JP5911461B2 - Sheet conveying apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus that convey a sheet by adsorbing the sheet to a conveying belt by suction adsorption and electrostatic adsorption.

  In general, an inkjet recording apparatus (an example of an image forming apparatus) that records an image by discharging ink from a recording head onto a sheet is known. One type of ink jet recording apparatus is a so-called line head type ink jet recording apparatus that includes recording heads of respective colors arranged along a sheet conveyance path. This type of ink jet recording apparatus is equipped with a sheet conveying apparatus that conveys a sheet with a conveying belt facing the ink ejection surface of each recording head, and ink is ejected from each recording head onto the sheet being conveyed. .

  In addition, a configuration in which an alternating charge pattern is formed on the conveyor belt to electrostatically attract the sheet to the conveyor belt, and the sheet is sucked and attracted to the conveyor belt by sucking air through a plurality of belt openings formed on the conveyor belt. It is known (see, for example, Patent Document 1). In the configuration using suction suction, a transport plate having a plurality of platen openings is provided below the transport belt. Then, air is sucked from the back surface side of the conveying plate through the platen opening and the belt opening, whereby the sheet is adsorbed to the conveying belt.

  Furthermore, a configuration is known in which suction is used at the center in the width direction perpendicular to the conveyance direction of the sheet by the conveyance belt and electrostatic adsorption is used at the end in the width direction to adsorb the sheet to the conveyance belt. (For example, refer to Patent Document 2).

JP 2008-230819 A JP 2011-255635 A

  By the way, the lift generated in the sheet conveyed by the conveying belt tends to occur at the corner of the sheet. On the other hand, after an image is formed on a sheet using a high humidity environment or ink, there is a possibility that the electrical resistance of the sheet is lowered, the charging efficiency is lowered, and the adsorption force of the sheet due to electrostatic adsorption is lowered. For this reason, in the configuration in which the end portion in the width direction of the sheet is attracted by electrostatic attraction, there is a possibility that lifting of the corner portion of the sheet cannot be suppressed. Further, in the configuration in which suction adsorption is performed using a plurality of belt openings formed on the entire conveyance belt, the conveyance belt is applied to the conveyance plate according to the presence or absence of the sheet on the conveyance belt or the size of the sheet. There is a possibility that the attractive force changes greatly and affects the driving of the conveyor belt.

  An object of the present invention is a sheet conveyance capable of suppressing the lift of the corner portion of the sheet while suppressing the influence on the driving of the conveyance belt in the configuration in which the sheet is attracted to the conveyance belt by the suction adsorption and the electrostatic adsorption and conveyed. An apparatus and an image forming apparatus are provided.

  A sheet conveying apparatus according to one aspect of the present invention includes a conveying belt, a conveying plate, an intake unit, and a charging unit. The conveyance belt has a plurality of belt openings formed in a predetermined suction suction region at an end in the width direction perpendicular to the sheet conveyance direction, and conveys the sheet. The transport plate has a plurality of platen openings formed at positions corresponding to the belt openings in the width direction, and is disposed on the back side of the transport belt. The intake portion sucks air from the back side of the transport plate through the belt opening and the platen opening. The charging unit charges a predetermined electrostatic adsorption region at the center in the width direction of the transport belt.

  An image forming apparatus according to another aspect of the present invention includes the sheet conveying device and an image forming unit. The image forming unit forms an image by discharging aqueous ink onto the sheet conveyed by the sheet conveying device.

  According to the present invention, in the configuration in which a sheet is adsorbed to a conveyance belt by suction adsorption and electrostatic adsorption and conveyed, the rise of the corner of the sheet can be suppressed while suppressing the influence on the driving of the conveyance belt.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic view of a conveyance belt provided in the image forming apparatus illustrated in FIG. 1 as viewed from above. FIG. 2 is a block diagram showing a system configuration of the image forming apparatus shown in FIG. 1. 3 is a flowchart illustrating an example of a conveyance control process executed by the image forming apparatus illustrated in FIG. 3 is a flowchart illustrating an example of a conveyance control process executed by the image forming apparatus illustrated in FIG.

  Embodiments of the present invention will be described below with reference to the accompanying drawings for understanding of the present invention. In addition, the following embodiment is an example which actualized this invention, Comprising: The thing of the character which limits the technical scope of this invention is not.

  First, a schematic configuration of an image forming apparatus 10 according to an embodiment of the present disclosure will be described with reference to FIG.

  The image forming apparatus 10 includes a paper feeding cassette 1, a paper feeding unit 2, an image forming unit 3, an ink tank unit 4, a sheet conveying unit 5, a paper discharging unit 6, an air intake unit 7, a charging unit 8, a control unit 11, and an operation. A display unit 12 and a main body frame 9 are provided. The image forming apparatus 10 is an ink jet printer that forms an image on a sheet using water-based ink based on print data (image data) input from an information processing apparatus such as a personal computer. The image forming apparatus according to the present invention can be applied not only to a printer but also to a copying machine, a facsimile machine, or a multifunction machine. An apparatus including at least the sheet conveying section 5, the intake section 7, and the charging section 8 is an example of a sheet conveying apparatus according to the present invention.

  The operation display unit 12 includes a display unit and an operation unit. The display unit is a liquid crystal display device or an organic EL display that displays various types of information in accordance with control instructions from the control unit 11. The operation unit includes a touch panel and hard keys for inputting various information to the control unit 11 according to a user operation.

  A plurality of sheets P are accommodated in the paper feed cassette 1. The sheet P is a recording medium such as paper or film, and the image forming apparatus 10 forms an image on the sheet P.

  The paper feed unit 2 includes a pickup roller 21, a transport roller 22, a transport path 23, a registration roller 24, a manual feeder 25, and a paper feed roller 26. The pickup roller 21 takes out the sheets P from the sheet feeding cassette 1 one by one. The transport roller 22 and the transport path 23 transport the sheet P taken out by the pickup roller 21 to the registration roller 24. The registration roller 24 conveys the sheet P to the image forming unit 3 at a predetermined conveyance timing (image writing timing). The manual feeder 25 and the paper feed roller 26 are used for supplying the sheet P from the outside.

  The image forming unit 3 includes a recording head 31 corresponding to K (black), a recording head 32 corresponding to C (cyan), a recording head 33 corresponding to M (magenta), and a recording head corresponding to Y (yellow). 34 is an ink jet recording unit. Each of the recording heads 31 to 34 is disposed so as to face a placement surface 51 </ b> A of a conveyance belt 51 provided in the sheet conveyance unit 5. Each of the recording heads 31 to 34 has a long shape in the width direction D2 perpendicular to the conveyance direction D1 of the sheet P by the sheet conveyance unit 5, and is arranged at predetermined intervals along the conveyance direction D1. . An ink ejection surface having a large number of nozzles (ejection ports) for ejecting ink is provided at the lower ends of the recording heads 31 to 34, respectively.

