Inkjet recording device

Abstract

To prevent flushing ink from being attached to a conveyance belt.SOLUTION: An inkjet recording device includes a recording head having a conveyance belt, a pressurization chamber for storing ink, a nozzle communicating with the pressurization chamber and a displacement element for applying a pressure to the pressurization chamber by being deformed by receiving voltage application, and discharging ink from the nozzle, and a control part, wherein the conveyance belt has a flushing region, the control part makes the recording head perform flushing treatment of discharging ink toward an opening of the flushing region not overlapped with a recording medium, separately from image formation processing of discharging ink toward the recording medium, and the control part controls the voltage application to the displacement element, and thereby sets flying speed of the ink discharged from the nozzle at the time of flushing treatment to be higher than flying speed of the ink discharged from the nozzle at the time of image formation treatment.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to an inkjet recording apparatus. [Background technology]

[0002] A conventional inkjet recording device includes a recording head that ejects ink. The recording head has nozzles that eject ink. The recording head ejects ink onto a recording medium while it is being transported, thereby recording an image on the recording medium. Such an inkjet recording device is disclosed in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-22673 A Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional inkjet recording devices, a flushing process is performed on the recording head to prevent clogging of the nozzles. For example, in a configuration in which the recording medium is transported by a transport belt, the transport belt has openings to collect the ink ejected in the flushing process. In the flushing process, ink is ejected toward the openings of the transport belt.

[0005] In this configuration, the flushing ink, which is the ink ejected from the recording head during the flushing process, passes through the openings in the transport belt, making it possible to collect the flushing ink without the flushing ink adhering to the transport belt.

[0006] However, the air flow between the recording head and the conveyor belt may be disturbed, causing the flushing ink to move in an unintended direction. In this case, for example, the flushing ink may not pass through the openings in the conveyor belt, resulting in an inconvenience in which the flushing ink adheres to the conveyor belt. If the flushing ink adheres to the conveyor belt, the flushing ink on the conveyor belt may transfer to the recording medium, thereby contaminating the recording medium.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide an inkjet recording device that is capable of suppressing flushing ink from adhering to a conveying belt in a configuration in which a recording medium is transported by a conveying belt. [Means for solving the problem]

[0008] In order to achieve the above object, an inkjet recording device according to one aspect of the present invention includes a conveyor belt for conveying a recording medium, a recording head having a pressure chamber for storing ink, a nozzle communicating with the pressure chamber, and a displacement element which deforms in response to application of a voltage to apply pressure to the pressure chamber to cause ink to be discharged from the nozzle, and which forms an image on the recording medium by discharging the ink onto the recording medium, and a control unit for controlling the recording head. The conveyor belt has a flushing area in which an opening is formed. A plurality of flushing areas are arranged at intervals in the moving direction of the conveyor belt. The control unit causes the recording head to perform a flushing process for discharging ink toward the openings of the flushing area that do not overlap with the recording medium, separate from the image forming process for discharging ink toward the recording medium. The control unit controls the application of a voltage to the displacement element to make the flying speed of ink discharged from the nozzle during the flushing process faster than the flying speed of ink discharged from the nozzle during the image forming process. Effect of the Invention

[0009] In the present invention, in a configuration in which a recording medium is transported by a transport belt, it is possible to prevent flushing ink from adhering to the transport belt. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an inkjet recording apparatus according to an embodiment. [Diagram 2] 1 is a plan view of a printing unit of an inkjet printing apparatus according to an embodiment. [Diagram 3] 1 is a schematic diagram of a conveyor belt and its surroundings of an inkjet recording apparatus according to an embodiment. [Figure 4] 1 is a block diagram of an inkjet recording apparatus according to an embodiment. [Diagram 5] 1 is a block diagram of a print head and its periphery in an inkjet printing apparatus according to an embodiment. [Figure 6] 1 is a cross-sectional view showing a schematic view of a nozzle and its periphery of an inkjet recording apparatus according to an embodiment. [Figure 7] FIG. 2 is a plan view of a conveyor belt of an inkjet recording apparatus according to an embodiment. [Figure 8] 5 is a diagram showing the positional relationship between a flushing area of ​​a transport belt and a print head of an inkjet printing apparatus according to an embodiment. FIG. [Figure 9] 5A and 5B are diagrams illustrating the positional relationship between a flushing area of ​​a transport belt of an inkjet recording apparatus according to an embodiment and a sheet. [Figure 10] 5A and 5B are diagrams for explaining timing of conveying a sheet to a conveying belt of an inkjet recording apparatus according to an embodiment. [Figure 11] 5 is a diagram showing a flow of processing performed by a control unit of the inkjet recording apparatus according to an embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present invention will be described below with reference to Figs. 1 to 11, taking as an example a printer 100 that prints on a sheet S as a recording medium. The type of sheet S is not particularly limited. For example, paper is used as the sheet S. In the following description, the direction perpendicular to the surface on which the printer 100 is placed (for example, a flat floor surface) is defined as the up-down direction.

