JP2008074065A - Inkjet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recorder which can keep a head unit constituting an inkjet head simply arranged and prevent the generation of color streaks and white streaks caused by a positional shift of the head unit. <P>SOLUTION: The head units 13a and 13b are equipped with 10 nozzles of nozzles 12a-12j and 12a'-12j', respectively. The nozzles 12h-12j and nozzles 12a'-12c' are arranged to overlap in a conveyance direction. The nozzles 12h-12j of the head unit 13a are selected as nozzles to be actually used from the left end at an overlapping part. A dot area of a dot array L10 formed by the nozzle 12j of the nozzles 12j and 12d' at a boundary part of switching from the head unit 13a to the head unit 13b is corrected to be smaller than a dot area formed by the other nozzle. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an inkjet recording apparatus that performs recording by ejecting ink onto a recording medium such as paper in a recording apparatus such as a facsimile, a copying machine, and a printer, and more particularly to an inkjet recording apparatus that includes a line head type inkjet head. Is.

  Recording apparatuses such as facsimiles, copiers, and printers are configured to record images on recording media such as paper, cloth, and OHP sheets. However, depending on the recording method, inkjet, wire dot, thermal It can be classified into formulas and the like. These recording methods can be further classified into a serial type in which recording is performed while the recording head scans the recording medium, and a line head type in which recording is performed by a recording head fixed to the apparatus main body.

  In the line head type ink jet recording apparatus, a recording medium such as a sheet is conveyed to a predetermined recording position by a conveying means (not shown) such as a conveying belt provided in the apparatus main body, and the recording medium as shown in FIG. One row (one horizontal row in the figure) of dot rows D1 is recorded collectively by the nozzles of the line head type inkjet head 11 having a recording area of a width or larger, and the recording medium is conveyed in the conveying direction (arrow X) by the conveying means. Direction), the dot row D2 of the next row is recorded all at once. Then, by repeating such an operation a plurality of times, dots are formed in a matrix, and the entire recording medium is recorded. This enables high-speed printing as compared with a serial type ink jet head in which the recording head reciprocates in the width direction of the recording medium.

  In such a line head type ink jet recording apparatus, for example, when the resolution is 600 dpi and the recording area is A3 length, about 7,000 nozzles must be arranged. If this is arranged on one line head body, there is a problem that it is difficult to obtain the nozzle position accuracy and the production yield of the line head is deteriorated. Therefore, as shown in FIG. 8, a method is used in which a single line head 11 is configured by arranging a plurality of head units on which a plurality of nozzles are mounted. In FIG. 8, only two head units 13a and 13b constituting a part of the line head 11 are shown, and each head unit 13a and 13b has eight nozzles 12a to 12h and 12a 'to 12h', respectively. It shall be equipped with.

  If the position is shifted when arranging the head units, color stripes or white stripes may occur at the joints of the head units. For example, as shown in FIG. 9, when the two head units 13a and 13b are displaced in the approaching direction, the distance between the right end nozzle 12h of the head unit 13a located at the joint and the left end nozzle 12a 'of the head unit 13b. δ is smaller than the nozzle interval Δ on the head unit determined from the resolution. Therefore, the dot row L8 in the transport direction formed by the nozzles 12h and the dot row L9 in the transport direction formed by the nozzles 12a ′ overlap, and a color streak C is generated.

  On the other hand, as shown in FIG. 10, when the two head units 13a and 13b are displaced away from each other, the right end nozzle 12h of the head unit 13a located at the joint and the left end nozzle 12a 'of the head unit 13b. The interval δ is larger than the nozzle interval Δ. Therefore, a gap between the dot row L8 in the transport direction formed by the nozzles 12h and the dot row L9 in the transport direction formed by the nozzles 12a ′ appears as white stripes W.

  Therefore, it is necessary to arrange the head units with high precision so that the nozzle interval δ at the joint of the head units becomes equal to the nozzle interval Δ on the head unit. For example, at a resolution of 600 dpi, the nozzle interval is extremely narrow at 42.3 μm. There is a limit to mechanically assuring the positional accuracy of the head unit when assembling the line head.

