JP7424135B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

Conventionally, an image forming apparatus is known that includes a plurality of inkjet heads arranged such that nozzles that eject ink overlap in the conveying direction of a recording medium (see, for example, Patent Document 1). ).

Furthermore, a hybrid image forming apparatus is known that uses both a screen image forming section and an inkjet image forming section using a plurality of inkjet heads as described above. In such an image forming apparatus, the conveyance pitch of the recording medium in the conveyance section that conveys the recording medium is set in advance so that the conveyance length is equivalent to the image forming range by the screen image forming section.

This is because an inkjet image forming section can change the image size formed in a single printing operation, that is, it can match the image forming range of a screen image forming section, whereas a screen image forming section usually This is because the image forming range is fixed.

Furthermore, in a hybrid image forming apparatus, the screen plates in the screen image forming section are different for each customer, and can be replaced with screen plates having different sizes in the transport direction for each customer. In this case, the conveyance pitch of the recording medium in the conveyance unit needs to be reset for each customer, that is, for each print job.

In an image forming apparatus having such a configuration, for example, when an inkjet image forming section seamlessly forms an image on a long recording medium, the overlapping area between the image ends in the conveyance direction, that is, the inter-pass overlap area is provided.

Japanese Patent Application Publication No. 2014-141079

By the way, in the above-mentioned hybrid image forming apparatus, the images screen printed by the screen image forming section are always good, but the images printed by inkjet printing by the inkjet image forming section suffer from overlap between passes. When there is overlap between heads, there is a risk that image quality will deteriorate.

An object of the present invention is to provide an image forming apparatus that can suppress deterioration of image quality.

The image forming apparatus according to the present invention includes:
a plurality of inkjet heads arranged so that nozzles for ejecting ink overlap in the conveyance direction of a recording medium, and the ink is ejected in a complementary manner to form an image;
a setting unit that sets an overlap between passes in which the ink is complementary discharged to form an image at an end in the transport direction of the image forming area in which an image is formed in one pass by the plurality of inkjet heads; , comprising:
When the inter-pass overlap overlaps the inter-head overlap, the setting unit sets the number of the inkjet heads that eject the ink in a complementary manner in the overlapped portion to the inter-pass overlap and the inter-head overlap. is set so that it is less than the number of heads involved in image formation.

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

1 is a side view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a plan view showing a schematic configuration of a screen image forming section and an inkjet image forming section. 1 is a block diagram showing the main functional configuration of an image forming apparatus. FIG. 4A is a plan view showing a case where the image forming ranges in the screen image forming section and the inkjet image forming section have the same width in the transport direction, and FIG. 4B is a plan view showing a case where the widths in the transport direction are different. 5A is a diagram illustrating a problem when printing a solid image by a 9-head type inkjet image forming unit, and FIG. 5A shows a case where no interference occurs between the inter-pass overlap and the inter-head overlap, and FIG. 5B shows a case where interference occurs. Indicate the case. FIGS. 6A, 6B, and 6C are diagrams illustrating a case in which interference between path overlap and inter-head overlap does not occur in a three-head configuration. 7A, FIG. 7B, and FIG. 7C are diagrams illustrating a case where interference occurs between an inter-path overlap portion and an inter-head overlap portion in a three-head configuration. FIGS. 8A, 8B, and 8C are diagrams illustrating a specific example of characteristic processing in this embodiment. 9A, FIG. 9B, and FIG. 9C are diagrams illustrating other specific examples of characteristic processing in this embodiment. It is a flowchart explaining characteristic processing in this embodiment.

Embodiments of the present invention will be described in detail below 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.

An image forming apparatus 1 shown in FIG. 1 is a hybrid image forming apparatus that uses both screen printing and inkjet printing. The image forming apparatus 1 includes a belt conveying section 2, a supply section 3, a screen image forming section 4 that performs screen printing, an inkjet image forming section 5 that performs inkjet printing, a discharge section 6, and the like.

The belt conveyance unit 2 includes a drive roller 21 and a driven roller 22 arranged in parallel at a predetermined interval, an endless conveyor belt 23 of a predetermined width that spans these rollers 21 and 22, and a drive roller 21. and a sub-scanning motor (not shown) that drives the . The upper surface of the conveying belt 23 in the belt conveying section 2 is a mounting surface on which the recording medium P is placed closely.

