JP6716100B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus that conveys a sheet and attaches ink to the sheet.

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

Such an image forming apparatus includes an ink head that ejects ink. Further, the image forming apparatus is provided with a conveyance belt which is arranged to face the ink head with a gap. When the image is printed on the sheet, the sheet is conveyed by the conveyor belt.

The conveyor belt is an endless belt and is supported so as to be able to rotate. When the sheet is conveyed by the conveyor belt, the sheet is placed on the outer peripheral surface of the conveyor belt, and the conveyor belt circulates in that state. Then, the ink is ejected toward the sheet on the conveyor belt (the sheet being conveyed).

JP, 2014-24231, A

In Patent Document 1, a plurality of suction holes are formed in the conveyor belt. Further, a suction fan unit is provided on the inner peripheral surface side of the conveyor 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 conveyor belt.

When a sheet with high elasticity and flexibility is used for printing in the configuration in which the sheet on the conveyor belt is sucked downward, the portion of the sheet that overlaps the suction hole of the conveyor belt (here, referred to as the overlapping portion) becomes the suction hole. The sheet may be sucked and deformed so that the overlapping portion of the sheet is recessed downward with respect to the sheet mounting surface of the transport belt.

Here, for example, it is assumed that the planned adhesion position (pixel on which ink is placed), which is the position on the sheet to which the ink from the ink head is to be attached, is the overlapping portion of the sheets. In this example, when there is no dent in the overlapping portion of the sheet, the ink is ejected at a predetermined reference timing from the ink head, so that the actual adhesion position of the ink and the expected adhesion position are substantially the same. Can be made. However, when a dent occurs in the overlapping portion of the sheet due to the suction of the sheet, the time from the ejection of ink to the landing of the ink on the sheet becomes long, so the actual position of ink The deviation between the planned adhesion position and the adhesion position exceeds the allowable range. As a result, there is an inconvenience that the print quality is deteriorated.

The present invention has been made to solve the above problems, and in a configuration in which a sheet on a conveyor belt is sucked downward, print image quality is deteriorated due to deformation (dent) of the sheet caused by suction of the sheet. An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of the inconvenience.

In order to achieve the above object, the image forming apparatus of the present invention includes a conveyor belt having a plurality of suction holes formed therein, and a belt conveyor that conveys a sheet placed on the conveyor belt by driving the conveyor belt. And a suction unit that generates a negative pressure on the side of the conveying belt opposite to the sheet mounting surface side and sucks the sheet on the conveying belt through a suction hole, and is opposed to the conveying belt at a distance. , An ink head that has a nozzle for ejecting ink, and that ejects the ink from the nozzle toward the conveyor belt to adhere the ink to the sheet on the conveyor belt, and the planned attachment position where the ink from the nozzle should adhere And a suction hole do not overlap each other, ink is ejected from the nozzle at a predetermined reference timing, and when the planned adhesion position and the suction hole overlap, ink is ejected from the nozzle at a timing earlier than the reference timing. , Is provided.

With the configuration of the present invention, when the planned deposition position (pixel) on the sheet to which the ink from the nozzle is to be deposited and the suction hole overlap, the ink is ejected at a timing earlier than a predetermined reference timing. Therefore, even if the overlapped portion of the sheet including the planned adhesion position (the portion that overlaps the suction hole of the conveyor belt) is deformed so as to be recessed downward with respect to the sheet mounting surface of the conveyor belt, that is, the ink is ejected Even when the time to land on the sheet is longer than the ideal time (the time when there is no dent on the sheet), the actual ink adhesion position and the expected adhesion position are displaced. Can be suppressed. As a result, it is possible to suppress deterioration of print image quality.

With the configuration of the present invention, it is possible to prevent the print image quality from deteriorating due to the deformation (dent) of the sheet caused by the suction of the sheet.

FIG. 1 is a diagram showing an overall configuration of an image forming apparatus according to an embodiment of the invention. FIG. 3 is a diagram showing a sheet mounting surface of a conveyor belt provided in a belt unit of an image forming apparatus according to an embodiment of the present invention. FIG. 1 is a diagram showing a configuration of a suction unit of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram showing an arrangement pattern of a plurality of negative pressure generating units provided in a suction unit of an image forming apparatus according to an embodiment of the present invention. FIG. 1 is a diagram showing a hardware configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram for explaining ejection timing of ink ejected from the ink head of the image forming apparatus according to the embodiment of the invention. FIG. 3 is a diagram for explaining ejection timing of ink ejected from an ink head of an image forming apparatus according to an embodiment of the present invention (timing when a suction hole of a conveyor belt and a planned adhesion position overlap). FIG. 3 is a diagram for explaining an ejection amount of ink ejected from the ink head of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a diagram for explaining an ejection amount of ink ejected from the ink head of the image forming apparatus according to the embodiment of the present invention. 6 is a flowchart showing a flow of correction processing relating to ink ejection, which is performed by the control unit of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a diagram for explaining a method for setting ink ejection timing, which is performed by the control unit of the image forming apparatus according to the embodiment of the present invention. 3 is a flowchart showing a flow of first suction control performed by the control unit of the image forming apparatus according to the embodiment of the present invention. 3 is a flowchart showing a flow of second suction control performed by the control unit of the image forming apparatus according to the embodiment of the present invention. 3 is a flowchart showing a flow of third suction control performed by the control unit of the image forming apparatus according to the embodiment of the present invention. 6 is a flowchart showing a flow of fourth suction control performed by the control unit of the image forming apparatus according to the embodiment of the present invention.

