JP2006306075A - Liquid ejection head, liquid ejection apparatus, and image formation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid ejection head, a liquid ejection apparatus, and an image formation apparatus which can reduce unevenness generated at the part where nozzle columns are connected (junction part). <P>SOLUTION: When a direction in which the ejection receiving medium is moved relatively with respect to the liquid ejection head is a first direction, in the liquid ejection head 50, a plurality of nozzles are two dimensionally disposed under the condition that L_pitch=L×k/(n-1) and k≤m+1 are satisfied, wherein L_pitch is a distance in the first direction on the nozzle surface between a pair of the nozzles that eject droplets to form dots that are aligned adjacently in a second direction which is substantially perpendicular to the first direction, L is a maximum distance between the nozzles in the first direction on the nozzle surface, n is a number of the nozzles in the first direction on the nozzle surface (n is an integer equal to or more than 4), m is a number of skipped nozzles indicating a number of nozzles disposed in the first direction within the distance between the pair of the nozzles in the first direction (m is an integer satisfying 1≤m≤n/2), and k is a positive integer equal to or more than 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid discharge head, a liquid discharge apparatus using the same, and an image forming apparatus, and in particular, a nozzle arrangement structure of a liquid discharge head in which a large number of discharge ports (nozzles) are two-dimensionally arranged at high density, and its The present invention relates to an image forming apparatus such as an ink jet recording apparatus that forms an image on a recording medium using a liquid discharge head.

  In the field of inkjet recording apparatuses, a liquid discharge head (so-called matrix array head) in which a large number of nozzles are two-dimensionally arranged has been proposed in order to print high-quality images at high speed. FIG. 17 is a plan view schematically showing a configuration example of a conventional matrix array head. The illustrated matrix array head 300 has a length corresponding to the entire width of the print medium 302 along a direction (main scan direction: arrow M direction) orthogonal to the transport direction (sub-scan direction: arrow S direction) of the print medium 302. This is a full-line type head in which a large number of nozzles 310 are two-dimensionally arranged.

  The pressure chambers 312 corresponding to the respective nozzles 310 communicate with a common flow path (not shown) for supplying ink via individual supply ports (not shown). The chamber 312 is filled with ink. Each pressure chamber 312 is provided with a pressure generating element (not shown) (for example, a piezoelectric element), and ink droplets can be ejected from the nozzle 310 by controlling the driving of the pressure generating element in accordance with print data. it can. By controlling the ink ejection timing of each nozzle while conveying the print medium, a desired image can be recorded on the print medium.

The conventional matrix array head 300 has a nozzle 310 and an ink chamber unit (droplet discharge element as one recording element unit) 314 composed of a pressure chamber 312 and a pressure generating element corresponding to the nozzle 310 as shown in FIG. It has a structure in which a large number of lines are arranged in an oblique grid pattern in a linearly constant arrangement pattern along the row direction along the scanning direction and the oblique column direction having a constant angle α not orthogonal to the main scanning direction. ing. If the sub-scanning direction nozzle row spacing (sub-scanning direction nozzle pitch) of the nozzle rows arranged in the main scanning direction within the nozzle surface 300A is d _Ns , the substantial nozzle spacing projected so as to be aligned in the main scanning direction (Main scanning direction projection nozzle pitch) P _N is d _Ns / tan α. With this configuration, the dot density of dots arranged adjacent to each other in the main scanning direction on the print medium 302 is narrowed, and the recording density is improved.

  By using the matrix arrangement head 300 configured as described above, it is possible to perform sub-scanning only once (the operation of moving the print medium 302 relative to the matrix arrangement head 300 in the sub-scanning direction only once). An image can be recorded on the entire surface of the print medium 302.

  However, such a conventional matrix array head 300 has a print medium that hits the joint (folded portion) of the nozzle row due to an angle error (attachment rotation position error) in the in-plane rotation direction of the head, skew of the print medium 302, or the like. There is a problem that streaky density unevenness is likely to occur in the upper portion 302.

The phenomenon will be outlined with reference to FIG. FIG. 18 shows a case where the head is installed in a state where it is slightly rotated counterclockwise in the plane parallel to the nozzle surface 300A from the original installation position (design reference position) (relative to the original main scanning direction). (When the installation angle of the head is tilted). A relatively equivalent phenomenon occurs when the print medium conveyance direction is inclined with respect to a head that is normally installed (at the reference position) (when skewed or meandered in the arrow direction S ′ in FIG. 18). It becomes.

  As shown in FIG. 18, when the matrix arrangement head 300 is installed with a rotational position error (when the print medium is conveyed at an angle with respect to the sub-scanning direction (skew, meander)). 18), the interval Pm in the main scanning direction on the print medium of the dots DA and DB ejected from the nozzle pair at the joint (folding portion) of the nozzle row indicated as A and B in FIG. 18 is adjacent to the other main scanning direction. It becomes larger than the distance between dots (refer to the enlarged view of FIG. 19). For this reason, a low density streak occurs at a position on the print medium corresponding to the nozzle pair A, B of the folded portion. When the rotation direction of the relative angular deviation between the matrix array head 300 and the printing medium is reversed, the interval between adjacent dots in the main scanning direction on the printing medium of the dots ejected from the pair of nozzles in the folded portion is narrow. As a result, streaks that increase the recording density on the print medium corresponding to the folded portion occur.

  Several solutions have been proposed in order to reduce the visibility of density unevenness that occurs at the joints (folded portions) of the nozzle rows (Patent Documents 1 to 3). In Patent Document 1, the nozzles are arranged so that the dot size ejected from the nozzles arranged in the sub-scanning direction changes in vibration, and the nozzles are arranged so that the position of the nozzles in the main scanning direction vibrates. Has proposed. Thereby, the nonuniformity which arises in the joint period of the nozzle row of a matrix arrangement | sequence can be reduced. Further, the document 1 also discloses that the unevenness is made inconspicuous by arranging the nozzles so that the joint cycle of the matrix arrangement is a high frequency with low visibility.

  Patent Document 2 discloses a line-type inkjet head in which nozzles arranged in a row (one straight line or two lines) are arranged on a head chip, and a plurality of the head chips are arranged along the line arrangement direction of the head. It has been proposed that the head chips are arranged on the same substrate in an inclined state in which the nozzle arrangement direction of the chips forms a predetermined angle with respect to the line arrangement direction. The technique disclosed in Patent Document 2 aims to increase the manufacturing accuracy and reduce the unevenness that occurs at the joints of the rows by arranging a plurality of head chips on a single substrate.

In Patent Document 3, visibility is lowered by arranging nozzles so that dots of different diameters can be ejected between dots of the same diameter aligned in the main scanning direction on the print medium, and changing the frequency of unevenness. Propose that.
Japanese Patent Laid-Open No. 2004-167982 JP 2002-273878 A JP 2004-90504 A

  However, the technique disclosed in Patent Document 1 has a problem that the density difference locally is large because the inter-dot distance error that occurs in the streaks cannot be reduced. In addition, since the dot diameter is intentionally non-uniform, the uniformity of the printed result is impaired. In other words, the periodicity irregularity of the joint is lowered by adding another period irregularity (variation) to the periodic irregularity at the joint where the countermeasure was originally taken by changing the dot size or the dot position. Only.

  Since the unevenness that can be reduced by the method of Patent Document 2 is only unevenness caused by an error in nozzle arrangement, unevenness caused by in-plane tilt of the head, skew of the medium, or the like cannot be reduced.

  The technique of Patent Document 3 requires a configuration such as hitting dots with different diameters. Only the frequency is changed, and since the error of the dot interval is large when viewed microscopically, the difference from the ideal print result becomes large.

  The present invention has been made in view of such circumstances, and a liquid discharge head capable of reducing unevenness caused by an attachment position error in the in-plane rotation direction of the head, skewing of a medium, and the like, and a liquid using the same An object is to provide an ejection device and an image forming apparatus.

In order to achieve the above object, an invention according to claim 1 is a liquid discharge head having a nozzle surface in which a plurality of nozzles for discharging a liquid are two-dimensionally arranged, and the liquid discharge head is covered with the liquid discharge head. When the direction in which the ejection medium is moved relative to the first direction is the first direction, on the nozzle surface of the nozzle pair that has a relationship of ejecting adjacent dots arranged in a second direction substantially orthogonal to the first direction on the ejection medium L_pitch is the distance in the first direction at L, L is the maximum distance between nozzles in the first direction in the nozzle surface, and n is the number of nozzles in the first direction in the nozzle surface (where n is 4 or more) An integer), and m is a nozzle skipping number representing the number of nozzles arranged in the first direction between the nozzle pairs in the first direction (where m is 1 ≦ m ≦ n) Integer satisfying / 2), k is 1 or more When the set to an integer, the following equation L_pitch = L × k / (n-1)
k ≦ m + 1
The plurality of nozzles are two-dimensionally arranged under a condition that satisfies

  According to the present invention, since there is no specific nozzle pair in which the pitch between nozzles in the first direction of the nozzle pair for ejecting adjacent dots arranged in the second direction on the medium to be ejected is significantly increased, the head and the printing medium Even when the relative angular error occurs, it is possible to reduce the error in the inter-dot distance between the dots arranged adjacent in the second direction on the ejection medium. As a result, unevenness caused by head mounting rotation position error, medium conveyance skew error due to skew or meandering of the medium to be ejected, or angular error (hereinafter collectively referred to as “rotation error”) due to a combination thereof. Can be reduced.