In the belt conveying section 2, the driving roller 21 is rotated clockwise in FIG. The conveyor belt 23 is rotated. Through this operation, the recording medium P placed on the upper surface of the conveyor belt 23 is conveyed in the direction of arrow A in the figure, which is the sub-scanning direction.

A gluing device 24 and a cleaning device 25 are provided on the lower surface side of the conveyor belt 23. The gluing device 24 is disposed on the upstream side of the supply section 3 in the rotational direction of the conveyor belt 23 (direction of arrow A), and serves as a glue to bring the lower surface of the recording medium P into close contact with the upper surface of the conveyor belt 23. Apply a so-called adhesive.

The cleaning device 25 is arranged upstream of the gluing device 24 in the rotational direction of the conveyor belt 23 . The cleaning device 25 cleans the adhesive material left on the conveyor belt 23 after the recording medium P is peeled off by the discharge section 6. The conveyor belt 23 that has been cleaned by the cleaning device 25 is coated with adhesive again by the gluing device 24 .

The supply section 3 supplies the recording medium P to the belt conveyance section 2 . The supply section 3 is provided on the upstream end side of the upper surface of the conveyance belt 23 in the conveyance direction of the recording medium P, and includes a feeding device 31, a guide roller 32, and a pressure roller 33. The conveyance direction of the recording medium P is from left to right in FIG. 1, and will be simply referred to as the "conveyance direction" in the following description.

The feeding device 31 is a device that feeds out the recording medium P wound into a roll. The recording medium P is, for example, a long recording medium such as paper, cloth, or plastic film, which is usually used for image formation by inkjet. Note that the recording medium P may be in the form of a sheet cut into a predetermined size.

The guide rollers 32 are plural conveyance rollers provided on the conveyance path of the recording medium P, and guide the recording medium P toward the belt conveyance section 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 conveyor belt 23, and brings the recording medium P into close contact with the conveyor belt 23 via the adhesive material.

The screen image forming section 4 is provided downstream of the supply section 3 in the transport direction. The screen image forming section 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 section 4 forms a first image on the recording medium P conveyed in the conveyance direction by the screen plate 41.

The screen plate 41 is coated with ink corresponding to the first image, 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, FIG. 2 illustrates the case where there is only one screen plate 41, but in reality, the screen plates 41 are arranged at equal intervals in the conveyance direction, as shown by dotted lines in FIG. is possible.

Note that the first image includes, for example, a monochromatic background image. Therefore, each screen plate 41 has ink of a different color from each other, and the screen plate 41 to be used is appropriately selected depending on the background image formed on the recording medium P.

The inkjet image forming section 5 is provided downstream of the screen image forming section 4 in the transport direction. The inkjet image forming section 5 includes a plurality of carriages 50 arranged in the transport direction. In this embodiment, as shown in FIG. 2, three carriages 50 are arranged in a width direction (scanning direction) perpendicular to the conveyance direction of the recording medium P (the direction of the white arrow in FIG. 2). 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 this embodiment, these three carriages 50 (Y, M, C) integrally move (scan) in the scanning direction (horizontal direction in FIG. 2) during image formation, thereby changing the colors used for image formation. By ejecting ink onto 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 section 5 prints a color image using a scanning method.

As shown in FIG. 2, each inkjet head 51 in the carriage 50 (Y, M, C) is arranged in a scanning direction that is parallel to the transport direction (see the white arrow in FIG. 2) and perpendicular to the transport direction. are lined up.

More specifically, the three inkjet heads 51 in one carriage 50 are arranged to have an overlapping part called "head-to-head overlap" where some of the above-mentioned many ink ejection holes overlap with each other. , are arranged in a staggered manner. Note that details of the inter-head overlap will be described later with reference to FIG. 5A and the like.

The inkjet image forming unit 5 forms one inkjet image by superimposing C, M, or Y images based on ink (ink dots) ejected from the inkjet heads 51 in each carriage 50 on the recording medium P. (hereinafter also referred to as a "second image").