<Structure of image forming apparatus>
As shown in FIG. 1, the image forming apparatus 100 of this embodiment includes a conveyance path 10 for conveying the sheet S. The transport path 10 is classified into a main transport path 1A and a double-sided printing transport path 1B. The main transport path 1A reaches the discharge position P4 from the paper feed position P1 through the registration position P2 and the print position P3 in this order. 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. To do. The double-sided printing conveyance path 1B is not used when performing one-sided printing in which an image is printed only on one side of the sheet S, and after the image is printed on one side of the sheet S, another side opposite to the one side of the sheet S is printed. It is used when performing double-sided printing, which prints an image on the other side as well. 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 also includes a transport 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 paper feed roller pair 21 is installed at the paper feed position P1. The paper feed side transport roller pair 22 is installed between the paper feed position P1 and the registration position P2. The number of the paper feed side transport rollers 22 installed may be plural or one.

The pair of paper feed rollers 21 pulls out the sheet S from the sheet cassette CA at the paper feed position P1 and supplies it to the transport path 10 (performs primary paper feed). Further, the paper feed roller pair 21 conveys the sheet S supplied to the conveyance path 10 along the conveyance path 10. The paper feed side transport roller pair 22 transports the sheet S along the transport path 10 together with the paper feed roller pair 21. As a result, the sheet S is conveyed from the paper feed position P1 toward the registration position P2.

The transport unit 20 also includes a registration roller pair 23. The registration roller pair 23 is installed at the registration 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 registration roller pair 23 is stopped rotating when the sheet S reaches the registration position P2. As a result, the progress of the sheet S is temporarily stopped, and the skew of the sheet S is corrected at that time (the leading end portion of the sheet S is bent). Then, the registration roller pair 23 temporarily stops the progress of the sheet S until a predetermined skew correction time elapses, and then conveys the sheet S reaching the registration position P2 to the printing position P3 (secondary feeding). Paper) to start.

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. The printing of the 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 conveyor belt 241, a driving roller 242, and a driven roller 243. The conveyor belt 241 has a plurality of suction holes 241a (see FIG. 2) formed so as to penetrate in the thickness direction of the conveyor belt 241. The transport belt 241 is an endless belt and is stretched around a drive roller 242 and a driven roller 243. The conveyor belt 241 is driven (circulated) by the 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 conveyor belt 241 is driving. 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 arranged on the inner peripheral surface side of the conveyor belt 241. The suction unit 25 generates a negative pressure on the inner peripheral surface side of the transport belt 241, and sucks the sheet S on the transport belt 241 toward the sheet mounting surface of the transport belt 241.

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

When a negative pressure is generated in the pressure chamber 251, the generated negative pressure causes the air on the conveyor belt 241 to be sucked into the pressure chamber 251 through the suction hole 241a. When the sheet S is placed on the conveyor belt 241, the suction force acts on the sheet S, so that the sheet S is attracted to the sheet mounting surface of the conveyor belt 241.

The pressure chamber 251 is divided into a plurality of parts by the partition plate 251a. That is, there are a plurality of pressure chambers 251. 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 portions that independently generate negative pressure. Hereinafter, the plurality of negative pressure generating units will be described by adding reference numeral 250 to each of them.

When the suction unit 25 is provided with a plurality of negative pressure generators 250, as shown in FIG. 4, the suction target area of the suction unit 25 is divided into a plurality of areas, and the suction force (negative pressure) is divided for each of the divided suction target areas. The negative pressure generated in the generator 250 can be different. In FIG. 4, each suction target area is indicated by a thick line, and the conveyor 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 generating 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 the direction orthogonal to the sheet conveying direction.

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

The discharge-side transport roller pair 26 transports the sheet S (printed sheet S on which an image has been printed) transported 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 duplex roller transport roller pair 27 (including a switchback roller pair 27S). The double-sided printing transport roller pair 27 is installed in the double-sided printing transport path 1B. For example, the number of double-sided printing conveyance roller pairs 27 installed is plural. The double-sided printing conveyance roller pair 27 is a pair of conveyance rollers used when performing double-sided printing, and conveys the sheet S along the double-sided printing conveyance 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 transport path 11B is connected to the position DP of the main transport path 1A. The second transport path 12B is a transport path for switching back the sheet S, and is connected to the position UP of the main transport path 1A.

