Inkjet recording device

Abstract

To suppress ink from leaking out from a nozzle unintentionally.SOLUTION: An inkjet recording device is provided with: a conveying belt; a recording head that has a pressurization chamber that stores ink, a nozzle communicated with the pressurization chamber, a displacement element that is applied with voltages to deform, so as to apply pressure to the pressurization chamber and a driver circuit that switches ON and OFF of application of voltages to the displacement element on the basis of an input driving signal in a pulse shape; and a control part. In a meniscus oscillation process that is performed before a flushing process, the control part makes a pulse width of the driving signal smaller than time constant of a circuit part including the driver circuit and the displacement element.SELECTED DRAWING: Figure 12

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 conventional inkjet recording device ejects ink from the recording head toward a sheet. This forms an image on the sheet. Such an inkjet recording device is disclosed, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-59875 Summary of the Invention [Problem to be solved by the invention]

[0004] When the ink inside the nozzle is viscous, the ink may be ejected in an unintended direction, which can cause problems. To address this issue, a meniscus oscillation process may be performed to oscillate the ink meniscus inside the nozzle.

[0005] By performing the meniscus oscillation process, thickening of the ink in the nozzles is suppressed. However, in some cases, ink may unintentionally overflow from the nozzles when the meniscus oscillation process is performed. For example, if ink unintentionally overflows from the nozzles, the ink may adhere to the sheet and stain the sheet. Furthermore, in a configuration in which the sheet is transported by a transport belt, the transport belt may become stained with ink.

[0006] The present invention has been made to solve the above-mentioned problems, and has an object to provide an inkjet recording apparatus that can prevent ink from unintentionally overflowing from the nozzles. [Means for solving the problem]

[0007] To achieve the above object, one aspect of the present invention provides an inkjet recording apparatus comprising: a conveyor belt for conveying a sheet; pressure chambers containing ink; nozzles communicating with the pressure chambers; displacement elements that deform when a voltage is applied to the pressure chambers to apply pressure to the pressure chambers; and a driver circuit that switches on and off the voltage applied to the displacement elements based on an input pulse-shaped drive signal, thereby forming an image on the sheet by applying pressure to the pressure chambers to eject ink from the nozzles; and a control unit that generates a drive signal and inputs it to the driver circuit. The conveyor belt has flushing areas in which openings are formed. A plurality of flushing areas are arranged at intervals in the direction of movement of the conveyor belt. While the conveyor belt is driven, the control unit causes the recording head to perform a flushing process in which ink is ejected toward the openings in the flushing areas that do not overlap with the sheet, separate from an image formation process in which ink is ejected toward the sheet. Before ejecting ink, the control unit inputs a meniscus oscillation process drive signal to the driver circuit to drive the displacement elements, thereby causing the recording head to perform a meniscus oscillation process in which the ink meniscus in the nozzle is oscillated. In the meniscus oscillation process before the flushing process, the control unit sets the pulse width of the drive signal to be smaller than the time constant of the circuit unit including the driver circuit and the displacement element. [Effects of the Invention]

[0008] The configuration of the present invention can prevent ink from unintentionally spilling out of the nozzles. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an inkjet recording apparatus according to an embodiment. [Figure 2] 1 is a plan view of a printing unit of an inkjet printing apparatus according to an embodiment. [Figure 3] 1 is a schematic diagram of a conveyor belt and its periphery in an inkjet recording apparatus according to an embodiment. [Figure 4]1 is a block diagram of an inkjet recording apparatus according to an embodiment. [Figure 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 schematically illustrating a nozzle and its periphery in an inkjet recording apparatus according to an embodiment. [Figure 7] FIG. 2 is a plan view of a conveyor belt of the inkjet recording apparatus according to the embodiment. [Figure 8] 5A and 5B are diagrams illustrating the positional relationship between a flushing area of ​​a transport belt and a print head of an inkjet printing apparatus according to an embodiment. [Figure 9] 5A and 5B are diagrams illustrating the positional relationship between a flushing area of ​​a conveyance 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] 6A and 6B are diagrams showing the timing of execution of a meniscus oscillation process performed by a print head of an inkjet printing apparatus according to an embodiment. [Figure 12] FIG. 4 is a diagram showing a flow of processing performed by a control unit of the inkjet recording apparatus according to an embodiment. [Figure 13] 10 is a diagram showing the relationship between the pulse width and the voltage applied to a piezoelectric element of an inkjet recording device according to an embodiment (a diagram in which the pulse width is set smaller than the time constant). FIG. [Figure 14] 10 is a diagram showing the relationship between the pulse width and the voltage applied to a piezoelectric element of an inkjet recording device according to an embodiment (a diagram in which the pulse width is greater than the time constant). FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1 to 14, an embodiment of the present invention will be described below using 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.