In this embodiment, the plurality of carriages 50 (C, M, Y) are integrally moved back and forth in the main scanning direction perpendicular to the conveyance direction by a guide rail or a drive mechanism (not shown). During such image formation (during ink ejection), the drive of the drive roller 21 is controlled, so that the conveyor belt 23 can be switched between a standby state in which it is stopped and a drive state in which it is driven at a predetermined conveyance length. Execute repeated intermittent movements.

When the conveyance belt 23 is in a 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) in the main scanning direction. Through this operation, second images are sequentially formed on the recording medium P on the stopped conveyor belt 23.

Note that the first image mainly includes a motif pattern, a fine image of around 100 μm, a mixed color gradation, a color image having several types of colors, such as tens of thousands of colors, and the like.

According to the image forming apparatus 1 configured as described above, the first image and the second image are printed in a superimposed manner by performing the following operations under the control of the control unit 100 described later in FIG. be done.

That is, a first image such as a background is formed on the recording medium P by the screen image forming unit 4 (screen plate 41), and then the recording medium P is intermittently conveyed on the conveyor belt 23, thereby forming the first image. The image moves directly below the inkjet image forming section 5, and the conveyance of the recording medium P is stopped.

From this state, a second image is formed on the first image by the inkjet image forming section 5 (each inkjet head 51), 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 a "completed image") is formed.

In addition, when a completed image is continuously formed in the conveyance direction of the recording medium P, the intermittent conveyance and printing (overlapping) of the recording medium P as described above is performed under the control of the control unit 100 (see FIG. 3). Repeat this action. Further, at this time, the following operations are repeatedly executed in the inkjet image forming section 5.

That is, the inkjet image forming unit 5 converts the image portion on the leading end side in the transport direction of the second image based on the ink ejected from the plurality of inkjet heads 51 into the image portion of the second image formed during the previous scan (image formation). Printing is performed so as to provide an overlapping image portion that overlaps the image portion on the rear end side in the conveyance direction.

Such overlapping image portions are commonly referred to as "interpass overlap." This inter-pass overlap means that ink is ejected in a complementary manner at the end (image end) in the transport direction of the image forming area where an image is formed in one pass (in this example, one scan). It can be defined as "a part or area on which an image is formed", and the details thereof will be described later.

In general, when forming the entire image in a plurality of passes, the inkjet image forming section 5 is controlled so as to eject ink complementary to each other from the plurality of inkjet heads 51 in the region of overlap between the passes. Images can be seamlessly formed in the transport direction of the recording medium P.

The ejecting section 6 ejects the portion of the recording medium P on which the completed image is formed. The discharge section 6 is provided downstream of the screen image forming section 4 in the conveyance direction, and includes a peeling device, a drying device, a shaking-off device, etc. (not shown).

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

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

FIG. 3 is a block diagram showing the main functional configuration of the image forming apparatus 1. As shown in FIG. The image forming apparatus 1 includes a control section 100, a first image drive section 110, a second image drive section 120, a transport drive section 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 this embodiment, the control unit 100 has functions as a “setting unit” and a “determination unit” of the present invention.

The CPU 101 reads various control programs and setting data stored in the ROM 103, stores them in the RAM 102, and executes the programs to perform various calculation processes. Further, the CPU 101 centrally controls the entire operation of the image forming apparatus 1 .

The RAM 102 provides a working memory space for the CPU 101 and stores temporary data. Note that the RAM 102 may include nonvolatile memory.

The ROM 103 stores various control programs executed by the CPU 101, setting data, and the like. Note that in place of the ROM 103, a rewritable nonvolatile 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) is used, and a DRAM (Dynamic Random Access Memory) or the like may also be used in combination.

The first image driving section 110 controls the carriage 50 of the inkjet image forming section 5 by supplying a driving signal according to the image data to the inkjet image forming section 5 at a predetermined timing based on the control of the control section 100. An amount of ink corresponding to the pixel value of image data is ejected from the nozzle.

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

The conveyance drive unit 130 intermittently moves the conveyance belt 23 at a predetermined speed and timing (i.e., “conveyance pitch”) by supplying a drive signal to the sub-scanning motor of the drive roller 21 based on the control of the control unit 100. Rotate and move.