[0012] <Overall printer configuration> As shown in FIG. 1, the printer 100 (corresponding to an "inkjet recording device") of this embodiment includes a first transport unit 11 and a second transport unit 12. The first transport unit 11 feeds a sheet S set in a paper feed cassette CA, and transports the sheet S toward a printing position. In a print job by the printer 100, ink is ejected onto the sheet S passing the printing position. This causes an image to be printed on the sheet S. In other words, in a print job by the printer 100, an image made of ink is formed on the sheet S. The second transport unit 12 transports the printed sheet S. The second transport unit 12 ejects the printed sheet S onto an ejection tray ET.

[0013] The first conveying section 11 includes a plurality of conveying roller members including a registration roller pair 10. In FIG. 1, only the registration roller pair 10 among the plurality of conveying roller members is labeled with a reference symbol. Each of the plurality of conveying roller members conveys the sheet S by rotating. The registration roller pair 10 includes a pair of rollers that are in pressure contact with each other. A registration nip is formed between the pair of rollers that constitute the registration roller pair 10. The sheet S fed from the paper feed cassette CA enters the registration nip. The registration roller pair 10 conveys the sheet S toward the belt conveying section 2, which will be described later, by rotating.

[0014] When the leading edge of the sheet S reaches the registration nip, the pair of registration rollers 10 stops rotating. On the other hand, the transport roller member upstream of the pair of registration rollers 10 in the transport direction of the sheet S is rotating. This causes the skew of the sheet S to be corrected.

[0015] The printer 100 includes a belt conveyor 2. The belt conveyor 2 receives the sheet S from the first conveyor 11 and conveys the sheet S. The belt conveyor 2 includes a plurality of tension rollers 20. The plurality of tension rollers 20 are rotatably supported. The belt conveyor 2 also includes a conveyor belt 3. The conveyor belt 3 is endless. The conveyor belt 3 is rotatably stretched by the plurality of tension rollers 20. The sheet S is conveyed from the first conveyor 11 toward the belt conveyor 2, and the sheet S reaches the outer circumferential surface of the conveyor belt 3.

[0016] One of the tension rollers 20 is connected to a belt motor BM (see FIG. 4), and rotates by the driving force of the belt motor BM being transmitted thereto. The rotation of the tension roller 20 connected to the belt motor BM drives the conveyor belt 3, and the other tension rollers 20 rotate accordingly. In other words, the conveyor belt 3 rotates.

[0017] The belt conveying section 2 further includes a suction unit 200. The suction unit 200 is disposed on the inner periphery side of the conveying belt 3. The suction unit 200 sucks the sheet S on the outer periphery surface of the conveying belt 3 from the inner periphery side of the conveying belt 3.

[0018] Specifically, the conveyor belt 3 has a plurality of suction holes (not shown). The suction holes of the conveyor belt 3 penetrate the conveyor belt 3 in the thickness direction. The suction unit 200 sucks the sheet S on the outer peripheral surface of the conveyor belt 3 through the suction holes of the conveyor belt 3. As a result, the sheet S is adsorbed to the outer peripheral surface of the conveyor belt 3. The conveyor belt 3 rotates while adsorbing and holding the sheet S on its outer peripheral surface. In other words, the conveyor belt 3 conveys the sheet S while adsorbing it to its outer peripheral surface. In yet another way, the conveyor belt 3 moves (i.e., rotates) to convey the sheet S. The rotation direction of the conveyor belt 3 corresponds to the "movement direction."

[0019] The printer 100 includes a recording unit 4. The recording unit 4 is disposed so as to face the outer peripheral surface of the conveyor belt 3 in the vertical direction. While the sheet S is being conveyed by the conveyor belt 3, the sheet S on the outer peripheral surface of the conveyor belt 3 and the recording unit 4 face each other at a distance in the vertical direction. As a result, while the sheet S is being conveyed by the conveyor belt 3, the sheet S passes between a nozzle surface of a recording head 40 (described later) and the outer peripheral surface of the conveyor belt 3. In other words, the space between the nozzle surface of the recording head 40 and the outer peripheral surface of the conveyor belt 3 forms part of the conveying path of the sheet S. The recording head 40 is disposed above the conveyor belt 3, and the nozzle surface of the recording head 40 faces downward.

[0020] As shown in Fig. 2, the recording unit 4 has four line heads 41 respectively corresponding to the colors cyan, magenta, yellow, and black. In Fig. 2, the cyan line head 41 is marked with the symbol "C", the magenta line head 41 is marked with the symbol "M", the yellow line head 41 is marked with the symbol "Y", and the black line head 41 is marked with the symbol "K" to distinguish them from one another. The same is true for Fig. 3, which will be referred to later in the description.

