JP2021146540A - Image formation apparatus - Google Patents

Abstract

To provide an image formation apparatus which can suppress the deterioration of image quality.SOLUTION: An image formation apparatus comprises: a plurality of ink jet heads which are arranged so as to have the inter-head overlap in which nozzles discharging ink are overlapped in the conveyance direction of a recording medium, ink is complementarily discharged and an image is formed; and a setting unit which sets the inter-pass overlap in which ink is complementarily discharged at an end in the conveyance direction of an image formation region where the image is formed in one pass and the image is formed. When the inter-pass overlap overlaps with the inter-head overlap, the setting unit sets the number of ink jet heads complementarily discharging ink in the overlapping portion to be less than the head number related to the image formation in the inter-pass overlap and the inter-head overlap.SELECTED DRAWING: Figure 8

Description

The present invention relates to an image forming apparatus.

Conventionally, there is known an image forming apparatus including a plurality of inkjet heads in which nozzles for ejecting ink are arranged so as to have head-to-head overlap in which the nozzles for ejecting ink overlap in the transport direction of the recording medium (see, for example, Patent Document 1). ).

Further, there is known a hybrid type image forming apparatus in which a screen image forming unit and an inkjet image forming unit using a plurality of inkjet heads as described above are used in combination. In such an image forming apparatus, the conveying pitch of the recording medium in the conveying section for conveying the recording medium is set in advance so as to have a conveying length equivalent to the image forming range by the screen image forming section.

This is because the inkjet image forming unit can change the size of the image formed by one printing operation, that is, it can be adjusted to the image forming range by the screen image forming unit, whereas the screen image forming unit usually has the same. This is because the image formation range is fixed.

Further, in the hybrid type image forming apparatus, the screen plate in the screen image forming unit is different for each customer, for example, and can be replaced with a screen plate having a different transport direction size for each customer. In this case, the transfer pitch of the recording medium in the transfer unit needs to be reset for each customer, that is, the print job.

In an image forming apparatus having such a configuration, for example, when a seamless image is formed on a long recording medium by an inkjet image forming portion, a superimposing region between image ends in the transport direction, that is, a region of overlap between passes is formed. Provided.

Japanese Unexamined Patent Publication No. 2014-141079

By the way, in the hybrid type image forming apparatus as described above, the image printed on the screen by the screen image forming unit is always good, whereas the image printed by the inkjet image forming unit is overlapped between passes. When the overlap between the heads overlaps, the image quality may deteriorate.

An object of the present invention is to provide an image forming apparatus capable of suppressing deterioration of image quality.

The image forming apparatus according to the present invention is
A plurality of inkjet heads arranged so that the nozzles for ejecting ink overlap in the transport direction of the recording medium and the inks are complementarily ejected to form an image.
A setting unit for setting an overlap between passes in which the ink is complementarily ejected at an end portion of an image forming region in which an image is formed by the plurality of inkjet heads in one pass in the transport direction to form an image. , With
When the overlap between passes overlaps with the overlap between heads, the setting unit sets the number of inkjet heads that complementarily eject the ink at the overlapping portion with respect to the overlap between passes and the overlap between heads. The number of heads related to image formation is set to be less than the number of heads.

According to the present invention, deterioration of image quality can be suppressed.

It is a side view which shows the schematic structure of the image forming apparatus which concerns on embodiment of this invention. It is a top view which shows the schematic structure of the screen image forming part and the inkjet image forming part. It is a block diagram which shows the main functional composition of an image forming apparatus. FIG. 4A is a plan view showing a case where the transport direction widths of the image forming ranges in the screen image forming section and the inkjet image forming section are the same, and FIG. 4B shows a case where the transport direction widths are different. It is a figure explaining the problem at the time of printing a solid image by a 9-head type inkjet image forming part, FIG. Show the case. 6A, 6B, and 6C are diagrams illustrating a case where interference between the path-to-pass overlap and the head-to-head overlap does not occur in the configuration of three heads. 7A, 7B, and 7C are diagrams illustrating a case where interference between the path-to-pass overlap portion and the head-to-head overlap portion occurs in the configuration of three heads. 8A, 8B, and 8C are diagrams illustrating a specific example of the characteristic processing in the present embodiment. 9A, 9B, and 9C are diagrams illustrating other specific examples of the characteristic processing in the present embodiment. It is a flowchart explaining the characteristic process in this Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention.

The image forming apparatus 1 shown in FIG. 1 is a hybrid type image forming apparatus in which screen printing and inkjet printing are used in combination. The image forming apparatus 1 includes a belt conveying section 2, a supply section 3, a screen image forming section 4 for performing screen printing, an inkjet image forming section 5 for performing inkjet printing, a discharging section 6, and the like.

The belt transport unit 2 includes a drive roller 21 and a driven roller 22 arranged in parallel at a predetermined interval, an endless transport belt 23 having a predetermined width spanned by the rollers 21 and 22, and a drive roller 21. A sub-scanning motor (not shown) for driving the motor. The upper surface of the conveyor belt 23 in the belt conveyor 2 is a mounting surface on which the recording medium P is placed in close contact with the belt 23.

In the belt transport unit 2, the drive roller 21 is bridged with the driven roller 22 by rotating at a predetermined speed in the clockwise direction (see arrow A) in FIG. 1 by the rotational drive of the sub-scanning motor. The conveyor belt 23 is rotated and moved. By such an operation, the recording medium P mounted on the upper surface of the transport belt 23 is conveyed in the direction of the arrow A in the drawing, which is the sub-scanning direction.

A gluing device 24 and a cleaning device 25 are provided on the lower surface side of the transport belt 23. The gluing device 24 is arranged on the upstream side of the supply unit 3 in the rotation direction of the transport belt 23 (direction of arrow A), and provides a grounding for bringing the lower surface of the recording medium P into close contact with the upper surface of the transport belt 23. Apply a so-called adhesive.