  According to a second aspect of the present invention, there is provided a liquid discharge head having a nozzle surface in which a plurality of nozzles for discharging droplets are two-dimensionally arranged, and the target medium is moved relative to the liquid discharge head. When the direction is the first direction, the second direction nozzle rows in which the nozzles are linearly arranged along the second direction substantially orthogonal to the first direction in the nozzle surface are mutually in the nozzle surface. N rows (where n is an integer of 4 or more) provided by changing the position in one direction, and the nozzles of any of the nozzle pairs in a relationship of ejecting adjacent dots arranged in the second direction on the ejection target medium. Having a structure in which the second direction nozzle rows of m rows (where m is an integer satisfying 1 ≦ m ≦ n / 2) are sandwiched between the distances in the first direction on the nozzle surface; Phase the target medium in the first direction with respect to the liquid discharge head. A second direction dot line in which dots are arranged along the second direction on the medium to be ejected is formed by adhering droplets ejected from the nozzles of each of the n rows to the medium to be ejected while moving. In the second direction dot line, the n consecutive dot groups that are ejected by the nozzles in each of the n rows correspond to the dots in the order of arrangement of adjacent dots in the second direction. When the nozzle to be tracked is tracked in the nozzle surface, the nozzle that hits the next dot in the arrangement order is the nozzle row of the nozzle group arranged on the upstream side in the first direction, and the next dot in the arrangement order. It is characterized by having a polygonal nozzle array structure in which nozzles to be hit are combined with nozzle rows of nozzle groups arranged on the downstream side in the first direction.

According to the second aspect of the present invention, the second direction dots are ejected onto the medium to be ejected by sequentially ejecting the liquid from each of the n-th row of nozzles in the second direction as the medium to be ejected moves relative to the liquid ejection head. A line can be formed. The second direction dot line is a group of dots in which n dots ejected from the second direction nozzle row in each row from the first row to the n-th row are arranged on a straight line while being adjacent to each other on the ejection target medium. The repeating unit is connected in the second direction with a repeating unit of (a line-shaped dot group of n consecutive dots).

  When attention is paid to this repeating unit (n dot groups continuously arranged in the second direction on the medium to be ejected), the nozzles corresponding to the dots are tracked in the nozzle surface in the order of arrangement of the dot groups. The drawn trajectory (a line formed by following the nozzle arrangement) has a polygonal line shape having at least one turning point where the inclination direction is reversed, such as a V shape or a W shape.

  With this configuration, there is no specific nozzle pair in which the pitch between nozzles in the first direction of the nozzle pair that ejects adjacent dots arranged in the second direction on the medium to be ejected is significantly increased. Similarly to the above, unevenness caused by a rotation error can be reduced.

According to a third aspect of the invention, there is provided the liquid ejection head according to the second aspect, wherein on the nozzle surface of the nozzle pair in a relationship of ejecting adjacent dots arranged in the second direction on the ejection target medium. L_pitch is the distance in the first direction at L, L is the maximum inter-nozzle distance in the first direction in the nozzle surface, and n is the number of rows in the second direction nozzle row in the nozzle surface (where n is 4 or more) ), M is the number of nozzle skips that represents the number of rows of the second direction nozzle row arranged between the distances in the first direction of the nozzle pair (where m is 1 ≦ m ≦ n / 2), where k is an integer greater than or equal to 1, the following formula: L_pitch = L × k / (n−1)
k ≦ m + 1
The plurality of nozzles are two-dimensionally arranged under a condition that satisfies

  According to the aspect concerning Claim 3, while being able to implement | achieve a high-density nozzle arrangement | positioning, generation | occurrence | production of the nonuniformity by a rotation error can be suppressed.

  According to a fourth aspect of the present invention, there is provided a liquid ejection apparatus that achieves the object. That is, a liquid ejection device according to a fourth aspect conveys at least one of the liquid ejection head according to any one of the first to third aspects, the liquid ejection head and the ejection target medium, and the liquid ejection head Conveying means for relatively moving the medium to be ejected in the first direction, and ejection control means for performing control to eject liquid from the nozzles of the liquid ejection head in accordance with the relative movement by the conveying means. It is characterized by having.

  According to the fourth aspect of the invention, it is possible to realize a liquid ejection apparatus that can reduce the occurrence of unevenness due to a rotation error.

  The invention according to claim 5 relates to an aspect of the liquid discharge apparatus according to claim 4, and discharges the medium to be discharged from the nozzle while moving the discharge medium relative to the liquid discharge head in the first direction by the transport unit. In the case where a second direction dot line in which dots are arranged along the second direction is formed on the medium to be ejected by adhering the droplets to the medium to be ejected, the second direction dot line of the second direction dot line is formed. When the nozzles corresponding to each dot are traced in the nozzle plane in the order of arrangement of dots adjacent in two directions, the nozzle that strikes the next dot in the arrangement order is arranged on the upstream side in the first direction. The nozzle group is divided into a nozzle group in which a nozzle that strikes the next dot in the arrangement order is arranged on the downstream side in the first direction, and the plurality of nozzles are grouped. , Characterized by comprising an ejection correction means for correcting the ejection state.

  In a nozzle group in which the nozzle that hits the next dot in the dot arrangement order of the second direction dot line is arranged on the upstream side in the first direction and the nozzle group arranged in the downstream side, a certain rotation error The increase / decrease direction of the inter-dot distance in the second direction on the medium to be ejected is reversed. Due to the rotation error, the dot density in the area where droplets are ejected tends to decrease in the nozzle group where the distance between dots in the second direction on the ejection medium increases. It is preferable to perform correction to increase the number).

  On the other hand, because of the rotation error, the dot density in the area where droplets are ejected tends to increase in the nozzle group where the distance between the dots in the second direction on the medium to be ejected decreases. Alternatively, it is preferable to perform a correction to reduce the number of droplet ejection).

  As described above, the unevenness can be further reduced by correcting the discharge state for each nozzle group in accordance with the difference in increase / decrease in the distance between the dots in the second direction with respect to the rotation error.

  A sixth aspect of the invention relates to an aspect of the liquid ejection apparatus according to the fifth aspect, wherein a head angle identifying unit that identifies an attachment angle of the liquid ejection head and the relative movement of the ejection target medium with respect to the liquid ejection head. Correction for controlling a correction amount for correcting the ejection state based on the identification result of the at least one angle identification unit. And a quantity control means.

  A mode in which the amount of rotation error is grasped by the head angle specifying means, the medium angle specifying means, or a combination thereof, and the ejection correction amount of each nozzle group is adaptively controlled according to the error amount is preferable.

  The invention described in claim 7 provides an image forming apparatus that achieves the object. That is, an image forming apparatus according to a seventh aspect includes the liquid ejecting apparatus according to any one of the fourth to sixth aspects, and forms an image on the ejection target medium by the ink liquid ejected from the nozzle. It is characterized by.

  In order to realize a high-resolution image output, a droplet discharge element (ink liquid chamber) configured to include a discharge port (nozzle) for discharging ink liquid, a pressure chamber corresponding to the nozzle, and a pressure generating element. An embodiment using a liquid discharge head (print head) in which a large number of units) are arranged at high density is preferable.

  As a configuration example of such a liquid discharge head for printing, a full line type head in which a plurality of nozzles are arranged over a length corresponding to the entire width of the discharge target medium can be used. A full-line type head is usually arranged along a direction perpendicular to the relative feed direction (relative transport direction) of a medium to be ejected (recording medium such as recording paper), but is perpendicular to the transport direction. On the other hand, there may be a mode in which the head is arranged along an oblique direction having a certain predetermined angle.

  In the case of forming a color image using an ink jet type liquid discharge head (print head), a head may be arranged for each color of a plurality of colors, or a configuration capable of discharging a plurality of colors from one head It is good.

  The “ejection medium” is a medium that receives adhesion of the liquid ejected from the nozzles of the liquid ejection head, and corresponds to a recording medium such as recording paper in the image forming apparatus. That is, the “ejection medium” can be called a recording medium, a printing medium, an image forming medium, a recording medium, an image receiving medium, etc., and is a continuous sheet, a cut sheet, a sealing sheet, a resin sheet such as an OHP sheet, Various media are included regardless of the material and shape, such as a printed board on which a film, cloth, wiring pattern, or the like is formed, an intermediate transfer medium, and the like.

