Inkjet recording device

Abstract

To reduce the ink consumption amount in flushing processing while suppressing reduction in the image quality.SOLUTION: When performing printing on a recording medium in a second size larger than a first size after printing on the recording medium in the first size, a control unit, after the recording medium in the first size passes through a position opposing a recording head and before the recording medium in the second size arrives at the position opposing the recording head, causes the recording head to perform preliminary flushing processing of discharging ink toward an opening from a first nozzle that is not set as a target nozzle in printing on the recording medium in the first size and is to be newly set as the target nozzle in printing on the recording medium in the second size.SELECTED DRAWING: Figure 10

Description

[Technical Field]

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

[0002] Conventionally, inkjet recording devices equipped with a recording head have been known. Conventional inkjet recording devices transport a recording medium using a transport belt. Then, ink is ejected from the recording head toward the recording medium being transported by the transport belt to form an image on the recording medium. 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. 2006-159556 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional inkjet recording devices perform a flushing process in which ink is forcibly ejected from all nozzles in the recording head to prevent the nozzles from clogging. By performing the flushing process, it is possible to prevent a deterioration in image quality.

[0005] For example, in the past, an opening area for flushing was formed on the conveyor belt. In the flushing process, ink was ejected toward the opening area. The ejected ink passed through the opening area. This prevented the ink ejected during the flushing process (ink that does not contribute to printing) from adhering to the conveyor belt and recording medium.

[0006] In conventional flushing processes, for example, the same amount of ink is ejected from all nozzles. That is, the same amount of ink is ejected from nozzles that do not contribute to printing as from nozzles that do contribute to printing during the flushing process. Conventional control has the disadvantage of increasing the amount of ink consumed during the flushing process.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide an inkjet recording apparatus that can reduce the amount of ink consumed in flushing processing while suppressing a deterioration in image quality. [Means for solving the problem]

[0008] To achieve the above object, an inkjet recording apparatus according to one aspect of the present invention includes a transport belt that is rotatably supported and transports a recording medium as it rotates, a recording head that is positioned opposite the recording medium and has a plurality of nozzles arranged in a width direction perpendicular to the rotation direction of the transport belt, and that prints on the recording medium by ejecting ink from the nozzles, and a control unit that controls a flushing process performed by the recording head. The transport belt has a flushing area in which openings are formed. The flushing area is arranged at intervals in the rotation direction. The control unit sets the nozzles that face the recording medium as target nozzles when printing on the recording medium, and when the recording head is opposite a flushing area that does not overlap the recording medium, causes the recording head to perform a flushing process in which ink is ejected from the target nozzles toward the openings. When printing on a recording medium of a second size whose width direction is larger than the first size after printing on a recording medium of a first size, the control unit causes the recording head to perform a preliminary flushing process after the recording medium of the first size has passed a position facing the recording head and before the recording medium of the second size has reached a position facing the recording head, in which ink is ejected toward the opening from a first nozzle that was not set as a target nozzle when printing on the recording medium of the first size but is to be newly set as a target nozzle when printing on the recording medium of the second size. [Effects of the Invention]

[0009] The configuration of the present invention can reduce the amount of ink consumed in the flushing process while suppressing degradation in image quality. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an inkjet recording apparatus according to an embodiment of the present invention. [Figure 2] 1 is a plan view of a printing unit of an inkjet printing apparatus according to an embodiment of the present invention; [Figure 3] 1 is a block diagram of an inkjet recording apparatus according to an embodiment of the present invention; [Figure 4] 1 is a schematic diagram of the periphery of a conveyor belt of an inkjet recording apparatus according to an embodiment of the present invention. [Figure 5] FIG. 2 is a plan view of a conveyor belt of the inkjet recording apparatus according to the embodiment of the present invention. [Figure 6] 4 is a diagram showing the positional relationship between a flushing area of ​​a transport belt and a print head of an inkjet printing apparatus according to an embodiment of the present invention; FIG. [Figure 7] 5 is a diagram showing the positional relationship between a flushing area of ​​a transport belt of an inkjet recording apparatus according to an embodiment of the present invention and a sheet of paper. FIG. [Figure 8] FIG. 2 is a diagram showing a state in which a sheet is being transported by a transport belt of the inkjet recording apparatus according to one embodiment of the present invention. [Figure 9] FIG. 2 is a diagram showing target nozzles of an inkjet recording apparatus according to an embodiment of the present invention. [Figure 10] 5A and 5B are diagrams for explaining control of a flushing process and a preliminary flushing process performed in an inkjet recording apparatus according to an embodiment of the present invention. [Figure 11] FIG. 2 is a diagram showing a first nozzle and a second nozzle of an inkjet recording apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The inkjet recording apparatus according to this embodiment will be described below using a printer as an example. For example, the printer prints images on paper as a recording medium. Various types of sheets, such as overhead projector sheets, can also be used as recording media.

