JP7459699B2 - Image forming system and image forming method - Google Patents

Description

The present invention relates to an image forming system and an image forming method.

Conventionally, an inkjet system is equipped with an ink ejection section provided with a group of nozzles that eject ink, and forms an image by ejecting ink from the nozzle group onto the recording medium while moving the recording medium and the ink ejection section relative to each other. There are several image forming apparatuses. In such an image forming apparatus, if there is a defective nozzle in which ink is not ejected or the amount or direction of ink ejection is incorrect, there is a problem in that the effect of the defective nozzle appears on the image and the image quality deteriorates.

To address this issue, there is a known technology that prevents the image quality from deteriorating by preventing ink from being ejected from the defective nozzle and increasing the amount of ink ejected from nozzles adjacent to the defective nozzle to compensate for the non-ejection of ink caused by the defective nozzle. (For example, Patent Document 1).

Japanese Patent Application Publication No. 2002-19101

However, if the adjacent nozzle was originally the target of ink ejection, or if the adjacent nozzle is also a defective nozzle, it may not be possible to increase the amount of ink ejected from the adjacent nozzle to compensate, and the appropriate It is not possible to perform complete completion. Therefore, the conventional technique described above has a problem in that it may not be possible to suppress image quality deterioration caused by defective nozzles.

The object of this invention is to provide an image forming system and an image forming method that can more reliably suppress degradation of image quality caused by defective nozzles.

In order to achieve the above object, the invention of an image forming system according to claim 1,
An image forming system comprising a first image forming device and a second image forming device,
The first image forming apparatus includes:
a first ink ejection unit having a first nozzle group and ejecting ink from the first nozzle group onto a recording medium;
a first image reading section that reads an image formed on a recording medium by ink ejection by the first ink ejection section;
a first control unit;
has
The second image forming apparatus includes:
a second ink ejection unit having a second nozzle group and ejecting ink from the second nozzle group onto a recording medium delivered from the first image forming apparatus;
a second control unit;
has
The first control unit is configured to detect a first image in which ink is not being ejected normally due to a defective nozzle being included in the first nozzle group in the image read by the first image reading unit. When an ejection failure area is detected, alternative ejection of ink by the second ink ejection unit is performed on a first alternative ejection area including an area corresponding to the first ejection failure area on the recording medium. generating first alternative ejection information for causing the ejection to occur;
The second control section causes the second ink ejection section to perform the alternative ejection on the first alternative ejection area based on the first alternative ejection information.

The invention according to claim 2 is the image forming system according to claim 1,
The second control section causes the second ink ejection section to perform the alternative ejection on the first alternative ejection area on the recording medium where the first ejection failure area has been detected.

The present invention relates to an image forming system according to claim 3,
the first alternative ejection information includes information for identifying the defective nozzle of the first nozzle group,
The second control unit causes the substitute ejection to be performed by a nozzle of the second nozzle group that has an ink ejection position corresponding to the defective nozzle of the first ink ejection unit.

The invention according to claim 4 is the image forming system according to claim 1, comprising:
The first alternative ejection information includes information identifying a sub nozzle group that is part of the first nozzle group and includes the defective nozzle and has ink ejection positions adjacent to each other,
In image formation after the first alternative ejection information is generated,
The first control unit causes the first ink ejection unit to eject ink from the first nozzle group excluding the sub nozzle group specified by the first alternative ejection information,
The second control unit causes a sub nozzle group of the second nozzle group whose ink ejection position corresponds to the sub nozzle group specified by the first alternative ejection information to perform the alternative ejection.

According to a fifth aspect of the present invention, in the image forming system according to the first aspect,
the first ink ejection unit has a plurality of first head units that eject inks of different colors from nozzles;
the second ink ejection unit has a plurality of second head units that eject ink of the same color as each of the plurality of first head units from nozzles,
the first alternative ejection information includes information for identifying a head unit having the defective nozzle among the plurality of first head units,
In the image formation after the first alternative ejection information is generated,
the first control unit causes the first ink ejection unit to eject ink from the remaining head units excluding the head unit specified by the first alternative ejection information among the plurality of first head units;
The second control unit causes a head unit among the plurality of second head units to perform the alternative ejection, the head unit ejecting ink of the same color as the head unit specified by the first alternative ejection information.

The invention according to claim 6 is the image forming system according to claim 1 or 2,
The first alternative ejection information is partial image data that includes a portion of the image data of the image to be formed that corresponds to the first alternative ejection area,
The second control section causes the second ink ejection section to eject ink based on the partial image data to perform the alternative ejection.

The invention according to claim 7 is the image forming system according to any one of claims 1 to 6,
The second control unit causes the alternative ejection to be performed when a predetermined alternative ejection execution condition is satisfied.

The invention described in claim 8 is the image forming system described in any one of claims 1 to 7,
the first image forming apparatus has a reversing unit that reverses a recording medium;
the first ink ejection unit of the first image forming device ejects ink onto a first surface of a recording medium;
the second ink ejection unit of the second image forming apparatus ejects ink onto a second surface opposite to the first surface when the recording medium is delivered from the first image forming apparatus after the ink ejection by the first ink ejection unit has been inverted by the inversion unit, and ejects ink onto the first surface when the recording medium is delivered from the first image forming apparatus without being inverted by the inversion unit after the ink ejection by the first ink ejection unit;
When the first control unit generates the first alternative ejection information, the first control unit causes the reversing unit to send the recording medium to the second image forming apparatus without reversing the recording medium.

The invention according to claim 9 is the image forming system according to claim 1, comprising:
The second image forming apparatus includes a second image reading section that reads an image formed on a recording medium by ink ejection by the second ink ejection section,
The second control unit is configured to detect a second image in which ink is not being ejected normally due to a defective nozzle being included in the second nozzle group in the image read by the second image reading unit. When an ejection failure area is detected, alternative ejection of ink by the first ink ejection unit to a second alternative ejection area including an area corresponding to the second ejection failure area on the recording medium is performed. generating second alternative ejection information for causing the ejection;
The first control section causes the first ink ejection section to perform the alternative ejection on the second alternative ejection area based on the second alternative ejection information.

According to a tenth aspect of the present invention, in the image forming system according to the ninth aspect,
the second alternative ejection information includes information for identifying the defective nozzle of the second nozzle group,
The first control unit causes the substitute ejection to be performed by a nozzle of the first nozzle group that has an ink ejection position corresponding to the defective nozzle of the second ink ejection unit.

The invention according to claim 11 is the image forming system according to claim 9,
The second alternative ejection information includes information specifying a sub nozzle group that is part of the second nozzle group and includes the defective nozzle and has ink ejection positions adjacent to each other,
In image formation after the second alternative ejection information is generated,
The first control unit causes a sub nozzle group of the first nozzle group whose ink ejection positions correspond to the sub nozzle group specified by the second alternative ejection information to perform the alternative ejection;
The second control section causes the second ink ejection section to eject ink from the nozzles in the second nozzle group excluding the sub nozzle group specified by the second alternative ejection information.

The invention according to claim 12 is the image forming system according to claim 9,
The first ink ejection unit includes a plurality of first head units that eject ink of mutually different colors from nozzles,
The second ink ejection unit includes a plurality of second head units each ejecting ink of the same color as each of the plurality of first head units from a nozzle,
The second alternative ejection information includes information that identifies a head unit having the defective nozzle among the plurality of second head units,
In image formation after the second alternative ejection information is generated,
The first control unit performs the alternative ejection by a head unit that ejects ink of the same color as the head unit specified by the second alternative ejection information, among the plurality of first head units. let it be,
The second control unit causes the second ink ejection unit to eject ink from the remaining head units of the plurality of second head units except for the head unit specified by the second alternative ejection information. to be discharged.

According to a thirteenth aspect of the present invention, in the ninth aspect of the image forming system,
The second alternative discharge information is partial image data including a portion of image data of an image to be formed that corresponds to the second alternative discharge area,
The first control unit causes the first ink ejection unit to eject ink based on the partial image data, thereby performing the substitute ejection.

The invention according to claim 14 is the image forming system according to any one of claims 9 to 13,
The first control unit causes the alternative ejection to be performed when a predetermined alternative ejection execution condition is satisfied.

The invention according to claim 15 is the image forming system according to any one of claims 9 to 14,
The first image forming apparatus has a reversing unit that reverses the front and back of the recording medium,
The first ink ejection unit of the first image forming apparatus ejects ink onto a first surface of a recording medium,
When the second alternative ejection information is generated, the first control section causes the first ink ejection section to eject ink onto the first surface of the recording medium, and then performs the reversal operation. The recording medium is turned over by the recording medium, and the first ink discharge unit performs the alternative discharge on a second surface of the recording medium opposite to the first surface.

The present invention relates to an image forming system according to claim 7 or 14,
The alternative ejection execution conditions relate to at least a part of the quality level of the formed image, the position of the faulty nozzle, the color of ink corresponding to the faulty nozzle, the presence or absence of an adjacent faulty nozzle, object attributes of the formed image, and the resolution of the formed image.

The invention according to claim 17 is the image forming system according to any one of claims 7, 14, and 16,
an input unit that receives an input operation for setting the alternative discharge execution conditions;
a display unit that displays the alternative discharge execution conditions;
Equipped with.

Furthermore, in order to achieve the above object, the invention of an image forming method according to claim 18,
a first ink ejection section having a first nozzle group and ejecting ink from the first nozzle group onto the recording medium; a first image forming apparatus having a first image reading section that reads an image;
a second image forming apparatus having a second nozzle group and a second ink ejection section that ejects ink from the second nozzle group onto a recording medium delivered from the first image forming apparatus; An image forming method using an image forming system comprising:
In the image read by the first image reading unit, a first ejection failure area where ink is not ejected normally due to a defective nozzle being included in the first nozzle group is detected. a first alternative for causing the second ink ejection unit to perform alternative ejection of ink to a first alternative ejection area on the recording medium that includes an area corresponding to the first ejection failure area; a step of generating discharge information;
causing the second ink ejection unit to perform the alternative ejection on the first alternative ejection area based on the first alternative ejection information;
including.

The present invention relates to an image forming method, comprising:
the second image forming device has a second image reading unit that reads an image formed on a recording medium by ink ejection from the second ink ejection unit,
The image forming method includes:
a step of generating second alternative ejection information for causing the first ink ejection unit to alternatively eject ink onto a second alternative ejection area on a recording medium, the second alternative ejection area including an area corresponding to the second defective ejection area, when a second defective ejection area in which ink is not normally ejected due to a defective nozzle being included in the nozzles of the second ink ejection unit is detected in the image read by the second image reading unit;
causing the first ink ejection unit to perform the alternative ejection onto the second alternative ejection region based on the second alternative ejection information;
including.

The present invention makes it possible to more reliably suppress degradation of image quality caused by defective nozzles.

