Inkjet recording apparatus

Abstract

An ink jet recording apparatus includes a conveyor belt, a recording head including a pressurizing chamber that accommodates ink, a nozzle that communicates with the pressurizing chamber, a displacement element that deforms by applying a voltage and applies a pressure to the pressurizing chamber, and a drive circuit. The drive circuit switches between proceeding and stopping of voltage application to the displacement element on the basis of an input pulse-shaped drive signal, and the control unit reduces the pulse width of the drive signal to be smaller than the time constant of a circuit unit including the drive circuit and the displacement element during meniscus swing processing before flushing processing.

Description

Technical Field

[0001] The present invention relates to an inkjet recording device. Background Art

[0002] In the related art, an inkjet recording device includes a recording head that discharges ink, and the inkjet recording device discharges ink from the recording head toward a sheet, thereby forming an image on the sheet. Summary of the invention 1. Technical issues to be resolved

[0003] When the ink in the nozzle becomes viscous, there is a possibility that the ejected ink will scatter in an undesired direction. Therefore, a meniscus oscillation process is sometimes performed to oscillate the meniscus of the ink in the nozzle.

[0004] The viscosity of the ink in the nozzle is suppressed by performing the meniscus swing process. However, depending on the situation, the ink may accidentally overflow from the nozzle when the meniscus swing process is performed. For example, when the ink accidentally overflows from the nozzle, the ink may adhere to the sheet and contaminate the sheet. In addition, in a structure in which the sheet is transported by a conveyor belt, the conveyor belt may be contaminated by the ink.

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an inkjet recording device capable of suppressing accidental overflow of ink from a nozzle. (II) Technical solution

[0006] In order to achieve the above-mentioned object, an inkjet recording device according to one aspect of the present invention comprises: a conveyor belt, a recording head, and a control unit. The conveyor belt conveys a sheet. The recording head comprises: a pressurized chamber for storing ink, a nozzle connected to the pressurized chamber, a displacement element that is deformed by applying voltage and applies pressure to the pressurized chamber, and a drive circuit. The drive circuit switches the application of voltage to the displacement element and stops based on an input pulse-shaped drive signal. The recording head ejects ink from the nozzle by applying pressure to the pressurized chamber to form an image on the sheet. The control unit generates a drive signal and inputs it to the drive circuit. The conveyor belt has a flushing area with an opening. A plurality of flushing areas are arranged at intervals in the moving direction of the conveyor belt. During the driving process of the conveyor belt, the control unit causes the recording head to perform an image forming process of ejecting ink toward the sheet, and also causes the recording head to perform a flushing process of ejecting ink toward the opening of the flushing area that does not overlap with the sheet. Before ejecting ink, the control unit drives the displacement element by inputting a driving signal for the meniscus oscillation process to the driving circuit, thereby causing the recording head to perform a meniscus oscillation process for oscillating the meniscus of the ink in the nozzle. In the meniscus oscillation process before the flushing process, the control unit makes the pulse width of the driving signal smaller than the time constant of the circuit unit including the driving circuit and the displacement element. (III) Beneficial effects

[0007] In the structure of the present invention, it is possible to suppress the ink from accidentally overflowing from the nozzle. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a schematic diagram of an inkjet recording device according to one embodiment. Figure 2 This is a plan view of a recording section of an inkjet recording device according to one embodiment. Figure 3 This is a schematic diagram of a conveyor belt and its surroundings of an inkjet recording apparatus according to one embodiment. Figure 4 This is a block diagram of an inkjet recording device according to one embodiment. Figure 5 This is a block diagram of a recording head and its periphery of an inkjet recording device according to an embodiment. Figure 6 This is a cross-sectional view schematically showing a nozzle and its surroundings of an inkjet recording device according to an embodiment. Figure 7 This is a plan view of a conveyor belt of an inkjet recording apparatus according to one embodiment. Figure 8 This is a diagram showing the positional relationship between the flushing area of ​​the conveyor belt and the recording head of the inkjet recording apparatus according to one embodiment. Fig. 9 This is a diagram showing the positional relationship between a flushing area of ​​a conveyor belt and a sheet in an inkjet recording apparatus according to one embodiment. Fig.10 This is a diagram for explaining the timing of conveying a sheet to a conveyor belt in an inkjet recording apparatus according to one embodiment. Fig.11 This is a diagram showing the execution timing of the meniscus oscillation process performed by the recording head of the inkjet recording apparatus according to one embodiment. Fig.12 This is a diagram showing the flow of processing performed by a control unit of the inkjet recording apparatus according to one embodiment. Fig.13 This is a diagram showing the relationship between the voltage applied to the piezoelectric element and the pulse width in the inkjet recording apparatus according to one embodiment (a diagram in the case where the pulse width is smaller than the time constant). Fig.14 This is a diagram showing the relationship between the voltage applied to the piezoelectric element and the pulse width in the inkjet recording apparatus according to one embodiment (a diagram in the case where the pulse width is made larger than the time constant). DETAILED DESCRIPTION

[0009] Refer to the following Figure 1 to Figure 14, an embodiment of the present invention is described by taking a printer 100 that prints on a sheet S as a recording medium as an example. The type of the sheet S is not particularly limited. For example, paper is used as the sheet S. In addition, in the following description, a direction perpendicular to the installation surface of the printer 100 (for example, a flat ground) is defined as a vertical direction.