  Then, the image forming unit 3 ejects ink from the ink ejection surface of the recording heads 31 to 34 onto the sheet P that is transported by being placed on the placement surface 51A of the transport belt 51 by the sheet transport unit 5. Then, an image is formed on the sheet P. That is, the image forming apparatus 10 is a so-called line head type ink jet recording apparatus. The ink used in the image forming unit 3 is a water-based ink. As the ink ejection method of the recording heads 31 to 34, for example, a piezo method that ejects ink using a piezo element or a thermal method that ejects ink by generating bubbles by heating is employed.

  The ink tank unit 4 includes an ink tank 41 corresponding to the recording head 31, an ink tank 42 corresponding to the recording head 32, an ink tank 43 corresponding to the recording head 33, and an ink tank corresponding to the recording head 34. 44. The ink tanks 41 to 44 are connected to the recording heads 31 to 34 of the same color by ink tubes (not shown), and replenish the recording heads 31 to 34 with ink of each color.

  The sheet conveying unit 5 is disposed below the recording heads 31 to 34. The sheet conveying unit 5 conveys the sheet P supplied from the sheet feeding unit 2 to the paper discharge unit 6 while facing the ink ejection surfaces of the recording heads 31 to 34. Specifically, the sheet conveying unit 5 includes a conveying belt 51, a driving roller 52, driven rollers 53, 54 and 55, a pressing roller 56, and a humidity sensor 57. The gap between the conveyance belt 51 and the ink ejection surfaces of the recording heads 31 to 34 is such that the interval between the sheet P conveyed by the conveyance belt 51 and the ink ejection surfaces of the recording heads 31 to 34 is 1 mm, for example. It is determined to be 2 mm or less.

  The conveyor belt 51 is an endless belt having a placement surface 51A on which the sheet P is placed, and is stretched by the driving roller 52 and the driven rollers 53 to 55 with a predetermined tension. The conveyance belt 51 conveys the sheet P placed on the placement surface 51A in the conveyance direction D1 by traveling along the conveyance direction D1 shown in FIG. The conveyor belt 51 is formed of a dielectric material such as urethane rubber, PET (polyethylene terephthalate) resin, ETFE (tetrafluoroethylene / ethylene copolymer) resin, PI (polyimide) resin, or PAI (polyamideimide) resin. ing. For example, the transport belt 51 has an inner layer having an electric resistance value of 5 [logΩ] to 7 [logΩ] and an outer layer provided on the outer periphery thereof having an electric resistance value of 14 [logΩ] to 17 [logΩ]. It is a multilayer belt.

  The drive roller 52 is connected to the rotation shaft of the motor 52A. When the driving roller 52 rotates counterclockwise by driving the motor 52A, the transport belt 51 travels along the transport direction D1. At this time, the driven rollers 53 to 55 are rotated by a driving force transmitted through the conveying belt 51 by driving the driving roller 52.

  The driven roller 54 is long in the width direction D2 and is a conductive metal roller or the like, and is connected to the common ground with the charging unit 8. Accordingly, the driven roller 54 acts as one electrode during the charging operation of the transport belt 51 by the charging unit 8.

  The pressing roller 56 is provided at a sheet feeding position of the sheet P from the sheet feeding unit 2 to the sheet conveying unit 5. The pressing roller 56 is disposed at a position facing the driven roller 55, and the transport belt 51 is sandwiched between the driven roller 55 and the pressing roller 56. The pressing roller 56 presses the sheet P supplied from the sheet feeding unit 2 against the conveyance belt 51 to bring it into close contact therewith.

  The humidity sensor 57 is a humidity detection unit that detects the humidity in the image forming apparatus 10. The humidity detected by the humidity sensor 57 is input to the control unit 11.

  The paper discharge unit 6 is provided on the downstream side of the image forming unit 3 in the transport direction D1 of the sheet transport unit 5. The paper discharge unit 6 includes a drying device 61, a conveyance path 62, a paper discharge roller 63, a paper discharge tray 64, a double-sided printing mechanism 65, and the like. The drying device 61 blows air on the sheet P to dry the ink attached to the sheet P. In addition, the conveyance destination of the sheet P that has been image-formed by the image forming unit 3 and dried by the drying device 61 is switched by the switching unit (not shown) that can be controlled by the control unit 11. And the double-sided printing mechanism 65. The sheet P conveyed to the conveyance path 62 is discharged to the paper discharge tray 64 by the paper discharge roller 63.

  On the other hand, the double-sided printing mechanism 65 inverts the front and back surfaces of the sheet P on which the image is formed by the image forming unit 3 and conveys the sheet P again to the image forming unit 3. Specifically, the double-sided printing mechanism 65 includes transport paths 651 to 653 and transport rollers 654 to 656 disposed on the transport paths 651 to 653. In the transport path 651, the sheet P is transported to the transport path 652 by the transport roller 654. The conveyance path 652 is a path for reversing the front and back surfaces of the sheet P. In the conveyance path 652, after the sheet P is accommodated in the conveyance path 652 by the conveyance roller 655, the conveyance roller 652 By the reverse driving of 655, the sheet P is conveyed from the rear end to the conveyance path 653. The transport path 652 is provided with a switching unit (not shown) that is controlled by the control unit 11 and switches the connection destination of the transport path 652 to either the transport path 651 or the transport path 653. . The transport path 653 is a path for transporting the sheet P to the image forming unit 3 again. In the conveyance path 653, the sheet P is conveyed by the conveyance roller 656 toward the pressing roller 56 on the upstream side of the image forming unit 3. As a result, the image forming unit 3 can perform image formation on the back surface of the sheet P after image formation on the front surface of the sheet P. That is, the image forming apparatus 10 has a double-sided printing function for forming images on the front and back surfaces of the sheet P.

  The intake portion 7 is disposed below the recording heads 31 to 34 and at a position inside the annular conveying belt 51. The intake unit 7 sucks the air from the back side of the conveyance belt 51 to adsorb the sheet P to the conveyance belt 51. The configuration of the intake section 7 will be described in detail later.