1 is a diagram showing a schematic configuration of an image forming system according to a first embodiment of the present invention; FIG. 3 is a schematic diagram showing the configuration of a head unit. FIG. 2 is a block diagram showing main functional configurations of a first image forming apparatus and a second image forming apparatus. 11A and 11B are diagrams illustrating alternative ejection of ink. It is a figure which shows the alternative discharge setting screen. 5 is a flowchart showing a control procedure of an image forming process executed by a first image forming apparatus. 7 is a flowchart showing a control procedure of image forming processing executed by the second image forming apparatus. 8 is a diagram showing an image forming process in the image forming process of FIGS. 6 and 7. FIG. 7 is a flowchart showing a control procedure of alternative ejection setting processing. FIG. 13 is a diagram showing an example of a test image. FIG. 6 is a diagram illustrating alternative ejection by a second image forming apparatus to compensate for ejection failure in the first image forming apparatus. FIG. 7 is a diagram illustrating alternative ejection by the first image forming apparatus to compensate for ejection failure in the second image forming apparatus. FIG. 7 is a diagram showing a control procedure of image forming processing in a second embodiment. 14 is a diagram showing an image forming process in the image forming process of FIG. 13. FIG. 13 is a flowchart showing a control procedure of an image forming process in Modification 2-1. 16 is a diagram showing an image forming process in the image forming process of FIG. 15. FIG. 16 is a diagram showing an image forming process in the image forming process of FIG. 15. FIG.

The following describes an embodiment of the image forming system and image forming method of the present invention with reference to the drawings.

First Embodiment
FIG. 1 is a diagram showing a schematic configuration of an image forming system 100 according to a first embodiment of the present invention.
The image forming system 100 includes a paper feed section 2, a first image forming device 1a that forms an image on a recording medium M supplied from the paper feed section 2, a second image forming device 1b that is connected to the first image forming device 1a and forms an image on the recording medium M delivered from the first image forming device 1a, and a paper discharge section 3 to which the recording medium M on which the image has been formed is discharged. The image forming system 100 is a serial tandem type system in which an image is formed on one sheet of recording medium M by the first image forming device 1a and the second image forming device 1b that are connected in series. As the recording medium M, various media that can fix ink that has landed on the surface, such as paper such as plain paper or coated paper, fabric or sheet-like resin, can be used.

The paper feed unit 2 has a paper feed tray that stores the recording medium M, and supplies the recording medium M one sheet at a time to the first image forming device 1a by a paper feed mechanism not shown.

The first image forming device 1a includes a first conveying unit 10a, a first ink ejection unit 20a, a first image reading unit 30a, a first reversing unit 40a, and a first control unit 50a.

The first conveyance section 10a includes a conveyance belt 11, a plurality of conveyance rollers 12, a medium detection section 14, a rotary encoder 15, and the like.
The conveyance belt 11 is a ring-shaped belt whose inner side is supported by a plurality of conveyance rollers 12 . A specific drive roller among the plurality of conveyance rollers 12 is driven by the conveyance drive unit 13 (see FIG. 3) and rotates around a rotation axis extending in the X direction in FIG. The conveyance belt 11 moves around the plurality of conveyance rollers 12 as the drive roller rotates. The first conveyance unit 10a moves the recording medium M onto the conveyor belt 11 by rotating the conveyor belt 11 at a speed corresponding to the rotational speed of the conveyor roller 12 with the recording medium M placed on the conveyor belt 11. 11 (Y direction in FIG. 1). The first transport section 10a is provided with a guide member (not shown) that abuts and guides the side edge of the recording medium M. This guide member makes it possible to correct misalignment of the recording medium M in the X direction and place the recording medium M at a predetermined position in the X direction.

The medium detection unit 14 detects the leading edge and side edges of the recording medium M placed on the conveyor belt 11 and conveyed, and outputs the detection results to the first control unit 50a. The detection method of the medium detection unit 14 can be, for example, an optical method that identifies the position of the leading edge and side edges from the image capture results of the leading edge and side edges of the recording medium M. However, it is not limited to this, and a method of contact detection of the leading edge and side edges of the recording medium M may also be used.

The rotary encoder 15 is attached to the drive roller of the conveyance rollers 12, and outputs a pulse signal to the first controller 50a every time the drive roller rotates by a predetermined angle. Based on the signal from the rotary encoder 15, the amount of rotation of the drive roller, that is, the amount of movement of the conveyor belt 11 (and the recording medium M) can be detected.

The first ink ejection section 20a has a plurality of head units 21 (a plurality of first head units) that eject ink of different colors from the nozzles. Specifically, the first ink ejection section 20a has four head units 21Y, 21M, 21C, and 21K that correspond to the four colors of ink, yellow (Y), magenta (M), cyan (C), and black (K). In the following, any one of the head units 21Y, 21M, 21C, and 21K will be referred to as "head unit 21". The head unit 21 has a nozzle surface that is exposed to the outside and has a plurality of nozzle openings that eject ink, and records an image by ejecting ink from the nozzle openings of the nozzle surface that faces the outer circumferential surface of the conveyor belt 11 to the recording medium M at an appropriate timing according to the rotation of the conveyor belt 11 on which the recording medium M is placed. The head unit 21 is arranged so that the nozzle surface and the outer circumferential surface are separated by a predetermined distance. In this embodiment, head units 21Y, 21M, 21C, and 21K are arranged in this order at a predetermined interval from the upstream side in the transport direction of the recording medium M. The entire set of nozzles provided in the first ink ejection unit 20a will be referred to as the "first nozzle group" below.

FIG. 2 is a schematic diagram showing the configuration of the head unit 21. As shown in FIG. FIG. 2 is a plan view of the entire head unit 21 viewed from the side facing the outer circumferential surface of the conveyor belt 11. As shown in FIG.
In this embodiment, the head unit 21 includes 16 recording heads 211, each having a nozzle row consisting of nozzles N arranged in the X direction (that is, in the width direction perpendicular to the transport direction). These 16 recording heads 211 are combined two by two to form eight head modules 211M. The positions of the plurality of nozzle rows included in each head module 211M in the X direction are adjusted so that the positions of the nozzles in the X direction do not overlap. A set of a plurality of nozzles N provided in one head module 211M is hereinafter referred to as a "sub nozzle group G." Note that the arrangement direction of the nozzles N in each recording head 211 is not limited to the width direction perpendicular to the transport direction, but may be a direction intersecting the transport direction at an angle other than a right angle.

The ink ejection mechanism for ejecting ink from each nozzle N is not particularly limited, but a piezoelectric type using a piezoelectric body can be used. Known piezoelectric ink ejection mechanisms include shear mode and vent mode. A shear mode ink ejection mechanism ejects ink by varying the pressure of the ink in the pressure chamber by generating a shear mode type displacement in the piezoelectric body on the wall of the pressure chamber that communicates with the nozzle N. A vent mode ink ejection mechanism ejects ink by varying the pressure of the ink in the pressure chamber by deforming a piezoelectric body fixed to a diaphragm that forms the wall of the pressure chamber.

Each head module 211M fits into an opening provided in the support plate 21a of the head unit 21, and is held on the support plate 21a with the nozzle surface of the recording head 211 exposed from the bottom surface (the surface facing the conveyor belt 11) of the support plate 21a. The eight head modules 211M are arranged in a staggered pattern so that the ranges in which ink can be ejected from the nozzles N are continuously connected in the X direction, and the arrangement ranges in the X direction partially overlap each other to form a line head.

The arrangement range in the X direction of the nozzles N of the head unit 21 covers the width in the X direction of the area on the recording medium M transported by the transport belt 11 where an image can be recorded. The head unit 21 is fixed in place when recording an image, and records an image using a single pass method by sequentially ejecting ink at predetermined intervals (transport direction intervals) to different positions in the transport direction as the recording medium M is transported.

The first image reading unit 30a shown in FIG. 1 is provided downstream of the first ink ejection unit 20a in the transport direction, facing the outer circumferential surface of the transport belt 11. The first image reading unit 30a reads a first image formed on the recording medium M by ink ejection by the first transport unit 10a, and outputs the reading result to the first control unit 50a. The first image reading unit 30a has a linear image sensor in which multiple imaging elements, such as a CCD (charge-coupled device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, are arranged along the X direction, a generation unit that generates image data (imaging data) according to an electrical signal output from the imaging element, and a light source that irradiates light onto the recording medium M.

The first reversing unit 40a reverses the recording medium M and sends the reversed recording medium M to the second image forming device 1b. The first reversing unit 40a includes a plurality of roller pairs 41 that sandwich and transport the recording medium M. When reversing the recording medium M, the first reversing unit 40a once pulls the recording medium M sent from the transport belt 11 toward the second image forming device 1b into a reversing path 42. By reversing the traveling direction of the recording medium M and returning it to the transport path to the second image forming device 1b, the recording medium M can be sent to the second image forming device 1b in a reversed state.
In addition, by advancing the recording medium M from the reversing path 42 to the return path 43, the recording medium M can be supplied again to the conveyor belt 11 of the first conveying unit 10a in an inverted state. This allows the first ink ejection unit 20a to record an image on the second side (the side opposite to the first side) of the recording medium M. In this way, the first image forming device 1a is also capable of forming images on both sides of the recording medium M.
The configuration of the first reversing unit 40a is not limited to that shown in FIG. 1, and any configuration may be used as long as it is possible to turn the recording medium M upside down.

The first control unit 50a comprehensively controls the operations of each unit of the first image forming apparatus 1a.
For example, the first control unit 50a causes the first transport unit 10a to transport the recording medium M, and causes the nozzles of the first ink ejection unit 20a to eject ink onto the recording medium M based on image data of the image to be formed, forming an image. In this image formation, the first control unit 50a identifies the position of the recording medium M based on the detection result of the leading end of the recording medium M by the medium detection unit 14 and the output signal from the rotary encoder 15, and ejects ink from the nozzles at the timing when the nozzles of the head unit 21 face the ink ejection target position on the recording medium M. In addition, when it is determined from the detection result of the side end of the recording medium M by the medium detection unit 14 that the position of the recording medium M in the X direction is deviated from a predetermined position, the first control unit 50a shifts the range of the nozzles used for image formation in the X direction according to the amount of deviation, and adjusts it so that the image is formed in a predetermined image formation range on the recording medium M.
Furthermore, the first control unit 50a detects whether or not there is a defective discharge area (first defective discharge area) in the read image, where ink is not discharged normally due to a defective nozzle being included in the nozzles (first nozzle group) of the first ink discharge unit 20a, based on the reading result by the first image reading unit 30a. If a defective discharge area is detected, the first control unit 50a executes various processes related to dealing with the defective discharge. The dealing with the defective discharge will be described in detail later.

The second image forming apparatus 1b includes a second transport section 10b, a second ink discharge section 20b, a second image reading section 30b, a second reversing section 40b, a second control section 50b, etc. Equipped with
The configuration of the second conveying section 10b, the second ink ejection section 20b, the second image reading section 30b, the second reversing section 40b, and the second control section 50b is the same as that of the first image forming apparatus 1a in the first image forming apparatus 1a. The configurations of the transport section 10a, the first ink discharge section 20a, the first image reading section 30a, the first reversing section 40a, and the first control section 50a are the same, so detailed explanations will be omitted.
The second ink ejection section 20b includes four head units 21Y, 21M, 21C, and 21K (a plurality of second heads) that eject ink of the same color as each of the first ink ejection sections 20a from their nozzles. unit). Further, the entire nozzle provided in the second ink ejection section 20b will be hereinafter referred to as a "second nozzle group."