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

On the other hand, when the double-sided printing is executed, when the printing of the one-sided image on the sheet S is completed, the carrying unit 20 performs the carrying process for the double-sided printing. Specifically, the transport unit 20 draws a sheet S (one side printed sheet S is referred to here) having a one-sided image printed on one side thereof into the first transport path 11B, and then the second transport path from the first transport path 11B to the second transport path 11B. The single-sided printing sheet S is made to enter the transport 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 orientation 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 transport path 11B and the second transport path 12B, and the branch point of the single-sided print sheet S is changed. The single-sided printing sheet S is switched back by rotating in reverse at the timing when the trailing edge passes. After that, the transport unit 20 returns the single-sided print sheet S to the position UP of the main transport path 1A.

After returning the single-sided print sheet S to the main transport path 1A, the transport unit 20 transports the single-sided print sheet S again from the registration position P2 to the printing position P3. That is, at the time of executing double-sided printing, the sheet S passes through the print position P3 twice. Then, at this time, the directions of the front and back surfaces of the single-sided printing sheet S are reversed (the orientation of the front and back surfaces of the sheet S that passes the printing position P3 again is opposite to the direction when it passed the printing position P3 last time. ). Therefore, the printing of the image by the printing unit 30 is performed on the other side (unprinted side) of the one-sided print sheet S. That is, the other side image is printed on the other side of the one-sided printing sheet P. After that, the transport unit 20 transports the sheet S having the one-side image and the other-side image printed on both sides along the main transport path 1A and discharges the sheet S to the discharge tray ET.

The printing unit 30 is arranged above the belt unit 24 so as to face the outer peripheral surface of the conveyor belt 241 with a space therebetween. Then, the printing unit 30 prints an image on the sheet S being conveyed (the sheet S on the conveyance 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 stores cyan ink. The ink head 3M contains magenta ink.

Further, each of the ink heads 3Y, 3K, 3C and 3M has a plurality of nozzles 31 (see FIG. 5) for ejecting ink. Although not shown, each nozzle 31 is provided with a piezoelectric element. 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 unit 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 a control program and data, and performs processing for controlling each unit of the image forming apparatus 100. The memory 42 stores a control program 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 transport motor that rotates the rollers of the transport unit 20 in order to control the transport of the sheet S by the transport unit 20. For example, as the transport motor, there are a paper feed side motor M1, a registration motor M2, a belt motor M3, a discharge side motor M4, a double-sided printing motor M5, a switchback motor M6, and the like.

The paper feed side motor M1 is connected to the paper feed roller pair 21 and the paper feed side transport roller pair 22. The control unit 40 controls the driving of the paper feed side motor M1 to appropriately rotate the paper feed roller pair 21 and the paper feed side transport roller pair 22. Further, the paper feed roller pair 21 receives a driving force from the paper feed motor M1 via a paper feed side clutch (not shown). The control unit 40 controls on/off of the sheet feeding side clutch, and switches connection and disconnection of the sheet feeding roller pair 21 and the sheet feeding side motor M1.

The registration motor M2 is connected to the registration roller pair 23. The control unit 40 controls the driving of the registration motor M2 and appropriately rotates the registration roller pair 23. Further, the registration roller pair 23 receives a driving force from the registration motor M2 via a registration clutch (not shown). The control unit 40 controls on/off of the registration clutch, and switches connection and disconnection of the registration roller pair 23 and the registration motor M2.

The belt motor M3 is connected to the drive roller 242 of the belt unit 24. The control unit 40 controls driving of the belt motor M3 and appropriately rotates the driving roller 242 of the belt unit 24. That is, the control unit 40 appropriately rotates the conveyor 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 transport roller pair 26. The control unit 40 controls driving of the discharge side motor M4 and appropriately rotates the discharge side transport roller pair 26. The discharge-side transport 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 to switch between connection and disconnection of the discharge side transport roller pair 26 and the discharge side motor M4.

The double-sided printing motor M5 is connected to the double-sided printing transport roller pair 27 other than the switchback roller pair 27S. The control unit 40 controls the driving of the double-sided printing motor M5 to appropriately rotate the double-sided printing transport roller pair 27. The double-sided printing conveyance roller pair 27 receives a driving force from the double-sided printing motor M5 via a double-sided 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 transport roller pair 27 and the double-sided printing motor M5.

