JP2007030503A - Image forming device and method for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device and a method for forming an image in which streak-like density variations or hollow parts caused by a joint part of adjoining short recording heads can be made inconspicuous, and density variations caused by uneven recording density characteristics of the short recording heads can be corrected, without arranging the short recording heads using a strict position adjustment. <P>SOLUTION: In an image forming device in which one long recording head is composed by arranging a plurality of short recording heads, a duplication correction control section 47 controls the driving of each nozzle of the short recording heads in nozzle train units 51-1 to 51-m depending on the phase difference of nozzle location between the duplicate short recording heads as a density correction for the image formed by the part in which nozzles of the short recording heads in the nozzle train units 51-1 to 51-m are duplicate. A density characteristic correction control section 46 controls the driving of each nozzle of the short recording heads in nozzle train units 51-1 to 51-m depending on the recording density characteristics for each nozzle train independently from the duplication correction control section 47. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that includes a recording head having a plurality of nozzle rows and forms an image on an image forming material, and more specifically, a single long recording head is formed by a plurality of short recording heads. The present invention relates to an image forming apparatus provided with at least one.

  For example, in a recording head of an ink jet image forming apparatus, there is a tendency to increase the number of recording elements (discharge nozzles) or lengthen them in order to satisfy the demand for speeding up image formation (image recording).

  As such an image forming apparatus, a configuration including a so-called line head that arranges (forms) recording elements (discharge nozzles) over one side (width direction) of an image forming material (recording medium) is known. .

  In an image forming apparatus including a line head, an image forming material is moved relatively in a direction (sub-scanning direction) perpendicular to the discharge nozzle arrangement direction of the line head, and ink is then ejected from the discharge nozzle to the image forming material. By discharging the image, it is possible to form an image on the entire surface of the image forming material. For this reason, an image forming apparatus including a line head does not require carriage movement or intermittent conveyance of an image forming material, so that image formation can be performed quickly and easily.

However, the line head has disadvantages such as higher cost than a short recording head, poor yield in quality and low reliability.
As an image forming apparatus that solves these problems, a short head is configured by arranging a plurality of short recording heads in which a plurality of ejection nozzles are arranged in one direction (main scanning direction) in the main scanning direction. There is also known an image forming apparatus that takes advantage of the cost, quality yield, and reliability of a recording head.

  However, in a line head constituted by such a short recording head, when a phase difference (inappropriate pitch) occurs in the pitch between nozzle rows at a joint portion between adjacent short recording heads, for example, it is formed. In some cases, streaky density unevenness or whiteness is formed on the image.

  In Patent Document 1, a high-quality image without color / density unevenness is recorded in an image recording apparatus in which a plurality of short heads (short recording heads) are arranged to form one recording head (line head). An image recording method is disclosed.

The image recording method disclosed in Patent Document 1 will be described with reference to FIGS.
The recording head 10 shown in FIG. 16A has a configuration including a plurality of short heads 12A and 12B. In this recording head 10, a plurality of ejection nozzles 11A in adjacent short heads 12A and a plurality of ejection nozzles 11B in short heads 12B are arranged so that they partially overlap (overlap) when viewed from the sub-scanning direction. ing. In this joining region (overlapping region), the short head 12A side corresponds to the discharge nozzles 11A-1 to 11A-3, and the short head 12B side corresponds to the discharge nozzles 11B-1 to 11B-3.

  In image recording by the recording head 10 having such a configuration, for example, as shown in a region a of FIG. 16B, the discharge nozzles 11A-1 to 11A-3 of the short head 12A and 11B-1 of the short head 12B. A high density recording area extending in the sub-scanning direction is generated in the joining area formed by ˜11B-3, and a high quality image cannot be recorded.

  In such a case, the recording control unit (not shown) that controls the recording head 10 to perform image recording in this case is shown by a dashed line in FIG. 16A as an example, and the ejection nozzle 11A-2 and the short length of the short head 12A. The discharge nozzle 11B-2 of the head 12B is determined as the joint position, and the use of the discharge nozzle 11A-1 and the discharge nozzle 11B-1 on the tip side is stopped.

  Further, since the gap between the discharge nozzle 11A-2 and the discharge nozzle 11B-2 at the seam position is narrower than the appropriate nozzle pitch, the density at the seam position is lower than the appropriate value as in the area a in FIG. Will also be high. In order to correct this, the recording control unit stops driving the one ejection nozzle 11 every other line in the sub-scanning direction at the joint position, and performs image recording with an appropriate density. In the example of the region b in FIG. 16B, the drive of the discharge nozzle 11B-2 of the short head 12B is stopped every other line in the sub-scanning direction.

In the image recording method of Patent Document 1, by performing such control, high-quality image recording without color / density unevenness is realized.
Here, in an ink jet recording head using a piezo element (PZT), the amount of ink discharged from the discharge nozzle at the end of the head generally increases or decreases as compared to a region other than the end, that is, a non-end region. Phenomenon occurs. In the case of an image recording apparatus constituted by a single recording head, even if a slight density change occurs due to a change in the amount of ink discharged from a fixed number of ejection nozzles due to the end portion, such a density is not affected by this phenomenon. Since the changed portion becomes the end portion in the image recording area, the density unevenness of the recorded image is hardly noticeable. However, in the case of an image recording apparatus provided with a line head in which a plurality of recording heads are arranged adjacent to each other, the joint portion between the recording heads adjacent to each other is inside the end portion of the image recording area, and thus density unevenness occurs in this portion. In the recorded image, streaky density unevenness, white spots, etc. are conspicuous.

Patent Document 2 discloses a method for visually reducing density unevenness caused by fluctuations in the ink discharge amount (ink discharge volume) at the end of the recording head.
In the method of Patent Document 2, it is determined whether an input image signal is a signal of an end region of a corresponding recording head or a signal of a non-end region, and when it is determined that the signal is an end region signal When the edge area correction process is performed and it is determined that the signal is a non-edge area signal, the non-edge area correction process is performed.

In the edge area correction processing, the edge area is corrected to such an extent that there is almost no difference in density between the non-edge area and the edge area visually. In the non-end region correction process, the non-end region is corrected so that there is almost no difference in density between the non-end region and the end region, and the density value extends from the end to the center. Corrections are made so as to decrease gradually. And in the method of this patent document 2, the density unevenness is reduced by the end region correction and the non-end region correction.
JP 2002-144542 A JP 2003-320647 A

  However, although Patent Document 1 discloses a method for improving density unevenness in an overlapping portion of nozzle rows between adjacent short heads, it discloses a method for improving unevenness due to non-uniformity in recording characteristics of nozzle rows. Not done. Therefore, the unevenness caused by the nonuniformity of the recording characteristics cannot be improved only by the method disclosed in Patent Document 1.

  Further, Patent Document 2 discloses a method for improving unevenness caused by non-uniformity in the amount of ink discharged from the discharge nozzles. One of the discharge nozzles at the joint portion of adjacent short heads is also connected to the other of the joint portions. The relative positions of the short heads are adjusted so as to match the discharge nozzles when viewed from the sub-scanning direction.

  The recording elements (discharge nozzles) are formed at very fine intervals. For example, when the resolution is 300 dpi, the interval is 85 μm. In the method disclosed in Patent Document 2, in this case, for example, a positioning mechanism for positioning the discharge nozzle by one short head and the discharge nozzle by the other adjacent short head without an error of 85 μm is required. Will increase the cost.

The density unevenness caused by the overlapping nozzle rows of the short head and the density unevenness caused by the non-uniformity of the recording characteristics due to the discharge nozzles are different in the generation factors and the density unevenness.
FIG. 17A shows a recording head (short head) in which the recording density by the discharge nozzles at the end of the nozzle row is higher than that at the non-end.