  The charging unit 8 is disposed on the upstream side of the pressing roller 56 in the transport direction D <b> 1 of the transport belt 51, that is, on the upstream side of the sheet feeding position of the sheet P from the sheet feeding unit 2. The charging unit 8 includes a charging member 81 and a power supply device 82, and charges the placement surface 51 </ b> A of the transport belt 51. The charging member 81 is electrically connected to the power supply device 82.

  The charging member 81 is a roller member that is disposed at a position facing the driven roller 54 with the conveyance belt 51 interposed therebetween, and is a roller member that rotates clockwise as the conveyance belt 51 travels in the conveyance direction D1. is there. The charging member 81 is a roller member having conductivity, and its electric resistance value is, for example, 3 [logΩ] or more and 9 [logΩ] or less. The charging member 81 is, for example, a resin material such as urethane resin, thermoplastic elastomer, epichlorohydrin rubber, ethylene-propylene-diene copolymer rubber (EPDM), silicon rubber, acrylonitrile-butadiene copolymer rubber, and linorbornene rubber. Formed by a mixture of one or more of the following: The charging member 81 may be a blade. Further, it is also conceivable as another embodiment that the charging unit 8 includes two or more charging members 81.

  The power supply device 82 is a constant voltage power supply that applies a predetermined voltage to the charging member 81. Specifically, the power supply device 82 has 5 k [Vp−p] in which +2.5 [kV] and −2.5 [kV] alternate with the charging member 81 at a preset alternating cycle T1 [s]. Apply the alternating voltage. For example, the power supply device 573 alternately switches the polarity of a constant voltage (2.5 kV) output from the output terminal connected to the charging member 81 at the alternating cycle T1 [s]. For example, the alternating cycle T1 is 1/100 [s] or more and 1/10 [s] or less, and the frequency of the alternating voltage output from the power supply device 82 is 10 [Hz] or more and 100 [Hz] or less. When the alternating voltage is applied to the charging member 81 by the power supply device 82, a belt-like charge pattern with alternating positive and negative is formed on the placement surface 51A of the conveyor belt 51. Accordingly, the sheet P supplied from the paper feeding unit 2 to the conveyance belt 51 is electrostatically attracted to the conveyance belt 51 and conveyed. Note that the voltage applied to the transport belt 51 by the charging member 81 is not limited to the alternating voltage as described above, and may be an arbitrary DC voltage or an AC voltage.

  By the way, the lift that occurs in the sheet P conveyed by the conveyance belt 51 tends to occur at the corners of the sheet P. On the other hand, after an image is formed on the sheet P using a high-humidity environment or ink, the electrical resistance of the sheet P decreases, charging efficiency decreases, and the adsorption force due to electrostatic adsorption may decrease. is there. For this reason, in the configuration in which the end portion in the width direction D2 of the sheet P is attracted by electrostatic attraction, there is a possibility that the rising of the corner portion of the sheet P cannot be sufficiently suppressed. In the configuration in which suction and adsorption is performed on the entire conveyance belt 51, the conveyance belt 51 is moved to the conveyance plate 71 in accordance with the presence or absence of the sheet P on the conveyance belt 51 or the size of the sheet P. There is a possibility that the attraction force of the toner will greatly change and affect the driving of the conveyor belt 51. On the other hand, in the image forming apparatus 10, as described below, it is possible to suppress the corners of the sheet P from being lifted while suppressing the influence on the driving of the transport belt 51.

  Next, the details of the intake section 7 and the charging section 8 will be described with reference to FIG. FIG. 2 is a schematic view of the conveyor belt 51 as viewed from above.

  As shown in FIG. 2, the conveyance belt 51 has a plurality of belt openings 511 that penetrate the placement surface 51A. The belt opening 511 is circular, elliptical, rectangular, or the like. The belt opening 511 is arranged at predetermined intervals in the transport direction D1 and the width direction D2 in a predetermined suction suction region R1 at the end of the width direction D2 perpendicular to the transport direction D1 of the sheet P. Is formed. For example, the suction suction region R1 includes an end portion of a maximum size (for example, A3) and a minimum size (for example, A3) of the sheet P that can be used in the image forming apparatus 10 at the end portion of the conveyance belt 51 in the width direction D2. This is a region including the end of A5). Each of the belt openings 511 may be arranged in a staggered manner on the transport belt 51.

  The intake section 7 includes a conveyance plate 71, an intake duct 72, and intake fans 73 to 75. The transport plate 71 is a plate-like member disposed on the back side of the transport belt 51 so as to face the ink ejection surfaces of the recording heads 31 to 34. The transport plate 71 includes a plurality of platen openings 711 that penetrate the front and back surfaces, and a plurality of grooves 712 formed on the front surface. The platen openings 711 are formed at predetermined intervals along the transport direction D1 at positions corresponding to the belt openings 511 in the width direction D2. The platen opening 711 is circular, elliptical, rectangular, or the like. Each of the groove portions 712 is a long groove formed so as to extend in a direction along the transport direction D1, and at least one platen opening 711 is formed in the groove portion 711. As a result, the suction force of the sheet P by the intake portion 7 acts not only in the formation region of the platen opening 711 but also in the formation region of the groove portion 712.

  The intake duct 72 is disposed below the transport plate 71 and joined to the back surface of the transport plate 71. The intake duct 72 is provided corresponding to the size of the sheet P conveyed by the conveyance belt 51, and a plurality of intake ducts 721 to form a ventilation path below the platen opening 711 of the conveyance plate 71. 723. Specifically, the intake duct 721 is a pair of ducts corresponding to a region including both end positions of a preset first size in the width direction D2. The intake duct 723 is a pair of ducts corresponding to a region including both end positions of a second size set in advance in the width direction D2. The intake duct 722 is a pair of ducts corresponding to a region including both end positions of a preset third size in the width direction D2.

  For example, the first size corresponding to the intake duct 721 is the maximum size that can be used in the image forming apparatus 10 and may be, for example, “A3”. Further, the third size corresponding to the intake duct 723 may be the minimum size that can be used in the image forming apparatus 10 and may be “A5”, for example. Further, the second size corresponding to the intake duct 722 may be an intermediate size between the maximum size and the minimum size, for example, “A4”. Note that each of the intake ducts 721 to 723 may correspond to a plurality of sizes. For example, the intake duct 721 corresponds to “A3” and “B4”, the intake duct 722 corresponds to “A4” and “B5”, and the intake duct 723 corresponds to “A5” and “A6”. Can be considered.