The switchback motor M6 is connected to the switchback roller 27S. The control unit 40 controls the drive of the switchback motor M6 and appropriately rotates 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 the fan motor M7 that rotates the fan 253. For example, the fan motor M7 is integrated with the casing of the fan 253. Then, the control unit 40 controls the drive of the fan motor M7 and appropriately rotates the fan 253 (generates a negative pressure in the pressure chamber 251). The control unit 40 independently controls the negative pressure (suction force) generated in each of the negative pressure generation units 250 for each negative pressure generation 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 ejection of 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 determines print data that defines the nozzles 31 (herein referred to as the ejection nozzles 31) that eject ink, the ejection amount of the ink from the ejection nozzles 31, and the like for each of the ink heads 3Y, 3K, 3C, and 3M. To generate. Then, the control unit 40 transmits the print data to the respective drivers 32 of the ink heads 3Y, 3K, 3C and 3M, thereby causing the respective drivers 32 to perform the ink ejection processing based on the print data. The control unit 40 also 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 ejection process is performed once.

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

As shown in FIG. 6, a space is provided between the sheet S on the conveyor belt 241 and the ejection nozzle 31. Therefore, there is a time difference between the ejection timing of the ink from the ejection nozzle 31 and the arrival timing of the ink to the sheet S. For this reason, the position where the ink from the ejection nozzle 31 is expected to adhere (the position on the sheet S to which the ink from the ejection nozzle 31 should be attached) is located downstream of the position of the ejection nozzle 31 in the sheet conveyance direction. The arrival timing (timing at which the interval between the ejection nozzle 31 and the planned adhesion position in the sheet transport direction becomes a predetermined interval) is set as the reference timing. In FIG. 6, a space is provided between the conveyor belt 241 and the sheet S in order to make the drawing easy to see, but in reality, the sheet S is in close contact with the conveyor belt 241. The same applies to FIGS. 7 to 9 to be referred to later.

Returning 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". The CIS unit 50 is installed, for example, at a position between the registration position P2 and the 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 the 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 part". The operation panel 60 receives settings and instructions regarding printing from the user. For example, the operation panel 60 includes a touch panel display and displays a reception screen for receiving settings and instructions regarding printing. The operation panel 60 is connected to the 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 also includes a storage unit 70. The storage unit 70 includes a non-volatile storage device such as a ROM (EEPROM or the like) or a 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 regarding ink ejection>
When a sheet S made of a material having high elasticity and flexibility (paper, cloth, leather, rubber, etc.) is used for printing, the sheet S is likely to be deformed due to suction by the suction unit 25. Specifically, as shown in FIG. 7, the portion of the sheet S that overlaps with the suction hole 241a of the conveyor belt 241 (herein referred to as the overlapping 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 transport belt 241.

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

In this case, when ink is ejected from the ejection nozzle 31 at the reference timing (timing in which the distance between the ejection nozzle 31 and the planned adhesion position in the sheet conveyance direction becomes a predetermined interval) as shown in FIG. There is a gap between the actual attachment position and the planned attachment position. This is because the vertical distance between the sheet S on the conveyor belt 241 and the discharge nozzle 31 is a distance D2 that is larger than the ideal distance D1 (the reference timing is the sheet S on the conveyor belt 241 and the discharge nozzle 31). (This is the timing when the vertical interval between and is the ideal interval D1).

In addition, when viewed from the planned deposition position, the ink deposited at the planned deposition position is ejected obliquely from 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 transport direction is the scheduled deposition position, that is, the scheduled deposition position in the overlapping portion of the sheet S. If the portion including the arrow inclines downward from the downstream side toward the upstream side in the sheet conveying direction, the ink ejected toward the planned adhesion 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 landed on the sheet S spreads over a plurality of pixels. As shown in FIG. 9, if the planned deposition position is away from the inner edge of the suction hole 241a of the transport belt 241 on the downstream side in the sheet transport direction, the ink flow falls within the allowable range (substantially does not occur).

In order to eliminate these inconveniences, the control unit 40 performs a correction process for correcting the ejection timing of the ink ejected from the nozzle 31. In the correction process by the control unit 40, the ejection amount of the ink ejected from the nozzle 31 is also corrected.

For example, the controller 40 controls the step of the belt motor M3 from when the reference portion (not shown) provided on the conveyor belt 241 is at a predetermined reference position (detection position of the detection portion for detecting the reference portion). Based on the number, the position of the suction hole 241a that moves in the circulating direction of the conveyor belt 241 is recognized. Further, the control unit 40 recognizes the planned adhesion position (pixels on which ink is placed) on the sheet S based on the image data (image data of the image to be printed on the sheet S) input to the image forming apparatus 100. Then, the control section 40 measures the timing from the registration position P2, and when the planned adhesion position on the sheet S that is secondarily fed overlaps the suction hole 241a of the transport belt 241, the ejection timing of the ink to be adhered to the planned adhesion position. To be earlier than the reference timing.

