Image forming device and image forming method

Abstract

To provide an image forming device and an image forming method which can prevent a stop time from elapsing unnecessarily and suppress a sheet from curling.SOLUTION: An image forming device comprises: an obtaining part that obtains, when double-side image formation processing for forming images on both sides of a sheet is executed, adhesion-amount information concerning amounts of adhesion amount of ink by image formation in each of a plurality of specific regions R20 preliminarily set in an image formation region R10 on a front surface of the sheet; a setting part that sets a stop time on the basis of a plurality of pieces of adhesion-amount information obtained by the obtaining part; and a stopping part that temporarily stops conveyance of the sheet on the basis of the stop time set by the setting part when the sheet is switched back.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Inkjet image forming devices include a discharge unit, such as a recording head, that discharges ink onto a sheet being conveyed. In this type of image forming device, during a double-sided image forming process in which images are formed on both sides of a sheet, the ink adhering to the front surface of the sheet may cause the sheet to curl after forming an image on the front surface but before forming an image on the back surface, resulting in problems such as the sheet coming into contact with the discharge unit during image formation on the back surface. To address this issue, some image forming devices are known that temporarily suspend the conveyance of the sheet after forming an image on the front surface of the sheet but before forming an image on the back surface of the sheet for a period of time based on the amount of ink adhering to the front surface of the sheet. Another related technology is an image forming device that sets the period of time based solely on the amount of ink adhering to the edge of the front surface of the sheet, where curling is likely to occur, to prevent the period of time from becoming unnecessarily long (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-349710 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a large amount of ink adheres to an area including the center of the surface of the sheet, the sheet also curls. Therefore, the image forming apparatus according to the above-mentioned related art may not be able to prevent the sheet from curling.

[0005] An object of the present invention is to provide an image forming apparatus and an image forming method that can prevent unnecessary long downtimes and prevent curling of sheets. [Means for solving the problem]

[0006] According to one aspect of the present invention, an image forming apparatus includes a discharge unit, an acquisition processing unit, a setting processing unit, and a stop processing unit. The discharge unit discharges ink onto a conveyed sheet. When a double-sided image formation process is performed using the discharge unit to form images on a first side and a second side of the sheet, the acquisition processing unit acquires adhesion amount information regarding the amount of ink adhesion resulting from image formation for each of a plurality of specific areas that are set in advance in an image formation area on the first side of the sheet. The setting processing unit sets a stop time for stopping conveyance of the sheet based on the adhesion amount information acquired by the acquisition processing unit. The stop processing unit temporarily suspends conveyance of the sheet after image formation on the first side of the sheet and before image formation on the second side of the sheet during execution of the double-sided image formation process, based on the stop time set by the setting processing unit. The plurality of specific areas include a center area set in the center of the image formation area and edge areas set at the edges of the image formation area.

[0007] An image forming method according to another aspect of the present invention is performed by an image forming apparatus including an ejection unit that ejects ink onto a conveyed sheet, and includes an acquiring step, a setting step, and a stopping step. In the acquiring step, when a double-sided image forming process is performed in which the ejection unit is used to form images on the first and second sides of the sheet, adhesion amount information regarding the amount of ink adhesion resulting from image formation is acquired for each of a plurality of specific areas that are set in advance in the image forming area on the first side of the sheet. In the setting step, a stop time for stopping the conveyance of the sheet is set based on the plurality of adhesion amount information acquired in the acquiring step. In the stopping step, the conveyance of the sheet is temporarily stopped after image formation on the first side of the sheet and before image formation on the second side of the sheet during the double-sided image forming process, based on the stop time set in the setting step. The plurality of specific areas include a center area set in the center of the image forming area and an edge area set at an edge of the image forming area. [Effects of the Invention]

[0008] According to the present invention, it is possible to prevent the stop time from becoming unnecessarily long and to prevent the sheet from curling. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing the system configuration of the image forming apparatus according to the embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing the configuration of the head unit of the image forming apparatus according to the embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing the configuration of the periphery of the nozzles of the image forming apparatus according to the embodiment of the present invention. [Figure 5] FIG. 5 is a diagram showing an example of a plurality of specific areas set on the front surface of a sheet in the image forming apparatus according to the embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing an example of first table data stored in the storage unit of the image forming apparatus according to the embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing an example of second table data stored in the storage unit of the image forming apparatus according to the embodiment of the present invention. [Figure 8] FIG. 8 is a diagram showing an example of third table data stored in the storage unit of the image forming apparatus according to the embodiment of the present invention. [Figure 9] FIG. 9 is a flowchart showing an example of a transport control process executed in the image forming apparatus according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the following embodiment is an example of a specific embodiment of the present invention and does not limit the technical scope of the present invention.

[0011] [Configuration of image forming apparatus 100] First, the configuration of an image forming apparatus 100 according to an embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a cross-sectional view showing the configuration of the image forming apparatus 100.