[0011] <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 as it passes through 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 sheet S after printing. The second transport unit 12 ejects the sheet S after printing onto an ejection tray ET.

[0012] 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 numeral. 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 make up 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.

[0013] 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 conveying roller member upstream of the pair of registration rollers 10 in the conveying direction of the sheet S continues to rotate. This corrects the skew of the sheet S.

[0014] The printer 100 includes a belt conveying unit 2. The belt conveying unit 2 receives the sheet S from the first conveying unit 11 and conveys the sheet S. The belt conveying unit 2 includes a plurality of tension rollers 20. The plurality of tension rollers 20 are rotatably supported. The belt conveying unit 2 also includes a conveying belt 3. The conveying belt 3 is endless. The conveying belt 3 is rotatably stretched by the plurality of tension rollers 20. The sheet S is conveyed from the first conveying unit 11 toward the belt conveying unit 2, and the sheet S reaches the outer peripheral surface of the conveying belt 3.

[0015] One of the multiple tension rollers 20 is connected to a belt motor BM (see FIG. 4), and rotates by transmitting the driving force of the belt motor BM. When the tension roller 20 connected to the belt motor BM rotates, the conveyor belt 3 is driven, and the other tension rollers 20 rotate accordingly. In other words, the conveyor belt 3 rotates.

[0016] The belt conveying section 2 also includes a suction unit 200. The suction unit 200 is disposed on the inner circumferential side of the conveying belt 3. The suction unit 200 sucks the sheet S on the outer circumferential surface of the conveying belt 3 from the inner circumferential side of the conveying belt 3.

[0017] 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 by adsorbing it to its outer peripheral surface. In yet another way, the conveyor belt 3 conveys the sheet S by moving (i.e., rotating). The rotation direction of the conveyor belt 3 corresponds to the "movement direction."

[0018] The printer 100 includes a recording unit 4. The recording unit 4 is disposed so as to face the outer circumferential 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 circumferential surface of the conveyor belt 3 and the recording unit 4 face each other with a gap in the vertical direction. As a result, while the sheet S is being conveyed by the conveyor belt 3, the sheet S passes between the nozzle surface of a recording head 40 (described later) and the outer circumferential surface of the conveyor belt 3. In other words, the space between the nozzle surface of the recording head 40 and the outer circumferential surface of the conveyor belt 3 forms part of the conveyance path of the sheet S. The recording head 40 is disposed above the conveyor belt 3, with the nozzle surface of the recording head 40 facing downward.

[0019] As shown in Fig. 2, the recording unit 4 has four line heads 41 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. This also applies to Fig. 3, which will be referred to later in the description.

[0020] The line head 41 of each color includes multiple (for example, 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 direction in which the sheet S is conveyed by the conveyor belt 3. In the following description, the direction perpendicular to the direction in which the sheet S is conveyed by the conveyor belt 3 will simply be referred to as the width direction.

[0021] The recording heads 40 are arranged at intervals in the vertical direction relative to the outer circumferential surface of the conveyor belt 3. In other words, the recording heads 40 are arranged at positions facing the sheet S conveyed by the conveyor belt 3 in the vertical direction. In other words, the conveyor belt 3 adsorbs and conveys the sheet S below the recording heads 40. The vertical direction is the direction perpendicular to the conveying direction and width direction of the sheet S by the conveyor belt 3.