  In FIG. 17B, two short heads having recording density characteristics as shown in FIG. 17A are arranged adjacent to each other so that a part of the discharge nozzles are overlapped when viewed from the sub-scanning direction described above. The recording density characteristics of the recording head (line head) are shown.

  As shown in FIG. 17A, the density unevenness due to the non-uniformity of the recording characteristics of the discharge nozzles is caused by a slight error in ink discharge amount (ink discharge volume) in the structure of the recording head or in manufacturing. Therefore, the density change value becomes a small and gentle change.

  As shown in FIG. 17B, the density unevenness in the nozzle overlap portion 21 of the recording head occurs due to a density change according to the phase difference of the ejection nozzle positions between the nozzle rows by the adjacent recording heads. The density change value is large and steep.

  Therefore, in order to correct the density unevenness due to these two factors, a sufficient correction effect cannot be obtained by simply combining the two methods (techniques) disclosed in Patent Document 1 and Patent Document 2. An image with high image quality cannot be obtained.

  Accordingly, the present invention provides an image forming apparatus in which a plurality of short recording heads are arranged to form one long recording head, and the connection between adjacent short recording heads can be achieved without arranging the short recording heads by strict position adjustment. Image forming apparatus and image forming method capable of correcting density unevenness caused by non-uniformity of recording density characteristics of short recording head, while making streaky density unevenness and white spots caused by portions inconspicuous The purpose is to provide.

  According to the present invention, a plurality of short recording heads each having a nozzle array of ejection nozzles arranged in one direction are arranged to form a recording head, and an image is formed by ejecting ink from the ejection nozzles based on image signal values. On the premise of the image forming apparatus to be performed, an overlap correction control unit and a density characteristic correction control unit are provided.

  The duplication correction control unit controls the driving of the ejection nozzles according to the phase difference depending on the position of the ejection nozzles between the overlapping short recording heads as the density correction of the image formed by the overlapping portions of the recording heads.

The density characteristic correction control unit controls the driving of the ejection nozzles according to the recording density characteristics of the nozzle rows by the ejection nozzles independently of the overlap correction control unit.
The present invention also includes in its scope the image forming method of the image forming apparatus.

  According to the present invention, in an image forming apparatus in which a plurality of short recording heads are arranged to constitute one long recording head, the adjacent short recording heads can be arranged without arranging the short recording heads by strict position adjustment. Image forming apparatus and image forming capable of correcting density unevenness caused by non-uniformity in recording density characteristics of a short recording head while making stripe-shaped density unevenness and white spots caused by joint portions inconspicuous Can provide a method.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating a conceptual configuration example of an image forming apparatus according to the present embodiment.
FIG. 1 shows one configuration example of the image forming apparatus 30 according to the present embodiment when the image forming apparatus 30 is configured as a serial type image forming apparatus or a full line type image forming apparatus.

  As a configuration of the serial type image forming apparatus in the image forming apparatus 30 of FIG. 1, a moving mechanism for placing and holding the image forming material 31 or a movement for holding the image forming material 31 so as to be movable in the sub-scanning direction. It has the mounting base 32 provided with the mechanism. Above the mounting table 32, at least one recording unit 34-1 to 34-m (m is 2 or more) having a plurality of nozzle rows (short recording heads) in which a plurality of ejection nozzles (ink ejection ports) are formed. An integer) is disposed on the moving body 33. The moving body 33 is movably supported by a moving mechanism (not shown) and moves in the main scanning direction (Hx0 to Hxn) and the sub-scanning direction (Hy0 to Hyn) or only in the main scanning direction (Hx0 to Hxn). Moved. In the case of this serial type image forming apparatus, at least one image forming material 31 placed on the mounting table 32 and held or movably held in the sub-scanning direction is disposed on the moving body 33. The two recording units 34-1 to 34-m perform image formation on the image formation 31 in the process of relative movement only in the main scanning direction or in the main scanning direction and the sub-scanning direction.

  Further, as a configuration of the full-line image forming apparatus in the image forming apparatus 30 of FIG. 1, a moving mechanism (not shown) for placing the image forming material 31 and moving and conveying it in the sub-scanning direction is provided. Above this moving mechanism (not shown), a carriage 35 in which at least one recording unit 36-1 to 36 -m (m is an integer of 2 or more) having a plurality of nozzle rows formed by a plurality of ejection nozzles is disposed. Are arranged opposite to each other. In the case of this full-line image forming apparatus, the image forming material 31 held so as to be movable in the sub-scanning direction by a moving mechanism (not shown) is at least one of the recording units 36-1 to 36-m. In the process of relative movement, image formation is performed on the image forming material 31.

  In the carriage 35 indicated by a two-dot chain line in the drawing, a plurality of ejection nozzles of at least one recording unit 36-1 to 36 -m are provided at least in the main scanning direction (Hx) of the image forming material 31. In this configuration, a plurality of nozzle rows (short recording heads) are disposed so as to extend over a length equal to or greater than the width of the recording medium.

  In the case of this full-line type image forming apparatus, the leading end portion 31a of the image forming material 31 in the sub-scanning direction (Hy) is moved to My0 to Myn in the drawing by a moving mechanism (not shown), and further While the rear end portion 31b of the image forming material 31 in the sub-scanning direction (Hy) is moved to My0 to Myn in the drawing, ink is applied to the image forming material 31 by at least one recording unit 36-1 to 36-m. Is discharged to form an image.

  As described above, in the image forming apparatuses having different configurations, as an operation process of the serial type image forming apparatus, the control unit 37 moves the moving body 33 having at least one recording unit 34-1 to 34-m in the main scanning direction. In the process of movement control, the image forming position (ink discharge position) on the image forming material 31 is adjusted by varying the discharge timing for each of the plurality of nozzle rows in at least one recording unit 34-1 to 34-m. Image formation is performed.

  Further, as an operation process of the full-line image forming apparatus, at least one recording unit 36-1 to 36-1 in the process in which the control unit 37 controls the movement of the image forming material 31 in the sub-scanning direction by a moving mechanism (not shown). For a plurality of nozzle rows at 36-m, image formation is performed by adjusting the image formation position (ink ejection position) on the image forming material 31 by varying the ejection timing.

  In the image forming apparatus 30 according to the present embodiment, the control unit 37 includes a density characteristic correction control unit and an overlap correction control unit which will be described later. The image forming apparatus 30 controls the density characteristic correction control based on the image forming mode set by the operator from the mode setting unit 38 or the correction value recorded in the control unit 37 as known when the image is formed. The input image signal 41 is corrected using the unit 46 and the overlap correction control unit 47.

FIG. 2 is a diagram illustrating a configuration example of the image forming apparatus according to the present embodiment.
The image forming apparatus 30 according to the present embodiment shown in the figure includes a moving body 33, at least one recording unit 34-1 to 34-m, and at least one recording unit 36-1 to 36-m shown in FIG. In addition to the control unit 37 and the mode setting unit 38, a moving mechanism 43 including the mounting table 32 described above that supports the moving body 33 so as to be movable in a predetermined direction is shown.

  The at least one recording unit 34-1 to 34-m or the recording unit 36-1 to 36-m includes at least one nozzle row driving circuit 50-1 to 50-m (m is an integer of 2 or more) and a nozzle. It has column units 51-1 to 51-m (m is an integer of 2 or more). At least one nozzle row unit 51-1 to 51-m has a plurality of nozzle rows (short recording heads). The control unit 37 includes a plane memory 44, a timing generation unit 45, a density characteristic correction control unit 46, and an overlap correction control unit 47. The moving mechanism 43 includes a moving mechanism driving unit 48 that moves the moving body 33 and a moving position information generating unit 49, and further includes a mounting table 32 in the case of a serial type image forming apparatus.