[0010] (Overall structure of the printer) like Figure 1 As shown, the printer 100 (equivalent to an "inkjet recording device") of this embodiment includes a first conveying unit 11 and a second conveying unit 12. The first conveying unit 11 supplies a sheet S set in a paper feed box CA and conveys the sheet S toward a printing position. In a printing task of the printer 100, ink is ejected to the sheet S passing through the printing position. Thus, an image is printed on the sheet S. In other words, in a printing task of the printer 100, an image composed of ink is formed on the sheet S. The second conveying unit 12 conveys the printed sheet S. The second conveying unit 12 discharges the printed sheet S to the discharge tray ET.

[0011] The first conveying unit 11 includes a plurality of conveying roller members including a pair of registration rollers 10. Figure 1 In the figure, only the positioning roller pair 10 among the plurality of conveying roller components is marked with a reference numeral. The plurality of conveying roller components convey the sheet S by rotating respectively. The positioning roller pair 10 includes a pair of rollers pressed against each other. A positioning roller gap is formed between the pair of rollers constituting the positioning roller pair 10. The sheet S supplied from the paper feed box CA enters the positioning roller gap. The positioning roller pair 10 conveys the sheet S toward the belt conveying unit 2 described later by rotating.

[0012] When the leading end of the sheet S reaches the registration nip, the registration roller pair 10 stops rotating. Meanwhile, the conveying roller member on the upstream side of the registration roller pair 10 in the conveying direction of the sheet S rotates. Thus, the skew of the sheet S is corrected.

[0013] The printer 100 includes a belt conveyor 2. The belt conveyor 2 receives a sheet S from the first conveyor 11 and conveys the sheet S. The belt conveyor 2 includes a plurality of mounting rollers 20. The plurality of mounting rollers 20 are rotatably supported. In addition, the belt conveyor 2 includes a conveyor belt 3. The conveyor belt 3 is annular. The conveyor belt 3 is rotatably mounted using the plurality of mounting rollers 20. The sheet S is conveyed from the first conveyor 11 to the belt conveyor 2, and the sheet S arrives on the outer peripheral surface of the conveyor belt 3.

[0014] One of the plurality of tension rollers 20 is connected to a belt motor BM (see Figure 4), the driving force of the belt motor BM is transmitted and the belt motor BM is rotated. The tension roller 20 connected to the belt motor BM rotates, thereby driving the conveyor belt 3, and the other tension rollers 20 rotate in a driven manner. In other words, the conveyor belt 3 rotates.

[0015] Moreover, the belt conveyor 2 includes a suction unit 200. The suction unit 200 is disposed on the inner peripheral side of the conveyor belt 3. The suction unit 200 suctions the sheet S on the outer peripheral surface of the conveyor belt 3 from the inner peripheral side of the conveyor belt 3.

[0016] Specifically, the conveyor belt 3 has a plurality of suction holes (not shown). The suction holes of the conveyor belt 3 penetrate in the thickness direction of the conveyor belt 3. 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 onto the outer peripheral surface of the conveyor belt 3. The conveyor belt 3 adsorbs and holds the sheet S onto the outer peripheral surface and rotates. In other words, the conveyor belt 3 adsorbs the sheet S onto the outer peripheral surface for conveyance. In other words, the conveyor belt 3 conveys the sheet S by moving (i.e. rotating). The rotation direction of the conveyor belt 3 is equivalent to the "moving direction".

[0017] The printer 100 includes a recording unit 4. The recording unit 4 is arranged so as to be disposed in the up-down direction with respect to the outer peripheral surface of the conveyor belt 3. In the process of conveying the sheet S by the conveyor belt 3, the sheet S on the outer peripheral surface of the conveyor belt 3 is disposed in the up-down direction with a gap between the recording unit 4. Thus, in the process of conveying the sheet S by the conveyor belt 3, the sheet S passes between the nozzle surface of the recording head 40 described later and the outer peripheral surface of the conveyor belt 3. That is, the portion between the nozzle surface of the recording head 40 and the outer peripheral surface of the conveyor belt 3 becomes a part of the conveying path of the sheet S. In addition, the recording head 40 is arranged above the conveyor belt 3, and the nozzle surface of the recording head 40 faces downward.

[0018] like Figure 2 As shown in FIG. 1 , the recording unit 4 includes four line heads 41 corresponding to cyan, magenta, yellow, and black, respectively. Figure 2 In the embodiment, the cyan line head 41 is marked with a reference symbol "C", the magenta line head 41 is marked with a reference symbol "M", the yellow line head 41 is marked with a reference symbol "Y", and the black line head 41 is marked with a reference symbol "K" to distinguish them. Figure 3 The same is true.

[0019] The line head 41 of each color includes a plurality of (for example, three) recording heads 40. For example, the plurality of recording heads 40 of each color are arranged in a staggered manner in a direction perpendicular to the conveying direction of the sheet S conveyed by the conveyor belt 3. In the following description, the direction perpendicular to the conveying direction of the sheet S conveyed by the conveyor belt 3 is referred to as the width direction.