The input/output interface 140 mediates data transmission and reception between the external device 8 and the control unit 100. The input/output interface 140 is configured of, for example, one 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, etc. to the control unit 100 via an input/output interface 140.

By the way, in the image forming apparatus 1 having the above configuration, the number of lines to be drawn in the conveying direction of the second image formed by the inkjet image forming section 5 is generally the same as the number of lines to be drawn in the conveying direction of the screen plate 41 of the screen image forming section 4. It was determined (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 section 5 are arranged with an overlap area between the heads as described above, the second image may be seamlessly formed in the transport direction depending on the set number of drawing lines. In some cases, image defects may occur. Hereinafter, the background of this problem and the problem will be explained in detail with reference to FIGS. 4A and 4B.

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

In FIG. 4A, the image size of the first image formed by the screen image forming section 4 is indicated by a double arrow 4W, and the image size of the second image formed by the inkjet image forming section 5 is indicated by a double 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 image forming apparatus 1 such as the present embodiment, the screen plate 41 in the screen image forming section 4 is different for each customer, so the size in the conveying direction is different for each customer. can be replaced with a different screen version 41.

Here, in FIG. 4B, the inkjet image forming section 5 is the same as the example shown in FIG. 4A, and the screen plate 41 of the screen image forming section 4 has a longer length (4Ws) in the conveyance direction 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 conveyance pitch of the recording medium P in the belt conveyance section 2 so that the conveyance length is equivalent to the image size of the screen plate 41 (4Ws 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 in one scan in the inkjet image forming section 5 is set to a length of 5Ws (which is shorter than the above-mentioned 5W). =4Ws) (setting change).

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

However, when the setting of the number of drawing lines for the image size of the second image formed by the inkjet image forming unit 5 as described above is changed, the print job in which the second image is seamlessly formed in the transport direction in multiple passes is changed. Image defects may occur during execution.

Hereinafter, problems in the prior art will be described in detail with reference to FIGS. 5A and 5B, which correspond 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 section 5 has nine inkjet heads arranged in a staggered manner. FIG. 3 is a plan view illustrating an example of forming a M-color solid image on the screen.

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

Furthermore, the first to ninth heads are arranged with overlap between the heads. In FIGS. 5A and 5B, the region of head-to-head overlap between the 8th head and the 9th head (that is, the overlapping portion between the nozzles) is indicated by a dotted line frame.

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

This inter-head overlap portion has a fixed length, and the positions (nozzle numbers) of the overlapping nozzles are known in advance. For this reason, the overlapping nozzle areas are set to eject ink in a complementary manner based on, for example, predetermined mask processing.

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 becomes 7840 lines (that is, becomes shorter). .

In addition, when forming such a solid image seamlessly in the conveying direction, for example, by using a predetermined mask process, an image forming an overlap between passes of a fixed length (256 lines in total in this example) is ejected. , the ink ejection mode is set for the heads at both ends of the image size (in the example shown in FIG. 5A, the No. 1 head and the No. 9 head).

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

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

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

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

Thus, in the example shown in FIG. 5A, the mist-like images (inter-pass mask images) constituting the inter-pass overlap at both ends in the conveyance direction (vertical direction in the figure) of the solid image are It can be seen that it was formed by being ejected from the numbered No. 9 head.

On the other hand, in the example shown in FIG. 5B, the mist-like image on one end (rear end side) in the conveying direction of the solid image, that is, on the lower side of the solid rectangular frame in FIG. Located in the area of head-to-head overlap of the heads. Therefore, the inter-pass mask image (fog image) is formed by being ejected from both the No. 8 head and the No. 9 head.

However, if the region of overlap between heads is located at the rear end of the image, in other words, at the rear end of the conveyance pitch of the recording medium P, so-called "interference between the overlap between heads and the overlap between passes" occurs. do.

It has been found that the image in this interference portion is easily recognized by human vision as a defective image component such as "streaks", "unevenness", or "stains".

This problem will be explained below with reference to FIG. 6 (FIGS. 6A to 6C) and FIG. 7 (FIGS. 7A to 7C), again showing a three-head configuration for ease of understanding.