[0022] Each recording head 40 has a nozzle surface that faces the outer peripheral surface of the conveyor belt 3 in the vertical direction. 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 the corresponding color downward. For example, each recording head 40 has the same number of nozzles 4N. 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, each recording head 40 will have more nozzles 4N.

[0023] 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. This forms an image 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.

[0024] 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 ejected in a flushing process, which will be described later. The ink in the waste ink tank 21 is discarded.

[0025] Returning to FIG. 1 , the printer 100 includes a drying unit 51 and a decurler 52. The drying unit 51 dries ink adhering to the sheet S while transporting the sheet S toward the decurler 52. The decurler 52 straightens out any curls in the sheet S. The decurler 52 transports the sheet S after the curl has been straightened toward the second transport section 12.

[0026] 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, as will be described in detail later, the control unit 6 controls a flushing process and a meniscus oscillation process.

[0027] A resist 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 resist sensor 61, the sheet sensor 62, and the belt sensor 63 are shown in FIG.

[0028] The registration sensor 61 has a detection position that is upstream of the registration nip in the conveyance 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 its output value depending on whether the sheet S is present or absent at the corresponding detection position.

[0029] The control unit 6 detects the arrival of the leading edge of the sheet S at the detection position of the registration sensor 61 and the passage of the trailing edge thereof based on the output value of the registration sensor 61. In other words, the control unit 6 detects the arrival of the leading edge of the sheet S at the registration nip and the passage of the trailing edge 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 registration sensor 61 detects the arrival of the leading edge of the sheet S at the detection position.

[0030] The sheet sensor 62 has a detection position between the printing position of the line head 41 that is furthest upstream in the conveyance direction of the sheet S among the multiple line heads 41 and the registration nip. The sheet sensor 62 changes its output value depending on the presence or absence of the sheet S at the corresponding detection position. The sheet sensor 62 may be a CIS (Contact Image Sensor), or may be a reflective optical sensor or a transmissive optical sensor. For example, a CIS is used as the sheet sensor 62.

[0031] The control unit 6 detects the arrival of the leading edge of the sheet S at the detection position of the sheet sensor 62 and the passing of the trailing edge 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 determines the timing of ejecting ink onto the sheet S being 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 being transported by the transport belt 3 may be determined based on the time from when the pair of registration rollers 10 starts transporting the sheet S.

[0032] The control unit 6 also 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 conveying direction. Therefore, the control unit 6 recognizes the size of the sheet S in the conveying direction conveyed by the conveyor belt 3 based on the sheet passing time. This allows the control unit 6 to detect the size of the sheet S in the conveying direction even if the sheet S conveyed by the conveyor belt 3 is an irregular size.

[0033] 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 pair of registration rollers 10 starts conveying the sheet S. In this case, the positional deviation of the sheet S is detected by the control unit 6.

[0034] It is also possible to install a plurality of sheet sensors 62. For example, two sheet sensors 62 may be installed.

[0035] 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 also be configured using a transmissive optical sensor or a reflective optical sensor.

[0036] 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 area 30 (see FIG. 7) in the rotation direction of the conveyor belt 3 based on the output value of the belt sensor 63.

[0037] 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, an 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.

[0038] The printer 100 is equipped with 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.

[0039] 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.

[0040] The user terminal PC sends print data for the print job (data including PDL data, etc.) to the printer 100. In other words, the user terminal PC sends a request to execute the print job 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 to be 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.

[0041] <Ink ejection configuration> As shown in FIGS. 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 the application of a drive voltage. Each nozzle 4N ejects ink by the deformation of the corresponding piezoelectric element PE.

[0042] 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 is connected to 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, thereby changing the volume of the pressure chamber 410. Note that a different displacement element may be used instead of the piezoelectric element PE, as long as it is deformed and driven by application of a voltage to change the volume of the pressure chamber 410.