[0012] <Overall printer configuration> As shown in FIG. 1, the printer 100 of this embodiment includes a first transport unit 1 and a second transport unit 2. The first transport unit 1 feeds paper S set in a paper feed cassette CA and transports it toward the printing position. In a print job performed by the printer 100, printing is performed on the paper S as it passes through the printing position. The second transport unit 2 transports the printed paper S and discharges it onto an output tray ET.

[0013] For example, although not shown, multiple paper feed cassettes CA are installed in the printer 100. The sizes of paper S set in each of the multiple paper feed cassettes CA may be the same or different. In a print job using the printer 100, one of the multiple paper feed cassettes CA in which the paper S to be used in the print job is set is set as the paper feed source, and the paper S is fed from the paper feed cassette CA that is the paper feed source.

[0014] The first conveying section 1 includes a plurality of conveying roller members including a registration roller pair 11. Each of the plurality of conveying roller members conveys the paper sheet S by rotating. The registration roller pair 11 is composed of a pair of rollers that are pressed against each other. A registration nip is formed between the pair of rollers. The paper sheet S fed from the paper feed cassette CA enters the registration nip. The registration roller pair 11 rotates to convey the paper sheet S that has entered the registration nip toward the belt conveying section 3, which will be described later.

[0015] The pair of registration rollers 11 stops rotating when the leading edge of the sheet S reaches the registration nip. At this point, the transport roller members upstream of the pair of registration rollers 11 in the sheet transport direction are rotating. This corrects the skew of the sheet S.

[0016] The printer 100 includes a belt transport unit 3. The belt transport unit 3 receives and transports the paper S from the first transport unit 1. The belt transport unit 3 includes a transport belt 30. The transport belt 30 is endless and is supported so that it can rotate. The belt transport unit 3 also includes a plurality of tension rollers 301. The plurality of tension rollers 301 are supported so that they can rotate. The transport belt 30 is tensioned by the plurality of tension rollers 301 and rotates.

[0017] One of the multiple tension rollers 301 is connected to a belt motor (not shown) and rotates by the driving force of the belt motor. When the tension roller 301 connected to the belt motor rotates, the conveyor belt 30 rotates, and the other tension rollers 301 rotate accordingly.

[0018] The belt conveying section 3 also includes a suction unit 300. The suction unit 300 is disposed inside the conveying belt 30. The conveying belt 30 has a plurality of suction holes (not shown) formed therein that penetrate the conveying belt 30 in the thickness direction.

[0019] The paper sheet S conveyed from the first conveying section 1 reaches the outer peripheral surface of the conveyor belt 30. The suction unit 300 sucks the paper sheet S through the suction holes. The paper sheet S on the outer peripheral surface of the conveyor belt 30 is adsorbed to the outer peripheral surface of the conveyor belt 30. The conveyor belt 30 rotates while adsorbing and holding the paper sheet S to the outer peripheral surface. In this way, the paper sheet S is conveyed.

[0020] In this way, the belt conveying section 3 conveys the paper S in the rotation direction of the conveyor belt 30. That is, the rotation direction of the conveyor belt 30 is the conveying direction of the paper S (the direction in which the paper S advances).

[0021] The printer 100 includes a recording unit 4. The recording unit 4 is disposed opposite the outer circumferential surface of the conveyor belt 30. When a sheet of paper S is held by suction on the outer circumferential surface of the conveyor belt 30, the sheet of paper S and the recording unit 4 face each other with a gap between them.

[0022] The recording unit 4 includes four line heads 41, each corresponding to one of the colors cyan, magenta, yellow, and black, as shown in Fig. 2. In Fig. 2, the cyan line head 41 is labeled with the symbol "C," the magenta line head 41 is labeled with the symbol "M," the yellow line head 41 is labeled with the symbol "Y," and the black line head 41 is labeled with the symbol "K" to distinguish them from one another.

[0023] Each color line head 41 is made up of 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 rotation direction of the conveyor belt 30 (the transport direction of the paper S). In the following description, the direction perpendicular to the rotation direction of the conveyor belt 30 will simply be referred to as the "width direction."

[0024] The recording heads 40 are arranged at intervals in the vertical direction relative to the outer circumferential surface of the conveyor belt 30. In other words, the recording heads 40 are arranged at positions that face the paper S conveyed by the conveyor belt 30 in the vertical direction. The vertical direction is perpendicular to the rotation direction and width direction of the conveyor belt 30.

[0025] Each recording head 40 has a nozzle surface that faces the conveyor belt 30 (paper S on the conveyor belt 30). The nozzle surface of each recording head 40 has a plurality of nozzles 4N. The plurality of nozzles 4N of each recording head 40 ejects ink of a corresponding color. 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 30. In FIG. 2, the nozzles 4N are indicated by dashed lines. In reality, more nozzles 4N are provided in each recording head 40.