[0012] The image forming apparatus 100 is a printer that forms an image on a sheet by inkjet printing. The present invention can be applied to a fax machine, a copy machine, a multifunction machine, and the like that form an image on a sheet by inkjet printing.

[0013] As shown in FIGS. 1 and 2, the image forming apparatus 100 includes an image forming unit 1, a sheet conveying unit 2, an operation display unit 3, a communication unit 4, a storage unit 5, and a control unit 6.

[0014] The image forming unit 1 forms an image on a sheet by inkjet printing based on image data input from an external information processing device such as a personal computer.

[0015] The sheet conveying section 2 conveys a sheet on which an image is to be formed by the image forming section 1.

[0016] The operation display unit 3 is a user interface of the image forming apparatus 100. The operation display unit 3 includes a display unit and an operation unit. The display unit displays various information in response to control instructions from the control unit 6. For example, the display unit is a flat panel display such as a liquid crystal display. The operation unit inputs various information to the control unit 6 in response to user operations. For example, the operation unit includes operation keys and a touch panel.

[0017] The communication unit 4 is a communication interface that executes wired or wireless data communication with an external information processing device.

[0018] The storage unit 5 is a non-volatile storage device, such as a flash memory.

[0019] The control unit 6 performs overall control of the image forming apparatus 100. As shown in FIG. 2, the control unit 6 includes a CPU 11, a ROM 12, and a RAM 13. The CPU 11 is a processor that executes various types of arithmetic processing. The ROM 12 is a non-volatile storage device that pre-stores information such as control programs for causing the CPU 11 to execute various processes. The RAM 13 is a volatile or non-volatile storage device used as a temporary storage memory (work area) for the various processes executed by the CPU 11. In the control unit 6, the CPU 11 executes various control programs pre-stored in the ROM 12. In this way, the control unit 6 performs overall control of the image forming apparatus 100. The control unit 6 may be configured with an electronic circuit such as an integrated circuit (ASIC). The control unit 6 may also be a control unit provided separately from a main control unit that performs overall control of the image forming apparatus 100.

[0020] [Configuration of image forming unit 1 and sheet conveying unit 2] Next, the configurations of the image forming unit 1 and the sheet conveying unit 2 will be described with reference to Figures 1, 3, and 4. Here, Figure 3 is a view of the head unit 21 as seen from the side in the ink ejection direction by the head unit 21. Also, Figure 4 is a cross-sectional view showing the configuration around the nozzle 30A.

[0021] As shown in FIG. 1, the image forming unit 1 includes a head unit 21, a cap unit 22, an ink storage unit 23, an ink supply passage unit 24, and a waste ink storage unit 25.

[0022] The head unit 21 ejects ink onto the sheet conveyed by the sheet conveying unit 2. The head unit 21 is an example of an ejection unit of the present invention.

[0023] As shown in FIG. 3, the head unit 21 includes line heads 31 to 34 and a head frame 35.

[0024] 3, each of the line heads 31 to 34 is elongated in a width direction D2 perpendicular to a sheet conveyance direction D1 by the sheet conveyance unit 2. Specifically, each of the line heads 31 to 34 has a length in the width direction D2 corresponding to the width of the largest size sheet that can be accommodated in the sheet feed cassette 41 of the sheet conveyance unit 2. The line heads 31 to 34 are arranged side by side at equal intervals along the conveyance direction D1.

[0025] As shown in FIG. 3, each of the line heads 31 to 34 has a plurality of recording heads 30. Each of the recording heads 30 ejects ink droplets toward a sheet transported by the sheet transport unit 2. Each of the recording heads 30 provided in the line head 31 ejects black ink droplets. Each of the recording heads 30 provided in the line head 32 ejects cyan ink droplets. Each of the recording heads 30 provided in the line head 33 ejects magenta ink droplets. Each of the recording heads 30 provided in the line head 34 ejects yellow ink droplets.

[0026] Each recording head 30 has a plurality of nozzles 30A (see FIG. 3) that eject ink droplets. Each nozzle 30A is provided on the surface of the recording head 30 that faces the sheet conveyed by the sheet conveying unit 2.

[0027] Each recording head 30 also includes a pressure chamber 30B (see FIG. 4), a piezoelectric element 30C (see FIG. 4), and an individual flow path 30D (see FIG. 4) corresponding to each nozzle 30A. The pressure chamber 30B communicates with the nozzle 30A and contains ink. The piezoelectric element 30C ejects ink droplets from the nozzle 30A in response to a predetermined drive signal. Specifically, the piezoelectric element 30C changes the pressure in the pressure chamber 30B in response to the drive signal, thereby ejecting ink droplets from the nozzle 30A. The individual flow path 30D is an ink flow path provided between the pressure chamber 30B and a common flow path (not shown) shared by the multiple nozzles 30A. A plurality of individual flow paths 30D corresponding to the multiple nozzles 30A are connected to the common flow path. The common flow path is connected to the ink storage unit 23 (see FIG. 1) via an ink supply flow path unit 24 (see FIG. 1).