[0043] Each nozzle 4N ejects ink by driving the piezoelectric element PE of the corresponding pressure chamber 410. In the meniscus oscillation process described below, a voltage is applied to each piezoelectric element PE that is low enough to prevent ink from being ejected from the nozzle 4N connected to the corresponding pressure chamber 410. As a result, in the meniscus oscillation process, the ink meniscus can be oscillated in each nozzle 4N without ejecting ink. In Figure 6, the ink meniscus is denoted by the symbol M.

[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, which is on the up-down side opposite the nozzle surface. 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 the 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 to drive 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 generation circuit 60 that generates a drive signal to the driver circuit DR. The signal generation circuit 60 generates a pulsed 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.

[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. As will be described in detail later, in the flushing process, ink is ejected from each recording head 40, passes through the openings 31, reaches the inner periphery 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 areas 30. The plurality of flushing areas 30 are arranged at predetermined intervals in the rotation direction of the conveyor belt 3. The conveyor belt 3 has flushing areas 30 and other areas (reference numerals omitted) alternately in the rotation direction.

[0050] Each flushing area 30 has a plurality (the same number) of openings 31. The openings 31 are elongated holes that are long in the width direction of the conveyor belt 3. The shape of the openings 31 (the shape when viewed 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 rows of openings. The rows of openings are rows of openings 31 that are arranged at equal intervals in the width direction of the conveyor belt 3. One row of openings has N openings 31 (six in FIG. 7), and the other row of openings has N-1 openings 31 (five in FIG. 7). The center positions of both rows of openings in the width direction are also located at the center position of the conveyor belt 3 in the width direction. That is, the multiple openings 31 in each flushing area 30 are arranged in a staggered pattern in the width direction. The length of the openings 31 in the width direction (opening width) is greater than the distance between adjacent openings 31 in the width direction.

[0052] 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, as the conveyor belt 3 rotates, each of the plurality of nozzles 4N faces at least one of the openings 31 in the vertical direction.

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

[0055] Here, in a continuous printing job, the control unit 6 recognizes the size of the sheet S conveyed 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 conveying the sheet S from the registration roller pair 10 to the conveyor belt 3 so that the flushing area 30 appears between sheets at regular intervals. The control unit 6 changes the timing to start conveying the sheet S from the registration roller pair 10 to the conveyor belt 3 depending on the size of the sheet S conveyed by the conveyor belt 3. The control unit 6 recognizes the size of the sheet S used in the print job (the sheet S conveyed 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 representing the sheet S. Note that, for convenience, FIG. 9 illustrates sheets S of multiple different sizes together.

[0057] Here, referring to FIG. 10, a detailed description will be given focusing on an A4 portrait size sheet S (the 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 the 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 numerals of the respective sheets S are assigned numbers 1 to 3 indicating the conveying order.

[0058] When the size of the sheets 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 sheets S2 or 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] <Flushing process overview> 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. To prevent this problem, while the conveyor belt 3 is in motion, each recording head 40 performs a flushing process in addition to the image formation process. The image formation 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 toward the openings 31 of the flushing areas 30 of the conveyor belt 3 that do not overlap with the sheet S. In other words, the flushing process is a process of ejecting ink at a timing different from the timing of forming an image on the sheet S. The ink ejected during the flushing process does not contribute to image formation. The ink ejected during the flushing process does not head toward the sheet S, but passes through the openings 31, reaches the inner periphery of the conveyor belt 3, and is stored 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 recording head 40. The following description is for reference only, and therefore the method for controlling the flushing process of the other recording heads 40 will be omitted. The same applies to the method for controlling the meniscus oscillation process, which will be described later.

[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 causes the ink to pass through the opening 31. Because the ink ejected during the flushing process passes through the opening 31, the ink does not adhere to the conveyor belt 3.

[0063] Here, in a continuous printing job, the transport of the sheet S is controlled so that the flushing area 30 appears between 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.