[0021] Each color line head 41 includes multiple (e.g., three) recording heads 40. For example, the multiple recording heads 40 of each color are arranged in a staggered pattern in a direction perpendicular to the conveying direction of the sheet S by the conveyor belt 3. In the following description, the direction perpendicular to the conveying direction of the sheet S by the conveyor belt 3 is simply referred to as the width direction.

[0022] The recording heads 40 are disposed at intervals in the up-down direction with respect to the outer circumferential surface of the conveyor belt 3. In other words, the recording heads 40 are disposed at positions facing the sheet S conveyed by the conveyor belt 3 in the up-down direction. In further other words, the conveyor belt 3 adsorbs and conveys the sheet S below the recording heads 40. The up-down direction is the direction perpendicular to the conveying direction and width direction of the sheet S by the conveyor belt 3.

[0023] Each recording head 40 has a surface facing the outer peripheral surface of the conveyor belt 3 in the vertical direction as a nozzle surface. The nozzle surface of each recording head 40 has a plurality of nozzles 4N. The plurality of nozzles 4N of each recording head 40 ejects ink of a corresponding color downward. For example, the number of nozzles 4N of each recording head 40 is the same. The plurality of nozzles 4N of each recording head 40 are arranged along the width direction of the conveyor belt 3. In FIG. 2, the nozzles 4N are indicated by dashed lines. In reality, more nozzles 4N are provided in each recording head 40.

[0024] Each recording head 40 ejects ink from the nozzles 4N toward the sheet S on the outer circumferential surface of the conveyor belt 3 based on image data to be printed on the sheet S in a print job. The ink ejected from each recording head 40 adheres to the sheet S. As a result, an image is formed on the sheet S. In other words, the space between each recording head 40 and the conveyor belt 3 is the printing position, and printing on the sheet S is performed at that printing position.

[0025] 3, a waste ink tank 21 is disposed on the inner circumferential side of the conveyor belt 3. The waste ink tank 21 stores ink discharged in a flushing process, which will be described later. The ink in the waste ink tank 21 is discarded.

[0026] Returning to FIG. 1 , the printer 100 includes a drying unit 51 and a decurler 52. The drying unit 51 dries the ink adhering to the sheet S while transporting the sheet S toward the decurler 52. The decurler 52 straightens out curls in the sheet S. The decurler 52 transports the sheet S after the curl has been straightened toward the second transport section 12.

[0027] As shown in FIG. 4, the printer 100 also includes a control unit 6. The control unit 6 includes processing circuits such as a CPU and an ASIC. The control unit 6 controls print jobs. Specifically, the control unit 6 controls the belt motor BM to appropriately move (i.e., rotate) the conveyor belt 3. The control unit 6 controls the conveyance of the sheet S by the conveyor belt 3. The control unit 6 also controls the ejection of ink by each recording head 40. Furthermore, the control unit 6 controls a flushing process, which will be described in detail later.

[0028] A registration sensor 61, a sheet sensor 62, and a belt sensor 63 are connected to the control unit 6. The detection positions (arrangement positions) of the registration sensor 61, the sheet sensor 62, and the belt sensor 63 are shown in FIG.

[0029] The registration sensor 61 has a detection position that is upstream of the registration nip in the conveying direction of the sheet S. The registration sensor 61 is, for example, a reflective optical sensor or a transmissive optical sensor. The registration sensor 61 changes an output value depending on the presence or absence of the sheet S at the corresponding detection position.

[0030] The control unit 6 detects the arrival of the leading end of the sheet S at the detection position of the registration sensor 61 and the passage of the trailing end thereof based on the output value of the registration sensor 61. In other words, the control unit 6 detects the arrival of the leading end of the sheet S at the registration nip and the passage of the trailing end thereof based on the output value of the registration sensor 61. The control unit 6 measures the timing at which the registration roller pair 10 starts conveying the sheet S (the timing at which the registration roller pair 10 starts rotating) based on the time from when the arrival of the leading end of the sheet S is detected at the detection position of the registration sensor 61.

[0031] The sheet sensor 62 has a detection position between the printing position of the line head 41 that is the most upstream in the conveying direction of the sheet S among the multiple line heads 41 and the registration nip. The sheet sensor 62 changes an output value depending on the presence or absence of the sheet S at the corresponding detection position. As the sheet sensor 62, a CIS (Contact Image Sensor) may be used, or a reflective optical sensor or a transmissive optical sensor may be used. For example, a CIS is used as the sheet sensor 62.