[0028] In the image forming apparatus 100, one of the first, second, third, fourth, and fifth drive signals is input to the piezoelectric element 30C. In response to the input of the first drive signal, the piezoelectric element 30C ejects extra-small ink droplets. In response to the input of the second drive signal, the piezoelectric element 30C ejects small ink droplets. In response to the input of the third drive signal, the piezoelectric element 30C ejects medium ink droplets. In response to the input of the fourth drive signal, the piezoelectric element 30C ejects large ink droplets. In response to the input of the fifth drive signal, the piezoelectric element 30C ejects extra-large ink droplets.

[0029] 3, the line head 31 includes three recording heads 30 arranged in a staggered pattern along the width direction D2. Similarly to the line head 31, each of the other line heads 32 to 34 also includes three recording heads 30 arranged in a staggered pattern along the width direction D2.

[0030] The head frame 35 supports the line heads 31 to 34.

[0031] The head unit 21 is provided so as to be movable between an image forming position where an image can be formed on a sheet conveyed by the sheet conveying unit 2, and a first retracted position retracted from the image forming position. Specifically, the head frame 35 is supported by the housing of the image forming apparatus 100 so as to be movable along a movement direction D3 shown in Fig. 1. In Fig. 1, the head unit 21 disposed at the image forming position is indicated by a solid line. In Fig. 1, the head unit 21 disposed at the first retracted position is indicated by a dashed line.

[0032] The number of line heads included in the head unit 21 does not have to be limited to four. Furthermore, the number of recording heads 30 included in each of the line heads 31 to 34 does not have to be limited to three.

[0033] The cap portion 22 caps each of the nozzles 30A of the head portion 21 that is disposed at the first retracted position.

[0034] The cap unit 22 is provided so as to be movable between a cap position where it can cap each of the nozzles 30A of the head unit 21 disposed at the first retracted position and a second retracted position retracted from the cap position. Specifically, the cap unit 22 is supported by the housing of the image forming apparatus 100 so as to be movable along a movement direction D4 shown in Fig. 1. In Fig. 1, the cap unit 22 disposed at the second retracted position is indicated by a solid line.

[0035] The cap unit 22 is moved along the movement direction D4 when the head unit 21 is disposed at the first retracted position. The cap unit 22 includes a brush-like cleaning unit that cleans the nozzle surface on which the nozzles 30A of the recording head 30 are formed during movement between the first retracted position and the cap position.

[0036] In the image forming apparatus 100, a purge process is executed to discharge ink from each of the nozzles 30A of the head unit 21 arranged at the first retracted position, while each of the nozzles 30A is capped by the cap unit 22. The ink discharged from each of the nozzles 30A by the purge process is collected in the waste ink collection unit 25 via a waste ink flow path (not shown) connected to the cap unit 22.

[0037] The ink storage section 23 stores ink of each color to be supplied to the head section 21 .

[0038] The ink supply flow path section 24 forms an ink flow path for each color ink that connects the ink storage section 23 and the head section 21 .

[0039] The waste ink storage section 25 stores the ink discharged from each of the nozzles 30A by the purging process.

[0040] 1, the sheet conveying unit 2 includes a paper feed cassette 41, a paper feed unit 42, a paper feed path 43, a conveying path 44, a pair of registration rollers 45, a conveying belt 46, a paper discharge path 47, a pair of paper discharge rollers 48, a paper discharge tray 49, a first reverse conveying path 50, a pair of reverse conveying rollers 51, and a second reverse conveying path 52. In FIG. 1, the paper feed path 43, the conveying path 44, the paper discharge path 47, the first reverse conveying path 50, and the second reverse conveying path 52 are indicated by thick solid lines.

[0041] The paper feed cassette 41 stores sheets on which an image is formed by the image forming unit 1. For example, the paper feed cassette 41 stores sheets such as inkjet plain paper and inkjet matte paper. The inkjet plain paper and inkjet matte paper have properties suitable for inkjet image formation.

[0042] The paper feed unit 42 supplies the sheets stored in the paper feed cassette 41 to the paper feed path 43 one by one.

[0043] The paper feed path 43 is a path along which a sheet moves from the paper feed unit 42 to a first position P1 (see FIG. 1) within the housing of the image forming apparatus 100. The paper feed path 43 is connected to the conveying path 44 at the first position P1. In the paper feed path 43, the sheet is conveyed toward the conveying path 44.

[0044] The conveying path 44 is a path along which the sheet moves from the first position P1 to a second position P2 (see FIG. 1) within the housing of the image forming apparatus 100. The conveying path 44 is connected to the paper discharge path 47 at the second position P2. In the conveying path 44, the sheet is conveyed in the conveying direction D1 shown in FIG.

[0045] The conveyor belt 46 forms a partial section of the conveying path 44. The conveyor belt 46 is provided in a position facing the head unit 21 arranged at the image forming position within the housing of the image forming apparatus 100. The conveyor belt 46 is stretched by a pair of tension rollers. A sheet that has been charged by a charging roller is electrostatically attracted to the outer circumferential surface of the conveyor belt 46. The conveyor belt 46 transports the sheet electrostatically attracted to its outer circumferential surface. The conveyor belt 46 also supports the sheet onto which ink droplets are ejected by the head unit 21.