  The intake fans 73 to 75 are centrifugal fans called sirocco fans, for example. The air suction unit 7 sucks air from the back surface side of the transport plate 71 through the belt opening 511 and the platen opening 711 to adsorb the sheet P to the transport belt 51. The presence / absence of driving of the intake fans 73 to 75 and the rotational speed can be individually controlled by the control unit 11. The intake fan 73 may be an axial fan such as a propeller fan.

  The intake fans 73 to 75 are provided corresponding to the intake ducts 721 to 723, respectively. The intake fan 73 and the intake duct 721 are connected by a connection duct 731. Thus, an air blowing path is formed from the platen opening 711 of the transport plate 71 formed at a position corresponding to the intake duct 721 to the intake fan 73 via the intake duct 721 and the connection duct 731. The

  Similarly, the intake fan 74 and the intake duct 722 are connected by a connection duct 741. As a result, an air blowing path is formed from the platen opening 711 of the transport plate 71 formed at a position corresponding to the intake duct 722 to the intake fan 74 through the intake duct 722 and the connection duct 741. The Further, the intake fan 75 and the intake duct 723 are connected by a connection duct 751. Thereby, an air blowing path is formed from the platen opening 711 of the transport plate 71 formed at a position corresponding to the intake duct 723 to the intake fan 75 via the intake duct 723 and the connection duct 751. The

  Therefore, in the intake section 7, the presence or absence of air suction in each of the areas corresponding to the intake ducts 721 to 723 in the suction adsorption area R1 is switched by switching the presence or absence of driving of the intake fans 73 to 75. It is possible to switch individually.

  Note that the image forming apparatus 10 may include a single intake fan instead of the intake fans 73 to 75 and a shutter that opens and closes a ventilation path from the intake fan to each of the intake ducts 721 to 723. . A configuration in which the image forming apparatus 10 includes six intake fans respectively corresponding to the six intake ducts 721 to 723 provided in the suction adsorption region R1 is also conceivable.

  On the other hand, the charging member 81 of the charging unit 8 has a width corresponding to a preset electrostatic attraction region R2 at the center in the width direction D2. As a result, the charging unit 8 can charge the electrostatic adsorption region R2 in the center of the transport belt 51 in the width direction D2 from the charging member 81. That is, in the charging unit 8, no voltage is applied to the suction suction region R1 of the transport belt 51, and therefore the suction suction region R1 of the transport belt 51 is not charged. Therefore, in the configuration in which the sheet P is attracted to the transport belt 51 and transported by using electrostatic suction and suction suction together, discharge that may occur in the belt opening 511 is suppressed, and the transport belt 51 and the charging member 81 are suppressed. And deterioration of the driven roller 54 and the like are suppressed.

  As described above, in the image forming apparatus 10, the end portion of the sheet P in the width direction D <b> 2 can be adsorbed to the transport belt 51 by suction adsorption by the air intake unit 7. Even after an image is formed on the sheet P, the flatness of the sheet P is maintained. Accordingly, the distance between the ink ejection surface of the recording heads 31 to 34 and the sheet P conveyed by the conveyance belt 51 is kept constant, and contact between the ink ejection surface and the sheet P is prevented. Further, as compared with a configuration in which suction and adsorption is performed on the entire conveyance belt 51, the conveyance belt 51 is moved to the conveyance plate 71 according to whether or not the sheet P is placed on the conveyance belt 51 or according to the size of the sheet P. The change in the adsorbing force becomes smaller. Therefore, the influence on the drive of the conveyance belt 51 is suppressed.

  Next, the system configuration of the image forming apparatus 10 will be described with reference to FIG.

  As shown in FIG. 3, the control unit 11 includes the paper feeding unit 2, the image forming unit 3, the ink tank unit 4, the sheet conveying unit 5, the paper discharging unit 6, the air intake unit 7, and the charging unit. The unit 8 and the operation display unit 12 are connected.

  The control unit 11 includes control devices such as a CPU, a ROM, a RAM, and an EEPROM. The CPU is a processor that executes various arithmetic processes. The control unit 11 may have a plurality of control entities (processors). The ROM is a non-volatile storage unit in which information such as a control program for causing the CPU to execute various processes is stored in advance. The CPU performs overall control of the image forming apparatus 10 by executing various processes according to various control programs stored in advance in the ROM. The RAM is a volatile storage unit, and the EEPROM is a non-volatile storage unit. The RAM and the EEPROM are used as a temporary storage memory (working area) for various processes executed by the CPU.

  The control unit 11 includes a first intake control unit 111, a usage amount specifying unit 112, a second intake control unit 113, a first stop control unit 114, a second stop control unit 115, and a selection control unit 116. Specifically, the control unit 11 uses the CPU to execute the control program stored in the ROM, thereby causing the first intake control unit 111, the usage amount specifying unit 112, and the second intake air. It functions as the control unit 113, the first stop control unit 114, the second stop control unit 115, and the selection control unit 116. When the control unit 5 is an electronic circuit such as an ASIC, the first intake control unit 111, the usage amount specifying unit 112, the second intake control unit 113, the first stop control unit 114, The second stop control unit 115 and the selection control unit 116 are circuit modules included in the control unit 5.

  The first air intake control unit 111 controls the operation of the air intake unit 7 when the surface of the sheet P is printed in the image forming apparatus 10. Specifically, the first intake control unit 111 controls the intake unit 7 such that the higher the humidity detected by the humidity sensor 57, the higher the air suction force. In the present embodiment, an example is described in which the first intake control unit 111 switches the suction force between “high” and “low” depending on whether the humidity is equal to or higher than a preset first threshold value. Will be described. The first intake control unit 111 can change the air suction force by the intake unit 7 by changing the rotational speed of the intake fans 73 to 75.

The usage amount specifying unit 112 specifies the amount of ink used that is ejected onto the surface of the sheet P by the image forming unit 3 in the image forming apparatus 10. The ink use amount is used as an index value of the amount of water contained in the sheet P after the image formation by the image forming unit 3. For example, the usage amount specifying unit 112 derives a printing rate or an ink amount rate based on image data input to the image forming apparatus 10, and determines the ink usage amount based on the printing rate or the ink amount rate. It is possible to specify. The printing rate is a value indicating the ratio of the printing area in the printable area of the sheet P. The ink amount rate is a value indicating a ratio of the ink amount discharged onto the sheet P by the recording heads 31 to 34 with respect to the maximum value.

