JP2012183721A - Image forming apparatus - Google Patents

Abstract

It is impossible to reduce the banding of head joints by suppressing an increase in image density difference between both ends of a head array.
A head 101A has a brightness difference | ΔEa | at the left and right ends, similarly, head 101B has a brightness difference | ΔEb |, head 101C has a brightness difference | ΔEc |, and head 101D has a brightness difference | ΔEd. Therefore, the nozzle with the high brightness of the head 101A and the nozzle with the high brightness of the head 101B are adjacent to each other, and the nozzle with the low brightness of the head 101B and the nozzle with the low brightness of the head 101C are adjacent to each other. Then, by arranging the heads 101A to 101D adjacent to the nozzle having the high brightness of the head 101C and the nozzle having the high brightness of the head 101D, the brightness difference in the entire head array is set to | ΔEmax |.
[Selection] Figure 4

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including a liquid discharge head array in which a plurality of heads are arranged.

  As an image forming apparatus such as a printer, a facsimile, a copying machine, a plotter, or a complex machine of these, for example, a liquid discharge recording type image forming using a recording head composed of a liquid discharge head (droplet discharge head) that discharges ink droplets. As an apparatus, an ink jet recording apparatus or the like is known. This liquid discharge recording type image forming apparatus means that ink droplets are transported from a recording head (not limited to paper, including OHP, and can be attached to ink droplets and other liquids). Yes, it is also ejected onto a recording medium or a recording medium, recording paper, recording paper, etc.) to form an image (recording, printing, printing, and printing are also used synonymously). And a serial type image forming apparatus that forms an image by ejecting liquid droplets while the recording head moves in the main scanning direction, and a line type head that forms images by ejecting liquid droplets without moving the recording head There are line type image forming apparatuses using

  In the present application, the “image forming apparatus” of the liquid discharge recording method is an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or the like. In addition, “image formation” means not only giving an image having a meaning such as a character or a figure to a medium but also giving an image having no meaning such as a pattern to the medium (simply It also means that a droplet is landed on a medium). “Ink” is not limited to ink, but is used as a general term for all liquids capable of image formation, such as recording liquid, fixing processing liquid, and liquid. DNA samples, resists, pattern materials, resins and the like are also included. In addition, the “image” is not limited to a planar image, and includes an image given to a three-dimensionally formed image and an image formed by three-dimensionally modeling a solid itself.

  By the way, as a line-type head used in the line-type image forming apparatus, a liquid discharge head array (hereinafter simply referred to as “head array”) including a head array in which a plurality of heads are arranged in a staggered manner in the nozzle arrangement direction is used. The In such a head array, in order to reduce the assembling cost of individual heads, the lengths of the respective heads to be joined are also increased.

  However, when the length of the head is increased, there arises a new problem that the density difference between both ends of the head becomes large in the distribution of the image density printed by each head in the head. As a factor causing such a density difference, there is an unevenness in the diameters of droplets ejected from each nozzle.

  That is, for example, as shown in FIG. 11A, when the droplet 1002 is ejected from the nozzle of the head 1001, the diameter of the droplet 1002 is uneven from one end to the other end of the nozzle row. As shown in (b), D1> D2 between the diameter D1 of the droplet 1002 ejected from the nozzle at one end and the diameter D2 of the droplet 1002 ejected from the nozzle at the other end. As a result, for example, as shown in FIG. 12, the brightness of the image (dot) formed by the liquid droplets ejected from the nozzle differs depending on the nozzle position in the head.

  In addition, the problem of such a lightness difference (also referred to as “density difference”) within one head is that the accumulated value of the tolerance within the head increases as the head lengthens, so each component in the head One of the factors is that a deviation occurs in the joining and the like.

  In the head array, since a plurality of heads having different densities at both ends in the nozzle arrangement direction are used in combination as described above, the density is different at the joint between the heads, banding occurs, and the image quality is deteriorated.

  Therefore, conventionally, in order to prevent the occurrence of banding due to the difference in density of each head incorporated adjacent to the head array, the drive voltage is generally adjusted to match the density of the joints of the heads (referred to as voltage correction). Has been done.

For example, an example of performing the voltage correction using three heads will be described with reference to FIGS.
In this example, the three heads A, B, and C each have a brightness gradient (referred to as “density gradient”) as shown in FIG. 13 in the nozzle arrangement direction (also referred to as nozzle row direction). Yes. At this time, in the arrangement of adjacent heads A and B, B and C, the end with high brightness of head A and the end with low brightness of head B, the end with high brightness of head B and the end with low brightness of head C are adjacent. In this case, the brightness differences at the joints of the heads are ΔEab and ΔEbc, respectively. The lightness difference in the entire head array is ΔEmax.

  Therefore, as shown in FIG. 14, by performing voltage correction, the brightness of the head A can be lowered as a whole and the brightness of the head C can be raised as a whole, thereby reducing the brightness difference at the joint of the heads. can do.

  However, although the brightness difference at the joint can be reduced, such a voltage correction causes the density difference ΔEmax of the entire recording area to be increased, resulting in density unevenness of the entire image and a reduction in image quality.