[0046] The pair of registration rollers 45 is provided on the conveying path 44 upstream of the conveying belt 46 in the conveying direction D1. The pair of registration rollers 45 is used to correct skew of the sheet.

[0047] The paper discharge path 47 is a path along which the sheet moves from the second position P2 to the paper discharge roller pair 48. In the paper discharge path 47, the sheet is transported toward the paper discharge roller pair 48.

[0048] The pair of paper discharge rollers 48 discharges the sheet onto a paper discharge tray 49 .

[0049] The sheet discharge tray 49 receives the sheets discharged by the pair of sheet discharge rollers 48 .

[0050] The first reverse conveying path 50 is a path along which the sheet moves from the second position P2 to a sheet discharge outlet 51A (see FIG. 1) formed in the upper part of the housing of the image forming apparatus 100. In the first reverse conveying path 50, the sheet is conveyed toward the sheet discharge outlet 51A.

[0051] The reverse transport roller pair 51 is provided at the sheet discharge port 51A. The reverse transport roller pair 51 switches back the sheet and supplies the sheet to the second reverse transport path 52. Specifically, the reverse transport roller pair 51 causes the sheet to protrude from the housing of the image forming apparatus 100 through the sheet discharge port 51A until the reverse transport roller pair 51 clamps the upstream end (trailing end) of the sheet in the transport direction D1. The reverse transport roller pair 51 then rotates in the reverse direction at the timing when the trailing end of the sheet is clamped, thereby switching back the sheet. A sheet support tray 51B (see FIG. 1) that supports the sheet protruding from the sheet discharge port 51A is formed on the top surface of the housing of the image forming apparatus 100.

[0052] The second reverse conveying path 52 is a path along which the sheet moves from the reverse conveying roller pair 51 to the first position P1 (see FIG. 1). In the second reverse conveying path 52, the sheet is conveyed toward the first position P1.

[0053] In the image forming apparatus 100, a double-sided image forming process is performed in which an image is formed on the front side (an example of the first side of the present invention) and back side (an example of the second side of the present invention) of a sheet transported by the sheet transport unit 2 using the head unit 21.

[0054] In conventional image forming devices, after an image is formed on the front side of a sheet but before an image is formed on the back side during the double-sided image formation process, the sheet may curl due to ink adhering to the front side, causing problems such as the sheet coming into contact with the head unit 21 when an image is formed on the back side. To address this issue, image forming devices are known that temporarily suspend sheet transport after an image is formed on the front side of the sheet but before an image is formed on the back side of the sheet for a stop time based on the amount of ink adhering to the front side of the sheet. Furthermore, a related art image forming device is known that sets the stop time based only on the amount of ink adhering to the edge of the front side of the sheet, which is prone to curling, in order to prevent the stop time from becoming unnecessarily long.

[0055] However, when a large amount of ink adheres to an area including the center of the surface of the sheet, the sheet also curls. Therefore, the image forming apparatus according to the above-mentioned related art may not be able to prevent the sheet from curling.

[0056] In contrast to this, in the image forming apparatus 100 according to the embodiment of the present invention, as will be described below, it is possible to prevent the stop time from becoming unnecessarily long and also to prevent the occurrence of curling in the sheet.

[0057] [Configuration of control unit 6] Next, the configuration of the control unit 6 will be described with reference to FIG.

[0058] As shown in FIG. 2, the control unit 6 includes an acquisition processing unit 61, a setting processing unit 62, and a stop processing unit 63.

[0059] Specifically, a transport control program for causing the CPU 11 to function as each of the above-mentioned processing units is stored in advance in the ROM 12 of the control unit 6. The CPU 11 executes the transport control program stored in the ROM 12 to function as each of the above-mentioned processing units.

[0060] The transport control program may be recorded on a computer-readable recording medium such as a CD, DVD, or flash memory, and may be read from the recording medium and stored in the storage unit 5. Some or all of the processing units included in the control unit 6 may be configured with electronic circuits. The transport control program may also be a program for causing multiple processors to function as the processing units included in the control unit 6.

[0061] When the double-sided image formation process is executed, the acquisition processing unit 61 acquires adhesion amount information regarding the amount of ink adhesion due to image formation for each of multiple specific areas R20 (R11 to R19) that are set in advance in the image formation area R10 (see Figure 5) on the front surface of the sheet.

[0062] FIG. 5 shows an example of an image forming area R10 (see FIG. 5) set on the front surface of a sheet, and a plurality of specific areas R20 (R11 to R19) set in the image forming area R10. Note that in FIG. 5, the image forming area R10 and each of the plurality of specific areas R20 are indicated by dotted lines. The image forming area R10 is an area having a size L1 in the width direction D2 and a size L2 in the conveying direction D1. Each of the specific areas R11 to R14 is an area having a size L3 in the width direction D2 and a size L3 in the conveying direction D1. Each of the specific areas R15 to R16 is an area having a size L1 in the width direction D2 and a size L4 in the conveying direction D1. Each of the specific areas R17 to R18 is an area having a size L4 in the width direction D2 and a size L2 in the conveying direction D1. The specific area R19 is an area having a size L1 in the width direction D2 and a size L2 in the conveying direction D1. In other words, the specific area R19 is the entire area of ​​the image forming area R10.