A transport unit that moves the ejected medium and the liquid ejecting head relative to each other is configured to convey the ejected medium with respect to the stopped (fixed) head, to move the head with respect to the stopped ejected medium, Alternatively, any of the modes in which both the head and the medium to be ejected are moved is included.

  According to the present invention, it is possible to reduce unevenness that occurs due to head mounting rotation position error, medium skew, and the like.

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

[First Embodiment: Structure of Liquid Discharge Head]
FIG. 1 is a plan view schematically showing the structure of the liquid discharge head according to the first embodiment of the present invention. The illustrated head 50 is a full-line type print head used in an ink jet recording apparatus (also referred to as a recording head or a print head), and a direction orthogonal to the conveyance direction of the print medium 60 (sub-scanning direction: arrow S direction). A number of nozzles 51 are two-dimensionally arranged over a length corresponding to the full width Wm of the print medium 60 along the (main scanning direction: arrow M direction). In the figure, reference numeral 52 denotes a pressure chamber corresponding to each nozzle 51. The print medium 60 is transported from the top to the bottom of the figure.

  2 is an enlarged view of one droplet discharge element (ink chamber unit corresponding to one nozzle) 53, and FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. As shown in FIG. 2, the pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape, and the outlet to the nozzle 51 is provided at one of the diagonal corners. (Nozzle flow path) is provided, and the supply ink inlet (supply port) 54 is provided on the other side. However, in the practice of the present invention, the shape of the pressure chamber 52 is not limited to this example, and the planar shape may be various, such as a quadrangle (rhombus, rectangle, etc.), pentagon, hexagon, other polygons, circle, ellipse, etc. There can be a form.

  As shown in FIG. 3, the pressure chamber 52 communicates with the common flow channel 55 through the supply port 54. The common channel 55 communicates with an ink tank (not shown) as an ink supply source, and the ink supplied from the ink tank is distributed and supplied to each pressure chamber 52 via the common channel 55.

  An actuator 58 having an individual electrode 57 is joined to a pressure plate (vibrating plate also serving as a common electrode) 56 constituting a part of the pressure chamber 52 (the top surface in FIG. 3). By applying a drive voltage between the individual electrode 57 and the common electrode, the actuator 58 is deformed and the volume of the pressure chamber 52 is changed, and ink is ejected from the nozzle 51 due to the pressure change accompanying this. The actuator 58 is preferably a piezoelectric element using a piezoelectric material such as lead zirconate titanate or barium titanate. After the ink is ejected, when the displacement of the actuator 58 returns to its original state, new ink is refilled into the pressure chamber 52 from the common channel 55 through the supply port 54.

  In addition, a liquid repellent layer 59 is provided on the nozzle surface 50A of the head 50 from the viewpoint of improving the discharge stability and the cleaning performance of the discharge surface (nozzle surface 50A). The method for imparting liquid repellency to the nozzle surface 50A (liquid repellent treatment method) is not particularly limited. For example, a method of applying a fluorine-based liquid repellent material or a liquid repellent such as fluorine-based polymer particles (PTFE). There is a method of depositing a material in vacuum and forming a thin layer on the surface.

By controlling the driving of the actuator 58 corresponding to each nozzle 51 according to the print data, ink droplets can be ejected from the nozzle 51. As described with reference to FIG. 1, by controlling the ink discharge timing of each nozzle 51 in accordance with the transport speed while transporting the print medium 60 in the sub-scanning direction at a constant speed, the desired print medium 60 is formed on the print medium 60. Images can be recorded.

  In FIG. 3, a method of ejecting ink droplets by deformation of an actuator 58 typified by a piezo element (piezoelectric element) is employed. However, the method of ejecting ink is not particularly limited in the practice of the present invention. Instead of the method, various methods such as a thermal jet method in which bubbles are generated by heating ink with a heating element such as a heater and ink droplets are ejected by the pressure can be applied.

  FIG. 4 is an enlarged view of a two-dimensional nozzle array in the head 50 shown in FIG. By arranging the ink chamber units 53 having the structure described in FIGS. 2 and 3 two-dimensionally as shown in FIG. 4, the high-density nozzle head of this example (reference numeral 50 in FIG. 1) is realized. FIG. 4 shows a case where the rotational error amount (head inclination amount or medium skew amount / meander amount) equivalent to that in FIG. 18 is provided to facilitate comparison with the conventional configuration described in FIG. .

  For the two-dimensional nozzle arrangement of the head 50 shown in FIG. 4, for convenience of explanation, the horizontal direction (main scanning direction) in FIG. 4 is the row direction and the vertical direction (sub-scanning direction) is the column direction, and from the top to the bottom of FIG. The first row, the second row,... The tenth row and the row number (i = 1 to 10) are determined in order. Further, column numbers (j = 1, 2,... J) are determined from the left to the right for the nozzle rows arranged in a straight line in the column direction (substantially vertical direction), and the position of the nozzle 51 is set to the row number i and the column number j. This is expressed as “51-ij” depending on the combination. However, in the case of i = 10, “51-Xj” is described for convenience of description.

  In this example, the number of nozzles (number of rows) n in the sub-scanning direction is set to “10”, but the number of nozzles (number of rows) n in the sub-scanning direction is not limited to n = 10 when the present invention is implemented. However, it is assumed that n is an integer of 4 or more for the reason described later.

  The nozzle interval NLm in the main scanning direction in each row is constant (the nozzle intervals in the main scanning direction in each row are all the same NLm), and the nozzles 51-ij in each row have their nozzle positions between the rows along the main scanning direction. Arranged in a zigzag pattern with different shapes. That is, the number of nozzle rows (the number of nozzles in the sub-scanning direction) of the head 50 is n (in the case of FIG. 4, n = 10), and the substantial nozzles for ejecting dots arranged in the main scanning direction on the print medium. When the pitch between nozzles in the main scanning direction is Nm, the relationship of NLm = n × Nm is satisfied. Further, when the row interval (inter-nozzle distance in the sub-scanning direction) Ls of each row is constant in the sub-scanning direction (column direction of the nozzle array) and L is the maximum inter-nozzle distance in the sub-scanning direction, L = n × Ls.

  In the example shown in FIG. 4, with reference to the arrangement of the nozzles 51-1j in the first row, the first row → the third row → the fifth row → the seventh row → the ninth row → the tenth row → the eighth row → The nozzle positions in the main scanning direction are arranged by shifting Nm in the right direction in FIG. 4 between the respective rows in the order of the sixth row → the fourth row → the second row.

  In the nozzle arrangement shown in the drawing, the droplet ejection timing from the nozzle 51-ij is controlled in synchronization with the conveyance of the printing medium, and the nozzles in the respective rows in the order of the first row → second row → third row →. By sequentially driving 51-ij, one dot line (main scanning direction dot line) 66 in which dots 64 are arranged in a straight line along the width direction (main scanning direction) of the print medium is printed.

  When the order of the dots 64 formed so as to be arranged adjacent to each other along the main scanning direction on the print medium is traced from the left to the right in FIG. 4 and the nozzle number corresponding to each dot 64 is traced, 51− X1 → 51-81 → 51-61 → 51-41 → 51-21 → 51-12 → 51-32 → 51-52 → 51-72 → 51-92 → 51-X2 → 51-82 → 51-62 → 51-42 → 51-22 → 51-13 → 51-33 →. Thus, the nozzle array pattern drawn by connecting the nozzles 51-ij corresponding to the dots 64 of the main scanning direction dot line 66 in the order of the arrangement of the dots 64 is a "W" -shaped (triangular waveform) polygonal line shape. Become. That is, the substantial arrangement form of the nozzles 51-ij in which the dots 64 arranged adjacent to each other in the main scanning direction on the print medium are arranged in the nozzle surface 50A is a W-letter type (triangular waveform type) polygonal nozzle array. It has become.

  This nozzle array has periodicity in the main scanning direction. Focusing on the row numbers of the nozzles 51-ij corresponding to the arrangement order of the dots 64 of the main scanning direction dot line 66 starting from the nozzle 51-1j in the first row, the first row → the third row → the fifth row → 7th row → 9th row → 10th row → 8th row → 6th row → 4th row → 2nd row → 1st row, and so on.

  Looking at the main scanning direction dot line 62 printed on the printing medium, the first line → the third line → the fifth line → the seventh line → the ninth line → the tenth line → the eighth line → the sixth line → the sixth line A group of dots in which n dots 64 ejected from the nozzles in each of the 4th row to the 2nd row are arranged in a straight line while being adjacent to each other on the print medium (a linear dot group of n consecutive dots) ) 67 as a repeating unit, the dot group 67 of the repeating unit is connected in the main scanning direction.

  Considering the repeating unit (one period) on the nozzle arrangement corresponding to the dot group 67, the nozzles in the first row, the third row, the fifth row, the seventh row, the ninth row, and the tenth row are connected in order. A line (corresponding to the nozzle row in the first half of the repeating unit and arranged in a substantially straight line in the downward direction in FIG. 4) is folded back into a V-shape at the nozzle position of the 10th row, and the 10th row → Line connecting the nozzles in the order of the 8th row → the 6th row → the 4th row → the 2nd row → the 1st row (corresponding to the nozzle row in the latter half of the repeating unit and on the substantially straight line in the upward direction in FIG. Lined nozzle row). A W-shaped nozzle array is formed by repeating a plurality of such V-shaped repeating units in the main scanning direction.