[0020] The recording heads 40 are arranged at intervals in the vertical direction relative to the outer peripheral surface of the conveyor belt 3. In other words, the recording heads 40 are arranged to face the sheet S conveyed by the conveyor belt 3 in the vertical direction. In other words, the conveyor belt 3 conveys the sheet S by sucking it under each recording head 40. The direction perpendicular to the conveying direction and the width direction of the sheet S conveyed by the conveyor belt 3 is the vertical direction.

[0021] Each recording head 40 has a nozzle surface that is disposed in the vertical direction with respect to the outer peripheral surface of the conveyor belt 3. The nozzle surface of each recording head 40 has a plurality of nozzles 4N. The plurality of nozzles 4N of each recording head 40 eject ink of corresponding colors 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. Figure 2 The nozzles 4N are indicated by dotted lines in FIG. 1 . In reality, a large number of nozzles 4N are provided in each recording head 40 .

[0022] Each recording head 40 ejects ink from the nozzle 4N toward the sheet S on the outer peripheral surface of the conveyor belt 3 based on the image data to be printed on the sheet S in the printing task. The ink ejected from each recording head 40 adheres to the sheet S. Thus, an image is formed on the sheet S. In other words, between each recording head 40 and the conveyor belt 3 is a printing position, and printing on the sheet S is performed at this printing position.

[0023] In addition, if Figure 3 As shown, a waste ink tank 21 is disposed on the inner peripheral side of the conveyor belt 3. The waste ink tank 21 stores ink ejected in a flushing process described later. The ink in the waste ink tank 21 is discarded.

[0024] Back to Figure 1 The printer 100 includes a drying unit 51 and a decurler 52. The drying unit 51 conveys the sheet S toward the decurler 52 and dries the ink attached to the sheet S during conveyance. The decurler 52 corrects the curl of the sheet S. The decurler 52 conveys the curl-corrected sheet S to the second conveying unit 12.

[0025] In addition, if Figure 4 As shown, the printer 100 includes a control unit 6. The control unit 6 includes a processing circuit such as a CPU and an ASIC. The control unit 6 controls the printing task. Specifically, the control unit 6 controls the belt motor BM to move (i.e., rotate) the conveyor belt 3 appropriately. The control unit 6 controls the conveyance of the sheet S using the conveyor belt 3. In addition, the control unit 6 controls the ink ejection using each recording head 40. In addition, the control unit 6 controls the flushing process and the meniscus swing process, which will be described in detail later.

[0026] The control unit 6 is connected to a registration sensor 61, a sheet sensor 62, and a belt sensor 63. Figure 3Detection positions (arrangement positions) of the registration sensor 61 , the sheet sensor 62 , and the belt sensor 63 are shown in FIG.

[0027] The registration sensor 61 detects a position 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 its output value depending on whether the sheet S is present at the corresponding detection position.

[0028] The control unit 6 detects the arrival of the leading end of the sheet S and the passage of the trailing end thereof at the detection position of the registration sensor 61 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 and the passage of the trailing end thereof in the registration roller gap based on the output value of the registration sensor 61. The control unit 6 measures the time when the sheet S is conveyed by the registration roller pair 10 (the rotation start time of the registration roller pair 10) based on the time from the arrival of the leading end of the sheet S at the detection position of the registration sensor 61.

[0029] The sheet sensor 62 uses the position between the printing position of the line head 41 located on the most upstream side in the conveying direction of the sheet S among the plurality of line heads 41 and the registration roller gap as the detection position. The sheet sensor 62 changes the output value according to whether the sheet S is present 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.

[0030] The control unit 6 detects the arrival and the passing of the front 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 conveyed by the conveyor belt 3 based on the output value of the sheet sensor 62. The timing of ejecting ink onto the sheet S conveyed by the conveyor belt 3 may be measured based on the time from the start of conveyance of the sheet S by the registration roller pair 10.

[0031] In addition, the control unit 6 measures the sheet passage time from when the leading end of the sheet S reaches the detection position of the sheet sensor 62 to when the trailing end of the same sheet S passes the detection position of the sheet sensor 62. The sheet passage time at the detection position of the sheet sensor 62 changes according to 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 passage time. Thus, even if the sheet S conveyed by the conveyor belt 3 has an irregular size, the control unit 6 can detect the size of the sheet S in the conveying direction.

[0032] Furthermore, the control unit 6 detects positional deviation of the sheet S (including skewness of the sheet S) based on the output value of the sheet sensor 62 (read data obtained by reading the sheet sensor 62). For example, after the sheet S starts to be conveyed by the registration roller pair 10, positional deviation may occur on the sheet S. In this case, the positional deviation of the sheet S is detected by the control unit 6.

[0033] In addition, the number of sheet sensors 62 provided may be plural. For example, two sheet sensors 62 may be provided.

[0034] 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. Thus, the reference position of the conveyor belt 3 can be detected 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 transmission type optical sensor or a reflection type optical sensor.

[0035] 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 flushing area 30 (refer to Figure 7 )’s location.

[0036] In addition, if Figure 4 As shown, the printer 100 includes a storage unit 7. The storage unit 7 includes storage devices such as ROM, RAM, HDD, and SSD. The storage unit 7 stores various information. The storage unit 7 is connected to the control unit 6. The control unit 6 reads information from the storage unit 7. In addition, the control unit 6 writes information to the storage unit 7.

[0037] The printer 100 includes an operation panel 8. For example, a touch screen is provided on the operation panel 8. The touch screen displays software buttons and messages, etc., and accepts touch operations of the user. In addition, hardware buttons for accepting settings and instructions are also provided on the operation panel 8. 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). In addition, the control unit 6 detects the operation performed on the operation panel 8.

