JP2018176693A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration in printing quality.SOLUTION: An image forming device comprises: a belt conveyance part that includes a conveyance belt having a plurality of suction holes formed therein and carries a sheet placed on the conveyance belt; a suction part that sucks the sheet on the conveyance belt through the suction holes; an ink head that causes ink to adhere to the sheet on the conveyance belt by discharging the ink toward the conveyance belt through nozzles; and a control part that discharges the ink through the nozzles at reference timing, when an adhesion scheduled position to which the ink from the nozzles should adhere does not overlap with the suction holes, and discharges the ink through the nozzles at timing earlier than the reference timing, when the adhesion scheduled position overlaps with the suction holes.SELECTED DRAWING: Figure 10

Description

  BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an image forming apparatus that conveys a sheet and deposits ink on the sheet.

  When printing an image on a sheet, the inkjet type image forming apparatus conveys the sheet and discharges ink toward the sheet being conveyed. Then, the ink is attached to the sheet to form an image on the sheet (for example, see Patent Document 1).

  Such an image forming apparatus includes an ink head that discharges ink. Further, a conveyance belt disposed opposite to the ink head at a distance is provided in the image forming apparatus. Then, at the time of printing an image on a sheet, the sheet is transported by the transport belt.

  The transport belt is an endless belt and is rotatably supported. When the sheet is transported by the transport belt, the sheet is placed on the outer peripheral surface of the transport belt, and the transport belt revolves in that state. Then, the ink is discharged toward the sheet (the sheet being conveyed) on the conveyance belt.

JP 2014-24231 A

  In Patent Document 1, a plurality of suction holes are formed in the transport belt. Further, a suction fan unit is provided on the inner circumferential surface side of the conveyance belt. The suction fan unit generates negative pressure. As a result, the sheet on the transport belt is sucked downward. That is, the sheet is attracted to the transport belt.

  When a sheet with high elasticity and flexibility is used for printing in a configuration in which the sheet on the conveyance belt is suctioned downward, the portion of the sheet overlapping the suction hole of the conveyance belt (herein referred to as the overlapping portion) In some cases, the superimposed portion of the sheet may be deformed so as to be recessed downward with respect to the sheet mounting surface of the conveyance belt.

  Here, for example, it is assumed that the planned adhesion position (pixel on which the ink is to be placed), which is the position on the sheet to which the ink from the ink head should be attached, is the overlapping portion of the sheet. In this example, when no dent occurs in the overlapping portion of the sheet, the actual adhesion position and the planned adhesion position of the ink substantially coincide with each other by discharging the ink at a predetermined reference timing from the ink head. It can be done. However, when a dent occurs in the overlapping portion of the sheet due to the suction of the sheet, the time from the discharge of the ink to the landing of the ink on the sheet becomes long, so the actual adhesion position of the ink Deviation between the and adhesion planned position exceeds the allowable range. As a result, there arises a disadvantage that the print image quality is degraded.

  The present invention has been made to solve the above-described problems, and in the configuration in which the sheet on the transport belt is sucked downward, the printing image quality is reduced due to the deformation (depression) of the sheet generated by the suction of the sheet. It is an object of the present invention to provide an image forming apparatus capable of suppressing the occurrence of the inconvenience of

  In order to achieve the above object, an image forming apparatus according to the present invention includes a conveyance belt having a plurality of suction holes formed therein, and conveys a sheet placed on the conveyance belt by driving the conveyance belt. A suction unit that generates a negative pressure on the side opposite to the sheet loading surface side of the conveyance belt and the suction belt that sucks the sheet on the conveyance belt through the suction holes, and is disposed opposite to the conveyance belt at a distance An ink head having a nozzle for discharging the ink and for causing the ink to adhere to the sheet on the transport belt by discharging the ink from the nozzle toward the transport belt; and a planned adhesion position where the ink from the nozzle is to be deposited When ink does not overlap with the suction hole, the ink is ejected from the nozzle at a predetermined reference timing, and when the planned adhesion position and the suction hole overlap, the reference timing And a control unit to eject ink from the nozzle at an earlier timing.

  In the configuration of the present invention, when the planned adhesion position (pixel) on the sheet to which the ink from the nozzle is to be adhered and the suction hole overlap, the ink is ejected at a timing earlier than the predetermined reference timing. Therefore, even if the overlapping portion of the sheet (the portion overlapping the suction hole of the transport belt) including the planned adhesion position is deformed so as to be recessed downward with respect to the sheet mounting surface of the transport belt, Even if the time until the ink drops on the sheet is longer than the ideal time (the time when the sheet does not have dents), the actual adhesion position and the planned adhesion position of the ink deviate from each other. Can be suppressed. As a result, it is possible to suppress the decrease in print image quality.

  According to the configuration of the present invention, it is possible to suppress the decrease in printing image quality due to the deformation (dent) of the sheet generated by the suction of the sheet.

The figure which shows the whole structure of the image forming apparatus by one Embodiment of this invention. The figure which shows the sheet mounting surface of the conveyance belt provided in the belt unit of the image forming apparatus by one Embodiment of this invention. The figure which shows the structure of the suction unit of the image forming apparatus by one Embodiment of this invention. A diagram showing an arrangement pattern of a plurality of negative pressure generating portions provided in a suction unit of an image forming apparatus according to an embodiment of the present invention A diagram showing a hardware configuration of an image forming apparatus according to an embodiment of the present invention Diagram for explaining discharge timing of ink discharged from an ink head of an image forming apparatus according to an embodiment of the present invention Diagram for explaining the ejection timing of ink ejected from the ink head of the image forming apparatus according to an embodiment of the present invention (timing when the suction hole of the transport belt and the adhesion planned position overlap). Diagram for explaining the discharge amount of the ink discharged from the ink head of the image forming apparatus according to one embodiment of the present invention Diagram for explaining the discharge amount of the ink discharged from the ink head of the image forming apparatus according to one embodiment of the present invention A flow chart showing a flow of correction processing related to ink ejection performed by the control unit of the image forming apparatus according to an embodiment of the present invention The figure for demonstrating the setting method of the discharge timing of the ink performed by the control part of the image forming apparatus by one Embodiment of this invention. A flowchart showing a flow of first suction control performed by the control unit of the image forming apparatus according to an embodiment of the present invention Flowchart showing flow of second suction control performed by control unit of image forming apparatus according to one embodiment of the present invention Flowchart showing flow of third suction control performed by control unit of image forming apparatus according to one embodiment of the present invention A flowchart showing a flow of fourth suction control performed by the control unit of the image forming apparatus according to an embodiment of the present invention