  The control unit 37 is constituted by, for example, a CPU or the like. The control unit 37 controls the movement mechanism driving unit 48 of the movement mechanism 43, performs signal processing on the signal indicating the position of the moving body 33 notified from the movement position information generation unit 49, and the timing generation unit 45. It controls overall control of the image forming apparatus 30 as a whole, such as a control instruction for the input and storage of the input image signal 41 input from the outside in the plane memory 44. The control unit 37 corrects the input image signal 41 by the density characteristic correction control unit 46 and the overlap correction control unit 47. The density characteristic correction control unit 46 controls the drive of each ejection nozzle in accordance with the recording density characteristics of the nozzle arrays (short recording heads) constituting the nozzle array units 51-1 to 51-m, thereby controlling the ink ejection amount. decide. Further, the overlap correction control unit 47 determines the ink discharge amount by controlling the drive of each discharge nozzle according to the phase difference of the discharge nozzle positions between the nozzle rows (short recording heads). Details of this correction processing will be described later.

  The moving mechanism drive unit 48 of the moving mechanism 43 is configured by a motor or the like, for example, and moves the moving body 33 only in the main scanning direction, only in the sub-scanning direction, or in the main scanning direction and the sub-scanning direction based on the control instruction of the control unit 37. To move to a predetermined position. Moreover, the movement position information generation part 49 is comprised, for example with a rotary encoder etc., and notifies the movement amount and the position of the moving body 33 to the control part 37 as a signal. Note that the movement position information generation unit 49 may include a high frequency generation circuit that multiplies the frequency of the pulse signal generated by the rotary encoder as an integral number as necessary.

  The mode setting unit 38 is provided as a part of the input operation panel for the entire image forming apparatus 30 or is provided as an individual input operation panel. The operator instructs the mode setting unit 38 to set an image forming mode such as the correction function stop in the density characteristic correction control unit 46 and the correction function stop in the overlap correction control unit 47 in the image forming apparatus 30. A density characteristic correction control unit 46 and an overlap correction control unit 47, which will be described later, enter a correction mode selected by the operator according to the type of the image forming material 31 from the mode setting unit 38 based on the correction mode. Thus, the input image signal 41 is corrected.

  An image device 42 shown in FIG. 2 is an external device such as a scanner that has a function of detecting the density of an image formed on the image forming material 31 and is connected to the image forming apparatus 30. For example, according to an instruction from the control unit 37, the image device 42 detects the density of the image formed on the image forming material 31 set in the image device 42 and notifies the control unit 37 of the detected density.

  In the embodiment shown in FIG. 2, the image forming apparatus 30 and the image equipment 42 are apparatuses having different configurations. However, the present embodiment is not limited to this configuration, and the inside of the image forming apparatus 30. The image device 42 may be provided, and the adjustment information of the image density unevenness may be calculated based on the detection result of the image device 42.

  The density characteristic correction control unit 46 drives each ejection nozzle according to the nozzle row density characteristic for each nozzle row (short recording head) from the detection value notified by the image device 42 which is an external device of the image forming apparatus 30. To correct image density unevenness. In addition, the overlap correction control unit 47 uses the detection value notified from the image device 42 to detect the phase difference (the discharge nozzle by one nozzle row and the discharge nozzle by the other nozzle row) due to the overlap portion of each nozzle row (short recording head). According to the relative position), the drive of the ejection nozzles in each nozzle row (short recording head) is controlled to correct the image density unevenness.

  The density characteristic correction control unit 46 and the overlap correction control unit 47 may be realized by dedicated hardware, or may be realized by a software method by the CPU in the control unit 37 executing a program. good. Further, when configured by hardware, in order to prevent the influence of mutual correction processing, it is preferable to configure as separate and independent hardware.

  The timing generation unit 45 uses each nozzle row (short recording) of at least one nozzle row unit 51-1 to 51-m based on a position adjustment parameter set in advance according to position information of each nozzle row in the sub-scanning direction. Each discharge timing in the head) is instructed, and discharge position adjustment is controlled and instructed to at least one recording unit 34-1 to 34-m or at least one recording unit 36-1 to 36-m. . The recording units 34-1 to 34-m or the recording units 36-1 to 36-m have the nozzle rows (short recording heads) of at least one nozzle row unit 51-1 to 51-m at each discharge timing. By forming an image, the image for one line corresponding to the input image signal 41 notified from the control unit 37 is formed.

Next, an arrangement example of nozzle row units when the image forming apparatus according to the present embodiment is configured as a full line type image forming apparatus will be described.
As shown in FIG. 3, the carriage 35 fixedly arranged facing the moving mechanism 43 has nozzle row units 51-1 to 51-m (FIG. 3) configured by joining two short recording heads. Then, m = 4, (K) black nozzle row unit 51-1, (C) cyan nozzle row unit 51-2, (M) magenta nozzle row unit 51-3, and (Y) yellow nozzle row. Four nozzle array units 51) of the unit 51-4 are arranged at predetermined intervals in the sub-scanning direction from the upstream side in the transport direction of the image forming material 31. Each nozzle array unit 51-1 to 51-m includes a plurality of short recording heads 51A-1, 51B-1 to 51A-m, 51B-m (m = 4 in FIG. Short recording heads 51A-1, 51B-1, (C) short recording heads 51A-2, 51B-2, (M) short recording heads 51A-3, 51B-3, and (Y) short recording heads. Recording heads 51A-4 and 51B-4) are arranged corresponding to the respective nozzle array units 51-1 to 51-m. Each short recording head 51A-1, 51B-1 to 51A-4, 51B-4 has one to a plurality of nozzle rows for each short recording head.

  The ink ejection from the ink ejection ports (ejection nozzles) of the nozzle array units 51-1 to 51-4 is configured to eject a plurality of ink droplets having the same volume, for example. Thereby, the control with respect to the nozzle row units 51-1 to 51-4 is performed by the control unit 37 by the number of ink droplets ejected from the nozzle row units 51-1 to 51-4 by the nozzle row drive circuits 50-1 to 50-4. The so-called multi-drop method can be used in which density gradation is adjusted by controlling the above.

  For example, when each of the ink ejection ports of the nozzle array units 51-1 to 51-4 can eject a maximum of 7 ink droplets, 0 to 7 ink droplets including the case where the ink ejection is not performed are imaged. The ink is discharged onto the forming material 31 to form dots corresponding to the number of ink droplets. Thereby, the control unit 37 can perform gradation control of density of 8 gradations including 0 gradation.

Further, the nozzle row units 51-1 to 51-4 for the respective colors have a predetermined number of liquid ejection / ejection ports (ejection nozzles) over a length equal to or greater than the width in the main scanning direction of the image forming material 31 to be conveyed. Have. For example, in the (K) nozzle row unit 51-1 configured by joining two short recording heads, a plurality of discharge nozzles in the end discharge nozzles of the short recording head 51A-1 and the short recording head 51B-1. The plurality of discharge nozzles in the end discharge nozzles are joined so as to overlap when viewed from the sub-scanning direction. (The nozzle row units 51-2 to 51-4 have the same configuration as the nozzle row unit 51-1.)
As described above, when the end portions of the nozzle rows of the respective short recording heads 51A and 51B are disposed so as to overlap each other, the control unit 37 is provided for each short recording head disposed on the carriage 35. Since the input image signal 41 can be selectively input to form an image, strict position adjustment in the nozzle row direction (main scanning direction) with respect to each short recording head can be omitted, and an inexpensive position adjustment mechanism It can be.