The cleaning device 25 is arranged on the upstream side of the gluing device 24 in the rotation direction of the transport belt 23. The cleaning device 25 cleans the adhesive material left on the transport belt 23 after the recording medium P has been peeled off by the discharge unit 6. The adhesive material is applied again to the transport belt 23 cleaned by the cleaning device 25 by the gluing device 24.

The supply unit 3 supplies the recording medium P to the belt transport unit 2. The supply unit 3 is provided on the upstream end side of the upper surface of the transfer belt 23 in the transfer direction of the recording medium P, and has a feeding device 31, a guide roller 32, and a pressing roller 33. The transport direction of the recording medium P is a direction from left to right in FIG. 1, and is simply referred to as a “transport direction” in the following description.

The feeding device 31 is a device for feeding the recording medium P wound in a roll shape. The recording medium P is a long recording medium usually used for image formation by inkjet, such as paper, cloth, and plastic film. The recording medium P may be in the form of a sheet cut to a predetermined size.

The guide rollers 32 are a plurality of transfer rollers provided in the transfer path of the recording medium P, and guide the recording medium P toward the belt transfer unit 2 while keeping the tension of the recording medium P constant.

The pressing roller 33 presses the recording medium P guided by the guide roller 32 against the transport belt 23, and brings the recording medium P into close contact with the transport belt 23 via the adhesive material.

The screen image forming unit 4 is provided on the downstream side of the supply unit 3 in the transport direction. The screen image forming unit 4 has a screen plate 41 for forming a screen image (first image) such as a background on the recording medium P. The screen image forming unit 4 forms the first image on the recording medium P which is conveyed in the conveying direction by the screen plate 41.

An ink corresponding to the first image is applied to the screen plate 41, and the ink is applied to the recording medium P through the pores provided in the screen plate 41 by driving a squeegee (not shown).

For the sake of simplicity, the case where there is only one screen plate 41 is illustrated in FIG. 2, but in reality, as shown by the dotted line in FIG. 1, the screen plates 41 are arranged side by side at equal intervals in the transport direction. Is possible.

The first image includes, for example, a monochromatic background image. Therefore, each screen plate 41 has inks of different colors, and the screen plate 41 to be used is appropriately selected according to the background image formed on the recording medium P.

The inkjet image forming unit 5 is provided on the downstream side of the screen image forming unit 4 in the transport direction. The inkjet image forming unit 5 has a plurality of carriages 50 arranged in the transport direction. In the present embodiment, as shown in FIG. 2, the three carriages 50 are arranged so as to be arranged in the width direction (scanning direction) orthogonal to the transport direction (the direction of the white arrow in FIG. 2) of the recording medium P. ing.

Each of the plurality of carriages 50 has three inkjet heads 51 that eject ink of any color Y, M, or C. Each inkjet head 51 is provided with a large number of ink ejection holes on the bottom surface (not shown) facing the recording medium P.

In the present embodiment, these three carriages 50 (Y, M, C) are integrally moved (scanned) in the scanning direction (left-right direction in FIG. 2) at the time of image formation, so that the color used for image formation is changed. By ejecting ink to the recording medium P from the ink ejection holes of the inkjet head 51, a multicolor image is formed on the recording medium P. That is, the inkjet image forming unit 5 prints a color image by a scanning method.

As shown in FIG. 2, each inkjet head 51 in the carriage 50 (Y, M, C) has a scanning direction parallel to the transport direction (see the white arrow in FIG. 2) and orthogonal to the transport direction. Lined up in.

More specifically, the three inkjet heads 51 in one carriage 50 are provided with overlapping portions called "head-to-head overlaps" in which some of the above-mentioned large number of ink ejection holes overlap each other. , Arranged in a staggered pattern. The details of the head-to-head overlap will be described later in FIG. 5A and the like.

The inkjet image forming unit 5 superimposes each image of C, M, or Y based on ink (ink dots) ejected from the inkjet head 51 in each carriage 50 on the recording medium P to obtain one inkjet image. (Hereinafter, also referred to as "second image") is formed.

In the present embodiment, the plurality of carriages 50 (C, M, Y) are integrally reciprocated in the main scanning direction orthogonal to the transport direction by a guide rail or a drive mechanism (not shown). At the time of forming such an image (during ink ejection), the drive of the drive roller 21 is controlled so that the transfer belt 23 can be in a stopped standby state and a drive state in which the transfer belt 23 is driven with a predetermined transfer length. Performs repetitive intermittent operations.

When the transport belt 23 is in the standby state, the inkjet image forming unit 5 ejects ink from a large number of ink ejection holes (hereinafter referred to as “nozzles”) arranged on the bottom surface of the inkjet head 51 while ejecting ink from the carriage 50 (C, M, Y) is moved in the main scanning direction. By such an operation, the second image is sequentially formed on the recording medium P on the stopped transport belt 23.

The first image mainly includes a motif pattern, a fine image of about 100 μm, a color mixing gradation, a color image having several kinds of colors such as tens of thousands of colors, and the like.

According to the image forming apparatus 1 having the above-described configuration, the first image and the second image are printed in an overlapping manner by performing the following operations under the control of the control unit 100 described later in FIG. Will be done.

That is, the screen image forming unit 4 (screen plate 41) forms a first image such as a background on the recording medium P, and then the recording medium P is intermittently conveyed on the transfer belt 23 to obtain the first image. The image moves directly below the inkjet image forming unit 5, and the transport of the recording medium P is stopped.

From this state, the inkjet image forming unit 5 (each inkjet head 51) forms a second image on the first image, so that, for example, color images such as various patterns are superimposed on the background image. As a result, a final image (hereinafter referred to as "completed image") is formed.

