Image forming apparatus, image forming method, and image forming program

Abstract

To provide an image forming apparatus, an image forming method, and an image forming program capable of easily reducing deviation of an operation amount in a plurality of recording elements.SOLUTION: An image forming apparatus includes a sheet conveying device 4, an image forming part 5, a sheet shift part 9, and a shift processing part. The sheet conveying device 4 conveys the sheet Sh1 along a conveyance path. The image forming unit 5 forms an image on the sheet Sh1 by ejecting ink onto the sheet D1 with a plurality of recording heads 51 aligned on the sheet D2 in the widthwise direction orthogonal to the conveying direction Sh1 of the sheet Sh1. The sheet shift unit 9 changes the position of the width-direction D1 of the sheet Sh1 on the upstream side of the conveyance-direction D2 with respect to the image forming unit 5. The shift processing unit controls the sheet shift unit 9 in accordance with the operation status of the plurality of printheads 51.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, an image forming method, and an image forming program. [Background technology]

[0002] As a related art, there is known an image forming apparatus (inkjet recording apparatus) equipped with a line head as inkjet recording means having a length sufficient to cover the entire width of a sheet (recording material) (see, for example, Patent Document 1). In the image forming apparatus according to the related art, a plurality of recording elements (discharge ports) are formed in a predetermined arrangement on the discharge port surface of the line head. The image forming apparatus forms an image on a sheet by discharging ink from the plurality of recording elements of the line head.

[0003] In the image forming apparatus according to the related art, the sheet setting position (setting position) is determined from the image formation history and the setting position is displayed. Therefore, by appropriately changing the sheet setting position, the user can prevent the operation amount of some of the multiple recording elements from becoming excessively large. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-334935 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the configuration of the above-mentioned related technology, the user needs to intentionally change the setting position of the sheet, and depending on the usage environment of the image forming device, such as if the user does not change the setting position of the sheet, the operation amount of some of the multiple recording elements may become extremely high.

[0006] An object of the present invention is to provide an image forming apparatus, an image forming method, and an image forming program that can easily reduce bias in the amount of operation among a plurality of recording elements. [Means for solving the problem]

[0007] According to one aspect of the present invention, an image forming apparatus includes a sheet conveying device, an image forming unit, a sheet shifting unit, and a shifting processing unit. The sheet conveying device conveys a sheet along a conveying path. The image forming unit forms an image on the sheet by ejecting ink onto the surface of the sheet using a plurality of recording elements arranged in a width direction perpendicular to the conveying direction of the sheet. The sheet shifting unit changes the position of the sheet in the width direction upstream of the image forming unit in the conveying direction. The shifting processing unit controls the sheet shifting unit depending on the operating status of the plurality of recording elements.

[0008] An image forming method according to another aspect of the present invention is used in an image forming apparatus including a sheet conveying device, an image forming unit, and a sheet shifting unit. The sheet conveying device conveys a sheet along a conveying path. The image forming unit forms an image on the sheet by ejecting ink onto the surface of the sheet using a plurality of recording elements arranged in a width direction perpendicular to the conveying direction of the sheet. The sheet shifting unit changes the position of the sheet in the width direction upstream of the image forming unit in the conveying direction. The image forming method includes controlling the sheet shifting unit in accordance with the operating status of the plurality of recording elements.

[0009] An image forming program according to another aspect of the present invention is used in an image forming apparatus including a sheet conveying device, an image forming unit, and a sheet shifting unit. The sheet conveying device conveys a sheet along a conveying path. The image forming unit forms an image on the sheet by ejecting ink onto the surface of the sheet using a plurality of recording elements arranged in a width direction perpendicular to the conveying direction of the sheet. The sheet shifting unit changes the position of the sheet in the width direction upstream of the image forming unit in the conveying direction. The image forming program is a program for causing one or more processors to control the sheet shifting unit in accordance with the operating status of the plurality of recording elements. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an image forming apparatus, an image forming method, and an image forming program that can easily reduce bias in the amount of operation among a plurality of recording elements. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an image forming system according to the first embodiment. [Figure 2] FIG. 2 is a block diagram showing the configuration of the image forming apparatus according to the first embodiment. [Figure 3] FIG. 3 is a schematic diagram showing the configuration of the image forming unit of the image forming apparatus according to the first embodiment. [Figure 4] FIG. 4 is a schematic diagram illustrating an example of the configuration of the sheet shifting unit in the image forming apparatus according to the first embodiment. [Figure 5] FIG. 5 is a schematic diagram illustrating an example of the configuration of the sheet shifting unit in the image forming apparatus according to the first embodiment. [Figure 6] FIG. 6 is a flowchart illustrating an example of the operation of the shift processing unit in the image forming apparatus according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description will discuss preferred embodiments of the present invention with reference to the accompanying drawings. The preferred embodiments are merely examples of the present invention and are not intended to limit the technical scope of the present invention.

[0013] (Embodiment 1) [1] Overall configuration of image forming device First, the overall configuration of an image forming apparatus 10 according to this embodiment will be described with reference to FIGS.