  According to the nozzle arrangement shown in FIG. 4, the minimum value and the maximum value of the inter-nozzle distance L_pitch in the sub-scanning direction of a nozzle pair that strikes dots arranged adjacent to each other in the main scanning direction on the print medium are Ls. Here, Ls is a nozzle pitch in the sub-scanning direction between pressure chambers arranged adjacent to each other in the sub-scanning direction in the head.

  On the other hand, in the conventional configuration described with reference to FIGS. 17 to 19, the nozzles corresponding to the dots are tracked in the order of the dots that are ejected so as to be arranged adjacent to each other in the main scanning direction on the print medium. Then, the nozzles from the first row to the tenth row are arranged side by side on a straight line in an oblique direction (upwardly in the right direction in FIG. 18) within the discharge surface, and the nozzles from the tenth row to the nozzles in the first row. The nozzle row is folded back suddenly. In such a conventional nozzle arrangement arranged in a sawtooth shape, the minimum value of the distance between nozzles in the sub-scanning direction of the nozzle pair that strikes dots arranged adjacent to each other in the main scanning direction on the print medium is Ls. Is 10Ls, and the difference between the two is large. Therefore, in the conventional head, when an in-plane rotation mounting position error of the head or skewing of the medium occurs, the position on the print medium corresponding to the maximum nozzle pair (nozzle pair of the folded portion). As described above, the non-uniformity occurred.

  In this regard, according to the embodiment described with reference to FIGS. 1 to 4, the variation in the distance between the nozzles in the sub-scanning direction of the nozzle pair that strikes dots arranged adjacently in the main scanning direction on the print medium (the minimum value and the maximum value). Therefore, even when an in-plane rotation mounting position error of the head or skewing of the medium occurs, the change in dot pitch is small, and the occurrence of unevenness is suppressed.

  FIG. 5 is an enlarged view of the dot line 66 in the main scanning direction shown in FIG. As is clear when the enlarged view of the main scanning direction dot line 66 shown in FIG. 5 is compared with the conventional main scanning direction dot line of FIG. 19, according to the present embodiment, the dot spacing is smaller than that of FIG. It can be seen that the occurrence of density unevenness is suppressed without significantly increasing the distance.

  The conditions of the nozzle arrangement of the liquid ejection head 50 according to this embodiment are summarized below.

  In the liquid ejection head 50 having the two-dimensionally arranged nozzles 51, the distance between the nozzles in the sub-scanning direction on the nozzle surface is set for the nozzle pair in which the dots ejected onto the print medium are adjacent to each other in the main scanning direction. Assuming L_pitch, when the maximum distance L between the nozzles in the sub-scanning direction of all the nozzles in the nozzle surface is set, the nozzle 51 is arranged under a condition that satisfies the following formula (formula 1).

L_pitch = L × k / (n−1) (Formula 1)
k ≦ m + 1
The meaning of each parameter is as follows.

L_pitch: Distance in the sub-scanning direction within the nozzle surface of the nozzle that strikes adjacent dots on the print medium m: Number of nozzle skips in the sub-scanning direction (however, an integer satisfying 1 ≦ m ≦ n / 2)
n: Number of nozzles in the sub-scanning direction (number of rows)
k: integer greater than or equal to L: maximum distance between nozzles in the sub-scanning direction. “Nozzle skipping number” refers to a “pressure chamber etc.” sandwiched between a pair of nozzles that deposit adjacent dots on a print medium. No. of nozzle components ”. In the case of FIG. 4, for example, the eighth nozzle 51-81 and the nozzle 51-01 in the tenth row are in a relationship of a nozzle pair that ejects adjacent dots on the print medium. One row (m = 1) of nozzle rows (the ninth row of nozzles) is disposed between the distances in the direction (L_pitch = 2Ls). In order to generally describe such an arrangement relationship, the concept of parameter “m” was introduced. The “nozzle component” in this example is the droplet discharge element (ink chamber unit 53) described with reference to FIG. 3, and includes the nozzle 51, the pressure chamber 52, the actuator 58, and the individual electrodes 57 of the actuator 58. It is element unit.

Further, the condition of the above (formula 1) is applied when n ≧ 4. The reason is that when n = 3 (Equation 1),
L_pitch = L × k / 2
k ≦ 2
This is because there is a case where L_pitch takes the maximum value L, and the characteristics of the present invention are not utilized. The same applies when n = 2 and n = 1.

  As described above, when the liquid ejection head 50 according to the present embodiment is used, the density of the streaks can be lowered and the visibility can be reduced as compared with the printing result of the conventional matrix array head 300.

  In the above-described embodiment, the pressure chambers 52 corresponding to the nozzles 51 are two-dimensionally arranged on a plane parallel to the nozzle surface 50A. However, in implementing the present invention, the pressure chambers 52 correspond to the nozzles. The arrangement structure of the pressure chamber is not particularly limited. That is, in the present invention, the arrangement form of the discharge ports (nozzles) needs to be the two-dimensional arrangement, but the pressure chambers may be arranged hierarchically in a direction away from the print medium. .

[Combination with droplet ejection control]
By combining the liquid ejection head 50 according to the above-described embodiment and droplet ejection control (ejection control), a further effect of reducing unevenness can be obtained. For example, the nozzle array arranged on a substantially straight line along the substantially sub-scanning direction on the nozzle surface 50A is regarded as one nozzle group, and the following control is performed for each nozzle group, thereby further reducing unevenness. Can be achieved.

  That is, in the W-shaped folded nozzle array described with reference to FIG. 4, the nozzle numbers {51-X1, 51-81, 51-61, 51-41, 51-21} are assigned to one group, the nozzle numbers {51-12, 51-32, 51-52, 51-72, 51-92} for other groups, nozzle numbers {51-X2, 51-82, 51-62, 51-42, 51-22} for other groups, In this manner, the nozzle groups are grouped in units of nozzle rows corresponding to the respective line segments of the “W” -shaped folded nozzle array (substantially straight line portions having the same inclination direction with respect to the sub-scanning direction).

  In FIG. 4, a row of nozzles lined up along a line segment in the downward direction (in terms of row numbers, nozzles in the first row → the third row → the fifth row → the seventh row → the ninth row → the tenth row) Column) and nozzle columns aligned along the line segment in the upward direction (in terms of row numbers, nozzles in the 10th row → the 8th row → the 6th row → the 4th row → the 2nd row → the 1st row) Column). At this time, the nozzles at the boundaries of the groups (the nozzles in the first row and the nozzles in the tenth row) may be included in either group.

  When this grouping is described in another expression, when considering a nozzle that strikes the next adjacent dot (right adjacent dot in FIG. 4) from a certain nozzle, it is arranged on the upstream side in the sub-scanning direction or on the downstream side This is equivalent to grouping according to the arrangement.

  In the W-shaped folded nozzle array of FIG. 4, in a nozzle array arranged side by side on a substantially straight line in the downward direction of the right shoulder, main scanning is performed on the print medium for dots ejected by the target nozzle in the nozzle array. A nozzle that hits a dot in contact with the right side of the direction is arranged downstream of the target nozzle in the sub-scanning direction. On the other hand, in the W-shaped folded nozzle array of FIG. 4, in the nozzle array arranged side by side on the substantially straight line in the upward direction of the right shoulder, the printing medium is applied to the dots ejected by the target nozzle in the nozzle array. The nozzle that hits the dot adjacent to the right side in the main scanning direction is arranged upstream of the target nozzle in the sub-scanning direction.

  From this point of view, the nozzle group in which the next dot is placed in the main scanning direction dot line arrangement order is arranged on the upstream side in the sub-scanning direction on the nozzle surface, and the nozzle group is arranged on the downstream side. And divide.

  A group of first half nozzle rows (nozzle rows arranged side by side in the downward direction in FIG. 4) of the repeated nozzle row unit (V-shaped arrangement) in the W-shaped folded nozzle arrangement, and the latter nozzle row ( In FIG. 4, a group of nozzle rows arranged side by side on the line in the upward direction of the right shoulder), the mounting angle error in the in-plane rotation direction of the head, or the slant of the print medium relative to the head, the inclination due to meandering, or these The effects of relative inclination errors (hereinafter collectively referred to as “rotational errors”) due to the combination of the two are different (reverse).

  For example, when the head is installed with an angular error in which the head rotates counterclockwise on the paper surface of FIG. 4, the former group increases the interval between adjacent dots in the main scanning direction, while the latter group performs main scanning. The interval between adjacent dots in the direction becomes narrower. For this reason, it is preferable to group the nozzle groups that have the same influence by the rotation error as nozzle blocks, and perform droplet ejection control (density correction) in consideration of the influence of the rotation error for each group.