[0032] The control unit 6 detects the arrival of the leading end and the passing of the trailing end of the sheet S at the detection position of the sheet sensor 62 based on the output value of the sheet sensor 62. The control unit 6 measures the timing of ejecting ink onto the sheet S transported by the transport belt 3 based on the output value of the sheet sensor 62. The timing of ejecting ink onto the sheet S transported by the transport belt 3 may be measured based on the time from when the pair of registration rollers 10 starts transporting the sheet S.

[0033] Furthermore, the control unit 6 measures the sheet passing time from when the leading edge of the sheet S reaches the detection position of the sheet sensor 62 until the trailing edge of the same sheet S passes the detection position of the sheet sensor 62. The sheet passing time at the detection position of the sheet sensor 62 varies depending on the size of the sheet S in the transport direction. Therefore, the control unit 6 recognizes the size of the sheet S transported by the transport belt 3 in the transport direction based on the sheet passing time. This allows the control unit 6 to detect the size of the sheet S in the transport direction even if the sheet S transported by the transport belt 3 is of an irregular size.

[0034] Furthermore, the control unit 6 detects positional deviation of the sheet S (including skew of the sheet S) based on the output value of the sheet sensor 62 (read data obtained by reading by the sheet sensor 62). For example, there are cases where positional deviation of the sheet S occurs after the conveyance of the sheet S by the registration roller pair 10 starts. In this case, the positional deviation of the sheet S is detected by the control unit 6.

[0035] It is also possible to install a plurality of sheet sensors 62. For example, two sheet sensors 62 may be installed.

[0036] The belt sensor 63 is a sensor for detecting a predetermined reference position (home position) of the conveyor belt 3. A predetermined mark is provided at the reference position of the conveyor belt 3. This makes it possible to detect the reference position of the conveyor belt 3 based on the output value of the belt sensor 63. For example, a CIS is used as the belt sensor 63. The belt sensor 63 may be configured using a transmission type optical sensor or a reflection type optical sensor.

[0037] The control unit 6 detects the reference position of the conveyor belt 3 based on the output value of the belt sensor 63. In other words, the control unit 6 detects the position of the flushing region 30 (see FIG. 7) in the rotation direction of the conveyor belt 3 based on the output value of the belt sensor 63.

[0038] As shown in FIG. 4, the printer 100 also includes a storage unit 7. The storage unit 7 includes storage devices such as a ROM, a RAM, a HDD, and an SSD. The storage unit 7 stores various types of information. The storage unit 7 is connected to the control unit 6. The control unit 6 reads information from the storage unit 7. The control unit 6 also writes information to the storage unit 7.

[0039] The printer 100 has an operation panel 8. The operation panel 8 is provided with, for example, a touch screen. The touch screen displays software buttons and messages, and accepts touch operations from the user. The operation panel 8 is also provided with hardware buttons that accept settings, instructions, and the like. The operation panel 8 is connected to the control unit 6. The control unit 6 controls the display operation of the operation panel 8 (touch screen). The control unit 6 also detects operations performed on the operation panel 8.

[0040] The printer 100 includes a communication unit 9. The communication unit 9 includes a communication circuit and the like. The communication unit 9 is connected to a user terminal PC via a network NT. The user terminal PC is an information processing device such as a personal computer. The control unit 6 uses the communication unit 9 to communicate with the user terminal PC.

[0041] Print data for the print job (data including PDL data, etc.) is sent from the user terminal PC to the printer 100. In other words, a request to execute the print job is sent from the user terminal PC to the printer 100. The print data for the print job includes various setting data related to printing, such as the size of the sheet S used in the print job. The communication unit 9 receives the print data for the print job. When the communication unit 9 receives the print data for the print job, the control unit 6 determines that a request to execute the print job has been received.

[0042] <Ink ejection configuration> As shown in Figures 5 and 6, each recording head 40 has a piezoelectric element PE. The piezoelectric element PE corresponds to a "displacement element." One piezoelectric element is assigned to each nozzle 4N. The piezoelectric element PE is deformed and driven by application of a driving voltage. Each nozzle 4N ejects ink by the deformation of the corresponding piezoelectric element PE. In Figure 6, the meniscus of ink in the nozzle 4N is denoted by the symbol M.

[0043] Specifically, each recording head 40 has a pressure chamber 410 for each nozzle 4N. Each pressure chamber 410 receives ink from an ink tank (not shown) via a common flow path 420. Each pressure chamber 410 contains ink supplied from the ink tank. Each pressure chamber 410 communicates with a corresponding nozzle 4N. A piezoelectric element PE is assigned to each pressure chamber 410. Each piezoelectric element PE applies pressure to the corresponding pressure chamber 410 by being deformed and driven by application of a voltage, thereby changing the volume of the corresponding pressure chamber 410. As a result, each piezoelectric element PE ejects ink from the nozzle 4N of the corresponding pressure chamber 410. Note that, if it is possible to change the volume of the pressure chamber 410 by being deformed and driven by application of a voltage, another displacement element may be used instead of the piezoelectric element PE.