The flow of the correction process relating to ink ejection performed by the controller 40 will be described below with reference to the flowchart shown in FIG. The flowchart shown 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 process regarding ink ejection will be described by focusing on one of the plurality of nozzles 31, but the same correction process (including a process of determining whether or not to perform the correction process is performed for the other nozzles 31. ) Is done. In addition, the correction process related to ink ejection (including the process of determining whether or not to perform the correction process) is performed for each line (1 dot).

Here, the storage unit 70 stores information indicating the special sheet S, which is the sheet S (sheet S having low elasticity and flexibility) that is not sucked into the suction holes 241a even when sucked by the suction unit 25 on the transport belt 241. To be done. For example, the metallic sheet S is the special sheet S. Then, when executing printing, the operation panel 60 receives the type of the sheet S used in printing from the user. 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 regarding ink ejection. In the following description, it is assumed that the operation panel 60 accepts from the user that the sheet S different from the special sheet S is used.

In step S1, the control unit 40 determines whether or not the planned adhesion position (pixel) of the ink from the nozzle 31 on the sheet S and the suction hole 241a of the transport belt 241 overlap. As a result, when the control unit 40 determines that the suction hole 241a of the transport belt 241 and the planned adhesion position overlap, the process proceeds to step S2.

In step S2, the control unit 40 recognizes the distance from the center position of the suction hole 241a of the transport belt 241 to the planned adhesion position. At this time, the control unit 40 classifies the distance from the center position to the planned adhesion position into a plurality of distance levels. The information defining the classification method is stored in the storage unit 70, and the control unit 40 performs the classification based on the information.

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

In step S3, the control unit 40 performs an ejection timing correction process for correcting (setting) the ejection timing of ink from the nozzles 31 as one process of the correction process. In the ejection timing correction process, any 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 ejection timing to the first timing, the ejection timing of the ink from the nozzle 31 becomes earliest. When the control unit 40 sets the ejection timing to the third timing, the ejection timing of the ink from the nozzle 31 becomes the latest (however, the ink is ejected from the nozzle 31 at a timing earlier than the reference timing). When the control unit 40 sets the ejection timing to the second timing, the ejection timing of the ink from the nozzle 31 is later than the first timing and earlier than the third timing.

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

In step S4, the control unit 40 determines whether or not a condition (predetermined condition) for performing the ejection 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 the region downstream of the central position in the sheet transport direction and the distance between the planned adhesion position and the central position exceeds the 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 the planned adhesion position is in the area near the downstream side of the sheet conveyance direction on the inner edge of the suction hole 241a of the conveyance belt 241.

In step S5, the control unit 40 performs a process of correcting (setting) the ink ejection amount from the nozzle 31 as the ejection amount correction process. In the ejection amount correction processing, either the first ejection amount or the second ejection amount is set as the ink ejection amount. When the control unit 40 sets the ejection amount to the first ejection amount, the ejection amount of ink from the nozzles 31 is smaller than when the control unit 40 sets the ejection amount to the second ejection amount. Note that, regardless of whether the control unit 40 sets the ejection amount to the first ejection amount or the second ejection amount, the ejection amount of the ink from the nozzle 31 is smaller than the default setting.

When performing the ejection amount correction process, the control unit 40 determines that the ink from the nozzle 31 is ejected if the distance between the planned deposition position and the central position exceeds a second predetermined threshold distance that is larger than the first threshold distance. The ejection amount is set to the first ejection amount (the decrease amount of the ink ejection amount is made larger). On the other hand, if the distance between the planned deposition position and the central position exceeds the first threshold distance but does not exceed the second threshold distance, the control unit 40 sets the ink ejection amount from the nozzle 31 to the second ejection amount. Set to (reduce the amount of ejected ink but reduce the amount of decrease). That is, when the suction hole 241a of the conveyor belt 241 and the planned adhesion position overlap, the control unit 40 moves from the nozzle 31 as the predicted adhesion position is closer to the inner edge of the suction hole 241a of the conveyor belt 241 on the downstream side in the sheet conveying direction. Set so that the ink ejection amount is smaller.

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

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

<Suction control of sheet>
(First suction control)
In some cases, a sheet S that is unlikely to be deformed due to suction by the suction unit 25 is set in the image forming apparatus 100 (the sheet S may be used for printing). When the amount of deformation (deformation amount) of the overlapping portion of the sheet S that overlaps the suction holes 241a of the transport belt 241 becomes smaller than expected as a result of the sheet S being used for printing, ink is ejected from the nozzle 31. If the timing is set earlier than the reference timing, a deviation occurs between the actual adhesion position of the ink on the sheet S and the expected adhesion position.