  In this case, it is possible to reduce the density difference at both ends of the head array by selecting and using a head that has no density difference at both ends of the head, and further correcting the voltage. Therefore, there is a problem in that the manufacturing cost increases due to a decrease in the yield when the head array is manufactured. Further, as the head becomes longer, more heads leak from the sorting, and the manufacturing cost will increase further.

  Therefore, a nozzle module for a specific color such as black that is obtained by combining other inks with a nozzle module that has the best dot printing accuracy among the plurality of nozzle modules that make up the print head. In addition, it is known that white stripes and dark stripes due to the banding phenomenon are eliminated or made almost inconspicuous by adjusting the color use ratio so that the specific color is used to the maximum extent (Patent Document 1). ).

JP 2006-297732 A

  In the configuration disclosed in Patent Document 1 described above, banding can be made inconspicuous, but in order to apply the above configuration, the print density in the head is uniform and the left and right ends (in the nozzle arrangement direction). Heads with no difference in density at both ends must be secured at a certain rate. For example, in the case of an image forming apparatus using CMYK four-color inks, more than a quarter, and only one type of liquid is ejected, such as a monochrome image forming apparatus. It must have no edge density difference. Furthermore, with the above configuration, the density difference between both ends of the head array can be reduced only for a specific color, but there is a problem that the density difference between both ends of the head array becomes large in an image where the color is not used so much. is there.

  The present invention has been made in view of the above problems, and an object of the present invention is to reduce the banding of head joints without increasing the image density difference between both ends of the head array.

In order to solve the above problems, a liquid ejection head array according to the present invention includes:
An image forming apparatus comprising a liquid ejection head array comprising at least one head row in which a plurality of heads each having a nozzle row in which a plurality of nozzles for ejecting liquid droplets are arranged in a staggered manner in the nozzle arrangement direction,
The head has a density difference between an image density formed by droplets ejected from the nozzle at one end of the nozzle row and an image density formed by droplets ejected from the nozzle at the other end,
All of the heads arranged in the recording area are configured such that the nozzles having the high density or the nozzles having the low density are arranged adjacent to each other in the liquid ejection head array.

  Here, the recording area can be configured to be a recording area of the smallest recording medium among the recording media on which recording is performed by the liquid discharge head array.

  Further, the density difference between the joints of two adjacent heads can be configured to be within 1.0 in terms of the brightness value in the CIELAB color space.

Further, at least two of the head rows are arranged in a direction orthogonal to the nozzle arrangement direction,
The relationship between the density differences between adjacent heads in one head row and the relationship between the density differences between adjacent heads in the other head row can be reversed.

  Further, only a head adjacent to a head having a density difference of 1.5 or more in the CIELAB color space at both ends of the nozzle row is a head in which the density difference is 1.5 or more in the brightness value. On the other hand, it can be set as the structure with which the nozzle with the said high density | concentration or the nozzle with a low density | concentration is arrange | positioned adjacently.

In addition, it has a plurality of head rows that eject droplets of different colors,
The head row for discharging liquid droplets having a higher density than the other colors among the different colors is such that at least two adjacent heads are nozzles having a high density in the nozzle arrangement direction or nozzles having a low density. It can be set as the structure arrange | positioned adjacent to each other.

Further, it has four head rows for ejecting droplets of each color of cyan, magenta, yellow and black,
In a head row that ejects black or black and cyan droplets, at least two adjacent heads are arranged such that nozzles with high density or nozzles with low density are adjacent to each other in the nozzle arrangement direction. Can be configured.

  According to the image forming apparatus of the present invention, the head has an image density formed by droplets ejected from the nozzles at one end of the nozzle row and an image density formed by droplets ejected from the nozzles at the other end. Since all of the heads arranged in the recording area are arranged in the liquid ejection head array so that the nozzles having a high density or the nozzles having a low density are adjacent to each other. The increase in image density difference between both ends can be suppressed, and the banding of the head joint can be reduced.

It is a plane explanatory view of the head array in a 1st embodiment of the present invention. (A) is plane explanatory drawing of one head, (b) is front explanatory drawing similarly. FIG. 3 is a cross-sectional explanatory view along the liquid chamber longitudinal direction (a direction orthogonal to the nozzle arrangement direction) along the line AA in FIG. It is explanatory drawing explaining the relationship between the position of the nozzle row direction of the same embodiment, and the brightness. It is explanatory drawing explaining the relationship between the position of the nozzle row direction of 2nd Embodiment of this invention, and the brightness. It is a plane explanatory view of the head array in a 3rd embodiment of the present invention. It is explanatory drawing explaining the relationship between the position of the nozzle row direction of the same embodiment, and the brightness. It is explanatory drawing explaining the relationship between the position of the nozzle row direction of 4th Embodiment of this invention, and the brightness. It is explanatory drawing explaining the relationship between the position of the nozzle row direction of 7th Embodiment of this invention, and the brightness. 1 is a schematic configuration diagram illustrating an example of an overall configuration of an image forming apparatus according to the present invention. It is explanatory drawing which shows the change of the diameter of the droplet discharged from the head with which it uses for description of brightness distribution in a head. It is explanatory drawing explaining an example of the brightness distribution in a head. It is explanatory drawing explaining the relationship of the position and the brightness of the nozzle row direction of a comparative example. It is explanatory drawing explaining the relationship of the position and the brightness of a nozzle row direction when performing voltage correction similarly.