[0064] Therefore, during execution of a continuous printing job, the control unit 6 causes the recording head 40 to perform the flushing process multiple times. During execution of a continuous printing job, the control unit 6 causes the recording head 40 to perform the flushing process every time the recording head 40 and the flushing area 30 face each other in the vertical direction.

[0065] <Outline of meniscus oscillation treatment> If the ink in the nozzle 4N becomes viscous and is forcibly ejected from the nozzle 4N in this state, the ink ejected from the nozzle 4N may proceed in an unintended direction. For example, the ink may adhere to the conveyor belt 3. If the ink adheres to the conveyor belt 3, the sheet S being conveyed by the conveyor belt 3 may become stained with ink.

[0066] Therefore, the recording head 40 performs a meniscus oscillation process to oscillate the meniscus of the ink in the nozzle 4N. The recording head 40 performs the meniscus oscillation process for each of the multiple nozzles 4N. The recording head 40 performs the meniscus oscillation process before ejecting ink. That is, the recording head 40 performs the meniscus oscillation process before the flushing process (in other words, immediately before the flushing process). The recording head 40 also performs the meniscus oscillation process before the image forming process (in other words, immediately before the image forming process).

[0067] The control unit 6 controls the meniscus oscillation process performed by the recording head 40. The control unit 6 controls the number of times the meniscus oscillates in the meniscus oscillation process (in other words, the number of drive pulses applied to the piezoelectric element PE). The control unit 6 controls the oscillation amplitude of the meniscus in the meniscus oscillation process (in other words, the amplitude of the drive voltage applied to the piezoelectric element PE). The control unit 6 also controls the execution timing of the meniscus oscillation process.

[0068] Before ink is ejected, the control unit 6 causes the recording head 40 to perform a meniscus oscillation process. When causing the recording head 40 to perform the meniscus oscillation process, the control unit 6 inputs a drive signal for the meniscus oscillation process to the driver circuit DR and applies a drive voltage to the piezoelectric element PE to be driven (i.e., the piezoelectric element PE assigned to the nozzle 4N that should oscillate the ink meniscus). In the meniscus oscillation process, a minute voltage is applied to the piezoelectric element PE as the drive voltage. This causes the piezoelectric element PE to deform, causing the diaphragm 430 to vibrate. At this time, the vibration is transmitted to the ink meniscus via the ink in the nozzle 4N. As a result, the ink meniscus oscillates.

[0069] By performing the meniscus oscillation process, the ink in the nozzle 4N is agitated, which prevents the ink in the nozzle 4N from thickening. Even if the ink meniscus oscillates, the oscillation is small, so leakage of ink from the nozzle 4N is prevented.

[0070] <Amplitude control of meniscus oscillation> As shown in FIG. 11, upon receiving a request to execute a print job, the control unit 6 starts driving the conveyor belt 3 (time point P0). Thereafter, during a flushing period Tf, which is the period from when the rotation speed of the conveyor belt 3 stabilizes at a constant speed until time point P1 before the sheet S reaches the printing position, the control unit 6 causes the recording head 40 to perform a flushing process. Then, after the sheet S reaches the printing position, the control unit 6 causes the recording head 40 to perform an image formation process. In FIG. 11, the time point at which the flushing process is executed is indicated by "Pf," and the time point at which the image formation process is executed is indicated by "Pi."

[0071] During the flushing period Tf, the control unit 6 causes the recording head 40 to perform the flushing process multiple times for each of the plurality of nozzles 4N. Furthermore, the control unit 6 causes the recording head 40 to perform the meniscus oscillation process multiple times for each of the plurality of nozzles 4N before each flushing process. In Figure 11, the execution period of the meniscus oscillation process is indicated by hatching.