[0026] The recording unit 4 (recording head 40) ejects ink from the nozzles 4N onto the paper S based on image data to be printed in the print job. The ink ejected from the recording unit 4 adheres to the paper S. This causes an image to be printed on the paper S. In other words, the position between the conveyor belt 30 and the recording head 40 is the printing position. In other words, the position vertically facing the nozzle surface (nozzles 4N) of the recording head 40 is the printing position.

[0027] Here, 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, each recording head 40 performs a flushing process. In the flushing process by each recording head 40, ink accumulated in the nozzles 4N is ejected. This prevents clogging. Details will be described later.

[0028] 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 paper S while transporting the paper S toward the decurler 52. The decurler 52 straightens out any curls in the paper S. The decurler 52 transports the paper S after the curl has been straightened toward the second transport section 2.

[0029] As shown in FIG. 3 , 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 executed by the printer 100. In other words, the control unit 6 controls the operations of the first conveyance unit 1, the second conveyance unit 2, the belt conveyance unit 3, the recording unit 4, the drying unit 51, and the decurler 52. In other words, the control unit 6 controls the conveyance of the paper S and the ink ejection of each recording head 40. The control unit 6 also controls the flushing process performed by each recording head 40.

[0030] A resist sensor 61, a paper 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 paper sensor 62, and the belt sensor 63 are shown schematically in FIG.

[0031] The registration sensor 61 has a detection position upstream of the registration nip in the paper transport direction. The registration sensor 61 is, for example, a reflective or transmissive optical sensor. The registration sensor 61 changes its output value depending on whether the paper S is present at the corresponding detection position.

[0032] 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 pair of registration rollers 11 starts to transport the sheet S (the timing at which the pair of registration rollers 11 start to rotate) based on the elapsed time after the arrival of the leading edge of the sheet S is detected at the detection position of the registration sensor 61. Even if the sheet S is skewed, the pair of registration rollers 11 starts to transport the sheet S with the skew corrected.

[0033] The paper sensor 62 has a detection position between the printing position of the line head 41 that is furthest upstream in the paper transport direction among the multiple line heads 41 and the registration nip. The paper sensor 62 changes its output value depending on whether or not paper S is present at the corresponding detection position. The paper sensor 62 may be a CIS (Contact Image Sensor), or a reflective or transmissive optical sensor. For example, a CIS is used as the paper sensor 62.

[0034] The control unit 6 detects the arrival of the leading edge of the paper S at the detection position of the paper sensor 62 and the passing of the trailing edge of the paper S based on the output value of the paper sensor 62. The control unit 6 determines the timing of ejecting ink onto the paper S being transported by the transport belt 30 based on the output value of the paper sensor 62. Note that the timing of ejecting ink onto the paper S being transported by the transport belt 30 may also be determined based on the elapsed time since the pair of registration rollers 11 started transporting the paper S.

[0035] The control unit 6 also measures the paper passage time from when the leading edge of the paper S reaches the detection position of the paper sensor 62 until the trailing edge of the paper S passes the detection position of the paper sensor 62. The paper passage time at the detection position of the paper sensor 62 varies depending on the size of the paper S in the transport direction. Therefore, the control unit 6 recognizes the size of the paper S in the transport direction transported by the conveyor belt 30 based on the paper passage time. This allows the control unit 6 to recognize the size of the paper S in the transport direction even if the paper S transported by the conveyor belt 30 is an irregular size.

[0036] Furthermore, the control unit 6 detects misalignment (skew) of the paper S based on the output value of the paper sensor 62 (read data obtained by reading by the paper sensor 62). For example, there are cases where misalignment of the paper S occurs after the pair of registration rollers 11 starts transporting the paper S. In this case, the misalignment of the paper S is detected by the control unit 6.

[0037] It is also possible to install a plurality of paper sensors 62. For example, two paper sensors 62 may be installed.

[0038] The belt sensor 63 is a sensor for detecting a predetermined reference position (home position) of the conveyor belt 30. A predetermined mark is provided at the reference position of the conveyor belt 30. This makes it possible to detect the reference position of the conveyor belt 30 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 or reflective optical sensor.

[0039] The control unit 6 detects the reference position of the conveyor belt 30 based on the output value of the belt sensor 63. In other words, the control unit 6 detects the position in the circumferential direction of the flushing area 31 (opening 310), which will be described later, based on the output value of the belt sensor 63.

[0040] As shown in FIG. 3 , the printer 100 also includes a storage unit 7. The storage unit 7 includes storage devices such as ROM, RAM, HDD, and SSD. 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.

[0041] 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.

[0042] 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. For example, print data (data including PDL data, etc.) of a 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 various setting data related to printing, such as the size of the paper S to be used in the print job.

