the following.

  FIG. 3 is a perspective plan view showing an example of the structure of the print head 50, and FIG. 4 is a cross-sectional view (cross-sectional view along line 4-4 in FIG. 3) showing the three-dimensional configuration of the ink chamber unit.

  In order to increase the dot pitch printed on the recording paper surface, it is necessary to increase the nozzle pitch in the print head 50. As shown in FIGS. 3 and 4, the print head 50 of this example includes a plurality of ink chamber units 53 including nozzles 51 for ejecting ink droplets and pressure chambers 52 corresponding to the nozzles 51. In this way, a high density of the apparent nozzle pitch is achieved.

  That is, in the print head 50 according to the present embodiment, as shown in FIG. 3, a plurality of nozzles 51 that eject ink are arranged over a length corresponding to the entire width of the print medium in a direction substantially orthogonal to the print medium feed direction. This is a full line head having one or more nozzle rows.

  As shown in FIG. 3, the nozzle 51 (ink chamber unit 53) provided in the print head 50 has a row direction along the main scanning direction and an oblique column direction having a constant angle that is not orthogonal to the main scanning direction. Are arranged in a lattice pattern with a constant arrangement pattern.

Furthermore, in the print head 500 according to the prior art shown in FIG. 22A, the nozzle row 510 in which six nozzles are arranged in a row along the row direction is the print head 50 according to the present invention shown in FIG. Are divided into a nozzle row 512 consisting of nozzles 51-11, 51-12 and 51-13 and a nozzle row 514 consisting of nozzles 51-14, 51-15 and 51-16, and further, nozzle row 512 and nozzle row. 514 is arranged with a phase shifted in the main scanning direction. That is, the nozzle row 510 arranged along the oblique direction composed of six nozzles is a nozzle row 512 having three nozzles each in the sub-scanning direction. The nozzle row 512 and the nozzle row 514 are arranged with a phase shifted in the main scanning direction. The nozzle rows 512 and 514 and other nozzle rows arranged in the main scanning direction have the same structure.

  In other words, the nozzles 51 in the print head 50 are aligned in a direction parallel to the nozzle group 512 and the nozzle array 514 that are composed of a number of nozzle arrays aligned in a direction parallel to the nozzle array 512 and the main scanning direction. A nozzle group 524 composed of a number of nozzle rows is divided into two in the sub-scanning direction by one nozzle group (for example, the nozzle group 522) and the other nozzle group (for example, the nozzle group 524). Are arranged out of phase in the main scanning direction.

  Further, in the projected nozzle array in which the nozzles 51 of the nozzle group 522 and the nozzle group 524 are projected in the main scanning direction, the phase in the main scanning direction of each nozzle group is determined so that the nozzle pitch is equal.

  In this example, a plurality of nozzles arranged in an oblique direction in each nozzle group is called a nozzle row. Further, for example, a nozzle row that belongs to two nozzle groups and functions as one nozzle row for droplet ejection control, such as the nozzle row 510 in FIG. 3, is also referred to as a nozzle row. When the nozzles of the nozzle group 510 are driven in a predetermined order, one cycle of droplet ejection (one cycle of discharge operation) can be performed.

  Note that one cycle of droplet ejection refers to a droplet ejection operation in the minimum unit that forms one dot row in the main scanning direction, and all nozzles of the nozzle rows arranged in an oblique direction with respect to the main scanning direction are in a predetermined order. There is a mode of driving at (timing). Of course, some of the nozzles in the nozzle row may be turned off at a predetermined timing.

  Further, the print head 50 includes an ink supply system having a common flow channel 55 including a main flow channel 55A and a branch flow channel 55B. The main flow paths 55A are provided in two upper and lower rows so as to sandwich the ink chamber units 53 arranged in a matrix in a staggered manner, and are arranged, for example, along the main scanning direction. Details of the nozzle arrangement of the print head 50 shown in FIG. 3 will be described later.

  A main supply port (not shown in FIG. 3 and shown as reference numeral 108 in FIG. 6) is formed at the left and right ends of the main channel 55A, and an ink supply system (ink storage / loading in FIG. 1) is formed through the main supply port. Part 14 etc.). The two main channels 55A shown in FIG. 3 communicate with a common channel 55B common to the nozzle rows 512 and 514, and ink is supplied from the ink supply system to the pressure chambers 52 via the main channel 55A and the common channel 55B. Is supplied.

  Similarly to the print head 500 ′ shown in FIG. 24 (b) described in the prior art, the print head 50 is composed of short two-dimensionally arranged heads 50 ′ arranged in a staggered manner and joined together. The length may correspond to the entire width of the print medium (recording paper 16).

  The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape, and the nozzle 51 and the supply port 54 are provided at both corners on the diagonal line. Each pressure chamber 52 communicates with a common flow path (branch flow path) 55B through a supply port 54.

  An actuator 58 having an individual electrode 57 is joined to the pressure plate 56 constituting the top surface of the pressure chamber 52, and the actuator 58 is deformed by applying a driving voltage to the individual electrode 57, and the nozzle 51 Ink is ejected. When ink is ejected, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54.

  As shown in FIG. 5, a large number of ink chamber units 53 having such a structure are arranged in a row direction along the main scanning direction and an oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. The structure is arranged in a lattice pattern. With a structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along the direction of an angle θ with respect to the main scanning direction, the pitch P0 of the nozzles projected so as to be aligned in the main scanning direction is (d × cos θ). / 2.

  That is, in the main scanning direction, each nozzle 51 can be handled equivalently as a linear arrangement with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction. Hereinafter, for convenience of explanation, it is assumed that the nozzles 51 are linearly arranged at a constant interval (pitch P0) along the longitudinal direction (main scanning direction) of the head.

  Here, the standard specification of the print head 50 according to the present invention is the same as the standard specification of the print head 500 according to the prior art. For example, the size of the pressure chamber 52 is 700 μm × 700 μm, The size of the actuator 58 is 500 μm × 500 μm, the pitch P1 between nozzles of nozzles adjacent in the main scanning direction (the pitch between nozzles of nozzles that perform droplet ejection at the same timing) is 0.846 mm (= 30 npi), and droplet ejection in the sub-scanning direction The interval is 1 mm, and the ink viscosity normally used is 2 cp to 3 cp.

  When the nozzles are driven by a full line head having a nozzle row corresponding to the full width of the paper, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially driven from one side to the other (3) ) The nozzle is divided into blocks, and each block is sequentially driven from one side to the other, etc., and a line of dots or a plurality of lines in the width direction of the paper (direction perpendicular to the paper conveyance direction) Nozzle driving that prints a line of dot rows is defined as main scanning.

  In particular, when the nozzles 51 arranged in the matrix as shown in FIG. 5 are driven, the main scanning as described in the above (3) is preferable. That is, the nozzles 51-11, 51-12, 51-13, 51-14, 51-15, 51-16 are made into one block (other nozzles 51-21,..., 51-26 are made into one block, The nozzles 51-31,..., 51-36 are set as one block,..., And the recording paper 16 is driven by sequentially driving the nozzles 51-11, 51-12,. One line is printed in the width direction.