  Various methods have been proposed for reducing white streaks due to variations in dot positions or dot areas resulting from nozzle ejection defects. For example, Patent Documents 1 and 2 disclose an ink jet recording apparatus that increases the amount of ink ejected from nozzles in the vicinity of nozzles that are not ejected or whose ejection direction is deviated to make white lines inconspicuous. Patent Document 3 discloses an ink jet recording apparatus that includes two line heads and compensates for ejection failure of one line head with the other line head. Patent Documents 4 and 5 disclose a method of making white stripes inconspicuous by moving the head in a direction orthogonal to the paper conveyance direction and shifting the dot positions formed by the same nozzle.

  However, the maximum discharge amount from the nozzle of the line head is that the thermal ink jet system that generates air bubbles by the heating element and discharges the ink by applying pressure causes the ink to be discharged using the volume of the cavity and the piezoelectric element (piezo element). Since the piezoelectric method to be extruded is limited by the amount of distortion of the piezoelectric element, it is difficult to form dots that greatly exceed the dot diameter used for normal image formation even using the methods of Patent Documents 1 and 2. .

  On the other hand, in the method of Patent Document 3, the defective mechanism is compensated by controlling the dot density or the transport mechanism after detecting the ejection defect, so that the control mechanism becomes complicated. In the methods of Patent Documents 4 and 5, it is necessary to move the head at a speed several tens of times faster than the paper conveyance speed. For example, an apparatus having a resolution of 600 dpi and a dot formation speed of 20 kHz (20,000 / second). In this case, the paper conveyance speed is 847 mm / sec, and it is difficult to move the head at a speed several tens of times faster. Although it is conceivable to reduce the sheet conveying speed in accordance with the head moving speed, there is a problem in that the image recording efficiency is greatly reduced.

Further, none of the above techniques can fundamentally solve the occurrence of black stripes and white stripes resulting from the nozzle placement accuracy.
JP-A-2005-59402 Japanese Patent Laid-Open No. 2005-70956 JP 2000-255067 A JP 2005-205828 A JP 2005-280050 A

  In the present invention, in view of the above-described circumstances, an ink jet recording in which a plurality of head units constituting a line head can be easily arranged and generation of color streaks and white streaks due to the positional deviation of the head units can be eliminated. An object is to provide an apparatus.

  In order to achieve the above object, the present invention provides a conveying means for conveying a recording medium, a line head type inkjet head in which a plurality of nozzles are arranged in a direction orthogonal to the conveying direction of the recording medium, An ink jet recording apparatus comprising: gradation control means for adjusting the amount of ink ejected from each nozzle according to the gradation of a pixel and controlling the gradation of dots formed on a recording medium by the ink jet head. The inkjet head is composed of a plurality of head units, and is arranged so that a part of the nozzles provided in each head unit overlaps, and the gradation control means is a head adjacent to the nozzle to be used. The area of dots formed by any one of the nozzles at the boundary that switches to the unit depends on the gradation of the pixels in the image data It is characterized by smaller than the dot area determined.

In the ink jet recording apparatus having the above-described configuration, the nozzle interval on each head unit is Δ, the nozzle interval at the boundary portion is δ, and the dot area determined according to the gradation of the pixel is S. In this case, the area S ′ of dots formed by any one nozzle in the boundary portion is determined by the following conditional expression (1).
S ′ = S × δ / Δ (1)

  The present invention also provides a conveying means for conveying a recording medium, a line head type inkjet head in which a plurality of nozzles are arranged in a direction orthogonal to the conveying direction of the recording medium, and the gradation of pixels in image data. And a gradation control unit that adjusts the amount of ink ejected from each of the nozzles and controls the gradation of dots formed on the recording medium by the inkjet head. Is composed of a plurality of head units, arranged so that a part of the nozzles provided in each head unit overlap, and the gradation control means is a boundary part where the nozzles to be used are switched to the adjacent head unit The area of dots formed by these two nozzles is determined from the dot area determined according to the gradation of the pixels in the image data. It is characterized by reduced.