Further, when the completed image is continuously formed in the transport direction of the recording medium P, the control unit 100 (see FIG. 3) controls the intermittent transport and printing (superimposition) of the recording medium P as described above. Repeat the operation of. At this time, the inkjet image forming unit 5 repeatedly executes the following operations.

That is, the inkjet image forming unit 5 captures the image portion on the tip side of the second image based on the ink ejected from the plurality of inkjet heads 51 in the conveying direction of the second image formed at the time of the immediately preceding scan (image forming). Printing is performed so as to provide an overlapping image portion that overlaps with the image portion on the rear end side in the transport direction.

Such overlapping image portions are generally referred to as "pass-to-pass overlap". In this inter-pass overlap, "ink is complementaryly ejected at the end (image end) in the transport direction of the image forming region where the image is formed in one pass (one scan in this example). It can be defined as "a part or region where an image is formed", and the details thereof will be described later.

Generally, when the entire image is formed by a plurality of passes, the inkjet image forming unit 5 is controlled so as to eject ink complementarily from the plurality of inkjet heads 51 in the region of overlap between the passes, so that the second ink jet image forming unit 5 is controlled. Images can be seamlessly formed in the transport direction of the recording medium P.

The discharge unit 6 discharges the portion of the recording medium P on which the completed image is formed. The discharge unit 6 is provided on the downstream side of the screen image forming unit 4 in the transport direction, and has a peeling device, a drying device, a shake-off device, and the like (not shown).

The peeling device is a device that peels the recording medium P from the transport belt 23. The drying device is a device provided on the downstream side of the peeling device and removes the moisture of the image formed on the recording medium P peeled from the transport belt 23 by the peeling device.

The shake-off device is provided on the downstream side of the drying device, and shakes the recording medium P to the accommodating device (for example, a trolley).

FIG. 3 is a block diagram showing a main functional configuration of the image forming apparatus 1. The image forming apparatus 1 includes a control unit 100, a first image driving unit 110, a second image driving unit 120, a transport driving unit 130, an input / output interface 140, and the like.

The control unit 100 includes a CPU 101 (Central Processing Unit), a RAM 102 (Random Access Memory), a ROM 103 (Read Only Memory), and a storage unit 104. The control unit 100 controls the entire image forming apparatus 1.

Further, in the present embodiment, the control unit 100 has functions as a "setting unit" and a "determining unit" of the present invention.

The CPU 101 reads out various control programs and setting data stored in the ROM 103, stores them in the RAM 102, executes the programs, and performs various arithmetic processes. Further, the CPU 101 comprehensively controls the overall operation of the image forming apparatus 1.

The RAM 102 provides the CPU 101 with a working memory space and stores temporary data. The RAM 102 may include a non-volatile memory.

The ROM 103 stores various control programs, setting data, and the like executed by the CPU 101. Instead of the ROM 103, a rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used.

The storage unit 104 stores a print job (image recording command) input from the external device 8 via the input / output interface 140 and image data related to the print job. As the storage unit 104, for example, an HDD (Hard Disk Drive) may be used, or a DRAM (Dynamic Random Access Memory) or the like may be used in combination.

The first image driving unit 110 supplies a driving signal according to the image data to the inkjet image forming unit 5 at a predetermined timing based on the control of the control unit 100, so that the carriage 50 of the inkjet image forming unit 5 An amount of ink corresponding to the pixel value of the image data is ejected from the nozzle.

The second image driving unit 120 records ink based on the screen plate 41 of the screen image forming unit 4 by supplying a driving signal to the screen image forming unit 4 at a predetermined timing based on the control of the control unit 100. It is applied to the medium P.

The transport drive unit 130 intermittently feeds the transport belt 23 at a predetermined speed and timing (that is, “convey pitch”) by supplying a drive signal to the sub-scanning motor of the drive roller 21 under the control of the control unit 100. Rotate and move.

The input / output interface 140 mediates the transmission and reception of data between the external device 8 and the control unit 100. The input / output interface 140 is composed of, for example, any of various serial interfaces, various parallel interfaces, or a combination thereof.

The external device 8 is, for example, a personal computer, and supplies an image recording command (print job), image data, and the like to the control unit 100 via the input / output interface 140.

By the way, in the image forming apparatus 1 having the above-described configuration, generally, the number of drawing lines in the conveying direction of the second image formed by the inkjet image forming section 5 is the conveying of the screen plate 41 of the screen image forming section 4. It was decided (set) to match the image size in the direction.

On the other hand, in the case where the inkjet heads 51 of the inkjet image forming unit 5 are arranged by providing the overlap region between the heads as described above, the second image is seamlessly formed in the transport direction depending on the set number of drawing lines. At that time, image defects may occur. Hereinafter, the background and problems in which this problem occurs will be described in detail with reference to FIGS. 4A and 4B.

Here, FIG. 4A shows a case where the screen image forming unit 4 and the inkjet image forming unit 5 have the same length in the transport direction of the image forming range (hereinafter, also simply referred to as “image size” for the sake of simplicity). It is a plan view. Further, FIG. 4B is a plan view showing an example in which the image size of the screen image forming unit 4 and the image size of the inkjet image forming unit 5 are different.

In FIG. 4A, the image size of the first image formed by the screen image forming unit 4 is indicated by the double-headed arrow 4W, and the image size of the second image formed by the inkjet image forming unit 5 is indicated by the double-headed arrow 5W. That is, in the example shown in FIG. 4A, the image size of the first image is 4W = the image size of the second image is 5W.

On the other hand, as described above, in the hybrid type image forming apparatus 1 as in the present embodiment, the screen plate 41 in the screen image forming unit 4 is different for each customer, for example, so that the size in the transport direction is different for each customer. Can be replaced with a different screen version 41.