[0072] For example, in some cases, the non-ink-ejection period between the previous execution of a print job and the current execution of the print job becomes long. The longer the non-ink-ejection period, the more likely the ink in the nozzles 4N to thicken. For this reason, the control unit 6 extends the period during which the meniscus oscillation process is performed before the first flushing process in the flushing period Tf compared to before the second or subsequent flushing processes. In other words, the control unit 6 executes the meniscus oscillation process more times before the first flushing process in the flushing period Tf compared to before the second or subsequent flushing processes.

[0073] With this configuration, the meniscus oscillation process is performed more frequently during the flushing period Tf. The more frequently the meniscus oscillation process is performed, the more the ink in the nozzle 4N can be prevented from thickening. On the other hand, if the meniscus oscillation process is performed more frequently, ink may overflow from the nozzle 4N when the meniscus oscillation process is performed. If ink overflows from the nozzle 4N when the meniscus oscillation process is performed, the conveyor belt 3 will become stained with ink.

[0074] To prevent this, the control unit 6 controls the meniscus oscillation process before the flushing process (i.e., before ink ejection) so that the oscillation amplitude of the ink meniscus in the nozzle 4N is small. Details will be described later. This makes it possible to prevent ink from overflowing from the nozzle 4N during the meniscus oscillation process before the flushing process.

[0075] On the other hand, if the image formation process is performed with the ink in the nozzle 4N having increased viscosity, the image quality may be adversely affected. For this reason, in the meniscus oscillation process before the image formation process, it is necessary to reliably prevent the ink in the nozzle 4N from increasing in viscosity.

[0076] Therefore, the control unit 6 causes the recording head 40 to perform the meniscus oscillation process multiple times before each image formation process (i.e., before ink ejection) for the print contributing nozzles 4N that are used in the image formation process.

[0077] The control unit 6 controls the oscillation amplitude of the ink meniscus in the print contributing nozzle 4N to be larger in at least one meniscus oscillation process among the multiple meniscus oscillation processes that the print contributing nozzle 4N is caused to perform before the image forming process than in the other meniscus oscillation processes. Details will be described later.

[0078] When causing the recording head 40 to perform the meniscus oscillation process, the control unit 6 performs the process according to the flow shown in Fig. 12. The meniscus oscillation process is performed for each nozzle 4N. That is, the process according to the flow shown in Fig. 12 is performed for each nozzle 4N.

[0079] For example, the flushing process is performed on all the nozzles 4N. That is, the meniscus oscillation process before the flushing process is performed on all the nozzles 4N.

[0080] On the other hand, not all nozzles 4N are necessarily used in the image forming process. Various sheets S are used in a print job. Nozzles 4N that do not face the sheet S in the vertical direction while it is being transported by the transport belt 3 are not used in the image forming process. Furthermore, even nozzles 4N that face the sheet S in the vertical direction while it is being transported by the transport belt 3 are not used in the image forming process depending on the image data to be printed in the print job.

[0081] In this way, there are nozzles 4N that are not used in the print job. For the nozzles 4N that are not used in the print job, ink is not ejected in the image forming process, and therefore the meniscus oscillation process before the image forming process is not performed.

[0082] Depending on the image data to be printed in a print job, a single nozzle 4N may perform image formation processing multiple times. In this case, each time the nozzle 4N performs image formation processing, the meniscus oscillation processing is performed on the nozzle 4N.

[0083] When causing the recording head 40 to perform a meniscus oscillation process, the control unit 6 determines whether the current meniscus oscillation process is a meniscus oscillation process before a flushing process (step #1). If it is a meniscus oscillation process before a flushing process, the process proceeds to step #2. If it is not a meniscus oscillation process before a flushing process, i.e., if it is a meniscus oscillation process before an image forming process, the process proceeds to step #3.

[0084] When the process proceeds to step #2, the control unit 6 performs a first process to reduce the oscillation amplitude of the ink meniscus in the nozzle 4N. On the other hand, when the process proceeds to step #3, the control unit 6 performs a second process to increase the oscillation amplitude of the ink meniscus in the nozzle 4N.