[0014] In this embodiment, as an example, the image forming apparatus 10 is an inkjet recording apparatus (printer) that has a recording head 51 that ejects ink onto the surface of a sheet Sh1 and is capable of performing a print process using an inkjet method in which an image is formed on the sheet Sh1 by the recording head 51. The print process is a process in which an image is formed on an image forming target. The sheet Sh1 is an example of an image forming target (recording medium) on which an image is formed by the image forming apparatus 10, and is a sheet-like medium such as paper or a resin film.

[0015] The image forming apparatus 10 may be a multifunction machine having multiple functions such as a print function, a scanning function for reading image data from a document, a facsimile function, and a copy function, as long as it has the function of forming an image by inkjet printing. The image forming apparatus 10 may also be a facsimile machine or a copy machine.

[0016] As shown in FIG. 1 , the image forming apparatus 10, together with the sheet feeding device 11, the drying device 12, and the discharge device 13, constitutes an image forming system 100. In other words, the image forming system 100 according to this embodiment includes the image forming apparatus 10, the sheet feeding device 11, the drying device 12, and the discharge device 13. Here, the image forming apparatus 10, the sheet feeding device 11, the drying device 12, and the discharge device 13 are connected in this order from upstream to downstream in the conveyance direction of the sheet Sh1. This allows the image forming system 100 to continuously perform a series of processes on the sheet Sh1, which are performed by the sheet feeding device 11, the image forming apparatus 10, the drying device 12, and the discharge device 13. Furthermore, each device in the image forming system 100 is centrally managed by a control device 7 of the image forming apparatus 10. However, this configuration is not limiting, and a control device that centrally manages each device may be provided separately from the control device 7.

[0017] The paper feeder 11 can accommodate a plurality of sheets Sh1. The paper feeder 11 supplies the sheets Sh1 one by one to the image forming apparatus 10. The image forming apparatus 10 ejects ink from the recording head 51 onto the sheets Sh1 supplied from the paper feeder 11, forming an image (ink image) by an inkjet method. The image forming apparatus 10 sends the sheets Sh1 on which the images have been formed to a drying device 12 in the downstream stage.

[0018] The drying device 12 has a drying chamber therein, which is equipped with a heater or a heat pump type heating unit or the like. The drying device 12 dries the ink image formed on the sheet Sh1 by heating the surface of the sheet Sh1 conveyed into the drying chamber from the image forming apparatus 10. The drying device 12 has an exhaust fan that exhausts (discharges) moisture from the drying chamber. The drying device 12 sends the dried sheet Sh1 to the discharge device 13 at the downstream stage. As a result, the sheet Sh1 on which the image has been formed by the inkjet method in the image forming apparatus 10 is discharged to the discharge device 13.

[0019] The discharge device 13 stocks the sheet Sh1 conveyed from the drying device 12. The discharge device 13 may also have a post-processing function such as a staple function or a punch function. In this case, the discharge device 13 can perform appropriate post-processing on the sheet Sh1 on which an image has been formed. In single-sided printing, in which an image is formed on only one side of the sheet Sh1, the sheet Sh1 is dried in the drying device 12 and sent to the discharge device 13. In double-sided printing, in which images are formed on both sides of the sheet Sh1, the sheet Sh1 is dried in the drying device 12 and then returned to the image forming device 10. An image is then formed on the back side of the sheet Sh1 in the image forming device 10, and the sheet Sh1 is dried in the drying device 12 and then sent to the discharge device 13.

[0020] 1 and 2, the image forming apparatus 10 includes a sheet conveying device 4, an image forming unit 5, an ink supply unit 6, a control device 7, an image reading unit 8, a sheet shifting unit 9, etc. The image forming unit 5 has a plurality of recording heads 51. The sheet conveying device 4, the image forming unit 5, the ink supply unit 6, the control device 7, the image reading unit 8, the sheet shifting unit 9, etc. are housed in a housing 21 that forms the outer shell of the image forming apparatus 10.

[0021] The sheet conveying device 4 conveys the sheets Sh1 supplied from the paper feeder 11 one by one through the conveying path 40. As a result, the sheet Sh1 taken into the housing 21 of the image forming apparatus 10 from the paper feeder 11 is conveyed through the conveying path 40 in the conveying direction D1 below the image forming unit 5 and discharged to the drying device 12. The conveying path 40 is a path for conveying the sheet Sh1 within the housing 21 and includes a front-stage conveying path 401 on the upstream side with respect to the image forming unit 5 and a rear-stage conveying path 402 on the downstream side. The sheet conveying device 4 conveys the sheet Sh1 supplied from the paper feeder 11 through the front-stage conveying path 401 to the image forming unit 5 and discharges the sheet Sh1 from the image forming unit 5 to the drying device 12 through the rear-stage conveying path 402.

[0022] The sheet transport device 4 includes a sheet sending section 41, a correction unit 42, a main transport unit 43, and a discharge roller pair 44. The sheet sending section 41 sends out the sheets Sh1 supplied from the paper feed device 11 to the front-stage transport path 401 one by one.