The second image forming device 1b transports the recording medium M handed over from the first image forming device 1a in the Y direction by the second transport unit 10b, and forms an image by ejecting ink from the second ink ejection unit 20b onto the recording medium M.
When the recording medium M, which has been inverted by the first reversing unit 40a after the first ink ejection unit 20a of the first image forming device 1a has ejected ink onto the first side, is handed over from the first image forming device 1a, the second ink ejection unit 20b ejects ink onto the second side. On the other hand, when the recording medium M is handed over from the first image forming device 1a without being inverted by the first reversing unit 40a after the ink ejection by the first ink ejection unit 20a, the second ink ejection unit 20b ejects ink onto the first side.

The second control section 50b controls the overall operation of each section of the second image forming apparatus 1b.
For example, the second control unit 50b transports the recording medium M using the second transport unit 10b, and forms an image on the recording medium M by ejecting ink from the nozzles of the second ink ejection unit 20b based on image data of the image to be formed.
Furthermore, the second control unit 50b detects whether or not there is a defective discharge area (second defective discharge area) in the read image, where ink is not discharged normally due to a defective nozzle being included in the nozzles (second nozzle group) of the second ink discharge unit 20b, based on the reading result by the second image reading unit 30b. If a defective discharge area is detected, the second control unit 50b executes various processes related to dealing with the defective discharge. The dealing with the defective discharge will be described in detail later.

The paper discharge section 3 has a paper discharge tray on which the recording medium M on which image formation by the second image forming device 1b has been completed is placed.

FIG. 3 is a block diagram showing the main functional configuration of the first image forming apparatus 1a and the second image forming apparatus 1b.
In FIG. 3 and the following description, the first image forming apparatus 1a or the second image forming apparatus 1b will be referred to as the "image forming apparatus 1", the first transport section 10a or the second transport section 10b as the "transport section 10", the first ink ejection section 20a or the second ink ejection section 20b as the "ink ejection section 20", the first image reading section 30a or the second image reading section 30b as the "image reading section 30", the first inversion section 40a or the second inversion section 40b as the "inversion section 40", and the first control section 50a or the second control section 50b as the "control section 50".
The image forming apparatus 1 includes a transport unit 10 having a transport drive unit 13, a medium detection unit 14 and a rotary encoder 15, an ink ejection unit 20 having a recording head 211 and a recording head drive unit 212, an image reading unit 30, an inversion unit 40 having a roller drive unit 44, a control unit 50, an image processing unit 61, an operation display unit 62 (input unit, display unit), a communication unit 63, a bus 64, etc. In the following, a description of the components that have already been described will be omitted.

The conveyance drive unit 13 supplies a drive signal to a motor that drives the conveyance belt 11 based on a control signal supplied from the control unit 50, and rotates the conveyance belt 11 at a predetermined speed and timing.

The recording head drive unit 212 supplies the ink ejection mechanism of the recording head 211 with a drive signal that causes the piezoelectric body to deform in accordance with the image data at appropriate timing, so that the image data is output from the nozzles N of the recording head 211. An amount of ink corresponding to the pixel value is ejected.

The roller drive section 44 rotates the roller pair 41 of the reversing section 40 by a rotation amount and a rotation direction according to a control signal from the control section 50 to move the recording medium M within the reversing section 40 .

The control unit 50 has a CPU 51 (Central Processing Unit), a RAM 52 (Random Access Memory), a ROM 53 (Read Only Memory), and a storage unit 54 .
The CPU 51 reads out various control programs and setting data stored in the ROM 53, stores them in the RAM 52, and executes the programs to perform various arithmetic processing. The control unit 50 centrally controls the overall operation of the image forming apparatus 1 by the CPU 51 performing these arithmetic processing.
The RAM 52 provides a working memory space for the CPU 51 and stores temporary data. The RAM 52 may include a non-volatile memory.
The ROM 53 stores various control programs and setting data executed by the CPU 51. Note that the ROM 53 may be replaced by a rewritable non-volatile memory such as a flash memory.

The storage unit 54 stores a print job (image recording command) input from an external device via the communication unit 63 and image data 543 of an image to be recorded related to the print job. The storage unit 54 also stores first alternative discharge information 541 and second alternative discharge information 542. The first alternative discharge information 541 is information for causing the second image forming device 1b to perform alternative discharge when a discharge failure area caused by a defective nozzle of the first image forming device 1a is detected, and is generated by the first image forming device 1a. The second alternative discharge information 542 is information for causing the first image forming device 1a to perform alternative discharge when a discharge failure area caused by a defective nozzle of the second image forming device 1b is detected, and is generated by the second image forming device 1b. The storage unit 54 also stores partial image data 544 generated for alternative discharge. For example, a hard disk drive (HDD) is used as the storage unit 54, and a dynamic random access memory (DRAM) or the like may also be used in combination.

The image processing unit 61 performs various image processing. The image processing unit 61 performs, for example, analysis processing that generates vector data by analyzing data written in a page description language included in job data input via the communication unit, and generates raster image bitmap data from vector data. Performs image processing such as rasterization processing. Each data string in this bitmap data corresponds to one nozzle of the head unit 21, and an image can be formed by ejecting ink from each nozzle according to the pixel value of the bitmap data. In this way, the image processing section 61 functions as a RIP (raster image processor). Note that the image processing performed by the image processing unit 61 is not limited to the example illustrated above.

The operation display section 62 outputs various displays related to the operation of the image forming apparatus 1 and receives various input operations from the user regarding the operations of the image forming apparatus 1. Specifically, the operation display unit 62 includes, for example, a display device including a touch panel type input device, switches provided according to various input operation contents, and the like.

The communication unit 63 is a communication interface that controls communication operations with the other image forming apparatus 1 and external devices. Here, the other image forming apparatus 1 refers to the second image forming apparatus 1b with respect to the communication section 63 of the first image forming apparatus 1a, and refers to the first image forming apparatus 1b with respect to the communication section 63 of the second image forming apparatus 1b. refers to the image forming apparatus 1a. The communication interface includes one or more communication interfaces compatible with various communication protocols, such as a network interface card. The communication unit 63 transmits various commands including the first alternative ejection information 541 and the second alternative ejection information 542 to the other image forming apparatus 1 under the control of the control unit 50 . It also acquires image data to be recorded and setting data (job data) related to image recording from an external device, and transmits status information and the like to the external device.

The bus 64 is a path for transmitting and receiving signals between the control unit 50 and other components.

Next, the image forming operation of the image forming system 100 will be explained.
In the image forming system 100, when performing normal image formation, a first image is formed on the first surface (front surface) of the recording medium M by the first image forming apparatus 1a. A second image is formed on the second side (back side) by the second image forming apparatus 1b.
Further, when a discharge defect is detected in the first image formed by the first image forming apparatus 1a, the second image forming apparatus 1b applies ink to the first surface so as to compensate for the discharge defect. An alternative discharge is performed. After this alternative ejection, a second image is formed on the second side.

FIG. 4 is a diagram illustrating alternative ejection of ink.
FIG. 4A shows a first image formed on a first surface of a recording medium M by a first image forming apparatus 1a. Here, it is assumed that the nozzles of the first ink ejection unit 20a include a defective nozzle that cannot eject ink. For this reason, in the first image of FIG. 4A, an ejection failure region r1 occurs due to non-ejection of ink from the defective nozzle. The ejection failure region r1 is a region where ink of a color corresponding to a defective nozzle is not ejected, but in FIG. 4A, the ejection failure region r1 is shown with dots for convenience of explanation. In addition, the ejection failure region r1 is usually a very narrow region corresponding to one nozzle, but in FIG. 4A, the width of the ejection failure region r1 is exaggerated.

The ejection failure area r1 is detected by the first control unit 50a based on the result of reading the first image by the first image reading unit 30a. In this embodiment, the image data read by the first image reading unit 30a and the image data 543 (bitmap data generated by the image processing unit 61) used to form the first image are The ejection failure region r1 is detected by comparing and analyzing. Furthermore, a defective nozzle is identified from the position of the defective ejection region r1 in the image.

When the ejection failure area r1 is detected in the first image, the first control unit 50a of the first image forming apparatus 1a causes the second image forming apparatus 1b to perform alternative ejection for the ejection failure area r1. First alternative ejection information 541 is generated and transmitted to the second image forming apparatus 1b. More specifically, the first alternative ejection information 541 indicates whether the second image forming apparatus 1b This is information for causing the second ink ejection unit 20b to perform alternative ejection of ink. In this embodiment, the ejection failure region r1 and the alternative ejection region R1 are the same region. Further, in this embodiment, the first alternative ejection information 541 includes information that identifies a defective nozzle among the first nozzle group included in the first ink ejection unit 20a. The information is, for example, the arrangement number of the nozzle in the X direction.

Upon receiving the first alternative ejection information 541, the second control unit 50b of the second image forming apparatus 1b controls the second ink ejection to the alternative ejection area R1 based on the first alternative ejection information 541. The alternative discharge is performed by the section 20b. That is, the second control unit 50b controls the nozzle whose ink ejection position in the X direction corresponds to the defective nozzle of the first ink ejection unit 20a among the second nozzle group included in the second ink ejection unit 20b. Perform alternative discharge. Further, in the present embodiment, the second control unit 50b causes alternative ejection to be performed on the alternative ejection area R1 (that is, the ejection failure area r1) on the same recording medium M in which the ejection failure area r1 has been detected. . Further, from the detection result of the side edge portion of the recording medium M by the medium detection unit 14, the placement position of the recording medium M in the X direction on the conveyance belt 11 of the second conveyance unit 10b is determined from that of the first conveyance unit 10a. When it is detected that the recording medium M is deviated from the placement position in the X direction on the conveyance belt 11, the second conveyance unit 10b moves the nozzle that performs alternative discharge according to the amount of deviation in the placement position. Shift in the X direction accordingly.

FIG. 4B shows an extracted partial image formed in the alternative ejection region R1 by this alternative ejection. On the first surface of the recording medium M, the partial image shown in FIG. 4(b) is formed superimposed on the first image shown in FIG. 4(a), resulting in ejection failure as shown in FIG. A first image is formed in which the images are complemented. After this first image is formed, the recording medium M is turned over by the second reversing unit 40b of the second image forming apparatus 1b, and a second ink is printed on the second side by the second ink ejecting unit 20b. image is formed.

Such alternative discharge is performed when a predetermined alternative discharge execution condition is satisfied when the discharge failure area r1 is detected. That is, the first control unit 50a generates first alternative discharge information 541 when this alternative discharge execution condition is satisfied. Therefore, the second control unit 50b performs alternative discharge based on the first alternative discharge information 541 when the alternative discharge execution condition is satisfied. The alternative discharge execution condition can be set by the user through input operations on the alternative discharge setting screen 621 displayed on the operation display unit 62.

FIG. 5 is a diagram showing the alternative ejection setting screen 621. As shown in FIG.
The alternative discharge setting screen 621 shows alternative discharge execution conditions, and is displayed on the display device of the operation display unit 62. In the alternative discharge setting screen 621, various condition items related to the alternative discharge execution conditions and setting content candidates for each item are displayed. In detail, the condition items displayed are "quality level", "detection color", "detection position", "number of consecutive defective nozzles", "image attribute", and "image resolution". Among these, "detection color", "detection position", and "number of consecutive defective nozzles" are condition items related to the detection result of defective nozzles. The operation button or text box showing the setting content candidates provided for each condition item can be selected or input by the user's touch operation on the touch panel. In other words, the operation display unit 62 can accept an input operation for setting the alternative discharge execution conditions.