  On the other hand, it is defined as sub-scanning that the above-described full-line head and paper are moved relative to each other to repeatedly perform a line composed of one row of dots or a line composed of a plurality of dot rows formed by the above-described main scanning.

  In the implementation of the present invention, the nozzle arrangement structure is not limited to the illustrated example. In the present embodiment, a method of ejecting ink droplets by deformation of an actuator 58 typified by a piezo element (piezoelectric element) is adopted. However, in the practice of the present invention, the method of ejecting ink is not particularly limited. Instead of the piezo jet method, various methods such as a thermal jet method in which ink is heated by a heating element such as a heater to generate bubbles and ink droplets are ejected by the pressure can be applied.

  In order to attach the print head 50 having the above-described structure to the ink jet recording apparatus 10, the head assembly (assembly) 100 shown in FIG. That is, after the print head 50 is fitted in the holder 102, the attachment 104 is sandwiched and fixed by the connecting plate 106.

  Reference numeral 108 denotes a main supply port connected to the main flow path shown in FIG. 3, and reference numeral 110 denotes an ink supply system including the ink storage / loading unit 14 shown in FIG. This is an ink conduit that communicates with each other. Reference numeral 112 denotes a rubber packing for preventing ink leakage that seals the main supply port 108 and the ink conduit 110.

  Although not shown, the attachment 104 and the connecting plate 106 are also attached to the front side of the figure.

  FIG. 7 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10.

  The ink supply tank 60 is a base tank for supplying ink, and is installed in the ink storage / loading unit 14 described with reference to FIG. There are two types of ink supply tank 60: a system that replenishes ink from a replenishment port (not shown) and a cartridge system that replaces the entire tank when the remaining amount of ink is low. A cartridge system is suitable for changing the ink type according to the intended use. In this case, it is preferable that the ink type information is identified by a barcode or the like, and ejection control is performed according to the ink type.

  As shown in FIG. 7, a filter 62 is provided between the ink supply tank 60 and the print head 50 in order to remove foreign substances and bubbles. The filter mesh size is preferably equal to or smaller than the nozzle diameter (generally about 20 μm).

  Although not shown in FIG. 7, a configuration in which a sub tank is provided in the vicinity of the print head 50 or integrally with the print head 50 is also preferable. The sub-tank has a function of improving a damper effect and refill that prevents fluctuations in the internal pressure of the head.

  Further, the inkjet recording apparatus 10 is provided with a cap 64 as a means for preventing the nozzle 51 from drying or preventing an increase in ink viscosity near the nozzle, and a cleaning blade 66 as a nozzle surface cleaning means.

  The maintenance unit including the cap 64 and the cleaning blade 66 can be moved relative to the print head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the print head 50 as necessary. The

  The cap 64 is displaced up and down relatively with respect to the print head 50 by an elevator mechanism (not shown). The cap 64 is raised to a predetermined raised position when the power is turned off or during printing standby, and is brought into close contact with the print head 50, thereby covering the nozzle surface with the cap 64.

  During printing or standby, if the frequency of use of a specific nozzle 51 is reduced and ink is not ejected for a certain period of time, the ink solvent near the nozzle evaporates and the ink viscosity increases. In such a state, ink cannot be ejected from the nozzle 51 even if the actuator 58 operates.

  Before such a state is reached (within the range of the viscosity that can be discharged by the operation of the actuator 58), the actuator 58 is operated, and the cap 64 (ink near the nozzle whose viscosity has increased) is discharged. Preliminary ejection (purging, idle ejection, collar ejection, dummy ejection) is performed toward the ink receiver.

  Further, when air bubbles are mixed into the ink in the print head 50 (in the pressure chamber 52), the ink cannot be ejected from the nozzle even if the actuator 58 is operated. In such a case, the cap 64 is applied to the print head 50, the ink in the pressure chamber 52 (ink mixed with bubbles) is removed by suction with the suction pump 67, and the suctioned and removed ink is sent to the collection tank 68. .

  In this suction operation, the deteriorated ink with increased viscosity (solidified) is sucked out when the ink is initially loaded into the head or when the ink is used after being stopped for a long time. Since the suction operation is performed on the entire ink in the pressure chamber 52, the amount of ink consumption increases. Therefore, it is preferable to perform preliminary ejection when the increase in ink viscosity is small.

  The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the ink discharge surface (surface of the nozzle plate) of the print head 50 by a blade moving mechanism (wiper) (not shown). When ink droplets or foreign substances adhere to the nozzle plate, the nozzle plate surface is wiped by sliding the cleaning blade 66 on the nozzle plate to clean the nozzle plate surface. It should be noted that when the ink ejection surface is cleaned by the blade mechanism, preliminary ejection is performed in order to prevent foreign matter from being mixed into the nozzle 51 by the blade.

  FIG. 8 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, a memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as USB, IEEE 1394, Ethernet, and wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted. The image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the memory 74. The memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 is a control unit that controls the communication interface 70, the memory 74, the motor driver 76, the heater driver 78, and the like. The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 86, read / write control of the memory 74, and the like, and controls the motor 88 and heater 89 of the transport system. A control signal to be controlled is generated.

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heater 89 such as the post-drying unit 42 in accordance with an instruction from the system controller 72.

  The print control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from image data in the memory 74 in accordance with the control of the system controller 72, and the generated print control. A control unit that supplies a signal (print data) to the head driver 84. Necessary signal processing is performed in the print controller 80, and the ejection amount and ejection timing of the ink droplets of the print head 50 are controlled via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 8, the image buffer memory 82 is shown in a form associated with the print control unit 80, but it can also be used as the memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with a single processor.

  The head driver 84 drives the actuators of the print heads 12K, 12C, 12M, and 12Y for each color based on the print data given from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  Various control programs are stored in a program storage unit (not shown), and the control programs are read and executed in accordance with instructions from the system controller 72. The program storage unit 90 may use a semiconductor memory such as a ROM or an EEPROM, or may use a magnetic disk or the like. An external interface may be provided and a memory card or PC card may be used. Of course, you may provide several recording media among these recording media. The program storage unit may also be used as a recording unit (not shown) for operating parameters.

  As described with reference to FIG. 1, the print detection unit 24 is a block including a line sensor, reads an image printed on the recording paper 16, performs necessary signal processing, and the like to perform a print status (whether ejection is performed, droplet ejection And the detection result is provided to the print control unit 80.

  The print control unit 80 performs various corrections on the print head 50 based on information obtained from the print detection unit 24 as necessary.

  In the example shown in FIG. 1, the print detection unit 24 is provided on the print surface side, and the print surface is illuminated by a light source (not shown) such as a cold cathode tube disposed in the vicinity of the line sensor. Although the configuration is such that the reflected light is read by the line sensor, other configurations may be used in the implementation of the present invention.