[0038] 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 communicates with the user terminal PC using the communication unit 9.

[0039] The print data (including data such as PDL data) of the print job 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 of the print job includes the size of the sheet S used in the print job and various setting data related to printing. The communication unit 9 receives the print data of the print job. When the communication unit 9 receives the print data of the print job, the control unit 6 determines that the request to execute the print job has been received.

[0040] (Structure of ejecting ink) like Figure 5 and Figure 6 As shown, each recording head 40 has a piezoelectric element PE. The piezoelectric element PE is equivalent to a "displacement element". One piezoelectric element is allocated to each nozzle 4N. The piezoelectric element PE is deformed and driven by the application of a driving voltage. Each nozzle 4N ejects ink due to the deformation of the corresponding piezoelectric element PE.

[0041] Specifically, each nozzle 4N of each recording head 40 has a pressurization chamber 410. Each pressurization chamber 410 receives a supply of ink from an ink cartridge (not shown) via a common flow path 420. Each pressurization chamber 410 stores the ink supplied from the ink cartridge. Each pressurization chamber 410 is connected to the corresponding nozzle 4N. A piezoelectric element PE is assigned to each pressurization chamber 410. Each piezoelectric element PE applies pressure to the corresponding pressurization chamber 410 by deformation driving, thereby changing the volume of the pressurization chamber 410. In addition, as long as the volume of the pressurization chamber 410 is changed by deformation driving by applying a voltage, other displacement elements may be used instead of the piezoelectric element PE.

[0042] Each nozzle 4N ejects ink by being driven by the piezoelectric element PE of the corresponding pressurized chamber 410. In the meniscus oscillation process described later, a voltage is applied to each piezoelectric element PE to such an extent that ink is not ejected from the nozzle 4N connected to the corresponding pressurized chamber 410. Thus, in the meniscus oscillation process, the meniscus of ink can be oscillated in each nozzle 4N in such a manner that ink is not ejected. Figure 6 In the figure, the meniscus of the ink is denoted by the reference symbol M.

[0043] 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 opposite side of the nozzle surface in the vertical direction. A common electrode 401 is arranged on the vibration plate 430. In addition, 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 vertical direction (i.e., between the common electrode 401 and the individual electrode 402 in the vertical direction). Other piezoelectric elements PE are also arranged on the common electrode 401. The individual electrode 402 is arranged for each piezoelectric element PE.

[0044] Each recording head 40 has a voltage generating circuit VG. Each recording head 40 has a driving circuit DR. The voltage generating circuit VG generates a voltage for driving each piezoelectric element PE and supplies it to the driving circuit DR. The driving circuit DR applies the driving voltage supplied from the voltage generating circuit VG to each piezoelectric element PE. Thus, the driving circuit DR drives each piezoelectric element PE to deform.

[0045] A pulsed driving signal is input to the driving circuit DR. The driving circuit DR applies a voltage to the piezoelectric element PE to be driven as the driving signal rises. The driving circuit DR stops applying a voltage to the piezoelectric element PE as the driving signal falls. That is, the driving circuit DR switches between starting and stopping the voltage application to each piezoelectric element PE based on the inputted pulsed driving signal. In addition, the driving circuit DR does not apply a voltage to the piezoelectric element PE that is not driven.

[0046] The driving circuit DR is connected to the control unit 6. The control unit 6 includes a signal generating circuit 60, and the signal generating circuit 60 generates a driving signal for the driving circuit DR. The signal generating circuit 60 generates a pulsed driving signal. The driving signal is a signal for periodically driving each piezoelectric element PE. The control unit 6 generates the driving signal and inputs it to the driving circuit DR.

[0047] (Conveyor belt structure) like Figure 7 As shown, the conveyor belt 3 has a flushing area 30. Figure 7 The flushing area 30 is surrounded by a dotted line. The flushing area 30 is an area where an opening 31 is formed to penetrate the conveyor belt 3 in the thickness direction. In the flushing process, ink is ejected from each recording head 40, and the ejected ink reaches the inner peripheral side of the conveyor belt 3 through the opening 31 and is stored in the waste ink tank 21, which will be described in detail later.

[0048] Furthermore, a plurality of flushing areas 30 are provided on the conveyor belt 3. 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 the flushing areas 30 and other areas (reference numerals omitted) alternately in the rotation direction.

[0049] Each flushing area 30 has a plurality of (same number) 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 of the conveyor belt 3 as viewed from the thickness direction) is not particularly limited, and may be rectangular, circular, elliptical, or oval.

[0050] For example, each flushing area 30 includes two rows of openings. The opening rows are rows of openings 31 arranged at equal intervals in the width direction of the conveyor belt 3. One opening row has N (in Figure 7There are 6 openings 31 in the opening row, and another opening row has N-1 openings (in Figure 7 In the embodiment of the present invention, the plurality of openings 31 are arranged in a staggered manner in the width direction. In the embodiment of the present invention, the plurality of openings 31 are arranged in a staggered manner in the width direction. In addition, the width direction length (opening width) of the opening 31 is larger than the interval between the opening 31 and one or more openings 31 adjacent to the opening 31 in the width direction.