"Quality level" is a condition item regarding the quality level of the formed image, and represents the quality of the formed image desired by the user.
If you select "High" for the "quality level" as shown in Figure 5, alternative ejection will be performed even if there is a slight or inconspicuous ejection defect, and a high-quality image will be created in which the ejection defect has been accurately compensated for. is formed.
On the other hand, if "low" is selected, image quality is not prioritized and alternative ejection is not performed. Alternatively, only alternative ejection may be performed for large-area ejection failures or ejection failures at conspicuous positions. "Low" is selected when the quality of the formed image is not important, such as in test printing, for example.
When "Medium" is selected, alternative ejection that is intermediate between "High" and "Low" is performed.

"Detection color" is a condition item related to the color of ink corresponding to the faulty nozzle, and indicates the color for which alternative ejection is performed out of Y, M, C, and K. The ease with which defective ejection is recognized varies depending on the color; for example, defective ejection is easily recognized as a white streak in K (black), but is not noticeable in Y (yellow). For this reason, by omitting substitute ejection of colors that are less noticeable, it is possible to reduce the frequency of substitute ejection while minimizing the impact on quality, thereby increasing productivity. In Figure 5, C, M, and K, in which defective ejection is easily noticeable, are selected as the targets for substitute ejection.

"Detection position" is a condition item related to the position of the detected defective nozzle. In cases where items other than the main image, such as registration marks (trim marks), are printed at the edge of the recording medium, the quality of the image at the edge may not be important. In such cases, as shown in Figure 5, by selecting "center" as the target for alternative ejection, alternative ejection can be omitted when a defective nozzle is detected at the edge.

“Number of consecutive defective nozzles” is a condition item regarding the presence or absence of adjacent defective nozzles and the number of consecutively adjacent defective nozzles. If "1" is selected, alternative discharge will be performed regardless of the adjacency status of defective nozzles, and if "2" is selected, substitution will be performed only if two or more defective nozzles are adjacent. When ejection is performed and "3" is selected, alternative ejection is performed only when three or more defective nozzles are adjacent to each other. Here, "adjacent" means that the ink ejection positions (landing positions) in the X direction on the recording medium M are adjacent, and do not necessarily mean that they are adjacent in the nozzle array of the recording head 211. The greater the number of consecutively adjacent defective nozzles, the more likely it is that ejection defects will be recognized as white stripes. Therefore, by setting this condition item, it is possible to select how many white stripes are allowed.

"Image attribute" is a condition item related to the object attributes of the formed image. The ease with which discharge defects are recognized varies depending on the object attributes of the formed image (here, text, graphics, and image). Here, "text" is an attribute of an image that is mainly composed of characters, "graphics" is an attribute of an image that is mainly composed of figures, and "image" is an attribute of a multi-tone image that is mainly composed of photographs and the like. Of these, discharge defects are easily recognized as white streaks in text and graphics, but discharge defects may not be noticeable in images because multiple colors and gradations are mixed. In this "image attribute" condition item, it is possible to select which object attribute to perform alternative discharge for.

"Image resolution" is a condition item related to the resolution of the formed image. When an image is formed using a high-resolution (e.g., 1200 dpi) image forming device 1 based on low-resolution (e.g., 150 dpi) image data, ink is ejected from multiple nozzles onto an area corresponding to one pixel of the original image data. For this reason, ejection defects may not be noticeable when forming an image with low resolution. Therefore, by specifying the lower limit of the image resolution for alternative ejection in the "image resolution" condition item, it is possible to prevent alternative ejection from being performed for images with a resolution lower than that lower limit.

When an ejection failure is detected, the first control unit 50a determines whether or not the alternative output execution conditions consisting of the above condition items are satisfied, and if the conditions are met, the first alternative ejection is performed. Information 541 is generated.

Next, the control procedure for the image forming process executed by the image forming system 100 will be explained, dividing it into the process performed by the first image forming device 1a and the process performed by the second image forming device 1b.

FIG. 6 is a flowchart showing a control procedure of the image forming process executed by the first image forming apparatus 1a.
This image forming process is executed when a print job and image data 543 are input to the first control unit 50a from an external device via the communication unit 63, for example.

When the image forming process is started, the first control unit 50a causes a first image to be formed on the first side of the recording medium M based on the image data 543 (step S101). Specifically, the first control unit 50a causes the first conveyance unit 10a to convey the recording medium M, and injects the recording medium M from the nozzles of each head unit 21 of the first ink ejection unit 20a at an appropriate timing according to the image data 543. Ink is ejected to form a first image on the first surface.

The first control unit 50a causes the first image reading unit 30a to read the first image formed on the first surface (Step S102). Further, the image data 543 used for image formation in step S101 and the read image data acquired in step S102 are compared to detect ejection failure, and if ejection failure is detected, the defective nozzle is identified. (Step S103).

If a discharge defect is detected ("YES" in step S104), the first control unit 50a determines whether or not a preset alternative discharge execution condition is met (step S105). If it is determined that the alternative discharge execution condition is met ("YES" in step S105), the first control unit 50a generates first alternative discharge information 541 including information identifying the defective nozzle (step S106) and transmits an image formation command (alternative discharge command) for the first surface based on the first alternative discharge information 541 to the second image forming device 1b (step S107).

On the other hand, if no ejection defect is detected in step S104 ("NO" in step S104), or if it is determined in step S105 that the conditions for performing alternative ejection are not met ("NO" in step S105), the first control unit 50a inverts the recording medium M by the first inversion unit 40a (step S108) and sends an image formation command for the second side to the second image forming device 1b (step S109).

When step S107 or step S109 ends, the first control unit 50a causes the second image forming apparatus 1b to send out the recording medium M (step S110).
Here, if steps S106 and S107 are passed, the recording medium M is not turned over, so it is sent to the second image forming apparatus 1b with the first side facing upward. That is, when the first control section 50a generates the first alternative ejection information 541, the first control section 50a causes the first reversing section 40a to send the recording medium M to the second image forming apparatus 1b without reversing it.
Further, if the recording medium M is passed through steps S108 and S109, the recording medium M is reversed, and therefore is sent to the second image forming apparatus 1b with the second side facing upward.
When step S110 ends, the first control unit 50a ends the image forming process on the first image forming apparatus 1a side.

FIG. 7 is a flowchart showing a control procedure of image forming processing executed by the second image forming apparatus 1b.
When the image forming process is started, the second control unit 50b determines whether or not an image forming command has been received from the first image forming apparatus 1a (step S201), and determines whether the image forming command has not been received. If it is determined that (“NO” in step S201), the process of step S201 is executed again. If it is determined that the image forming command has been received (“YES” in step S201), the second control unit 50b determines whether or not the first alternative ejection information 541 has been received (step S202). .

If it is determined that the first alternative ejection information 541 has been received (“YES” in step S202), the second control unit 50b generates a partial image for alternative ejection based on the first alternative ejection information 541. Data 544 is generated (step S203). Here, the partial image data 544 includes a data string corresponding to the defective nozzle specified by the first alternative ejection information 541 among the image data related to the first image formed on the first surface, and This is image data in which pixels other than , have values corresponding to ink non-ejection.

Based on the partial image data 544, the first control unit 50a causes the second ink ejection unit 20b to perform alternative ejection onto the first surface of the recording medium M (step S204). In detail, the second control unit 50b causes the second transport unit 10b to transport the recording medium M, and causes the nozzles of each head unit 21 of the second ink ejection unit 20b to eject ink at an appropriate timing according to the partial image data 544, thereby performing alternative ejection onto the first surface. Here, by using the partial image data 544, ink is ejected only from nozzles whose ink ejection positions correspond to the defective nozzles of the first ink ejection unit 20a. As a result, ink is ejected into the defective ejection area r1 (alternative ejection area R1) where ink was not ejected from the defective nozzles in the first image forming device 1a, to complement it.

When the alternative ejection is completed, the second control unit 50b causes the second reversing unit 40b to reverse the recording medium M, and places the recording medium M on the conveyor belt 11 again (step S205).

When the process of step S205 is completed, or when it is determined that the first alternative ejection information 541 has not been received in the process of step S202 (“NO” in step S202), the second control unit 50b , a second image is formed on the second surface of the recording medium M (step S206).
When the process in step S206 ends, the second control unit 50b ends the image forming process.
The image forming processes shown in FIGS. 6 and 7 are performed in parallel for each color of Y, M, C, and K. The determination as to whether there is an ejection failure in step S104 branches to "YES" if an ejection failure is detected for any one color. As a result, the images of the four colors described above are formed on one recording medium M, and a color image is formed.

FIG. 8 is a diagram showing the image forming process in the image forming process of FIGS. 6 and 7.
The left side of FIG. 8 shows the image forming process on the first side of the recording medium M, and the left side shows the image forming process on the first side.
As shown in the upper part of FIG. 8, in step S101, a first image is formed on the first surface by the first image forming apparatus 1a. Here, a defective ejection region r1 occurs due to a nozzle defect.
As shown in the middle part of FIG. 8, in step S204, the second image forming apparatus 1b performs alternative ejection on the alternative ejection area R1 (ejection failure area r1) on the first surface to compensate for the ejection failure. .
Then, as shown in the lower part of FIG. 8, in step S205, a second image is formed on the second surface by the second image forming apparatus 1b.

(Variation 1-1)
Next, a modified example 1-1 of the first embodiment will be described.
In the first embodiment described above, the first alternative ejection information 541 includes information for identifying the faulty nozzle, and in the second image forming apparatus 1b, partial image data 544 is generated based on the first alternative ejection information 541, and alternative ejection is performed based on the partial image data 544.
In contrast to this, in this modified example, image data identical to the partial image data 544 is directly generated as the first alternative discharge information 541. That is, the first control unit 50a of the first image forming apparatus 1a generates the first alternative discharge information 541, which is image data having the same content as the partial image data 544 in the first embodiment, based on the identified defective nozzle, and transmits it to the second image forming apparatus 1b. The second image forming apparatus 1b performs alternative discharge using the first alternative discharge information 541 as the partial image data.
This method also makes it possible to execute substitute ejection by the second image forming apparatus 1b.