  The second intake control unit 113 controls the operation of the intake unit 7 when the sheet P is conveyed again to the image forming unit 3 by the double-sided printing mechanism 65, that is, when the back side of the sheet P is printed. Specifically, the second intake control unit 113 determines the ink use amount specified by the use amount specifying unit 112 when the sheet P is conveyed again to the image forming unit 3 by the double-sided printing mechanism 65. The intake section 7 is controlled so that the air suction force increases as the amount of air increases. In the present embodiment, the second air intake control unit 113 increases the suction force at the time of printing the back surface of the sheet P according to whether or not the ink usage amount is equal to or higher than a second threshold value set in advance. ”And“ low ”will be described as an example.

  The first stop control unit 114 is configured such that the humidity detected by the humidity sensor 57 is less than a preset third threshold value, or a pre-ink use amount specified by the use amount specifying unit 112 is set in advance. When it is less than 4 thresholds, the suction of air by the intake section 7 is stopped.

  The second stop control unit 115 is configured such that the humidity detected by the humidity sensor 57 is equal to or higher than a preset fifth threshold value, or a pre-ink use amount specified by the use amount specifying unit 112 is set in advance. If it is less than 6, the charging by the charging unit 8 is stopped.

  The selection control unit 116 selects one or a plurality of the air intake ducts used for air suction by the air intake unit 7 among the air intake ducts 721 to 723, the size of the sheet P, the humidity, the ink usage amount, and the like. Select according to.

[Transport control processing]
Hereinafter, an example of the procedure of the conveyance control process executed by the control unit 11 will be described with reference to the flowcharts of FIGS. 4 and 5. Here, each processing procedure executed by the control unit 11 is referred to as steps S1, S2,. The conveyance control process is executed by the control unit 11 when an image forming process for forming an image on the sheet P using the image forming unit 3 is executed in the image forming apparatus 10.

<Step S1>
First, in step S <b> 1, the control unit 11 detects humidity in the image forming apparatus 10 using the humidity sensor 57.

<Step S2>
In step S2, the second stop control unit 115 of the control unit 11 determines whether or not the humidity detected in the step S1 is greater than or equal to a preset fifth threshold value. The fifth threshold value is an arbitrary value set in advance to determine whether or not the attracting force due to electrostatic attraction is sufficiently small. For example, the fifth threshold value may be a value set in advance in a range of 50% to 80%. Here, if the said control part 11 judges that the said humidity is more than the said 5th threshold value (Yes side of S2), it will transfer a process to step S3. On the other hand, if the said control part 11 judges that the said humidity is less than the said 5th threshold value (No side of S2), it will transfer a process to step S4.

<Step S3>
In step S <b> 3, the second stop control unit 115 of the control unit 11 sets “no drive” as to whether or not the charging unit 8 is driven during the front surface printing of the image forming process. As a result, during surface printing in the image forming process, charging by the charging unit 8 is stopped and electrostatic adsorption is not performed. As described above, in the image forming apparatus 10, when the humidity is sufficiently high and the attracting force due to electrostatic attraction is low, the driving of the charging unit 8 is stopped to save power. Figured.

<Step S4>
In step S4, the first stop control unit 114 of the control unit 11 determines whether or not the humidity detected in step S1 is less than a preset third threshold value. The third threshold value is an arbitrary value set in advance to determine whether or not the attracting force by electrostatic attraction is sufficiently high. For example, the third threshold value may be a value set in advance in a range of 10% to 50%. Here, if the said control part 11 judges that the said humidity is less than the said 3rd threshold value (Yes side of S4), it will transfer a process to step S41. On the other hand, if the said control part 11 judges that the said humidity is more than the said 3rd threshold value (No side of S4), it will transfer a process to step S5.

<Step S41>
In step S <b> 41, the first stop control unit 114 of the control unit 11 sets “no drive” as to whether or not the intake unit 7 is driven during the front surface printing of the image forming process. As a result, during the surface printing of the image forming process, the suction of air by the suction portion 7 is stopped and suction suction is not performed. As described above, in the image forming apparatus 10, when the humidity is sufficiently low and the attracting force by electrostatic attraction is high, the driving of the intake unit 7 is stopped to save power.

<Step S5>
In step S5, the first intake control unit 111 of the control unit 11 determines whether the humidity detected in the step S1 is equal to or higher than a preset first threshold value. The first threshold value is an arbitrary value set in advance to determine whether or not the attractive force due to electrostatic attraction is reduced. For example, the fifth threshold value may be a value set in advance in a range of 50% to 80%. Here, if the said control part 11 judges that the said humidity is more than the said 1st threshold value (Yes side of S5), it will transfer a process to step S51. On the other hand, if the said control part 11 judges that the said humidity is less than the said 1st threshold value (No side of S5), it will transfer a process to step S6.

<Step S51>
In step S51, the first intake control unit 111 of the control unit 11 sets the suction force by the intake unit 7 at the time of surface printing of the image forming process to a preset “high”. That is, when the humidity is high, a shortage of electrostatic attraction force due to a decrease in charging efficiency of the sheet P by the charging unit 8 is caused by the suction force by the intake unit 7 being set high. Be compensated.

<Step S6>
In step S6, the first intake control unit 111 of the control unit 11 preliminarily reduces the suction force by the intake unit 7 during the surface printing of the image forming process, which is lower than the “high” set in the step S51. Set to the set “low”. That is, when the humidity is low, since the charging efficiency of the sheet P by the charging unit 8 is high and the suction force by electrostatic adsorption is high, the suction force by the suction unit 7 is set low, so that the suction unit The power consumption in 7 is suppressed.

<Step S7>
In step S <b> 7, the selection control unit 116 of the control unit 11 sets one or a plurality of intake ducts of the intake ducts 721 to 723 according to the size and the humidity of the seat P. Select the intake duct to be used when printing on the front side. In the present embodiment, the selection of the intake ducts 721 to 723 is synonymous with the selection of the intake fans 73 to 75. For example, the control unit 11 selects the intake duct in the following procedure.

  First, the control unit 11 selects the intake ducts 721 to 723 that are present at the end positions of the size of the sheet P in the width direction D2. For example, when the size of the seat P is “A3”, the intake duct 721 is selected, and when the size of the seat P is “A4”, the intake duct 722 is selected. When the size of the seat P is “A5”, the intake duct 723 is selected.

  Thereby, since the intake duct located at the end of the size of the sheet P is selected from the intake ducts 721 to 723 and is used when the sheet is conveyed, the end of the sheet P, in particular, the corner is lifted. It is suppressed.