[Description of nozzle arrangement]
Next, the nozzle arrangement of the print head 50 according to the present invention will be described in detail.

  As shown in FIGS. 3 and 5, the configuration of each nozzle row in which a plurality of nozzles are arranged in an oblique direction not orthogonal to the main scanning direction in the print head 50 is the same. This will be described using the nozzle rows 512 and 514 as a representative.

  FIG. 9 is a diagram illustrating nozzle arrangement and droplet ejection timing of the print head 50 according to the present invention.

  As shown in FIG. 9, the print head 50 according to the present invention has six nozzles in an oblique row direction having a constant angle θ ′ that is not orthogonal to the main scanning direction in the print head 500 according to the prior art. The nozzle row 510 is divided into two nozzle rows (nozzle row 512 and nozzle row 514) having three nozzles, and the nozzle row 512 and the nozzle row 514 are divided by 1/2 of the inter-nozzle pitch P in the main scanning direction. They are shifted in the main scanning direction.

  That is, in the print head 50, a nozzle group (corresponding to an ejection hole group) in which a plurality of nozzle rows having a predetermined inclination angle θ ′ with respect to the main scan direction in the print head 500 according to the related art is arranged in the main scan direction is a secondary. The nozzle group 522 and the nozzle group 524 divided into two in the scanning direction and thus divided into two in the sub-scanning direction are arranged with their phases shifted in the main scanning direction by 1/2 of the inter-nozzle pitch P in the main scanning direction. Nozzles (nozzle rows).

  In other words, the nozzles 51 arranged in a matrix along the row direction along the main scanning direction and the column direction forming a predetermined angle θ with the main scanning direction are divided into n nozzle groups in the sub-scanning direction. The nozzle groups are arranged with a phase shifted in the main scanning direction.

  Therefore, when the nozzle row 512 and the nozzle row 514 are projected so as to be arranged in the main scanning direction, the nozzles 51-11 to 51-16 constituting the nozzle rows 512 and 514 are arranged at equal intervals along the main scanning direction. Furthermore, a nozzle 51-14 is arranged between the nozzle 51-11 and the nozzle 51-12, a nozzle 51-15 is arranged between the nozzle 51-12 and the nozzle 51-13, and the nozzle 51-16 is a nozzle. The nozzle 51-15 is disposed on the opposite side of the nozzle 51-15 which is separated from the nozzle 51-13 by P / 2 in the main scanning direction.

  It should be noted that the nozzle pitch P in the main scanning direction (inter-nozzle pitch of the projected nozzle row projected so as to be aligned in the main scanning direction) so that the ink droplets ejected at timing t1 to timing t3 do not interfere on the recording paper 16. ) Is decided.

  That is, of the dots formed continuously in the main scanning direction, the distance between two dots arranged every other dot is set such that these two dots do not overlap. It can be said that the inter-nozzle pitch P in the main scanning direction is larger than the inter-nozzle pitch P0 shown in the prior art (FIG. 23) (that is, P> P0).

  9, the numbers shown in the circles representing the nozzles 51 indicate the droplet ejection timing, and at the timing t1, the nozzles 51-11, 51-21, 51-31 (not shown in FIG. 9),. Dropping is performed. Next, at timing t2, droplet ejection is performed from the nozzles 51-12,. Further, from timing t3 to timing t6, the nozzles 51-13,..., Nozzle 51-16, nozzle 51-26, nozzles 51-36,. Thus, one line of dot row can be formed in the main scanning direction.

  Here, in the droplet ejection performed at the timings t1 to t3, the ink droplets ejected at each timing do not come into contact with the other ink droplets on the recording paper 16, and the ink droplets by each droplet ejection alone form dots. Form.

  On the other hand, at timing t4 to timing t6, when the ejected ink droplets have landed, ink droplets have already been deposited at the landing positions on both sides adjacent to each other in the main scanning direction, and landed on the recording paper 16 first. Therefore, it lands to come into contact with the ink droplets on both sides.

  That is, the ink droplets ejected at timing t4 land between ink droplets ejected at timing t1 and timing t2, and ink droplets ejected at timing t5 are similarly ejected at timing t2 and timing t3. The ink droplets that have landed between the dropped ink droplets and have been ejected at timing t6 land between the ink droplets that have been ejected at timing t1 and timing t3.

  Since the ink droplets ejected at the timing t4 to the timing t6 are attracted to the adjacent ink droplets that have landed first, the ink droplets ejected at the timing t4 to the timing t6 do not cause a phenomenon that approaches one direction. The dots formed by the ink droplets ejected at the timing t4 to the timing t6 have symmetry and can reduce the unevenness of streaks caused by unidirectional aggregation.

  In the prior art shown in FIG. 26, the ink droplets 501 land independently, and the ink droplets 506 land between the ink droplets 511 and 505 and are affected by aggregation from both sides. Other ink droplets are affected by aggregation from one direction by ink droplets that have already landed. Therefore, streaks due to the difference in aggregation conditions occurred near the ink droplet 506.

  In this specification, in the print head 50 whose nozzle arrangement is shown in FIG. 9, it is a boundary between nozzle rows adjacent in the main scanning direction of the nozzle rows (512, 514, etc.) of each nozzle group 522, 524, and The inter-nozzle position where the inter-nozzle pitch in the sub-scanning direction is larger than the others is defined as the folding position A.

  That is, in the nozzle arrangement shown in FIG. 9, between the nozzle 51-11 and the nozzle 51-23 (folding position A-1), between the nozzle 51-14 and the nozzle 51-26 (folding position A-3), etc. Is the folding position A.

  The landing time difference between the ink droplets at the turn-back position A (for example, the difference in landing time between the ink droplet ejected from the nozzle 51-11 and the ink droplet ejected from the nozzle 51-23) is the same nozzle row. Ink that has landed first because of a difference in landing time difference between the droplets of the droplets ejected from adjacent nozzles (for example, nozzle 51-11 and nozzle 51-12, nozzle 51-12 and nozzle 51-13, etc.) The amount of ink droplets remaining on the recording paper 16 is different. For this reason, since the aggregation condition changes between the folding position A and a position other than the folding position, streaking due to aggregation occurs at the folding position A.

  In FIG. 9, the interval between the folding positions in the nozzle group 522 (pitch between the folding positions) P2B, such as the spacing between the folding position A-1 and the folding position A-3, is P2B = 0.94 mm. The spatial frequency of the unevenness due to the generated aggregation is equivalent to 1.061 lp / mm, and according to the visibility curve 600 shown in FIG.

  However, the interval P2C between the folding positions in the nozzle group 524, such as the interval between the folding position A-3 and the folding position A-4, is also P2C = 0.94 mm, and the spatial frequency is the same as the folding position of the nozzle row 512. Although it has 1.061 lp / mm, as shown in FIG. 9, since the folding position A-1 and the folding position A-4 are close to each other, the spatial frequency visually recognized in the recorded image is about 1.061 lp / mm. Can be thought of as

  On the other hand, in the nozzle arrangement shown in FIG. 10, in the main scanning direction, the intervals P2 between the folding position A-1 in the nozzle group 522 and the folding position A-3 in the nozzle group 524 are equal. The nozzle arrangement is shifted in phase by a half pitch of the pitch between the folding positions.