As described above, the image forming system 100 according to the first embodiment includes the first image forming apparatus 1a and the second image forming apparatus 1b. The first image forming apparatus 1a has a first nozzle group, and includes a first ink ejection unit 20a that ejects ink from the first nozzle group onto a recording medium M, a first image reading unit 30a that reads an image formed on the recording medium M by ink ejection by the first ink ejection unit 20a, and a first control unit 50a. The second image forming apparatus 1b has a second nozzle group, and includes a second ink ejection unit 20a that ejects ink from the second nozzle group onto the recording medium M delivered from the first image forming apparatus 1a. The image reading device has a first image reading unit 30a, a second control unit 50b, and when a defective ejection region r1 where ink is not ejected normally due to the inclusion of a defective nozzle in the first nozzle group is detected in an image read by the first image reading unit 30a, the first control unit 50a generates first alternative ejection information 541 for causing the second ink ejection unit 20b to perform alternative ejection of ink onto an alternative ejection region R1 on the recording medium M, the alternative ejection information 541 including an area corresponding to the defective ejection region r1, and the second control unit 50b causes the second ink ejection unit 20b to perform alternative ejection onto the alternative ejection region R1 based on the first alternative ejection information 541.
In this way, by compensating for the ejection failure in the first image forming device 1a with the alternative ejection by the second image forming device 1b, it is possible to more reliably suppress the deterioration of image quality caused by the defective nozzle. That is, in the conventional technology in which alternative ejection was performed by the nozzle adjacent to the defective nozzle, appropriate complementation could not be performed when the nozzle adjacent to the defective nozzle was originally the target for ejecting ink or when the adjacent nozzle was also a defective nozzle, but according to the configuration of this embodiment, it is possible to perform complementary ejection regardless of the status of the nozzle adjacent to the defective nozzle.
This makes it possible to reduce the occurrence of waste paper (waste paper) caused by the formation of images that do not meet a predetermined quality standard.
Furthermore, even if a defective nozzle occurs in the first image forming device 1a, the second image forming device 1b can perform complementary ejection, which reduces the frequency of replacing parts such as the head module 211M and the head unit 21. This reduces the cost of replacing parts and also suppresses the decline in productivity due to part replacement work.

The second control unit 50b also causes the second ink ejection unit 20b to perform alternative ejection onto the alternative ejection area R1 on the recording medium M where the ejection defect area r1 was detected. In this way, by performing alternative ejection onto the very recording medium M where the ejection defect was detected, the occurrence of waste paper can be suppressed.

The first alternative ejection information 541 also includes information identifying the defective nozzles of the first nozzle group, and the second control unit 50b causes alternative ejection to be performed by nozzles of the second nozzle group whose ink ejection positions correspond to the defective nozzles of the first ink ejection unit 20a. This allows alternative ejection to be selectively performed only on the detected defective ejection area r1, making it possible to perform alternative ejection on the recording medium M itself where the ejection defect was detected.

Further, the second control unit 50b causes alternative ejection to be performed when a predetermined alternative ejection execution condition is satisfied. Thereby, alternative ejection can be performed without excess or deficiency, and it is possible to suppress a decrease in productivity due to execution of unnecessary alternative ejection.

Further, the first image forming apparatus 1a has a first reversing section 40a for reversing the front and back sides of the recording medium M, and the first ink ejecting section 20a of the first image forming apparatus 1a is configured to invert the recording medium M. The second ink ejection section 20b of the second image forming apparatus 1b ejects ink onto the first surface, and after the first ink ejection section 20a ejects ink, the first inversion section 40a inverts the front and back sides. When the printed recording medium M is delivered from the first image forming apparatus 1a, ink is ejected onto the second surface opposite to the first surface, and the ink is ejected by the first ink ejecting section 20a. If the recording medium M is delivered from the first image forming apparatus 1a without being reversed by the first reversing unit 40a after ejection, ink is ejected onto the first surface and the first control is performed. When the unit 50a generates the first alternative ejection information 541, the unit 50a causes the first reversing unit 40a to send the recording medium M to the second image forming apparatus 1b without reversing it. According to this, the second image forming apparatus 1b can perform alternative ejection for the ejection failure area r occurring on the first surface without reversing the delivered recording medium M.

The conditions for performing alternative ejection relate to at least part of the quality level of the formed image, the position of the defective nozzle, the color of ink corresponding to the defective nozzle, the presence or absence of adjacent defective nozzles, the object attributes of the formed image, and the resolution of the formed image. This allows the user to flexibly set the conditions for performing alternative ejection according to the quality level desired by the user, the purpose of the image, etc.

The image forming system 100 also includes an operation display unit 62, which functions as an input unit that accepts input operations for setting alternative discharge execution conditions, and as a display unit that displays the alternative discharge execution conditions. This allows the user to easily set the alternative discharge execution conditions.

Further, in the image forming method of the present embodiment, in the image read by the first image reading unit 30a, ink is not ejected normally due to a defective nozzle being included in the first nozzle group. For causing the second ink ejection unit 20b to perform alternative ejection of ink on an alternative ejection area R1 on the recording medium M that includes an area corresponding to the ejection failure area r1 when a defective area r1 is detected. The process includes a step of generating first alternative ejection information 541, and a step of causing the second ink ejection unit 20b to perform alternative ejection on the alternative ejection region R1 based on the first alternative ejection information 541. Thereby, it is possible to more reliably suppress image quality deterioration caused by defective nozzles, and to reduce the occurrence of paper waste. Furthermore, it is possible to reduce the frequency of parts replacement, thereby reducing the cost of replacement parts, and it is also possible to suppress a decrease in productivity due to parts replacement work.

(Second embodiment)
Next, a second embodiment will be described.
In the second embodiment, defective nozzles in the first image forming apparatus 1a and the second image forming apparatus 1b are detected in advance using a predetermined test image, and based on the detection results, the defective nozzles are detected in the first image forming apparatus 1a. This embodiment differs from the first embodiment in that the second image forming apparatus 1b performs alternative ejection for a defective ejection of the other image forming apparatus 1. In the following, differences from the first embodiment will be mainly described, and descriptions of contents common to the first embodiment will be omitted.

In the second embodiment, before normal image formation is performed, an alternative ejection setting process is executed to identify faulty nozzles and set alternative ejection.

FIG. 9 is a flowchart showing a control procedure of the alternative discharge setting process.
In this flow chart, steps S301 to S305 are executed by the first control unit 50a of the first image forming apparatus 1a, and steps S306 to S309 are executed by the second control unit 50b of the second image forming apparatus 1b.

When the alternative ejection setting process is started, the first control unit 50a of the first image forming device 1a forms a test image T on the first surface of the recording medium M based on the image data of a predetermined test image T (step S301).

FIG. 10 is a diagram showing an example of the test image T.
The test image T is an image in which multiple lines L are arranged in a staggered pattern so that they do not overlap one another. Each line L is formed by continuously ejecting ink from one nozzle, and the multiple lines L correspond one-to-one to the multiple nozzles of the head unit 21. Therefore, if a line L is missing or faded, the nozzle corresponding to that line L can be identified as a defective nozzle.
The test image T is not limited to the one shown in FIG. 10, but may be any image that allows confirmation of the ink ejection status from each nozzle.

Returning to FIG. 9, the first control unit 50a causes the first image reading unit 30a to read the test image T, and identifies a defective nozzle in the first ink ejection unit 20a using the method described above based on the reading result. (Step S302).

If a defective nozzle is detected (“YES” in step S303), the first control unit 50a generates first alternative ejection information 541 for causing the second image forming apparatus 1b to perform alternative ejection. (Step S304).

When the processing of step S304 is completed, or when it is determined in step S303 that no defective nozzle has been detected ("NO" in step S303), the first control unit 50a causes the first reversing unit 40a to reverse the recording medium M and send it to the second image forming device 1b (step S305).

When the recording medium M is delivered, the second control unit 50b of the second image forming apparatus 1b causes a test image T to be formed on the second side of the recording medium M based on the image data of the test image T ( Step S306).

The second control unit 50b causes the second image reading unit 30b to read the test image T, and identifies faulty nozzles of the second ink ejection unit 20b based on the results of the reading using the method described above (step S307).

If a defective nozzle is detected (“YES” in step S308), the second control unit 50b generates second alternative ejection information 542 for causing the first image forming apparatus 1a to perform alternative ejection. (Step S309).

When step S309 is completed, or when it is determined in step S308 that no defective nozzle has been detected ("NO" in step S308), the second control unit 50b ends the alternative ejection setting process.
Note that, before step S304, it may be determined whether or not the alternative discharge execution condition is satisfied, and only when the alternative discharge execution condition is satisfied, the first alternative discharge information 541 may be generated in step S304. Also, before step S309, it may be determined whether or not the alternative discharge execution condition is satisfied, and only when the alternative discharge execution condition is satisfied, the second alternative discharge information 542 may be generated in step S309.

The first alternative discharge information 541 and the second alternative discharge information 542 generated in the alternative discharge setting process are shared by the first image forming apparatus 1a and the second image forming apparatus 1b. That is, the first alternative discharge information 541 generated by the first image forming apparatus 1a is transmitted to the second image forming apparatus 1b, and the second alternative discharge information 542 generated by the second image forming apparatus 1b is transmitted to the first image forming apparatus 1a.
The alternative ejection setting process is performed for each of the four colors Y, M, C, and K. Alternatively, a test image T for each of the four colors may be formed on one sheet of recording medium M, and the alternative ejection setting process may be performed in parallel for each of the four colors.

In this manner, in this embodiment, the faulty nozzles of the first image forming apparatus 1a and the second image forming apparatus 1b are identified in advance using the test image T, and first alternative ejection information 541 and second alternative ejection information 542 are generated. Then, in normal image formation, ejection defects caused by faulty nozzles of the first image forming apparatus 1a are complemented by alternative ejection by the second image forming apparatus 1b, and ejection defects caused by faulty nozzles of the second image forming apparatus 1b are complemented by alternative ejection by the first image forming apparatus 1a.
That is, when a defective discharge region r2 is detected in the image formed on the second surface, the second control unit 50b of the second image forming apparatus 1b in this embodiment generates second alternative discharge information 542 for causing the first image forming apparatus 1a to perform alternative discharge, and transmits it to the first image forming apparatus 1a. In detail, the second alternative discharge information 542 is information for causing the first ink discharge unit 20a of the first image forming apparatus 1a to perform alternative discharge of ink onto an alternative discharge region R2 (second alternative discharge region) on the recording medium M that includes a region corresponding to the defective discharge region r2.
In the following description, the combination of "discharge failure region r1, alternative discharge region R1" and the combination of "discharge failure region r2, alternative discharge region R2" will be referred to as "discharge failure region r, alternative discharge region R".

In this embodiment, since the defective nozzle is identified before normal image formation is performed, in addition to performing alternative ejection using the defective ejection region r itself corresponding to the defective nozzle as the alternative ejection region R as in the first embodiment, alternative ejection can also be performed on an alternative ejection region R that includes the defective ejection region r and is wider than the defective ejection region r. Below, an example will be described in which the alternative ejection region R is wider than the defective ejection region r.

FIG. 11 is a diagram for explaining substitute ejection by the second image forming apparatus 1b for compensating for ejection defects of the first image forming apparatus 1a.
FIG. 11 shows alternative ejection for an image of a color among Y, M, C, and K in which an ejection defect has been detected.
11A shows a first image formed by a first image forming apparatus 1a in which a defective nozzle was detected on a first surface of a recording medium M. Here, ink is not discharged into an alternative discharge region R1 including an area corresponding to the discharge defective region r1, and an image is formed in an area excluding the alternative discharge region R1.

The alternative ejection region R1 can be, for example, a region corresponding to a sub-nozzle group G that includes the identified defective nozzle and whose ink ejection positions in the X direction are adjacent to each other, that is, one head module 211M.
In order to perform such control, the first alternative ejection information 541 includes information that identifies the head module 211M that includes the defective nozzle. The first control unit 50a controls the first ink ejection unit 20a to control the nozzles of the head module 211M excluding the head module 211M specified by the first alternative ejection information 541 among the first nozzle group of the head unit 21. The ink is ejected from the ink.