Here, in FIG. 4B, the inkjet image forming unit 5 is the same as the example shown in FIG. 4A, and the screen plate 41 of the screen image forming unit 4 has a length (4 Ws) in the transport direction more than the example shown in FIG. 4A. A short case (4W> 4Ws) is shown.

In such a case, in the image forming apparatus 1, it is necessary to set the transport pitch of the recording medium P in the belt transport unit 2 so as to have a transport length equivalent to the image size of the screen plate 41 (4 Ws in the example of FIG. 4B). There is.

In addition, in the image forming apparatus 1, as shown in FIG. 4B, the image size of the second image that can be printed by one scan in the inkjet image forming unit 5 is set to a length of 5 Ws (5 Ws) shorter than the above 5 W. = 4Ws) needs to be set (changed).

Thus, the number of drawing lines in the transport direction of the second image formed by the inkjet image forming unit 5 is set to match the image size (4W, 4Ws, etc.) in the transport direction of the screen plate 41 of the screen image forming unit 4. NS.

However, when the setting of the number of drawing lines of the image size of the second image formed by the inkjet image forming unit 5 as described above is changed, the print job that seamlessly forms the second image in the transport direction in a plurality of passes At the time of execution, image defects may occur.

Hereinafter, problems in the prior art will be described in detail with reference to FIGS. 5A and 5B corresponding to FIGS. 4A and 4B.

Here, FIGS. 5A and 5B show a configuration in which one carriage 50 (for example, a carriage for M ink) of the inkjet image forming unit 5 has nine inkjet heads arranged in a staggered pattern on the recording medium P. It is a top view explaining the example of forming a solid image of M color.

In FIGS. 5A and 5B, a solid image formed on the recording medium P by M ink ejected from nine inkjet heads (heads 1 to 9, hereinafter collectively abbreviated as "head"). Is shown on the left side. Further, the length (printing width) of the solid image in the transport direction is indicated by a double-headed arrow as the "solid image size".

Further, the No. 1 head to the No. 9 head are arranged so as to have an overlap between the heads. In FIGS. 5A and 5B, the area of head-to-head overlap between the 8th head and the 9th head (that is, the overlapping portion between the nozzles) is shown by a dotted line frame.

In this way, the portion where the nozzles between the two heads overlap in the transport direction (sub-scanning direction) and the ink is ejected in a superimposed manner on the recording medium P is called "head-to-head overlap".

The head-to-head overlap portion has a fixed length, and the positions (nozzle numbers) of overlapping nozzles are known in advance. Therefore, in the overlapping nozzle regions, ink is complementarily ejected based on, for example, a predetermined mask treatment.

In one specific example, the "solid image size" shown in FIG. 5A is 8704 lines, and the "solid image size" shown in FIG. 5B after changing the setting of the number of drawing lines is 7840 lines (that is, shortened). ..

Further, when the solid image is seamlessly formed in the transport direction, for example, an image constituting a fixed length (in this example, 256 lines in total) overlap between paths is ejected by a predetermined mask process. , The ink ejection mode is set for the heads on both ends of the image size (heads 1 and 9 in the example shown in FIG. 5A).

More specifically, in the example shown in FIG. 5A, 128 (= 256/2) lines of ink are misted from the nozzle on the lower side of the 9th head under the control of the control unit 100 during the first scanning of the print job. It is discharged in a shape. Then, during the second and subsequent scans, 128 (= 256/2) lines of ink are ejected in the form of mist from the nozzle on the upper side of the No. 1 head, and 128 (=) from the nozzle on the lower side of the No. 9 head. 256/2) Lines of ink are ejected in the form of mist.

In the following, an image based on mask processing (a mist-like image in the above example) constituting the inter-pass overlap is also referred to as an "inter-pass mask image". Further, an image based on the above-mentioned mask processing that constitutes the head-to-head overlap is also referred to as a “head-to-head mask image”.

Then, under the control of the control unit 100, the recording medium P is conveyed at a transfer pitch such that the mist-like inter-pass mask images (downstream side and upstream side ends) of the 128 lines are overlapped with each other. As a result, a seamless solid image is formed.

At the time of the first scanning of the print job, the inter-pass mask image is not formed in the image portion on one end side (upper side in the example of FIG. 5A) of the solid image, and the corresponding head (the first head in the example of FIG. 5A) Ink is ejected from a predetermined nozzle at a printing rate of 100%. This "predetermined nozzle" is the nozzle at the "writing position FS" shown in FIG. 5A.

Thus, in the example shown in FIG. 5A, the mist-like image (inter-pass mask image) constituting the overlap between the paths at both ends in the transport direction (vertical direction in the figure) of the solid image is the first head and the maximum. It can be seen that it was formed by being discharged from the 9th head having a number.

On the other hand, in the example shown in FIG. 5B, one end side (rear end side) of the solid image in the transport direction, that is, the lower mist-like image in the solid rectangular frame in FIG. 5B is the 8th head and the 9th head. It is located in the area of head-to-head overlap. Therefore, the inter-pass mask image (mist-like image) is formed by being ejected from both the 8th head and the 9th head.

However, when the region of the head-to-head overlap is located at the rear end of the image, in other words, at the rear end of the transport pitch of the recording medium P, so-called "interference between the head-to-head overlap and the pass-to-pass overlap" occurs. do.

Then, it was found that the image in this interference portion is easily visually recognized as a component of a defective image such as "streak", "unevenness", or "dirt" by human vision.

Hereinafter, this problem will be described with reference to FIGS. 6 (6A to 6C) and 7 (7A to 7C), which are shown again in a three-head configuration for easy understanding.