[0043] <Conveyor belt configuration> As shown in FIG. 5, the conveyor belt 30 has a flushing area 31. In FIG. 5, the flushing area 31 is surrounded by a dashed line. The flushing area 31 is an area in which openings 310 are formed, penetrating the conveyor belt 30 in the thickness direction. In the flushing process, ink is ejected from each recording head 40, and the ejected ink passes through the openings 310 and reaches a receiving section 302 (see FIG. 4) arranged inside the conveyor belt 30. The ink in the receiving section 302 is collected and discarded.

[0044] The conveyor belt 30 is provided with a plurality of flushing areas 31. The plurality of flushing areas 31 are arranged at predetermined intervals from one another in the rotation direction of the conveyor belt 30.

[0045] Each flushing area 31 has a plurality (the same number) of openings 310. The openings 310 are elongated holes that are long in the width direction of the conveyor belt 30. The shape of the openings 310 (the shape when viewed from the thickness direction of the conveyor belt 30) is not particularly limited, and may be rectangular, circular, elliptical, or oval.

[0046] For example, each flushing area 31 includes two rows of openings. The rows of openings are rows of openings 310 that are arranged at equal intervals in the width direction of the conveyor belt 30. One row of openings has six openings 310, and the other row of openings has five openings 310. The center positions of both rows of openings in the width direction coincide with the center position of the conveyor belt 30 in the width direction. That is, the multiple openings 310 in each flushing area 31 are arranged in a staggered pattern in the width direction. The length of the openings 310 in the width direction (opening width) is greater than the distance between adjacent openings 310 in the width direction.

[0047] 6, 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 31. Specifically, the width W2 corresponds to the widthwise length from the end of the opening 310 located on the furthest side in the width direction to the end of the opening 310 located on the other side in the width direction.

[0048] As a result, by rotating the conveyor belt 30, the multiple nozzles 4N of each recording head 40 can be made to face up and down to at least one of the openings 310. As a result, in the flushing process, ink that does not contribute to printing is ejected from each nozzle 4N, but the ink can be controlled to pass through the opening 310 (the ink can be controlled so as not to adhere to the conveyor belt 30 and the paper S).

[0049] <Paper transport> When printing is continuously performed on multiple sheets of paper S of the same size that are transported sequentially by the transport belt 30, the control unit 6 controls the paper spacing (the width in the transport direction of the area between the rear end of the preceding sheet S and the front end of the following sheet S), which is the distance in the transport direction between the rear end of the preceding sheet S and the front end of the following sheet S (the sheet S transported after the preceding sheet S), to be constant. That is, in this case, the control unit 6 controls the multiple sheets of paper S to be transported at constant intervals (maintaining a constant interval between each of the multiple sheets of paper S). Continuous printing on multiple sheets of paper S of the same size that are transported sequentially at intervals by the transport belt 30 corresponds to "continuous printing," and will be simply referred to as "continuous printing" in the following explanation.

[0050] Here, during continuous printing, a flushing process is performed in each recording head 40. The control unit 6 controls the flushing process by each recording head 40. The ink ejected during the flushing process does not contribute to printing. For this reason, the control unit 6 controls the ink ejected during the flushing process so that it passes through the opening 310. In other words, the control unit 6 ejects ink from each nozzle 4N at a timing when the nozzle 4N faces an opening 310 that does not overlap with the paper S.

[0051] To perform this control, the control unit 6 recognizes the size of the paper S transported by the conveyor belt 30. The control unit 6 also detects the reference position of the conveyor belt 30. The control unit 6 then measures the timing to start transporting the paper S from the registration roller pair 11 to the conveyor belt 30 so that the flushing area 31 appears between the papers at regular intervals. The control unit 6 changes the timing to start transporting the paper S from the registration roller pair 11 to the conveyor belt 30 depending on the size of the paper S transported by the conveyor belt 30. Before executing a print job, the control unit 6 recognizes the size of the paper S to be used in the print job (paper S transported by the conveyor belt 30) based on the print data of the print job to be executed this time.

[0052] FIG. 7 shows the positional relationship between the sheet S transported by the transport belt 30 and the flushing area 31. In FIG. 7, the rotation direction of the transport belt 30 (the transport direction of the sheet S) is from right to left on the paper surface. In FIG. 7, the flushing area 31 is shown with a hatched pattern, and the opening 310 is omitted. Also, in FIG. 7, the symbol for the sheet S is omitted, and instead the size of the sheet S is indicated within the figure representing the sheet S. For convenience, FIG. 7 illustrates sheets S of multiple different sizes together.

[0053] Here, a detailed description will be given with reference to Fig. 8, focusing on A4 portrait size. The rotation direction of the conveyor belt 30 in Fig. 8 (the conveyance direction of the paper S) is from bottom to top on the paper surface. For convenience, Fig. 8 shows three sheets of paper S, and the reference numerals of the respective sheets of paper S are assigned numbers 1 to 3 indicating the conveyance order.