<Configuration of Image Forming Apparatus>
As shown in FIG. 1, the image forming apparatus 100 of the present embodiment is provided with a conveyance path 10 for conveying the sheet S. The conveyance path 10 is classified into a main conveyance path 1A and a conveyance path 1B for double-sided printing. From the sheet feeding position P1, the main conveyance path 1A passes through the registration position P2 and the printing position P3 in this order, and reaches the discharge position P4. The double-sided printing conveyance path 1B branches from the main conveyance path 1A at a position DP downstream of the printing position P3 in the sheet conveyance direction, and merges with the main conveyance path 1A at a position UP upstream of the registration position P2 in the sheet conveyance direction. Do. The conveyance path 1B for double-sided printing is not used when performing single-sided printing in which an image is printed only on one side of the sheet S, and after printing an image on one side of the sheet S It is used when performing double-sided printing, which also prints an image on the side. In FIG. 1, the conveyance path of the sheet S is indicated by a broken line, and the conveyance direction of the sheet S is indicated by an arrow.

  The image forming apparatus 100 further includes a conveyance unit 20 and a printing unit 30. The transport unit 20 transports the sheet S along the transport path 10. The printing unit 30 prints an image on the sheet S conveyed along the conveyance path 10.

  The transport unit 20 includes a paper feed roller pair 21 and a paper feed side transport roller pair 22. The sheet feeding roller pair 21 is installed at the sheet feeding position P1. The paper feed side conveyance roller pair 22 is disposed between the paper feed position P1 and the registration position P2. The number of the paper feed side transport roller pairs 22 may be plural or one.

  The sheet feeding roller pair 21 pulls out the sheet S from the sheet cassette CA at the sheet feeding position P1 and supplies the sheet S to the conveyance path 10 (performs the primary sheet feeding). Further, the sheet feeding roller pair 21 conveys the sheet S supplied to the conveyance path 10 along the conveyance path 10. The sheet feed side conveyance roller pair 22 conveys the sheet S along the conveyance path 10 together with the sheet feed roller pair 21. Thus, the sheet S is transported from the sheet feeding position P1 to the registration position P2.

  The transport unit 20 also includes a registration roller pair 23. The resist roller pair 23 is installed at the resist position P2. The registration roller pair 23 conveys the sheet S conveyed from the sheet feeding position P1 toward the printing position P3 (performs secondary sheet feeding). In other words, the registration roller pair 23 supplies the sheet S to the belt unit 24 described later.

  The resist roller pair 23 stops rotating when the sheet S reaches the resist position P2. As a result, the progress of the sheet S is temporarily stopped, and at that time, the skew of the sheet S is corrected (the leading end of the sheet S is bent). Then, the registration roller pair 23 temporarily stops the movement of the sheet S until the predetermined skew correction time elapses, and then conveys the sheet S which has reached the registration position P2 to the printing position P3 (secondary feeding Start the paper).

  The transport unit 20 also includes a belt unit 24 (corresponding to a "belt transport unit"). The belt unit 24 is installed at the printing position P3. Then, the belt unit 24 conveys the sheet S at the printing position P3. Printing of an image on the sheet S by the printing unit 30 is performed on the sheet S conveyed by the belt unit 24.

  The belt unit 24 includes a transport belt 241, a drive roller 242 and a driven roller 243. The conveyance belt 241 has a plurality of suction holes 241 a (see FIG. 2) formed to penetrate in the thickness direction of the conveyance belt 241. Further, the transport belt 241 is an endless belt, and is stretched by the drive roller 242 and the driven roller 243. The transport belt 241 is driven (rotated) by rotation of the drive roller 242.

  The sheet S supplied to the belt unit 24 is placed on the outer peripheral surface of the transport belt 241. At this time, the transport belt 241 is driven. As a result, the sheet S placed on the transport belt 241 is transported in the sheet transport direction.

  The transport unit 20 also includes a suction unit 25 (corresponding to a “suction unit”). The suction unit 25 is disposed on the inner circumferential surface side of the conveyance belt 241. The suction unit 25 generates a negative pressure on the inner circumferential surface side of the conveyance belt 241, and sucks the sheet S on the conveyance belt 241 toward the sheet placement surface of the conveyance belt 241.

  As shown in FIG. 3, the suction unit 25 includes a pressure chamber 251 made of a box-like member. A lid member 252 having a through hole 252a penetrating in the thickness direction is provided on the upper surface side of the pressure chamber 251 (the opening of the upper surface of the pressure chamber 251 is closed by the lid member 252). A fan 253 is installed on the lower surface side of the pressure chamber 251. The pressure chamber 251 is in a state where a negative pressure is generated by driving (rotating) the fan 253.

  When a negative pressure is generated in the pressure chamber 251, the air on the transport belt 241 is drawn into the pressure chamber 251 through the suction holes 241a by the generated negative pressure. When the sheet S is placed on the conveyance belt 241, the suction force acts on the sheet S, so the sheet S is adsorbed on the sheet placement surface of the conveyance belt 241.

  The pressure chamber 251 is divided into a plurality of sections by the partition plate 251a. That is, a plurality of pressure chambers 251 exist. The lid member 252 is installed on each upper surface side of the plurality of pressure chambers 251, and the fan 253 is installed on each lower surface side of the plurality of pressure chambers 251. That is, the suction unit 25 includes a plurality of negative pressure generating units each generating a negative pressure independently. Hereinafter, the plurality of negative pressure generating units will be described with reference numeral 250.

  When a plurality of negative pressure generating units 250 are provided in the suction unit 25, as shown in FIG. 4, the suction target area of the suction unit 25 is divided into a plurality of suction powers (negative pressure) for each of the divided suction target areas. The negative pressure generated by the generating unit 250 can be made different. In FIG. 4, each suction target area is indicated by a thick line, and the conveyance belt 241 is indicated by a broken line.

  The number of negative pressure generating units 250 installed is not particularly limited. Further, the arrangement pattern of the negative pressure generation unit 250 is not particularly limited. For example, the plurality of negative pressure generating units 250 may be arranged in a line in the sheet conveying direction or a direction orthogonal to the direction.

  Returning to FIG. 1, the transport unit 20 includes the discharge side transport roller pair 26. The discharge side transport roller pair 26 is disposed between the printing position P3 and the discharge position P4. For example, the installation number of the discharge side conveyance roller pair 26 is plural.

  The discharge side conveyance roller pair 26 conveys the sheet S (the printed sheet S on which the image is printed) conveyed from the belt unit 24 toward the discharge position P4. A discharge tray ET is installed at the discharge position P4. Then, the discharge side transport roller pair 26 transports the printed sheet S and discharges the printed sheet S to the discharge tray ET.