(When there is no interference between the path-to-pass overlap and the head-to-head overlap)
First, a case where interference between the path-to-pass overlap and the head-to-head overlap does not occur will be described with reference to FIGS. 6A to 6C. Here, FIG. 6 (FIGS. 6A to 6C) is a diagram corresponding to FIGS. 4A and 5A described above, and illustrates a case where interference between the path-to-pass overlap and the head-to-head overlap does not occur.

In FIGS. 6A to 6C, the head numbers of the three inkjet heads 51 arranged so as to have head-to-head overlap are indicated by reference numerals H1, H2, and H3.

Further, in FIGS. 6A to 6C, the portion on the rear end side (region of overlap between passes) of the image formed during the previous ink ejection operation, here, during scanning in the first pass, is indicated by the reference numeral “OL (P1)”. It is shown by the dotted line frame. Further, the next ink ejection operation, here, the portion on the front end side (area of overlap between passes) of the image formed during scanning in the second pass is indicated by a dotted line frame of the symbol "OL (P2)".

Further, in FIGS. 6A to 6C, for example, the start position of the inter-pass overlap (the above-mentioned inter-pass mask image) during scanning in the first pass and the second pass is indicated by the reference numeral "Ls", and the inter-pass overlap is indicated by the reference numeral "Ls". The end position is indicated by the symbol "Le".

In addition, in order to facilitate the distinction, the term "overlap" of the overlap between passes is abbreviated as "OL" as appropriate.

First, when the print size in the transport direction is, for example, the maximum length at which an image can be formed, the area of the inter-pass OL (the portion on the recording medium P on which the inter-pass mask image is formed) is the area of head-to-head overlap (head). The portion on the recording medium P on which the inter-mask image is formed) does not overlap (see, as appropriate, both ends of the double-headed arrow 4W in FIGS. 5A and 6A). Therefore, interference between the path-to-pass OL and the head-to-head overlap does not occur.

The case where such interference does not occur will be described in more detail with reference to FIGS. 6B and 6C. Here, FIG. 6B shows the nozzle on the upper side of the head with the head number H1 shown in FIG. 6A (hereinafter, also simply referred to as “head H1”) and the head of the head H3 (hereinafter, also referred to as “head H3”). It is a characteristic graph which shows an example of the printing rate (%) for each nozzle of the ink ejected from the lower nozzle.

In the graph shown in FIG. 6B, the printing rate is shown on the vertical axis, and the position of each nozzle along the conveying direction, in other words, the position of the recording medium P in the conveying direction is shown on the horizontal axis.

Further, FIG. 6C is a diagram for explaining the ratio (breakdown of the printing rate) of the ink ejected from the heads H1 and H3 among the inks printed in the area of the inter-pass OL (P1, P2). In general, FIG. 6C corresponds to a figure in which the portion (figure) of "H1" shown in FIG. 6B is turned upside down and then the entire figure in the graph is rotated 90 degrees clockwise.

The significance of each of the above-mentioned symbols and figures is the same for the figures after FIGS. 7 (7A to 7C) described later.

When there is no head-to-head overlap in the inter-pass OL (P1, P2), as shown in FIGS. 6B and 6C, from the start position Ls to the end position Le of the inter-pass OL (P1, P2). It can be seen that the ink is ejected complementarily from the two heads of the head H3 and the head H1. Normally, in such an ink ejection mode, the noise component of the image as described above does not occur.

(When interference between path-to-pass OL and head-to-head overlap occurs)
Next, a case where interference between the path-to-pass OL and the head-to-head overlap occurs will be described with reference to FIGS. 7A to 7C.

7 (7A to 7C) are views corresponding to FIGS. 4B and 5B described above, and show an example in which a noise image is likely to occur due to interference between the path-to-pass OL and the head-to-head overlap portion. More specifically, in the illustrated example, when ink is complementarily ejected from both the heads of the heads H2 and H3 from the start position Ls on the rear end side of the inter-pass OL (P1) in the transport direction to the end position Le. Is shown.

In other words, the nozzles that overlap in the transport direction in the heads H2 and H3 perform a ejection operation that forms both the inter-head mask image and the inter-pass mask image.

As described above, when the region of the head-to-head overlap exists in the inter-pass OL (P1, P2) at the maximum size, as shown in FIGS. 7B and 7C, the inter-pass overlap OL (P1, P2) From the start position Ls to the end position Le, ink is ejected complementarily from the three heads H2, H3, and H1.

From another point of view, as shown in FIGS. 7B and 7C, at the start position Ls on the rear end side of the inter-pass OL (P1) in the transport direction in the first pass, the ink ratio of the head-to-head overlap, that is, the head H2 and The proportion of ink that is complementarily ejected by the two heads of H3 is approximately 100%.

On the other hand, at the end position Le on the tip side of the inter-pass OL (P2) in the transport direction in the next second pass, the ink ratio occupied by the head-to-head overlap (the ratio of ink ejected from the two heads H2 and H3). ) Drops to almost 0%.

Thus, the present inventors have found that a short and dark streak-like noise image is easily visible on the portion on the recording medium P in which the ink is complementarily ejected from the three heads.

In view of the above problems, in the present embodiment, it is used in the overlapping region of the path-to-pass OL and the head-to-head overlap based on the positional relationship between the path-to-pass OL and the head-to-head overlap in the transport direction. In order to reduce the number of heads, the ink ejection mode, that is, the setting of the number of nozzles responsible for complementary ink ejection is changed.

In other words, in the present embodiment, when the inter-pass OL overlaps with the head-to-head overlap, the control unit 100 sets the number of inkjet heads that complementarily eject ink at the overlapping portion between the pass-to-pass OL and the head-to-head overlap. The number of heads related to image formation in the lap is set to be less than 3 (less than 3 or less, that is, 2 or less).