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, a head array according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is an explanatory plan view of the head array.
The head array 100 includes a head row in which a plurality of heads 101A to 101D (referred to as “head 101” when not distinguished from each other) are arranged in a staggered pattern in the nozzle arrangement direction. The head 101 includes nozzle rows 102a and 102b (referred to as “nozzle row 102” as a whole) in which a plurality of nozzles 4 for discharging droplets are arranged.

Here, an example of one head will be described with reference to FIGS. 1A is a plan view of the head, FIG. 1B is a front view of the head, and FIG. 3 is a longitudinal direction of the liquid chamber along the line AA in FIG. 2A (perpendicular to the nozzle arrangement direction). FIG.
The head 101 includes a flow channel member (liquid chamber substrate) 1, a vibration plate member 2 bonded to the lower surface of the flow channel member 1, and a nozzle plate 3 bonded to the upper surface of the flow channel member 1. Individual flow paths (hereinafter also referred to as “pressurized liquid chambers”) 6 that communicate with the nozzles 4 that discharge the droplets are formed, and the communication portions 9 and flow paths provided in the diaphragm member 2 in the respective pressurized liquid chambers 6. Liquid ink is supplied from the common liquid chamber 8 through the communication path 10 formed in the member 1 and the fluid resistance portion 7. The common liquid chamber 8 is formed in a frame member 17 described later.

  Here, the flow path member 1 is formed by anisotropically etching a single crystal silicon substrate having a crystal plane orientation (110) using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), thereby allowing each pressurized liquid chamber 6 or Openings and grooves such as the fluid resistance portion 7 and the communication passage 10 are formed. In addition, the flow path member 1 can also form each pressurization liquid chamber 6 etc. by carrying out mechanical processing, such as etching or punching, using an acidic etching liquid, and the flow path member 1 can also be formed. 1 and the nozzle plate 3 or the diaphragm member 2 can be integrally formed by electroforming. Other photosensitive resins can also be used.

  The diaphragm member 2 is formed of a nickel plate having a three-layer structure of the first layer 2a, the second layer 2b, and the third layer 2c from the pressurized liquid chamber 6 side, and is manufactured by electroforming, for example. As the diaphragm member 2, for example, a laminated member of a resin member such as polyimide and a metal plate such as a SUS substrate, or a member formed from a resin member can be used.

  The nozzle plate 3 forms a large number of nozzles 4 corresponding to the pressurized liquid chambers 6 and is bonded to the flow path member 1 with an adhesive. As this nozzle plate 3, what consists of metals, such as stainless steel and nickel, resin, such as a polyimide resin film, silicon | silicone, and those combinations can be used. Further, the inner shape (inner shape) of the nozzle 4 is formed in a horn shape (may be a substantially cylindrical shape or a substantially frustum shape), and the hole diameter of the nozzle 4 is about 14 to about the diameter of the ink droplet outlet side. 35 μm.

  Further, a water repellent treatment layer having a water repellent surface treatment (not shown) is provided on the nozzle surface (surface in the ejection direction: ejection surface) of the nozzle plate 3. Examples of the water-repellent treatment layer include PTFE-Ni eutectoid plating, fluororesin electrodeposition coating, vapor-deposited fluororesin (e.g., fluorinated pitch), silicon resin / fluorine resin A water-repellent treatment film selected according to the ink physical properties such as baking after solvent application is provided to stabilize the droplet shape and flying characteristics of the recording liquid and to obtain high-quality image quality.

  The diaphragm member 2 includes a second layer 2b and a third layer at the center of a diaphragm portion (vibration region) 2A that is a deformable region formed by the first layer 2a corresponding to each pressurized liquid chamber 6. A convex portion 2B having a laminated structure of the layer 2c is formed, and a laminated piezoelectric column (multilayered piezoelectric element column) 12A constituting pressure generating means (actuator means) is joined to the convex portion 2B.

  The plurality of piezoelectric columns 12A are formed in a comb-like shape without being divided into one piezoelectric member 12 by half-cut grooving (slit processing). The piezoelectric member 12 includes a plurality of piezoelectric columns 12A. It is fixedly arranged on the base member 13 along the arrangement direction (nozzle arrangement direction). In this case, the plurality of piezoelectric columns arranged in a row become a driving piezoelectric column 12A that is alternately driven and a non-driven piezoelectric column (not shown) that is simply driven as a column portion. The non-driving piezoelectric column 12 </ b> B serving as the support column is joined to a portion corresponding to the liquid chamber interval wall.