[0054] When the size of the sheet S is A4 portrait size, the flushing area 31 does not appear between the first sheet S1 and the second sheet S2. The flushing area 31 appears between the second sheet S2 and the third sheet S3. The flushing area 31 between the sheets S2 and S3 does not overlap with either the sheets S2 or S3 at all. Although not shown, the flushing area 31 does not appear between the third sheet S3 and the fourth sheet S, but the flushing area 31 appears between the fourth sheet S and the fifth sheet S.

[0055] <Flushing process> The following describes the control of the flushing process by each recording head 40, focusing on one recording head 40. The same control as for that recording head 40 is also performed for the other recording heads 40. Therefore, a description of the control of the other recording heads 40 will be omitted.

[0056] The control unit 6 sets the control period for the flushing process in continuous printing to the period from when the leading edge of the paper S to be printed first (first paper S) reaches the printing position (position facing the recording head 40) of the recording head 40 until the paper S to be printed last (final paper S) in the continuous printing passes the printing position (position facing the recording head 40) of the recording head 40. Then, the control unit 6 causes the target nozzle 4Nt (see FIG. 9) of the multiple nozzles 4N of the recording head 40 to perform the flushing process during the set control period.

[0057] Here, the target nozzle 4Nt will be described in detail. The control unit 6 sets a target of the flushing process among the multiple nozzles 4N. The set nozzle 4N is the target nozzle 4Nt. During the control period of the flushing process, the control unit 6 performs a process of ejecting ink from the target nozzle 4Nt as the flushing process.

[0058] When setting the target nozzle 4Nt, the control unit 6 recognizes the size of the paper S to be used in continuous printing (paper S transported by the transport belt 30). Then, based on the size of the paper S in the width direction, one of the multiple nozzles 4N is set as the target nozzle 4Nt.

[0059] For example, suppose the paper S used in continuous printing and the recording head 40 (plurality of nozzles 4N) have the positional relationship shown in FIG. 9. In this case, the control unit 6 sets the nozzles 4N located in an area inside the width direction of a range R1 corresponding to the width direction size of the paper S used in continuous printing as the target nozzles 4Nt. In other words, the control unit 6 sets the nozzles 4N that vertically face the paper S when printing on the paper S as the target nozzles 4Nt. The target nozzles 4Nt are nozzles 4N that contribute to printing on the paper S. On the other hand, nozzles 4N located in an area outside the width direction of range R1 (nozzles 4N that do not vertically face the paper S when printing on the paper S) do not contribute to printing, and are not set as the target nozzles 4Nt.

[0060] During continuous printing (during the control period of the flushing process), when the recording head 40 faces a flushing area 31 that does not overlap with the paper S at all, the control unit 6 causes the recording head 40 to perform a flushing process in which ink is ejected from the target nozzles 4Nt toward the openings 310. Hereinafter, the flushing area 31 that does not overlap with the paper S at all will be referred to as a non-overlapping flushing area 31 to distinguish it from other flushing areas 31.

[0061] In the example shown in FIG. 8, if the first sheet of continuous printing is sheet S1, the start point of the control period is the time when the leading edge of sheet S1 reaches the printing position of the recording head 40. In the example shown in FIG. 8, the flushing process is performed when the non-overlapping flushing region 31 located between sheets S2 and S3 faces the recording head 40. Although not shown, a non-overlapping flushing region 31 also appears between the fourth sheet S and the fifth sheet S, and the flushing process is performed when this non-overlapping flushing region 31 faces the recording head 40. Thereafter, a non-overlapping flushing region 31 appears between an even-numbered sheet S and an odd-numbered sheet S, and the flushing process is performed when this non-overlapping flushing region 31 faces the recording head 40. In other words, each time the non-overlapping flushing region 31 located between sheets S transported by the transport belt 30 reaches a position facing the recording head 40, the flushing process is performed once.

[0062] During the control period of the flushing process, even if a flushing area 31 that partially overlaps with paper S (a flushing area 31 that only partially overlaps with paper S) faces the recording head 40, the control unit 6 does not cause the recording head 40 to perform the flushing process. In the example shown in Fig. 8, even if the flushing area 31 that overlaps with paper S1, the flushing area 31 that overlaps with paper S2, and the flushing area 31 that overlaps with paper S3 face the recording head 40, the flushing process is not performed.

[0063] An example of control of the flushing process (including the preliminary flushing process described below) is shown in Figure 10. As shown in Figure 10, during a period Tn in which the non-overlapping flushing region 31 faces the recording head 40, the control unit 6 causes each of the target nozzles 4Nt to eject ink for n1 lines (eject ink n1 times). Each time the non-overlapping flushing region 31 faces the recording head 40 (each time the period Tn arrives), the control unit 6 causes each of the target nozzles 4Nt to eject ink for n1 lines as one flushing process. For example, n1 lines is 30 lines.