[0051] In addition, if Figure 8 As shown, the width W1 (mm) is smaller than the width W2 (mm). In addition, the width W1 corresponds to the length of the line head 41 in the width direction. Specifically, the width W1 corresponds to the length in the width direction from the end of the recording head 40 located on one side in the width direction to the end of the other side of the recording head 40 located on the other side in the width direction. The width W2 corresponds to the length in the width direction of the flushing area 30. Specifically, the width W2 corresponds to the length in the width direction from the end of the opening 31 located on one side in the width direction to the end of the other side of the opening 31 located on the other side in the width direction.

[0052] Thus, each of the plurality of nozzles 4N is opposed to at least one of the openings 31 in the up-down direction due to the rotation of the conveyor belt 3 .

[0053] (Sheet conveyance control) In a printing task that continuously forms images on a plurality of sheets S of the same size that are sequentially conveyed by the conveyor belt 3, i.e., a continuous printing task, the control unit 6 controls so that the interval in the conveying direction between the rear end of the preceding sheet S and the front end of the succeeding sheet S (the sheet S that is conveyed next to the preceding sheet S), i.e., the inter-sheet interval, is kept constant. In other words, the control unit 6 controls so that the plurality of sheets S are continuously conveyed at a constant interval. In other words, the control unit 6 keeps each inter-sheet interval generated when the plurality of sheets S are continuously conveyed at a constant interval.

[0054] Here, in the continuous printing task, the control unit 6 recognizes the size of the sheet S conveyed by the conveyor belt 3. In addition, the control unit 6 detects the reference position of the conveyor belt 3. In addition, the control unit 6 measures the start time of conveying the sheet S from the registration roller pair 10 to the conveyor belt 3 so that the flushing area 30 appears in the paper interval at a constant cycle. The control unit 6 changes the start time of conveying the sheet S from the registration roller pair 10 to the conveyor belt 3 according to the size of the sheet S conveyed by the conveyor belt 3. In addition, the control unit 6 recognizes the size of the sheet S (sheet S conveyed by the conveyor belt 3) used in the printing task based on the printing data of the printing task.

[0055] Fig. 9FIG. 2 shows the positional relationship between the sheet S conveyed by the conveyor belt 3 and the flushing area 30. Fig. 9 In FIG. 1 , 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 surface. Fig. 9 The flushing area 30 is indicated by hatching and the opening 31 is omitted. Fig. 9 The reference numerals of the sheets S are omitted, and the size of the sheets S is instead indicated in the graphic representing the sheets S. Fig. 9 For convenience, a plurality of sheets S of different sizes are collectively illustrated.

[0056] Refer to this Fig.10 For A4 vertical size sheet S (in Fig. 9 The third sheet S from the top is described in detail. Fig.10 In the embodiment, the rotation direction of the conveyor belt 3 (i.e., the conveying direction of the sheet S) is from bottom to top of the paper surface. Fig.10 For the sake of convenience, three sheets S are shown, and numbers 1 to 3 indicating the conveyance order are added to the reference numerals of the sheets S.

[0057] When the size of the sheet S is A4 in the longitudinal direction, the flushing area 30 does not appear in the paper gap between the first sheet S1 and the second sheet S2. The flushing area 30 appears in the paper gap between the second sheet S2 and the third sheet S3. The flushing area 30 in the paper gap between the sheet S2 and the sheet S3 does not overlap with the sheet S2 and the sheet S3 at all. Although not shown in the figure, the flushing area 30 does not appear in the paper gap between the third sheet S3 and the fourth sheet S, and the flushing area 30 appears in the paper gap between the fourth sheet S and the fifth sheet S.

[0058] (Overview of Flushing Process) The viscosity of the ink in the nozzle 4N with a low ink jetting frequency among the plurality of nozzles 4N increases with time. As a result, clogging may occur and image quality may be reduced. In order to suppress such undesirable conditions, during the driving process of the conveyor belt 3, each recording head 40 performs an image forming process and a flushing process. In addition, the image forming process is a process of ejecting ink toward the sheet S to form an image on the sheet S.

[0059] The flushing process is a process of ejecting ink toward the opening 31 of the flushing area 30 that does not overlap with the sheet S among the plurality of flushing areas 30 of the conveyor belt 3. That is, the flushing process is a process of ejecting ink at a time different from the time of forming an image on the sheet S. The ink ejected by the flushing process is not used for image formation. The ink ejected by the flushing process does not go toward the sheet S, but reaches the inner peripheral side of the conveyor belt 3 through the opening 31 and is stored in the waste ink tank 21. Clogging is suppressed by performing the flushing process.

[0060] The following describes a control method for the flushing process of one recording head 40. The following description is repeated for the control method for the flushing process of the other recording heads 40 and is omitted. The same is true for the control method for the meniscus oscillation process described later.

[0061] During the driving process of the conveyor belt 3, the control unit 6 causes the recording head 40 to perform a flushing process at the time when the flushing area 30 that does not overlap with the sheet S and the recording head 40 are opposed to 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 the time when the flushing area 30 is opposed to each other in the vertical direction, and the ink passes 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.

[0062] Here, the conveyance of the sheet S is controlled in the continuous printing job so that the flushing area 30 appears at the paper interval at a constant cycle. That is, the flushing area 30 that does not overlap the sheet S is repeatedly opposed to the recording head 40 in the vertical direction during the execution of the continuous printing job.