  The piezoelectric member 12 has, for example, a lead zirconate titanate (PZT) piezoelectric layer having a thickness of 10 to 50 μm / layer and an internal electrode layer made of silver / palladium (AgPd) having a thickness of several μm / layer alternately. The internal electrodes are alternately electrically connected to the individual electrodes and the common electrodes, which are end face electrodes (external electrodes) on the end faces, respectively. The liquid region 6 is contracted and expanded by displacing the vibration region 2A by expansion and contraction of the piezoelectric column 12A whose piezoelectric constant is d33 (d33 indicates expansion / contraction perpendicular to the internal electrode surface (thickness direction)). ing. When the drive signal is applied to the piezoelectric column 12A and charging is performed, the piezoelectric column 12A expands, and when the charge charged to the piezoelectric column 12A is discharged, the piezoelectric column 12A contracts in the opposite direction.

  It should be noted that the configuration in which the ink in the pressurized liquid chamber 6 is pressurized using the displacement in the d33 direction as the piezoelectric direction of the piezoelectric member 12 or the pressurized liquid chamber is used by using the displacement in the d31 direction as the piezoelectric direction of the piezoelectric member 12. It is also possible to employ a configuration in which the ink in the six is pressurized. In the present embodiment, a configuration using displacement in the d33 direction is adopted.

  The base member 13 is preferably formed of a metal material. If the material (material) of the base member 13 is a metal, heat storage due to self-heating of the piezoelectric element member 12 can be prevented.

  Further, a frame member 17 is joined around the diaphragm member 2 with an adhesive. A common liquid chamber 8 for supplying liquid to each liquid chamber 6 is formed in the frame member 17. A liquid is supplied from the common liquid chamber 8 to the liquid chamber 6 through the communication portion 9 formed in the diaphragm member 2. The frame member 17 is also formed with a recording liquid supply port for supplying a recording liquid from the outside to the common liquid chamber 8.

  The common liquid chamber 8 is formed in a rectangular shape in a planar shape in the direction in which the pressurized liquid chambers 6 are arranged (nozzle arrangement direction, which is also referred to as “common liquid chamber longitudinal direction”). Of the wall surfaces forming the common liquid chamber 8, at least one wall surface is formed by the first layer 2 a of the diaphragm member 2, so that rigidity is higher than other wall surfaces formed by the frame member 17. The low damper member 20 is used.

  The damper member 20 may be two layers instead of one layer, or only the damper member 20 may be made of a material different from that of the diaphragm member 2. The damper member 20 is preferably made of a material having low gas permeability, such as metal Ni, but may be formed of a resin film or the like.

  In the head configured in this manner, for example, by lowering the voltage applied to the piezoelectric column 12A of the piezoelectric member 12 from the reference potential, the piezoelectric column 12A contracts, and the diaphragm member 2 descends to reduce the volume of the pressurized liquid chamber 6. As the ink expands, the ink flows into the pressurized liquid chamber 6 and then the voltage applied to the piezoelectric column 12A is increased to extend the piezoelectric column 12A in the stacking direction, thereby deforming the diaphragm member 2 in the nozzle 4 direction. By contracting the volume of the pressurized liquid chamber 6, the ink in the pressurized liquid chamber 6 is pressurized, and ink droplets are ejected (jetted) from the nozzle 4.

  Then, the diaphragm member 2 is restored to the initial position by returning the voltage applied to the piezoelectric column 12A to the reference potential, and the pressurized liquid chamber 6 expands to generate a negative pressure. The pressurized liquid chamber 6 is filled with ink. Therefore, after the vibration of the meniscus surface of the nozzle 4 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Note that the driving method of the head is not limited to the above example (drawing-pushing), and striking or pushing can be performed depending on the direction of the drive waveform. Strike is to lower the potential from the reference potential, contract the piezoelectric element, increase the internal volume of the pressurized liquid chamber, and then return the potential to the reference potential, thereby returning the diaphragm to the initial position and ejecting droplets. The hitting method and the pressing method are methods of discharging droplets by raising the potential from a reference potential and pushing the diaphragm into the pressurized liquid chamber side.

  Next, density gradients (lightness gradients) and head arrangements of the heads 101A to 101D in the head array 100 according to this embodiment will be described with reference to FIG. FIG. 4 is an explanatory diagram for explaining the relationship between the position in the nozzle row direction and the brightness.

  When the four heads 101A to 101D are filled with the same liquid and print a uniform image chart, an image formed by droplets ejected from the nozzle 4 at one end of the nozzle row 102 in the nozzle array direction is displayed. There is a density difference (hereinafter referred to as “brightness difference”) between the density and the density of the image formed by the droplets ejected from the nozzle 4 at the other end. For example, all the nozzles constituting the nozzle row 102 When looking at 4, there is a brightness gradient (concentration gradient) as shown in FIG.

  That is, the head 101A has a brightness difference | ΔEa | at the left and right ends (meaning one end and the other end in the nozzle arrangement direction). Similarly, the head 101B has a brightness difference | ΔEb |, and the head 101C has a brightness difference | ΔEc | The head 101D has a brightness difference | ΔEd |. Therefore, the end nozzle with high brightness of the head 101A and the end nozzle with high brightness of the head 101B are adjacent, the end nozzle with low brightness of the head 101B and the end nozzle with low brightness of the head 101C are adjacent, and the head 101C. The heads 101A to 101D are arranged adjacent to the nozzle having the higher brightness of the head and the nozzle having the higher brightness of the head 101D. As a result, the brightness difference in the entire head array becomes | ΔEmax |.