[0023] The correction unit 42 takes over the conveyance of the sheet Sh1 from the sheet sending unit 41 and conveys the sheet Sh1 toward the main conveyance unit 43. The correction unit 42 corrects the tilt (inclination) of the sheet Sh1 with respect to the conveyance direction D1. That is, if the sheet Sh1 is sent to the image forming unit 5 in an inclined state, an inclination (inclination) of the scanning line called skew occurs in the image formed on the sheet Sh1 by the image forming unit 5. Therefore, the sheet conveying device 4 corrects the tilt of the sheet Sh1 using the correction unit 42, thereby avoiding such an inclination (skew) of the image.

[0024] A mechanical registration mechanism is known as an example of a means for correcting the skew of the sheet Sh1. The correction unit 42, which is made up of the mechanical registration mechanism, performs skew correction (skew correction) to correct the skew of the sheet Sh1 being conveyed, using a pair of registration rollers 421 (see FIG. 4) arranged upstream of the image forming unit 5 on the conveyance path 40.

[0025] Specifically, the correction unit 42, which is made up of a mechanical registration mechanism, corrects the skew of the sheet Sh1 by causing the leading edge of the sheet Sh1 being conveyed through the conveyance path 40 to collide with the nip portion of the registration rollers 421, which are in a stopped state. After the posture of the sheet Sh1 has been adjusted in this way (the skew has been corrected), the correction unit 42 rotates the registration rollers 421 to correct the skew of the sheet Sh1 being conveyed.

[0026] The main transport unit 43 is disposed below the image forming unit 5. The upstream transport path 401 is a path that runs from the paper feeder 11 to below the image forming unit 5 (above the main transport unit 43). The main transport unit 43 transports the sheet Sh1 while aligning the first side (front side) of the sheet Sh1 with the image forming unit 5. The first side of the sheet Sh1 is the side on which an ink image is formed. The main transport unit 43 has a plurality of tension rollers 431 and a main transport belt 432, and the plurality of tension rollers 431 support and rotate the main transport belt 432. As a result, the main transport unit 43 places the sheet Sh1 on the main transport belt 432 and transports it toward the discharge roller pair 44.

[0027] The discharge roller pair 44 discharges the sheet Sh1 on which the ink image is formed to the drying device 12. The subsequent transport path 402 is a path that leads from below the image forming section 5 (above the main transport unit 43) to the drying device 12.

[0028] The image forming unit 5 is located above the main conveying unit 43. The image forming unit 5 ejects inks of multiple colors toward the sheet Sh1 conveyed by the main conveying unit 43 of the sheet conveying device 4, thereby forming an ink image on the first surface of the sheet Sh1.

[0029] The image forming unit 5 includes a plurality of recording heads 51 and a head frame 52 that supports the plurality of recording heads 51. The plurality of recording heads 51 form an image on the sheet Sh1 by ejecting ink of a plurality of colors onto the sheet Sh1 being transported by the main transport unit 43.

[0030] In the example of FIG. 1, the multiple recording heads 51 are divided into four line heads 50 corresponding to inks of black, cyan, magenta, and yellow, respectively. The ink supply unit 6 supplies each color ink (K, C, M, Y) to the recording head 51 of the corresponding line head 50. The four line heads 50 are arranged side by side in the sub-scanning direction D11 and are fixed in a predetermined positional relationship (see FIG. 3). The number of line heads 50 provided in the image forming unit 5 is not limited to four, and may be, for example, two, three, five or more. The sub-scanning direction D11 is the same as the transport direction D1 of the sheet Sh1 on the main transport belt 432.

[0031] The multiple recording heads 51 are arranged at positions where a gap of about 1 millimeter is formed between the ink ejection surface provided on the lower surface of each head and the upper surface of the sheet Sh1 on the main transport belt 432. As shown in FIG. 3, the multiple recording heads 51 are arranged with their respective longitudinal directions aligned with the main scanning direction D12. In the present embodiment, as an example, each line head 50 for each color includes three recording heads 51. The ink ejection surface of each recording head 51 is formed with multiple ink nozzles 53 that eject ink onto the sheet Sh1 transported along the transport path 40. Each recording head 51 has multiple piezoelectric elements corresponding to the multiple ink nozzles 53. When a drive signal is supplied from the control device 7, each piezoelectric element vibrates, thereby pressurizing the ink and causing it to be ejected (squirted) from each ink nozzle 53.

[0032] The image reading unit 8 reads the image on the sheet Sh1. The image reading unit 8 reads the image from the sheet Sh1 and outputs image data corresponding to the read image to the control device 7. The image reading unit 8 includes a light source, multiple mirrors, an optical lens, a CCD (Charge Coupled Device), and the like.

[0033] In this embodiment, the image reading unit 8 is located above the subsequent conveying path 402. The image reading unit 8 is disposed downstream of the image forming unit 5 in the conveying direction D1 of the sheet Sh1 by the sheet conveying device 4. This allows the image reading unit 8 to read, downstream, an image formed on the sheet Sh1 by the image forming unit 5. In other words, while the sheet Sh1 is being conveyed by the sheet conveying device 4, it is possible to both form an image on the sheet Sh1 and read the image.