[0064] When the control unit 6 receives a request to execute a print job, the control unit 6 adds the received print job to a queue. If there are multiple print jobs in the queue, the control unit 6 executes the multiple print jobs in the order in which they were received.

[0065] If the size of paper S used in a first print job that is Nth in the received order and a second print job that is N+1th in the received order are the same, the control unit 6 executes the first print job and the second print job as a single job. In this case, the control unit 6 sets the control period for the flushing process to the period from when the first paper S of the first print job reaches the printing position of the recording head 40 until the last paper S of the second print job passes the printing position of the recording head 40.

[0066] <Preliminary flushing process> Below, the control of the preliminary flushing process by each recording head 40 will be explained, focusing on one recording head 40. The same control as that of the recording head 40 is also performed on the other recording heads 40. Therefore, the explanation of the control of the other recording heads 40 will be omitted.

[0067] When the size of the first sheet S, which is the sheet S that is transported first by the transport belt 30 and printed on, differs from the size of the second sheet S, which is the sheet S that is transported next to the first sheet S and printed on, the control unit 6 performs a switching process to switch the paper feed source. This increases the gap between the first sheet S and the second sheet S. As a result, the viscosity of the ink in the nozzle 4N increases before printing on the second sheet S, causing clogging.

[0068] For example, the sizes of the sheets S used in a first print job that is Nth in the received order and a second print job that is N+1th in the received order may differ. In this case, the control unit 6 performs a switching process after feeding the final sheet S (first sheet S) of the first print job, and starts feeding the first sheet S (second sheet S) of the second print job. This increases the gap between the first sheet S and the second sheet S.

[0069] If the width of the second paper S is larger than that of the first paper S, the nozzles 4N that were not used when printing the first paper S are used when printing the second paper S. Because the nozzles 4N have not been used for a long time, the viscosity of the ink inside the nozzles 4N is likely to become high. For this reason, before printing the second paper S, it is preferable to perform a process to forcibly eject ink from the nozzles 4N that were not used when printing the first paper S (i.e., a flushing process).

[0070] Therefore, when printing on a sheet S (hereinafter referred to as the first sheet S) having a first width size and then on a sheet S (hereinafter referred to as the second sheet S) having a width size larger than the first size, the control unit 6 causes the recording head 40 to perform a preliminary flushing process after the first sheet S has passed the printing position of the recording head 40 (a position facing the recording head 40) and before the second sheet S reaches the printing position of the recording head 40, in which ink is ejected toward the opening 310 from nozzle 4N (corresponding to the "first nozzle") that was not set as the target nozzle 4Nt when printing on the first sheet S but will be newly set as the target nozzle 4Nt when printing on the second sheet S. Hereinafter, the nozzle 4N corresponding to the "first nozzle" will be given the reference numeral 401 and will be referred to as the first nozzle 401.

[0071] Furthermore, as a preliminary flushing process, the control unit 6 causes the recording head 40 to further perform a process of ejecting ink toward the opening 310 from the nozzle 4N (corresponding to the "second nozzle") that was set as the target nozzle 4Nt when printing on the first paper S. Hereinafter, the nozzle 4N that corresponds to the "second nozzle" will be assigned the reference symbol 402 and referred to as the second nozzle 402.

[0072] For example, when the flushing area 31 closest to the second paper S and downstream of the second paper S in the transport direction faces the recording head 40, the control unit 6 causes the recording head 40 to perform a preliminary flushing process. Hereinafter, the flushing area 31 closest to the second paper S and downstream of the second paper S in the transport direction will be referred to as the preliminary flushing area 31 to distinguish it from other flushing areas 31. The preliminary flushing area 31 is a flushing area 31 that does not overlap with the paper S at all.

[0073] In the example shown in Fig. 8, the second sheet S is assumed to be sheet S1. In this case, the flushing area 31 shown directly above sheet S1 is the preliminary flushing area 31. Although not shown, a flushing area 31 further downstream in the sheet transport direction than the flushing area 31 shown directly above sheet S1 in Fig. 8 may also be set as the preliminary flushing area 31.

[0074] Here, the first nozzle 401 and the second nozzle 402 will be specifically described with reference to Fig. 11. In Fig. 11, the first sheet S is given the symbol Sa, and the second sheet S is given the symbol Sb to distinguish them.

[0075] The first paper Sa in Fig. 11 is a first-size paper S, and is the same size as the paper S shown in Fig. 9. That is, when printing on the first paper Sa, the nozzles 4N located in an area inside the width direction of a range R1 that corresponds to the width direction size of the first paper Sa are set as target nozzles 4Nt (see Fig. 9). On the other hand, when printing on the first paper Sa, the nozzles 4N located in an area outside the width direction of range R1 are not set as target nozzles 4Nt.