  Note that the brightness difference in the present embodiment is measured using a spectrophotometer and is calculated based on the brightness value in the CIELAB color space. The brightness difference may be calculated by a method other than the above. For example, the dot size of the image formed by the ink ejected from the head and the ink adhesion area are measured and converted to the brightness. Or may be performed by directly observing the size of the ink droplets ejected from the head without checking the image formed on the paper.

  With this configuration, the lightness differences ΔEab, ΔEbc, ΔEcd at the head joint can be reduced, and banding at the joint can be suppressed. Also, the brightness difference | ΔEmax | is not different from the normal random arrangement, and the brightness difference | ΔEmax | is not increased unlike the conventional configuration shown in FIG.

  In this case, a head having substantially the same lightness gradient as the heads 101A and 101B and a head having substantially the same lightness gradient as the heads 101C and 101D are selected and arranged, so that the heads are randomly selected and assembled. Thus, the maximum brightness difference | ΔEmax | of the entire head array can be effectively reduced.

  Further, when this head array is driven, the density difference between the joints of two heads adjacent in the nozzle array direction is within 1 or 0 in terms of brightness in the CIELAB color space, that is, ΔEab in FIG. , ΔEbc, ΔEcd are preferably adjusted so that the drive voltages of the respective heads 101A to 101D are within 1.0.

  In this way, the head has a density difference between the density of the dots formed by the droplets ejected from the nozzles at one end of the nozzle array and the density of the dots formed by the droplets ejected from the nozzles at the other end. The head row has a configuration in which adjacent heads are arranged such that high density nozzles or low density nozzles are adjacent to each other, thereby increasing the density difference in the nozzle array direction of the entire head array. The image quality can be improved by suppressing the banding of the joints of the heads.

  Further, it is not necessary to select whether or not the head can be used from the viewpoint of the density difference in the nozzle arrangement direction (left and right ends), the yield in manufacturing the head array can be improved, and the manufacturing cost of the head array can be reduced.

  In this case, by adjusting the driving voltage of each of the heads 101A to 101D so that the density difference between the two heads adjacent in the nozzle arrangement direction is within 1 or 0 in terms of the brightness value in the CIELAB color space, Differences in image density due to differences in ejection characteristics between adjacent heads are less likely to be recognized by the human eye. Further, in the conventional configuration shown in FIG. 14, the brightness difference | ΔEmax | is increased by voltage correction for eliminating the banding, but in the present embodiment, the brightness difference | ΔEmax | is rather reduced. As a result, banding can be eliminated and the density difference between both ends of the head array can be reduced, and density unevenness in the nozzle arrangement direction of the output image is less noticeable.

  Further, by adopting a configuration in which the density gradients of the adjacent heads are the same, the density gradients in the heads of the adjacent heads can be canceled more effectively, and density unevenness in the nozzle arrangement direction of the output image can be eliminated. It can reduce more effectively.

Next, a printing inspection method for manufacturing the above-described head array will be described.
In the printing inspection, a combination of heads to be incorporated into the head array and a driving voltage value applied when driving each head are set. In the printing inspection, the density values at the left and right ends of each head are measured and recorded at three levels of voltage magnification common to all heads. Further, from the obtained result, it is determined whether the density gradient at the right and left ends of the head is rising or falling right. At this time, in order to further reduce the maximum brightness difference | ΔEmax |, rank classification of the magnitude of the density difference between the left and right ends of each head is also performed. The rank is set so that the density difference between the right and left ends of the head is divided by 0.5 in terms of brightness, and each head is managed by giving a rank value as a density difference rank. Thus, each head is managed with five pieces of information: the density value at the right end, the density value at the left end, the density fluctuation rate when the drive voltage is changed, the direction of the density gradient in the head, and the density difference rank.

  Therefore, first, two sets of two heads having the same rank value and opposite density gradients are selected, and an array is formed (assembled) so that the combined heads are adjacent to each other. Then, the drive voltage values of the individual heads are set so that the brightness differences between the ends of adjacent heads are all 1.0 or less.

  In the present embodiment, the head array having one head row (meaning the entire head row arranged in a staggered manner) has been described. However, in the case where a plurality of head rows are provided, each head row is described above. The printed inspection may be performed. In this embodiment, the number of heads is four. However, other numbers may be used. When the number of heads is an odd number, the correction based on the density difference rank is “1” based on the number of heads. It is sufficient to carry out only for the number of heads minus "."

  The printing inspection method is performed by printing the same image chart under the same conditions, and measuring the density or brightness of any of the CMYK colors using a spectrocolorimetric system. However, in order to perform the measurement more precisely, the dot diameter may be measured by using a high magnification CCD camera or the like, and the value may be approximately converted into a lightness value. Alternatively, the image may be binarized and the ratio of black and white data may be approximately converted to a brightness value. Note that the density, brightness, and binarized data of the image from the camera have a strong correlation when using the same color ink, and the printed dot shape can maintain a clean circle with respect to the dot diameter. As long as there is a strong correlation with the lightness and density, the image characteristics represented by the density, lightness, dot diameter, and binarized data are collectively expressed as “density”.