Further, in the present embodiment, the control unit 100 determines whether or not the area of head-to-head overlap and the area of inter-pass OL overlap (overlap), in other words, "there is an area where three heads are used. Whether or not "is determined.

Then, when the control unit 100 determines that they overlap (there is an area where the number of used heads is three), the control unit 100 reduces the number of heads used in the overlapping portion (the area where the number of used heads is three) by one (that is, two). The setting process for changing the ink ejection mode in the head-to-head overlap region is performed.

In one specific example, when the control unit 100 determines that they overlap (there is an area where three heads are used), the control unit 100 does not form an inter-head mask image in the area, but forms only an inter-pass mask image. In addition, the ink ejection mode of the nozzle in the region is set.

Such characteristic processing will be described in more detail with reference to FIGS. 8A to 8C and the like.

Here, FIGS. 8A to 8C are views corresponding to the above-mentioned FIGS. 7A to 7C, and FIG. 8A is the same as FIG. 7A.

That is, in FIG. 8A, it is assumed that the region of OL between passes (length in the transport direction) is equal to the region of overlap between heads (same length), and the rear end side in the first pass (during scanning). The case where the region of the OL between the paths coincides with the region of the overlap between the heads of the heads H2 and H3 is illustrated.

In this case, the control unit 100 determines that the OL between the paths and the overlap between the heads overlap (there is an area where the number of heads used is three), reduces the number of heads used in the overlapping portion to two, and reduces the number of heads used between the heads. It is set so that a mask image is not formed, specifically, ink is not ejected from the head H3.

By making such a setting, when the print job is executed, the nozzle of the head H2 in the region overlapping with the head H3 ejects ink so as to form only the inter-pass mask image. According to such an ink ejection operation, as shown in FIGS. 8B and 8C, from the start position Ls to the end position Le of the inter-pass overlap OL (P1, P2), the two heads H2 and H1 complement each other. Ink is ejected.

That is, as can be seen by comparing FIGS. 7B and 8B, conventionally, from the start position Ls on the rear end side of the inter-pass OL (P1) in the transport direction to the end position Le in the first pass, the heads H2 and H3 Ink was ejected complementarily by the two heads (see FIG. 7B).

On the other hand, according to the present embodiment, only the head H2 (one head) is used from the start position Ls to the end position Le on the rear end side of the inter-pass OL (P1) in the transport direction in the first pass. An inter-pass mask image (eg, the mist-like image described above in FIG. 5) is formed (see FIG. 8B).

As described above, in the present embodiment, when the path-to-pass OL and the head-to-head overlap overlap, the path does not perform the image formation process (formation of the head-to-head mask image) of the head-to-head overlap in the overlapping portion. It is set to perform only the image formation process of the inter-OL (formation of the inter-pass mask image).

According to the present embodiment in which the setting process as described above is performed, the number of heads used in the inter-pass OL can always be two, so that the seam portion of the image between the two paths (scanning) is described above. It is possible to effectively prevent the occurrence of quality deterioration such as streaks and uneven density.

In order to facilitate understanding, in FIGS. 8A to 8C, as a relatively simple example, a case where the path-to-pass OL and the head-to-head overlap completely overlap (match) has been described. On the other hand, in the actual operation of the device, there may be a case where the OL between paths and the overlap between heads do not completely overlap, and these partially overlap (partially overlap).

Hereinafter, processing when the area of the head-to-head overlap overlaps a part of the area of the path-to-pass OL will be described with reference to FIGS. 9A to 9C.

In FIG. 9A, it is assumed that the area of OL between paths (length in the transport direction) is equal to the area of overlap between heads (same length), and the rear end side (convey direction) in the first pass (during scanning). The case where a part of the region of the head-to-head overlap of the heads H2 and H3 overlaps with a part of the region of the inter-pass OL (on the upstream side in the above) is illustrated.

In this case, the control unit 100 determines that the OL between passes and the overlap between heads overlap (there is an area where the number of heads used is three), and reduces the number of heads used in the overlapping portion to two (head H3). Ink is not ejected from).

Further, the control unit 100 ejects ink from the head H3 to form a part of the inter-pass mask image for the rear end side (upstream end) of the inter-pass OL in the first pass (during scanning). Set to.

By making such a setting, as shown in FIGS. 9B and 9C, from the start position Ls to the end position Le of the inter-pass OL (P1, P2), the two heads of the heads H2 and H1, or the heads H3 and H1 Ink is ejected complementarily from the two heads of H1.

In addition, the control unit 100 forms a mask image between heads in the area of the overlap between the heads of the heads H2 and H3 (inside the “normal printing unit” in FIG. 9A) other than the above-mentioned overlapping portion, as in the conventional case. That is, the ink is ejected complementarily by the heads H2 and H3.

Alternatively, the control unit 100 does not form a mask image between the heads in the area of the overlap between the heads of the heads H2 and H3 (inside the “normal printing unit” in FIG. 9A) other than the overlapped portion described above, and the heads H2 and H3 Ink may be ejected from only one of H3 (for example, head H2).

In the examples shown in FIGS. 8 and 9, as the initial state or the default setting, the case where the image size (length in the transport direction) of the OL between passes is equal to the image size (length in the transport direction) of the overlap between the heads. It was assumed.

With such a configuration, it is possible to simplify the control when the area of the OL between the paths and the area of the overlap between the heads do not overlap (do not interfere with each other). Specifically, the control when printing the inter-pass mask image complementarily formed by the two heads in the inter-pass OL region is complementarily formed by the two heads in the inter-head overlap region. Since the control may be the same as the control when printing the mask image between heads, the control is simplified.