[0044] Each recording head 40 has a vibration plate 430. The vibration plate 430 constitutes the upper surface of the wall surface of the recording head 40 on the side opposite to the nozzle surface in the up-down direction. A common electrode 401 is arranged on the vibration plate 430. A piezoelectric element PE is arranged on the common electrode 401. An individual electrode 402 is arranged on the piezoelectric element PE. In other words, the piezoelectric element PE is sandwiched between a pair of electrodes in the up-down direction (i.e., between the common electrode 401 and the individual electrode 402 in the up-down direction). Another piezoelectric element PE is also arranged on the common electrode 401. An individual electrode 402 is arranged for each piezoelectric element PE.

[0045] Each recording head 40 has a voltage generation circuit VG. Each recording head 40 has a driver circuit DR. The voltage generation circuit VG generates a voltage for driving each piezoelectric element PE and supplies it to the driver circuit DR. The driver circuit DR applies the drive voltage supplied from the voltage generation circuit VG to each piezoelectric element PE. As a result, the driver circuit DR drives and deforms each piezoelectric element PE.

[0046] A pulse-shaped drive signal is input to the driver circuit DR. When the drive signal rises, the driver circuit DR applies a voltage to the piezoelectric element PE to be driven. When the drive signal falls, the driver circuit DR stops applying voltage to the piezoelectric element PE. In other words, the driver circuit DR switches the voltage application to each piezoelectric element PE on and off based on the input pulse-shaped drive signal. The driver circuit DR does not apply voltage to piezoelectric elements PE that are not to be driven.

[0047] The driver circuit DR is connected to a control unit 6. The control unit 6 includes a signal generating circuit 60 that generates a drive signal to the driver circuit DR. The signal generating circuit 60 generates a pulse-shaped drive signal. The drive signal is a signal for periodically driving each piezoelectric element PE. The control unit 6 generates the drive signal and inputs it to the driver circuit DR. That is, the control unit 6 controls the application of voltage to each piezoelectric element PE.

[0048] <Conveyor belt configuration> As shown in Fig. 7, the conveyor belt 3 has a flushing area 30. In Fig. 7, the flushing area 30 is surrounded by a dashed line. The flushing area 30 is an area in which openings 31 are formed, penetrating the conveyor belt 3 in the thickness direction. Although details will be described later, in the flushing process, ink is ejected from each recording head 40, and the ejected ink passes through the openings 31, reaches the inner peripheral side of the conveyor belt 3, and is stored in the waste ink tank 21.

[0049] The conveyor belt 3 is provided with a plurality of flushing regions 30. The plurality of flushing regions 30 are arranged at predetermined intervals from one another in the rotation direction of the conveyor belt 3. The conveyor belt 3 has the flushing regions 30 and other regions (reference numbers omitted) alternately in the rotation direction.

[0050] Each flushing area 30 has a plurality (the same number) of openings 31. The openings 31 are long holes that are long in the width direction of the conveyor belt 3. The shape of the openings 31 (the shape seen from the thickness direction of the conveyor belt 3) is not particularly limited, and may be rectangular, circular, elliptical, or oval.

[0051] For example, each flushing area 30 includes two aperture rows. The aperture rows are rows of apertures 31 arranged at equal intervals in the width direction of the conveyor belt 3. One aperture row has N apertures 31 (six apertures in FIG. 7), and the other aperture row has N-1 apertures 31 (five apertures in FIG. 7). The center positions of both aperture rows in the width direction are located at the center position in the width direction of the conveyor belt 3. That is, the multiple apertures 31 in each flushing area 30 are arranged in a staggered pattern in the width direction. The length in the width direction of the apertures 31 (aperture width) is greater than the distance between adjacent apertures 31 in the width direction.

[0052] As shown in FIG. 8, the width W1 (mm) is smaller than the width W2 (mm). The width W1 corresponds to the widthwise length of the line head 41. Specifically, the width W1 corresponds to the widthwise length from the end of the recording head 40 located on one side in the width direction to the end of the recording head 40 located on the other side in the width direction. The width W2 corresponds to the widthwise length of the flushing region 30. Specifically, the width W2 corresponds to the widthwise length from the end of the opening 31 located on the furthest side in the width direction to the end of the opening 31 located on the other side in the width direction.

[0053] As a result, each of the multiple nozzles 4N faces at least one of the openings 31 in the vertical direction as the conveyor belt 3 rotates.