[0034] The sheet shifting unit 9 is disposed on the upstream side (toward the paper feeder 11) of the image forming unit 5 in the conveying path 40 in the conveying direction D1. The sheet shifting unit 9 changes the position of the sheet Sh1 in the width direction D2 (see FIG. 4). The width direction D2 is a direction perpendicular to the conveying direction D1 in a plan view (i.e., in a plane along the surface of the sheet Sh1). In this embodiment, the conveying direction D1 is the same as the sub-scanning direction D11, and the width direction D2 perpendicular to the conveying direction D1 is the same as the main scanning direction D12.

[0035] In this embodiment, the sheet shift unit 9 is disposed between the sheet sending unit 41 and the main transport unit 43, and changes the position in the width direction D2 of the sheet Sh1 transported on the upstream transport path 401. The sheet shift unit 9 can move the sheet Sh1 by a desired shift amount toward the front F (see FIG. 4) side in the width direction D2 or the rear R (see FIG. 4) side in the width direction D2. This allows the position of the sheet Sh1 in the width direction D2 to be adjusted by the sheet transport device 4 while the sheet Sh1 is being transported, and the image forming unit 5 forms an image on the sheet Sh1 after the position in the width direction D2 has been adjusted by the sheet shift unit 9.

[0036] In the present embodiment, as an example, the sheet shifting unit 9 moves the correction unit 42 in the width direction D2, thereby moving the sheet Sh1 held by the correction unit 42 in the width direction D2 together with the correction unit 42. The configuration of the sheet shifting unit 9 will be described in detail in the section "[2] Details of the sheet shifting unit."

[0037] The control device 7 performs overall control of the image forming apparatus 10. The control device 7 is primarily composed of a computer system having one or more processors and one or more non-volatile memories. In the image forming apparatus 10, the functions of the control device 7 are realized by the one or more processors executing programs. The programs may be pre-recorded in memory (storage unit), provided via a telecommunications line such as the Internet, or provided by being recorded on a non-transitory recording medium readable by a computer system, such as a memory card or optical disk. The one or more processors are composed of one or more electronic circuits including semiconductor integrated circuits. Furthermore, the computer system referred to here includes a microcontroller having one or more processors and one or more memories.

[0038] The control device 7 controls the sheet conveying device 4, image forming unit 5, ink supply unit 6, image reading unit 8, sheet shift unit 9, etc. included in the image forming apparatus 10. In other words, the control device 7 is electrically connected to each unit of the image forming apparatus 10, and can, for example, control the image forming unit 5 to form a desired image on the sheet Sh1, or control the sheet shift unit 9 to move the sheet Sh1 in the width direction D2. In other words, the control device 7 implements an image forming method that controls each unit of the image forming apparatus 10 by executing an image formation program recorded in memory.

[0039] In this embodiment, the control device 7 has at least the function of a shift processing unit 71, as shown in Fig. 2. The shift processing unit 71 controls the sheet shifting unit 9. In this embodiment, the shift processing unit 71 particularly controls the sheet shifting unit 9 in accordance with the operating status of the multiple recording heads 51 in the image forming unit 5. The shift processing unit 71 may be provided separately from the main control device 7 that controls the image forming apparatus 10 in an integrated manner.

[0040] The image forming apparatus 10 also includes a head cooling device, a maintenance unit, a cap unit, an operation display unit, and the like. The head cooling device cools the recording head 51. The maintenance unit performs a wiping operation to wipe the ink ejection surface (the lower surface of the recording head 51) and clean the ink ejection surface. The cap unit covers the ink ejection surface of the recording head 51 to protect it from drying out. The operation display unit is a user interface in the inkjet recording apparatus. The operation display unit has a display unit such as an LCD display that displays various information in response to control instructions from the control device 7, and an operation unit such as a switch or touch panel that inputs various information to the control device in response to user operations.

[0041] As a related art, an image forming apparatus (inkjet recording apparatus) equipped with a line head as inkjet recording means having a length sufficient to cover the entire width of a sheet (recording material) is known. In the image forming apparatus according to the related art, a plurality of recording elements (discharge ports) are formed in a predetermined arrangement on the discharge port surface of the line head. The image forming apparatus forms an image on a sheet by discharging ink from the plurality of recording elements of the line head.

[0042] In the image forming apparatus according to the related art, the sheet setting position (setting position) is determined from the image formation history and the setting position is displayed. Therefore, by appropriately changing the sheet setting position, the user can prevent the operation amount of some of the multiple recording elements from becoming excessively large.

[0043] However, in the configuration of the above-mentioned related technology, the user needs to intentionally change the setting position of the sheet, and depending on the usage environment of the image forming device, such as if the user does not change the setting position of the sheet, the operation amount of some of the multiple recording elements may become extremely high.

[0044] In contrast to this, in this embodiment, the configuration described below makes it possible to realize an image forming apparatus 10 that can easily reduce bias in the amount of operation among a plurality of recording elements.

