Inkjet recording apparatus

Abstract

To reduce the ink consumption amount in flushing processing while suppressing reduction in the image quality.SOLUTION: A control unit, during continuous printing on a plurality of recording media, every time a flushing region that is not superimposed on the recording medium opposes a recording head, causes the recording head to perform flushing processing, but does not cause the recording head to perform the flushing processing even when the flushing region that is at least partially superimposed on the recording medium opposes the recording head. The control unit increases the individual ink discharge amount of the nozzle in the present flushing processing as a period from the last flushing processing to the present flushing processing is longer.SELECTED DRAWING: Figure 10

Description

Technical Field

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

Background Art

[0002] Conventionally, an inkjet recording apparatus including a recording head has been known. A conventional inkjet recording apparatus conveys a recording medium using a conveyance belt. Then, ink is ejected from the recording head toward the recording medium conveyed by the conveyance belt to form an image on the recording medium. Such an inkjet recording apparatus is disclosed in, for example, Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to suppress clogging of the nozzles of the recording head, a conventional inkjet recording apparatus performs a flushing process in which ink is forcibly ejected from all the nozzles. By performing the flushing process, a decrease in image quality can be suppressed.

[0005] For example, conventionally, an opening area for flushing is formed in the conveyance belt. In the flushing process, ink is ejected toward the opening area. The ejected ink passes through the opening area. Thereby, it is possible to suppress the adhesion of the ink ejected in the flushing process (ink that does not contribute to printing) to the conveyance belt and the recording medium.

[0006] A plurality of opening areas are arranged at regular intervals in the conveyance direction on the conveyance belt. When the size of the paper (conveyed paper) in the conveyance direction for continuous printing on a plurality of sheets of paper sequentially conveyed by the conveyance belt is smaller than the interval, by controlling so that the paper is arranged between the opening areas, the execution frequency of the flushing process can be increased. That is, when the opening area reaches the printing position of the recording head, the flushing process can be performed each time.

[0007] However, the sizes of the papers used for continuous printing vary. There are cases where the size of the paper in the conveyance direction for continuous printing is larger than the interval. In this case, one of the opening areas overlaps with the paper. When the flushing process is performed on the opening area that overlaps with the paper, ink that does not contribute to printing adheres to the paper (the paper gets dirty). Therefore, the flushing process for the opening area that overlaps with the paper is not performed.

[0008] For this reason, depending on the size of the paper used for continuous printing, the period from the previous flushing process to the current one (hereafter referred to as the non - flushing period) becomes long. The longer the non - flushing period, the more the ink in the nozzles dries out, and clogging is more likely to occur.

[0009] To solve such inconveniences, the discharge amount of each individual ink of the nozzles in one flushing process may be increased. However, when the non - flushing period can be shortened in continuous printing (when it is possible to control so that the paper is arranged between the opening areas), there is no need to increase the discharge amount of each individual ink of the nozzles in one flushing process. Therefore, when the discharge amount of each individual ink of the nozzles in one flushing process is increased, ink is wasted in the flushing process of continuous printing where the non - flushing period can be shortened.

[0010] The present invention has been made to solve the above problems, and an object thereof is to provide an inkjet recording apparatus capable of reducing the consumption amount of ink in the flushing process while suppressing a decrease in image quality.

Means for Solving the Problem

[0011] To achieve the above object, an inkjet recording apparatus according to an aspect of the present invention includes a conveyance belt that is rotatably supported and conveys a recording medium by rotating, a recording head that is disposed at a position facing the recording medium and has a plurality of nozzles arranged in a width direction orthogonal to the circumferential direction of the conveyance belt, and performs printing on the recording medium by discharging ink from the nozzles, and a control unit that controls a flushing process performed by the recording head. The conveyance belt has a flushing area in which an opening is formed. A plurality of flushing areas are arranged at predetermined intervals from each other in the circumferential direction. During continuous printing on a plurality of recording media sequentially conveyed by the conveyance belt, the control unit causes the recording head to perform a process of discharging ink from the nozzles toward the opening as a flushing process each time a non-overlapping flushing area, which is a flushing area that does not overlap with the recording medium, faces the recording head. On the other hand, even when an overlapping flushing area, which is a flushing area where at least a part overlaps with the recording medium, faces the recording head, the control unit does not cause the recording head to perform a flushing process. When causing the recording head to perform a flushing process during continuous printing, the control unit increases the discharge amount of each individual ink from the nozzles in the current flushing process as the period from the previous flushing process to the current flushing process is longer.

Advantages of the Invention

[0012] In the configuration of the present invention, it is possible to reduce the consumption amount of ink in the flushing process while suppressing a decrease in image quality.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0014] Hereinafter, an inkjet recording apparatus according to the present embodiment will be described by taking a printer as an example. For example, the printer prints an image on a sheet of paper as a recording medium. Various sheets such as OHP sheets can also be used as the recording medium.