[0054] <Sheet transport control> In a continuous printing job, which is a printing job for continuously forming images on multiple sheets S of the same size that are transported in sequence by the transport belt 3, the control unit 6 controls the sheet spacing, which is the distance in the transport direction between the rear end of the preceding sheet S and the front end of the following sheet S (the sheet S transported next to the preceding sheet S), so that it is constant. In other words, the control unit 6 controls so that multiple sheets S are transported continuously at constant intervals. In yet other words, the control unit 6 maintains the spacing between each sheet, which occurs when multiple sheets S are transported continuously, at a constant interval.

[0055] Here, in a continuous printing job, the control unit 6 recognizes the size of the sheet S transported by the conveyor belt 3. The control unit 6 also detects the reference position of the conveyor belt 3. The control unit 6 then measures the timing to start transporting the sheet S from the registration roller pair 10 to the conveyor belt 3 so that the flushing area 30 appears between the sheets at a constant cycle. The control unit 6 changes the timing to start transporting the sheet S from the registration roller pair 10 to the conveyor belt 3 depending on the size of the sheet S transported by the conveyor belt 3. The control unit 6 recognizes the size of the sheet S used in the print job (the sheet S transported by the conveyor belt 3) based on the print data of the print job.

[0056] FIG. 9 shows the positional relationship between the sheet S conveyed by the conveyor belt 3 and the flushing area 30. In FIG. 9, the rotation direction of the conveyor belt 3 (i.e., the conveying direction of the sheet S) is from right to left on the paper. In FIG. 9, the flushing area 30 is shown with a hatched pattern, and the opening 31 is omitted. Also, in FIG. 9, the reference numeral for the sheet S is omitted, and instead, the size of the sheet S is indicated within the figure showing the sheet S. Note that, for convenience, FIG. 9 illustrates a plurality of sheets S of different sizes together.

[0057] Here, a detailed description will be given with reference to Fig. 10, focusing on an A4 portrait-sized sheet S (sheet S shown in the third row from the top in Fig. 9). In Fig. 10, the rotation direction of the conveyor belt 3 (i.e., the conveying direction of sheet S) is from the bottom to the top of the page. For convenience, three sheets S are shown in Fig. 10, and the reference numbers of each sheet S are assigned numbers 1 to 3 indicating the conveying order.

[0058] When the size of the sheet S is A4 portrait size, the flushing area 30 does not appear between the first sheet S1 and the second sheet S2. The flushing area 30 appears between the second sheet S2 and the third sheet S3. The flushing area 30 between the sheets S2 and S3 does not overlap with either the sheet S2 or the sheet S3 at all. Although not shown, the flushing area 30 does not appear between the third sheet S3 and the fourth sheet S, but the flushing area 30 appears between the fourth sheet S and the fifth sheet S.

[0059] <Ink flushing process> The viscosity of ink in the nozzles 4N that eject ink less frequently among the multiple nozzles 4N increases over time. As a result, clogging occurs and image quality deteriorates. In order to prevent such problems, while the conveyor belt 3 is in motion, each recording head 40 performs a flushing process in addition to the image forming process. The image forming process is a process in which ink is ejected toward the sheet S to form an image on the sheet S.

[0060] The flushing process is a process of ejecting ink from the nozzles 4N of each recording head 40 toward the openings 31 of the flushing areas 30 that do not overlap with the sheet S among the multiple flushing areas 30 of the conveyor belt 3. In other words, the flushing process is a process of ejecting ink from the nozzles 4N of each recording head 40 at a timing different from the timing of forming an image on the sheet S. The ink ejected from the nozzles 4N of each recording head 40 in the flushing process (hereinafter, this ink may be referred to as flushing ink) does not contribute to image formation. The flushing ink does not head toward the sheet S, but passes through the openings 31, reaches the inner peripheral side of the conveyor belt 3, and is collected in the waste ink tank 21. By performing the flushing process, clogging is suppressed.

[0061] The following describes a method for controlling the flushing process, focusing on one of the recording heads 40. The following description of the method for controlling the flushing process of the other recording heads 40 is omitted, as it is applicable to the above description.

[0062] While the conveyor belt 3 is being driven, the control unit 6 causes the recording head 40 to perform a flushing process at a timing when the flushing area 30 that does not overlap the sheet S and the recording head 40 face each other in the vertical direction. For example, the recording head 40 ejects ink from each nozzle 4N multiple times in one flushing process. The recording head 40 ejects ink from the nozzle 4N at a timing when the recording head 40 faces the flushing area 30 in the vertical direction, and passes the ink through the opening 31. Since the ink ejected in the flushing process passes through the opening 31, the ink does not adhere to the conveyor belt 3.