  Therefore, the substantial cycle of the folding position A is P2 = 0.47 mm, and the spatial frequency of the folding position having this cycle is 2.13 lp / mm. As can be seen from the visibility curve 600 shown in FIG. 27, compared to the nozzle arrangement shown in FIG. 9, a nozzle arrangement shifted in a direction in which it is difficult to visually recognize density unevenness in the recorded image is possible.

  In addition, it is preferable that the turn-back position pitch P2 has a turn-back cycle of 2.0 lp / mm or more. If the turn-up cycle is set to 3.0 lp / mm or more, the visibility of the stripe unevenness can be greatly reduced. More preferable.

In a print head having a nozzle arrangement in which the pitches P2 between the folding positions are equally spaced as shown in FIG. 10, the number n of nozzle groups in the sub-scanning direction is an even number.
[Explanation of landing time difference]
Depending on the type of ink and the type of recording paper 16 (media type), density unevenness can be obtained by optimizing the landing time difference (droplet ejection time difference) instead of optimizing the pitch P2 between the folding positions shown in FIGS. Can be effectively reduced. That is, it is preferable to determine the nozzle arrangement of the print head 50 so that the landing time difference between ink droplets forming adjacent dots is smaller than the maximum landing time difference of the print head 50.

  When forming a dot row arranged on one line continuously in the main scanning direction using the print head 50 having the nozzle arrangement shown in FIG. 9, two nozzles that eject ink droplets that form adjacent dots For the combination of nozzles having a maximum landing time difference δTmax1, a nozzle that performs droplet ejection (for example, nozzle 51-11) at timing t1 and a nozzle that performs droplet ejection at timing t6 (for example, nozzle 51-26). Etc.).

  Of the combinations of nozzles that eject ink droplets that form adjacent dots, the combination of nozzles that has a maximum landing time difference between the nozzles is the maximum value δTmax1 is the nozzle that has the maximum landing time difference in the nozzle arrangement shown in FIG. It is a combination of. In other words, in the nozzle arrangement shown in FIG. 9, in order to perform droplet ejection that forms a dot adjacent in the main scanning direction using a nozzle that satisfies the relationship of δTmax1 = δTmax2 and has a maximum inter-nozzle distance in the sub-scanning direction. The landing time difference is larger than that of other nozzles that form droplets adjacent to each other in the main scanning direction. Depending on the type of the recording paper 16 and the type of ink, the stripe unevenness caused by this landing time difference may be recorded. May occur.

  In the nozzle arrangements shown in FIGS. 11 (a) and (b), the landing time difference is optimized with respect to the nozzle arrangement shown in FIG. The nozzle arrangement is determined so that a combination of nozzles different from the combination of nozzles having the maximum value δTmxa2 is used.

  That is, in the nozzle arrangement shown in FIGS. 11A and 11B, when forming a dot row arranged on one line continuously in the main scanning direction, the difference in the landing time of the nozzles of the print head 50 is the maximum value. As in the nozzle arrangement shown in FIG. 9, the combination of nozzles that achieves δTmax2 is a nozzle that ejects droplets at timing t1 (for example, nozzle 51-11) and a nozzle that ejects droplets at timing t6 (for example, nozzle 51). -16 etc.).

  On the other hand, for a combination of nozzles in which the difference in landing time between two nozzles that eject ink droplets that form adjacent dots is the maximum value δTmax1, nozzles that eject droplets at timing t2 (for example, nozzles 51-12) And a nozzle that performs droplet ejection at timing t6 (for example, nozzle 51-16 or the like).

  Therefore, in the nozzle arrangement shown in FIGS. 11 (a) and 11 (b), when forming a dot row arranged on one line continuously in the main scanning direction, nozzles that perform droplet ejection for forming adjacent dots. The relationship between the maximum value δTmax1 of the adjacent maximum landing time difference and the maximum value δTmax2 of the maximum landing time difference of the nozzles of the print head 50 satisfies δTmax1 <δTmax2.

  That is, ink droplets that form adjacent dots are ejected using nozzles other than the two nozzles that have the maximum inter-nozzle distance in the sub-scanning direction within the print head 50, so that they are adjacent to each other in the main scanning direction. The difference in landing time is not significantly different from nozzles that eject ink droplets that form dots, and streaks caused by aggregation due to an extreme difference in landing time can be suppressed.

  In addition, when the dot row arranged on one line continuously in the main scanning direction is formed using the print head 50 having the nozzle arrangement shown in FIG. 11A, adjacent dots in the main scanning direction are formed. For the combination of nozzles in which the landing time difference between the nozzles that eject ink droplets is the minimum value δTmin1, nozzles that eject ink at timing t3 and nozzles that eject ink at timing t4 (for example, 51-23 and nozzle 51- 14 combinations).

  As shown in FIG. 11B, the inter-nozzle distance between these nozzles in the sub-scanning direction is set equal to the minimum value Ptmin of the inter-nozzle distance between the nozzles in the print head 50.

  On the other hand, when forming a dot row that is continuously arranged on one line in the main scanning direction, a nozzle (for example, nozzle 51-23) in which the landing time difference between nozzles that form adjacent dots in the main scanning direction becomes the maximum value δTmax1. The nozzle pitch in the sub-scanning direction of the nozzles 51-16 and the like is set to 4 × Ptmin. At this time, the relationship between the minimum value δTmin1 of the landing time difference and the maximum value δTmax1 of the landing time difference is δTmin1 / δTmax1 = 0.25.

  When forming a dot row arranged on one line continuously in the main scanning direction using the print head 50 having the nozzle arrangement shown in FIG. 11C, nozzles for forming dots adjacent in the main scanning direction In the combination of nozzles in which the difference in landing time is the minimum value δTmin1, a nozzle that performs droplet ejection at timing t3 (for example, 51-12) and a nozzle that performs droplet ejection at timing t4 (for example, nozzle 51-14). Can be mentioned.

  As shown in FIG. 11C, the inter-nozzle distance between these nozzles in the sub-scanning direction is the minimum inter-nozzle distance Ptmin (for example, the nozzle 51-11 and the nozzle between the nozzles in the print head 50). The distance between nozzles in the sub-scanning direction with 51-12 is set to 4 × Ptmin.

  Further, the nozzle pitch in the sub-scanning direction of the nozzle (for example, nozzle 51-12 and nozzle 51-16, etc.) in which the landing time difference between the nozzles forming adjacent dots in the main scanning direction becomes the maximum value δTmax1 is 7 × Ptmin. Is set. At this time, the relationship between the minimum value δTmin1 of the landing time difference and the maximum value δTmax1 of the landing time difference is δTmin1 / δTmax1 = 0.57.