  The transport unit 20 also includes a transport roller pair 27 for duplex printing (including a switchback roller pair 27S). The double-sided printing conveyance roller pair 27 is installed in the double-sided printing conveyance path 1B. For example, the number of installed conveying roller pairs 27 for double-sided printing is plural. The duplex printing transport roller pair 27 is a transport roller pair used when performing duplex printing, and transports the sheet S along the duplex printing transport path 1B.

  Here, double-sided printing will be described. The double-sided printing conveyance path 1B is classified into a first conveyance path 11B and a second conveyance path 12B. The first conveyance path 11B is connected to the position DP of the main conveyance path 1A. The second conveyance path 12B is a conveyance path for switching back the sheet S, and is connected to the position UP of the main conveyance path 1A.

  When single-sided printing is performed, the printing unit 30 prints a one-sided image on one side of the sheet S. Then, the conveyance unit 20 conveys the sheet S on which the one-side image is printed along the main conveyance path 1A, and discharges the sheet S to the discharge tray ET as it is.

  On the other hand, when double-sided printing is performed, when printing of the one-sided image on the sheet S is completed, the conveyance unit 20 performs conveyance processing for double-sided printing. Specifically, the conveyance unit 20 draws in the sheet S (herein, referred to as a single-sided print sheet S) on one side of which the one-side image is printed into the first conveyance path 11B, from the first conveyance path 11B to the second The single-sided print sheet S is advanced into the conveyance path 12B. Then, the transport unit 20 performs a reversing process (a process of switching back the single-sided printing sheet S) for reversing the direction of the front and back surfaces of the single-sided printing sheet S. At this time, the switchback roller pair 27S rotates forward until the rear end of the single-sided printing sheet S passes the branch point between the first conveyance path 11B and the second conveyance path 12B. The single-sided printing sheet S is switched back by reverse rotation at the timing when the trailing edge passes. Thereafter, the transport unit 20 returns the single-sided print sheet S to the position UP of the main transport path 1A.

  When the single-sided printing sheet S is returned to the main conveyance path 1A, the conveyance unit 20 conveys the single-sided printing sheet S from the registration position P2 toward the printing position P3 again. That is, when performing double-sided printing, the sheet S passes the printing position P3 twice. At this time, the front and back sides of the single-sided printing sheet S are reversed (the direction of the front and back of the sheet S passing the printing position P3 again is opposite to that when the printing position P3 was passed last time ). Therefore, the printing of the image by the printing unit 30 is performed on the other side (unprinted side) of the single-sided print sheet S. That is, the other side image is printed on the other side of the single-sided print sheet P. Thereafter, the transport unit 20 transports the sheet S on which the one-side image and the other-side image are printed on both sides along the main conveyance path 1A, and discharges it to the discharge tray ET.

  The printing unit 30 is disposed above the belt unit 24 so as to face the outer circumferential surface of the conveyance belt 241 at a distance. Then, the printing unit 30 prints an image on the sheet S being transported (the sheet S on the transport belt 241).

  The printing unit 30 includes ink heads 3Y, 3K, 3C, and 3M for four colors. The ink heads 3Y, 3K, 3C and 3M are arranged in this order from the upstream side to the downstream side in the sheet conveying direction. The ink head 3Y contains yellow ink. The ink head 3K contains black ink. The ink head 3C contains cyan ink. The ink head 3M contains magenta ink.

  Each of the ink heads 3Y, 3K, 3C and 3M has a plurality of nozzles 31 (see FIG. 5) for discharging ink. Although not shown, each nozzle 31 is provided with a piezoelectric element, and by applying a drive voltage to the piezoelectric element of the nozzle 31, the nozzle 31 corresponding to the piezoelectric element to which the drive voltage is applied is driven (nozzle 31 Ink is ejected from

  Further, as shown in FIG. 5, the image forming apparatus 100 includes a control unit 40 that controls each part of the image forming apparatus 100. The control unit 40 includes a CPU 41, a memory 42 and an ASIC 43. The CPU 41 operates based on control programs and data, and performs processing for controlling each part of the image forming apparatus 100. The memory 42 stores control programs and data for operating the CPU 41. The ASIC 43 performs specific processing such as image processing.

  The control unit 40 is connected to a conveyance motor that rotates a roller of the conveyance unit 20 in order to control the conveyance of the sheet S by the conveyance unit 20. For example, as the transport motor, there are a sheet feed motor M1, a resist motor M2, a belt motor M3, a discharge motor M4, a duplex printing motor M5, and a switchback motor M6.

  The sheet feeding motor M 1 is connected to the sheet feeding roller pair 21 and the sheet feeding conveyance roller pair 22. The control unit 40 controls the driving of the sheet feeding motor M1, and appropriately rotates the sheet feeding roller pair 21 and the sheet feeding conveyance roller pair 22. Further, the sheet feeding roller pair 21 receives driving force from the sheet feeding motor M1 via a sheet feeding side clutch (not shown). The control unit 40 controls on / off of the sheet feeding clutch, and switches between coupling and uncoupling of the sheet feeding roller pair 21 and the sheet feeding motor M1.

  The resist motor M 2 is connected to the resist roller pair 23. The control unit 40 controls the drive of the resist motor M2 to rotate the resist roller pair 23 appropriately. The resist roller pair 23 also receives a driving force from the resist motor M2 through a resist clutch (not shown). The control unit 40 controls on / off of the registration clutch, and switches between connection and disconnection of the registration roller pair 23 and the registration motor M2.

  The belt motor M3 is coupled to the drive roller 242 of the belt unit 24. The control unit 40 controls the drive of the belt motor M3 to properly rotate the drive roller 242 of the belt unit 24. That is, the control unit 40 appropriately circulates the transport belt 411 of the belt unit 24. For example, the belt motor M3 is a stepping motor.

  The discharge side motor M4 is connected to the discharge side conveyance roller pair 26. The control unit 40 controls the driving of the discharge side motor M4, and appropriately rotates the discharge side conveyance roller pair 26. Further, the discharge side conveyance roller pair 26 receives a driving force from the discharge side motor M4 via a discharge side clutch (not shown). The control unit 40 controls on / off of the discharge side clutch, and switches connection and disconnection of the discharge side conveyance roller pair 26 and the discharge side motor M4.