  In addition, as a position adjustment mechanism for each nozzle row unit 51-1 to 51-4, for example, a mechanical adjustment mechanism that minutely moves the nozzle row units 51-1 to 51-4 in the rotation direction may be provided.

Next, a configuration example when the image forming apparatus 30 in the present embodiment is configured as a full-line image forming apparatus will be described.
As shown in FIG. 3, the moving mechanism 43 disposed to face the carriage 35 is downstream of the edge sensor 62 that detects at least one end of the image forming material 31 in the conveyance path of the image forming material 31. Arranged on the side.

  An endless belt forming a plurality of holes in the moving body 33 in FIG. 1 is rotatably mounted on one roller 63a and the other roller 63b, and the other roller 63b is connected to a motor in the moving mechanism driving unit 48. And a configuration in which the rotary encoder in the movement position information generation unit 49 is connected to one of the rollers 63a. Below the endless belt, for example, a suction fan (not shown) is provided to suck the image forming material 31.

  The control unit 37 in FIG. 1 places the image forming material 31 conveyed from the upstream side of the moving mechanism 43 on the endless belt of the moving mechanism 43 and sucks it, and each color disposed on the carriage 35 described above. In the process of moving below the short recording heads 51A-1, 51B-1 to 51A-4, 51B-4 corresponding to the nozzle array units 51-1 to 51-4, image formation is performed.

  The control unit 37 separates the distance from the edge sensor 62 described above to the nozzle row of the short recording head 51A-1 corresponding to the nozzle row units 51-1 to 51-4 of each color, and the nozzles of the short recording head 51B-1. The separation distance to the row, the separation distance to the nozzle row of the short recording head 51A-2, the separation distance to the nozzle row of the short recording head 51B-2, and the separation distance to the nozzle row of the short recording head 51A-3 And the separation distance to the nozzle row of the short recording head 51B-3, the separation distance to the nozzle row of the short recording head 51A-4, and the separation distance to the nozzle row of the short recording head 51B-4. It is converted into the cumulative number of pulses and stored in advance in the nonvolatile memory of the control unit 37.

  Accordingly, the control unit 37 uses the detection signal when the edge sensor 62 detects, for example, the leading end of the image forming material 31 conveyed on the conveyance path as trigger information, and the rotary encoder in the movement position information generation unit 49. The pulse signal count starts. The control unit 37 then stores the rotary encoder stored in advance corresponding to the count number of the pulse signal of the rotary encoder and the nozzle row positions of the respective short recording heads 51A-1, 51B-1 to 51A-4, 51B-4. Image formation is performed based on the input image signal 41 at each ink ejection timing when the cumulative number of pulses of the encoder matches.

Next, details of a control method by the control unit of the image forming apparatus in the present embodiment will be described.
The input image signal 41 input from the outside of the image forming apparatus 30 is stored as 1 to n line image signals (n is an integer of 2 or more) in the plane memory 44 under the control of the control unit 37. The image signals of 1 to n lines correspond to one line in the width direction in the recording area of the image forming material 31 when the image forming apparatus 30 of the present embodiment is configured as a full line type image forming apparatus.

  Note that the plain memory 44 is configured so that each of the short recording heads 51 </ b> A- 1 is configured when the image forming apparatus 30 of the present embodiment includes, for example, the nozzle array units 51-1 to 51-4 for each color illustrated in FIG. 3 described above. , 51B-1 to 51A-4 and 51B-4, the 1-n line image signals are divided and stored.

  The control unit 37 generates 1 to n line image signals in the input image signal 41 stored in the plane memory 44 by, for example, conveying the image forming material 31 after the leading edge is detected by the edge sensor 62 described above. The data is read out in synchronization with the count value of the movement position information generating unit 49 and input to the density characteristic correction control unit 46.

  The density characteristic correction control unit 46 performs a process described later on the density correction coefficient set in advance according to the recording density characteristic of each ejection nozzle and the ejection nozzles of each short recording head joined together as viewed from the sub-scanning direction. A density correction signal is calculated based on the image signal value of each pixel formed on the image forming material 31 by each ejection nozzle in the non-overlapping (non-overlapping portion).

  This density correction signal is a quantized density correction signal at a signal level that can be input to each short recording head, that is, the eighth floor from 0 to 7 in each discharge nozzle of the nozzle array units 51-1 to 51-4 of this embodiment. Convert to key value.

Note that the quantization error generated by the quantization conversion is preferably diffused to surrounding pixels by an error diffusion method or the like.
The image signal converted into the quantized density correction signal by the density characteristic correction control unit 46 is processed by the image forming apparatus 30 according to the present embodiment, for example, in each of the nozzle row units 51-1 to 51-4 shown in FIG. In the case of the configuration having the above, the image signal of each line of 1 to n lines corresponds to each nozzle row of each of the short recording heads 51A-1, 51B-1 to 51A-4, 51B-4. The signal is divided into signals and input to the overlap correction control unit 47.

Next, nozzle row overlap correction will be described with reference to FIGS. 4, 5, and 6.
In the description of the nozzle row overlap correction, when one nozzle row and the other nozzle row are arranged adjacent to each other with an overlap portion, the discharge nozzles by the one nozzle row of the overlap portion and the other nozzle row are used. Assume that a phase difference occurs between the discharge nozzles.

  The distance a between the ejection nozzles of the recording head shown in FIG. 4 is about 85 μm, for example, when the resolution is 300 dpi. A distance δ in the figure indicates a phase difference in the main scanning direction between the ejection nozzles of the recording head 71 and the ejection nozzles of the recording head 72. The distance δ in this phase difference is the distance between the ejection nozzle 73 of the recording head 71 and the ejection nozzle 74 of the recording head 72 in FIG. Further, the distance δ in this phase difference is the distance between the discharge nozzle 75 of the recording head 71 and the discharge nozzle 76 of the recording head 72 in FIG.

  4A and 4B, the image signals are divided and input to the discharge nozzles with hatching of the recording heads 71 and 72, and are discharged from the discharge nozzles of the respective recording heads 71 and 72. An image is formed by output dots (dot images) formed by the ink.

Note that ink is not ejected from the ejection nozzles that are not shaded in FIG.
The output dots formed on the image forming material 31 are shown in FIG. 5A when the recording head 71 and the recording head 72 are arranged in a positional relationship as shown in FIG. It is formed in such a positional relationship. In this case, the principal direction difference δ has a relationship of δ> a, and the distance between the output dot 81 by the discharge nozzle 73 and the output dot 82 by the discharge nozzle 74 becomes large.

  Thereby, since the density of output dots formed on the image forming material 31 is low in the nozzle row overlapping portion, the nozzle row overlapping portion with respect to the density of the output dots by the discharge nozzles adjacent to the nozzle row overlapping portion. As a result, streaky density unevenness occurs.

  Further, the output dots formed on the image forming material 31 are shown in FIG. 5B when the recording head 71 and the recording head 72 are arranged in the positional relationship as shown in FIG. It is formed in the positional relationship as shown. In this case, the principal direction difference δ has a relationship of δ <a, and the distance between the output dot 83 by the discharge nozzle 73 and the output dot 84 by the discharge nozzle 74 becomes small.

  Thereby, in the nozzle row overlapping portion, the density of output dots formed on the image forming material 31 is increased. Therefore, the nozzle row overlapping portion with respect to the output dot density by the discharge nozzles adjacent to the nozzle row overlapping portion. As a result, streaky density unevenness occurs.

  In this embodiment, when one nozzle row and the other nozzle row are arranged adjacent to each other with overlapping portions, the phase difference between the discharge nozzles of one of the overlapping portions and the discharge nozzles of the other nozzle row Density unevenness generated according to the correction is corrected by varying the output dots formed on the image forming material 31 by the overlap correction control unit 47 controlling the ejection of the ejection nozzles of the recording head.