[0015] <Overall Configuration of Printer> As shown in FIG. 1, the printer 100 of the present embodiment includes a first conveyance unit 1 and a second conveyance unit 2. The first conveyance unit 1 feeds the paper S set in the paper feed cassette CA and conveys it toward the printing position. In the printing job by the printer 100, printing is performed on the paper S passing through the printing position. The second conveyance unit 2 conveys the printed paper S and discharges it to the discharge tray ET.

[0016] For example, although not shown, a plurality of paper feed cassettes CA are attached to the printer 100. The sizes of the papers S set in the plurality of paper feed cassettes CA may be the same as or different from each other. In the printing job by the printer 100, among the plurality of paper feed cassettes CA, the paper feed cassette CA in which the paper S used in the printing job is set is set as the paper feed source, and the paper S is fed from the paper feed cassette CA of the paper feed source.

[0017] The first conveyance unit 1 includes a plurality of conveyance roller members including a registration roller pair 11 (corresponding to a “registration unit”). Each of the plurality of conveyance roller members conveys the paper S by rotating.

[0018] The registration roller pair 11 conveys the paper S at a position upstream in the conveyance direction from the installation position of the conveyance belt 30 described later. In the following description, the conveyance position of the paper S by the registration roller pair 11 (the installation position of the registration roller pair 11) is referred to as the registration position. The registration roller pair 11 is composed of a pair of rollers that are in pressure contact with each other. A registration nip is formed between the pair of rollers and is arranged at the registration position.

[0019] The paper S fed from the paper feed cassette CA enters the registration nip. The registration roller pair 11 rotates to convey the paper S that has entered the registration nip toward the belt conveyance unit 3 described later.

[0020] Note that when the leading edge of the sheet S reaches the registration nip (registration position), the registration roller pair 11 stops rotating. At this time, the conveying roller member on the upstream side in the sheet conveying direction from the registration roller pair 11 is rotating. Thereby, the skew of the sheet S is corrected.

[0021] The printer 100 includes a belt conveyance unit 3. The belt conveyance unit 3 receives and conveys the sheet S from the first conveyance unit 1. The belt conveyance unit 3 includes a conveyance belt 30. The conveyance belt 30 is endless and is supported so as to be rotatable. Further, the belt conveyance unit 3 includes a plurality of tension rollers 301. The plurality of tension rollers 301 are rotatably supported. The conveyance belt 30 is stretched by the plurality of tension rollers 301 and rotates.

[0022] One of the plurality of tension rollers 301 is connected to a belt motor (not shown), and the driving force of the belt motor is transmitted thereto to rotate. When the tension roller 301 connected to the belt motor rotates, the conveyance belt 30 rotates, and the other tension rollers 301 rotate in a driven manner.

[0023] Further, the belt conveyance unit 3 includes a suction unit 300. The suction unit 300 is disposed inside the conveyance belt 30. A plurality of suction holes (not shown) penetrating in the thickness direction are formed in the conveyance belt 30.

[0024] The sheet S conveyed from the first conveyance unit 1 reaches the outer peripheral surface of the conveyance belt 30. The suction unit 300 sucks the sheet S through the suction holes. The sheet S on the outer peripheral surface of the conveyance belt 30 is adsorbed to the outer peripheral surface of the conveyance belt 30. The conveyance belt 30 rotates while adsorbing and holding the sheet S on the outer peripheral surface. Thereby, the sheet S is conveyed.

[0025] In this way, the belt conveyance unit 3 conveys the sheet S in the circumferential direction of the conveyance belt 30. That is, the circumferential direction of the conveyance belt 30 is the conveyance direction of the sheet S (the direction in which the sheet S advances).

[0026] Printer 100 includes a recording unit 4. The recording unit 4 is disposed opposite to the outer peripheral surface of the conveyance belt 30. When a sheet S is adsorbed and held on the outer peripheral surface of the conveyance belt 30, the sheet S and the recording unit 4 face each other with a gap therebetween.

[0027] As shown in FIG. 2, the recording unit 4 includes four line heads 41 corresponding to cyan, magenta, yellow, and black colors respectively. 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" for distinction.

[0028] Each color line head 41 is composed of a plurality (for example, three) of recording heads 40. For example, the plurality of recording heads 40 of each color are arranged in a staggered pattern in a direction orthogonal to the circumferential direction (the conveyance direction of the sheet S) of the conveyance belt 30. In the following description, the direction orthogonal to the circumferential direction of the conveyance belt 30 is simply referred to as the "width direction".