[0063] 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 faces the flushing area 30 in the vertical direction.

[0064] (Overview of Meniscus Swinging Processing) When the ink in the nozzle 4N is in a viscous state and the ink is forcibly ejected from the nozzle 4N in this state, the ink ejected from the nozzle 4N may move in an undesired direction, for example, the ink adheres to the conveyor belt 3. If the ink adheres to the conveyor belt 3, the sheet S conveyed by the conveyor belt 3 may be contaminated by the ink.

[0065] Therefore, the recording head 40 performs a meniscus oscillation process: the meniscus of the ink in the nozzle 4N is oscillated. The recording head 40 performs a meniscus oscillation process on each of the plurality of nozzles 4N. The recording head 40 performs a meniscus oscillation process before ejecting the ink. That is, the recording head 40 performs a meniscus oscillation process before the flushing process (in other words, immediately before the flushing process). In addition, the recording head 40 performs a meniscus oscillation process before the image forming process (in other words, immediately before the image forming process).

[0066] The control unit 6 controls the meniscus oscillation process of the recording head 40. The control unit 6 controls the number of meniscus oscillations in the meniscus oscillation process (in other words, the number of driving pulses applied to the piezoelectric element PE). The control unit 6 controls the meniscus oscillation amplitude in the meniscus oscillation process (in other words, the amplitude of the driving voltage applied to the piezoelectric element PE). In addition, the control unit 6 controls the execution timing of the meniscus oscillation process.

[0067] Before ejecting the ink, the control unit 6 causes the recording head 40 to perform a meniscus oscillation process. When causing the recording head 40 to perform a meniscus oscillation process, the control unit 6 inputs a driving signal for the meniscus oscillation process to the driving circuit DR, and applies a driving voltage to the piezoelectric element PE that should be driven (i.e., the piezoelectric element PE assigned to the nozzle 4N that should cause the meniscus of the ink to oscillate). During the meniscus oscillation process, a small voltage is applied to the piezoelectric element PE as a driving voltage. As a result, the piezoelectric element PE is deformed and the vibration plate 430 vibrates. At this time, the vibration is transmitted to the meniscus of the ink via the ink in the nozzle 4N. As a result, the meniscus of the ink oscillates.

[0068] The ink in the nozzle 4N is stirred by performing the meniscus oscillation process, thereby preventing the ink in the nozzle 4N from becoming viscous. In addition, even if the meniscus of the ink oscillates, the oscillation is small, so that leakage of the ink from the nozzle 4N can be prevented.

[0069] (Amplitude control of meniscus oscillation) like Fig.11 As shown in FIG. 1 , when receiving a request to execute a printing job, the control unit 6 starts driving the conveyor belt 3 (time P0). Thereafter, during the flushing period Tf, which is the period from when the rotation speed of the conveyor belt 3 stabilizes to a constant speed until the time P1 before the sheet S reaches the printing position, the control unit 6 causes the recording head 40 to perform a flushing process. After the sheet S reaches the printing position, the control unit 6 causes the recording head 40 to perform an image forming process. Fig.11 In FIG. 1 , the execution time of the flushing process is represented by “Pf”, and the execution time of the image forming process is represented by “Pi”.

[0070] During the flushing period Tf, the control unit 6 causes each of the plurality of nozzles 4N of the recording head 40 to perform a plurality of flushing processes. In addition, the control unit 6 causes each of the plurality of nozzles 4N of the recording head 40 to perform a plurality of meniscus swing processes before each flushing process. Fig.11 In FIG. 1 , the execution period of the meniscus oscillation process is indicated by hatching.

[0071] For example, depending on the situation, the non-ink ejection period from the last execution of the printing task to the current execution of the printing task may be extended. The longer the non-ink ejection period is, the more viscous the ink in the nozzle 4N is. Therefore, the control unit 6 makes the execution period of the meniscus oscillation process longer before the first flushing process in the flushing period Tf than before the second and subsequent flushing processes. In other words, the control unit 6 makes the execution number of the meniscus oscillation process before the first flushing process in the flushing period Tf greater than before the second and subsequent flushing processes.

[0072] In this structure, the meniscus oscillation process is executed more often in the flushing period Tf. The more times the meniscus oscillation process is executed, the more the ink in the nozzle 4N can be suppressed from becoming viscous. On the other hand, when the meniscus oscillation process is executed more often, the ink may overflow from the nozzle 4N when the meniscus oscillation process is executed. If the ink overflows from the nozzle 4N when the meniscus oscillation process is executed, the conveyor belt 3 will be contaminated by the ink.

[0073] In order to suppress this, the control unit 6 controls the meniscus oscillation process before the flushing process (i.e., before the ink is ejected) so that the oscillation amplitude of the meniscus of the ink in the nozzle 4N is small, which will be described in detail later. Thus, in the meniscus oscillation process before the flushing process, it is possible to suppress the ink from overflowing from the nozzle 4N.

[0074] On the other hand, if the image forming process is performed in a state where the ink in the nozzle 4N is viscous, the image quality may be degraded. Therefore, it is necessary to reliably suppress the viscosity of the ink in the nozzle 4N by the meniscus swing process before the image forming process.