[0076] 11 is a second-size sheet of paper S that is larger in the width direction than the first size. When printing on the second sheet of paper Sb, the nozzles 4N located in the area inside the width direction of range R2, which corresponds to the width direction size of the second sheet of paper Sb, are set as target nozzles 4Nt. On the other hand, when printing on the second sheet of paper Sb, the nozzles 4N located in the area outside the width direction of range R2 are not set as target nozzles 4Nt.

[0077] In the example shown in Fig. 11, the switching process is performed after the feeding process of the first sheet Sa. As a result, the gap between the first sheet Sa and the second sheet Sb becomes larger. Note that, for convenience, the reference numeral 4Nt is omitted in Fig. 11.

[0078] In the example shown in Figure 11, when printing on the first paper Sa, the nozzles 4N located in the area outside the range R1 in the width direction are not set as target nozzles 4Nt. When printing on the second paper Sb, the nozzles 4N located in the area inside the range R2 in the width direction are set as target nozzles 4Nt. Therefore, in the example shown in Figure 11, the nozzles 4N located in the area outside the range R1 in the width direction but inside the range R2 in the width direction are set as first nozzles 401. Furthermore, the nozzles 4N located in the area inside the range R1 in the width direction are set as second nozzles 402.

[0079] When the preliminary flushing area 31 faces the recording head 40, the control unit 6 causes the recording head 40 to perform a preliminary flushing process in which a first amount of ink is ejected from each of the first nozzles 401. Furthermore, at this time, the control unit 6 causes the recording head 40 to perform a preliminary flushing process in which a second amount of ink, which is less than the first amount, is ejected from each of the second nozzles 402.

[0080] The first amount is greater than the second amount. That is, the amount of ink ejected from each of the first nozzles 401 during the preliminary flushing process is greater than the amount of ink ejected from each of the second nozzles 402 during the preliminary flushing process. Note that the amount of ink ejected from each of the second nozzles 402 during the preliminary flushing process is equal to or greater than the amount of ink ejected from each of the target nozzles 4Nt during the normal flushing process.

[0081] 10, during a period T0 in which the preliminary flushing region 31 faces the recording head 40, the control unit 6 causes each of the first nozzles 401 to eject ink for n2 lines (eject ink n2 times), which is more than the number of ink ejection lines in the normal flushing process of the target nozzle 4Nt. For example, n2 lines is 100 lines.

[0082] Furthermore, during a period T0 in which the preliminary flushing region 31 faces the recording head 40, the control unit 6 causes each of the second nozzles 402 to eject ink for n3 lines (eject ink n3 times), which is greater than the number of ink ejection lines in the normal flushing process of the target nozzle 4Nt. For example, n3 lines is 50 lines.

[0083] In this embodiment, as described above, when printing on a second paper Sb (paper S of a second size that is wider than the first size) after printing on a first paper Sa (paper S of a first size), the control unit 6 causes the recording head 40 to perform a preliminary flushing process in which ink is ejected toward the opening 310 from the first nozzle 401, which was not set as the target nozzle 4Nt when printing on the first paper Sa but will be newly set as the target nozzle 4Nt when printing on the second paper Sb, after the first paper Sa has passed the printing position of the recording head 40 (the position facing the recording head 40) and before the second paper Sb reaches the printing position of the recording head 40.

[0084] Here, the first nozzle 401 is a nozzle 4N that does not contribute to printing during continuous printing. Therefore, even if the nozzle 4N corresponding to the first nozzle 401 is not set as the target nozzle 4Nt (even if the flushing process for that nozzle 4N is not performed), it does not affect image quality. In this way, by controlling so that the flushing process for the nozzle 4N that does not contribute to printing is not performed, the amount of ink consumed in the flushing process can be reduced.

[0085] On the other hand, the first nozzle 401 is the nozzle 4N that will contribute to printing during the next print. Therefore, if the viscosity of the ink in the nozzle 4N corresponding to the first nozzle 401 is high, it will affect the image quality during the next print. Therefore, before the next print, a preliminary flushing process is performed in which ink is forcibly ejected from the first nozzle 401. This makes it possible to prevent clogging of the first nozzle 401 during the next print even if the flushing process for the first nozzle 401 is not performed during continuous printing. In other words, it is possible to prevent a decrease in image quality during the next print.

[0086] As a result, in this embodiment, it is possible to reduce the amount of ink consumed in the flushing process while suppressing degradation in image quality.

[0087] Furthermore, in this embodiment, as described above, the control unit 6 further causes the recording head 40 to perform a preliminary flushing process in which ink is ejected from the second nozzles 402, which were set as the target nozzles 4Nt when printing on the first paper sheet Sa, toward the openings 310. This configuration can prevent clogging of the second nozzles 402. As a result, it is possible to further prevent a decrease in image quality in the next print.