[0045] That is, as described above, the image forming apparatus 10 according to this embodiment includes the sheet conveying device 4, the image forming unit 5, the sheet shifting unit 9, and the shift processing unit 71. The sheet conveying device 4 conveys the sheet Sh1 along the conveying path 40. The image forming unit 5 forms an image on the sheet Sh1 by ejecting ink onto the surface of the sheet Sh1 using a plurality of recording elements aligned in a width direction D2 perpendicular to the conveying direction D1 of the sheet Sh1. The sheet shifting unit 9 changes the position of the sheet Sh1 in the width direction D2, upstream of the image forming unit 5 in the conveying direction D1. The shifting processing unit 71 controls the sheet shifting unit 9 depending on the operating status of the plurality of recording elements.

[0046] In this embodiment, the recording head 51 is an example of a recording element. That is, in this embodiment, the line head 50 of each color of the image forming unit 5 includes three recording heads 51 as described above. These three recording heads 51 are arranged side by side in the main scanning direction D12 (width direction D2) in a manner that they partially overlap. That is, the image forming unit 5 has recording heads 51 as three recording elements arranged side by side in the width direction D2.

[0047] According to the above-described configuration, the sheet shift unit 9 can change the position of the sheet Sh1 in the width direction D2 upstream of the image forming unit 5 in the conveying direction D1. Therefore, in the image forming unit 5, which of the multiple recording elements (the recording heads 51 in this embodiment) arranged in the width direction D2 is to be used preferentially (focusedly) can be changed depending on the position of the sheet Sh1 in the width direction D2. Moreover, the sheet shift unit 9 is controlled by the shift processing unit 71 according to the operating conditions of the multiple recording elements. Therefore, for example, by controlling the sheet shift unit 9 so as to prevent the operating amount of some of the multiple recording elements from becoming extremely large, there is an advantage in that it is easy to reduce imbalances in the operating amount of the multiple recording elements.

[0048] [2] Details of the seat shifter Next, the sheet shifting unit 9 of the image forming apparatus 10 according to this embodiment will be described in more detail with reference to Figures 4 and 5. Figures 4 and 5 show only one line head 50 located at the upstream end of the conveying direction D1 out of the multiple (four) line heads 50 aligned in the sub-scanning direction D11 (conveying direction D1) in the image forming unit 5.

[0049] The sheet shift unit 9 is disposed on the conveying path 40 upstream of the image forming unit 5 in the conveying direction D1, and changes the position of the sheet Sh1 in the width direction D2 (the same as the main scanning direction D12).

[0050] In this embodiment, as described above, the sheet shifting unit 9 changes the position of the sheet Sh1 in the width direction D2 by moving the correction unit 42, which corrects the inclination of the sheet Sh1, in the width direction D2. In other words, the sheet shifting unit 9 adjusts the position of the sheet Sh1 in the width direction D2 by moving the sheet Sh1 together with the correction unit 42 in the width direction D2.

[0051] According to this configuration, the correction unit 42 for skew correction can be used to change the position in the width direction D2 of the sheet Sh1 being conveyed by the sheet conveying device 4. Therefore, it is easier to simplify the configuration compared to a case where a mechanism for changing the position in the width direction D2 of the sheet Sh1 is provided separately from the correction unit 42.

[0052] Specifically, as shown in Fig. 4, the seat shifting unit 9 has a stage 90, a pair of rails 91, and a driving unit 92. Fig. 4 shows an example of a specific configuration of the seat shifting unit 9, and is not intended to limit the configuration of the seat shifting unit 9 to the configuration shown in Fig. 4.

[0053] The stage 90 is positioned below the correction unit 42 and supports the correction unit 42 so that it can move in the width direction D2 (main scanning direction D12). Each of the pair of rails 91 has a length in the width direction D2 (main scanning direction D12) and functions as a guide for the movement of the correction unit 42. The pair of rails 91 are arranged on the stage 90 with a predetermined gap between them in the transport direction D1 (sub-scanning direction D11).

[0054] The drive unit 92 is made up of a motor, and applies a driving force to the correction unit 42 on the stage 90 via a rack and pinion or other gear mechanism. In other words, the drive unit 92 can move the correction unit 42 along the width direction D2 (main scanning direction D12) using the pair of rails 91 as guides.

[0055] Here, the sheet shift unit 9 is controlled by a shift processing unit 71 provided in the control device 7. That is, the shift processing unit 71 drives the drive unit 92 to drive the sheet shift unit 9, and moves the sheet Sh1 together with the correction unit 42 in the width direction D2, thereby adjusting the position of the sheet Sh1 in the width direction D2.

[0056] 4 shows a state in which the sheet shifting section 9 moves the correction unit 42 as far as possible toward the rear R in the width direction D2 within the movement range. In other words, in the state shown in FIG. 4, the sheet Sh1 is positioned as far as possible toward the rear R in the width direction D2.