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

In FIGS. 6A to 6C, the head numbers of the three inkjet heads 51 arranged with head-to-head overlap are indicated by symbols H1, H2, and H3.

In addition, in FIGS. 6A to 6C, the trailing edge portion of the image formed during the previous ink ejection operation, here the first pass scanning (region of overlap between passes), is denoted by the symbol "OL (P1)". ” is indicated by a dotted line frame. Further, the front end side portion of the image formed during the next ink ejection operation, here the second pass scanning (region of overlap between passes), is indicated by a dotted line frame labeled “OL(P2)”.

Furthermore, 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 symbol "Ls", and the start position of the inter-pass overlap (the above-mentioned inter-pass mask image) is The end position is indicated by the symbol "Le".

Note that, in order to facilitate distinction, the term "overlap" in the overlap between paths will be abbreviated as "OL" as appropriate below.

First, when the printing size in the transport direction is, for example, the maximum length that can be used to form an image, the inter-pass OL area (the part on the recording medium P where the inter-pass mask image is formed) has an inter-head overlap area (head (The portion on the recording medium P where the mask image is formed) do not overlap (as appropriate, see both ends of the double-headed arrow 4W in FIGS. 5A and 6A). Therefore, no interference occurs between the inter-path OL and the inter-head overlap.

A case in which such interference does not occur will be described in more detail with reference to FIGS. 6B and 6C. Here, FIG. 6B shows the upper nozzles of the head with head number H1 (hereinafter also simply referred to as "head H1") and the head of head H3 (hereinafter also referred to as "head H3") shown in FIG. 6A. It is a characteristic graph showing an example of the printing rate (%) for each nozzle of 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 transport direction, in other words, the position of the recording medium P in the transport direction is shown on the horizontal axis.

Further, FIG. 6C is a diagram for explaining the proportion of ink ejected from the heads H1 and H3 (breakdown of printing rate) among the ink printed in the inter-pass OL (P1, P2) region. In general, FIG. 6C corresponds to a figure obtained by vertically inverting the "H1" portion (figure) shown in FIG. 6B and then rotating the entire figure in the graph 90 degrees clockwise.

The meanings of the above-mentioned symbols and figures also apply to the figures after FIG. 7 (FIGS. 7A to 7C), which will be described later.

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

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

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

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

In this way, when the inter-head overlap area exists at the maximum size in the inter-path OL (P1, P2), as shown in FIGS. 7B and 7C, the inter-path overlap OL (P1, P2) From the start position Ls to the end position Le, ink is ejected from the three heads H2, H3, and H1 in a complementary manner.

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

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

Thus, the inventors have found that short, dark streak-like noise images are easily visible on the portions of the recording medium P where ink has been ejected from the three heads in a complementary manner.

In view of the above-mentioned problems, in this embodiment, based on the positional relationship between the inter-pass OL and the inter-head overlap in the transport direction, the OL is used in the overlap region between the inter-pass OL and the inter-head overlap. In order to reduce the number of heads, the setting of the ink ejection mode, that is, the number of nozzles that play the role of complementary ejecting ink, is changed.

In other words, in the present embodiment, when the inter-pass OL overlaps the inter-head overlap, the control unit 100 controls the number of inkjet heads that eject ink in a complementary manner in the overlapping portion to the inter-pass OL and the inter-head overlap. It is set so that the number of heads involved in image formation in the lap is less than (less than three, ie, two or less).

Furthermore, in the present embodiment, the control unit 100 determines whether or not the inter-head overlap area and the inter-path OL area overlap (overlap), in other words, ``There is an area where three heads are used. "Whether or not" is determined.

If it is determined that there is an overlap (there is an area where three heads are used), the control unit 100 reduces the number of heads used in the overlapped area (area where three heads are used) by one (that is, decreases the number of heads by two). A setting process is performed to change the ink ejection mode in the inter-head overlap region, as shown in FIG.

In one specific example, when the control unit 100 determines that there is an overlap (there is an area where three heads are used), the control unit 100 is configured to form only an inter-pass mask image without forming an inter-head mask image in the area. Next, the ink ejection mode of the nozzle in the area is set.

Such characteristic processing will be explained in more detail with reference to FIG. 8 (FIGS. 8A to 8C) and the like.