  And the said control part 11 judges the presence or absence of the use of the intake duct which exists inside the said intake duct selected according to the size of the said sheet | seat P among the said intake ducts 721-723 according to the said humidity. For example, when the control unit 11 selects the intake duct 721 according to the size of the seat P and the humidity is equal to or higher than a preset first humidity, the intake duct 722 and the It is determined that the intake duct 723 is used together with the intake duct 721. In addition, when the control unit 11 selects the intake duct 721 according to the size of the seat P, the humidity is less than the first humidity and is equal to or higher than a preset second humidity. The intake duct 722 is determined to be used together with the intake duct 721. Further, when the control unit 11 selects the intake duct 721 according to the size of the seat P and the humidity is less than the second humidity, the intake duct 722 and the intake duct 723 are selected. Is determined not to be used.

  Thus, when the humidity is high and the electrostatic attraction force is low, an intake duct existing inside the intake duct is used together with the intake duct selected according to the size of the sheet P, Insufficient electroadsorption force is compensated for by suction adsorption by the intake part 7. Further, when the humidity is low and the electrostatic adsorption force is high, unnecessary driving of the intake fans 73 to 75 is prevented, so that power consumption by the intake unit 7 is suppressed. Note that the control unit 11 may omit the step S7 when the intake unit 7 is set to “no drive” in the step S41.

<Step S8>
In step S <b> 8, the control unit 11 determines whether the image forming process is a double-sided printing process using the double-sided printing mechanism 65. Here, when the control unit 11 determines that it is the double-sided printing process (Yes side of S8), the control unit 11 shifts the process to step S9 and executes a back side conveyance setting process (see FIG. 5) described later. On the other hand, when the control unit 11 determines that it is not the double-sided printing process (No in S8), the process proceeds to step S10.

<Step S9>
Here, the back surface conveyance setting process will be described with reference to FIG.

<Step S91>
First, in step S91, the usage amount specifying unit 112 of the control unit 11 specifies an ink usage amount during surface printing in the image forming process. In the image forming apparatus 10, when ink is ejected onto the sheet P and the moisture content of the sheet P increases, the electrical resistance of the sheet P decreases and the charging efficiency of the sheet P decreases. The step S91 is a process for obtaining the ink usage amount at the time of printing the front surface of the sheet P as a determination index of the charging efficiency of the sheet P at the time of printing the back surface of the sheet P.

  In particular, in the sheet P, when the surface of the sheet P is printed, when a large amount of ink is ejected to the end portion in the width direction D2 at the front end or the rear end in the transport direction D1 of the sheet P, the sheet P Lifting is likely to occur at the corners of the sheet P during backside printing. Therefore, the amount of ink used specified in step S91 is not the total amount of ink ejected on the entire sheet P, but the amount of ink used in a predetermined specific area in the sheet P. Can be considered. The specific area is an area set in advance from the leading or trailing edge of the sheet P in the transport direction D1, and includes an area set in advance from the end in the width direction D2. For example, the distance from the leading edge or the trailing edge of the transport direction D1 of the sheet P in the specific region is in the range of 0.1 cm to 3.0 cm, and the distance from the edge of the sheet P in the width direction D2 is It may be set in advance in a range of 0.1 cm to 3.0 cm. The usage amount specifying unit 112 of the control unit 11 calculates the printing rate or the ink amount rate in the specific region based on the image data to be subjected to the image forming process, and the printing rate or the ink amount is calculated. Based on the amount ratio, the ink usage amount in the specific area is specified. Further, the specific area may be an area within a preset range from the leading edge in the transport direction D1 of the sheet P when the double-sided printing mechanism 65 transports the image P to the image forming unit 3 again.

<Step S92>
In step S92, the second stop control unit 115 of the control unit 11 determines whether or not the ink usage specified in step S91 is equal to or greater than a preset sixth threshold value. The sixth threshold value is an arbitrary value set in advance to determine whether or not the attracting force due to electrostatic attraction is sufficiently small. For example, the sixth threshold value is a value set in advance as an ink use amount corresponding to a range where the printing rate is 50% or more and 80% or less or a range where the ink amount rate is 50% or more and 100% or less. Can be considered. In addition, the second stop control unit 115 determines whether the ink usage amount is greater than or equal to the sixth threshold according to whether the printing rate or the ink amount rate is greater than or equal to a predetermined value. Also good. Here, when the control unit 11 determines that the ink use amount is equal to or greater than the sixth threshold (Yes in S92), the process proceeds to Step S93. On the other hand, when the control unit 11 determines that the ink usage amount is less than the fifth threshold value (No side of S92), the process proceeds to step S94.

<Step S93>
In step S <b> 93, the second stop control unit 115 of the control unit 11 sets “no drive” as to whether or not the charging unit 8 is driven during the back side printing of the image forming process. As a result, during the back side printing of the image forming process, charging by the charging unit 8 is stopped and electrostatic adsorption is not performed. As described above, in the image forming apparatus 10, when the attracting force due to electrostatic attraction is low because the amount of ink used is sufficiently large, the driving of the charging unit 8 is stopped to save power. Is achieved.

<Step S94>
In step S94, the first stop control unit 114 of the control unit 11 determines whether or not the ink usage specified in step S91 is less than a preset fourth threshold value. The fourth threshold value is an arbitrary value set in advance to determine whether or not the attracting force by electrostatic attraction is sufficiently high. For example, the fourth threshold value is a value set in advance as an ink usage amount corresponding to a range where the printing rate is 10% to 50% or a range where the ink amount rate is 10% to 50%. Can be considered. Further, the first stop control unit 114 determines whether the ink usage amount is less than the fourth threshold according to whether the printing rate or the ink amount rate is less than a predetermined value. Also good. Here, when the control unit 11 determines that the ink use amount is less than the fourth threshold value (Yes side of S94), the control unit 11 shifts the process to step S941. On the other hand, when the control unit 11 determines that the amount of ink used is equal to or greater than the fourth threshold (No in S94), the process proceeds to step S95.

<Step S941>
In step S <b> 941, the first stop control unit 114 of the control unit 11 sets “no drive” as to whether or not the intake unit 7 is driven during the back side printing of the image forming process. As a result, during the back side printing of the image forming process, the suction of air by the suction unit 7 is stopped and suction suction is not performed. As described above, in the image forming apparatus 10, when the amount of ink used is sufficiently small and the attracting force by electrostatic attraction is high, the drive of the air intake unit 7 is stopped to save power.