[0088] Furthermore, in this embodiment, as described above, the amount of ink ejected from each of the first nozzles 401 during the preliminary flushing process is greater than the amount of ink ejected from each of the second nozzles 402 during the preliminary flushing process. Here, the first nozzles 401 are not used in continuous printing, and therefore are more susceptible to clogging than the second nozzles 402, which are used in continuous printing. However, the amount of ink ejected from the first nozzles 401 during the preliminary flushing process is greater than that of the second nozzles 402. This makes it possible to reliably prevent clogging of the first nozzles 401.

[0089] Furthermore, in this embodiment, as described above, the amount of ink ejected from each of the second nozzles 402 during the preliminary flushing process is equal to or greater than the amount of ink ejected from each of the target nozzles 4Nt during the normal flushing process. In other words, the amount of ink ejected from each of the first nozzles 401 during the preliminary flushing process is greater than the amount of ink ejected from each of the target nozzles 4Nt during the normal flushing process. This more reliably prevents clogging of the first nozzles 401.

[0090] Here, when printing is performed on second paper Sb (paper S of a second size) after continuous printing on multiple first paper Sa (paper S of a first size) conveyed sequentially by the conveyor belt 30, the more first paper Sa used in the continuous printing (the number of prints in the continuous printing), the longer the time that the first nozzles 401 are unused. Note that a capping process is performed to cover the nozzle surface of the recording head 40 with a cap, which prevents the nozzle surface of the recording head 40 (the ink in the nozzles 4N) from drying out. However, the capping process is not performed on the recording head 40 while printing is in progress. Therefore, the longer the time of continuous printing, the longer the time that the first nozzles 401 are unused, and the higher the viscosity of the ink in the first nozzles 401 (the more likely it is that the first nozzles 401 will dry out).

[0091] Therefore, in this embodiment, when printing is performed on second paper Sb after continuous printing on multiple first paper Sa transported sequentially by the transport belt 30, the control unit 6 recognizes the number of prints in the continuous printing, and the greater the recognized number of prints, the greater the amount of ink ejected from each of the first nozzles 401 in the preliminary flushing process. This makes it possible to suppress degradation in image quality even when using paper S that is larger in width than the paper S used in the continuous printing in the printing following continuous printing with a large number of prints.

[0092] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims rather than the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0093] 4N nozzle 4Nt target nozzle 6 Control Unit 30 conveyor belt 31 Flushing Area 40 Recording head 100 Printers (inkjet recording devices) 310 Aperture 401 No. 1 nozzle 402 Second Nozzle S Paper (recording medium)

Claims

1. a conveyor belt that is supported so as to be rotatable and that conveys a recording medium by rotating; a recording head that is disposed in a position facing the recording medium, has a plurality of nozzles arranged in a width direction perpendicular to the rotation direction of the conveyor belt, and prints on the recording medium by ejecting ink from the nozzles; a control unit that controls a flushing process by the recording head, the conveyor belt has a flushing area in which an opening is formed, The flushing area is a plurality of areas arranged at intervals in the circumferential direction, the control unit sets the nozzles that face the recording medium when printing on the recording medium as target nozzles, and when the flushing area that does not overlap the recording medium faces the recording head, causes the recording head to perform the flushing process of ejecting ink from the target nozzles toward the openings, During continuous printing, in which printing is continuously performed on a plurality of sheets of the same size of the recording medium that are sequentially conveyed by the conveyance belt, when the recording head faces the flushing area that does not overlap the recording medium at all, the control unit causes the recording head to perform the flushing process, when printing is performed on a recording medium of a second size larger than the first size in the width direction after printing on the recording medium of a first size in the width direction, the control unit causes the recording head to perform a preliminary flushing process after the recording medium of the first size has passed a position facing the recording head and before the recording medium of the second size has reached a position facing the recording head, in which ink is ejected toward the opening from a first nozzle that was not set as the target nozzle when printing on the recording medium of the first size but is to be newly set as the target nozzle when printing on the recording medium of the second size, the control unit further causes the recording head to perform, as the preliminary flushing process, a process of ejecting ink from second nozzles that have been set as target nozzles when printing on the recording medium of the first size toward the openings, an inkjet recording device, wherein when printing is performed on the recording medium of the second size following the continuous printing on the recording medium of the first size, the control unit recognizes the number of prints in the continuous printing, and the greater the number of prints, the greater the individual amount of ink ejected from the first nozzles in the preliminary flushing process.

2. 2. The inkjet recording apparatus according to claim 1, wherein the amount of ink ejected from each of the first nozzles in the preliminary flushing process is greater than the amount of ink ejected from each of the second nozzles in the preliminary flushing process.

3. 3. The inkjet recording apparatus according to claim 1, wherein the amount of ink ejected from each of the second nozzles in the preliminary flushing process is equal to or greater than the amount of ink ejected from each of the target nozzles in the flushing process.

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