Here, FIGS. 8A to 8C are diagrams corresponding to FIGS. 7A to 7C described above, and FIG. 8A is the same as FIG. 7A.

That is, in FIG. 8A, it is assumed that the inter-pass OL area (length in the transport direction) is equal to the inter-head overlap area (same length), and the rear end side in the first pass (during scanning) 12 illustrates a case in which the area of inter-path OL coincides with the area of overlap between heads H2 and H3.

In this case, the control unit 100 determines that the inter-path OL and the inter-head overlap overlap (there is an area where three heads are used), and reduces the number of heads used in the overlapped portion to two, and A setting is made so that no mask image is formed, specifically, no ink is ejected from the head H3.

By making such settings, when a print job is executed, the nozzles of the head H2 in the overlapping area with the head H3 eject ink so as to form only the inter-pass mask image. According to this 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), complementary ink is emitted from the two heads H2 and H1. Ink is ejected.

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

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

As described above, in the present embodiment, when the inter-pass OL and the inter-head overlap overlap, the pass-through is performed without performing image formation processing (formation of an inter-head mask image) for the inter-head overlap in the overlapped portion. The setting is made so that only the interpass OL image forming process (formation of interpass mask image) is performed.

According to this embodiment, which performs the setting process as described above, the number of heads used in the inter-pass OL can always be two, so that the above-mentioned It is possible to effectively prevent quality deterioration such as streaks and uneven density from occurring.

To facilitate understanding, FIGS. 8A to 8C describe a case in which the inter-path OL and the inter-head overlap completely overlap (match) as a relatively simple example. On the other hand, in actual operation of the device, the inter-path OL and the inter-head overlap may not completely overlap, but may partially overlap (partially overlap).

Hereinafter, with reference to FIG. 9 (FIG. 9A to FIG. 9C), a description will be given of processing when the inter-head overlap region overlaps a part of the inter-path OL region.

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

In this case, the control unit 100 determines that the inter-path OL and the inter-head overlap overlap (there is an area where three heads are used), and reduces the number of heads used in the overlapped portion to two (head H3 Set so that ink is not ejected from

The control unit 100 also controls the head H3 to eject ink from the head H3 at the rear end (upstream end) of the inter-pass OL in the first pass (scanning) to form a part of the inter-pass mask image. Set to .

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

Note that the control unit 100 forms an inter-head mask image in the area of overlap between heads H2 and H3 (inside the "normal printing area" in FIG. 9A) other than the above-mentioned overlapping area, as in the past. In other words, the heads H2 and H3 are set to eject ink complementary to each other.

Alternatively, the control unit 100 does not form an inter-head mask image for the area of overlap between heads H2 and H3 (inside the "normal printing area" in FIG. 9A) other than the overlapping area described above, and The setting may be such that ink is ejected from only one of the heads H3 (for example, head H2).

In the examples shown in FIGS. 8 and 9, the initial state or default setting is such that the image size (length in the transport direction) of the inter-pass OL is equal to the image size (length in the transport direction) of the overlap between heads. Assumed.

With this configuration, control can be simplified when the inter-path OL area and the inter-head overlap area do not overlap (do not interfere). Specifically, the control when printing an inter-pass mask image that is formed complementary by two heads in the area of inter-pass OL is controlled by the control when printing the inter-pass mask image that is formed complementary by two heads in the area of inter-head overlap. The control is simplified because it may be the same as the control when printing the inter-head mask image.

On the other hand, as another configuration example, it is possible that the inter-pass OL area (length in the transport direction) and the inter-head overlap area (same length) are different in the initial state. The inter-OL and the inter-head overlap do not completely overlap, but partially overlap.

Even in such a case, the control unit 100 may perform setting processing to reduce the number of heads that form inter-pass mask images using a method similar to the example described in FIGS. 9A to 9C.

More specifically, when it is determined that the inter-head overlap area overlaps with the inter-path OL area, the control unit 100 specifies the position of the overlapping part in the inter-path OL, and performs settings according to the identification result. Execute processing. At this time, the control unit 100 makes settings to reduce the number of heads that form the inter-pass mask image at the position of the identified overlapping portion.