  Further, it is preferable that the density values at the left and right ends necessary for correction can be measured using only the position closest to the end of the head as much as possible within a range that is not affected by variations in fine ejection characteristics in units of one nozzle. . However, in the case of connecting the heads, when providing overlapping nozzles in the nozzle rows of adjacent heads, it is sufficient that the both ends of the heads that do not overlap are included in the density measurement range. Both ends need not be included in the measurement range.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is an explanatory diagram for explaining the relationship between the position in the nozzle row direction and the brightness in the embodiment.
In the present embodiment, the heads 101A to 101F are combined so that the in-head density gradient is reversed by two heads, which is the minimum recording medium width. As a result, at least for printing on the minimum size paper, density unevenness in the nozzle array direction of the output image can be reduced to | ΔEmax ′ |.

  Here, of the six heads 101A to 101F, only the four heads 101B to 101E at the center are arranged so that the density gradients are reversed, but the overall width may be larger. The number may be large. Also, the number of heads arranged so that the gradient of the density gradient is reversed can take an arbitrary value according to the minimum width of the recording medium and the length per head. Further, when the paper is not passed through the center, the position of the head arranged so that the density gradient is reversed may be shifted to the left or right instead of the center.

  In general, a minimum-size sheet for recording an image is often a postcard, and high-quality recording such as a photograph is often required. Therefore, by disposing the head only in this recording area as described above, high-quality recording can be performed on the postcard, and the manufacturing cost such as head selection as the entire image forming apparatus can be suppressed.

Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 6 is an explanatory plan view of the head array in the same embodiment, and FIG. 7 is an explanatory view for explaining the relationship between the position in the nozzle row direction and the brightness in the same embodiment.
The head array 100 includes a first head row 111 in which a plurality of heads 101A1 to 101D1 are arranged in a staggered manner in the nozzle arrangement direction, and a second head row 112 in which a plurality of heads 101A2 to 101D2 are arranged in a staggered manner in the nozzle arrangement direction. And the recording medium feeding direction (direction orthogonal to the nozzle arrangement direction). Here, each head 101 of the first head row 111 and each head 101 of the second head row 112 are arranged at the same position in the main scanning direction.

  The four heads 101A1 to 101D1 of the first head row 111 are liquid droplets ejected from the nozzle 4 at one end of the nozzle row 102 in the nozzle arrangement direction when the same liquid is filled and a uniform image chart is printed. There is a density difference (brightness difference) between the density of the dots formed by the nozzle 4 and the density of the dots formed by the droplets ejected from the nozzle 4 at the other end. For example, all the nozzles constituting the nozzle row 102 When looking at 4, there is a brightness gradient (concentration gradient) as shown in FIG.

  Then, the nozzle with the high brightness of the head 101A1 and the nozzle with the high brightness of the head 101B1 are adjacent, the nozzle with the low brightness of the head 101B1 and the nozzle with the low brightness of the head 101C1 are adjacent, and the head 101C1. The heads 101A1 to 101D1 are arranged adjacent to the nozzle having the higher brightness of the head and the nozzle having the higher brightness of the head 101D1.

  The four heads 101A2 to 101D2 of the second head row 112 are also ejected from the nozzle 4 at one end of the nozzle row 102 in the nozzle arrangement direction when the same liquid is filled and a uniform image chart is printed. There is a density difference (brightness difference) between the density of the dots formed by the liquid droplets and the density of the dots formed by the liquid droplets ejected from the nozzle 4 at the other end. When the nozzles 4 are viewed, there is a brightness gradient (density gradient) as shown in FIG.

  The nozzle with the low brightness of the head 101A2 and the nozzle with the low brightness of the head 101B2 are adjacent to each other, the nozzle with the high brightness of the head 101B2 and the nozzle with the high brightness of the head 101C2 are adjacent to each other, and the head 101C2 The heads 101A2 to 101D2 are arranged so that the nozzle with the lower lightness and the nozzle with the lower lightness of the head 101D2 are adjacent to each other.

  In other words, between the first head row 111 and the second head row 112, the heads at the same position in the nozzle arrangement direction have the heads 101A1 to 101D1, 101A2 to 101D2 are arranged.

  As a result, the heads 101A1 to 101D1 of the first head row 111 and the heads 101A2 to 101D2 of the second head row 112 eject the same type of ink (liquid) and print them at the same position (overprinting). ) Even at this time, since the density difference between the both ends can be canceled out, the density variation of the entire head array can be reduced.

Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 8 is an explanatory diagram for explaining the relationship between the position in the nozzle row direction and the brightness in the embodiment.
The head arrangement (except for the direction of density gradient) in this embodiment is the same as that in FIG. That is, a first head row 111 composed of four heads 101A1 to 101D1 and a second head row 112 composed of four heads 101A2 to 101D2 are provided.

  For the first head row 111, as in the third embodiment, the end nozzle with high brightness of the head 101A1 and the end nozzle with high brightness of the head 101B1 are adjacent to each other, and the end of the head 101B1 with low brightness is the same. The heads 101A1 to 101D1 are arranged such that the nozzles at the end of the head 101C1 with the low brightness are adjacent to each other, the nozzles at the end of the head 101C1 with the high brightness and the nozzles at the end of the head 101D1 are adjacent to each other.