[0029] Each recording head 40 is arranged at an interval in the vertical direction with respect to the outer peripheral surface of the conveyance belt 30. In other words, each recording head 40 is arranged at a position facing the sheet S conveyed by the conveyance belt 30 in the vertical direction. Note that the vertical direction is a direction orthogonal to the circumferential direction and the width direction of the conveyance belt 30.

[0030] Each recording head 40 has a nozzle surface facing the conveyance belt 30 (the sheet S on the conveyance 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 discharge the corresponding color ink. 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 conveyance belt 30. In FIG. 2, the nozzles 4N are shown by dashed lines. Actually, more nozzles 4N are provided for each recording head 40.

[0031] The recording unit 4 (recording head 40) ejects ink from the nozzles 4N toward the paper S based on the image data to be printed in a printing job. The ink ejected from the recording unit 4 adheres to the paper S. Thereby, an image is printed on the paper S. That is, the position between the conveyor belt 30 and the recording head 40 is the printing position. In other words, the position facing the nozzle surface (nozzles 4N) of the recording head 40 in the vertical direction is the printing position.

[0032] Here, among the plurality of nozzles 4N, the ink viscosity in the nozzles 4N with a small number of ink ejection times increases over time. As a result, clogging occurs and the image quality deteriorates. To suppress such inconveniences, each recording head 40 performs a flushing process. In the flushing process by each recording head 40, the ink accumulated in the nozzles 4N is ejected. Thereby, clogging is suppressed. Details will be described later.

[0033] Returning to FIG. 1, the printer 100 includes a drying unit 51 and a decurler 52. The drying unit 51 dries the ink adhering to the paper S being conveyed while conveying the paper S toward the decurler 52. The decurler 52 corrects the curl of the paper S. The decurler 52 conveys the paper S after curl correction toward the second conveying unit 2.

[0034] Also, as shown in FIG. 3, the printer 100 includes a control unit 6. The control unit 6 includes processing circuits such as a CPU and an ASIC. The control unit 6 controls the printing job executed by the printer 100. In other words, the control unit 6 controls the operations of the first conveying unit 1, the second conveying unit 2, the belt conveying unit 3, the recording unit 4, the drying unit 51, and the decurler 52. Further in other words, the control unit 6 controls the conveyance of the paper S and the ink ejection of each recording head 40. As control regarding the conveyance of the paper S, the control unit 6 adjusts the paper gap, which is the interval in the conveyance direction between the paper S conveyed (fed) previously and the paper S to be conveyed (fed) next, by controlling the conveyance of the paper S to the conveyor belt 30 by the registration roller pair 11. Also, the control unit 6 controls the flushing process by each recording head 40.

[0035] 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 schematically shown in FIG. 4.

[0036] The detection position of the resist sensor 61 is set at a position upstream of the resist nip (resist position) in the paper conveyance direction. The resist sensor 61 is, for example, a reflective or transmissive optical sensor. The resist sensor 61 changes its output value according to the presence or absence of the paper S at the corresponding detection position.

[0037] Based on the output value of the resist sensor 61, the control unit 6 detects the arrival of the leading edge and the passage of the trailing edge of the paper S at the detection position of the resist sensor 61. In other words, based on the output value of the resist sensor 61, the control unit 6 detects the arrival of the leading edge and the passage of the trailing edge of the paper S at the resist nip (resist position). The control unit 6 measures the conveyance start timing of the paper S by the resist roller pair 11 (the rotation start timing of the resist roller pair 11) based on the elapsed time since the arrival of the leading edge of the paper S was detected at the detection position of the resist sensor 61. Even if the paper S is skewed, the conveyance of the paper S by the resist roller pair 11 is started in a state where the skew is corrected.

[0038] The detection position of the paper sensor 62 is set at a position between the printing position of the line head 41 on the most upstream side in the paper conveyance direction among the plurality of line heads 41 and the resist nip (resist position). The paper sensor 62 changes its output value according to the presence or absence of the paper S at the corresponding detection position. As the paper sensor 62, a CIS (Contact Image Sensor) may be used, or a reflective or transmissive optical sensor may be used. For example, a CIS is used as the paper sensor 62.

[0039] The control unit 6 detects the arrival of the leading edge and the passage of the trailing edge of the sheet S at the detection position of the sheet sensor 62 based on the output value of the sheet sensor 62. The control unit 6 measures the ink ejection timing for the sheet S conveyed by the conveyance belt 30 based on the output value of the sheet sensor 62. Note that the ink ejection timing for the sheet S conveyed by the conveyance belt 30 may be measured based on the elapsed time since the start of conveyance of the sheet S by the registration roller pair 11.