By performing the inter-head overlap and inter-pass OL setting processing as described above, the inter-pass OL area (image parts where ink is ejected complementary to each other between the preceding pass and the subsequent pass, in other words, the two (image seams between two passes) are imaged using two heads instead of three.

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

Thus, in this embodiment, settings are made (settings are changed) to reduce the number of used heads to two in the overlapping area between path-to-path OL and head-to-head overlap (conventionally, an area where the number of used heads increases to three). Accordingly, it is possible to prevent or suppress deterioration of image quality in the OL portion between passes.

In one specific example, the control unit 100 determines whether there is an overlapping portion (an area where three heads are used) between the above-mentioned inter-pass OL and inter-head overlap 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 in the conveying direction of the recording medium P (that is, seamlessly in a plurality of passes), The above determination is made regardless of whether or not the screen image forming section 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 performs the above determination based on 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 in a plurality of passes) form the first image and the second image in the transport direction of the recording medium P. The above determination is also made if the job is to be printed.

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

Note that in this embodiment, the image writing position FS (see FIG. 5A) in the first pass (first scan) is fixed. For this reason, the control unit 100 sets the corresponding nozzle of the corresponding head to form an image exactly as the input image for the end of the image to be printed on the upstream side of the recording medium P on the writing start position FS side. or control.

Similarly, the control unit 100 controls the corresponding head so that the end portion of the image printed on the downstream side of the recording medium P in the n-th pass (last scan) also forms an image exactly as the input image. Set or control the corresponding nozzle.

(Modified example of settings for overlap between heads and OL between paths)
As another specific example (modified example), the control unit 100 determines that the inter-head overlap area overlaps with the inter-path OL area, and the position of the overlapping part in the inter-path OL is as described above. If it is determined that it is the "upstream side (image end side)", the following settings may be made.

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

In other words, if the control unit 100 determines that the inter-pass OL overlaps the inter-head overlap (there are three areas in which three heads are used), the control unit 100 generates an image formed by a plurality of inkjet heads in one pass. By moving the formation area along the transport direction, the inter-pass OL is set at a position that does not overlap with the inter-head overlap.

Even if such settings are made, the number of heads used in the inter-pass OL area will be reduced from three to two, and the number of heads that eject ink in a complementary manner will be reduced, so the image quality will be affected as described above. It is possible to prevent or suppress a decrease in

As mentioned above, when adopting a configuration in which the entire image forming area is set to move along the transport direction, the movable size (in other words, the area from the downstream end of the head H1 to the writing position FS) is Make sure to secure a large nozzle in advance.

Specifically, the movable size is preferably larger than the sum of the length of the inter-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 with reference to FIGS. 8A to 8C, in which the control unit 100 sets the number of heads that eject mask images to 1 (head H2) in the inter-head overlap area that overlaps the inter-pass OL area. The following explanation assumes an example in which processing is performed to set

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

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

On the other hand, in this embodiment, since the screen image forming section 4 is provided, the control section 100 determines the inter-pass OL and the head-to-head distance based on the length in the conveying direction of the image formed by the screen image forming section 4. It may also be determined whether or not they overlap.

In this embodiment, the control unit 100 controls the above-mentioned write start position FS (i.e., the position of the image to be printed in the first pass) at the start of execution of the print job, regardless of whether or not the above-described characteristic setting process is performed. The downstream end in the transport direction) is fixed (see FIG. 5A as appropriate).

Thus, during scanning at the start of image formation (first pass) in a print job, the control unit 100 performs printing according to the input image from the nozzles having a predetermined nozzle number (number n) or later of the head H1. control to eject ink at a certain rate.

In addition, in each pass (at the time of each scan), the control unit 100 controls the head-to-head overlap region where heads H1 and heads H2 overlap in the transport direction, and the head-to-head overlap region where heads H2 and heads H3 overlap in the transport direction. Ink is ejected from nozzles in an overlapping area in a complementary manner to form an image defined by input image data.

Specifically, the control unit 100 controls the two heads at a printing rate based on predetermined mask pattern processing in the above-mentioned inter-head overlap area (area on the recording medium P where the inter-head mask image is formed). control so that ink is ejected from the nozzles in a complementary manner.