Note that the variable output dot is at least one of a change in a target discharge nozzle for discharging ink or a dot diameter formed by discharging ink from the discharge nozzle.
In FIG. 6A, as shown in FIG. 5A, the image formation after the nozzle row overlap correction is performed in the case where the principal direction difference δ is in the relationship of δ> a. Output dots formed on the material 31 are shown.

  The output dots 86 shown in FIG. 6A are output dots formed on the image forming material 31 by the discharge nozzles 77 of the recording head 72 shown in FIG. As for the ink discharge amount when forming the output dots 86, the overlap correction control unit 47 multiplies the input image signal 41 by the density correction coefficient corresponding to the aforementioned inspection direction phase difference δ, and this multiplication value is obtained on the eighth floor. It is determined by quantizing the key value.

  As described above, in the present embodiment, the density unevenness of the nozzle row overlapping portion is corrected by adding the output dot 86 as shown in FIG. 6A by the nozzle row overlapping correction by the overlap correction control unit 47. be able to.

  Further, FIG. 6B shows a state after the nozzle row overlap correction is performed in the case where the main scanning direction phase difference δ is in the relationship of δ <a as shown in FIG. Output dots formed on the image forming material 31 are shown.

  Output dots 84 shown in FIG. 6B are output dots formed on the image forming material 31 by the discharge nozzles 76 of the recording head 72 shown in FIG. As for the ink discharge amount when forming the output dots 84, the overlap correction control unit 47 multiplies the input image signal 41 by the density correction coefficient corresponding to the aforementioned inspection direction phase difference δ, and this multiplication value is the eighth floor. It is determined by quantizing the key value.

  As described above, in this embodiment, the dot diameter of the output dot 84 shown in FIG. 5B is changed to the output dot 84 ′ as shown in FIG. 6B by the nozzle row overlap correction by the overlap correction control unit 47. By varying (reducing) the dot diameter, the density unevenness of the overlapping nozzle rows is corrected.

  The nozzle row overlap correction by the overlap correction control unit 47 as described above is performed on several lines of image signals among a plurality of line image signals (the image signals of 1 to n lines described above) in the input image signal 41. . In this nozzle row overlap correction process, the quantization error generated when quantizing to eight gradation values is diffused to the next one-line image signal.

FIG. 7A shows output dots formed on the image forming material 31 by a plurality of line image signals after nozzle row overlap correction.
As shown in FIG. 7A, the joint portion of the output dots formed on the image forming material 31 is formed linearly when viewed from the sub-scanning direction.

  As shown in FIG. 7B, the joint portion of the output dots formed on the image forming material 31 can be made to be less noticeable by moving it randomly in the main scanning direction, for example.

  In order to make the joint portion of the output dots random when viewed from the sub-scanning direction, the switching position between the divided image signal divided into one nozzle row of the overlapping portion and the divided image signal divided into the other nozzle row This can be done by moving.

  In the nozzle row overlap correction of the present embodiment, the dot for which the density correction of the nozzle row overlap portion is performed is performed only for one output dot corresponding to the joint portion, and the quantization error caused by the nozzle row overlap correction is corrected. The output dots adjacent to the output dots at the joint are not diffused.

  In the density correction processing of the present embodiment, the density characteristic correction control unit 46 is provided in the preceding stage and the overlap correction control part 47 is provided in the subsequent stage, so that the quantization error generated in the nozzle row overlapping part correction can be reduced to other than the nozzle row overlapping part. It realizes processing that does not diffuse.

  As a result, in the density correction processing of the present embodiment, the density unevenness caused by the overlapping nozzle array where the density value is large and the gradient due to the change in the density value is steep, and the nozzle array where the density value change is small and gentle. It is possible to correct both density unevenness due to non-uniform formation characteristics (recording characteristics) due to the nozzle rows adjacent to the overlapping portion.

  In the present embodiment, the density correction for the nozzle row overlapping portion is performed only for one output dot by the discharge nozzle corresponding to the joint portion as described above. However, the present invention is not limited to this. You may go to the subject.

  In the density correction for the nozzle row overlapping portion of the present embodiment, for example, as shown in FIG. 8, control is performed by multiplying the input image signal 41 to the plurality of ejection nozzles corresponding to the nozzle row overlapping portion by the density correction coefficient. By doing so, the density unevenness can be corrected.

  In FIG. 8A, when one nozzle row and the other nozzle row are arranged adjacent to each other with overlapping portions, density correction coefficients to be multiplied to the respective discharge nozzles of one nozzle row (left side) in the overlapping portion are shown. It is shown. Further, FIG. 8B shows a density correction for multiplying each discharge nozzle of the other nozzle row (right side) in the overlapping portion when one nozzle row and the other nozzle row are provided adjacent to each other with an overlapping portion. The coefficients are shown.

  In the density correction for the nozzle row overlapping portion of the present embodiment, as shown in FIG. 8C, the input image signal 41 to each discharge nozzle of one nozzle row (left side) in the overlapping portion is shown in FIG. 8), the input image signal 41 to each discharge nozzle of the other nozzle row (right side) in the overlapping portion is multiplied by the density correction coefficient shown in FIG. As a result, density unevenness can be corrected.

  In FIG. 8C, a nozzle row overlap correction area 93 in which nozzle row overlap correction is performed is indicated by dotted lines 91 and 92. In this nozzle row overlap correction process, the quantization error generated when quantizing to 8 gradation values is diffused only to the input image signal 41 corresponding to this nozzle row overlap correction region 93.

  In the density correction for the nozzle row overlapping portion of this embodiment, for example, as shown in FIG. 9, a plurality of error conversion distribution coefficients for diffusing the quantization error from the processing pixel to the surrounding pixels are provided and used.

The error conversion distribution coefficient shown in FIG. 9 is a pixel subject to quantization error generation indicated by X,
The error diffusion distribution coefficient (number / 16) to the surrounding pixels is shown. For example, if the pixel is “7”, the quantization error generated by the quantization is a ratio of 7/16. It indicates that the pixel is diffused to the corresponding pixel.

The error conversion distribution coefficient K1 shown in FIG. 9A is a normal diffusion coefficient, and is applied in the nozzle row overlap correction region 93 excluding the dotted lines 91 and 92 shown in FIG.
Further, the error conversion distribution coefficient K2 shown in FIG. 9B is set so as not to diffuse the error to the right side of the pixel indicated by X, and in the dotted line 92 shown in FIG. This is applied to the right boundary pixel of the nozzle row overlap correction region 93. Further, the error conversion distribution coefficient K3 in FIG. 9C is set so as not to diffuse the error to the left side of the pixel indicated by X. FIG.
This is applied to the left boundary pixel of the nozzle row overlap correction region 93 on the dotted line 91 shown in (c).

  As described above, in the density correction for the nozzle row overlap portion according to the present embodiment, by limiting the diffusion range of the quantization error, it occurs when quantizing to 8 gradation values in the nozzle row overlap correction process. It is possible to prevent the quantized error from diffusing to the region adjacent to the nozzle row overlap correction region 93.

  Therefore, in the density correction processing of the present embodiment, even if the density correction for the nozzle row overlapping portion is performed on a plurality of ejection nozzles, the nozzle row overlapping portion where the density value is large and the gradient due to the change in the density value is steep. It is possible to correct both the density unevenness caused by the non-uniformity and the density unevenness caused by the nonuniformity in the formation characteristics (printing characteristics) of the nozzle rows adjacent to the overlapping nozzle row where the change in density value is gentle.