On the other hand, as another configuration example, in the initial state, the area of the OL between paths (length in the transport direction) and the area of overlap between heads (same length) may be different. In this case as well, the path may be different. The space OL and the head-to-head overlap do not completely overlap, but partially overlap.

Even in such a case, the control unit 100 may perform a setting process for reducing the number of heads forming the inter-pass mask image by the same method as the case described with reference to FIGS. 9A to 9C.

More specifically, when the control unit 100 determines that the area of the head-to-head overlap overlaps with the area of the inter-pass OL, the control unit 100 specifies the position of the overlapping portion in the inter-pass OL and sets according to the specific result. Execute the process. At this time, the control unit 100 is set to reduce the number of heads forming the inter-pass mask image at the positions of the specified overlapping portions.

By performing the head-to-head overlap and inter-pass OL setting processing as described above, the inter-pass OL region (image portions in which ink is ejected complementarily between the preceding path and the succeeding path, in other words, 2 The seams of the image between the paths) are imaged using two heads instead of three.

The control unit 100 similarly performs the above-mentioned characteristic settings from the first pass (first pass) to the last pass (nth pass) in the print job.

Thus, in the present embodiment, the number of used heads in the overlapping portion between the path-to-pass OL and the head-to-head overlap (conventional area where the number of used heads increases to 3) is reduced to 2 (setting is changed). Therefore, deterioration of image quality in the OL portion between passes can be prevented or suppressed.

In one specific example, the control unit 100 determines whether or not there is an overlapping portion (area in which three heads are used) between the path-to-pass OL and the head-to-head overlap described above based on the content of the print job.

Specifically, when the print job is a job in which the inkjet image forming unit 5 prints the second image continuously (that is, seamlessly in a plurality of passes) in the transport direction of the recording medium P by the inkjet image forming unit 5. The above determination is made regardless of whether or not the screen image forming unit 4 is used. In this case, the control unit 100 determines the number of drawing lines of the second image in the transport direction from the input image of the print job, and makes the above determination from the determined number of drawing lines.

Further, the control unit 100 uses both the screen image forming unit 4 and the inkjet image forming unit 5 to continuously (seamlessly take a plurality of paths) the first image and the second image in the transport direction of the recording medium P. The above determination is also made for a job to be printed.

In this case, the control unit 100 acquires the image size of the screen plate 41 to be used in the transport direction, and determines the number of drawing lines in the transport direction of the second image formed by the inkjet image forming unit 5 from the acquired image size. Then, the above determination is made from the determined number of drawing lines.

In the present embodiment, the image writing position FS (see FIG. 5A) in the first pass (at the time of the first scanning) is fixed. Therefore, the control unit 100 sets the corresponding nozzles of the corresponding heads so as to form an image according to the input image at the end portion on the FS side of the writing position of the image printed on the upstream side of the recording medium P. Or control.

Similarly, the control unit 100 also forms the image as the input image at the end of the image in the nth pass (at the time of the last scan) printed on the downstream side of the recording medium P. Set or control the corresponding nozzle.

(Modified example of setting of overlap between heads and OL between paths)
As another specific example (modification example), the control unit 100 determines that the region of the head-to-head overlap overlaps with the region of the inter-pass OL, and the position of the overlapping portion in the inter-pass OL is described above. When it is determined that it is the "upstream side (image end side)", the following settings may be made.

That is, the control unit 100 has the entire image forming region (“normal printing unit” shown in FIG. 9A and the like and the inter-pass OL) in the inkjet image forming unit 5 so that the above-mentioned overlapping portions (three used heads) are eliminated. The region) may be set to be shifted (moved) to the downstream side (lower side of FIG. 9A or the like) or the upstream side (upper side of FIG. 9A or the like) in the transport direction.

In other words, when the control unit 100 determines that the OL between passes overlaps with the overlap between heads (the heads used have three areas), the image is formed by a plurality of inkjet heads in one pass. By moving the formation region along the transport direction, the path-to-pass OL is set to a position that does not overlap with the head-to-head overlap.

Even with such a setting, the number of heads used in the inter-pass OL region is reduced from three to two, and the number of heads that complementarily eject ink is reduced. Therefore, the image quality is the same as described above. Can be prevented or suppressed from decreasing.

As described above, when adopting the configuration in which the entire image forming region is moved along the transport direction, the movable size (in other words, between the downstream end side of the head H1 and the writing position FS) is adopted. (Nozzle located in) should be secured in advance in a large size.

Specifically, it is preferable that the movable size is equal to or larger than the sum of the length of the head-to-head overlap in the transport direction and the length of the inter-pass OL in the transport direction.

The following is a specific example described above in FIGS. 8A to 8C, that is, the number of heads for ejecting a mask image by the control unit 100 in a region of head-to-head overlap overlapping with an inter-pass OL region is one (head H2). Only) will be described on the premise of an example of performing the process to be set.

In one specific example, the control unit 100 determines whether or not the path-to-pass OL and the head-to-head overlap overlap based on the image size (that is, the length in the transport direction) of the image formed by the inkjet image forming unit 5. judge.

This is because a problem occurs when the end portion of the actually formed ink image in the transport direction (in this example, the rear end side of the inter-pass OL portion) overlaps with the inter-head overlap portion. The above-mentioned determination method can be commonly used even in the case of an image forming apparatus that does not include the screen image forming unit 4, that is, an inkjet image forming apparatus that is not a hybrid type as in the present embodiment. ..

On the other hand, in the present embodiment, since the screen image forming unit 4 is provided, the control unit 100 has the path-to-pass OL and the head-to-head based on the length of the image formed by the screen image forming unit 4 in the transport direction. It may be determined whether or not the overlap overlaps.