Further, the second control unit 50b of the second image forming apparatus 1b controls the head whose ink ejection position corresponds to the head module 211M specified by the first alternative ejection information 541 among the second ink ejection units 20b. Alternative discharge is performed by module 211M.
FIG. 11B shows a partial image formed in the alternative ejection area R1 by this alternative ejection. On the first surface of the recording medium M, the partial image shown in FIG. 11(b) is formed overlapping the first image shown in FIG. 11(a), resulting in ejection failure as shown in FIG. A first image is formed in which the images are complemented.

FIG. 12 is a diagram illustrating alternative ejection by the first image forming apparatus 1a to compensate for ejection failure in the second image forming apparatus 1b.
In this case as well, the alternative ejection region R2 is a region corresponding to the sub-nozzle group G that includes the identified defective nozzle and whose ink ejection positions in the X direction are adjacent to each other, that is, one head module 211M. . In order to perform such control, the second alternative ejection information 542 includes information that identifies the head module 211M that includes the defective nozzle.

When compensating for poor ejection by the second image forming device 1b with alternative ejection by the first image forming device 1a, the first image forming device 1a performs alternative ejection prior to image formation by the second image forming device 1b. This is because in the image forming system 100, the first image forming device 1a is located upstream of the second image forming device 1b.

That is, as shown in FIG. 12(a), first, the first control unit 50a of the first image forming device 1a causes the head module 211M of the first ink ejection unit 20a, whose ink ejection position corresponds to the head module 211M specified by the second alternative ejection information 542, to perform alternative ejection. As a result, a partial image is formed in the alternative ejection region R2.

Next, the second control unit 50b of the second image forming apparatus 1b performs the following process, as shown in FIG.
The second ink ejection unit 20b ejects ink from the nozzles of the head modules 211M excluding the head module 211M specified by the second alternative ejection information 542 among the second nozzle group of the head unit 21. As a result, a second image is formed in the area excluding the alternative ejection area R2.
A second image as shown in FIG. 12(b) is formed on the second surface of the recording medium M, superimposed on the partial image as shown in FIG. 12(a), thereby forming a second image in which the ejection failure has been compensated for, as shown in FIG. 12(c).

FIG. 13 is a diagram showing a control procedure for image forming processing in the second embodiment.
In the flowchart, steps S401 to S407 and S409 are executed by the first control unit 50a of the first image forming apparatus 1a, and steps S408 and S410 to S413 are executed by the second control unit 50b of the second image forming apparatus 1b. Executed by

When the image formation process is started, the first control unit 50a of the first image forming device 1a determines whether the first alternative discharge information 541 has been generated in the alternative discharge setting process and whether the alternative discharge execution conditions are met (step S401).

If it is determined that the first alternative ejection information 541 has been generated and the alternative ejection execution conditions are satisfied (“YES” in step S401), the first control unit 50a generates the first alternative ejection information. By supplying the image data 543 of the first image to the head modules 211M other than the head module 211M specified in 541, the image data 543 of the first image is 1 image is formed (step S402).

If it is determined that the first alternative ejection information 541 has not been generated or that the alternative ejection execution conditions are not satisfied (“NO” in step S401), the first control unit 50a controls the recording medium M. A first image is formed on the first surface using all head modules 211M (step S403).

When step S402 or S403 ends, the first control unit 50a causes the first reversing unit 40a to reverse the recording medium M (step S404).

The first control unit 50a determines whether the second alternative ejection information 542 has been generated in the alternative ejection setting process and satisfies the alternative ejection execution conditions (step S405). If it is determined that the second alternative ejection information 542 has been generated and the alternative ejection execution conditions are satisfied (“NO” in step S405), the first control unit 50a controls the first transport unit 10a. Among them, by supplying the image data 543 of the second image to the head module 211M corresponding to the head module 211M of the second image forming apparatus 1b specified by the second alternative ejection information 542, recording is performed. Alternative ejection is performed on the alternative ejection region R2 on the second surface of the medium M (step S406).
After that, the first control unit 50a causes the second image forming apparatus 1b to send out the recording medium M (step S407).

When the recording medium M is handed over, the second control unit 50b of the second image forming device 1b supplies image data 543 of the second image to the head modules 211M excluding the head module 211M specified in the second alternative ejection information 542, thereby forming a second image on the area of the second surface of the recording medium M excluding the alternative ejection area R2 (step S408).

On the other hand, if it is determined in step S405 that the second alternative ejection information 542 is not generated or that the alternative ejection execution condition is not satisfied (“NO” in step S405), the first control unit 50a , causes the second image forming apparatus 1b to send out the recording medium M (step S409).

When the recording medium M is delivered, the second control unit 50b of the second image forming apparatus 1b causes a second image to be formed on the second surface of the recording medium M using all the head modules 211M ( Step S410).

When the process of step S408 or S410 is completed, the second control unit 50b determines whether the first alternative ejection information 541 has been generated and the alternative ejection execution conditions are satisfied (step S411). If it is determined that the first alternative ejection information 541 has been generated and the alternative ejection execution conditions are satisfied (“YES” in step S411), the second control unit 50b controls the second inverting unit 40b. The recording medium M is turned over and placed on the conveyor belt 11 again (step S412). Further, the second control unit 50b sends image data 543 of the first image to the head module 211M corresponding to the head module 211M of the first image forming apparatus 1a specified by the first alternative ejection information 541. By supplying this, alternative ejection is performed on the alternative ejection area R1 on the first surface of the recording medium M (step S413).
If the process of step S413 is completed, or if it is determined in step S411 that the first alternative ejection information 541 has not been generated or that the alternative ejection execution condition is not satisfied (“NO” in step S411), The second control unit 50b ends the image forming process.
The image forming process in FIG. 13 is performed in parallel for each color of Y, M, C, and K. As a result, the images of the four colors described above are formed on one recording medium M, and a color image is formed.

FIG. 14 is a diagram showing the image forming process in the image forming process of FIG.
As shown in the first row of FIG. 14, in step S402, the first image is formed on the first surface by the first image forming apparatus 1a in the area excluding the alternative ejection area R1.
As shown in the second row of FIG. 14, in step S406, the first image forming apparatus 1a performs alternative discharge to the alternative discharge region R2 on the second surface.
14, in step S408, the second image is formed on the second surface by the second image forming apparatus 1b in the region excluding the alternative ejection region R2. This completes the second image on the second surface.
14, in step S413, the second image forming apparatus 1b performs alternative discharge on the alternative discharge region R1 on the first surface, thereby completing the first image on the first surface.

As described above, in the image forming system 100 according to the second embodiment, the second image forming apparatus 1b uses a second It has an image reading section 30b. In addition, the first control unit 50a detects an ejection failure in which ink is not ejected normally due to a defective nozzle being included in the first nozzle group in the image read by the first image reading unit 30a. When the area r1 is detected, the second ink ejection unit 20b performs alternative ejection of ink to the alternative ejection area R1 on the recording medium M that includes the area corresponding to the ejection failure area r1. Based on the first alternative ejection information 541, the second control section 50b causes the second ink ejection section 20b to perform alternative ejection on the alternative ejection region R1. Further, the second control unit 50b detects an ejection failure in which ink is not ejected normally due to a defective nozzle being included in the second nozzle group in the image read by the second image reading unit 30b. When the area r2 is detected, the first ink ejection unit 20a performs alternative ejection of ink to the alternative ejection area R2 on the recording medium M that includes the area corresponding to the ejection failure area r2. Based on the second alternative ejection information 542, the first control section 50a causes the first ink ejection section 20a to perform alternative ejection on the alternative ejection region R2. Thereby, an ejection failure occurring in one of the first image forming apparatus 1a and the second image forming apparatus 1b can be compensated for by alternative ejection by the other. Therefore, the occurrence of paper waste can be further reduced. Furthermore, the frequency of replacing parts such as the head module 211M can be further reduced.

The first alternative ejection information 541 includes information for identifying the head module 211M including the defective nozzle, which is a part of the first nozzle group (information for identifying the sub-nozzle group G whose ink ejection positions are adjacent to each other), and in the image formation after the first alternative ejection information 541 is generated, the first control unit 50a causes the first ink ejection unit 20a to eject ink from the sub-nozzle group G of the head module 211M excluding the head module 211M specified by the first alternative ejection information 541 from the first nozzle group, and the second control unit 50b causes the sub-nozzle group G of the head module 211M whose ink ejection position corresponds to the head module 211M specified by the first alternative ejection information 541 from the second nozzle group to perform alternative ejection. As a result, when a defective nozzle is detected in the first image forming device 1a, the second image forming device 1b can perform alternative ejection by using the head module 211M as a unit. Also, even if the defective nozzle cannot be precisely identified, the supplementation by alternative ejection can be appropriately performed.

Further, the second alternative ejection information 542 includes information that specifies the head module 211M that includes a defective nozzle and is part of the second nozzle group (information that specifies the sub nozzle group G whose ink ejection positions are adjacent to each other). ), and in image formation after the second alternative ejection information 542 is generated, the first control unit 50a controls the head module specified by the second alternative ejection information 542 from among the first nozzle group. The second control unit 50b causes the sub nozzle group G of the head module 211M whose ink ejection position corresponds to that of the head module 211M to perform alternative ejection, and the second control unit 50b causes the second ink ejection unit 20b to perform alternative ejection. Ink is ejected from the sub nozzle group G of the head modules 211M excluding the head module 211M specified by the alternative ejection information 542. Thereby, when a defective nozzle is detected in the second image forming apparatus 1b, alternative ejection can be performed by the first image forming apparatus 1a using the head module 211M as a unit. Further, even when a defective nozzle cannot be precisely identified, it is possible to appropriately compensate for the defective nozzle by using alternative ejection.

Further, the first control unit 50a causes alternative ejection to be performed when a predetermined alternative ejection execution condition is satisfied, and the second control unit 50b causes alternative ejection to be performed when a predetermined alternative ejection execution condition is satisfied. Perform alternative discharge. Thereby, alternative ejection can be performed without excess or deficiency, and it is possible to suppress a decrease in productivity due to execution of unnecessary alternative ejection.

When the second alternative ejection information 542 is generated, the first control unit 50a ejects ink onto the first surface of the recording medium M using the first ink ejection unit 20a, then inverts the recording medium M using the first reversal unit 40a, and causes the first ink ejection unit 20a to perform alternative ejection onto the second surface opposite the first surface of the recording medium M. This allows the first image forming device 1a to perform alternative ejection onto the alternative ejection region R2 on the second surface.