[0063] The area outside the image forming area R10 on the sheet is a margin area. The size of the margin area may be set arbitrarily. The image forming area R10 may also be the entire area on the surface of the sheet.

[0064] 5, the specific region R19 is set in the center of the image forming region R10. The specific region R19 is an example of the central region of the present invention. Note that the specific region R19 may include the center of the image forming region R10 and may be a portion of the image forming region R10.

[0065] 5, the specific regions R11 to R12 are set at the corners on the upstream side of the image forming region R10 in the transport direction D1. The specific regions R11 to R12 are an example of the first region of the present invention, and are also an example of the edge region of the present invention.

[0066] 5, the specific regions R13 to R14 are set at the corners on the downstream side of the image forming region R10 in the transport direction D1. The specific regions R13 to R14 are an example of the second region of the present invention, and are also an example of the edge region of the present invention.

[0067] As shown in Fig. 5, specific regions R15-R16 are set at the respective ends of image forming region R10 in the transport direction D1. Also, as shown in Fig. 5, specific regions R17-R18 are set at the respective ends of image forming region R10 in the width direction D2. Specific regions R15-R18 are examples of edge regions of the present invention.

[0068] For example, the adhesion amount information is information indicating the printing rate in each specific region R20.

[0069] In the image forming apparatus 100, the printing rate is the ratio of the number of dots of a predetermined specific size formed in the specific region R20 to the number of dots that can be formed in the specific region R20. For example, the specific size dots are dots formed on the sheet by medium-sized ink droplets ejected from the nozzle 30A. In other words, when medium-sized ink droplets are ejected onto all dot-formable regions included in the specific region R20, the printing rate in the specific region R20 is 100 percent. Furthermore, when large-sized ink droplets are ejected onto all dot-formable regions included in the specific region R20, the printing rate in the specific region R20 exceeds 100 percent.

[0070] For example, in the image forming apparatus 100, bitmap image data to be used for image formation is decomposed into four color component data corresponding to the colors black, cyan, magenta, and yellow. Furthermore, in the image forming apparatus 100, a conversion process is executed for each of the color component data to convert each pixel data included in the color component data into either ejection pixel data used to eject an ink droplet from the nozzle 30A corresponding to the pixel data, or non-ejection pixel data used to not eject an ink droplet from the nozzle 30A corresponding to the pixel data. The ejection pixel data includes first ejection pixel data used to generate the first drive signal, second ejection pixel data used to generate the second drive signal, third ejection pixel data used to generate the third drive signal, fourth ejection pixel data used to generate the fourth drive signal, and fifth ejection pixel data used to generate the fifth drive signal.

[0071] For example, the acquisition processing unit 61 calculates the printing rate in the specific region R20 in the following procedure.

[0072] First, the acquisition processing unit 61 acquires the number of black ink droplets to be ejected into the specific region R20 for each ink droplet size based on the color component data after the conversion processing corresponding to black.

[0073] Next, the acquisition processing unit 61 calculates the black printing rate in the specific region R20 according to the following formula (1). Note that "B1" included in formula (1) indicates the black printing rate in the specific region R20. Also, "a1" included in formula (1) indicates the number of extra-small black ink droplets ejected in the specific region R20. Also, "a2" included in formula (1) indicates the ink volume of extra-small black ink droplets. Also, "b1" included in formula (1) indicates the number of small black ink droplets ejected in the specific region R20. Also, "b2" included in formula (1) indicates the ink volume of small black ink droplets. Also, "c1" included in formula (1) indicates the number of medium black ink droplets ejected in the specific region R20. Also, "c2" included in formula (1) indicates the ink volume of medium black ink droplets. Furthermore, "d1" included in formula (1) indicates the number of large black ink droplets ejected into the specific region R20. Furthermore, "d2" included in formula (1) indicates the ink volume of the large black ink droplets. Furthermore, "e1" included in formula (1) indicates the number of extra-large black ink droplets ejected into the specific region R20. Furthermore, "e2" included in formula (1) indicates the ink volume of the extra-large black ink droplets. Furthermore, "r1" included in formula (1) indicates the number of dot formable regions included in the specific region R20. The ink volume of each size of black ink droplet is obtained using first table data X10 shown in FIG. 6 (see FIG. 6). The first table data X10 is stored in advance in the storage unit 5.

[0074] B1=(a1×a2+b1×b2+c1×c2+d1×d2+e1×e2)÷(r1×c2) ··· (1)

[0075] Next, the acquisition processing unit 61 calculates the printing rate of each color other than black in the specific region R20 in the same manner as described above.