  Examples of droplet ejection control include (1) an aspect in which the dot size is increased or decreased, and (2) an aspect in which the number of droplet ejections is increased or decreased (providing additional dots and thinned dots). The above control may be performed for all nozzles in the group, or control may be performed for some nozzles extracted (or selected) from the group. Furthermore, if the trend of the entire group (corrected result) becomes the target result (correction tendency such as increasing recording density or decreasing recording density), any nozzle in the group (some nozzles) ) May be corrected in the opposite direction. That is, if the nozzles in the group are always corrected in the same direction, an extreme correction (overcorrection) may cause a negative effect that the effect of the correction becomes noticeable. Therefore, it is conceivable that correction is performed in the reverse direction for some of the nozzles in the group to achieve appropriate correction for the entire group.

  FIG. 6 is an example of a droplet ejection result when control is performed to change the dot size for each group. As shown in the figure, for nozzle groups that tend to increase the spacing between adjacent dots in the main scanning direction due to rotation errors, correction is performed to make the dot size larger than the reference value, and conversely due to rotation errors. For nozzle groups that tend to narrow the interval between adjacent dots in the main scanning direction, the density variation between the groups can be adjusted substantially uniformly by performing correction that makes the dot size smaller than the reference value.

  FIG. 7 is an example of droplet ejection results when control is performed to increase or decrease the number of droplet ejections for each group. A break indicated by a broken line in the figure represents a boundary (separation) of each group. In addition, dot positions indicated by broken-line circles in the figure are thinned dots (non-droplet dots) at which droplet ejection is suspended, and black circles (●) in the figure are additional dots ( Additional droplets).

  As shown in the drawing, for the group corresponding to the section where the distance between adjacent dots of the dot row arranged in the main scanning direction due to the rotation error is narrowed, the dot density is appropriately reduced to lower the recording density. On the other hand, for the group corresponding to the section where the distance between adjacent dots is widened, additional dots are ejected to increase the density. By doing so, the density variation between the groups can be adjusted substantially uniformly.

  When the droplet ejection control described with reference to FIGS. 6 and 7 is performed, the mounting angle in the in-plane rotation direction of the head 50 and the skew amount of the print medium 60 (including the skew amount due to meandering) are detected. It is preferable to control the correction amount of droplet ejection control based on the relative relationship between the two. That is, the droplet ejection control exemplified in FIGS. 6 and 7 identifies a rotation error, and a correction amount (a density correction amount by changing the dot size or adding the number of droplet ejections) is determined according to the identified rotation error. Is done.

  FIG. 8 is a diagram showing an example of means for grasping the rotation error, where (a) is a plan view and (b) is a side view.

  Regarding the inclination (attachment angle error) in the in-plane rotation direction A of the head 50, the inclination angle of the head 50 with respect to the conveyance direction of the print medium 60 is measured using a measuring device (not shown) after the head 50 is attached to the ink jet recording apparatus. Know by measuring. As a sensor used for this measurement, a laser diode (LD), a light emitting diode (LED) or the like as a light source, and a position sensor having a phototransistor or a photo detector such as a CCD can be used.

  Alternatively, the inclination of the head 50 may be measured by performing a reference print (test print) after mounting and measuring a printed print medium (print result).

  Information on the mounting angle error of the head 50 obtained by the measurement as described above is stored in a nonvolatile storage means such as an EEPROM, and the information on the mounting angle of the head 50 is read out as necessary. Get.

In addition, in order to grasp the skew amount of the print medium 60, at least one sensor 71 to 74 for measuring the skew amount is provided. 8 illustrates the sensors 71 to 73 that measure the moving direction of the medium on the front surface (recording surface or back surface) of the printing medium 60 and the sensor 74 that measures the moving direction of the medium on the end face of the printing medium 60. In carrying out the present invention, it is sufficient to provide at least one sensor. Also, the sensor installation position is not limited to the illustrated example, and the head 50 just before the sub-scanning direction (upstream side), just after the head 50 in the sub-scanning direction (downstream side), or the print medium 60 is sandwiched between the heads. It can be installed at an appropriate place such as immediately below 50 (position facing the nozzle surface 50A).

  As the sensors 71 to 74 for measuring the skew amount, a position sensor having a laser diode (LD), a light emitting diode (LED), or the like as a light source, and a phototransistor or a photo detector such as a CCD can be used. For example, the sensors 71 to 73 that measure the surface of the print medium 60 irradiate the surface of the print medium 60 from a light source (light projecting unit) such as an LD, and observe the movement of the surface roughness with a CCD or the like. The skew amount of the print medium 60 is measured.

  FIG. 9 is a block diagram showing the configuration of a control system that controls the driving of the head 50. The image input unit 76 is a unit that captures image data for printing, and corresponds to a communication interface or a media interface of an external storage medium (such as a memory card or an optical disk). The image data input from the image input unit 76 is sent to the image processing unit 78. The image processing unit 78 includes a color conversion unit 78A, a halftoning processing unit 78B, and a droplet ejection data generation unit 78C.

  The color conversion unit 78A performs a process of converting the RGB data of each pixel in the input image data into corresponding KCMY data. The KCMY data generated by the color conversion unit 78A is subjected to processing such as gradation correction and then sent to the digital halftoning unit 78B.

  The digital halftoning unit 78B is a processing unit that converts multi-value KCMY data into lower-gradation image data (multi-value dot data in consideration of binary or dot size change). In an inkjet recording device, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the tone (lightness of the image) as faithfully as possible. The digital halftoning unit 78B quantizes the multi-value data using a digital halftoning technique represented by a dither method, an error diffusion method, a blue noise mask method, and the like to generate dot data of each color.

  The result obtained by the digital halftoning unit 78B is sent to the droplet ejection data generation unit 78C, where the droplet ejection data for each nozzle in consideration of the nozzle arrangement of the head 50 (ejection data used for ink ejection drive control). Is converted to In this way, droplet ejection data before correction is generated.

  The medium angle detection unit 80 illustrated in FIG. 9 corresponds to the sensors 71 to 74 described with reference to FIG. 8 and is a unit that detects the skew amount of the print medium 60. The detection signal obtained by the medium angle detection unit 80 in FIG. 9 is sent to the medium angle calculation unit 81, and the medium angle calculation unit 81 obtains the skew amount (medium angle) of the print medium 60 based on the detection signal. Information on the medium angle thus obtained is given to the unevenness correction control unit 82.

  Similarly, the head angle calculation unit 85 obtains the mounting angle error of the head 50 based on the signal obtained from the head angle detection unit 84, and the information is given to the unevenness correction control unit 82. The head angle detector 84 may be a sensor provided in the ink jet recording apparatus, or may be a measuring apparatus used after mounting the head in a manufacturing process or the like as described with reference to FIG. Alternatively, instead of the head angle detection unit 84 and the head angle calculation unit 85 in FIG. 9, a storage unit that stores information on the head mounting angle error in advance can be used.

  The unevenness correction control unit 82 determines the correction amount of each nozzle by referring to the table in the angle correction data storage unit 87 from the acquired medium angle information and head mounting angle error information. The angle correction data storage unit 87 holds table data that correlates the correction amount with the medium angle and the head mounting angle. It has a parameter for how many corrections to take for each angle. For example, it may have nozzle arrangement data including the distance between nozzles, or may have a correlation coefficient with the concentration and viscosity of the liquid to be ejected. Since the appearance of unevenness is affected by the degree of overlap of droplet ejection, etc., an embodiment in which such parameters are taken into consideration is preferable.

  In this way, the unevenness correction control unit 82 determines a correction amount according to the rotation error, and the droplet ejection data is corrected according to the correction amount. The head ejection control unit 88 controls the head driver 89 based on the corrected droplet ejection data, and controls the ink ejection operation from the head 50. With the above configuration, the droplet ejection control described with reference to FIGS. 6 to 7 is realized. In FIG. 9, the range surrounded by the alternate long and short dash line can be realized by a combination of a processor including peripheral circuits such as a CPU and a memory and software.

[Second Embodiment]
Next, the structure of the liquid discharge head according to the second embodiment of the present invention will be described. FIG. 10 is an enlarged view schematically showing the nozzle arrangement of the liquid ejection head according to the second embodiment of the present invention. In description of FIG. 10, the description method similar to FIG. 4 was employ | adopted. However, in FIG. 10, the number of nozzles (number of rows) n in the sub-scanning direction is “12”. Therefore, in the description of the nozzle position, the nozzle in the eleventh row (i = 11) is described as “51-Yj”, and the nozzle in the twelfth row is described as “51-Zj”.