<Step S95>
In step S95, the first intake control unit 111 of the control unit 11 determines whether or not the ink use amount specified in step S91 is equal to or greater than a preset second threshold value. The second threshold value is an arbitrary value that is set in advance to determine whether or not the suction force due to electrostatic suction is reduced due to the large amount of ink used. For example, the second threshold value is a value set in advance as an ink use amount corresponding to a range where the printing rate is 50% or more and 80% or less, or a range where the ink amount rate is 50% or more and 100% or less. Can be considered. Further, the first intake control unit 111 determines whether the ink usage amount is equal to or greater than the second threshold according to whether the printing rate or the ink amount rate is equal to or greater than a predetermined value. Also good. Here, when the control unit 11 determines that the amount of ink used is equal to or greater than the second threshold (Yes in S95), the process proceeds to Step S951. On the other hand, when the control unit 11 determines that the ink use amount is less than the second threshold (No in S95), the process proceeds to step S96.

<Step S951>
In step S951, the first intake control unit 111 of the control unit 11 sets the suction force by the intake unit 7 at the time of printing on the back surface of the image forming process to a preset “high”. That is, when the amount of ink used at the time of surface printing of the sheet P is large, an insufficient suction force of electrostatic adsorption due to a decrease in charging efficiency of the sheet P by the charging unit 8 is caused by the suction unit 7. It is compensated for by setting the suction force by high.

<Step S96>
In step S96, the first intake control unit 111 of the control unit 11 preliminarily sets the suction force by the intake unit 7 at the time of backside printing of the image forming process to be lower than “high” set in the step S951. Set to the set “low”. That is, when the amount of ink used at the time of surface printing of the sheet P is small, the charging efficiency of the sheet P by the charging unit 8 is high and the adsorption force by electrostatic adsorption is high. Is set low, power consumption in the intake section 7 is suppressed.

<Step S97>
In step S97, the selection control unit 116 of the control unit 11 sets any one or more of the intake ducts 721 to 723 to the sheet according to the size of the sheet P and the amount of ink used. Select the intake duct to be used when printing the back side of P. In the present embodiment, the selection of the intake ducts 721 to 723 is synonymous with the selection of the intake fans 73 to 75. For example, the control unit 11 selects the intake duct in the following procedure.

  First, the control unit 11 selects the intake ducts 721 to 723 that are present at the end positions of the size of the sheet P in the width direction D2. For example, when the size of the seat P is “A3”, the intake duct 721 is selected, and when the size of the seat P is “A4”, the intake duct 722 is selected. When the size of the seat P is “A5”, the intake duct 723 is selected.

  Thereby, since the intake duct located at the end of the size of the sheet P is selected from the intake ducts 721 to 723 and is used when the sheet is conveyed, the end of the sheet P, in particular, the corner is lifted. It is suppressed.

  Then, the control unit 11 determines whether or not an intake duct existing inside the intake duct selected according to the size of the sheet P among the intake ducts 721 to 723 is used according to the ink usage amount. To do. For example, when the control unit 11 selects the intake duct 721 according to the size of the sheet P, and the ink usage amount is equal to or greater than a preset first usage amount, the intake duct 722 and the intake duct 723 are determined to be used together with the intake duct 721. In addition, the control unit 11 selects the intake duct 721 according to the size of the sheet P, and the ink usage amount is less than the first usage amount and is equal to or more than a preset second usage amount. If it is, it is determined that the intake duct 722 is used together with the intake duct 721. Further, when the control unit 11 selects the intake duct 721 according to the size of the sheet P, and the ink usage is less than the second usage, the intake duct 722 and the It is determined that the intake duct 723 is not used.

  Thus, when the amount of ink used is large and the attractive force of electrostatic adsorption is low, the intake duct existing inside the intake duct is used together with the intake duct selected according to the size of the sheet P. Insufficiency of the electrostatic adsorption force is compensated for by the suction adsorption by the intake part 7. Further, when the amount of ink used is small and the attractive force of electrostatic adsorption is high, unnecessary driving of the intake fans 73 to 75 is prevented, so that power consumption by the intake unit 7 is suppressed. Note that the control unit 11 may omit the step S97 when the intake unit 7 is set to “no drive” in the step S941.

<Step S10>
Returning to FIG. 4, in step S <b> 10, the control unit 11 controls the intake unit 7 and the charging unit 8 based on various settings in the conveyance control process, and the sheet conveyance unit 5 performs the above-described process. The conveyance operation of the sheet P is started. Specifically, the setting contents include the presence / absence of driving of the air intake unit 7, the presence / absence of driving of the charging unit 8, the air suction force of the air intake unit 7, and the intake air to be used among the air intake ducts 721 to 723. Includes content related to ducts. For example, the controller 11 drives the intake fans 71 to 73 corresponding to the intake duct selected in step S7 among the intake ducts 721 to 723 when the front surface of the sheet P is printed. Further, the controller 11 drives the intake fans 71 to 73 corresponding to the intake duct selected in step S7 among the intake ducts 721 to 723 when the back surface of the sheet P is printed. The various settings are stored in the RAM or EEPROM of the control unit 11 in the transport control process.

  As described above, in the image forming apparatus 10, when the conveyance control process is executed by the control unit 11, the air intake unit according to the size of the sheet P, the humidity, the ink usage amount, and the like. 7 and the charging unit 8 are controlled to prevent the sheet P from being lifted and to save power.

  In the present embodiment, the case has been described where, in the step S9, the setting for the back side printing of the sheet P is different from that for the front side printing of the sheet P. On the other hand, a configuration in which the back surface printing mechanism 65 is not provided and the steps S8 to S9 are omitted is also conceivable as another embodiment. In the configuration including the double-sided printing mechanism 65, the control unit 11 determines whether or not the process of step S9 is performed in response to a user operation of the operation display unit 12 in an initial setting of the image forming apparatus 10 or the like. A configuration that can be set in advance is also conceivable as another embodiment. Further, when the back side of the sheet P is printed, the operations of the intake unit 7 and the charging unit 8 may be controlled based on the humidity as in the front side printing of the sheet P.

  In the present embodiment, the intake duct to be used in the intake section 7 is selected from the intake ducts 721 to 723 in accordance with not only the size of the sheet P but also the humidity or the amount of ink used. Explained. On the other hand, it is also conceivable as another embodiment that an intake duct to be used in the intake section 7 is selected from the intake ducts 721 to 723 according to only the size of the seat P.

  Furthermore, in the present embodiment, a case has been described in which the air suction force by the air intake unit 7 can be switched between two stages of “high” or “low” with respect to the humidity or the ink usage amount based on a predetermined threshold. . On the other hand, the first intake control unit 111 and the second intake control unit 112 of the control unit 11 increase the air suction force by the intake unit 7 as the humidity increases or as the ink usage increases. As described above, controlling the suction force step by step is also conceivable as another embodiment. The charging unit 8 may increase the voltage level applied from the power supply device 82 to the charging member 811 as the humidity is higher and the ink usage is higher, depending on the humidity or the ink usage. Conceivable.