[0076] The acquisition processing unit 61 then calculates the printing rate in the specific region R20 according to the following formula (2). Note that "V1" included in formula (2) indicates the printing rate in the specific region R20. Also, "C1" included in formula (2) indicates the printing rate of cyan in the specific region R20. Also, "M1" included in formula (2) indicates the printing rate of magenta in the specific region R20. Also, "Y1" included in formula (2) indicates the printing rate of yellow in the specific region R20.

[0077] V1=B1+C1+M1+Y1 (2)

[0078] The setting processing unit 62 sets a stop time for stopping the conveyance of the sheet based on the plurality of pieces of adhesion amount information acquired by the acquisition processing unit 61.

[0079] For example, the setting processing unit 62 sets the stop time based on a combination of the plurality of pieces of adhesion amount information, the type of sheet, and the basis weight of the sheet acquired by the acquisition processing unit 61. Note that the type and basis weight of the sheet used for forming images in the double-sided image forming process are set in advance by the user before the double-sided image forming process is executed.

[0080] For example, the setting processing unit 62 corrects each of the adhesion amount information using a correction coefficient (see Figure 7) that is set in advance for each specific region R20, and sets the stop time to the time obtained based on the maximum value of the adhesion amount information after correction.

[0081] For example, in the image forming apparatus 100, second table data X20 shown in Fig. 7 is stored in advance in the storage unit 5. The second table data X20 is data indicating the correspondence between the specific region R20 and the correction coefficients.

[0082] 7, the correction coefficients set for each of the specific regions R11 to R12 are the largest among the multiple correction coefficients corresponding to the multiple specific regions R20. This is because, in the image forming region R10 on the front surface of the sheet, the corners on the upstream side in the conveying direction D1 are most likely to curl.

[0083] 7, the correction coefficients set for the specific regions R13 to R14 are the second largest among the correction coefficients corresponding to the specific region R20. This is because, in the image forming region R10 on the front surface of the sheet, the corners on the downstream side in the conveying direction D1 are second most likely to curl.

[0084] 7, the correction coefficient set for the specific region R15 is the third largest among the multiple correction coefficients corresponding to the multiple specific regions R20. This is because, within the image forming region R10 on the front surface of the sheet, the upstream end in the conveying direction D1 is the third most likely to curl.

[0085] 7, the correction coefficient set for the specific region R16 is the fourth largest among the multiple correction coefficients corresponding to the multiple specific regions R20. This is because, within the image forming region R10 on the front surface of the sheet, the downstream end in the conveying direction D1 is the fourth most likely to curl.

[0086] 7, the correction coefficients set for the specific regions R17 to R18 are the fifth largest among the correction coefficients corresponding to the specific region R20. This is because, within the image forming region R10 on the front surface of the sheet, the ends in the width direction D2 are the fifth most likely to curl.

[0087] 7, the correction coefficient set for the specific region R19 is the smallest among the multiple correction coefficients corresponding to the multiple specific regions R20. This is because, within the image forming region R10 on the front surface of the sheet, the region including the center is the region least likely to curl.

[0088] 8 is stored in advance in the storage unit 5. The third table data X30 is data indicating the correspondence relationship between the corrected adhesion amount information (the printing rate), the sheet basis weight, the sheet type, and the time set for the stop time.

[0089] The setting processing unit 62 uses the second table data X20 to acquire the correction coefficient corresponding to the specific region R20 to be corrected. Then, the setting processing unit 62 corrects the printing rate by multiplying the printing rate in the specific region R20 to be corrected by the acquired correction coefficient.

[0090] Furthermore, the setting processing unit 62 uses the third table data X30 to acquire the time corresponding to the combination of the maximum value among the multiple pieces of corrected adhesion amount information (the printing rates), the basis weight of the sheet, and the sheet type. Then, the setting processing unit 62 sets the acquired time as the stop time. For example, when the basis weight of the sheet is "80", the sheet type is "inkjet plain paper", and the maximum value among the multiple pieces of corrected adhesion amount information (the printing rates) is "120", the setting processing unit 62 sets the stop time to 1 second.

[0091] The third table data X30 may be provided for each specific region R20. In this case, the third table data X30 corresponding to the specific region R20 may be created according to the likelihood of curling in that specific region R20. The setting processing unit 62 may obtain, for each specific region R20, a time (a candidate time for the stop time) corresponding to that specific region R20 using the third table data X30 corresponding to that specific region R20. The setting processing unit 62 may set the longest time among the times obtained for each specific region R20 as the stop time.

[0092] When the third table data X30 is provided for each specific region R20, the setting processing unit 62 does not need to correct each piece of adhesion amount information. Also, when the third table data X30 is provided for each specific region R20, the adhesion amount information may be information indicating the amount of ink adhesion in each specific region R20.

[0093] In addition, the setting processing unit 62 may use a predetermined calculation formula instead of the third table data X30 to obtain the time corresponding to the combination of the maximum value among the multiple pieces of adhesion amount information (printing rate) after correction, the sheet basis weight, and the sheet type.