  In FIG. 10, it is assumed that the nozzle interval NLm in the main scanning direction in each row is constant (the nozzle intervals in the main scanning direction in each row are all the same NLm), and the nozzles 51-ij in each row are mutually nozzles along the main scanning direction. It is arranged in a zigzag pattern with different positions. When a substantial nozzle pitch between nozzles for ejecting dots arranged in the main scanning direction on the printing medium is Nm, a relationship of NLm = n × Nm is satisfied. Further, when the row interval (inter-nozzle distance in the sub-scanning direction) Ls of each row is constant in the sub-scanning direction (column direction of the nozzle array) and L is the maximum inter-nozzle distance in the sub-scanning direction, L = n × Ls. This is the same as the example described in FIG.

  In the example shown in FIG. 10, with reference to the arrangement of the nozzles 51-1j in the first row, the first row → the fifth row → the ninth row → the eleventh row → the seventh row → the third row → the second row → The nozzle position in the main scanning direction is arranged in the order of 6th row → 10th row → 12th row → 8th row → 4th row by shifting Nm in the right direction in FIG.

  In the nozzle arrangement shown in the drawing, the droplet ejection timing from the nozzle 51-ij is controlled in synchronization with the conveyance of the printing medium, and the nozzles in the respective rows in the order of the first row → second row → third row →. By sequentially driving 51-ij, one dot line (main scanning direction dot line) in which dots are arranged in a straight line along the width direction (main scanning direction) of the print medium is printed.

  If the nozzle number corresponding to each dot is traced following the arrangement order of the dot lines in the main scanning direction, if the nozzle “51-12” in the figure is the starting point, 51-12 → 51-52 → 51-92 → 51-Y2 → 51-72 → 51-32 → 51-22 → 51-62 → 51-X2 → 51-Z2 → 51-82 → 51-42 → 51-13 →

In such a W-shaped polygonal line nozzle array, the minimum value of the inter-nozzle distance L_pitch in the sub-scanning direction of the nozzle pair that strikes dots arranged adjacently on the print medium in the main scanning direction is Ls, and the maximum value is 4Ls.

  In the conventional configuration described with reference to FIGS. 17 to 19, the minimum value of the distance between the nozzles in the sub-scanning direction of the nozzle pair that strikes dots arranged adjacent to each other in the main scanning direction on the print medium is Ls, and the maximum value is 10Ls. When this is applied to 12 rows, the maximum value is 12 Ls, and the difference between the two is large.

  In this regard, according to the embodiment shown in FIG. 10, there is a variation in the distance between the nozzles in the sub-scanning direction of the nozzle pair that strikes dots arranged adjacently in the main scanning direction on the print medium (difference between the minimum value and the maximum value). Therefore, even when an in-plane rotation mounting position error of the head or skewing of the medium occurs, the change in the pitch between dots is small and the occurrence of unevenness is suppressed.

  Compared with the configuration of FIG. 10 and the example of FIG. 4, the configuration of FIG. 10 is a variation in the distance between nozzles in the sub-scanning direction of the nozzle pair that strikes dots arranged adjacent to each other in the main scanning direction on the print medium (minimum). (The difference between the value and the maximum value) increases, but the number of times of folding within the repetition unit increases (the frequency of folding is doubled). By increasing the return frequency of the nozzle row on the nozzle surface, the visibility of unevenness on the print medium decreases, so the variation in the distance between nozzles in the sub-scanning direction of the nozzle pair that ejects adjacent dots in the main scanning direction Combined with the suppression of the amount, the unevenness becomes inconspicuous.

  FIG. 11 is a graph of a visual curve showing the relationship between the repetition frequency (spatial frequency) of streaky unevenness and the density difference ΔD visually recognized as unevenness. The horizontal axis in the figure represents the repetition frequency (spatial frequency) of unevenness (unit: lines / mm) (however, logarithmic scale), and the vertical axis represents the visible difference in density.

  The area below the visual recognition curve g is an area that is not visually recognized as unevenness, and the area above the visual recognition curve g is an area that is visually recognized as unevenness.

  As shown in the drawing, when the spatial frequency of the unevenness is set to a high frequency (preferably 3 lines / mm or more, more preferably 4 lines / mm or more), the unevenness is hardly visually recognized.

  The occurrence position of the streaks on the print medium 60 corresponds to the position of the turning point (singular point) of the nozzle row on the nozzle surface 50A, and therefore the period of the turning point of the nozzle row is not easily visible. The visibility of unevenness can be reduced by using a high frequency of at least 1 book / mm.

  In the conventional matrix arrangement described with reference to FIG. 17, if 48 nozzle rows are arranged in the sub-scanning direction on the nozzle surface in order to realize a recording density of 2400 dpi in the main scanning direction, the cycle of the turning point of the nozzle row Is 2400dpi x 48 nozzles = 0.5mm pitch, and the frequency of stripes is 2 lines / mm, making it easy to see.

  On the other hand, in the W-shaped broken line nozzle arrangement described with reference to FIG. 4, the frequency of stripes is 4 lines / mm under the same conditions (2400 dpi, 48 lines), and the W-shaped double-frequency broken line shape described with reference to FIG. In the nozzle arrangement, the frequency of the same condition (2400 dpi, 48 lines) stripes is 8 lines / mm, and the visibility of unevenness is lower than the conventional one from the viewpoint of the viewing curve described with reference to FIG.

  10 is the same as the example described with reference to FIGS. 1 to 9 in that droplet ejection control (density correction) can be performed for each group to further reduce unevenness.

Compare the characteristics of the three types of nozzle arrangements of the configuration of the first embodiment described in FIGS. 1 to 4, the configuration of the second embodiment described in FIG. 10, and the conventional configuration described in FIGS. For this purpose, graphs showing the pitch error between adjacent dots in the main scanning direction on the print medium under the same conditions (2400 dpi, 48 lines in the sub-scanning direction, rotation error β) are shown in FIGS. The rotation error β is assumed to be that the head 50 is mounted inclined at an angle β in the clockwise direction from the normal mounting position on the paper surface of FIG.

  12 is based on the configuration of the first embodiment, FIG. 13 is based on the configuration of the second embodiment, and FIG. 14 is based on the conventional configuration. In each figure, the horizontal axis indicates the nozzle number in the main scanning direction, and the vertical axis indicates the pitch error between adjacent dots in the main scanning direction. In each nozzle arrangement, the nozzle interval NLm in the main scanning direction in the row is 480 μm, and the nozzle pitch Nm in the main scanning direction is substantially 10 μm for nozzles that deposit dots arranged along the main scanning direction on the print medium. The inter-nozzle distance Ls in the sub-scanning direction is 500 μm.

  In each figure, the plus area on the vertical axis means that the distance between adjacent dots increases, and the larger the value, the lower the density as the print result. On the contrary, the minus area on the vertical axis means that the distance between adjacent dots becomes narrower. The larger the absolute value, the higher the density as the print result.

  As shown in FIG. 12, according to the configuration of the first embodiment, the sign of the dot error is inverted at the position of the turning point of the nozzle row, and the absolute value of the dot error remains within a very small value. That is, it can be seen that the density difference of streaks generated at the position of the turning point can be made very small, and the occurrence of density unevenness is suppressed.

  According to the configuration of the second embodiment shown in FIG. 13, the dot error sign is reversed at the position of the turning point of the nozzle row as in FIG. 12, but the cycle is short ( The frequency is high). This is due to an increase in the number of times of nozzle row folding. Further, although the absolute value of the dot error is larger than that in the case of FIG. 12, as described above, the density unevenness is difficult to be visually recognized in relation to the visual recognition curve.

  According to the conventional configuration shown in FIG. 14, the dot error changes abruptly at the position of the turning point of the nozzle row, and the absolute value thereof is very large. For this reason, the density difference from the peripheral portion is large, and unevenness is easily visible.

[Configuration of inkjet recording apparatus]
Next, the configuration of the ink jet recording apparatus using the liquid ejection head described in the first embodiment and the second embodiment will be described.

  FIG. 15 is an overall configuration diagram of an ink jet recording apparatus showing an embodiment of an image forming apparatus according to the present invention. As shown in the figure, the ink jet recording apparatus 110 includes a plurality of ink jet recording heads (hereinafter referred to as “ink jet recording heads”) corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. A printing unit 112 having 112K, 112C, 112M, and 112Y, an ink storage / loading unit 114 that stores ink to be supplied to each of the heads 112K, 112C, 112M, and 112Y, and recording paper as a recording medium The paper feeding unit 118 that supplies the paper 116, the decurling unit 120 that removes curl of the recording paper 116, and the nozzle surface (ink ejection surface) of the printing unit 112 are disposed so as to improve the flatness of the recording paper 116. A belt conveyance unit 122 that conveys the recording paper 116 while holding it, a print detection unit 124 that reads a printing result by the printing unit 112, and recorded And a discharge unit 126 for discharging recording paper (printed matter) to the outside.

  The liquid ejection head 50 described in the first embodiment or the second embodiment is used for each of the heads 112K, 112C, 112M, and 112Y of the printing unit 112.