[0075] Therefore, the control unit 6 causes the nozzles 4N used in the image forming process of the recording head 40, that is, the nozzles 4N used for printing, to perform the meniscus swing process a plurality of times before each image forming process (that is, before ink ejection).

[0076] In addition, for at least one of the multiple curved liquid surface oscillation processes performed on the nozzle 4N used for printing before the image formation process, the control unit 6 controls in the following manner: compared with other curved liquid surface oscillation processes, the oscillation amplitude of the curved liquid surface of the ink in the nozzle 4N used for printing is larger, and the details will be described later.

[0077] When the recording head 40 performs the meniscus oscillation process, the control unit 6 performs the following Fig.12 The meniscus oscillation process is performed for each nozzle 4N. Fig.12 The processing of the shown flow is performed for each nozzle 4N.

[0078] For example, the flushing process is performed on all the nozzles 4N. In other words, the meniscus oscillation process before the flushing process is performed on all the nozzles 4N.

[0079] On the other hand, the image forming process is not limited to the case where all the nozzles 4N are used. There are multiple types of sheets S used in the printing task. At least the nozzles 4N that are not located in the vertical direction opposite to the sheet S when being conveyed by the conveyor belt 3 are not used for the image forming process. In addition, even the nozzles 4N that are located in the vertical direction opposite to the sheet S when being conveyed by the conveyor belt 3 may not be used for the image forming process depending on the difference in image data to be printed in the printing task.

[0080] Thus, there are nozzles 4N that are not used in the print job. Since the nozzles 4N that are not used in the print job do not eject ink in the image forming process, the meniscus oscillation process before the image forming process is not performed.

[0081] In addition, depending on the image data to be printed in the print job, a single nozzle 4N may perform multiple image forming processes. In this case, when the nozzle 4N performs the image forming process, the meniscus swing process is performed on the nozzle 4N each time.

[0082] When the recording head 40 is caused to perform the meniscus oscillation process, the control unit 6 determines whether the meniscus oscillation process is the meniscus oscillation process before the flushing process (step #1). If it is the meniscus oscillation process before the flushing process, the process proceeds to step #2. If it is not the meniscus oscillation process before the flushing process, that is, if it is the meniscus oscillation process before the image forming process, the process proceeds to step #3.

[0083] When the process proceeds to step #2, the control unit 6 performs a first process to reduce the swing amplitude of the meniscus of the ink 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 swing amplitude of the meniscus of the ink in the nozzle 4N.

[0084] Here, the control unit 6 controls the swing amplitude of the meniscus of the ink in the nozzle 4N by changing the pulse width of the drive signal input to the drive circuit DR. Fig.13 and Fig.14 In the following description, a portion including the drive circuit DR, the piezoelectric element PE, and a wiring portion connecting them is denoted by reference numeral 400 and is referred to as a circuit portion 400 (see Figure 5 ).

[0085] exist Fig.13 and Fig.14In FIG. 1 , the upper diagram shows the pulse width of the driving signal input to the driving circuit DR, and the lower diagram shows the change in the driving voltage applied to the piezoelectric element PE due to the driving signal input to the driving circuit DR. In addition, the displacement of the piezoelectric element PE depends on the driving voltage applied to the piezoelectric element PE. That is, Fig.13 and Fig.14 In the example, the change of the driving voltage applied to the piezoelectric element PE is also the change of the displacement of the piezoelectric element PE. Fig.13 and Fig.14 In FIG. 4 , the time constant of the circuit portion 400 is represented by “T”, and the pulse width of the driving signal is represented by “W”.

[0086] When the recording head 40 is subjected to the meniscus oscillation process before the flushing process, that is, when the swing amplitude of the meniscus of the ink in the nozzle 4N is made small, the control unit 6 performs a first process of making the pulse width of the driving signal input to the driving circuit DR smaller than the time constant of the circuit unit 400. On the other hand, when the recording head 40 is subjected to the meniscus oscillation process before the image forming process, that is, when the swing amplitude of the meniscus of the ink in the nozzle 4N is made large, the control unit 6 performs a second process of making the pulse width of the driving signal input to the driving circuit DR larger than the time constant of the circuit unit 400.

[0087] In this embodiment, the first treatment is performed before the rinse treatment, so that Fig.13 As shown in FIG. 1 , the voltage applied to the piezoelectric element PE is stopped before the driving voltage applied to the piezoelectric element PE reaches a stable state. In other words, the voltage applied to the piezoelectric element PE is stopped before the piezoelectric element PE reaches its maximum displacement. Thus, when the first process is performed, the swing amplitude of the meniscus of the ink in the nozzle 4N is small.

[0088] In addition, by performing the second process before the image forming process, Fig.14 As shown in FIG. 1 , the voltage applied to the piezoelectric element PE is stopped after the driving voltage applied to the piezoelectric element PE reaches a stable state. In other words, the voltage applied to the piezoelectric element PE is stopped after the piezoelectric element PE reaches its maximum displacement. Thus, when the second process is performed, the swing amplitude of the meniscus of the ink in the nozzle 4N is large.

[0089] Here, there is a case where the oscillation amplitude of the meniscus of the ink in the nozzle 4N is relatively large in the meniscus oscillation process before the image forming process (hereinafter sometimes referred to as the meniscus oscillation amplitude). In this case, even if the meniscus oscillation amplitude in the meniscus oscillation process before the flushing process is set to be relatively smaller than the meniscus oscillation amplitude in the meniscus oscillation process before the image forming process, it is still insufficient and the ink may still overflow from the nozzle 4N.