  Next, a procedure for determining a density correction parameter including a density correction coefficient and the like set in advance in the nozzle row density characteristic correction unit 46 and the overlap correction control unit 47 in the density correction processing of this embodiment will be described.

The determination of the density correction parameter is performed when the image forming apparatus 30 is shipped from the factory or when readjustment is performed after replacing the recording head in the nozzle array unit.
FIG. 10 is a flowchart showing the procedure for determining the density correction parameter.

  The density correction parameter is set by reading a test image formed on the image forming material 31 by the image forming apparatus 30 with the image device 42 connected to the image forming apparatus 30 and determining the density correction parameter based on the result. To do.

The density correction process of the present embodiment is performed by setting the determined density correction parameter in the density characteristic correction control unit 46 and the overlap correction control unit 47 of the image forming apparatus 30.
The density correction parameter is set in a predetermined pattern at the same position on the image forming material 31 as the test image on the main scanning direction position and the sub-scanning direction position of the test image formed on the image forming material 31. It is preferably performed after basic parameters for image formation such as heavy color position information for forming an image by overlaying several colors of ink are set.

  Therefore, in the determination procedure of the density correction parameter shown in FIG. 10, first, in step S1, nozzle row density correction in the correction function by the density characteristic correction control unit 46 and nozzle row duplication correction in the correction function by the duplication correction control unit 47 are performed. Stop.

  The determination procedure of the density correction parameter according to the present embodiment is configured such that the switching of the correction function stop (off) / operation (on) is switched by, for example, the operator operating the operation panel of the image forming apparatus 30 or the like. When the correction parameter determination mode is started, the image forming apparatus 30 may be configured to automatically switch the stop (off) / operation (on) of the correction function.

  Next, in step S <b> 2, the density correction parameter determination procedure forms an image of the test image 1 for determining the nozzle row overlap correction parameter on the image forming material 31 in the image forming apparatus 30. As described above, the test image 1 formed in this step S2 is overlapped with the nozzle array units arranged such that the ends of the nozzle arrays of the plurality of recording heads overlap when viewed from the sub-scanning direction. What is suitable for detecting the phase difference of the discharge nozzle positions between the nozzle rows is preferable.

Therefore, as the test image 1, an image that can measure the distance between the discharge nozzles serving as a reference or an image that can estimate the phase difference from the density unevenness caused by the phase difference is used.
Since the test image 1 is an image serving as a reference for correction, image formation is performed after the correction is stopped in step S1.

  FIG. 11A shows an example of a recording head having nozzle rows with non-uniform formation characteristics (recording characteristics) that differ in density when an image is formed on the image forming material 31 depending on the positions of ejection nozzles of the nozzle arrays. Has been.

  Further, FIG. 11B shows a main part of a nozzle array unit in which recording heads having non-uniform formation characteristics (recording characteristics) as shown in FIG. The density is shown when an image is formed on the image forming material 31 with the density correction of the embodiment stopped.

  The overlapping part of the nozzle rows shown in FIG. 11B has a large density value, and the slope due to the change in the density value is steep. The test image 1 is used to determine the nozzle row overlap correction parameter for correcting the density of the nozzle row overlap portion.

Next, in step S3, the density correction parameter determination procedure reads the test image 1 formed in step S2 with the image device 42.
Next, in step S4, the density correction parameter determination procedure detects the phase difference of the ejection nozzle positions between the overlapping nozzle rows on the basis of the image reading result in step S3, and the nozzles such as the density correction coefficient accordingly. Determine the column overlap correction parameter. The determined nozzle row overlap correction parameter is stored in a nonvolatile memory included in the overlap correction control unit 47.

  In the determination of the nozzle row overlap correction parameter in step S4, since a parameter for correcting only the density unevenness caused by the phase difference of the ejection nozzle positions between the overlapping nozzle rows is determined, the nozzle row whose density value change is small and gentle. It is preferable to increase the accuracy of the nozzle row overlap correction parameter by removing a measurement component of density unevenness caused by non-uniform formation characteristics (recording characteristics).

  Next, in step S5, the density correction parameter determining procedure operates (turns on) nozzle row overlap correction by the overlap correction control unit 47 and stops (off) nozzle row density correction by the density characteristic correction control unit 46.

  Next, the density correction parameter determination procedure forms an image of the test image 2 for determining the nozzle row density correction parameter on the image forming material 31 in step S6. The test image 2 is preferably an image in which density unevenness due to non-uniform formation characteristics (recording characteristics) for each nozzle array can be detected, for example, a halftone image formed by dots of 1 to 7 gradations.

  Note that the test image 2 formed in step S6 is an image in which the density unevenness due to the nozzle row overlap portion is corrected by the nozzle row overlap correction as shown in FIG. 11C.

Next, in the determination procedure of the density correction parameter, in step S7, the image device 42 reads the test image 2 formed in step S6.
Next, in step S8, the density correction parameter determination procedure determines the nozzle array density correction parameter based on the reading result in step S7. The determined correction parameter is stored in a nonvolatile memory included in the density characteristic correction control unit 46.

  The nozzle row density correction parameter determined in step S8 is determined based on the image in which the density unevenness due to the nozzle row overlap portion is corrected by the nozzle row overlap correction. Therefore, the accuracy of the nozzle row density correction parameter is increased. Can be increased.

  Next, in the density correction processing by the image forming apparatus 30 of the present embodiment, the mode setting process when the operator performs image formation and the operation of the density correction processing based on this mode setting process will be described.

  The image forming apparatus 30 according to the present embodiment has an image forming mode suitable for a difference in image data (input image signal 41) formed on the image forming material 31 or a difference in material of the image forming material 31. The mode setting unit 38 can be set by the operator.

  The image forming apparatus 30 according to the present embodiment determines the density correction processing method by the density characteristic correction control unit 46 and the overlap correction control unit 47 based on the selected image forming mode, and performs image formation.

When the operator does not set (select) the image forming mode, correction that gives priority to density correction processing, which will be described later, is set at the time of image formation.
Next, image forming modes that can be set by the operator will be described.

  There are two types of image forming modes of the image forming apparatus 30 of the present embodiment, for example, a line priority mode in which image data is text information or graphics, and a hue priority (density priority) mode in which image data is a photograph or the like. Mode.

The straight line priority mode is a mode in which priority is given to the linearity of each line in character information, graphics, etc., and therefore no density correction processing is performed.
In the hue priority (density priority) mode, for example, (K) black, (C) cyan, (M) magenta, and (Y) hue for each ink color by yellow, and dots by the respective ink colors are formed. In this mode, priority is given to the reproducibility of hues by heavy colors when formed at the same position on the material 31, and thus density correction processing is performed.

The density correction processing at the time of image formation is suitable in terms of improving the uniformity of the image density, but on the other hand, the density of the entire image formed tends to be reduced.
This is because a general density correction process has a high formation density in a low density portion where the formation density on the image forming material 31 is low, that is, an image density in a portion where the diameter of the output dots ejected from the recording head is small. This is because correction processing is performed to reduce the output dots of the high density portion so that the image density of the density portion is made uniform and uniform.

  Further, the decrease in the density of the entire image varies depending on the difference in the material of the image forming material 31 and the like. In the image formation on the inkjet-dedicated coated paper, the image density is kept high due to the characteristics of the inkjet-dedicated coated paper and the ink, so that the influence of the image density reduction during the density correction process is small. On the other hand, in the image formation on cardboard or cardboard, the dedicated coating process is not performed on the surface of the cardboard or cardboard, and the amount of ink soaked increases, so the influence of the image density reduction during the density correction process is large.