  The ink storage / loading unit 114 includes ink tanks that store inks of colors corresponding to the heads 112K, 112C, 112M, and 112Y, and the tanks are connected to the heads 112K, 112C, 112M, and 112Y via a required pipe line. Communicated with. Further, the ink storage / loading unit 114 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.

  In FIG. 15, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 118, 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 a plurality of types of recording media (media) can be used, an information recording body such as a barcode or a wireless tag that records media type information is attached to a magazine, and information on the information recording body is read by a predetermined reader. It is preferable to automatically determine the type of recording medium to be used (media type) and to perform ink ejection control so as to realize appropriate ink ejection according to the media type.

  The recording paper 116 delivered from the paper supply unit 118 retains curl due to having been loaded in the magazine. In order to remove this curl, the decurling unit 120 applies heat to the recording paper 116 by the heating drum 130 in the direction opposite to the curl direction of the magazine. 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 using roll paper, a cutter (first cutter) 128 is provided as shown in FIG. 15, and the roll paper is cut into a desired size by the cutter 128. Note that the cutter 128 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 116 is sent to the belt conveyance unit 122. The belt conveyance unit 122 has a structure in which an endless belt 133 is wound between rollers 131 and 132, and at least portions facing the nozzle surface of the printing unit 112 and the sensor surface of the printing detection unit 124 are horizontal (flat). Surface).

  The belt 133 has a width that is greater than the width of the recording paper 116, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 15, an adsorption chamber 134 is provided at a position facing the nozzle surface of the print unit 112 and the sensor surface of the print detection unit 124 inside the belt 133 that is stretched between the rollers 131 and 132. The recording paper 116 is sucked and held on the belt 133 by sucking the suction chamber 134 with a fan 135 to a negative pressure. In place of the suction adsorption method, an electrostatic adsorption method may be adopted.

  When the power of the motor (reference numeral 188 in FIG. 16) is transmitted to at least one of the rollers 131 and 132 around which the belt 133 is wound, the belt 133 is driven in the clockwise direction in FIG. The held recording paper 116 is conveyed from left to right in FIG.

  Since ink adheres to the belt 133 when a borderless print or the like is printed, the belt cleaning unit 136 is provided at a predetermined position outside the belt 133 (an appropriate position other than the print region). Although details of the configuration of the belt cleaning unit 136 are not illustrated, for example, there are a method of niping a brush roll, a water absorption 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 in place of the belt conveyance unit 122 is also conceivable, if the roller / nip conveyance is performed in the printing area, the image is likely to blur because the roller contacts the printing surface of the sheet immediately after printing. There's 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 140 is provided on the upstream side of the printing unit 112 on the paper conveyance path formed by the belt conveyance unit 122. The heating fan 140 heats the recording paper 116 by blowing heated air onto the recording paper 116 before printing. Heating the recording paper 116 immediately before printing makes it easier for the ink to dry after landing.

  Each of the heads 112K, 112C, 112M, and 112Y of the printing unit 112 has a length corresponding to the maximum paper width of the recording paper 116 targeted by the inkjet recording device 110, and the nozzle surface has a recording medium of the maximum size. The head is a full-line type in which a plurality of nozzles for ink ejection are arranged over a length exceeding at least one side (full width of the drawable range) (see FIG. 1).

  In FIG. 15, heads 112K, 112C, 112M, and 112Y are arranged 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 116. The heads 112K, 112C, 112M, and 112Y are fixedly installed so as to extend along a direction substantially orthogonal to the conveyance direction of the recording paper 116.

  A color image can be formed on the recording paper 116 by discharging different colors of ink from the heads 112K, 112C, 112M, and 112Y while the recording paper 116 is being conveyed by the belt conveyance unit 122.

  As described above, according to the configuration in which the full-line heads 112K, 112C, 112M, and 112Y having nozzle rows that cover the entire width of the paper are provided for each color, the recording paper 116 and the printing unit in the paper feeding direction (sub-scanning direction). An image can be recorded on the entire surface of the recording paper 116 by performing the operation of relatively moving the 112 once (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 recording head reciprocates in a direction orthogonal to the paper transport 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, dark ink, and special color ink are used as necessary. May be added. For example, it is possible to add an ink jet head that discharges light ink such as light cyan and light magenta. Also, the arrangement order of the color heads is not particularly limited.

  The print detection unit 124 shown in FIG. 15 includes an image sensor (line sensor or area sensor) for imaging the droplet ejection result of the printing unit 112, and clogging of nozzles or the like from the droplet ejection image read by the image sensor. It functions as a means for checking ejection defects such as landing position deviation. It is also possible to measure the head mounting rotation error using the print detection unit 124.

  Test patterns or practical images printed by the heads 112K, 112C, 112M, and 112Y of the respective colors are read by the print detection unit 124, and ejection determination of each head is performed. 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 142 is provided following the print detection unit 124. The post-drying unit 142 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 144 is provided following the post-drying unit 142. The heating / pressurizing unit 144 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 145 having a predetermined uneven surface shape while heating the image surface, and transfers the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 126. 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 110 is provided with a sorting means (not shown) that switches the paper discharge path in order to select the prints of the main image and the prints of the test print and send them to the discharge units 126A and 126B. 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 the cutter (second cutter) 148. Although not shown in FIG. 15, the paper output unit 126A for the target prints is provided with a sorter for collecting prints according to print orders.

[Explanation of control system]
FIG. 16 is a block diagram showing a system configuration of the inkjet recording apparatus 110. As shown in the figure, the inkjet recording apparatus 110 includes a communication interface 170, a system controller 172, an image memory 174, a ROM 175, a motor driver 176, a heater driver 178, a print control unit 180, an image buffer memory 182, a head driver 89, and the like. It has. In FIG. 16, the heads of the respective colors are representatively indicated by reference numeral 150 for simplification of illustration.

  The communication interface 170 is an interface unit that receives image data sent from the host computer 186. As the communication interface 170, a serial interface such as USB, IEEE 1394, Ethernet (registered trademark), a 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 communication interface unit 170 corresponds to the image input unit 76 described with reference to FIG.

  Image data sent from the host computer 186 shown in FIG. 16 is taken into the inkjet recording apparatus 110 via the communication interface 170 and temporarily stored in the image memory 174. The image memory 174 is a storage unit that stores an image input via the communication interface 170, and data is read and written through the system controller 172. The image memory 174 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

The system controller 172 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 110 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 172 controls the communication interface 170, the image memory 174, the motor driver 176, the heater driver 178, and the like, and performs communication control with the host computer 186, read / write control of the image memory 174 and ROM 175, and the like. With
A control signal for controlling the motor 188 and the heater 189 of the transport system is generated.

  The ROM 175 stores programs executed by the CPU of the system controller 172 and various data necessary for control. The ROM 175 may be a non-rewritable storage unit or a rewritable storage unit such as an EEPROM. The image memory 174 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 176 is a driver (driving circuit) that drives the conveyance motor 188 in accordance with an instruction from the system controller 172. The heater driver 178 is a driver that drives the heater 189 such as the post-drying unit 142 in accordance with an instruction from the system controller 172.

  The print control unit 180 has a signal processing function for performing various processes such as processing and correction for generating a print control signal from image data (original image data) in the image memory 174 in accordance with the control of the system controller 172. And a control unit that supplies the generated dot data (droplet ejection data) to the head driver 89.

  The print control unit 180 includes an image buffer memory 182, and image data, parameters, and other data are temporarily stored in the image buffer memory 182 when image data is processed in the print control unit 180. In FIG. 16, the image buffer memory 182 is shown in a form associated with the print control unit 180, but it can also be used as the image memory 174. Also possible is an aspect in which the print controller 180 and the system controller 172 are integrated and configured with one processor.

  An overview of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 170 and stored in the image memory 174. At this stage, for example, RGB image data is stored in the image memory 174.

  The original image (RGB) data stored in the image memory 174 is sent to the print control unit 180 via the system controller 172, and the print control unit 180 undergoes color conversion and halftoning processing to generate dots for each ink color. Converted to data.

  That is, the print control unit 180 performs a process of converting the input RGB image data into dot data of four colors K, C, M, and Y. Thus, the dot data generated by the print control unit 180 is stored in the image buffer memory 182.

  As described in FIG. 9, the head driver 89 corresponds to each nozzle 51 of the head 150 based on droplet ejection data (that is, dot data stored in the image buffer memory 182) given from the print control unit 180 in FIG. 16. A drive signal for driving the actuator 58 is output. The head driver 89 may include a feedback control system for keeping the head driving conditions constant.

  When the drive signal output from the head driver 89 is applied to the head 150, ink is ejected from the corresponding nozzle 51. An image is formed on the recording paper 116 by controlling ink ejection from the head 150 in synchronization with the conveyance speed of the recording paper 116.

As described above, the ejection amount and ejection timing of ink droplets from each nozzle are controlled via the head driver 89 based on the dot data generated through the required signal processing in the print control unit 180. Thereby, a desired dot size and dot arrangement are realized.