Therefore, the control unit 40 performs the first suction control. Since the control unit 40 is caused to perform the first suction control, information indicating the correspondence relationship between the level of easiness of deformation of the sheet S on the transport belt 241 by the suction of the suction unit 25 and the type of the sheet S is stored in the storage unit. Stored in 70. When executing printing, the operation panel 60 receives the type of the sheet S used in printing from the user. 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 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 two levels, for example, a standard level and a low level lower than the standard level. The lower the level, the poorer the elasticity and flexibility of the sheet S, and the less likely the deformation of the sheet S due to the suction by the suction unit 25 occurs.

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

When the process proceeds to step S13, the control unit 40 maintains the suction force of the suction unit 25 at the default setting. That is, the control unit 40 sets the rotation speed of the fan motor M7 to a predetermined reference rotation speed.

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 rotation speed of the fan motor M7 higher than the reference rotation speed). Accordingly, when the sheet S used for printing has low elasticity and flexibility, the suction force of the suction unit 25 increases.

(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 the one-sided image on one side of the sheet S, the stretchability and flexibility of the sheet S become lower than that before printing. That is, deformation due to suction by the suction unit 25 is less likely to occur. Therefore, when the other surface image is printed on the other surface of the sheet S, if the ejection timing of the ink from the nozzles 31 is made earlier than the reference timing, the actual adhesion position of the ink on the sheet S and the planned adhesion position are displaced. Occurs.

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

In step S21, the control unit 40 determines whether or not there is the 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 portion enters the suction target area larger than the suction force of the other negative pressure generation unit 250. That is, the control unit 40 increases the rotation speed of the fan motor M7 of the negative pressure generating unit 250.

In step S23, the control unit 40 determines whether or not the target portion has passed through the suction target area of the negative pressure generating unit 250 having the increased suction force. As a result, if the control unit 40 determines that the target portion has left the suction target area, the process proceeds to step S24, and if the control unit 40 determines that the target portion has not left 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 generating unit 250 having the increased suction force. After that, when the target portion enters another suction target area, the control unit 40 increases the suction force of the negative pressure generating unit 250 that targets the suction target area.

(Third suction control)
In some cases, the sheet S used for printing may have a defective portion (for example, a bent portion, a broken portion, a punched portion, or the like). In this case, when the ink passes through the defective portion of the sheet S, the ink adheres to the conveyor belt 241 (the conveyor belt 241 becomes dirty). In addition, the other sheet S may be stained with 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. The control unit 40 determines whether or not there is a defective portion on the sheet S based on the read data obtained by reading the sheet S by the CIS unit 50. Then, when the sheet S has a defective portion, 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 the sheet S has a defective portion. 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, if the control unit 40 determines that there is no missing portion, this flow ends.

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

In step S33, the control unit 40 determines whether or not the defective portion has passed through the suction target area of the negative pressure generation unit 250 that 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 generating unit 250 that has stopped suction. After that, when the defective portion enters another suction target area, the control unit 40 stops the suction of the negative pressure generating unit 250 that targets the suction target area.

(4th suction control)
When the printing unit 30 prints an image on the sheet S, yellow (Y), black (K), cyan (C), and magenta (M) inks are ejected onto the sheet S in this order. Depending on the image to be printed on the sheet, the ejection amount of ink such as yellow or black on the upstream side in the sheet conveying direction increases (the amount of the ink adhered to the sheet S increases). For example, even when the sheet S is not curled at the time of supplying the sheet S to the belt unit 24, if the ink ejection amount on the upstream side in the sheet conveying direction is large, the sheet S is curled during printing. 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 ink ejection amount. Since the control unit 40 performs the fourth suction control, the control unit 40 accumulates the ejection amount of ink ejected during printing (the amount of ink adhering to the sheet S).

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 or not the ejection amount of the ink ejected toward the sheet S on the conveyance belt 241 exceeds a predetermined threshold amount during the conveyance of the sheet S by the belt unit 24. To do. As a result, when the control unit 40 determines that the ink ejection amount exceeds the threshold amount, the process proceeds to step S42. After shifting to step S42, the control unit 40 makes the suction force of the suction unit 25 larger than that before printing.

When the control unit 40 determines in step S41 that the ink ejection amount does not exceed the threshold amount, the process proceeds to step S43. When the process proceeds to step S43, the control unit 40 determines whether the printing on the sheet S on the transport 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, this flow ends. That is, if the ink ejection amount 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 of the present embodiment includes the conveyor belt 241 in which the plurality of suction holes 241a are formed, and by driving the conveyor belt 241, the sheet S placed on the conveyor belt 241 is conveyed. Negative pressure is generated on the belt unit 24 (belt conveying unit) for conveying and the inner peripheral surface side of the conveying belt 241 (the surface opposite to the sheet mounting surface side), and the negative pressure is generated on the conveying belt 241 via the suction holes 241a. A suction unit 25 (suction unit) for sucking the sheet S is arranged to face the conveyance belt 241 with a space therebetween, has a nozzle 31 for ejecting ink, and ejects ink from the nozzle 31 toward the conveyance belt 241. By doing so, the ink heads 3Y, 3K, 3C and 3M for adhering the ink to the sheet S on the conveyor belt 241 do not overlap the planned adhesion position where the ink from the nozzle 31 is to adhere and the suction hole 241a of the conveyor belt 241. At this time, when the ink is ejected from the nozzle 31 at the reference timing, and when the suction hole 241a of the transport belt 241 and the planned adhesion position overlap, the control unit 40 that ejects the ink from the nozzle 31 at a timing earlier than the reference timing is provided. ..