In addition, the image forming method of this embodiment includes, when a defective discharge region r1 in which ink is not normally discharged due to the inclusion of a defective nozzle in the first nozzle group is detected in an image read by the first image reading unit 30a, a step of generating first alternative discharge information 541 for causing the second ink discharge unit 20b to perform alternative discharge of ink to an alternative discharge region R1 on the recording medium M, the alternative discharge including an area corresponding to the defective discharge region r1, and a step of causing the second ink discharge unit 20b to perform alternative discharge to the alternative discharge region R1 based on the first alternative discharge information 541. , when a defective discharge area r2 where ink is not normally discharged due to a defective nozzle included in the nozzles of the second ink discharge unit 20b is detected in the second image read by the second image reading unit 30b, the method includes a step of generating second alternative discharge information 542 for causing the first ink discharge unit 20a to perform alternative discharge of ink to the alternative discharge area R2 on the recording medium M, the alternative discharge being included in the area corresponding to the defective discharge area r2, and a step of causing the first ink discharge unit to perform alternative discharge to the alternative discharge area R2 based on the second alternative discharge information 542. As a result, a discharge defect occurring in one of the first image forming device 1a and the second image forming device 1b can be complemented by alternative discharge by the other. Therefore, the occurrence of waste paper can be further reduced. In addition, the frequency of component replacement such as the head module 211M can be further reduced.

(Variation 2-1)
Next, a modified example 2-1 of the second embodiment will be described.
In Figures 13 and 14, when a faulty nozzle is detected in the second image forming device 1b, the first image forming device 1a performs alternative ejection onto the alternative ejection area R2, and then the second image forming device 1b ejects ink onto the remaining area to form a second image, but instead of this, the following method may be used.
That is, when a defective nozzle is detected in the second image forming apparatus 1b, the entire second image is formed on the second surface by the first image forming apparatus 1a. As a result, the defective discharge area r2 included in the alternative discharge area R2 is complemented by the first image forming apparatus 1a. However, when the first image forming apparatus 1a has a defective nozzle and the first alternative discharge information 541 is generated, ink is not discharged to the portion of the second image on the second surface that corresponds to the alternative discharge area R1, so that the second image forming apparatus 1b performs alternative discharge to the alternative discharge area R1.

FIG. 15 is a flowchart showing a control procedure for image forming processing in Modification 2-1.
The flowchart in FIG. 15 corresponds to the flowchart in FIG. 13 in which step S406 is changed to step S406a, step S408 is deleted, and steps S414 to S417 are added. Below, differences from the flowchart of FIG. 13 will be explained.

In step S405, if it is determined that the second alternative discharge information 542 has been generated and that the alternative discharge execution condition is satisfied ("YES" in step S405), the first control unit 50a forms a second image on the second surface of the recording medium M (step S406a). In detail, if it is determined that the first alternative discharge information 541 has been generated in step S401, the first control unit 50a forms a second image on the area of the second surface of the recording medium M excluding the alternative discharge area R1 by supplying image data 543 of the second image to the head modules 211M excluding the head module 211M specified in the first alternative discharge information 541. Also, if it is determined that the first alternative discharge information 541 has not been generated in step S401, the first control unit 50a forms a second image on the second surface of the recording medium M using all the head modules 211M.

When the recording medium M is handed over to the second control unit 50b of the second image forming device 1b, and it is determined in step S411 that the first alternative discharge information 541 has been generated and that the alternative discharge execution conditions are met ("YES" in step S411), the second control unit 50b executes alternative discharge on the alternative discharge region R1 of the second surface of the recording medium M by supplying image data 543 of the second image to the head module 211M corresponding to the head module 211M of the first image forming device 1a specified in the first alternative discharge information 541 (step S414). Thereafter, the second control unit 50b inverts the recording medium M (step S412) and executes alternative discharge on the alternative discharge region R1 of the first surface (step S413).

On the other hand, if it is determined in step S405 that the second alternative ejection information 542 has not been generated or that the alternative ejection execution condition is not satisfied ("NO" in step S405), the same procedure as in FIG. 13 is performed. Processing progresses. That is, the recording medium M is sent to the second image forming apparatus 1b (step S409), and the second image is formed on the entire second surface by the second image forming apparatus 1b (step S410). Further, if the first alternative ejection information 541 has been generated and the alternative ejection execution conditions are satisfied (“YES” in step S415), the front and back sides of the recording medium M are reversed (step S416), and the recording medium The second image forming apparatus 1b performs alternative ejection on the alternative ejection area R1 on the first surface of M (step S417). The processing in steps S415 to S417 is the same as the processing in steps S411 to S413 in FIG.

When the processing of step S413 or step S417 is completed, or when it is determined in steps S411 and S415 that the first alternative discharge information 541 has not been generated or that the alternative discharge execution conditions are not met (steps S411 and S415 are "NO"), the second control unit 50b ends the image formation process.

16 and 17 are diagrams showing the image forming process in the image forming process of FIG. 15.
Of these, FIG. 16 is a diagram showing the image forming process when the branch is "YES" in all steps S401, S405, and S411.
As shown in the first row of FIG. 16, in step S402, the first image forming apparatus 1a forms a first image on the first surface in an area excluding the alternative ejection area R1.
As shown in the second stage of FIG. 16, in step S406a, a second image is formed on the second surface by the first image forming apparatus 1a in an area excluding the alternative ejection area R1. At this time, since ink is ejected to the alternative ejection area R2 (see FIG. 14) on the second surface, the alternative ejection to compensate for the ejection failure of the second image forming apparatus 1b is completed.
As shown in the third row of FIG. 16, in step S414, the second image forming apparatus 1b performs alternative ejection on the alternative ejection area R1 on the second surface. This completes the second image on the second surface.
As shown in the fourth row of FIG. 16, in step S413, the second image forming apparatus 1b performs alternative ejection on the alternative ejection area R1 on the first surface. This completes the first image on the first surface.

FIG. 17 is a diagram showing an image formation process in each of the cases where "YES" is determined in step S401, "NO" is determined in step S405, and "YES" is determined in step S411.
As shown in the first row of FIG. 17, in step S402, the first image is formed on the first surface by the first image forming apparatus 1a in the area excluding the alternative ejection area R1.
As shown in the second row of FIG. 17, in step S410, the second image is formed in its entirety on the second side by the second image forming apparatus 1b.
17, in step S417, the second image forming apparatus 1b performs alternative discharge on the alternative discharge region R1 on the first surface, thereby completing the first image on the first surface.

(Variation 2-2)
Next, a modified example 2-2 of the second embodiment will be described. This modified example may be combined with the modified example 2-1.
In the second embodiment described above, alternative ejection is performed for each head module 211M including a defective nozzle. Alternatively, alternative ejection may be performed for each head unit 21.

In order to perform such alternative ejection, the first alternative ejection information 541 includes information for identifying a head unit 21 having a defective nozzle among the multiple head units 21 possessed by the first ink ejection section 20a of the first image forming apparatus 1a.
Furthermore, in image formation after the first alternative ejection information 541 is generated, the first control unit 50a of the first image forming device 1a causes the first ink ejection unit 20a to eject ink from the remaining head units 21 among the multiple head units 21, excluding the head unit 21 identified by the first alternative ejection information 541, and the second control unit 50b of the second image forming device 1b causes alternative ejection to be performed by a head unit 21 among the multiple head units 21 that ejects ink of the same color as the head unit 21 identified by the first alternative ejection information 541.
As a result, when a defective nozzle is detected in the first image forming device 1a, alternative ejection can be performed by the second image forming device 1b using the head unit 21 as a unit. By using the head unit 21 as a unit, images of the same color are formed by the same image forming device 1, so that deterioration in image quality caused by deviations in the ejection position within an image of the same color can be suppressed.

Similarly, the second alternative ejection information 542 includes information that identifies the head unit 21 having a defective nozzle among the plurality of head units 21 included in the second ink ejection section 20b of the second image forming apparatus 1b.
In addition, in image formation after the second alternative ejection information 542 is generated, the first control unit 50a of the first image forming apparatus 1a uses the second alternative ejection information 542 among the plurality of head units. The first control section 50a of the second image forming apparatus 1b causes the second ink ejection section 20b to perform alternative ejection using a head unit that ejects ink of the same color as the identified head unit. Ink is ejected from the remaining head units excluding the head unit specified by the second alternative ejection information 542.
Thereby, when a defective nozzle is detected in the second image forming apparatus 1b, alternative ejection can be performed by the first image forming apparatus 1a using the head unit 21 as a unit. By using the head unit 21 as a unit, images of the same color are formed by the same image forming apparatus 1, so it is possible to suppress deterioration in image quality due to displacement of ejection positions in images of the same color. Can be done.

(Variation 2-3)
Next, a modified example 2-3 of the second embodiment will be described. This modified example may be combined with the modified example 2-1.
In this modified example, similarly to the first embodiment, ink ejection from the identified defective nozzle is stopped, and alternative ejection is performed by a nozzle in the other image forming apparatus 1 that corresponds to the ink ejection position.

That is, the first alternative ejection information 541 includes information that identifies a defective nozzle in the first nozzle group included in the head unit 21 of the first ink ejection section 20a, and The control section 50b causes alternative ejection to be performed by a nozzle whose ink ejection position corresponds to the defective nozzle of the first ink ejection section 20a among the second nozzle group included in the head unit 21 of the second ink ejection section 20b. .
Further, the second alternative ejection information 542 includes information for specifying a defective nozzle in the second nozzle group included in the head unit 21 of the second ink ejection section 20b, and The control section 50a causes alternative ejection to be performed by a nozzle whose ink ejection position corresponds to the defective nozzle of the second ink ejection section 20b among the first nozzle group included in the head unit 21 of the first ink ejection section 20a. .
Thereby, alternative discharge can be performed using the minimum number of nozzles necessary.

(Modification 2-4)
Next, modification 2-4 of the second embodiment will be described. This modification may be combined with modification 2-1.
In this modification, the same image data as the partial image data 544 for alternative ejection is directly generated as the first alternative ejection information 541 and the second alternative ejection information 542. This modification corresponds to modification 1-1 of the first embodiment.

That is, the first alternative ejection information 541 of this modification is partial image data that includes a portion corresponding to the alternative ejection region R1 of the image data of the image to be formed, and is The control section 50b causes the second ink ejection section 20b to perform alternative ejection by ejecting ink based on the partial image data.
Further, the second alternative ejection information 542 is partial image data including a portion corresponding to the alternative ejection region R2 of the image data of the image to be formed, and is The method causes the first ink ejection unit 20a to eject ink based on the partial image data, thereby performing alternative ejection.
According to this, the data processing process for alternative ejection can be reduced.

The present invention is not limited to the above-described embodiment and each of the modified examples, and various modifications are possible.
For example, in the above embodiment, an example has been described in which a plurality of head modules 211M are arranged in a staggered pattern in the head unit 21, but instead, the recording heads 211 may be arranged in a staggered pattern. In this case, alternative ejection may be performed for each recording head 211.
Furthermore, the head unit 21 may be configured to have a single recording head 211 or a single head module 211M.

In the above embodiment, a nozzle group provided in one head module 211M was exemplified as a "sub-nozzle group," but this is not limited to this. The sub-nozzle group may be a certain number of nozzles including defective nozzles whose ink ejection positions are adjacent to each other, that is, a part of the multiple nozzles that the head module 211M has.