  The ink jet recording apparatus 110 of this example includes a medium angle detection unit 80 and a head angle detection unit 84. The functions of the medium angle detection unit 80 and the head angle detection unit 84 are as described in FIG. Information obtained from these detection units is sent to the print control unit 180 and used for droplet ejection control (correction of ejection state) of each nozzle.

  That is, the configuration of the system controller 172 shown in FIG. 16 or the print control unit 180 or a combination thereof is the image processing unit 78, medium angle calculation unit 81, unevenness correction control unit 82, head angle calculation unit 85, It functions as an angle correction data storage unit 87 and a head ejection control unit 88.

  As described with reference to FIG. 15, the print detection unit 124 is a block including an image sensor. The print detection unit 124 reads an image printed on the recording medium 116, performs necessary signal processing, and the like to perform a print status (whether ejection is performed, droplet ejection). Variation, optical density, etc.) and the detection result is provided to the print controller 180. It should be noted that other discharge detection means (corresponding to discharge abnormality detection means) may be provided instead of or in combination with the print detection unit 124.

  As another ejection detection means, for example, a pressure sensor is provided in or near each pressure chamber of the head 150, and ejection abnormality is detected from a detection signal obtained from the pressure sensor when ink is ejected or when a pressure measurement actuator is driven. Or an optical detection system consisting of a light source and a light receiving element such as a laser light emitting element, and irradiating the droplet discharged from the nozzle with light such as laser light, There may be a mode (external detection method) of detecting flying droplets based on the amount of received light).

  The print control unit 180 performs various corrections on the head 150 based on information obtained from the print detection unit 124 or other discharge detection means (not shown) as necessary, and performs preliminary discharge, suction, wiping, etc. as necessary. To perform the cleaning operation (nozzle recovery operation).

  According to the ink jet recording apparatus 110 having the above configuration, occurrence of unevenness is suppressed, and good image formation is possible.

FIG. 2 is a plan view schematically showing the structure of the liquid ejection head according to the first embodiment of the present invention. Enlarged view of one droplet discharge element (ink chamber unit corresponding to one nozzle) Sectional drawing which follows the 3-3 line in FIG. Enlarged view of the two-dimensional nozzle array in the head shown in FIG. Enlarged view of main scanning direction dot lines shown in FIG. The figure which shows the example of a droplet ejection result at the time of performing control which changes dot size for every group The figure which shows the example of the droplet ejection result at the time of performing control which increases / decreases the droplet ejection number for every group It is the figure which showed the example of the means for grasping | ascertaining a rotation error, (a) is a top view, (b) is a side view Block diagram showing the configuration of the control system that controls the drive of the head The enlarged view which showed typically the nozzle arrangement of the liquid discharge head which concerns on 2nd Embodiment of this invention. A graph of a visual curve showing the relationship between the repetition frequency (spatial frequency) of streaky unevenness and the density difference ΔD visually recognized as unevenness The graph which showed the pitch error between the nozzle position by the structure of 1st Embodiment, and the main scanning direction adjacent dot. The graph which showed the pitch error between the nozzle position by the structure of 2nd Embodiment, and the main scanning direction adjacent dot. A graph showing the pitch error between the nozzle position and the adjacent dots in the main scanning direction according to the conventional configuration 1 is an overall configuration diagram of an ink jet recording apparatus showing an embodiment of an image forming apparatus according to the present invention. The block diagram which shows the system configuration | structure of the inkjet recording device shown in FIG. A plan view schematically showing a configuration example of a conventional matrix array head Enlarged view of nozzle array of conventional matrix array head Enlarged view of the dot line in the main scanning direction shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 50 ... Liquid discharge head, 50A ... Nozzle surface, 51 ... Nozzle, 52 ... Pressure chamber, 53 ... Ink chamber unit, 60 ... Print medium, 71-74 ... Sensor, 80 ... Medium angle detection part, 84 ... Head angle detection part 82 ... Unevenness correction control unit, 87 ... Angle correction data storage unit, 88 ... Head ejection control unit, 110 ... Inkjet recording apparatus, 112K, 112C, 112M, 112Y ... Head, 116 ... Recording paper, 118 ... Media supply unit, 112: Printing unit, 1222 ... Belt conveying unit, 124 ... Printing detection unit

Claims (7)

A liquid discharge head having a nozzle surface in which a plurality of nozzles for discharging liquid are two-dimensionally arranged,
When the first direction is the direction in which the medium to be ejected is moved relative to the liquid ejection head,
L_pitch is a distance in the first direction on the nozzle surface of a pair of nozzles that are in a relationship of ejecting adjacent dots arranged in a second direction substantially orthogonal to the first direction on the ejection target medium.
L is the maximum distance between the nozzles in the first direction in the nozzle surface.
The number of nozzles in the first direction in the nozzle surface is n (where n is an integer of 4 or more),
The number of nozzle skips representing the number in the first direction of the nozzles disposed between the distances in the first direction of the nozzle pair is m (where m is an integer satisfying 1 ≦ m ≦ n / 2) ),
When k is an integer equal to or greater than 1, the following formula is used: L_pitch = L × k / (n−1)
k ≦ m + 1
The liquid discharge head, wherein the plurality of nozzles are two-dimensionally arranged under a condition satisfying A liquid discharge head having a nozzle surface in which a plurality of nozzles for discharging droplets are two-dimensionally arranged,
When the first direction is the direction in which the medium to be ejected is moved relative to the liquid ejection head,
The second direction nozzle row in which the nozzles are linearly arranged along the second direction substantially orthogonal to the first direction in the nozzle surface changes the position of the first direction in the nozzle surface to n rows. (Where n is an integer of 4 or greater)
M rows (where m is 1 ≦ 1) between the distances in the first direction on the nozzle surface of any nozzle pair that has a relationship of ejecting adjacent dots arranged in the second direction on the ejection target medium. an integer satisfying m ≦ n / 2) and the second direction nozzle row is sandwiched and arranged.
The droplets ejected from the nozzles in each of the n rows are attached to the ejection medium while the ejection medium is relatively moved in the first direction with respect to the liquid ejection head. A second direction dot line in which dots are arranged along the second direction can be formed;
For n consecutive dot groups ejected by the nozzles of each of the n rows of the second direction dot lines, the nozzles corresponding to the dots are arranged in the order of arrangement of adjacent dots in the second direction. When tracking in the nozzle plane, the nozzle row of the nozzle group in which the nozzle that hits the next dot in the arrangement order is arranged on the upstream side in the first direction, and the nozzle that hits the next dot in the arrangement order A liquid discharge head having a polygonal line nozzle arrangement structure in which nozzle rows of nozzle groups arranged on the downstream side in the first direction are combined in a polygonal line shape. L_pitch is a distance in the first direction on the nozzle surface of a nozzle pair that has a relationship of ejecting adjacent dots arranged in the second direction on the ejection target medium.
L is the maximum distance between the nozzles in the first direction in the nozzle surface.
The number of rows of the second direction nozzle row in the nozzle surface is n (where n is an integer of 4 or more),
The number of nozzle skips representing the number of rows of the second direction nozzle row arranged between the distances in the first direction of the nozzle pair is m (where m is an integer satisfying 1 ≦ m ≦ n / 2) ),
When k is an integer equal to or greater than 1, the following formula is used: L_pitch = L × k / (n−1)
k ≦ m + 1
The plurality of nozzles are two-dimensionally arranged under a condition satisfying
The liquid discharge head described. A liquid discharge head according to any one of claims 1 to 3,
Transport means for transporting at least one of the liquid ejection head and the medium to be ejected, and relatively moving the medium to be ejected in the first direction with respect to the liquid ejection head;
Discharge control means for performing control to discharge liquid from the nozzles of the liquid discharge head in accordance with the relative movement by the transport means;
A liquid ejection apparatus comprising:   The droplets ejected from the nozzles are adhered to the ejection medium while the ejection medium is moved relative to the liquid ejection head in the first direction by the transporting means, thereby allowing the ejection medium to adhere to the ejection medium. When forming a second direction dot line in which dots are arranged along two directions, nozzles corresponding to the dots are arranged in the nozzle surface in the order of arrangement of dots adjacent in the second direction of the second direction dot line. , The nozzle group that hits the next dot in the arrangement order is arranged on the upstream side in the first direction, and the nozzle that hits the next dot in the arrangement order on the downstream side in the first direction. And a nozzle correction unit configured to divide the plurality of nozzles into groups and to correct a discharge state for each group. Liquid ejecting apparatus according. At least one angle specifying means of a head angle specifying means for specifying the mounting angle of the liquid discharge head and a medium angle specifying means for specifying the transport direction angle of the relative movement of the discharged medium with respect to the liquid discharge head; ,
A correction amount control means for controlling a correction amount for correcting the discharge state based on the identification result of the at least one angle identification means;
The liquid ejection apparatus according to claim 5, further comprising:   An image forming apparatus comprising the liquid ejection device according to claim 4, wherein an image is formed on the ejection target medium by ink liquid ejected from the nozzle.

Images