In the configuration of the present embodiment, even if the overlapped 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 is ejected from the ejection of the ink. Even when the time to land on the ink becomes longer than the ideal time (time when the dent is not formed on the sheet S), the actual adhesion position of ink and the planned adhesion position of ink deviate from each other. Can be suppressed. As a result, it is possible to suppress deterioration of print image quality.

Further, in the present embodiment, as described above, when the suction hole 241a of the transport belt 241 and the planned adhesion position overlap, the control unit 40 moves closer to the center position of the suction hole 241a of the transport belt 241 when the planned adhesion position is closer to the center position. The timing of ink ejection from the nozzle 31 is advanced. Here, the closer the planned adhesion position is to the center position of the suction hole 241a of the transport belt 241, the longer the time from the ejection of ink to the deposition of the ink on the planned adhesion position is longer than the ideal time. Therefore, it is preferable that the closer the planned deposition position is to the central position of the suction hole 241a of the transport belt 241, the earlier the ink ejection timing from the nozzle 31 is. This makes it possible to further reduce the deviation between the actual ink adhesion position and the expected ink adhesion position.

Further, in the present embodiment, as described above, when the suction hole 241a of the transport belt 241 and the planned adhesion position overlap, the control unit 40 determines that the planned adhesion position is downstream of the suction hole 241a of the transport belt 241 in the sheet transport direction. The amount of ink ejected from the nozzle 31 is reduced as the position is closer to the inner edge of. As a result, even if the portion of the overlapping portion of the sheet S including the planned adhesion position is inclined obliquely downward from the downstream side toward the upstream side in the sheet conveying direction, the sheet is discharged toward the planned adhesion position and reaches the sheet S. It is possible to prevent the dropped ink from flowing upstream in the sheet conveying direction. As a result, it is possible to further suppress deterioration in print 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 relationship between the level of easiness of deformation of the sheet S on the conveyor belt 241 due to 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 is (the lower the stretchability and flexibility of the sheet S used for printing is), The suction force 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 a recess in the overlapping portion of the sheets S. As a result, when the sheet S having low elasticity and flexibility is used for printing, since the ejection timing correction process (the process of advancing the ink ejection timing) is performed by the control unit 40, the actual ink adhesion position and the ink adhesion position It is possible to suppress the inconvenience that the deviation from the planned position becomes large.

Further, in the present embodiment, as described above, when executing double-sided printing, the control unit 40 recognizes the portion of the sheet S on which the one-sided image is printed as the target portion, based on the image data of the one-sided image. When the process is performed and the other surface image 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 unit 250. As a result, the target portion of the sheet S (the portion whose elasticity and flexibility have decreased due to the ink adhering to the one surface of the sheet S when printing on the other surface of the sheet S) is the suction hole 241 a of the transport belt 241. In the case where the inks overlap with each other, there is an inconvenience that the deviation between the actual adhesion position of ink and the planned adhesion position becomes large because the ejection timing correction process (the process of advancing the ink ejection timing) is performed by the controller 40. It can be suppressed. That is, it is possible to suppress the deterioration of the image quality of the printed matter (the deterioration of the image quality of the other surface image) obtained by executing 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 reading the sheet S by the CIS unit 50 (reading unit). Determine if it exists. When the sheet S has a defective portion, the control unit 40 stops the suction of the negative pressure generating unit 250 in which the defective portion of the sheet S has entered the suction target area. Thus, it is possible to prevent the ink ejected toward the transport belt 241 from entering the sheet mounting surface of the transport belt 241 (dirt on the sheet mounting surface of the transport belt 240) via the defective portion of the sheet S. You can

Further, in the present embodiment, as described above, when the control unit 40 conveys the sheet S by the conveyance belt 241, when the ejection amount of the ink ejected toward the sheet S being conveyed 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 prevent the sheet S from curling during the transportation of the sheet S.