[0057] 4, of the three recording heads 51 (recording elements) aligned in the width direction D2, two recording heads 51, the recording head 51R located on the rear R side and the recording head 51C located in the center, are used to form an image on the sheet Sh1. That is, in the example of FIG. 4, the image forming unit 5 forms an image on the sheet Sh1 by ejecting ink onto the sheet Sh1 from the two recording heads 51R and 51C, and does not use the recording head 51F located on the front F side.

[0058] 5 shows a state in which the sheet shifting unit 9 moves the correction unit 42 from the state shown in FIG. 4 to the extent that the correction unit 42 is moved to the front F side in the width direction D2 within the movement range. In other words, in the state shown in FIG. 5, the sheet Sh1 is in a position that is moved to the extent that it is moved to the front F side in the width direction D2.

[0059] 5, of the three recording heads 51 (recording elements) aligned in the width direction D2, two recording heads 51, the recording head 51F located on the front F side and the recording head 51C located in the center, are used to form an image on the sheet Sh1. That is, in the example of Fig. 5, the image forming unit 5 forms an image on the sheet Sh1 by ejecting ink onto the sheet Sh1 from the two recording heads 51F and 51C, and does not use the recording head 51R located on the rear R side.

[0060] As described above, by changing the position of the sheet Sh1 in the width direction D2, the sheet shift unit 9 can switch between a state in which the recording heads 51R and 51C are used (the state in FIG. 4) and a state in which the recording heads 51F and 51C are used (the state in FIG. 5) among the multiple recording heads 51 (recording elements). As a result, which of the multiple recording heads 51 arranged in the width direction D2 is used preferentially (primarily) can be changed depending on the position of the sheet Sh1 in the width direction D2, thereby reducing bias in the operation amounts of the multiple recording heads 51.

[0061] Here, the shift processing unit 71 controls the sheet shift unit 9 so as to reduce bias in the frequency of use of the multiple recording elements (recording heads 51). In other words, the sheet shift unit 9 controls the sheet shift unit 9 to change the position of the sheet Sh1 in the width direction D2 so as to equalize the frequency of use of the multiple recording heads 51. As an example, every time images are formed on a predetermined number of sheets Sh1, the shift processing unit 71 controls the sheet shift unit 9 to sequentially switch the position of the sheet Sh1 between the rear R side in the width direction D2 (position in FIG. 4), the center in the width direction D2, and the front F side in the width direction D2 (position in FIG. 5).

[0062] This configuration equalizes (averages) the frequency of use of the multiple recording elements (recording heads 51), preventing an excessively high operation amount in some of the multiple recording elements, and reducing bias in the operation amount among the multiple recording elements. As a result, it is possible to prevent an increase in the viscosity of the ink in a specific recording head 51 due to the fact that the specific recording head 51 has not been used for a while. Furthermore, by preventing an increase in viscosity, it is possible to reduce the frequency of line flushing, which ejects ink droplets with increased viscosity, thereby reducing ink consumption while maintaining a normal ink ejection state and maintaining the quality of the formed image.

[0063] In this embodiment, the operating status of the multiple recording elements (recording heads 51) includes the ink ejection amount of each of the multiple recording elements (recording heads 51). In other words, the shift processing unit 71 that controls the sheet shift unit 9 controls the sheet shift unit 9 taking into consideration at least the ink ejection amount of each of the recording heads 51.

[0064] When the sheet shift unit 9 changes the position of the sheet Sh1 in the width direction D2, a mechanical operation is performed, and therefore the conveyance of the sheet Sh1 in the conveyance direction D1 is temporarily stopped. Therefore, frequently changing the position of the sheet Sh1 in the width direction D2 (for example, every time several sheets are imaged) leads to a decrease in productivity (printing efficiency). Therefore, in the image forming apparatus 10 according to this embodiment, the shift processing unit 71 causes the sheet shift unit 9 to change the position of the sheet Sh1 in the width direction D2, taking into account the actual amount of ink ejection, so as not to change the position of the sheet Sh1 in the width direction D2 too frequently.

[0065] Specifically, the shift processing unit 71 calculates the amount of ink ejected from the recording head 51 using the printing rate in the image forming unit 5, which is managed by the control device 7, and the number of sheets Sh1 on which images are formed. The "printing rate" here refers to the ratio of the cumulative area of ​​the image, such as characters, formed to the area of ​​the sheet. When the calculated ink ejection rate exceeds a threshold, the shift processing unit 71 controls the sheet shift unit 9 to change (switch) the position of the sheet Sh1 in the width direction D2.

[0066] This makes it possible to reduce the bias in the amount of operation among the multiple recording elements (recording heads 51) while suppressing a decrease in productivity (printing efficiency).

[0067] Furthermore, the threshold value compared with the ink ejection amount may be a variable value. As an example, the threshold value is determined according to the ink ejection amount (printing rate) per sheet Sh1. Basically, the threshold value is variably determined so that the lower the printing rate (smaller the ink ejection amount), the smaller the threshold value, and the higher the printing rate (larger the ink ejection amount), the larger the threshold value. For example, assuming that the printing rate does not change significantly in offset printing, etc., the threshold value is determined according to the printing rate (or ink ejection amount) of the first (initial) sheet Sh1. As an example, if the ink ejection amount of the first sheet Sh1 is 1 ml, the threshold value is set to 100 ml, whereas if the ink ejection amount of the first sheet Sh1 is 10 ml, the threshold value is set to 1000 ml.