  Comparing streaks due to aggregation between the nozzle arrangement shown in FIG. 11B and the nozzle arrangement shown in FIG. 11C, the ratio δTmin1 / δTmax1 of the landing time difference between the ink droplets forming the adjacent dots is close to 1. (There is little variation in the ratio of landing time difference) The nozzle arrangement shown in FIG. 11C shows a better tendency.

  In particular, it has been found from experiments that the ratio of landing time difference δTmin1 / δTmax1 changes with 0.5 as a boundary, and the tendency of the unevenness of streaks caused by agglomeration changes. .

  That is, by optimizing the distance in the sub-scanning direction between the nozzle groups, it is possible to reduce the variation in the landing time difference between the ink droplets that land on adjacent landing positions, and to suppress the visibility of streak unevenness caused by aggregation. be able to.

  In this example, a print head including a nozzle group in which a plurality of nozzle arrays having three nozzles are arranged along the main scanning direction is illustrated, but the number of nozzles included in the nozzle array is not limited to three. Two nozzle rows may be provided, or three or more nozzles may be provided. In this example, a plurality of nozzle groups having the same nozzle arrangement are shifted in the main scanning direction and arranged in the sub scanning direction. However, a plurality of nozzle groups having different nozzle arrangements may be arranged in the sub scanning direction. Good. The different nozzle arrangements described above include, for example, a mode in which the number of nozzles included in the nozzle row of each nozzle group is different, and a mode in which the pitch between nozzles in the sub-scanning direction of each nozzle group is different.

[Application example]
Next, application examples of the present invention will be described.
FIG. 12 shows a nozzle arrangement of a print head 50 ″ having a nozzle row 530 having 20 nozzles 51 in an oblique row direction having a constant angle θ that is not orthogonal to the main scanning direction according to the prior art, Fig. 13 shows the relationship between the nozzle arrangement and the droplet ejection timing shown in Fig. 12. In Fig. 13, parts that are the same as or similar to those in Fig. 24 are given the same reference numerals, and descriptions thereof are omitted.

  As shown in FIG. 12, in the print head 50 ″, the nozzle 51-101, the nozzle 51-102, the nozzle 51-103,..., The nozzle 51-118, the nozzle 51-119, the nozzle are arranged in an oblique direction not orthogonal to the main scanning direction. A plurality of nozzle rows in which 20 nozzles are arranged in one row in the order of 51 to 120 are arranged in the main scanning direction.

  Further, the nozzle pitch P1 (for example, the interval between the nozzles 51-101 and 51-201) P1 of the nozzles adjacent in the main scanning direction is 0.846 mm, and the nozzle pitch P (for example, the nozzles 51-101 in the main scanning direction). And the distance between the nozzles 51-102) is 0.042 mm.

  In addition, the standard of the matrix head shown in the prior art or the like is applied to the other standard of the print head 50 ″.

  In the print head 50 ″ having the nozzle arrangement shown in FIG. 12, droplets are ejected from the nozzles 51-101, 51-201, etc. at the timing t1, as shown in FIG. 13, and the nozzles 51-102, 51 are ejected at the timing t2. -202, etc. Similarly, nozzle 51-103, etc. at timing t3, nozzle 51-104, etc. at timing t4, nozzle 51-105, etc. at timing t5, nozzle 51-106, etc. at timing t6, timing At t18, droplets are ejected from the nozzles 51-118, etc., at timing t19, at timing t20, droplets are ejected from the nozzles 51-120, etc. At timing t20, droplets are ejected from the nozzles 51-120, etc., at timing t1. Returning to the above, the above-described droplet ejection is repeated.

  As described above, when one cycle of droplet ejection is performed, a dot row is formed on the recording paper 16 so as to be arranged on one line continuously in the main scanning direction.

  In the nozzle arrangement described in FIG. 12, as described in the prior art, streaks in the sub-scanning direction occur at the turn-back position A (for example, the portion between the nozzles 51-120 and 51-201) due to landing interference. There are things to do.

  This is due to the nonuniformity of density unevenness due to the specificity of the landing interference occurring at the turn-back position A, and furthermore, the inter-nozzle pitch P1 of the nozzles adjacent in the main scanning direction has a spatial frequency that is easily perceived as unevenness. Because it is.

  FIG. 14 shows a print head 500 ″ having a nozzle arrangement for solving the problems of the prior art described with reference to FIGS.

  As shown in FIG. 14, the nozzles arranged in a matrix of the print head 500 ″ are divided into four in the sub-scanning direction, and the divided blocks (nozzle groups) 542, 544, 546, and 548 are phased in the main scanning direction, respectively. Are arranged.

  This is because the print head 50 ″ shown in FIG. 12 is divided into four blocks (nozzle groups 542, 544, 546, and 548) in the sub-scanning direction, and the nozzle groups are arranged with phases shifted in the main scanning direction. Is equivalent to

  As described above, when the print head 50 ″ shown in FIG. 12 is divided into four in the sub-scanning direction, and each nozzle group is arranged with a phase shifted in the main scanning direction, the nozzles 51-105 and 51-121 are arranged as nozzles. Folding positions A are formed at four positions between 51-110 and nozzle 51-126, between nozzle 51-115 and nozzle 51-131, and between nozzle 51-120 and nozzle 51-136. The spatial frequency can be made four times (high frequency) as compared with the nozzle arrangement shown in Fig. 12. Therefore, the specificity at the folding position A can be improved, and the visibility of the stripe unevenness at the folding position A can be suppressed. Can do.

  Further, in the nozzle arrangement shown in FIG. 14, as shown in FIG. 10, the nozzle groups 542, 544, 546, and 548 are shifted in the main scanning direction so that the pitch P2 between the folding positions is uniform. Yes.

  That is, in the print head 500 ″, n nozzle groups described above are arranged in the sub-scanning direction (however, n is an integer of 2 or more, and n is an even number of 2 or more in a mode in which the pitch between turn-back positions is uniform). The nozzle groups are arranged with their phases shifted in the main scanning direction, and in order to obtain a higher resolution image, an embodiment where n ≧ 4 is preferable.

  Further, the nozzle pitch P1 in the main scanning direction is equal to the distance obtained by dividing the nozzle pitch P adjacent in the main scanning direction by n. This is equivalent to assigning each nozzle group in the main scanning direction with a shift amount in units of P / n.

  The arrangement of the nozzle rows in the print head 500 ″ is the same, and the nozzle row 530 consisting of 20 nozzles 51-101 to 51-120 will be described as a representative of these nozzle rows. I will do it.

  The nozzle row 530 includes a nozzle row 532 composed of nozzles 51-101 to 51-105, a nozzle row 534 composed of nozzles 51-106 to 51-110, a nozzle row 536 composed of nozzles 51-111 to 51-115, The nozzle row 538 includes nozzles 51-116 to 51-120, the nozzle row 532 belongs to the nozzle group 542, the nozzle row 534 belongs to the nozzle group 544, the nozzle row 536 belongs to the nozzle group 546, and the nozzle row 538 belongs to the nozzle group 548.