[0063] In a continuous printing job, the transport of the sheet S is controlled so that the flushing area 30 appears between the sheets at a constant cycle. That is, during the execution of the continuous printing job, the flushing area 30 that does not overlap with the sheet S and the recording head 40 repeatedly face each other in the vertical direction. Therefore, during the execution of the continuous printing job, the control unit 6 causes the recording head 40 to perform the flushing process multiple times. During the execution of the continuous printing job, the control unit 6 causes the recording head 40 to perform the flushing process each time the recording head 40 and the flushing area 30 face each other in the vertical direction.

[0064] Ideally, the flushing ink ejected from the recording head 40 passes through the opening 31, so that ink does not adhere to the conveying belt 3. However, in some cases, airflow is disturbed between the nozzle surface of the recording head 40 and the outer circumferential surface of the conveying belt 3 in the vertical direction. This airflow disturbance may cause the flushing ink to be blown by the airflow, and the flushing ink may not pass through the opening 31. As a result, the flushing ink may adhere to the outer circumferential surface of the conveying belt 3. If the flushing ink adheres to the outer circumferential surface of the conveying belt 3, the flushing ink adhering to the outer circumferential surface of the conveying belt 3 contaminates the sheet S that is subsequently conveyed (i.e., the sheet S that is adsorbed and held on the outer circumferential surface of the conveying belt 3). Note that the flushing ink may directly land on the sheet S, thereby contaminating the sheet S.

[0065] Furthermore, the flushing ink may be blown back due to turbulence in the airflow between the nozzle surface of the recording head 40 and the outer circumferential surface of the conveyor belt 3 in the vertical direction, and may adhere to the nozzle surface of the recording head 40. In this case, clogging may occur due to the flushing ink adhering to the nozzle surface.

[0066] Therefore, in this embodiment, the control unit 6 adjusts the flying speed of the flushing ink. Specifically, the control unit 6 controls the voltage application to the piezoelectric element PE to make the flying speed of the ink ejected from the nozzle 4N during the flushing process (i.e., the flushing ink) faster than the flying speed of the ink ejected from the nozzle 4N during the image forming process. The flying speed of the flushing ink is, in other words, the moving speed of the flushing ink from the nozzle surface of the recording head 40 to the outer circumferential surface of the conveyor belt 3.

[0067] In this embodiment, the control unit 6 performs processing according to the flow shown in Fig. 11. That is, the control unit 6 judges whether the processing to be performed is the flushing processing out of the image forming processing and the flushing processing (step #1). As a result, if the image forming processing is to be performed, the process proceeds to step #2, and if the flushing processing is to be performed, the process proceeds to step #3.

[0068] When proceeding to step #2, the control unit 6 controls the voltage application to the piezoelectric element PE so that the flight speed of the ink ejected from the recording head 40 becomes a predetermined speed. When proceeding to step #3, the control unit 6 controls the voltage application to the piezoelectric element PE so that the flight speed of the ink ejected from the recording head 40 becomes faster than the predetermined speed.

[0069] In this embodiment, the flight speed of the ink ejected from the nozzles 4N during the flushing process (i.e., the flushing ink) is faster than the flight speed of the ink ejected from the nozzles 4N during the image forming process. Therefore, even if there is a large amount of turbulence in the airflow between the nozzle surface of the recording head 40 and the outer peripheral surface of the conveyor belt 3 in the vertical direction, the flow direction of the flushing ink is less likely to deviate between the nozzle surface of the recording head 40 and the outer peripheral surface of the conveyor belt 3 in the vertical direction. In other words, the flow direction of the flushing ink is less likely to be affected by the turbulence in the airflow. Since the flow direction of the flushing ink is less likely to deviate, it is possible to prevent the flushing ink from landing around the opening 31 without passing through the opening 31.

[0070] As a result, in this embodiment, it is possible to suppress the adhesion of flushing ink to the outer peripheral surface of the conveyor belt 3. This makes it possible to suppress contamination of the sheet S caused by the flushing ink adhering to the outer peripheral surface of the conveyor belt 3 being transferred to the sheet S. Furthermore, it is also possible to suppress contamination of the sheet S caused by the flushing ink directly landing on the sheet S on the outer peripheral surface of the conveyor belt 3.

[0071] In addition, it is possible to prevent the flushing ink from being blown back and adhering to the nozzle surface after the flushing ink is ejected from the nozzle surface of the recording head 40. This makes it possible to prevent clogging. In other words, it is possible to prevent deterioration of image quality. It is also possible to prevent failure of the recording head 40 caused by the flushing ink adhering to the recording head 40.

[0072] For example, in this embodiment, the control unit 6 performs at least one of the first process and the second process to make the flight speed of ink ejected from the nozzle 4N during the flushing process (i.e., the flushing ink) faster than the flight speed of ink ejected from the nozzle 4N during the image formation process.