[0068] Furthermore, in the image forming apparatus 10 according to this embodiment, the operating status of the multiple recording elements includes whether or not the multiple recording elements (recording heads 51) are abnormal. The shift processing unit 71 controls the sheet shifting unit 9 so as to avoid abnormal recording elements (recording heads 51). In short, the sheet shifting unit 9 changes the position of the sheet Sh1 in the width direction D2 not only to reduce bias in the usage frequency of the multiple recording elements but also to avoid using abnormal recording elements.

[0069] Specifically, the shift processing unit 71 causes the image reading unit 8 to read the image (including the test image formed in the margin area of ​​the sheet Sh1) formed on the sheet Sh1 by the image forming unit 5. In other words, by reading the image formed on the sheet Sh1 by the image reading unit 8, which is disposed downstream of the image forming unit 5 in the conveying direction D1, it becomes possible to detect whether or not there is an abnormality in the multiple recording heads 51.

[0070] The shift processing unit 71 determines whether or not the read image has a defect caused by defective ink ejection, such as missing dots, and if the defect is present, determines that there is a malfunction (defective ink ejection) in the image forming unit 5. Furthermore, the shift processing unit 71 identifies which of the multiple recording elements (recording heads 51) has the defective ink ejection, based on the position in the image where the defect occurred.

[0071] For example, if the recording head 51R located on the rear R side of the three recording heads 51 (recording elements) aligned in the width direction D2 has an abnormality such as poor ink ejection, the shift processing unit 71 controls the sheet shift unit 9 to avoid the recording head 51R. In other words, the shift processing unit 71 controls the sheet shift unit 9 to move the correction unit 42 to the front F side from the state shown in Fig. 4 to the state shown in Fig. 5. This makes it possible to form an image on the sheet Sh1 using the recording heads 51F and 51C, avoiding the abnormal recording head 51R.

[0072] With this configuration, even if any of the recording elements (recording heads 51) has an abnormality, the image forming apparatus 10 can continue to form images normally by avoiding the abnormality. Therefore, with the image forming apparatus 10 according to this embodiment, it is possible to reduce downtime due to abnormalities in the recording elements and improve productivity (printing efficiency).

[0073] [3] Image forming method 6, an image forming method executed mainly by the shift processing unit 71 in the image forming apparatus 10 having the above-described configuration will be described below. Here, steps S1, S2, etc. represent the numbers of the processing procedures (steps) executed by the shift processing unit 71. Also, here, a description of the operation of the sheet shift unit 9 for avoiding the use of abnormal recording elements will be omitted.

[0074] <Step S1> First, in step S1, the shift processing unit 71 determines a threshold value to be compared with the ink ejection amount. Here, the shift processing unit 71 determines the threshold value according to the ink ejection amount of the first (initial) sheet Sh1 so that the threshold value decreases as the ink ejection amount decreases.

[0075] <Step S2> In step S2, the shift processing unit 71 calculates the amount of ink ejected from the recording head 51 using the printing rate in the image forming unit 5 and the number of sheets Sh1 on which images are formed. That is, as the number of sheets Sh1 on which images are formed increases, the calculated amount of ink ejected increases.

[0076] <Step S3> In step S3, the shift processing unit 71 compares the discharge amount calculated in step S2 with the threshold determined in step S1. If the discharge amount exceeds the threshold (S3: Yes), the shift processing unit 71 shifts the process to step S4. On the other hand, if the discharge amount is equal to or less than the threshold (S3: No), the shift processing unit 71 returns the process to step S2.

[0077] <Step S4> In step S4, the shift processing unit 71 controls the sheet shift unit 9 to sequentially switch the position of the sheet Sh1 between the rear R side in the width direction D2, the center in the width direction D2, and the front F side in the width direction D2. For example, when the sheet Sh1 is located on the rear R side in the width direction D2, the shift processing unit 71 controls the sheet shift unit 9 to change the position of the sheet Sh1 to the center in the width direction D2.

[0078] The procedure of the image forming method described above is merely an example, and the order of the processes shown in the flowchart of FIG. 6 may be changed as appropriate, and processes may be added or omitted as appropriate.

[0079] [4] Variation The multiple components included in the image forming apparatus 10 may be distributed across multiple housings. For example, the image forming unit 5 and the ink supply unit 6 may be provided in separate housings.

[0080] Conversely, in the first embodiment, at least one of the components provided separately from the image forming apparatus 10 may be provided in the image forming apparatus 10 as a component of the image forming apparatus 10. For example, at least one of the paper feeder 11, the dryer 12, and the discharger 13 may be provided in the housing 21, or may be configured integrally with the image forming apparatus 10.