In the ink jet recording apparatus having the above-described configuration, the nozzle interval on each head unit is Δ, the nozzle interval at the boundary portion is δ, and the dot area determined according to the gradation of the pixel is S. In this case, the area S ′ of the dots formed by the nozzles in the boundary portion is determined by the following conditional expression (2).
S ′ = S × (1 + δ / Δ) / 2 (2)

  According to the first configuration of the present invention, the head units are arranged in an overlapping manner, and the dot area formed by any one nozzle in the boundary portion is made smaller than the dot area determined from the gradation of the pixel. Thus, it is possible to effectively suppress the occurrence of white stripes and color stripes according to the alignment error of the head unit after assembly without improving the mechanical alignment accuracy of the head unit.

  Also, according to the second configuration of the present invention, in the ink jet recording apparatus having the first configuration, it is determined according to the nozzle interval Δ on each head unit, the nozzle interval δ at the boundary portion, and the gradation of the pixel. When the relationship between the dot area S and the area S ′ of dots formed by any one of the nozzles in the boundary portion satisfies the conditional expression (1), it corresponds to the alignment error of the head unit without performing image output. An appropriate dot area can be determined.

  Further, according to the third configuration of the present invention, the head units are arranged in an overlapping manner, and the area of the dots formed by the two nozzles in the boundary portion is made smaller than the dot area determined from the gradation of the pixels. Thus, it is possible to effectively suppress the occurrence of white stripes and color stripes according to the alignment error of the head unit after assembly without improving the mechanical alignment accuracy of the head unit. Further, since the dot area reduction rate can be reduced as compared with the case where the area of the dots formed by any one nozzle is reduced, the continuity of images at the boundary portion and both sides thereof can be further increased.

  Also, according to the fourth configuration of the present invention, in the ink jet recording apparatus of the third configuration described above, it is determined according to the nozzle interval Δ on each head unit, the nozzle interval δ at the boundary portion, and the pixel gradation. When the relationship between the dot area S and the dot area S ′ formed by the nozzles at the boundary satisfies the conditional expression (2), an appropriate dot area corresponding to the alignment error of the head unit without performing image output. Can be determined.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing a schematic configuration of the ink jet recording apparatus of the present invention, and FIG. 2 is a plan view of the conveyance belt of the ink jet recording apparatus shown in FIG.

  As shown in FIG. 1, a paper feed tray 2 that stores recording paper P is provided on the left side of the inkjet recording apparatus 100, and the recording paper P that is stored at one end of the paper feed tray 2 is A feed roller 3 for feeding and feeding one sheet at a time in order from the uppermost recording sheet P and a driven roller 4 that is in pressure contact with the feed roller 3 and is driven to rotate are provided.

  A transport belt 5 is rotatably disposed on the downstream side (right side in FIG. 1) of the paper feed roller 3 and the driven roller 4 in the paper transport direction. The conveying belt 5 is stretched between a belt driving roller 6 disposed on the downstream side in the sheet conveying direction and a belt roller 7 disposed on the upstream side and rotated by the belt driving roller 6 via the conveying belt 5. The recording paper P is conveyed in the direction of arrow X by the belt driving roller 6 being driven to rotate clockwise.

  Here, since the belt driving roller 6 is arranged on the downstream side in the paper conveyance direction X, the paper feeding side (upper side in FIG. 1) of the conveyance belt 5 is pulled by the belt driving roller 6, so that the belt tension is applied. Therefore, the recording paper P can be stably conveyed. In addition, a sheet made of dielectric resin is used for the transport belt 5, and a belt that is endlessly formed by overlapping both ends thereof, a belt without a seam (seamless), and the like are preferably used.

  Further, on the downstream side of the conveying belt 5 in the sheet conveying direction, the recording sheet P on which an image is recorded driven in the clockwise direction in the drawing is discharged to the outside of the apparatus main body, and is pressed against the upper portion of the discharging roller 8. A driven roller 9 that is driven to rotate is provided, and a discharge tray 10 on which the recording paper P discharged outside the apparatus main body is stacked is provided on the downstream side of the discharge roller 8 and the driven roller 9.

  An image is recorded on the recording paper P that is supported above the conveying belt 5 at a height that forms a predetermined interval with respect to the upper surface of the conveying belt 5. Line heads 11C, 11M, 11Y and 11K to be performed are arranged. These line heads 11C to 11K are filled with colored inks of four different colors (cyan, magenta, yellow and black), and recording is performed by ejecting the respective colored inks from the line heads 11C to 11K. A color image is formed on the paper P.