  The image forming unit 3 of the image forming apparatus 10 may be an electrophotographic image forming unit including a photosensitive drum, a charging unit, an exposure device, a developing device, a transfer roller, a fixing device, a toner container, and the like. Conceivable. In the electrophotographic image forming unit, the exposure device irradiates the photosensitive drum charged with a predetermined potential by the charging unit with a laser beam based on image data to form an electrostatic latent image. Thereafter, the developing device develops the electrostatic latent image as a toner image using toner supplied from the toner container. On the other hand, the sheet P is transported by the sheet transport unit 5 on the sheet transport path from the sheet feeding cassette 1 to the photosensitive drum and the transfer roller. The photoconductive drum and the transfer roller transfer the toner image formed on the photoconductive drum to the sheet P.

DESCRIPTION OF SYMBOLS 1: Paper feed cassette 2: Paper feed part 3: Image formation parts 31-34: Recording head 4: Ink tank part 41-44: Ink tank 5: Sheet conveyance part 51: Conveyance belt 52: Drive roller 52A: Motor 53- 55: driven roller 56: pressure roller 57: humidity sensor 6: paper discharge unit 61: drying device 62: transport path 63: paper discharge roller 64: paper discharge tray 65: duplex printing mechanism 7: air intake unit 71: transport plate 72: Intake ducts 721, 722, 723: Intake ducts 73, 74, 75: Intake fans 731, 741, 751: Connection duct 8: Charging section 81: Charging member 82: Power supply device 9: Main body frame 10: Image forming apparatus 11: Control Unit 111: first intake control unit 112: usage amount specifying unit 113: second intake control unit 114: first stop control unit 115: second stop control unit 116: selection control 12: operation display unit D1: conveying direction D2: Width direction P: Sheet

Claims (11)

A plurality of belt openings formed in a predetermined suction suction region at the end in the width direction perpendicular to the sheet conveyance direction, and a conveyance belt for conveying the sheet;
A transport plate having a plurality of platen openings formed at positions corresponding to the belt openings in the width direction, and disposed on the back side of the transport belt;
An air intake section for sucking air through the belt opening and the platen opening from the back side of the transport plate;
A charging unit that charges a predetermined electrostatic adsorption region at the center in the width direction of the transport belt;
A use amount specifying unit for specifying the amount of ink used to be discharged onto the surface of the sheet by an image forming unit that discharges ink to form an image in an image forming apparatus in which the sheet conveying device is mounted;
A double-sided printing mechanism that reverses the front and back surfaces of the sheet on which an image has been formed by the image forming unit and conveys the sheet again to the image forming unit;
When the sheet is conveyed again to the image forming unit by the double-sided printing mechanism, the suction unit is configured so that the air suction force increases as the ink usage amount specified by the usage amount specifying unit increases. A second intake control unit for controlling;
A sheet conveying apparatus comprising: A humidity detector for detecting humidity;
A first intake control unit that controls the intake unit such that the higher the humidity detected by the humidity detection unit, the higher the air suction force;
The sheet conveying apparatus according to claim 1.   The sheet conveying apparatus according to claim 2, wherein the first intake control unit switches the suction force according to whether the humidity is equal to or higher than a preset first threshold value. The intake air when the humidity detected by the humidity detection unit is less than a preset third threshold value or the ink usage amount specified by the usage amount specifying unit is less than a preset fourth threshold value. sheet conveying device according to claim 2 or 3 comprising a first stop control unit stopping the suction of air by parts. The charging is performed when the humidity detected by the humidity detection unit is equal to or higher than a preset fifth threshold value or the ink usage amount specified by the usage amount specifying unit is equal to or higher than a preset sixth threshold value. sheet conveying apparatus according to any one of claims 2-4 comprising a second stop control unit stopping the charging of the conveyor belt by parts. Any second intake control unit, according to claim 1 to 5 for switching the suction force depending on whether the ink usage specified by the usage specific portion is smaller than the second threshold value which is set in advance sheet conveying apparatus according to any. The intake section is provided corresponding to the size of the sheet conveyed by the conveyor belt, and includes a plurality of intake ducts that form a ventilation path below the platen opening,
The sheet conveying apparatus, wherein one or more of the intake duct is used to suction of air by the suction unit to any one of claims 1 to 6, further comprising a selection control unit for selecting in accordance with the size of the sheet Sheet transport device. A plurality of belt openings formed in a predetermined suction suction region at the end in the width direction perpendicular to the sheet conveyance direction, and a conveyance belt for conveying the sheet;
A transport plate having a plurality of platen openings formed at positions corresponding to the belt openings in the width direction, and disposed on the back side of the transport belt;
An air intake section for sucking air through the belt opening and the platen opening from the back side of the transport plate;
A charging unit that charges a predetermined electrostatic adsorption region at the center in the width direction of the transport belt;
A sheet conveying apparatus comprising:
The intake section is provided corresponding to the size of the sheet conveyed by the conveyor belt, and includes a plurality of intake ducts that form a ventilation path below the platen opening,
The sheet conveying device includes a selection control unit for selecting in accordance with one or more of the intake duct is used to suction of air by the suction unit to the size of the sheet, and a humidity sensor for detecting humidity,
The selection control unit, Cie over preparative conveying device to select one or more of the intake duct according to the humidity detected by the size and the humidity detecting portion of the sheet. A use amount specifying unit for specifying the amount of ink used to be discharged onto the surface of the sheet by an image forming unit that discharges ink to form an image in an image forming apparatus in which the sheet conveying device is mounted;
A double-sided printing mechanism that reverses the front and back surfaces of the sheet on which an image has been formed by the image forming unit and conveys the sheet again to the image forming unit;
With
When the selection control unit transports the sheet again to the image forming unit by the double-sided printing mechanism according to the size of the sheet and the ink usage amount specified by the usage amount specifying unit, the suction unit The sheet conveying apparatus according to claim 7 or 8 , wherein one or a plurality of the air intake ducts used for air suction by the air compressor are selected. The sheet conveying apparatus according to claim 9 , wherein the usage amount specifying unit specifies the ink usage amount in a predetermined specific range in the sheet. A sheet conveying device according to any one of claims 1 to 10 ,
An image forming unit that forms an image by discharging aqueous ink onto the sheet conveyed by the sheet conveying device;
An image forming apparatus comprising:

Images