  On the other hand, for the second head row 112, the nozzle with the high brightness of the head 101A2 is adjacent to the nozzle with the low brightness of the head 101B2, and the nozzle with the high brightness of the head 101B2 and the end of the head 101C2 with the low brightness. The heads 101A2 to 101D2 are arranged such that the nozzle of the head 101C2 is adjacent to the nozzle having the high brightness of the head 101C2 and the nozzle of the head 101D2 having the high brightness.

  In this embodiment, the heads 101A1 to 101D1 of the first head row 111 eject black ink, and the heads 101A2 to 101D2 of the second head row 112 eject magenta ink. That is, only the black ink with the highest density is arranged so that the density gradients of the adjacent heads are reversed. On the other hand, for magenta ink, even in an image output from a head having the same ejection characteristics, if the density of the ejected ink is low, the difference in lightness becomes difficult to recognize. It is not arranged to face.

  Accordingly, it is possible to effectively reduce the density unevenness in the nozzle arrangement direction of the output image while further reducing the cost due to head selection and yield reduction when producing the head array.

Next, a fifth embodiment of the present invention will be described.
In the present embodiment, there are four head rows that discharge droplets of cyan, magenta, yellow, and black, the head row that discharges black droplets having the highest density, and cyan droplets. The head array to be ejected has the same head arrangement as in the first embodiment.

Next, a sixth embodiment of the present invention will be described.
In this embodiment, a head array that is used for printing a specification, a predetermined pattern, etc., and is the same head as in the first embodiment only for a head row that discharges liquid droplets that consume particularly large amounts of color. It is arranged.

  In any of these fourth to sixth embodiments, an image that is output while further reducing costs by performing head selection and rearrangement only for a head row that forms an image that is easily visible to the human eye. The density unevenness in the nozzle array direction can be effectively reduced.

Next, a seventh embodiment of the present invention will be described with reference to FIG. FIG. 9 is an explanatory diagram for explaining the relationship between the position in the nozzle row direction and the brightness in the embodiment.
In the present embodiment, similarly to the first embodiment, a head row in which the heads 101A to 101D are arranged is provided. The density differences in the density gradients of the heads 101A to 101D are | ΔEa |> 1.5 and | ΔEb |> 1.5, and | ΔEc | <1.5 and | ΔEd | <1. Suppose that it is 5.

  Here, only the head 101A and the head 101B, which are heads having a density difference between the head right and left ends larger than 1.5, and the head C adjacent to these heads, the density gradients of the adjacent heads are reversed. Are arranged as follows.

  By adopting such a configuration, the present invention can be applied without preparing the same number of heads with the right and left edges of the head rising right and lowering the right shoulder, and the density of the right and left ends of the head. Even when there is a bias in the inclination, for example, a large amount of downward sloping, more heads can be incorporated into the product, so that the image quality can be improved while reducing the cost.

Next, an example of the overall configuration of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 10 is a schematic configuration diagram of the image forming apparatus.
This image forming apparatus is a line type image forming apparatus, has an image forming unit 402 and the like inside the apparatus main body 401, and can supply a large number of recording media (sheets) 403 on the lower side of the apparatus main body 401. A paper tray 404 is provided, a sheet 403 fed from the sheet feeding tray 404 is taken in, a required image is recorded by the image forming unit 402 while the sheet 403 is conveyed by the conveying mechanism 405, and then the side of the apparatus main body 401. The paper 403 is discharged to a paper discharge tray 406 attached to the printer.

  Also, a duplex unit 407 that can be attached to and detached from the apparatus main body 401 is provided, and when performing duplex printing, the sheet 403 is conveyed into the duplex unit 407 while being transported in the reverse direction by the transport mechanism 405 after one-side (front) printing is completed. Then, the other side (back side) is sent back to the transport mechanism 405 as the printable side, and the paper 403 is discharged to the paper discharge tray 406 after the other side (back side) printing is completed.

  Here, the image forming unit 402 is, for example, four full-line liquids according to the present invention that discharge droplets of each color of black (K), cyan (C), magenta (M), and yellow (Y). The recording heads 411k, 411c, 411m, and 411y (which are referred to as “recording heads 411” when the colors are not distinguished from each other) configured by an ejection head array are provided. The head holder 413 is attached to the head.

  In addition, a maintenance / recovery mechanism 412k, 412c, 412m, 412y (referred to as “maintenance / recovery mechanism 412” when colors are not distinguished) is provided to maintain and recover the performance of the head corresponding to each recording head 411. During the head performance maintenance operation such as wiping processing, the recording head 411 and the maintenance / recovery mechanism 412 are relatively moved so that the capping member constituting the maintenance / recovery mechanism 412 faces the nozzle surface of the recording head 411.

  Here, the recording head 411 is arranged to eject droplets of each color in the order of blank, cyan, magenta, and yellow from the upstream side in the paper conveyance direction, but the arrangement and the number of colors are not limited to this. Further, as the line type head, one or a plurality of heads provided with a plurality of nozzle rows for discharging droplets of each color at a predetermined interval can be used, or a head and a liquid cartridge for supplying ink to the head are integrated. Or a separate body.