  As shown in FIG. 2, these line heads 11C to 11K have a plurality of (here, five) head units 13a to 13e arranged in a zigzag manner in a direction orthogonal to the paper conveyance direction, and are conveyed. It has a recording area that is equal to or larger than the width of P, so that one line of images can be recorded collectively on the recording paper P conveyed on the conveying belt 5. The head units 13a to 13e are arranged so that a part of the nozzles provided in the head units 13a to 13e overlap in the transport direction.

  As the ink ejection method of the line heads 11C to 11K, for example, a piezo method that pushes out ink using a piezo element (not shown), or a thermal ink jet method that generates air bubbles by a heating element and ejects ink by applying pressure. Various methods can be applied.

  FIG. 3 is a block diagram showing the configuration of the ink jet recording apparatus of the present invention. Portions common to FIGS. 1 and 2 are denoted by the same reference numerals and description thereof is omitted. The inkjet recording apparatus 100 includes a control unit 20, and an interface 21, ROM 22, RAM 23, encoder 24, motor control circuit 25, line head control circuit 26, voltage control circuit 27, and the like are connected to the control unit 20. Has been.

  The interface 21 transmits / receives data to / from a host device such as a personal computer (not shown). The control unit 20 converts the image signal received via the interface 21 into image data by performing scaling processing or gradation processing as necessary. And a control signal is output to the various control circuits mentioned later. Further, the control unit 20 adjusts the amount of ink ejected from each nozzle of the line heads 11C to 11K according to the gradation of the pixels in the image data, and the gradation (dot area) of the dots formed on the recording medium. It also serves as a gradation control means for controlling the image. For example, in the case of a piezo (piezoelectric element) method, the ink discharge amount is adjusted by changing a drive voltage value or a drive pulse width applied to each nozzle.

  The ROM 22 stores a control program or the like for recording the image by driving the line heads 11C to 11K. The RAM 23 stores the image data subjected to scaling processing or gradation processing by the control unit 20 in a predetermined area.

  The encoder 24 is connected to the belt driving roller 6 on the paper discharge side that drives the conveyance belt 5, and outputs a pulse train according to the rotational displacement amount of the rotating shaft of the belt driving roller 6. The control unit 20 calculates the rotation amount by counting the number of pulses transmitted from the encoder 24, and grasps the sheet feed amount (sheet position). Then, the control unit 20 outputs a control signal to the motor control circuit 25 and the line head control circuit 26 based on the signal from the encoder 24.

  The motor control circuit 25 drives the recording medium transport motor 28 by an output signal from the control unit 20. The recording medium conveying motor 28 is driven to rotate the belt roller 6 and rotate the conveying belt 5 clockwise in FIG. 1 to convey the sheet in the direction of arrow X.

  The line head control circuit 26 transfers the image data stored in the RAM 23 to the line heads 11C to 11K based on the output signal from the control unit 20, and the line heads 11C to 11K receive the image data based on the transferred image data. Controls ink ejection. By this control and the control of the conveyance of the sheet by the conveyance belt 5 driven by the recording medium conveyance motor 28, the recording process on the sheet is performed.

  The voltage control circuit 27 generates an alternating electric field by applying a voltage to the belt roller 7 on the sheet feeding side based on an output signal from the control unit 20, and electrostatically attracts the sheet to the transport belt 2. The electrostatic adsorption is released by grounding the belt roller 7 or the belt driving roller 6 based on an output signal from the control unit 20. Here, the voltage is applied to the belt roller 7 on the paper feed side, but the voltage may be applied to the belt drive roller 6 on the paper discharge side.

  Next, a method for arranging the head units 13a to 13e constituting the line heads 11C to 11K will be described. FIG. 4 is an enlarged plan view showing a part of a line head used in the ink jet recording apparatus of the present invention and a dot row before correction formed on a sheet. X indicates the conveyance direction of the recording paper. Here, for convenience of explanation, only the arrangement of the head units 13a and 13b in the line head 11C that discharges cyan ink is shown, but the other head units 13c to 13e constituting the line head 11C, and others are shown. The line heads 11Y to 11K (all refer to FIG. 2) will be described in exactly the same manner.