[0090] On the other hand, in the present embodiment, the amplitude of the meniscus oscillation before the flushing process is not simply set to be smaller than the amplitude of the meniscus oscillation before the image forming process. Specifically, when the recording head 40 is subjected to the meniscus oscillation process before the flushing process, the control unit 6 makes the pulse width of the drive signal input to the drive circuit DR smaller than the time constant of the circuit unit 400. Thus, the amplitude of the meniscus oscillation in the meniscus oscillation process before the flushing process can be reliably reduced. As a result, it is possible to suppress the overflow of ink from the nozzle 4N during the meniscus oscillation process before the flushing process. In other words, it is possible to suppress the accidental overflow of ink from the nozzle 4N. If it is possible to suppress the accidental overflow of ink from the nozzle 4N, it is possible to suppress the conveyor belt 3 from being contaminated by ink.

[0091] In addition, in the present embodiment, at least one of the multiple curved liquid surface oscillation processes performed on the nozzle 4N used for printing (i.e., the nozzle 4N used in the image forming process) before the image forming process is controlled in the following manner, that is, the oscillation amplitude of the curved liquid surface of the ink in the nozzle 4N used for printing is larger than that of other curved liquid surface oscillation processes.

[0092] For example, when the recording head 40 is subjected to multiple meniscus oscillation processes before the image forming process, the control unit 6 makes the pulse width of the driving signal input to the driving circuit DR larger than the time constant of the circuit unit 400 for all the multiple meniscus oscillation processes. That is, the nozzle 4N used for printing is subjected to multiple meniscus oscillation processes before the image forming process, and the meniscus of the ink in the nozzle 4N used for printing oscillates relatively greatly in all the multiple meniscus oscillation processes. Thus, it is possible to reliably suppress the ink in the nozzle 4N used for printing from becoming viscous.

[0093] In addition, for example, when the recording head 40 is subjected to multiple meniscus oscillation processes before image formation, the control unit 6 makes the pulse width of the driving signal input to the driving circuit DR larger than the time constant of the circuit unit 400 for the predetermined number of meniscus oscillation processes among the multiple meniscus oscillation processes, and on the other hand, makes the pulse width of the driving signal input to the driving circuit DR smaller than the time constant of the circuit unit 400 for the remaining meniscus oscillation processes other than the predetermined number of times. That is, the multiple meniscus oscillation processes are performed in the nozzle 4N for printing before image formation, but the meniscus of the ink in the nozzle 4N for printing oscillates relatively greatly only when the predetermined number of meniscus oscillation processes are performed among the multiple meniscus oscillation processes. Thus, it is possible to suppress the ink in the nozzle 4N for printing from becoming viscous and suppress the ink from overflowing from the nozzle 4N for printing.

[0094] In addition, the predetermined number of times may be not particularly limited. Alternatively, for a predetermined number of meniscus oscillation processes from the first time among a plurality of meniscus oscillation processes before image formation, the pulse width of the drive signal input to the drive circuit DR may be greater than the time constant of the circuit unit 400.

[0095] The embodiments disclosed this time are illustrative in all respects and are not restrictive. The scope of the present invention is indicated by the scope of claims rather than the description of the embodiments above, and includes all modifications within the meaning and scope equivalent to the scope of claims.

Claims

1. An inkjet recording device comprising: a conveyor belt, a recording head, and a control unit, The conveyor belt conveys the sheet material. The recording head includes: a pressurized chamber for storing ink, a nozzle connected to the pressurized chamber, a displacement element that is deformed by applying voltage and applies pressure to the pressurized chamber, and a drive circuit, wherein the drive circuit switches between starting and stopping the application of voltage to the displacement element based on an input pulse-shaped drive signal, and the recording head ejects the ink from the nozzle by applying pressure to the pressurized chamber to form an image on the sheet. The control unit generates the driving signal and inputs it into the driving circuit. The conveyor belt has a flushing area formed with openings, A plurality of the flushing areas are 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 an image forming process of ejecting the ink toward the sheet, and also causes the recording head to perform a flushing process of ejecting the ink toward the opening of the flushing area that does not overlap with the sheet. Before ejecting the ink, the control unit drives the displacement element by inputting the drive signal for meniscus oscillation processing to the drive circuit, thereby causing the recording head to perform meniscus oscillation processing for oscillating the meniscus of the ink in the nozzle. In the meniscus oscillation process before the flushing process, the control unit makes a pulse width of the drive signal smaller than a time constant of a circuit unit including the drive circuit and the displacement element.

2. The inkjet recording device according to claim 1, It is characterized in that In the meniscus oscillation process before the image forming process, the control unit makes the pulse width of the drive signal larger than the time constant of the circuit unit.

3. The inkjet recording device according to claim 1 or 2, It is characterized in that The control unit causes the recording head to perform the meniscus swing process a plurality of times before the image forming process. The control unit makes the pulse width of the drive signal larger than the time constant of the circuit unit for a specified number of the curved liquid surface oscillation processes among the multiple curved liquid surface oscillation processes before the image formation process, and on the other hand, makes the pulse width of the drive signal smaller than the time constant of the circuit unit for the remaining curved liquid surface oscillation processes other than the specified number of times.

Images