[0094] The stop processing unit 63 temporarily stops the conveyance of the sheet after the image is formed on the front side of the sheet and before the image is formed on the back side of the sheet during the double-sided image formation process, based on the stop time set by the setting processing unit 62. In other words, the stop processing unit 63 stops the conveyance of the sheet, and resumes the conveyance of the sheet when the stop time has elapsed since the conveyance was stopped.

[0095] For example, the stop processing unit 63 temporarily stops the conveyance of the sheet when the rear end of the sheet is pinched by the pair of reverse conveying rollers 51 and when the rotation direction of the pair of reverse conveying rollers 51 is switched. This temporarily stops the conveyance of the sheet when most of the sheet is outside the housing of the image forming apparatus 100, which can promote drying of the sheet.

[0096] [Transport control processing] 9, an example of the procedure of the transport control process executed by the control unit 6 in the image forming apparatus 100 and the image forming method of the present invention will be described below. Here, steps S11, S12, etc. represent the numbers of the processing procedures (steps) executed by the control unit 6. Note that the transport control process is executed together with the double-sided image formation process when the double-sided image formation process is executed.

[0097] <Step S11> First, in step S11, the control unit 6 acquires the adhesion amount information for each specific region R20 on the surface of the sheet. Here, the process of step S11 is an example of an acquisition step of the present invention, and is executed by the acquisition processing unit 61 of the control unit 6.

[0098] <Step S12> In step S12, the control unit 6 corrects each piece of adhesion amount information acquired in step S11 using the correction coefficient (see FIG. 7) previously set for each specific region R20.

[0099] <Step S13> In step S13, the control unit 6 sets the stop time based on a combination of the maximum value of the adhesion amount information after correction in the process of step S12, the type of sheet, and the basis weight of the sheet. The processes of steps S12 and S13 are an example of a setting step of the present invention, and are executed by the setting processing unit 62 of the control unit 6.

[0100] <Step S14> In step S14, the control section 6 determines whether or not the sheet has reached the position where the pair of reverse conveying rollers 51 is disposed, which is the stop position.

[0101] Here, when the control unit 6 determines that the sheet has reached the stop position (Yes in step S14), it shifts the process to step S15. On the other hand, when the sheet has not reached the stop position (No in step S14), the control unit 6 waits for the sheet to reach the stop position in step S14.

[0102] <Step S15> In step S15, the control unit 6 temporarily stops the conveyance of the sheet based on the stop time set by the process of step S13. The process of step S15 is an example of a stop step of the present invention, and is executed by the stop processing unit 63 of the control unit 6.

[0103] In this way, when the double-sided image formation process is performed in the image forming apparatus 100, the adhesion amount information is acquired for each of a plurality of specific regions R20, including a specific region R19 set in the center of the image forming region R10 and specific regions R11 to R18 set at the edges of the image forming region R10. The stop time is then set based on the acquired adhesion amount information for each of the plurality of specific regions R20. This prevents the stop time from being unnecessarily long, compared to a configuration in which the stop time is set based only on the adhesion amount information for the entire image forming region R10. Furthermore, it prevents curling in the region including the center of the sheet, compared to a configuration in which the stop time is set based only on the adhesion amount information for the edges of the image forming region R10.

[0104] The image forming apparatus 100 may include an image reading unit that reads an image of the surface of a sheet having an image formed on its surface that is conveyed by the sheet conveying unit 2. In this case, the acquisition processing unit 61 may acquire the adhesion amount information for each of the specific regions R20 based on the reading result by the image reading unit.

[0105] The present invention may also be applied to an image forming apparatus having two head units 21 (a head unit 21 used to form an image on the front surface of a sheet, and a head unit 21 used to form an image on the back surface of a sheet).

[0106] [Notes on the Invention] The following will provide an outline 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.

[0107] <Appendix 1> an acquisition processing unit that acquires, when a double-sided image formation process is performed in which images are formed on a first side and a second side of the sheet using the ejection unit, adhesion amount information regarding the amount of ink adhesion due to image formation for each of a plurality of specific areas that are set in advance in the image formation area on the first side of the sheet; a setting processing unit that sets a stop time for stopping the conveyance of the sheet based on the plurality of adhesion amount information acquired by the acquisition processing unit; and a stop processing unit that temporarily suspends the conveyance of the sheet after image formation on the first side of the sheet and before image formation on the second side of the sheet during execution of the double-sided image formation process, based on the stop time set by the setting processing unit, wherein the plurality of specific areas include a central area that is set in the center of the image formation area and an end area that is set at the end of the image formation area.

[0108] <Appendix 2> The image forming apparatus described in Appendix 1, wherein the adhesion amount information is information indicating the printing rate in the specific area, and the setting processing unit corrects each of the adhesion amount information using a correction coefficient previously set for each of the specific areas, and sets the stop time to the time obtained based on the maximum value of the adhesion amount information after correction.