  In the nozzle row in which the nozzles 51-101 to 51-120 are projected so as to be aligned in the main scanning direction, the nozzle row 532 is arranged such that the nozzle 51-109 is disposed between the nozzle 51-101 and the nozzle 51-102. And the nozzle row 534 are arranged with their phases shifted in the main scanning direction, and the nozzle row 534 and the nozzle row 536 are arranged so that the nozzle 51-115 is arranged between the nozzle 51-101 and the nozzle 51-109. Are arranged with the phase shifted in the main scanning direction, and the nozzle row 536 and the nozzle row 538 are arranged in the main scanning direction so that the nozzle 51-118 is arranged between the nozzle 51-102 and the nozzle 51-109. It has a structure in which the phases are shifted.

  That is, in the projected nozzle row in which the nozzles 51-101 to 51-120 included in each nozzle row 532, 534, 536, 538 are projected so as to be aligned in the main scanning direction, between adjacent nozzles in the same nozzle group, The nozzles of nozzle groups adjacent to each other in the sub-scanning direction are arranged. For example, in the projection nozzle row described above, between the nozzles 51-101 and 51-102 belonging to the nozzle group 532, the nozzles 51-109 belonging to the nozzle group 534 and the nozzle group 534 adjacent in the sub-scanning direction are positioned. is doing.

  In the nozzle arrangement shown in FIG. 14, the pitch between nozzles in the main scanning direction (the pitch between adjacent nozzles in a nozzle row projected so as to line up in the main scanning direction within the same nozzle group) P = 0.169 mm, adjacent in the main scanning direction. The inter-nozzle pitch P1 of the matching nozzles is 0.846 mm, and the turn-back position pitch P2 is 0.21 mm.

  FIG. 15 shows the relationship between the nozzle arrangement shown in FIG. 14 and the droplet ejection timing.

  As shown in FIG. 15, at time t1, droplets are ejected from the nozzles arranged in the main scanning direction with the nozzles 51-101, and at timing t2, ink droplets are ejected from the nozzles arranged in the main scanning direction with the nozzles 51-102. Done. In this way, from timing t3 to timing t20, droplet ejection is performed from the nozzles arranged in the main scanning direction to the nozzles 51-103 to the nozzles arranged in order in the main scanning direction with the nozzles 51-120.

  FIG. 16 shows projection nozzle groups 542 ′ 544 ′, 546 ′ 548 ′ in which the nozzle rows of the nozzle groups 542, 544, 546, and 548 are projected so as to be aligned in the main scanning direction.

  In FIG. 16, one of the nozzles at both ends of the folding position of each projection nozzle group is shown as a semicircle, and the other nozzle is shown as a circle. The pitch P2 between the folding positions is uniform, and the value is 0.212 mm.

  In the print head 500 ″ configured as described above, the nozzle row in which the nozzles 51 are arranged in an oblique direction not orthogonal to the main scanning direction is divided into n (where n is an even number) in the sub-scanning direction. Since the phase is shifted in the main scanning direction, it is possible to improve the peculiarity of the landing interference of the ink droplet generated at the folding position A.

  Further, if the nozzle rows are arranged so that the pitches P2 between the folding positions are substantially equal, the visibility of the stripe unevenness occurring at the folding position A can be improved.

  Further, in a multi-color head provided with a print head corresponding to each color, if the present invention is applied to the turn-back position of the head (nozzle group) corresponding to each color, the unevenness can be further reduced.

  In the present embodiment, an embodiment has been described in which ink droplets are ejected from all nozzles in one nozzle row to form one line of dot rows in the main scanning direction. When ejecting ink droplets from a nozzle to form a line of one line in the main scanning direction, the ink is formed in a state where only one of the adjacent dots is formed at both ends of the formed dots. Drops may land, and in this case, a phenomenon in which ink droplets move in one direction due to aggregation may occur. Such a phenomenon often occurs at the edge of an image, and is hardly visually recognized as unevenness in density or unevenness in density.

[Manufacturing method and processing accuracy]
Next, a method for manufacturing the print head shown in this embodiment will be described.

  FIG. 17A shows a processing example in which five nozzles 51 are formed in one row by single hole continuous processing. For single hole continuous machining, press working of SUS (plate thickness t = 80 μm, hole diameter D = 30 μm), polyimide laser processing (plate thickness t = 70 μm, hole diameter D = 30 μm), or the like is applied.

  In single-hole continuous machining, a workpiece is fixed on an XY stage, and the XY stage (hereinafter referred to as a stage) is driven in accordance with NC data (data that records positional information of holes to be machined). However, drilling is performed at a predetermined position of the workpiece.

  As indicated by the arrow lines in FIG. 17 (a), while moving the stage in the X direction by the pitch P1 between adjacent nozzles in the main scanning direction, the nozzle 51-11, nozzle 51-21, nozzle 51-31,. The first line is processed from right to left in FIG. 17A in the order of the nozzles 51-1n. When the processing of the first row is completed, the stage is moved by the pitch Ps between nozzles in the sub-scanning direction (hereinafter referred to as nozzle pitch in the sub-scanning direction) Ps projected so as to be arranged in the Y-direction in the sub-scanning direction. Eye processing is performed.

  In the processing of the second row, the XY stage is moved by the pitch P1 between the nozzles adjacent to each other in the main scanning direction in the X direction in the direction opposite to that of the first row, and the nozzles 51-2n,. Processing is performed.

  Similarly, the third row is processed in the order from nozzle 51-31 to nozzle 51-3n, the fourth row is processed in order from nozzle 51-4n to nozzle 51-41, and the fifth row is processed in order from nozzle 51-51 to nozzle 51-5n. Is done.

  In the above-described method, since the feed error in the X direction of the stage is accumulated, a large error occurs in the inter-nozzle pitch P2 at the turn-back position. Further, the stage also causes a feeding error in the Y direction, but this can be corrected at the droplet ejection timing.

  In laser processing, when output fluctuations occur due to temperature drift or the like, the hole diameter difference (hole diameter variation) at the turn-back position increases discontinuously.

  FIG. 17 (b) shows an example of machining a plurality of holes simultaneously.

  For multi-hole simultaneous processing, SUS press processing using a 5-hole bunch type, polyimide laser processing using a 5-hole excimer laser mask, or the like is applied.

  As shown in FIG. 17B, in the multi-hole simultaneous machining, the accuracy of the die and the mask directly affects the machining accuracy, and if the die (mask) 200 is rotationally displaced, the machining accuracy is greatly affected.

  For example, when a rotational deviation of Δα occurs in the mold 200, a reference numeral 200 'indicated by a broken line is obtained. When the inter-nozzle pitch Ps in the sub-scanning direction is 1 mm and the inclination in the rotation direction is Δα = 25 ″, the error ΔP2 in the inter-nozzle pitch between the nozzles adjacent in the main scanning direction is approximately 0.5 μm. In the case of 20 nozzles, when tilted approximately 5 ″ in the rotation direction (ie, Δα = 5 ″), the error ΔP2 between the nozzles of the nozzles adjacent in the main scanning direction is approximately 0.5 μm.