  As shown in FIG. 4, each of the head units 13a and 13b includes 10 nozzles, that is, nozzles 12a to 12j and nozzles 12a 'to 12j', and a part of the nozzles 12a to 12j and the nozzles 12a 'to 12j'. Here, the nozzles 12h to 12j and the nozzles 12a 'to 12c' are arranged so as to overlap in the transport direction.

  The nozzles 12h, 12i, and 12j of the head unit 13a are selected as the use nozzles, and the nozzles 12a ′, 12b ′, and 12c ′ of the head unit 13b are not used. At this time, the nozzle interval δ of the two nozzles (here, the nozzle 12j and the nozzle 12d ′) at the boundary portion where the head unit 13a switches to the head unit 13b is smaller than the nozzle interval Δ on the head unit, which is always determined from the nozzle resolution. . Therefore, when a solid image is formed using the line head 11C of FIG. 4, the dot line L10 formed by the nozzle 12j and the dot line L11 formed by the nozzle 12d ′ are overlapped to generate a color streak C.

  Therefore, as shown in FIG. 5, among the nozzles 12j and 12d ′ at the boundary portion, the dot area of the dot row L10 formed by the nozzle 12j is larger than the dot area determined from the gradation of the pixels in the image data. Make corrections to make it smaller. Thereby, the overlap of the dot rows L10 and L11 formed at the joint (boundary portion) between the head units 13a and 13b is alleviated, and the occurrence of color streaks can be suppressed. The same effect can be obtained by correcting the dot area of the dot row L11 formed by the nozzle 12d ′ instead of the dot row L10.

  Further, although the nozzles 12h, 12i, and 12j of the head unit 13a are selected from the left end of the overlapping portion as the nozzles used here, the nozzles 12c ', 12b', and 12a 'of the head unit 13b are selected from the right end. good. In that case, since the nozzles at the boundary portion are the nozzle 12g and the nozzle 12a ', the dot area of the dot row L7 or L8 formed by either one of the nozzles may be corrected.

  Further, for example, the nozzles to be used can be selected from both ends of the overlapping portion, such as the nozzles 12h and 12i and the nozzles 12c ′ or the nozzles 12h and the nozzles 12c ′ and 12b ′. In this case, the nozzles at the boundary portions are the nozzle 12i and the nozzle 12c ′, and the nozzle 12h and the nozzle 12b ′, respectively.

  Note that the number of nozzles to be overlapped in adjacent head units is not particularly limited, and it is sufficient that one or more nozzles overlap. However, if a large number of nozzles are overlapped, the number of unused nozzles increases, which is not efficient. About 3 is preferable.

  Another correction pattern of the dot area is shown in FIG. In FIG. 6, correction is performed so that the dot areas of the dot rows L10 and L11 formed by the two nozzles 12j and 12d ′ in the boundary portion are smaller than the dot area determined from the gradation of the pixels in the image data. ing. As a result, similarly to the case of FIG. 5, the overlap of the dot rows at the joint (boundary portion) between the head units 13a and 13b is alleviated, and the occurrence of color streaks can be suppressed.

  In addition, since the dot area reduction rate can be reduced as compared with the case of FIG. 5 in which the dot area of either one of the dot rows L10 and L11 is reduced, the difference in dot area between adjacent dot rows is also reduced and the boundary portion is reduced. The continuity of images can be further increased. As for the selection of the nozzles used, various patterns are possible as in the case of FIG.

  For controlling the dot area, a control signal is transmitted from the control unit 20 to the line head control circuit 26, and the drive voltage applied to the nozzles at the boundary portion (nozzles 12j and / or 12d 'in FIGS. This is done by lowering the drive voltage applied to the nozzle or changing the shape of the drive pulse to reduce the ink ejection amount.

  As a result, it is possible to effectively suppress the occurrence of white stripes and color stripes according to the alignment error of the head unit after assembly without improving the mechanical alignment accuracy of each head unit. The alignment efficiency of the head unit is improved, and the defect occurrence rate of the line head due to the misalignment of the head unit is reduced, and the yield is increased.