However, image data on cardboard or cardboard is often relatively large character data, and slight uneven density is not a problem.
In addition, in image formation on plain paper that is not coated exclusively for inkjet, it has intermediate characteristics between inkjet-dedicated coated paper and cardboard or cardboard.

  Therefore, in the image forming apparatus 30 of the present embodiment, image formation suitable for the difference in image data (input image signal 41) formed on the image forming material 31 or the difference in the material of the image forming material 31 or the like. The mode can be set by the operator from the mode setting unit 38.

  Next, the density after the image forming apparatus 30 of the present embodiment has caused the density characteristic correction control unit 46 and the overlap correction control unit 47 to perform density correction processing based on each selected hue priority (density priority) mode. The state of distribution (density unevenness) will be described with reference to FIG.

  FIG. 12A shows only the nozzle row overlap correction by the overlap correction control unit 47 for the nozzle row units arranged so that the ends of the nozzle rows by the plurality of recording heads overlap when viewed from the sub-scanning direction. The density distribution (density unevenness) when an image is formed on the image forming material 31 after performing the above is shown.

FIG. 12B shows an example of a density correction value (density correction parameter) added by the nozzle row density correction by the density characteristic correction control unit 46.
FIG. 12C shows a density distribution (density unevenness) when an image is formed on the image forming material 31 after the nozzle row density correction is performed with the density correction value shown in FIG. .

  Of the three types of density correction values shown in FIG. 12B, the solid line 101 is an inverse function of the density distribution (density unevenness) shown in FIG. 12A, and an input image corresponding to this inverse function. By correcting the signal 41, it is possible to perform density correction processing to a density distribution (density unevenness) as indicated by the solid line 104 shown in FIG.

The density correction process indicated by the solid line 104 is suitable for forming an image such as a photograph on an inkjet-dedicated coated paper because density unevenness hardly occurs.
Also, among the three types of density correction values shown in FIG. 12B, the dotted line 103 is the density correction value when the nozzle row density correction is not performed, and as shown by the dotted line 106 in FIG. The input image signal 41 is formed as it is. The density correction process indicated by the dotted line 106 is suitable when an image is formed on cardboard, cardboard, or the like, which is greatly affected by a decrease in image density during the density correction process.

  Also, among the three types of density correction values shown in FIG. 12B, a dotted line 102 is an intermediate density correction value between the density correction value indicated by the solid line 101 and the density correction value indicated by the dotted line 103. Since a moderate density correction effect can be obtained with a slight decrease in image density during the density correction process, it is suitable for forming an image on plain paper that is not coated exclusively for inkjet.

  The intermediate density correction value is specified as an inverse function of the density distribution obtained by reading the image formed on the image forming material 31 with the image device 42, as indicated by the dotted line 102 in FIG. It can be obtained by multiplying by the coefficient of the size of.

  In the image forming apparatus 30 of the present embodiment, a plurality of density correction values such as a solid line 101, a dotted line 102, and a dotted line 103 in the three types of density correction values shown in FIG.

  The operator selects and sets conditions such as the type of the image data (image signal 41) and the type of the image forming material 31 from the mode setting unit 38 of the image forming apparatus 30 as the selection setting excluding the straight line priority mode. The hue priority (density priority) mode corresponding to the selected content is selected, and it is possible to form an image with appropriate nozzle row density correction.

  As a hue priority (density priority) mode to be selected by the operator, when performing the density correction process, the image quality, that is, the correction amount of the density correction process is selected, or the density of the density of the corrected image is selected. Also good.

The density correction by the image forming apparatus 30 of the present embodiment can be realized not only in the full line type as shown in FIG. 3 but also in a serial type image forming apparatus.
FIG. 13 is a diagram illustrating a configuration example when the image forming apparatus 30 in the present embodiment is configured as a serial type image forming apparatus.

FIG. 13 is a simplified diagram of the configuration of the serial image forming apparatus, which is a serial type image forming apparatus in which the image forming material 31 is not moved in the sub-scanning direction.
In FIG. 13, in addition to the carriage 33A in the moving body 33 in which the color nozzle row units are arranged in parallel at predetermined intervals in the main scanning direction, the carriage 33A is an arrangement form of the color nozzle row units. Different carriages 33B are shown schematically in the two-dot chain line.

  In the serial type image forming apparatus shown in FIG. 13, the carriage 33 </ b> A or 33 </ b> B is supported by a support member 118 so as to be reciprocally movable above the image forming material 31 that is fixedly placed. One end of the support member 118 is provided with a motor in one moving mechanism driving unit 48 for rotating the pulley 115 and a rotary encoder in one moving position information generating unit 49 provided on the rotation shaft of the motor. The moving mechanism 43 is configured. A pulley 116 is disposed at the other end of the support member 118 so as to face the pulley 115 in the main scanning direction. An endless belt 117 is installed between the pulley 115 and the pulley 116 so as to reciprocate in the main scanning direction, and is connected to the carriage 33A or 33B by a connecting portion 117a.

  Thus, the carriage 33A or 33B is reciprocated in the main scanning direction by the rotation of the motor in one moving mechanism driving unit 48, and the carriage 33A or 33B is moved by the rotary encoder in the one moving position information generating unit 49. The position is notified to the control unit 37 of the image forming apparatus 30.

  A pulley 122 is disposed in the vicinity of the other end side of the support member 118. At a position facing this pulley 122 in the sub-scanning direction, a motor in the other moving mechanism driving unit 48 that rotates the pulley 121 and a rotary in the other moving position information generating unit 49 provided on the rotating shaft of this motor are provided. The other moving mechanism 43 is constituted by the encoder. An endless belt 123 is installed between the pulley 121 and the pulley 122 so as to reciprocate in the sub-scanning direction, and is connected to the other end of the support member 118 by a connecting portion 123a.

  As a result, the support member 118 is reciprocated in the sub-scanning direction by the rotation of the motor in the other movement mechanism drive unit 48, and the movement position of the support member 118 is adjusted by the rotary encoder in the other movement position information generation unit 49. This is notified to the control unit 37 of the image forming apparatus 30.

  In the case where the image forming apparatus 30 in the present embodiment is configured as a serial type image forming apparatus, such a configuration makes it possible to move the carriage 33A or 33B in the moving body 33 in the main scanning direction and the sub scanning direction. The carriage 33 </ b> A or 33 </ b> B scans the image forming material 31 along the scanning locus 125 while notifying the control unit 37 of the moving position, thereby forming an image.

FIG. 14 is a diagram illustrating a carriage configuration example when the image forming apparatus according to the present embodiment is configured as a serial type image forming apparatus, and an arrangement example of nozzle row units on the carriage.
Carriage 33A shown in FIG. 14 includes (K) nozzle row unit 51-1, (C) nozzle row unit 51-2, (M) nozzle row unit 51-3 as color-compatible nozzle row units. And (Y) nozzle row units 51-4 are arranged in parallel at predetermined intervals in the main scanning direction. Each color nozzle row unit 51-1 to 51-4 is constituted by the nozzle row of each short recording head 51A-1, 51B-1 to 51A-4, 51B-4.

  FIG. 15 is a diagram illustrating another configuration example of the carriage when the image forming apparatus according to the present embodiment is configured as a serial type image forming apparatus, and an example of arrangement of the nozzle row units on the carriage.

  Carriage 33B shown in FIG. 15 has nozzle row units (K), (C), (M), and (Y) as color-compatible nozzle row units 51-1, 51-2, (51-3, And 51-4 are not shown), each color nozzle row unit is arranged so that the nozzle row is parallel to the sub-scanning direction without a predetermined interval or substantially in the sub-scanning direction. Each color nozzle row unit 51-1 to 51-4 is constituted by the nozzle row of each short recording head 51A-1, 51B-1 to 51A-4, 51B-4.