  Therefore, when the mold 200 is slightly inclined, the error ΔP2 between the nozzles of the nozzles adjacent in the main scanning direction becomes large.

  Although not shown, it is preferable to perform the finishing process as described above because the nozzles are integrally formed using nickel electroforming because the hole diameter varies greatly and the yield is not so good.

  Such processing problems can be improved by arranging the pitches P2 between the nozzles adjacent to each other in the main scanning direction at the folding position A so as to be equally spaced. Furthermore, when the pitch P2 between the nozzles adjacent to each other in the main scanning direction at the folding position is set so that the spatial frequency at the folding position is 2 lp / mm or more, relatively good quality is obtained. It is more preferable that the spatial frequency at the folding position is 3 lp / mm or more.

  Further, even in the nozzle arrangement shown in FIG. 22 (a) of the prior art, if the machining is divided as shown in FIG. 18 (a), each nozzle caused by machining defects such as machining position deviation and machining hole diameter variation. The spatial frequency of the inter-nozzle pitch P in the main scanning direction becomes high, and the visibility of streak unevenness and density unevenness due to processing errors of each nozzle can be lowered.

  In the embodiment shown in FIG. 18 (a), a three-hole simultaneous machining is applied, and a nozzle row composed of six nozzles is formed by two machining operations. That is, the nozzle row 210 is divided into a nozzle row 212 and a nozzle row 214, and is formed by two processes. Similarly, the nozzle row 220 is divided into a nozzle row 222 and a nozzle row 224, and the nozzle row 230 is divided into a nozzle row 232 and a nozzle row 234, and each is formed by two processes.

  When the nozzles are formed by the above-described processing method, misalignment of the dot position due to the processing variation in the nozzle row division part and the folding position of the six nozzles may occur, but since the spatial frequency is high, It is possible to reduce the visibility of stripe unevenness and density unevenness due to processing errors of each nozzle.

  FIG. 18 (b) shows dots formed by ink droplets ejected from a print head having the nozzle arrangement shown in FIG. 18 (a).

  In FIG. 18B, dots formed by ink droplets ejected at each droplet ejection timing are indicated by solid lines, and dots formed by ink droplets ejected by each droplet ejection timing are indicated by one-dot broken lines. Show.

  On the other hand, in the embodiment shown in FIGS. 18 (a) and 18 (b), the effect of improving the unevenness caused by the specificity of the landing interference at the turn-back position cannot be expected so much. Therefore, as shown in FIG. The nozzles 51 are arranged so that the nozzle pitches P2 in the main scanning direction are equally spaced.

  FIG. 19 (b) shows dots formed by ink droplets ejected from a print head having the nozzle arrangement shown in FIG. 19 (a).

  In FIG. 19B, dots formed by ink droplets ejected at each droplet ejection timing are indicated by solid lines, and dots formed by ink droplets ejected by each droplet ejection timing are indicated by one-dot broken lines. Show.

  As described above, the processing of one nozzle is divided, and further, the nozzle row is divided and the position is adjusted, so that the accuracy and the yield can be improved.

  Further, the divided matrix structure shown in FIGS. 4 and 14 is manufactured as a head block having substantially the same shape (for example, a head block including the nozzle groups 542, 544, 546, and 548 in FIG. 14). When a long print head 300 is formed by arranging head blocks (print heads) 560, 562, 564, 566, 568 and the like having four nozzle groups 542 to 548 in a staggered manner as shown in FIG. Compared with the case of manufacturing a head having an integrated structure, it is possible to facilitate processing and improve processing accuracy and yield.

  In the print head 300 shown in FIG. 20, the adjustment mechanism and the test print described in Patent Document 3 (Japanese Patent Laid-Open No. 2002-337320) also function effectively. In addition, the landing interference is different between the case where droplets are ejected at a landing position at a distant position (particularly the first head block) and the case where droplets are deposited at an adjacent landing position (particularly the head block at the rear). Although the shape and density of the dots formed at the landing positions may be different, droplet ejection is performed so as to fill the space between the dots, so the spatial frequency is high and the visibility as unevenness is low. Moreover, you may perform discharge control according to the position of a nozzle.

  In the print head 300 shown in FIG. 20, the main stream of the upper head blocks 560, 564, and 568 in FIG. 20 is communicated to form an upper main stream 310 and an intermediate main stream 312. Similarly, the main streams of the lower head blocks 562 and 564 are communicated to form a lower main stream 314 and an intermediate main stream 312. The intermediate main stream 312 formed between the upper head block and the lower head block is formed by sharing the lower main stream of the upper head block and the upper main stream of the lower head block. ing.

  Therefore, as shown in FIG. 20, if the main flow channel 55A shown in FIGS. 3 and 14 is configured to be connectable, further downsizing can be achieved. In addition, as shown in FIG. 21, a leak test can be performed with a single head block.

  FIG. 21 shows a leak test (air tightness test) apparatus 400 such as the head block 560 shown in FIG. Since the head blocks 560, 562 and the like described in FIG. 20 have the same structure, description will be made using the head block 560 here.

  In the leak test apparatus 400, a head block 560 is housed in a test jig 402, and the nozzle 51 is sealed with a sealing member 404 such as a rubber plate.

  Also, one of the openings serving as branch ends provided at both ends of the head block 560 is communicated with a pipe 406 (shown by a broken line) in the jig 402, and the other opening serving as a branch end is a jig. It is sealed by being stored in 402.

  The head block 560 thus housed in the test jig 402 is placed in a liquid (pure water or other liquid that does not contain a substance that contaminates the print head 560) 408, and a gas that does not dissolve in the liquid 408 such as chlorofluorocarbon is filled. The airtightness of the head block 560 can be tested by filling the head block 560 with 410 and determining whether or not gas is emitted into the liquid 408.

  In this embodiment, a print head used in an inkjet recording apparatus is exemplified as a droplet discharge head. However, the present invention is not limited to liquids (water, chemicals) on a discharge medium such as a wafer, a glass substrate, or an epoxy substrate. In addition, the present invention can also be applied to a discharge head used in a liquid discharge apparatus that forms shapes such as images, circuit wirings, and processing patterns by discharging a resist and a processing liquid.