In this embodiment, the control unit 100 determines the above-mentioned writing position FS (that is, the image printed in the first pass) at the start of execution of the print job regardless of whether or not the above-mentioned characteristic setting processing is performed. The downstream end in the transport direction) is fixed (see FIG. 5A as appropriate).

Thus, the control unit 100 prints according to the input image from the nozzles having the nozzle numbers after the predetermined number (n) of the head H1 at the time of scanning at the start of image formation (first pass) in the print job. Control to eject ink at a rate.

Further, in each pass (during each scanning), the control unit 100 has an overlap region between heads that overlaps in the transport direction between the head H1 and the head H2, and between the heads that overlap in the transport direction between the head H2 and the head H3. Ink is ejected complementarily from the nozzles in the overlap region, and control is performed so that an image defined in the input image data is formed.

Specifically, in the area of the head-to-head overlap (the area on the recording medium P on which the head-to-head mask image is formed), the control unit 100 has two heads at a printing rate based on a predetermined mask pattern processing. It is controlled to eject ink complementarily from the nozzle of.

Hereinafter, characteristic processing executed by the control unit 100 in the present embodiment will be described with reference to the flowchart of FIG.

The flowchart shown in FIG. 10 is a case where the inkjet image forming unit 5 executes a print job for printing a second image continuously (that is, seamlessly in a plurality of passes) in the transport direction of the recording medium P, and the second image. 2 Shows the processing after the number of drawing lines in the transport direction of the image is determined.

In step S10, the control unit 100 refers to the path-to-pass OL and the head-to-head overlap (hereinafter, referred to as "both overlaps" for convenience) based on the determined number of drawing lines (length in the transport direction) of the second image. ) Overlap.

Here, when the control unit 100 determines that the two overlaps overlap (YES in step S10), the control unit 100 determines that the image quality may deteriorate, and proceeds to step S20. On the other hand, when the control unit 100 determines that the two overlaps do not overlap (steps S10 and NO), the control unit 100 skips the process of step S20 and proceeds to step S30.

In step S20, the control unit 100 reduces the number of heads used for the head-to-head overlap in the overlapping portion (to one) so that the number of inkjet heads used in the overlapping portion is two. The setting of the ejection mode of the ink ejected from the corresponding nozzle is changed (see FIGS. 8C and 9C as appropriate).

In step S30, the control unit 100 intermittently moves the recording medium P and forms an image so that the first image forming unit 4 and the second image forming unit print the first image and the second image. Each part of the device 1 (belt transport part 2, each image forming part 4, 5, etc.) is controlled.

According to the present embodiment in which such control is performed, it is possible to suppress deterioration of image quality in the inter-pass OL portion in the image forming apparatus 1 provided with a plurality of inkjet heads in which head-to-head overlap is formed.

In the above embodiment, it is assumed that the screen image forming unit 4 is arranged on the upstream side of the inkjet image forming unit 5 in the conveying direction in the conveying direction, but the arrangement is not limited to this, and the reverse arrangement is used. It doesn't matter if there is one.

In addition, the above-described embodiments are merely examples of embodiment of the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

1 Image forming device 2 Belt conveying part 3 Supply part 4 Screen image forming part 5 Inkjet image forming part 6 Discharging part 8 External device 21 Drive roller 22 Driven roller 23 Conveying belt 24 Gluing device 25 Cleaning device 31 Feeding device 32 Guide roller 33 Pressing Roller 41 Screen version 50 Carriage 51 Inkjet head 100 Control unit (setting unit, judgment unit)
110 1st image drive unit 120 2nd image drive unit 130 Transport drive unit 140 Input / output interface FS write-out position H (H1, H2, H3) Head OL (P1) Area of overlap between paths on one end side of the first path OL (P2) Area of overlap between passes on one end side of the second pass P Recording medium W (4W, 5W) Length of image per pass in transport direction (image size)

Claims (7)

A plurality of inkjet heads arranged so that the nozzles for ejecting ink overlap in the transport direction of the recording medium and the inks are complementarily ejected to form an image.
A setting unit for setting an overlap between passes in which the ink is complementarily ejected at an end portion of an image forming region in which an image is formed by the plurality of inkjet heads in one pass in the transport direction to form an image. , With
When the overlap between passes overlaps with the overlap between heads, the setting unit sets the number of inkjet heads that complementarily eject the ink at the overlapping portion with respect to the overlap between passes and the overlap between heads. Is set so that the number of heads is less than the number of heads related to image formation.
Image forming device. When the inter-pass overlap overlaps with the head-to-head overlap, the setting unit forms an image of the inter-pass overlap without forming an image of the head-to-head overlap at the overlapping portion. Set,
The image forming apparatus according to claim 1. When the overlap between passes overlaps with the overlap between heads, the setting unit moves the image forming region in which an image is formed by the plurality of inkjet heads in one pass along the conveying direction. Therefore, the overlap between passes is set at a position that does not overlap with the overlap between heads.
The image forming apparatus according to claim 1. A determination unit for determining whether or not the inter-pass overlap overlaps with the head-to-head overlap is provided based on the length of the image formed by the plurality of inkjet heads in the transport direction.
The image forming apparatus according to any one of claims 1 to 3. A screen image forming unit for forming an image on the recording medium by a screen plate is provided on the upstream side or the downstream side of the plurality of inkjet heads in the conveying direction.
The image forming apparatus according to claim 4. The determination unit determines whether or not the inter-pass overlap overlaps with the head-to-head overlap based on the length of the image formed by the screen image forming unit in the transport direction.
The image forming apparatus according to claim 5. In the first pass when the entire image is formed by a plurality of passes, the position of the downstream end portion of the image formed by the plurality of inkjet heads in the transport direction is predetermined. A control unit that controls the ejection of ink from the nozzle is provided.
The image forming apparatus according to any one of claims 1 to 6.

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