  The duplex printing motor M5 is connected to the duplex printing transport roller pair 27 other than the switchback roller pair 27S. The control unit 40 controls the driving of the duplex printing motor M5 to properly rotate the duplex printing transport roller pair 27. The duplex printing conveying roller pair 27 receives driving force from the duplex printing motor M5 via a duplex printing clutch (not shown). The control unit 40 controls on / off of the double-sided printing clutch, and switches connection and disconnection between the double-sided printing conveyance roller pair 27 and the double-sided printing motor M5.

  The switchback motor M6 is coupled to the switchback roller 27S. The control unit 40 controls the drive of the switchback motor M6 to appropriately rotate the switchback roller pair 27S. That is, the control unit 40 switches between the forward rotation and the reverse rotation of the switchback roller pair 27S.

  The control unit 40 also controls suction by the suction unit 25. That is, the control unit 40 is connected to a fan motor M7 that rotates the fan 253. For example, fan motor M7 is integrated into the casing of fan 253. Then, the control unit 40 controls the driving of the fan motor M7, and appropriately rotates the fan 253 (generates a negative pressure in the pressure chamber 251). The control unit 40 controls the negative pressure (suction force) generated by each of the plurality of negative pressure generating units 250 independently for each negative pressure generating unit 250.

  The control unit 40 is also connected to the driver 32 of the printing unit 30 and controls the printing operation of the printing unit 30. The driver 32 is a circuit for controlling the discharge of the ink from the nozzle 31, and is provided for each of the ink heads 3Y, 3K, 3C and 3M. Then, the control unit 40 gives an operation instruction to each driver 32 of the ink heads 3Y, 3K, 3C and 3M.

  The control unit 40 sets printing data in which the discharge amount of ink from the nozzles 31 (here, referred to as discharge nozzles 31) and the discharge nozzles 31 that discharge ink are determined for each of the ink heads 3Y, 3K, 3C, and 3M. Generate Then, the control unit 40 transmits the print data to the drivers 32 of the ink heads 3Y, 3K, 3C, and 3M, thereby causing the drivers 32 to perform the ink ejection process based on the print data. Further, the control unit 40 controls the conveyance of the sheet S such that the sheet S advances by the width of one line (one dot) each time the ink discharge process is performed once.

  Each of the drivers 32 applies a drive voltage to the piezoelectric element provided in the discharge nozzle 31 indicated by the print data, and discharges the ink from the discharge nozzle 31 as the ink discharge process. The ink ejection process by each driver 32 is repeated at a predetermined reference cycle (reference timing).

  As shown in FIG. 6, an interval is provided between the sheet S on the conveyance belt 241 and the discharge nozzle 31. Therefore, a time difference occurs between the discharge timing of the ink from the discharge nozzle 31 and the arrival timing of the ink to the sheet S. Therefore, the planned adhesion position of the ink from the discharge nozzle 31 (the position on the sheet S to which the ink from the discharge nozzle 31 should be adhered) is at the downstream side in the sheet conveyance direction than the position of the discharge nozzle 31 in the sheet conveyance direction. The reached timing (the timing at which the distance between the discharge nozzle 31 and the adhesion planned position in the sheet conveying direction is a predetermined distance) is taken as the reference timing. Although in FIG. 6 a gap is provided between the transport belt 241 and the sheet S in order to make the drawing easy to see, the sheet S is in close contact with the transport belt 241 in practice. The same applies to FIGS. 7 to 9 to be referred to later.

  Referring back to FIG. 5, the image forming apparatus 100 includes a CIS (Contact Image Sensor) unit 50. The CIS unit 50 corresponds to a "reading unit". CIS unit 50 is installed, for example, at a position between resist position P2 and printing position P3 (see FIG. 1). Then, the CIS unit 50 reads the sheet S supplied to the belt unit 24.

  The CIS unit 50 is connected to the control unit 40. The control unit 40 controls suction of the sheet S by the suction unit 25 based on read data obtained by reading the sheet S by the CIS unit 50. Details will be described later.

  The image forming apparatus 100 also includes an operation panel 60. The operation panel 60 corresponds to a "reception unit". Operation panel 60 receives settings and instructions related to printing from the user. For example, operation panel 60 includes a touch panel display, and displays a reception screen for receiving settings and instructions regarding printing. Operation panel 60 is connected to control unit 40. The control unit 40 controls the display operation of the operation panel 60 and detects an operation performed on the operation panel 60.

  The image forming apparatus 100 further includes a storage unit 70. The storage unit 70 includes a non-volatile storage device such as a ROM (EEPROM or the like) or an HDD. The control unit 40 is connected to the storage unit 70, reads information from the storage unit 70, and writes information to the storage unit 70.

<Correction processing related to ink discharge>
When a sheet S of a material (paper, cloth, leather, rubber, etc.) having high elasticity and flexibility is used for printing, deformation of the sheet S due to suction by the suction unit 25 is likely to occur. Specifically, as shown in FIG. 7, a portion of the sheet S overlapping the suction hole 241a of the transport belt 241 (here, referred to as a superimposed portion) is sucked into the suction hole 241a. That is, the overlapping portion of the sheet S is deformed so as to be recessed downward with respect to the sheet mounting surface of the conveyance belt 241.

  Here, it is assumed that the planned adhesion position of the ink on the sheet S from the nozzle 31 (here, referred to as the ejection nozzle 31) for ejecting the ink overlaps the suction hole 241a of the transport belt 241. That is, it is assumed that the overlapping portion of the sheet S is the adhesion planned position.

  In this case, when the ink is discharged from the discharge nozzle 31 at a reference timing (a timing when the distance between the discharge nozzle 31 and the adhesion planned position in the sheet conveying direction becomes a predetermined distance) as shown in FIG. A deviation occurs between the actual adhesion position on the upper side and the adhesion planned position. This is because the vertical distance between the sheet S on the conveyance belt 241 and the discharge nozzle 31 is larger than the ideal distance D1 (the reference timing is the sheet S on the conveyance belt 241 and the discharge nozzle 31). Timing in the vertical direction with the ideal distance D1).

  Further, when viewed from the adhesion planned position, the ink adhered to the adhesion planned position is discharged from obliquely above on the downstream side in the sheet conveying direction. Therefore, as shown in FIG. 8, if the position near the inner edge of the suction hole 241a of the transport belt 241 on the downstream side in the sheet conveying direction is the adhesion planned position, that is, the adhesion planned position among the overlapping portions of the sheet S. If the portion including the is inclined obliquely downward from the downstream side to the upstream side in the sheet conveying direction, the ink discharged toward the adhesion planned position and deposited on the sheet S may flow to the upstream side in the sheet conveying direction. is there. In this case, the ink for one pixel that has been deposited on the sheet S spreads so as to straddle a plurality of pixels. Note that, as shown in FIG. 9, when the planned adhesion position is apart from the inner edge of the suction hole 241 a of the conveyance belt 241 on the downstream side in the sheet conveyance direction, the flow of ink falls within the allowable range (substantially does not occur).