Hereinafter, with reference to the flowchart of FIG. 10, characteristic processing executed by control unit 100 in this embodiment will be described.

Note that the flowchart shown in FIG. 10 is for a case where the inkjet image forming unit 5 executes a print job in which the second image is printed continuously in the transport direction of the recording medium P (that is, seamlessly in multiple passes), and It shows the process after the number of drawing lines in the transport direction of two images is determined.

In step S10, the control unit 100 determines the inter-pass OL and inter-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, if the control unit 100 determines that the two overlaps overlap (step S10, YES), it determines that there is a risk that the image quality will deteriorate, and proceeds to step S20. On the other hand, when the control unit 100 determines that the two overlaps do not overlap (step S10, 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 in the head-to-head overlap in the overlapped part (to one) so that the number of inkjet heads used in the overlapped part becomes two. The setting of the ejection mode of ink ejected from the corresponding nozzle is changed (see FIG. 8C and FIG. 9C as appropriate).

In step S30, the control unit 100 intermittently moves the recording medium P and performs image formation so that the first image forming unit 4 and the second image forming unit print the first image and the second image. Controls each part of the apparatus 1 (belt conveyance part 2, each image forming part 4, 5, etc.).

According to the present embodiment that performs such control, it is possible to suppress deterioration of image quality in the inter-pass OL portion in the image forming apparatus 1 including 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 section 4 is arranged upstream of the inkjet image forming section 5 in the transport direction. It doesn't matter if there is.

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

1 Image forming device 2 Belt conveyance section 3 Supply section 4 Screen image forming section 5 Inkjet image forming section 6 Discharge section 8 External device 21 Drive roller 22 Followed roller 23 Conveyance belt 24 Gluing device 25 Cleaning device 31 Feeding device 32 Guide roller 33 Pressure Roller 41 Screen plate 50 Carriage 51 Inkjet head 100 Control section (setting section, determination section)
110 First image drive section 120 Second image drive section 130 Conveyance drive section 140 Input/output interface FS Write position H (H1, H2, H3) Head OL (P1) Inter-pass overlap area OL on one end side of the first pass (P2) Inter-pass overlap area on one end side of the second pass P Recording medium W (4W, 5W) Length of image in the transport direction per one pass (image size)

Claims (7)

a plurality of inkjet heads arranged so that nozzles that eject ink overlap in the conveyance direction of a recording medium, and the ink is ejected in a complementary manner to form an image;
a setting unit that sets an overlap between passes in which the ink is complementary discharged to form an image at an end in the transport direction of the image forming area in which an image is formed in one pass by the plurality of inkjet heads; , comprising:
When the inter-pass overlap overlaps the inter-head overlap, the setting unit sets the number of the inkjet heads that eject the ink in a complementary manner in the overlapping portion to the inter-pass overlap and the inter-head overlap. Set the number of heads to be less than the number of heads involved in image formation in
Image forming device. The setting unit is configured to, when the inter-pass overlap overlaps the inter-head overlap, form an image of the inter-pass overlap without forming an image of the inter-head overlap in the overlapping portion. set,
The image forming apparatus according to claim 1. The setting unit is configured to move the image forming area in which an image is formed in one pass by the plurality of inkjet heads along the transport direction when the inter-pass overlap overlaps the inter-head overlap. setting the inter-path overlap to a position that does not overlap with the inter-head overlap;
The image forming apparatus according to claim 1. a determination unit that determines whether the inter-pass overlap overlaps the inter-head overlap based on the length in the conveyance direction of the image formed by the plurality of inkjet heads;
The image forming apparatus according to claim 1 . A screen image forming unit that forms an image on the recording medium using a screen plate is provided on the upstream side or downstream side of the plurality of inkjet heads in the transport direction.
The image forming apparatus according to claim 4. The determining unit determines whether the inter-pass overlap overlaps the inter-head overlap based on the length in the conveying direction of the image formed by the screen image forming unit.
The image forming apparatus according to claim 5. In the first pass when all images are formed in a plurality of passes, the position of the downstream end of the image formed by the plurality of inkjet heads in the transport direction is determined in advance. a control unit that controls ejecting ink from the nozzle;
The image forming apparatus according to any one of claims 1 to 6.

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