  As described above, according to the image forming apparatus of this embodiment, in the image forming apparatus in which a plurality of short recording heads are arranged to constitute one long recording head, the short recording heads are arranged by strict position adjustment. Even if it is not provided, an image is also obtained with respect to density unevenness caused by non-conspicuous stripe-like density unevenness or white spots caused by the joint portions of adjacent short recording heads and non-uniformity of the recording density characteristics of the short recording head. It can be corrected at the time of formation.

  Further, according to the image forming apparatus of the present embodiment, since the quantization error generated by the nozzle row overlap portion correction is not diffused to other portions than the nozzle row overlap portion, the density value is large, and the gradient due to the change in the density value is steep. Both density unevenness caused by a certain nozzle row overlapping portion and density unevenness caused by uneven formation characteristics (printing characteristics) due to nozzle rows adjacent to the nozzle row overlapping portion where the density value change is small and gentle. It can be corrected.

In addition, although the nozzle row unit in this embodiment was set as the structure which has 2 rows of nozzle rows which formed the several nozzle, it is good also as a structure which has 3 or more rows of nozzle rows.
Further, the nozzle row unit in the present embodiment is a nozzle row unit equivalent to a configuration having a plurality of nozzle rows, and a short recording head is configured by joining a plurality of recording heads having one to a plurality of nozzle rows. In addition, a plurality of short recording heads may be arranged in one direction to constitute a long recording head.

1 is a diagram illustrating a conceptual configuration example of an image forming apparatus according to an exemplary embodiment. 1 is a diagram illustrating a configuration example of an image forming apparatus according to an embodiment. FIG. 2 is a diagram illustrating a configuration example when the image forming apparatus according to the present embodiment is configured as a full-line image forming apparatus, and an arrangement example of nozzle row units. FIG. 4 is a diagram for explaining a phase difference between ejection nozzle positions between nozzle rows by a recording head. It is the conceptual diagram which showed the formation dot of the duplication part when not performing nozzle row duplication correction | amendment. It is the conceptual diagram which showed the formation dot of the duplication part when nozzle row duplication correction | amendment was performed. FIG. 5 is a conceptual diagram illustrating formed dots that become a joint portion between overlapping nozzle rows of a recording head. FIG. 4 is a conceptual diagram in a case where nozzle row overlap correction is performed across a plurality of ejection nozzles in a nozzle row overlap portion of a recording head. It is a figure which shows the example of an error conversion distribution coefficient. It is a flowchart which shows the process at the time of a density | concentration correction parameter setting. It is a figure explaining the process of density correction parameter determination used for nozzle row duplication correction. It is a figure explaining the density correction method according to an image formation mode. 1 is a diagram illustrating a configuration example when an image forming apparatus according to an exemplary embodiment is configured as a serial type image forming apparatus. FIG. 2 is a diagram illustrating a carriage configuration example when the image forming apparatus according to the present embodiment is configured as a serial type image forming apparatus, and an arrangement example of nozzle row units on the carriage. It is a figure which shows another structural example of the carriage at the time of comprising the image forming apparatus in this embodiment as a serial type image forming apparatus, and the example of arrangement | positioning of the nozzle row unit to a carriage. It is a schematic diagram which shows nozzle row duplication correction of patent document 1. (A) is a recording density characteristic of a single recording head, and (b) is a diagram showing a recording density characteristic when two recording heads are overlapped and connected.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Recording head 11A, 11B Discharge nozzle 12A, 12B Short head 30 Image forming apparatus 31 Image forming material 32 Mounting base 33, 33A, 33B Moving body 34-1 to 34-m, 36-1 to 36-m Recording unit 35 Carriage 37 Control unit 38 Mode setting unit 41 Input image signal 42 Image equipment 43 Movement mechanism 44 Plane memory 45 Timing generation unit 46 Density characteristic correction control unit 47 Overlap correction control unit 48 Movement mechanism drive unit 49 Movement position information generation unit 50-1 -50-m Nozzle row drive circuit 51-1 to 51-m Nozzle row unit 62 Edge sensor 63a, 63b Roller

Claims (11)

Image formation in which a plurality of short recording heads each having a nozzle array of ejection nozzles arranged in one direction are arranged in an overlapping manner to form an image by ejecting ink from the ejection nozzles based on image signal values A duplication that controls the driving of the ejection nozzles according to a phase difference due to the position of the ejection nozzles between the overlapping short recording heads as a density correction of an image formed by overlapping portions of the recording heads. A correction control unit;
Independently of the overlap correction control unit, a density characteristic correction control unit that controls driving of the discharge nozzles according to a recording density characteristic of a nozzle row by the discharge nozzles;
An image formability apparatus comprising:   The image forming apparatus according to claim 1, wherein the overlap correction control unit and the density characteristic correction control unit are configured as independent hardware. The overlap correction control unit
Based on the first correction parameter set according to the phase difference depending on the position of the discharge nozzle between the overlapping short recording heads and the image signal value corresponding to at least one discharge nozzle in the overlapping portion. Calculate the density correction signal of the overlapping part,
The density correction signal of the overlapped portion is quantized to a value corresponding to the short recording head,
The density characteristic correction control unit
Each density correction signal based on the second correction parameter set according to the recording density characteristic of the discharge nozzle in the short recording head and each density value of the image signal value corresponding to each discharge nozzle of the short recording head. To calculate
Each density correction signal is quantized to a value corresponding to the short recording head,
The image forming apparatus according to claim 1, wherein the duplication correction control unit does not add a quantization error due to the quantization to the calculation of each density correction signal by the density characteristic correction control unit.   4. The value of the first correction parameter is determined and set in the overlap correction control unit, and then the value of the second correction parameter is determined and set in the density characteristic correction control unit. The image forming apparatus described in 1.   The first test image used when determining and setting the value of the first correction parameter is formed by stopping correction by the overlap correction control unit and the density characteristic correction control unit, respectively, The second test image used when determining and setting a parameter value is formed by performing correction by the overlap correction control unit and stopping correction by the density characteristic correction control unit. Item 4. The image forming apparatus according to Item 3.   The apparatus further includes a mode setting unit in which an operator inputs an instruction to execute / stop correction by each of the overlap correction control unit and the density characteristic correction control unit, and the overlap correction control unit and the density characteristic correction control unit include the mode setting. The image forming apparatus according to claim 1, wherein the correction processing based on the image signal value is executed / stopped based on an input from a unit.   The image forming apparatus according to claim 6, wherein the density characteristic correction control unit corrects the image signal value based on an image forming mode input and set by the operator from the mode setting unit.   The image forming apparatus according to claim 7, wherein the image forming mode corresponds to a type of an image forming material on which image forming is performed.   The image forming apparatus according to claim 7, wherein the image forming mode includes a linear priority mode that emphasizes linearity of a formed image and a hue priority mode that emphasizes density unevenness of the formed image.   The image forming apparatus according to claim 1, wherein when performing the image formation, the image signal value is corrected by the density characteristic correction control unit, and then corrected by the overlap correction control unit. Image formation in which a plurality of short recording heads each having a nozzle array of ejection nozzles arranged in one direction are arranged in an overlapping manner to form an image by ejecting ink from the ejection nozzles based on image signal values An image forming method for an apparatus, comprising:
As the density correction of the image formed by the overlapping portion of the recording head, the driving of the discharge nozzle is controlled according to the phase difference due to the position of the discharge nozzle between the overlapping short recording heads,
Independently of the overlap correction control unit, the drive of the discharge nozzle is controlled according to the recording density characteristic of the nozzle row by the discharge nozzle.
An image forming method.