In the above embodiment, an example in which an image is formed on both sides of the recording medium M has been described, but this is not limiting, and an image may be formed on only one side (first side) of the recording medium M. In this case, the alternative ejection is performed only by the second image forming device 1b. In other words, when a defective nozzle is detected in the first image forming device 1a and the first alternative ejection information 541 is generated, after the image is formed on the first side by the first image forming device 1a, the recording medium M is sent to the second image forming device 1b without being inverted by the first inversion unit 40a, and the alternative ejection on the first side by the second image forming device 1b is performed.

Further, in the above embodiment, the content of the alternative ejection execution condition is explained using an example in which the user sets the content, but the content is not limited to this, and whether or not to execute alternative ejection based on the fixed alternative ejection execution condition is explained. A judgment may be made.

Further, in the above embodiment, alternative ejection is performed only when the alternative ejection execution conditions are met, but the invention is not limited to this, and alternative ejection may be performed whenever an ejection failure is detected.

Further, in the embodiment described above, the recording medium M is conveyed by the conveying section 10 including the conveying belt 11, but the present invention is not limited thereto. The recording medium M may be held and conveyed on a surface.

Although several embodiments of the present invention have been described, the scope of the present invention is not limited to the above-described embodiments, but includes the scope of the invention described in the claims and its equivalents.

1a First image forming apparatus 1b Second image forming apparatus 2 Paper feed section 3 Paper discharge section 10a First transport section 10b Second transport section 11 Transport belt 12 Transport roller 13 Transport drive section 14 Medium detection section 15 Rotary encoder 20a First ink ejection section 20b Second ink ejection section 21, 21Y, 21M, 21C, 21K Head unit 21a Support plate 211 Recording head 211M Head module 212 Recording head drive section 30a First image reading section 30b Second image reading section 40a First reversing section 40b Second reversing section 41 Roller pair 42 Reversing path 43 Return path 44 Roller drive section 50a First control section 50b Second control section 51 CPU
52 RAM
53 ROM
54 Storage unit 541 First alternative discharge information 542 Second alternative discharge information 543 Image data 544 Partial image data 61 Image processing unit 62 Operation display unit (input unit, display unit)
621 Alternative discharge setting screen 63 Communication unit 64 Bus 100 Image forming system G Sub-nozzle group M Recording medium N Nozzle R1 Alternative discharge area (first alternative discharge area)
R2 Alternative discharge area (second alternative discharge area)
r1 ejection failure area (first ejection failure area)
r2 ejection failure area (second ejection failure area)
T Test Image

Claims (19)

An image forming system comprising a first image forming device and a second image forming device,
The first image forming apparatus includes:
a first ink ejection unit having a first nozzle group and ejecting ink from the first nozzle group onto a recording medium;
a first image reading section that reads an image formed on a recording medium by ink ejection by the first ink ejection section;
a first control unit;
has
The second image forming apparatus includes:
a second ink ejection unit having a second nozzle group and ejecting ink from the second nozzle group onto a recording medium delivered from the first image forming apparatus;
a second control unit;
has
The first control unit is configured to detect, in the image read by the first image reading unit, that ink is not being ejected normally due to a defective nozzle being included in the first nozzle group. When an ejection failure area is detected, alternative ejection of ink by the second ink ejection unit to a first alternative ejection area including an area corresponding to the first ejection failure area on the recording medium is performed. generating first alternative ejection information for causing the ejection to occur;
In the image forming system, the second control section causes the second ink ejection section to perform the alternative ejection on the first alternative ejection area based on the first alternative ejection information. The second control unit causes the second ink ejection unit to perform the alternative ejection on the first alternative ejection area on the recording medium where the first ejection failure area has been detected. Item 1. The image forming system according to item 1. the first alternative ejection information includes information for identifying the defective nozzle of the first nozzle group,
3 . The image forming system according to claim 1 , wherein the second control unit causes a nozzle of the second nozzle group, the nozzle having an ink ejection position corresponding to the defective nozzle of the first ink ejection unit, to perform the substitute ejection. the first alternative ejection information includes information for identifying a sub-nozzle group that is made up of a portion of the first nozzle group, includes the defective nozzle, and has ink ejection positions adjacent to each other;
In the image formation after the first alternative ejection information is generated,
the first control unit causes the first ink ejection unit to eject ink from nozzles of the first nozzle group excluding the sub-nozzle group specified by the first alternative ejection information;
2. The image forming system according to claim 1, wherein the second control unit causes the alternative ejection to be performed by a sub-nozzle group among the second nozzle group, the sub-nozzle group having an ink ejection position corresponding to the sub-nozzle group identified by the first alternative ejection information. The first ink ejection unit includes a plurality of first head units that eject ink of mutually different colors from nozzles,
The second ink ejection unit includes a plurality of second head units each ejecting ink of the same color as each of the plurality of first head units from a nozzle,
The first alternative ejection information includes information that identifies a head unit having the defective nozzle among the plurality of first head units,
In image formation after the first alternative ejection information is generated,
The first control unit causes the first ink ejection unit to eject ink from the remaining head units among the plurality of first head units except for the head unit specified by the first alternative ejection information. to discharge,
The second control unit performs the alternative ejection with a head unit that ejects ink of the same color as the head unit specified by the first alternative ejection information, among the plurality of second head units. The image forming system according to claim 1. The first alternative discharge information is partial image data including a portion of image data of an image to be formed that corresponds to the first alternative discharge region,
3 . The image forming system according to claim 1 , wherein the second control unit causes the second ink ejection unit to eject ink based on the partial image data, thereby performing the substitute ejection. The image forming system according to any one of claims 1 to 6, wherein the second control unit performs the alternative ejection when a predetermined alternative ejection execution condition is satisfied. The first image forming apparatus has a reversing unit that reverses the front and back of the recording medium,
The first ink ejection unit of the first image forming apparatus ejects ink onto a first surface of a recording medium,
The second ink ejection section of the second image forming apparatus receives the recording medium from the first image forming apparatus, which has been reversed by the reversing section after ink is ejected by the first ink ejection section. In this case, ink is ejected onto a second surface opposite to the first surface, and recording is performed without being reversed by the reversing section after ink is ejected by the first ink ejecting section. When the medium is delivered from the first image forming apparatus, ejecting ink onto the first surface;
Any one of claims 1 to 7, wherein the first control unit causes the reversing unit to send the recording medium to the second image forming apparatus without reversing the recording medium when the first alternative ejection information is generated. The image forming system according to item (1). the second image forming device has a second image reading unit that reads an image formed on a recording medium by ink ejection from the second ink ejection unit,
the second control unit generates second alternative ejection information for causing the first ink ejection unit to alternatively eject ink onto a second alternative ejection area on a recording medium, the second alternative ejection area including an area corresponding to the second defective ejection area, when a second defective ejection area in which ink is not ejected normally due to a defective nozzle being included in the second nozzle group is detected in the image read by the second image reading unit;
The image forming system according to claim 1 , wherein the first control unit causes the first ink ejection unit to perform the alternative ejection on the second alternative ejection region based on the second alternative ejection information. the second alternative ejection information includes information for identifying the defective nozzle of the second nozzle group,
10. The image forming system according to claim 9, wherein the first control unit causes the substitute ejection to be performed by a nozzle of the first nozzle group that has an ink ejection position corresponding to the defective nozzle of the second ink ejection unit. the second alternative ejection information includes information for identifying a sub-nozzle group that is made up of a portion of the second nozzle group, includes the defective nozzle, and has ink ejection positions adjacent to each other;
In the image formation after the second alternative ejection information is generated,
the first control unit causes the alternative ejection to be performed by a sub-nozzle group among the first nozzle group, the sub-nozzle group having an ink ejection position corresponding to the sub-nozzle group specified by the second alternative ejection information;
10. The image forming system of claim 9, wherein the second control unit causes the second ink ejection unit to eject ink from nozzles of the second nozzle group excluding the sub-nozzle group identified by the second alternative ejection information. the first ink ejection unit has a plurality of first head units that eject inks of different colors from nozzles;
the second ink ejection unit has a plurality of second head units that eject ink of the same color as each of the plurality of first head units from nozzles,
the second alternative ejection information includes information for identifying a head unit having the defective nozzle among the plurality of second head units,
In the image formation after the second alternative ejection information is generated,
the first control unit causes a head unit among the plurality of first head units that ejects ink of the same color as the head unit specified by the second alternative ejection information to perform the alternative ejection;
The image forming system according to claim 9, wherein the second control unit causes the second ink ejection unit to eject ink from the remaining head units among the plurality of second head units, excluding the head unit identified by the second alternative ejection information. The second alternative ejection information is partial image data that includes a portion of the image data of the image to be formed that corresponds to the second alternative ejection area,
The image forming system according to claim 9, wherein the first control section causes the first ink ejection section to eject ink based on the partial image data to perform the alternative ejection. The image forming system according to any one of claims 9 to 13, wherein the first control unit causes the alternative ejection to be performed when a predetermined alternative ejection execution condition is satisfied. the first image forming apparatus has a reversing unit that reverses a recording medium;
the first ink ejection unit of the first image forming device ejects ink onto a first surface of a recording medium;
An image forming system as described in any one of claims 9 to 14, wherein when the second alternative ejection information is generated, the first control unit ejects ink onto the first surface of the recording medium using the first ink ejection unit, then inverts the recording medium using the inversion unit, and causes the first ink ejection unit to perform the alternative ejection onto a second surface of the recording medium that is opposite the first surface. The alternative ejection execution condition includes at least one of the quality level of the formed image, the position of the defective nozzle, the color of ink corresponding to the defective nozzle, the presence or absence of an adjacent defective nozzle, the object attribute of the formed image, and the resolution of the formed image. The image forming system according to claim 7 or 14, wherein the image forming system relates to a section. an input unit that accepts an input operation for setting the alternative discharge execution condition;
A display unit that displays the alternative discharge execution condition;
The imaging system of claim 7, 14, or 16, comprising: a first image forming apparatus including a first ink ejection unit having a first nozzle group and ejecting ink from the first nozzle group onto a recording medium, and a first image reading unit reading an image formed on the recording medium by the ink ejection from the first ink ejection unit;
a second image forming apparatus having a second nozzle group, the second image forming apparatus having a second ink ejection unit that ejects ink from the second nozzle group onto a recording medium delivered from the first image forming apparatus,
a step of generating first alternative ejection information for causing the second ink ejection unit to alternatively eject ink onto a first alternative ejection area on a recording medium, the first alternative ejection area including an area corresponding to the first defective ejection area, when a first defective ejection area in which ink is not ejected normally due to a defective nozzle being included in the first nozzle group is detected in the image read by the first image reading unit;
performing the alternative ejection by the second ink ejection unit on the first alternative ejection region based on the first alternative ejection information;
An image forming method comprising the steps of: the second image forming device has a second image reading unit that reads an image formed on a recording medium by ink ejection from the second ink ejection unit,
The image forming method includes:
a step of generating second alternative ejection information for causing the first ink ejection unit to alternatively eject ink onto a second alternative ejection area on a recording medium, the second alternative ejection area including an area corresponding to the second defective ejection area, when a second defective ejection area in which ink is not normally ejected due to a defective nozzle being included in the nozzles of the second ink ejection unit is detected in the image read by the second image reading unit;
causing the first ink ejection unit to perform the alternative ejection onto the second alternative ejection region based on the second alternative ejection information;
The imaging method of claim 18, comprising:

Images