  In order to solve these problems, the control unit 40 performs a correction process to correct the discharge timing of the ink to be discharged from the nozzles 31. In addition, in the correction process by the control unit 40, the correction of the ejection amount of the ink ejected from the nozzle 31 is also performed.

  For example, the control unit 40 sets the step of the belt motor M3 from when the reference unit (not shown) provided on the transport belt 241 is at a predetermined reference position (the detection position of the detection unit for detecting the reference unit). Based on the number, the position of the suction hole 241 a moving in the circumferential direction of the transport belt 241 is recognized. Further, the control unit 40 recognizes an adhesion planned position (pixel on which ink is to be applied) on the sheet S based on the image data (image data of an image to be printed on the sheet S) input to the image forming apparatus 100. Then, when the adhesion planned position on the sheet S secondary-fed from the registration position P2 with timing from the registration position P2 overlaps the suction hole 241a of the conveyance belt 241, the discharge timing of the ink to be adhered to the adhesion planned position Earlier than the reference timing.

  The flow of the correction process related to ink ejection performed by the control unit 40 will be described below with reference to the flowchart shown in FIG. The flowchart illustrated in FIG. 10 starts when an image is printed on the sheet S (when the sheet S is secondarily fed).

  Hereinafter, the flow of the correction processing relating to the ink discharge will be described focusing attention on one of the plurality of nozzles 31, but similar correction processing (processing to determine whether or not correction processing is to be performed is included for the other nozzles 31). ) Is done. Further, the correction process (including the process of determining whether or not to perform the correction process) related to the ink discharge is performed for each line (one dot).

  Here, the storage unit 70 stores information indicating a special sheet S which is a sheet S (a sheet S having low elasticity and flexibility) which is not sucked into the suction holes 241 a even when suctioned by the suction unit 25 on the conveyance belt 241 Be done. For example, the metallic sheet S is a special sheet S. Then, when printing is performed, the operation panel 60 receives from the user the type of sheet S used for printing. As a result, when the operation panel 60 receives from the user that the special sheet S is used for printing, the control unit 40 does not perform the correction process related to the ink discharge. In the following description, it is assumed that the operation panel 60 receives an instruction from the user to use a sheet S different from the special sheet S.

  In step S <b> 1, the control unit 40 determines whether or not the planned adhesion position (pixel) of the ink from the nozzles 31 on the sheet S overlaps the suction holes 241 a of the transport belt 241. As a result, when the control unit 40 determines that the suction holes 241a of the transport belt 241 overlap the planned adhesion position, the process proceeds to step S2.

  In step S <b> 2, the control unit 40 recognizes the distance from the central position of the suction hole 241 a of the transport belt 241 to the adhesion planned position. At this time, the control unit 40 classifies the distance from the center position to the adhesion planned position into a plurality of levels of distance levels. The information defining the classification method is stored in the storage unit 70, and the classification by the control unit 40 is performed based on the information.

  For example, distance levels are classified into three levels, small, medium and large (see FIG. 11). When the adhesion planned position falls within the first range (a range including the center position), the control unit 40 classifies the distance level of the adhesion planned position into a small level. When the adhesion planned position falls within the second range, the control unit 40 classifies the distance level of the adhesion planned position into the middle level. When the adhesion planned position falls within the third range, the control unit 40 classifies the distance level of the adhesion planned position into a large level. The number of classifications of the distance level is not particularly limited, and may be classified into two levels, or may be classified into four or more levels. In FIG. 11, the center position is indicated by a black circle.

  In step S <b> 3, the control unit 40 performs an ejection timing correction process of correcting (setting) the ejection timing of the ink from the nozzles 31 as one process of the correction process. In the ejection timing correction process, any one of the first timing, the second timing, and the third timing is set as the ejection timing of the ink from the nozzle 31. When the control unit 40 sets the discharge timing to the first timing, the discharge timing of the ink from the nozzle 31 is the earliest. When the control unit 40 sets the discharge timing to the third timing, the discharge timing of the ink from the nozzle 31 is the latest (however, the ink is discharged from the nozzle 31 at a timing earlier than the reference timing). When the control unit 40 sets the discharge timing to the second timing, the discharge timing of the ink from the nozzles 31 is later than the first timing and earlier than the third timing.

  When the distance level is a small level (the distance from the center position to the planned adhesion position among the three steps is the shortest level), the control unit 40 sets the discharge timing of the ink from the nozzle 31 to the first timing. When the distance level is the middle level, the control unit 40 sets the discharge timing of the ink from the nozzle 31 to the second timing. When the distance level is a large level (the distance from the center position to the planned adhesion position among the three steps is the longest level), the control unit 40 sets the discharge timing of the ink from the nozzle 31 to the third timing. That is, when the suction holes 241 a of the transport belt 241 overlap the planned adhesion position, the control unit 40 sets the timing of discharging ink from the nozzles 31 earlier as the planned adhesion position is closer to the central position.

  In step S4, the control unit 40 determines whether a condition (predetermined condition) for performing the discharge amount correction process, which is one process of the correction process, is satisfied. As a result, when the control unit 40 determines that the predetermined condition is satisfied, the process proceeds to step S5.

  For example, when the planned adhesion position is in a region downstream of the central position in the sheet conveying direction and the distance between the planned adhesion position and the central position exceeds a predetermined first threshold distance, It is determined that the predetermined condition is satisfied. In other words, the control unit 40 determines that the predetermined condition is satisfied when there is a planned adhesion position in the vicinity of a portion on the downstream side in the sheet conveyance direction of the inner edge of the suction hole 241 a of the conveyance belt 241.

  In step S5, the control unit 40 performs a process of correcting (setting) the discharge amount of the ink from the nozzles 31 as the discharge amount correction process. In the discharge amount correction process, one of the first discharge amount and the second discharge amount is set as the ink discharge amount. When the control unit 40 sets the discharge amount to the first discharge amount, the discharge amount of the ink from the nozzles 31 is reduced as compared with the case where the control unit 40 sets the discharge amount to the second discharge amount. Note that the amount of ink ejected from the nozzles 31 is smaller than the default setting whether the control unit 40 sets the ejection amount to the first ejection amount or to the second ejection amount.