[0073] As the first process, the control unit 6 applies a voltage to the piezoelectric element PE during the flushing process higher than the voltage to be applied to the piezoelectric element PE during the image formation process, which makes it easy to make the flight speed of the flushing ink faster than the flight speed of the ink ejected during the image formation process.

[0074] As the second process, the control unit 6 makes the waveform of the voltage applied to the piezoelectric element PE during the flushing process different from the waveform of the voltage applied to the piezoelectric element PE during the image formation process. In this configuration, the optimum waveform of the voltage applied to the piezoelectric element PE during the flushing process is experimentally obtained and determined based on at least one of the material of each component of the recording head 40, the positional relationship of each component of the recording head 40, the vertical distance between the nozzle surface of the recording head 40 and the outer circumferential surface of the conveyor belt 3, the opening diameter of the nozzle 4N, the width of the ink flow path from the pressure chamber 410 to the nozzle 4N, the length of the ink path, the type of the piezoelectric element PE, and the type of ink (for example, viscosity), so that the flying speed of the flushing ink is faster than the flying speed of the ink ejected during the image formation process.

[0075] This makes it easy to make the flight speed of the flushing ink faster than the flight speed of the ink ejected during the image formation process. For example, the meniscus M of the ink in the nozzle 4N (see FIG. 6) oscillates up and down. For this reason, an optimal waveform for the voltage applied to the piezoelectric element PE during the flushing process is required so that ink is ejected from the nozzle 4N when the meniscus M oscillates downward.

[0076] For example, the flight speed of the flushing ink is set to 1.05 times or more the flight speed of the ink ejected from the nozzle 4N during the image formation process. This makes it possible to prevent the travel direction of the flushing ink from being affected by turbulence in the air current.

[0077] However, if the flight speed of the flushing ink is too fast, the flushing ink may become more misted, which may make the direction of travel of the flushing ink more susceptible to turbulence in the airflow. For this reason, the flight speed of the flushing ink is set to be no more than twice the flight speed of the ink ejected from the nozzle 4N during the image formation process. This makes it possible to prevent the flushing ink from becoming more misted (i.e., the direction of travel of the flushing ink from becoming more susceptible to turbulence in the airflow).

[0078] The embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is indicated by the claims, not by the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0079] 3 Conveyor belt 4N Nozzle 6 Control section 30 Flushing Area 31 Aperture 40 Recording head 100 Printers (inkjet recording devices) 410 Pressurized Room PE Piezoelectric element (death device) S sheet (recording medium)

Claims

1. A conveyor belt for conveying a recording medium; a recording head having a pressure chamber for storing ink, a nozzle communicating with the pressure chamber, and a displacement element which deforms in response to application of a voltage to apply pressure to the pressure chamber and eject the ink from the nozzle, and which forms an image on the recording medium by ejecting the ink onto the recording medium; a control unit for controlling the recording head, the conveyor belt has a flushing area in which an opening is formed, The flushing area includes a plurality of flushing areas arranged at intervals in the moving direction of the conveyor belt, the control unit causes the recording head to perform a flushing process of ejecting the ink toward the opening of the flushing region that does not overlap with the recording medium, separately from an image forming process of ejecting the ink toward the recording medium; The control unit controls the application of voltage to the displacement element to make the flight speed of the ink ejected from the nozzle during the flushing process faster than the flight speed of the ink ejected from the nozzle during the image formation process.

2. 2. The inkjet recording device according to claim 1, wherein the control unit makes the flight speed of the ink ejected from the nozzle during the flushing process faster than the flight speed of the ink ejected from the nozzle during the image formation process by making the voltage applied to the displacement element during the flushing process greater than the voltage applied to the displacement element during the image formation process.

3. 2. The inkjet recording device according to claim 1, wherein the control unit makes a flying speed of the ink ejected from the nozzle during the flushing process faster than a flying speed of the ink ejected from the nozzle during the image formation process by making a waveform of a voltage applied to the displacement element during the flushing process different from a waveform of a voltage applied to the displacement element during the image formation process.

4. 4. The inkjet recording apparatus according to claim 3, wherein a waveform of a voltage applied to the displacement element during the flushing process is determined based on at least one of the following: a material and a positional relationship of each component of the recording head, a distance between the nozzle and the conveying belt, an opening diameter of the nozzle, a width and a length of an ink flow path from the pressure chamber to the nozzle, a type of the displacement element, and a type of the ink.

5. 2. The inkjet recording apparatus according to claim 1, wherein a flying speed of the ink ejected from the nozzles during the flushing process is 1.05 times or more faster than a flying speed of the ink ejected from the nozzles during the image forming process.

6. 5. The inkjet recording apparatus according to claim 4, wherein a flying speed of the ink ejected from the nozzles during the flushing process is equal to or less than twice a flying speed of the ink ejected from the nozzles during the image forming process.

Images