  Next, a method for determining the dot area at the boundary will be described. Now, assuming that the dot area determined from the gradation of the pixels in the image data is S and the dot area at the boundary portion is S ′, the dot area S ′ is the narrowing ratio (nozzle interval δ) of the dot row interval at the boundary portion. It is preferable to make it smaller in proportion to (the narrowness ratio). When the relationship between the dot area ratio S ′ / S in the correction of FIGS. 5 and 6 and the ratio δ / Δ of the nozzle interval δ at the boundary portion to the nozzle interval Δ on each head unit is graphed, FIG. (B).

  In the case of FIG. 5 in which the dot area formed by one nozzle at the boundary portion is reduced, when the nozzle interval δ at the boundary portion is as close as possible to Δ, that is, when δ / Δ≈1, the dot area S ′ is also S. Therefore, S ′ / S≈1. On the other hand, when the nozzle interval δ at the boundary portion approaches 0 as much as possible, that is, when δ / Δ≈0, the dot area S ′ also approaches 0, so S ′ / S≈0. Therefore, the relationship between the nozzle interval ratio δ / Δ and the dot area ratio S ′ / S is represented by a straight line having an inclination of 1 passing through the origin as shown in FIG.

From FIG. 7A, the relationship S ′ / S = δ / Δ is established, so conditional expression (1)
S ′ = S × δ / Δ (1)
The dot area S ′ of the boundary portion is determined so as to satisfy the condition, and the ink discharge amount may be controlled according to the dot area S ′.

  On the other hand, in the case of the correction shown in FIG. 6 in which the dot area formed by the two nozzles in the boundary portion is reduced, each nozzle is used when the nozzle interval δ in the boundary portion approaches Δ infinitely, that is, when δ / Δ≈1. Since the two dot areas S ′ formed in (1) also approach S, S ′ / S≈1. On the contrary, when the nozzle interval δ at the boundary portion approaches 0 as much as possible, that is, when δ / Δ≈0, the sum of the two dot areas (= 2S ′) formed by each nozzle needs to be close to S. Therefore, 2S′≈S and S ′ / S≈0.5. Therefore, the relationship between the nozzle interval ratio δ / Δ and the dot area ratio S ′ / S is represented by a straight line having a slope of 1/2 passing through the Y intercept 0.5 as shown in FIG.

From FIG. 7B, the relationship of S ′ / S = ½ (δ / Δ) +0.5 is established, so conditional expression (2)
S ′ = S × (1 + δ / Δ) / 2 (2)
The dot area S ′ of the boundary portion is determined so as to satisfy the condition, and the ink discharge amount may be controlled according to the dot area S ′.

  As another method for determining the dot area S ′ at the boundary portion, a predetermined test image (solid image) is output, and the dot area is adjusted to a level at which no color streak and white streak occur while viewing the output image. Is mentioned. However, since it is necessary to repeatedly perform the test image output and the ink discharge amount adjustment work, a method of calculating using the conditional expressions as described above is more preferable.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the number of head units constituting the line head and the number of nozzles arranged in each head unit can be arbitrarily set according to the resolution and recording width of the apparatus.

  In the above embodiment, a color printer including line heads 11C to 11K corresponding to four colors of ink has been described as an example, but the present invention is applied to a monochrome inkjet printer including a single line head. Is equally applicable.

  The present invention relates to a conveying means for conveying a recording medium, a line head type inkjet head in which a plurality of nozzles are arranged in a direction orthogonal to the conveying direction of the recording medium, and the gradation of pixels in image data. And a gradation control unit that adjusts the amount of ink ejected from each nozzle and controls the gradation of dots formed on a recording medium by the inkjet head. It is composed of head units, and is arranged so that a part of the nozzles provided in each head unit overlaps, and the gradation control means has two nozzles at the boundary where the nozzles to be used are switched to the adjacent head unit. Among them, the area of dots formed on at least one side is determined according to the gradation of the pixels in the image data. Remote smaller.

  Accordingly, there is provided an ink jet recording apparatus capable of effectively suppressing the occurrence of white stripes and color stripes according to the alignment error of the head unit after assembly without improving the mechanical alignment accuracy of the head unit. be able to. In addition, it contributes to improving the alignment work efficiency of each head unit and the yield of the line head.

  In addition, since the area of dots formed by one or two nozzles in the boundary portion is determined by the conditional expression (1) or (2), it is possible to reduce the head unit alignment error without outputting a test image. Accordingly, it is possible to determine an appropriate dot area, and it is easy to adjust the dot area at the boundary portion.