  When the control unit 40 performs the discharge amount correction process, if the distance between the planned adhesion position and the center position exceeds the predetermined second threshold distance larger than the first threshold distance, the control unit 40 The discharge amount is set to the first discharge amount (the reduction range of the ink discharge amount is made larger). On the other hand, if the distance between the planned adhesion position and the center position exceeds the first threshold distance but does not exceed the second threshold distance, the control unit 40 sets the discharge amount of the ink from the nozzle 31 to the second discharge amount. (The ink discharge amount is reduced but the reduction width is reduced). That is, when the suction hole 241a of the conveyance belt 241 and the adhesion planned position overlap, the control unit 40 moves from the nozzle 31 as the adhesion planned position is closer to the inner edge of the suction hole 241a of the conveyance belt 241 downstream in the sheet conveyance direction. Set so as to reduce the amount of ejected ink.

  In step S4, when the control unit 40 determines that the predetermined condition is not satisfied, the discharge amount correction process is not performed, and the present flow ends (the discharge timing correction process is performed). That is, the distance between the planned adhesion position and the center position even when the planned adhesion position is in the area upstream of the central position in the sheet conveyance direction or the planned adhesion position is in the area downstream of the central position in the sheet conveyance direction. If the first threshold distance is not exceeded, the discharge amount correction process is not performed.

  Further, in step S1, when the control unit 40 determines that the suction holes 241a of the transport belt 241 and the planned adhesion position do not overlap, neither the discharge timing correction process nor the discharge amount correction process is performed. In this case, the ink is ejected from the nozzle 31 at the reference timing. Further, the discharge amount of the ink from the nozzle 31 is maintained at the default setting.

<Suction control of sheet>
(First suction control)
In the image forming apparatus 100, there may be a case where a sheet S in which deformation due to suction by the suction unit 25 is unlikely to occur is set (the sheet S may be used for printing). When such a sheet S is used for printing and the amount of depression (the amount of deformation) of the overlapping portion of the sheet S overlapping the suction holes 241 a of the transport belt 241 becomes smaller than expected, the ink is ejected from the nozzles 31 When the timing is advanced from the reference timing, a deviation occurs between the actual adhesion position and the adhesion planned position on the sheet S of the ink.

  Therefore, the control unit 40 performs the first suction control. In order to cause the control unit 40 to perform the first suction control, information indicating the correspondence between the level of ease of deformation of the sheet S on the conveyance belt 241 by suction of the suction unit 25 and the type of the sheet S is a storage unit It is stored in 70. Further, when printing is performed, the operation panel 60 receives from the user the type of sheet S used for printing. Then, the control unit 40 controls the suction of the suction unit 25 according to the type of the sheet S used for printing (performs the first suction control).

  The flow of the first suction control performed by the control unit 40 will be described below with reference to the flowchart shown in FIG.

  In step S11, the control unit 40 recognizes the level corresponding to the type of the sheet S received by the operation panel 60 from the user. The level is classified into, for example, two levels of a standard level and a low level lower than the standard level. As the level is lower, the stretchability and flexibility of the sheet S are poor, and deformation of the sheet S due to suction by the suction unit 25 is less likely to occur.

  In step S12, the control unit 40 determines whether the level recognized in step S11 is a standard level. As a result, when the control unit 40 determines that the level is the standard level, the process proceeds to step S13, and when the control unit 40 determines that the level is not the standard level (is the low level), the process proceeds to step S14. .

  When it transfers to step S13, control part 40 maintains suction power of suction unit 25 with default setting. That is, the control unit 40 sets the number of rotations of the fan motor M7 to a predetermined reference number of rotations.

  On the other hand, when the process proceeds to step S14, the control unit 40 increases the suction force of the suction unit 25 (makes the number of rotations of the fan motor M7 higher than the reference number of rotations). Thus, when the stretchability and flexibility of the sheet S used in printing are low, the suction force of the suction unit 25 is increased.

(Second suction control)
In double-sided printing, one side image is printed on one side of the sheet S, and then the other side image is printed on the other side of the sheet S. In this case, after printing one surface image on one surface of the sheet S, the stretchability and flexibility of the sheet S become lower than before printing. That is, deformation due to suction by the suction unit 25 is less likely to occur. Therefore, when the ejection timing of the ink from the nozzle 31 is advanced before the reference timing at the time of printing the other surface image on the other surface of the sheet S, the ink adheres to the actual adhesion position and the adhesion planned position on the sheet S. It occurs.

  Therefore, the control unit 40 performs the second suction control. In order to perform the second suction control, the control unit 40 performs a process of recognizing a portion of the sheet S on which the one-sided image is printed as a target portion based on the image data of the one-sided image. Then, the control unit 40 increases the suction force on the target portion of the sheet S (performs the second suction control).

  The flow of the second suction control performed by the control unit 40 will be described below with reference to the flowchart shown in FIG. The flowchart shown in FIG. 13 starts when the sheet S is supplied to the belt unit 24 (when the other side image is printed on the other side of the sheet S).

  In step S21, the control unit 40 determines whether there is a negative pressure generation unit 250 in which the target portion of the sheet S has entered the suction target area. As a result, when the control unit 40 determines that it exists, the process proceeds to step S22, while when the control unit 40 determines that it does not exist, the process of step S21 (determination by the control unit 40) is repeated.

  In step S22, the control unit 40 makes the suction force of the negative pressure generation unit 250 in which the target part enters the suction target area larger than the suction force of the other negative pressure generation units 250. That is, the control unit 40 increases the rotational speed of the fan motor M7 of the negative pressure generation unit 250.

  In step S23, the control unit 40 determines whether the target portion has passed through the suction target area of the negative pressure generation unit 250 whose suction power is increased. As a result, when the control unit 40 determines that the target portion has passed through the suction target area, the process proceeds to step S24, and when the control unit 40 determines that the target portion has not passed through the suction target area, the step The process of S23 (determination by the control unit 40) is repeated.

  In step S24, the control unit 40 restores the suction force of the negative pressure generation unit 250 having the suction force increased. Thereafter, when the target portion enters another suction target area, the control unit 40 increases the suction force of the negative pressure generation unit 250 that sets the area as the suction target.

(Third suction control)
In some cases, there may be a missing portion (for example, a bent portion, a torn portion, a punched portion, etc.) on the sheet S used in printing. In this case, when the ink passes through the missing portion of the sheet S, the ink adheres to the conveyance belt 241 (the contamination of the conveyance belt 241 occurs). In addition, the other sheets S may be stained with the ink.

  Therefore, the control unit 40 performs the third suction control. In the third suction control by the control unit 40, the CIS unit 50 reads the sheet S supplied to the belt unit 24. Based on the read data obtained by reading the sheet S by the CIS unit 50, the control unit 40 determines whether or not there is a missing portion in the sheet S. Then, when there is a missing portion in the sheet S, the control unit 40 performs the third suction control.