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

24 Belt unit (belt conveyor)
25 Suction unit (suction unit)
30 ink head 40 control unit 50 CIS unit (reading unit)
60 Operation panel (reception part)
70 Storage Unit 31 Nozzle 241 Conveyor Belt 241a Suction Hole 250 Negative Pressure Generation Unit

Claims (6)

A belt conveyor that includes a conveyor belt having a plurality of suction holes formed therein, and that conveys a sheet placed on the conveyor belt by driving the conveyor belt;
A suction unit configured to generate a negative pressure on the side of the conveyor belt opposite to the sheet mounting surface side, and to suck the sheet on the conveyor belt through the suction hole,
Ink that is arranged to face the conveyor belt with a space therebetween, has a nozzle for ejecting ink, and ejects the ink from the nozzle toward the conveyor belt to attach the ink to the sheet on the conveyor belt. Head and
When the planned adhesion position to which ink from the nozzle is to be adhered and the suction hole do not overlap, ink is ejected from the nozzle at a predetermined reference timing, and the planned adhesion position and the suction hole overlap, A control unit for ejecting ink from the nozzle at a timing earlier than the reference timing ,
When the planned adhesion position and the suction hole overlap, the control unit reduces the ink ejection amount from the nozzle as the planned adhesion position is closer to the inner edge of the suction hole on the downstream side in the sheet conveying direction. An image forming apparatus characterized by. A belt conveyor that includes a conveyor belt having a plurality of suction holes formed therein, and that drives the conveyor belt to convey a sheet placed on the conveyor belt;
A suction unit configured to generate a negative pressure on the side opposite to the sheet mounting surface side of the transport belt, and to suction the sheet on the transport belt via the suction hole,
Ink that is arranged to face the conveyor belt with a space therebetween, has a nozzle for ejecting ink, and ejects ink from the nozzle toward the conveyor belt to attach the ink to a sheet on the conveyor belt. Head and
When the planned adhesion position to which the ink from the nozzle is to be adhered and the suction hole do not overlap, ink is ejected from the nozzle at a predetermined reference timing, and the planned adhesion position and the suction hole overlap, A control unit for ejecting ink from the nozzle at a timing earlier than the reference timing,
The suction unit includes a plurality of negative pressure generation units that generate negative pressures independently of each other and have different areas as suction target areas,
When performing double-sided printing in which the control unit prints the one-sided image on one side of the sheet and then the other-sided image on the other side of the sheet, the one-sided image is based on the image data of the one-sided image. Is performed to recognize the portion of the sheet to be printed as the target portion, and when the other surface image is printed on the sheet, the suction force of the negative pressure generating unit in which the target portion enters the suction target area is changed. The image forming apparatus is characterized in that the suction force is larger than the suction force of the negative pressure generating section. A belt conveyor that includes a conveyor belt having a plurality of suction holes formed therein, and that drives the conveyor belt to convey a sheet placed on the conveyor belt;
A suction unit configured to generate a negative pressure on the side opposite to the sheet mounting surface side of the transport belt, and to suction the sheet on the transport belt via the suction hole,
Ink that is arranged to face the conveyor belt with a space therebetween, has a nozzle for ejecting ink, and ejects ink from the nozzle toward the conveyor belt to attach the ink to a sheet on the conveyor belt. Head and
When the planned adhesion position to which the ink from the nozzle is to be adhered and the suction hole do not overlap, ink is ejected from the nozzle at a predetermined reference timing, and the planned adhesion position and the suction hole overlap, A control unit for ejecting ink from the nozzle at a timing earlier than the reference timing,
A reading unit which is installed at a position upstream of the installation position of the conveyor belt in the sheet conveying direction and which reads a sheet supplied to the conveyor belt,
The suction unit includes a plurality of negative pressure generation units that generate negative pressures independently of each other and have different areas as suction target areas,
The control unit determines whether there is a defective portion in the sheet supplied to the conveyor belt based on the read data obtained by reading the sheet by the reading unit. An image forming apparatus, characterized in that suction of the negative pressure generating portion in which the defective portion has entered the suction target area is stopped. When the planned adhesion position and the suction hole overlap each other, the control unit advances the ink ejection timing from the nozzle as the planned adhesion position is closer to the center position of the suction hole. The image forming apparatus according to any one of Items 1 to 3 . A reception part that receives the type of sheet used for printing from the user,
A storage unit that stores a correspondence relationship between a level of easiness of deformation of a sheet on the conveyor belt due to suction of the suction unit and a sheet type, and the control unit includes the sheet received by the reception unit. recognizing the level corresponding to the type, the more the level of the recognized low, the image forming apparatus according to any one of claims 1 to 4, characterized in that to increase the suction force of the suction unit .. When the ejection amount of the ink ejected onto the sheet being conveyed exceeds a predetermined threshold amount during the conveyance of the sheet by the conveyance belt, the control unit causes the suction force of the suction unit to be larger than that before printing. the image forming apparatus according to any one of claims 1 to 5, characterized in that to increase.

Images