[0109] <Appendix 3> The image forming apparatus of Appendix 2, wherein the end area includes a first area set at each corner of the image forming area on the upstream side in the conveying direction of the sheet, and a second area set at each corner of the image forming area on the downstream side in the conveying direction, and the correction coefficient set in the first area is the largest of the multiple correction coefficients corresponding to the multiple specific areas, and the correction coefficient set in the second area is the second largest of the multiple correction coefficients corresponding to the multiple specific areas.

[0110] <Appendix 4> An image forming apparatus according to any one of appendices 1 to 3, wherein the setting processing unit sets the stop time based on a combination of the plurality of pieces of adhesion amount information acquired by the acquisition processing unit, the type of the sheet, and the basis weight of the sheet.

[0111] <Appendix 5> An image forming method performed by an image forming device equipped with an ejection unit that ejects ink onto a sheet being transported, wherein when a double-sided image formation process is performed in which images are formed on the first and second sides of the sheet using the ejection unit, the image forming method includes: an acquisition step for acquiring adhesion amount information regarding the amount of ink adhesion due to image formation for each of a plurality of specific areas that are set in advance in the image formation area on the first side of the sheet; a setting step for setting a stop time for stopping the transport of the sheet based on the plurality of adhesion amount information acquired by the acquisition step; and a stop step for temporarily suspending the transport of the sheet after image formation on the first side of the sheet and before image formation on the second side of the sheet during execution of the double-sided image formation process based on the stop time set by the setting step, wherein the plurality of specific areas include a central area set in the center of the image formation area and an end area set at the end of the image formation area. [Explanation of symbols]

[0112] 1 Image forming unit 2 Sheet transport section 3 Operation display section 4. Communications Department 5 Storage section 6 Control Unit 21 Head 22 Cap part 23 Ink storage section 24 Ink supply passage section 25 Waste ink storage compartment 30 Recording head 30A nozzle 31 Line Head 32 Line Head 33 Line Head 34 Line Head 35 Head Frame 41 Paper cassette 42 Paper feed section 43 Paper feed path 44 Transport path 45 registration roller pair 46 Conveyor belt 47 Paper ejection path 48 Paper ejection roller pair 49 Paper output tray 50 First reversing conveyance path 51 Reversing conveying roller pair 52 Second reversing transport path 61 Acquisition processing unit 62 Setting processing section 63 Stop processing unit 100 Image forming device

Claims

1. a discharge unit that discharges ink onto the conveyed sheet; an acquisition processing unit that acquires, when a double-sided image forming process is executed in which images are formed on a first surface and a second surface of the sheet using the ejection unit, adhesion amount information regarding the amount of ink adhesion caused by image formation for each of a plurality of specific areas that are set in advance in an image forming area on the first surface of the sheet; a setting processing unit that sets a stop time for stopping conveyance of the sheet based on the plurality of pieces of adhesion amount information acquired by the acquisition processing unit; a stop processing unit that temporarily stops conveyance of the sheet after image formation on the first side of the sheet and before image formation on the second side of the sheet during execution of the double-sided image formation process, based on the stop time set by the setting processing unit; Equipped with the plurality of specific regions include a central region set in the central portion of the image forming region and edge regions set at the edges of the image forming region; Image forming device.

2. The adhesion amount information is information indicating a printing rate in the specific area, the setting processing unit corrects each of the adhesion amount information using a correction coefficient that is set in advance for each of the specific regions, and sets a time acquired based on a maximum value of the adhesion amount information after the correction as the stop time. The image forming apparatus according to claim 1 .

3. the edge area includes a first area set at each corner on the upstream side in the conveying direction of the sheet in the image forming area, and a second area set at each corner on the downstream side in the conveying direction of the sheet in the image forming area, the correction coefficient set for the first region is the largest among the plurality of correction coefficients corresponding to the plurality of specific regions; the correction coefficient set for the second region is the second largest among the plurality of correction coefficients corresponding to the plurality of specific regions; The image forming apparatus according to claim 2 .

4. the setting processing unit sets the stop time based on a combination of the plurality of pieces of adhesion amount information acquired by the acquisition processing unit, the type of the sheet, and the basis weight of the sheet.

4. The image forming apparatus according to claim 1.

5. 1. An image forming method executed by an image forming apparatus including an ejection unit that ejects ink onto a sheet being conveyed, an acquisition step of acquiring adhesion amount information regarding the amount of ink adhesion caused by image formation for each of a plurality of specific areas that are set in advance in an image formation area on the first surface of the sheet when a double-sided image formation process is executed in which images are formed on a first surface and a second surface of the sheet using the ejection unit; a setting step of setting a stop time for stopping conveyance of the sheet based on the plurality of pieces of adhesion amount information acquired in the acquiring step; a stopping step of temporarily stopping conveyance of the sheet after image formation on the first side of the sheet and before image formation on the second side of the sheet during execution of the double-sided image formation process, based on the stop time set in the setting step; Including, the plurality of specific regions include a central region set in the central portion of the image forming region and edge regions set at the edges of the image forming region; Image forming method.

Images