  The flow of the third suction control performed by the control unit 40 will be described below with reference to the flowchart shown in FIG. The flowchart shown in FIG. 14 starts when the sheet S is supplied to the belt unit 24 (when the CIS unit 50 reads the sheet S).

  In step S31, the control unit 40 determines whether or not a missing portion exists in the sheet S. As a result, when the control unit 40 determines that there is a missing portion, the process proceeds to step S32. On the other hand, when the control unit 40 determines that there is no missing portion, the present flow ends.

  In step S32, the control unit 40 stops the suction of the negative pressure generation unit 250 in which the defect portion has entered the suction target area. That is, the control unit 40 stops the driving of the fan motor M7 of the negative pressure generation unit 250.

  In step S33, the control unit 40 determines whether or not the defect portion has passed through the suction target area of the negative pressure generation unit 250 which has stopped suction. As a result, when the control unit 40 determines that the defective portion has passed through the suction target area, the process proceeds to step S34, and when the control unit 40 determines that the defective portion has not passed through the suction target area, the step The process of S33 (determination by the control unit 40) is repeated.

  In step S34, the control unit 40 restores the suction force of the negative pressure generation unit 250 which has stopped suction. Thereafter, when the defect portion enters another suction target area, the control unit 40 stops the suction of the negative pressure generation unit 250 which sets the area as the suction target.

(4th suction control)
When the printing unit 30 prints an image on the sheet S, inks of yellow (Y), black (K), cyan (C) and magenta (M) are discharged onto the sheet S in this order. Depending on the image to be printed on the sheet, the discharge amount of ink on the upstream side in the sheet conveyance direction, such as yellow and black, increases (the amount of the ink attached to the sheet S increases). For example, even if curling does not occur in the sheet S when the sheet S is supplied to the belt unit 24, the curling may occur in the sheet S during printing if the ink discharge amount on the upstream side in the sheet conveying direction increases. Can occur.

  Therefore, the control unit 40 performs the fourth suction control. In the fourth suction control by the control unit 40, the suction force of the suction unit 25 is controlled based on the discharge amount of the ink. The control unit 40 accumulates the ejection amount of the ink ejected during printing (the adhesion amount of the ink attached to the sheet S) in order to perform the fourth suction control.

  The flow of the fourth suction control performed by the control unit 40 will be described below with reference to the flowchart shown in FIG. The flowchart shown in FIG. 15 starts when the sheet S is supplied to the belt unit 24 (when an image is printed on the sheet S).

  In step S41, the control unit 40 determines whether the discharge amount of the ink discharged toward the sheet S on the conveyance belt 241 exceeds the predetermined threshold amount while the sheet S is being conveyed by the belt unit 24. Do. As a result, when the control unit 40 determines that the ejection amount of the ink exceeds the threshold amount, the process proceeds to step S42. At step S42, the control unit 40 makes the suction force of the suction unit 25 larger than that before printing.

  If the control unit 40 determines that the ejection amount of the ink does not exceed the threshold amount in step S41, the process proceeds to step S43. In step S43, the control unit 40 determines whether the printing on the sheet S on the conveyance belt 241 is completed. As a result, when the control unit 40 determines that the printing is not completed, the process proceeds to step S41. On the other hand, when the control unit 40 determines that the printing is completed, the present flow ends. That is, if the discharge amount of the ink does not exceed the threshold amount during printing, the suction force of the suction unit 25 is maintained at the default setting.

  As described above, the image forming apparatus 100 according to the present embodiment includes the conveyance belt 241 in which the plurality of suction holes 241 a are formed, and the sheet S placed on the conveyance belt 241 by driving the conveyance belt 241 is A negative pressure is generated on the belt unit 24 (belt conveyance unit) to be conveyed and on the inner circumferential surface side (the opposite surface side to the sheet placement surface side) of the conveyance belt 241, and on the conveyance belt 241 via the suction hole 241 a. A suction unit 25 (suction unit) for suctioning the sheet S, and a nozzle 31 disposed opposite to the transport belt 241 at a distance to discharge the ink, and discharging the ink from the nozzle 31 toward the transport belt 241 The ink from the nozzles 31 is adhered to the ink heads 3Y, 3K, 3C, and 3M that cause the ink to adhere to the sheet S on the conveyance belt 241 by When the planned adhesion position to be caused does not overlap the suction hole 241 a of the conveyance belt 241, ink is ejected from the nozzle 31 at the reference timing, and when the suction hole 241 a of the conveyance belt 241 overlaps the predetermined adhesion position, And a control unit that causes ink to be ejected from the nozzle at an early timing.

  In the configuration of the present embodiment, even if the overlapping portion of the sheet S including the planned adhesion position is deformed so as to be recessed downward with respect to the sheet mounting surface of the transport belt 241, that is, the sheet S of the ink Even if the time to drop on the ink drops is longer than the ideal time (the time when the sheet S is not dented), the actual adhesion position of the ink and the planned adhesion position deviate from each other. Can be suppressed. As a result, it is possible to suppress the decrease in print image quality.

  Further, in the present embodiment, as described above, when the suction hole 241 a of the conveyance belt 241 and the adhesion planned position overlap, as the adhesion planned position is closer to the center position of the suction hole 241 a of the conveyance belt 241. The timing of ink ejection from the nozzles 31 is advanced. Here, as the planned adhesion position is closer to the center position of the suction hole 241 a of the transport belt 241, the time from the discharge of the ink to the deposition on the planned adhesion position of the ink becomes longer than the ideal time. Therefore, it is preferable that the timing at which the ink is discharged from the nozzles 31 be made earlier as the planned adhesion position is closer to the center position of the suction holes 241 a of the transport belt 241. This makes it possible to further reduce the deviation between the actual adhesion position of the ink and the planned adhesion position.

  Further, in the present embodiment, as described above, when the suction hole 241 a of the conveyance belt 241 and the adhesion planned position overlap, the adhesion planned position is the downstream side of the suction hole 241 a of the conveyance belt 241 in the sheet conveyance direction. The discharge amount of the ink from the nozzle 31 is reduced as it is closer to the inner edge of the nozzle. Thus, even if the portion including the planned adhesion position in the overlapping portion of the sheet S is inclined obliquely downward from the downstream side to the upstream side in the sheet conveyance direction, the sheet S is discharged toward the planned adhesion position and adhered to the sheet S It is possible to prevent the dropped ink from flowing upstream in the sheet conveyance direction. Thereby, it is possible to further suppress the deterioration of the printing image quality.