These are side surface sectional drawings which show schematic structure of the inkjet recording device of this invention. FIG. 2 is a plan view of the conveyance belt of the ink jet recording apparatus shown in FIG. 1 as viewed from above. These are block diagrams which show the structure of the inkjet recording device of this invention. FIG. 4 is an enlarged plan view showing a part of a line head used in the ink jet recording apparatus of the present invention and a dot row before correction formed on a recording paper. FIG. 5 is an enlarged plan view showing a dot row when dot area correction is performed for one nozzle at the boundary portion shown in FIG. 4. FIG. 5 is an enlarged plan view showing a dot row when dot area correction is performed for two nozzles at the boundary portion shown in FIG. 4. These are graphs showing the relationship between the dot area ratio S ′ / S and the ratio δ / Δ of the nozzle interval δ at the boundary portion to the nozzle interval Δ determined from the resolution in the correction of FIGS. 5 and 6. These are enlarged plan views showing a part of a line head used in a conventional ink jet recording apparatus and a dot row formed on a recording sheet. FIG. 9 is an enlarged plan view showing a state in which the head unit constituting the line head in FIG. 8 is shifted in the approaching direction. FIG. 9 is an enlarged plan view showing a state in which the head units constituting the line head in FIG. 8 are displaced in a direction away from each other.

Explanation of symbols

2 Feeding tray 3 Feeding roller 4 Driven roller 5 Conveying belt (conveying means)
6 Belt Drive Roller 7 Belt Roller 8 Discharge Roller 9 Driven Roller 10 Discharge Tray 11C, 11M, 11Y, 11K Line Head (Inkjet Head)
12a to 12j nozzles (head unit 13a)
12a ′ to 12j ′ nozzle (head unit 13b)
13a to 13e Head unit 20 control unit (gradation control means)
100 Inkjet recording device P Recording paper (recording medium)
S dot area (determined from pixel gradation)
S 'dot area (after correction)
Δ Nozzle spacing (on head unit)
δ Nozzle spacing (boundary part)

Claims (4)

Conveying means for conveying the recording medium;
A line head type inkjet head in which a plurality of nozzles are arranged in a direction orthogonal to the conveyance direction of the recording medium;
Gradation control means for adjusting the amount of ink ejected from each nozzle according to the gradation of the pixels in the image data, and controlling the gradation of dots formed on the recording medium by the inkjet head. In the inkjet recording apparatus,
The inkjet head is composed of a plurality of head units, and is arranged so that a part of the nozzles provided in each head unit overlaps,
The gradation control means determines the area of the dots formed by any one of the boundary portions where the nozzles to be used are switched to the adjacent head unit according to the gradation of the pixels in the image data. An inkjet recording apparatus characterized by being made smaller. When the nozzle interval on each head unit is Δ, the nozzle interval of the boundary portion is δ, and the dot area determined according to the gradation of the pixel is S, it is formed by any one nozzle of the boundary portion. 2. The ink jet recording apparatus according to claim 1, wherein the dot area S ′ is determined by the following conditional expression (1).
S ′ = S × δ / Δ (1) Conveying means for conveying the recording medium;
A line head type inkjet head in which a plurality of nozzles are arranged in a direction orthogonal to the conveyance direction of the recording medium;
Gradation control means for adjusting the amount of ink ejected from each nozzle according to the gradation of the pixels in the image data, and controlling the gradation of dots formed on the recording medium by the inkjet head. In the inkjet recording apparatus,
The inkjet head is composed of a plurality of head units, and is arranged so that a part of the nozzles provided in each head unit overlaps,
The gradation control means determines the area of the dots formed by the two nozzles at the boundary portion where the nozzles to be used are switched to the adjacent head unit, than the dot area determined according to the gradation of the pixels in the image data. An ink jet recording apparatus characterized by being made small. When the nozzle interval on each head unit is Δ, the nozzle interval at the boundary portion is δ, and the dot area determined according to the gradation of the pixel is S, dots formed by the two nozzles at the boundary portion The inkjet recording apparatus according to claim 3, wherein the area S ′ is determined by the following conditional expression (2).
S ′ = S × (1 + δ / Δ) / 2 (2)

Images