[0085] Here, the control unit 6 controls the oscillation amplitude of the ink meniscus in the nozzle 4N by changing the pulse width of the drive signal input to the driver circuit DR. A specific explanation will be given below with reference to Figures 13 and 14. In the following explanation, the part including the driver circuit DR, the piezoelectric element PE, and the wiring part connecting them will be given the reference numeral 400 and referred to as the circuit part 400 (see Figure 5).

[0086] 13 and 14, the upper diagram shows the pulse width of the drive signal input to the driver circuit DR, and the lower diagram shows the transition of the drive voltage applied to the piezoelectric element PE as a result of the drive signal being input to the driver circuit DR. Note that the displacement of the piezoelectric element PE depends on the drive voltage applied to the piezoelectric element PE. That is, in FIGS. 13 and 14, the transition of the drive voltage applied to the piezoelectric element PE also corresponds to the transition of the displacement of the piezoelectric element PE. In FIGS. 13 and 14, the time constant of the circuit section 400 is indicated by "T," and the pulse width of the drive signal is indicated by "W."

[0087] When causing the recording head 40 to perform a meniscus oscillation process before a flushing process, i.e., when reducing the oscillation amplitude of the ink meniscus in the nozzle 4N, the control unit 6 performs a first process of making the pulse width of the drive signal input to the driver circuit DR smaller than the time constant of the circuit unit 400. On the other hand, when causing the recording head 40 to perform a meniscus oscillation process before an image formation process, i.e., when increasing the oscillation amplitude of the ink meniscus in the nozzle 4N, the control unit 6 performs a second process of making the pulse width of the drive signal input to the driver circuit DR larger than the time constant of the circuit unit 400.

[0088] In this embodiment, by performing the first process before the flushing process, the voltage application to the piezoelectric element PE is turned off before the drive voltage applied to the piezoelectric element PE reaches a steady state, as shown in Fig. 13. In other words, the voltage application to the piezoelectric element PE is turned off before the piezoelectric element PE is displaced to its maximum. As a result, when the first process is performed, the oscillation amplitude of the ink meniscus in the nozzle 4N is reduced.

[0089] Furthermore, by performing the second process before the image formation process, the voltage application to the piezoelectric element PE is turned off after the drive voltage applied to the piezoelectric element PE reaches a steady state, as shown in Fig. 14. In other words, the voltage application to the piezoelectric element PE is turned off after the piezoelectric element PE has reached its maximum displacement. As a result, when the second process is performed, the oscillation amplitude of the ink meniscus in the nozzle 4N increases.

[0090] Here, there are cases where the oscillation amplitude of the ink meniscus in the nozzle 4N in the meniscus oscillation process before the image formation process (hereinafter, may be simply referred to as the meniscus oscillation amplitude) is relatively large. In this case, even if the meniscus oscillation amplitude in the meniscus oscillation process before the flushing process is made relatively smaller than the meniscus oscillation amplitude in the meniscus oscillation process before the image formation process, this is not sufficient, and there is a possibility that ink will overflow from the nozzle 4N.

[0091] On the other hand, in this embodiment, the meniscus oscillation amplitude before the flushing process is not simply made smaller than the meniscus oscillation amplitude before the image formation process. Specifically, when causing the recording head 40 to perform the meniscus oscillation process before the flushing process, the control unit 6 makes the pulse width of the drive signal input to the driver circuit DR smaller than the time constant of the circuit unit 400. This reliably reduces the meniscus oscillation amplitude during the meniscus oscillation process before the flushing process. As a result, ink overflow from the nozzle 4N during the meniscus oscillation process before the flushing process can be suppressed. In other words, unintended ink overflow from the nozzle 4N can be suppressed. Preventing unintended ink overflow from the nozzle 4N can prevent the conveyor belt 3 from being soiled with ink.

[0092] Furthermore, in this embodiment, of the multiple meniscus oscillation processes performed by the printing-contributing nozzle 4N (i.e., the nozzle 4N used in the image formation process) before the image formation process, at least one meniscus oscillation process is controlled so that the oscillation amplitude of the ink meniscus in the printing-contributing nozzle 4N is larger than in other meniscus oscillation processes.