1 is a basic configuration diagram of an ink jet recording apparatus equipped with a print head according to an embodiment of the present invention. FIG. 1 is a plan view of the main part around the printing of the ink jet recording apparatus shown in FIG. Plane perspective view showing structural example of print head Sectional drawing which follows the 4-4 line in FIG. FIG. 3 is an enlarged view showing the nozzle arrangement of the print head shown in FIG. The figure explaining the assembly process of the print head which concerns on embodiment of this invention. 1 is a conceptual diagram showing the configuration of an ink supply system in an ink jet recording apparatus according to an embodiment. Main part block diagram which shows the system configuration | structure of the inkjet recording device which concerns on this embodiment. The figure explaining the relationship between the nozzle arrangement of the print head which concerns on embodiment of this invention, and a droplet ejection timing The figure explaining the relationship between the other aspect of nozzle arrangement | positioning shown in FIG. 3, and a droplet ejection timing The figure explaining the relationship between the further another aspect of the nozzle arrangement shown in FIG. 10, and the droplet ejection timing Plane perspective view showing nozzle arrangement of print head according to prior art The figure explaining the relationship between the nozzle arrangement and the droplet ejection timing of the print head according to the prior art Plane perspective view showing an application example of the nozzle arrangement shown in FIG. The figure explaining the relationship between the nozzle arrangement shown in FIG. 14 and the droplet ejection timing The figure explaining the pitch between the nozzles of the main scanning direction of the return position of the nozzle arrangement shown in FIG. Diagram explaining single hole continuous machining and multi-hole simultaneous machining The figure which shows the nozzle formed by the division processing and the droplet ejection result The figure which shows the printing head which has the nozzle arrangement to which this invention formed by division | segmentation processing is applied, and a droplet ejection result The top view which shows the application example of the print head which concerns on this invention The figure explaining the test device of the print head concerning the present invention Plane perspective view showing nozzle arrangement of print head according to prior art FIG. 22 is an enlarged view showing the nozzle arrangement of the print head shown in FIG. The figure explaining the nozzle arrangement and the droplet ejection timing of the print head according to the prior art The figure explaining landing interference of the print head concerning a prior art The figure explaining landing interference in the return position of the print head concerning a prior art Graph showing visibility curve

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 50, 50 ', 50 ", 300, 500, 500', 500" ... Print head, 51 ... Nozzle, 510, 512, 514, 532, 534, 536, 538 ... Nozzle row, 522 524, 542, 544, 546, 548 ... Nozzle group

Claims (10)

Discharge holes in which discharge hole arrays in which a plurality of discharge holes are arranged in an oblique direction having a predetermined angle θ (0 ° <θ <90 °) with respect to the main scanning direction are arranged at predetermined intervals in the main scanning direction N groups (n is an integer of 2 or more) in the sub-scanning direction,
In the ejection hole groups adjacent in the sub-scanning direction, in the projected ejection hole array in which the ejection holes of each ejection hole group are projected so as to be aligned in the main scanning direction, the one ejection hole group is adjacent in the projected ejection hole array. The discharge hole groups adjacent to each other in the sub-scanning direction are arranged in the main scanning direction so that the discharge holes of the projection discharge hole row of the other discharge hole group are located between the discharge holes. Discharge head. An even number of the discharge hole groups are provided,
Of the ejection hole arrays of the ejection hole group, the position between the ejection holes that is the boundary between the ejection hole arrays adjacent in the main scanning direction and has a larger inter-ejection hole pitch in the sub-scanning direction than the other is the folding position. In this case, the ejection hole groups are arranged in different phases in the main scanning direction so that pitches between the folding positions when the folding positions are projected so as to be aligned in the main scanning direction are uniform. The ejection head according to claim 1.   3. The ejection head according to claim 1, wherein the plurality of ejection holes are arranged at different positions in a projected ejection hole array in which the plurality of ejection holes are projected so as to be aligned in the main scanning direction. Discharge holes in which discharge hole arrays in which a plurality of discharge holes are arranged in an oblique direction having a predetermined angle θ (0 ° <θ <90 °) with respect to the main scanning direction are arranged at predetermined intervals in the main scanning direction N groups (n is an integer of 2 or more) in the sub-scanning direction,
In the ejection hole groups adjacent in the sub-scanning direction, in the projected ejection hole array in which the ejection holes of each ejection hole group are projected so as to be aligned in the main scanning direction, the one ejection hole group is adjacent in the projected ejection hole array. An ejection head in which ejection hole groups adjacent to each other in the sub-scanning direction are arranged in different phases in the main scanning direction so that the ejection holes of the projection ejection hole array of the other ejection hole group are located between the ejection holes;
The liquid droplets are ejected from the ejection head so that the existing liquid droplets adjacent to each other in the main scanning direction exist on both sides or do not exist on both sides when the liquid droplets land on the medium to be ejected. Droplet ejection control means for controlling to form one dot row (excluding both ends of the dot row) along the main scanning direction on the medium to be ejected by the ejected droplets;
An image forming apparatus comprising: An even number of the discharge hole groups are provided,
Of the ejection hole arrays of the ejection hole group, the position between the ejection holes that is the boundary between the ejection hole arrays adjacent in the main scanning direction and has a larger inter-ejection hole pitch in the sub-scanning direction than the other is the folding position. In this case, the ejection hole groups are arranged in different phases in the main scanning direction so that pitches between the folding positions when the folding positions are projected so as to be aligned in the main scanning direction are uniform. The image forming apparatus according to claim 4. A transport unit configured to move at least one of the discharge head and the medium to be discharged and relatively transport the medium to be discharged with respect to the discharge head;
The droplet ejection control means moves the at least one of the ejection head and the ejection target medium from which the droplets are ejected from the ejection head in the sub-scanning direction while using the ejection head as a reference. One dot row in the main scanning direction is formed on the discharge target medium by one cycle of discharge in which discharge is sequentially performed from the discharge hole on the most upstream side in the relative movement direction to the discharge hole on the most downstream side. The image forming apparatus according to claim 4 or 5. The discharge head has a maximum value δTmax1 between adjacent landing time differences between discharge holes for ejecting ink droplets that form adjacent dots in the main scanning direction and a maximum value δTmax2 between landing time differences between discharge holes in the head. The relationship is
Tmax1 <δTmax2
The image forming apparatus according to claim 4, wherein the ejection hole group is arranged with a phase changed in the main scanning direction so as to satisfy the above. In the ejection head, the relationship between the minimum value δTmin1 of the adjacent landing time difference between the ejection holes for ejecting ink droplets that form dots adjacent in the main scanning direction and the maximum value δTmax1 of the adjacent landing time difference is expressed by the following equation: δTmin1 / ΔTmax1 ≧ 0.5
The image forming apparatus according to claim 4, wherein the ejection hole group is arranged with a phase changed in the main scanning direction so as to satisfy the above condition.   The discharge head includes a full-line discharge head having a plurality of discharge holes arranged in a length corresponding to the full printable width of the discharge medium. The image forming apparatus according to any one of the above. An image forming method of forming an image on a discharge target medium by discharging the drop onto a discharge target medium from a discharge head having a discharge hole for discharging the drop,
The liquid droplets are ejected from the ejection head so that the existing liquid droplets adjacent to each other in the main scanning direction exist on both sides or do not exist on both sides when the liquid droplets land on the medium to be ejected. An image forming method comprising: forming one dot row (excluding both ends of the dot row) along a main scanning direction on a medium to be ejected by ejected droplets.

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