  Further, in the present embodiment, as described above, the operation panel 60 (reception unit) receives the type of the sheet S used for printing from the user. The storage unit 70 also stores the correspondence between the level of ease of deformation of the sheet S on the conveyance belt 241 by the suction of the suction unit 25 and the type of the sheet S. Then, the control unit 40 recognizes the level corresponding to the type of the sheet S received by the operation panel 60, and the lower the recognized level (the lower the elasticity and flexibility of the sheet S used for printing), The suction power of the suction unit 25 is increased. That is, when the sheet S having low elasticity and flexibility is used for printing, the suction force of the suction unit 25 is increased to intentionally cause the overlapping portion of the sheet S to be dented. As a result, when the sheet S having low elasticity and flexibility is used for printing, the ejection timing correction process (process for advancing the ink ejection timing) by the control unit 40 is performed, and the actual adhesion position and adhesion of the ink are performed. It is possible to suppress the occurrence of the disadvantage that the deviation from the planned position is large.

  Further, in the present embodiment, as described above, when performing double-sided printing, the control unit 40 recognizes the portion of the sheet S on which the one-sided image is to be printed as the target portion based on the image data of the one-sided image. When the process is performed and the image on the other side is printed on the sheet S, the suction force of the negative pressure generation unit 250 in which the target portion enters the suction target area is made larger than the suction force of the other negative pressure generation units 250. As a result, when printing on the other side of the sheet S, the target portion of the sheet S (a portion where the elasticity and flexibility become lower due to the ink adhering to the one side of the sheet S) is the suction hole 241 a of the transport belt 241. In the case of overlapping, the discharge timing correction processing (processing to accelerate the discharge timing of the ink) by the control unit 40 is performed, so that the deviation between the actual adhesion position of the ink and the planned adhesion position becomes large. It can be suppressed to occur. That is, it is possible to suppress the image quality deterioration of the printed matter (the image quality deterioration of the other side image) obtained by the execution of the double-sided printing.

  Further, in the present embodiment, as described above, the control unit 40 causes the defective portion in the sheet S supplied to the belt unit 24 based on the read data obtained by the reading of the sheet S by the CIS unit 50 (reading unit). Determine if it exists. Then, when there is a missing portion in the sheet S, the control unit 40 stops the suction of the negative pressure generating unit 250 in which the missing portion of the sheet S has entered the suction target area. In this way, the ink discharged toward the transport belt 241 is prevented from invading the sheet placement surface of the transport belt 241 via the missing portion of the sheet S (the sheet placement surface of the transport belt 240 is soiled). Can.

  Further, in the present embodiment, as described above, when the control unit 40 transports the sheet S by the transport belt 241, the amount of ink ejected toward the sheet S being transported exceeds the threshold amount. The suction force of the suction unit 25 is made larger than that before printing. As a result, it is possible to suppress the occurrence of curling of the sheet S during conveyance of the sheet S.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is indicated not by the description of the above embodiment but by the scope of claims, and further includes all modifications within the meaning and scope equivalent to the scope of claims.

24 Belt unit (belt conveyance unit)
25 Suction unit (Suction unit)
30 ink head 40 control unit 50 CIS unit (reading unit)
60 Operation panel (reception section)
70 storage unit 31 nozzle 241 transport belt 241 a suction hole 250 negative pressure generating unit

Claims (7)

A belt conveyance unit that includes a conveyance belt in which a plurality of suction holes are formed, and conveys a sheet placed on the conveyance belt by driving the conveyance belt;
A suction unit that generates a negative pressure on the side opposite to the sheet mounting surface side of the conveyance belt, and sucks a sheet on the conveyance belt via the suction hole;
An ink which is disposed to face the transport belt at a distance and has a nozzle for discharging ink, and which causes the ink to adhere to a sheet on the transport belt by discharging the ink from the nozzle toward the transport belt With the head,
When the planned adhesion position where the ink from the nozzle should be adhered does not overlap the suction hole, the ink is ejected from the nozzle at a predetermined reference timing, and the planned adhesion position and the suction hole overlap. An image forming apparatus comprising: a control unit configured to eject ink from the nozzles at a timing earlier than the reference timing.   The controller is characterized in that, when the planned adhesion position and the suction hole overlap, as the planned adhesion position is closer to the central position of the suction hole, the timing of discharging ink from the nozzle is advanced. An image forming apparatus according to claim 1.   When the adhesion planned position and the suction hole overlap, the control unit reduces the discharge amount of the ink from the nozzle as the adhesion planned position is closer to the inner edge of the suction hole on the downstream side of the sheet conveyance direction. An image forming apparatus according to claim 1 or 2, characterized in that A reception unit that receives from the user the type of sheet used in printing;
A storage unit that stores a correspondence between the level of ease of deformation of the sheet on the transport belt by suction of the suction unit and the type of sheet; and the control unit is configured to receive the sheet received by the reception unit. The image forming apparatus according to any one of claims 1 to 3, wherein the level corresponding to the type of the object is recognized, and the suction power of the suction unit is increased as the recognized level is lower. . The suction unit includes a plurality of negative pressure generating units that respectively generate negative pressure independently and set areas different from each other as suction target areas,
When the control unit performs double-sided printing in which one surface image is printed on one surface of the sheet and then the other surface image is printed on the other surface of the sheet, the one surface image is printed based on the image data of the one surface image. When a portion of the sheet to be printed is recognized as a target portion, and the other side image is printed on the sheet, the suction force of the negative pressure generation portion where the target portion enters the suction target area is The image forming apparatus according to any one of claims 1 to 4, wherein the suction force of the negative pressure generating unit is larger than the suction force of the negative pressure generating unit. The image forming apparatus further includes a reading unit installed at a position upstream of the installation position of the conveyance belt in the sheet conveyance direction and reading a sheet supplied to the conveyance belt.
The suction unit includes a plurality of negative pressure generating units that respectively generate negative pressure independently and set areas different from each other as suction target areas,
The control unit determines whether or not a missing portion exists in the sheet supplied to the conveyance belt based on read data obtained by reading the sheet by the reading unit, and when the missing portion is present, The image forming apparatus according to any one of claims 1 to 5, wherein the suction of the negative pressure generation unit in which the defective portion enters the suction target area is stopped.   The controller controls the suction force of the suction unit to be higher than that before printing when the discharge amount of the ink discharged onto the sheet being conveyed exceeds a predetermined threshold amount while the sheet is being conveyed by the conveyance belt. The image forming apparatus according to any one of claims 1 to 6, wherein the size is increased.

Images