[0093] For example, when the recording head 40 is caused to perform a meniscus oscillation process multiple times before an image formation process, the control unit 6 sets the pulse width of the drive signal input to the driver circuit DR to be greater than the time constant of the circuit unit 400 for all of the multiple meniscus oscillation processes. In other words, the meniscus oscillation process is performed multiple times in the print-contributing nozzle 4N before the image formation process, and the ink meniscus in the print-contributing nozzle 4N oscillates relatively widely in all of the multiple meniscus oscillation processes. This reliably prevents the ink in the print-contributing nozzle 4N from thickening.

[0094] Furthermore, for example, when the recording head 40 is caused to perform a meniscus oscillation process multiple times before an image formation process, the control unit 6 increases the pulse width of the drive signal input to the driver circuit DR for a predetermined number of the meniscus oscillation processes among the multiple meniscus oscillation processes, making the pulse width of the drive signal input to the driver circuit DR greater than the time constant of the circuit unit 400, while decreasing the pulse width of the drive signal input to the driver circuit DR for the remaining meniscus oscillation processes, making the pulse width of the drive signal input to the driver circuit DR smaller than the time constant of the circuit unit 400. In other words, multiple meniscus oscillation processes are performed on the print-contributing nozzle 4N before the image formation process, but the ink meniscus in the print-contributing nozzle 4N oscillates relatively greatly only during the execution of a predetermined number of the meniscus oscillation processes among the multiple meniscus oscillation processes. This makes it possible to suppress ink thickening within the print-contributing nozzle 4N and ink overflow from the print-contributing nozzle 4N.

[0095] The predetermined number of times is not particularly limited. Furthermore, among the multiple times of meniscus oscillation processing before the image formation processing, the pulse width of the drive signal input to the driver circuit DR may be set to be larger than the time constant of the circuit section 400 for the predetermined number of meniscus oscillation processing from the first.

[0096] The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined 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]

[0097] 3 conveyor belt 4N nozzle 6 Control Unit 30 Flushing Area 31 Aperture 40 Recording head 100 Printers (inkjet recording devices) 400 Circuit section 410 Pressure Chamber DR driver circuit PE Piezoelectric element (displacement element) S seat

Claims

1. A conveyor belt for conveying a sheet; a recording head including a pressure chamber that contains ink, a nozzle that communicates with the pressure chamber, a displacement element that deforms when a voltage is applied to it to apply pressure to the pressure chamber, and a driver circuit that switches on and off the application of voltage to the displacement element based on an input pulse-shaped drive signal, and that ejects the ink from the nozzle by applying pressure to the pressure chamber to form an image on the sheet; a control unit that generates the drive signal and inputs it to the driver circuit; 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, During the driving 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 sheet, separately from an image forming process of ejecting the ink toward the sheet, before the ink is ejected, the control unit inputs the drive signal for meniscus oscillation processing to the driver circuit to drive the displacement element, thereby causing the recording head to perform a meniscus oscillation processing for oscillating the meniscus of the ink in the nozzle; In the meniscus oscillation process before the flushing process, the control section sets a pulse width of the drive signal to be smaller than a time constant of a circuit section including the driver circuit and the displacement element.

2. 2. The ink jet recording apparatus according to claim 1, wherein in the meniscus vibration process before the image forming process, the control section makes the pulse width of the drive signal larger than the time constant of the circuit section.

3. the control unit causes the recording head to perform the meniscus oscillation process a plurality of times before the image forming process; The inkjet recording device of claim 1, wherein the control unit makes the pulse width of the drive signal larger than the time constant of the circuit unit for a predetermined number of the meniscus oscillation processes among the multiple meniscus oscillation processes performed before the image formation process, while making the pulse width of the drive signal smaller than the time constant of the circuit unit for the remaining meniscus oscillation processes.

Images