  The paper 403 in the paper feed tray 404 is separated one by one by a paper feed roller (half-moon roller) 421 and a separation pad (not shown) and fed into the apparatus main body 401, and is registered along the guide surface 423 a of the transport guide member 423. It is sent between 425 and the conveyor belt 433, and is sent to the conveyor belt 433 of the conveyor mechanism 405 via the guide member 426 at a predetermined timing.

  In addition, the conveyance guide member 423 is also formed with a guide surface 423 b for guiding the paper 403 sent out from the duplex unit 407. Further, a guide member 427 for guiding the sheet 403 returned from the transport mechanism 405 to the duplex unit 407 during duplex printing is also provided.

  The conveyance mechanism 405 includes an endless conveyance belt 433 that is stretched between a conveyance roller 431 that is a driving roller and a driven roller 432, a charging roller 434 that charges the conveyance belt 433, and an image forming unit 402. A platen member 435 that maintains the flatness of the conveying belt 433 at the opposite portion, a pressing roller 436 that presses the paper 403 fed from the conveying belt 433 against the conveying roller 431 side, and other ink (not shown) that adheres to the conveying belt 433. It has a cleaning roller made of a porous body or the like as a cleaning means for removing.

  On the downstream side of the transport mechanism 405, a paper discharge roller 438 and a spur 439 for sending the paper 403 on which an image is recorded to the paper discharge tray 406 are provided.

  In the image forming apparatus configured as described above, the conveyance belt 433 moves in the direction indicated by the arrow, and is charged by contact with the charging roller 434 to which a high potential application voltage is applied. The conveyance belt is charged to this high potential. When the sheet 403 is fed onto the sheet 433, the sheet 403 is electrostatically attracted to the conveyance belt 433. In this way, the sheet 403 that is strongly adsorbed to the transport belt 433 is calibrated for warpage and unevenness, and forms a highly flat surface.

  Then, the paper 403 is moved around the conveyor belt 433 and droplets are ejected from the recording head 411, whereby a required image is formed on the paper 403, and the paper 403 on which the image has been recorded is the paper discharge roller 438. As a result, the paper is discharged to the paper discharge tray 406.

  As described above, by providing the liquid ejection head array according to the present invention as a recording head, the density difference between both ends of each recording head in the nozzle arrangement direction can be reduced, and density unevenness in the nozzle arrangement direction of the output image can be reduced. Is less noticeable and image quality is improved. Further, the cost of the image forming apparatus main body can be reduced by reducing the manufacturing cost of the head array.

  Although the line type image forming apparatus has been described in the above embodiment, the present invention can be applied to a serial type image forming apparatus in which a head array in which two or more heads are connected is mounted as a recording head.

100 Head Array 101A to 101D, 101A1 to 101D1, 101A2 to 101D2 Head 102 Nozzle 111 First Head Row 112 Second Head Row 410y, 410m, 410c, 410k Recording Head (Head Array)

Claims (7)

An image forming apparatus comprising a liquid ejection head array comprising at least one head row in which a plurality of heads each having a nozzle row in which a plurality of nozzles for ejecting liquid droplets are arranged in a staggered manner in the nozzle arrangement direction,
The head has a density difference between an image density formed by droplets ejected from the nozzle at one end of the nozzle row and an image density formed by droplets ejected from the nozzle at the other end,
An image forming apparatus, wherein all of the heads arranged in a recording region are arranged in a liquid ejection head array such that nozzles having a high density or nozzles having a low density are adjacent to each other.   The image forming apparatus according to claim 1, wherein the recording area is a recording area of the smallest recording medium among recording media on which recording is performed by the liquid discharge head array.   3. The image forming apparatus according to claim 1, wherein the density difference between the joints of two adjacent heads is 1.0 or less in brightness value in the CIELAB color space. At least two of the head rows are arranged in a direction perpendicular to the nozzle arrangement direction;
4. The density difference relationship between adjacent heads in one head row and the density difference relationship between adjacent heads in the other head row are opposite to each other. Image forming apparatus.   Only the head adjacent to the head having a density difference of 1.5 or more in the CIELAB color space at both ends of the nozzle array is compared with the head having the density difference of 1.5 or more in the brightness value. The image forming apparatus according to claim 1, wherein the nozzles having a high density or the nozzles having a low density are arranged adjacent to each other. It has a plurality of head rows that eject droplets of different colors,
The head row for discharging liquid droplets having a higher density than the other colors among the different colors is such that at least two adjacent heads are nozzles having a high density in the nozzle arrangement direction or nozzles having a low density. The image forming apparatus according to claim 1, wherein the image forming apparatuses are adjacent to each other. It has four head rows that eject droplets of cyan, magenta, yellow, and black colors,
In a head row that ejects black or black and cyan droplets, at least two adjacent heads are arranged such that nozzles with high density or nozzles with low density are adjacent to each other in the nozzle arrangement direction. The image forming apparatus according to claim 6.

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