[0081] Furthermore, the image forming object on which an image is formed by the image forming apparatus 10 is not limited to a sheet Sh1 such as paper or a resin film, but may also be, for example, a roll of fabric such as a nonwoven fabric or cloth. In this case, the image forming apparatus 10 is a textile printing machine (textile printer) that records an image on the fabric by ejecting ink onto the fabric and dyeing the fibers of the fabric with the ink.

[0082] Furthermore, the "recording element" is not limited to the recording head 51, but may be, for example, an ink nozzle 53 or a line head 50. Furthermore, if the image forming apparatus 10 is of a type other than an inkjet type, the recording element is changed as appropriate depending on the type of the image forming apparatus 10, etc.

[0083] Furthermore, the configuration of the correction unit 42 is not limited to the configuration described in embodiment 1. For example, the correction unit 42 may be configured to have a pull-in roller that moves the sheet Sh1 toward the rear R along the width direction D2 (main scanning direction D12). In this case, the correction unit 42 corrects the skew of the sheet Sh1 by abutting the side edge of the sheet Sh1 moved by the pull-in roller against an alignment member located at the end on the rear R side.

[0084] [Appendix to the invention] The following is a summary of the invention extracted from the above-described embodiment. Note that the configurations and processing functions described in the following supplementary notes can be selected and combined as desired.

[0085] <Appendix 1> a sheet conveying device that conveys the sheet along a conveying path; an image forming unit that forms an image on the sheet by ejecting ink onto the surface of the sheet using a plurality of recording elements that are arranged in a width direction perpendicular to the conveyance direction of the sheet; a sheet shift unit that changes a position of the sheet in the width direction, the sheet shift unit being located upstream of the image forming unit in the conveying direction; a shift processing unit that controls the sheet shift unit in accordance with the operating conditions of the plurality of recording elements, Image forming device.

[0086] <Appendix 2> the shift processing unit controls the sheet shift unit so as to reduce bias in the frequency of use of the plurality of recording elements. 2. The image forming apparatus according to claim 1.

[0087] <Appendix 3> the operating conditions of the plurality of recording elements include the ink ejection amount of each of the plurality of recording elements; 3. The image forming apparatus according to claim 1 or 2.

[0088] <Appendix 4> the operational status of the plurality of recording elements includes whether or not there is an abnormality in the plurality of recording elements; the shift processing unit controls the sheet shift unit so as to avoid the abnormal recording element. 4. The image forming apparatus according to claim 1.

[0089] <Appendix 5> the sheet shifting unit changes the position of the sheet in the width direction by moving a correction unit that corrects the inclination of the sheet in the width direction. 5. The image forming apparatus according to any one of claims 1 to 4. [Explanation of symbols]

[0090] 4 Sheet transport device 5. Image forming unit 9 Seat shift section 10 Image forming device 40 Transport path 42 Correction Unit 51 Recording head (recording element) 71 Shift processing section D1 Conveying direction D2 Width direction Sh1 sheet

Claims

1. a sheet conveying device that conveys the sheet along a conveying path; an image forming unit that forms an image on the sheet by ejecting ink onto the surface of the sheet using a plurality of recording elements that are arranged in a width direction perpendicular to the conveyance direction of the sheet; a sheet shift unit that changes a position of the sheet in the width direction, the sheet shift unit being located upstream of the image forming unit in the conveying direction; a shift processing unit that controls the sheet shift unit in accordance with the operating conditions of the plurality of recording elements, Image forming device.

2. the shift processing unit controls the sheet shift unit so as to reduce bias in the frequency of use of the plurality of recording elements. The image forming apparatus according to claim 1 .

3. the operating conditions of the plurality of recording elements include the ink ejection amount of each of the plurality of recording elements; 3. The image forming apparatus according to claim 1.

4. the operational status of the plurality of recording elements includes whether or not there is an abnormality in the plurality of recording elements; the shift processing unit controls the sheet shift unit so as to avoid the abnormal recording element.

3. The image forming apparatus according to claim 1.

5. the sheet shifting unit changes the position of the sheet in the width direction by moving a correction unit that corrects the inclination of the sheet in the width direction.

3. The image forming apparatus according to claim 1.

6. a sheet conveying device that conveys the sheet along a conveying path; an image forming unit that forms an image on the sheet by ejecting ink onto the surface of the sheet using a plurality of recording elements that are arranged in a width direction perpendicular to the conveyance direction of the sheet; a sheet shift unit that changes the position of the sheet in the width direction, the sheet shift unit being located upstream of the image forming unit in the conveying direction, controlling the sheet shift unit in accordance with the operating conditions of the plurality of recording elements; Image forming method.

7. a sheet conveying device that conveys the sheet along a conveying path; an image forming unit that forms an image on the sheet by ejecting ink onto the surface of the sheet using a plurality of recording elements that are arranged in a width direction perpendicular to the conveyance direction of the sheet; a sheet shift unit that changes the position of the sheet in the width direction, the sheet shift unit being located upstream of the image forming unit in the conveying direction, controlling the sheet shift unit in accordance with the operating conditions of the plurality of recording elements; An image forming program for causing one or more processors to execute the above.

Images