[0040] In addition, the control unit 6 measures the sheet passing time from when the leading edge of the sheet S reaches the detection position of the sheet sensor 62 until the trailing edge of the sheet S passes the detection position of the sheet sensor 62. The sheet passing time at the detection position of the sheet sensor 62 varies according to the size of the sheet S in the conveyance direction. Therefore, the control unit 6 recognizes the size of the sheet S in the conveyance direction conveyed by the conveyance belt 30 based on the sheet passing time. Thereby, even if the sheet S conveyed by the conveyance belt 30 has an irregular size, the control unit 6 can recognize the size of the sheet S in the conveyance direction.

[0041] Furthermore, the control unit 6 detects the misalignment (skew) of the sheet S based on the output value of the sheet sensor 62 (the reading data obtained by reading with the sheet sensor 62). For example, misalignment of the sheet S may occur after the conveyance of the sheet S by the registration roller pair 11 is started. In this case, the misalignment of the sheet S is detected by the control unit 6.

[0042] Note that the number of installed sheet sensors 62 may be plural. For example, two sheet sensors 62 may be installed.

[0043] The belt sensor 63 is a sensor for detecting a predetermined reference position (home position) of the conveyance belt 30. A predetermined mark is provided at the reference position of the conveyance belt 30. Thereby, the reference position of the conveyance belt 30 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 be configured using a transmissive or reflective optical sensor.

[0044] Based on the output value of the belt sensor 63, the control unit 6 detects the reference position of the conveyor belt 30. In other words, based on the output value of the belt sensor 63, the control unit 6 detects the circumferential position of the flushing area 31 (opening 310) described later.

[0045] Also, as shown in FIG. 3, 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 is connected to the control unit 6. The control unit 6 reads information from the storage unit 7. Also, the control unit 6 writes information to the storage unit 7.

[0046] 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, messages, etc., and accepts touch operations from the user. Also, hardware buttons for accepting settings, instructions, etc. are 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). Also, the control unit 6 detects operations performed on the operation panel 8.

[0047] The printer 100 includes a communication unit 9. The communication unit 9 includes a communication circuit, etc. The communication unit 9 is connected to the user terminal PC via the 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 transmitted from the user terminal PC to the printer 100. In other words, a request to execute a print job is transmitted 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 used in the print job.

[0048] <Configuration of the Conveyor Belt> 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 where an opening 310 penetrating in the thickness direction of the conveyor belt 30 is formed. In the flushing process, ink is ejected from each recording head 40, the ejected ink passes through the opening 310, and reaches a receiving portion 302 (see FIG. 4) disposed inside the conveyor belt 30. The ink in the receiving portion 302 is recovered and discarded.

[0049] The conveyor belt 30 is provided with a plurality of flushing areas 31. The plurality of flushing areas 31 are arranged at a predetermined interval FG from each other in the circumferential direction of the conveyor belt 30.

[0050] Each flushing area 31 has a plurality (the same number) of openings 310. The opening 310 is a long hole that is long in the width direction of the conveyor belt 30. The shape of the opening 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.

[0051] For example, each flushing area 31 includes two rows of opening rows. The opening row is a row of openings 310 arranged at equal intervals in the width direction of the conveyor belt 30. One opening row has six openings 310, and the other opening row has five openings 310. Also, the center position in the width direction of any opening row coincides with the center position in the width direction of the conveyor belt 30. That is, the plurality of openings 310 in each flushing area 31 are arranged in a staggered manner in the width direction. Note that the length in the width direction (opening width) of the opening 310 is larger than the interval between one adjacent opening 310 and the other opening 310 in the width direction.

[0052] Also, as shown in FIG. 6, the width W1 (mm) is smaller than the width W2 (mm). Note that the width W1 corresponds to the length in the width direction of the line head 41. Specifically, the width W1 corresponds to the length in the width direction from the end on one side of the recording head 40 located on one side in the width direction to the end on 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 31. Specifically, the width W2 corresponds to the length in the width direction from the end on one side of the opening 310 located on the most one side in the width direction to the end on the other side of the opening 310 located on the most other side in the width direction.

[0053] Thereby, by rotating the conveyor belt 30, the plurality of nozzles 4N of each recording head 40 can be made to face at least one of the openings 310 in the vertical direction. As a result, in the flushing process, ink that does not contribute to printing is discharged from each nozzle 4N, but it can be controlled so that the ink passes through the opening 310 (it can be controlled so that the ink does not adhere to the conveyor belt 30 and the paper S).

[0054] <Conveyance of Paper> When continuously printing on a plurality of sheets of paper S of the same size sequentially conveyed by the conveyor belt 30, the control unit 6 controls so that the paper gap, which is the interval in the conveyance direction between the rear end of the preceding paper S and the front end of the succeeding paper S (the paper S conveyed next to the preceding paper S), is constant. That is, in this case, the control unit 6 controls so that the plurality of sheets of paper S are conveyed at a constant interval (maintains each paper gap of the plurality of sheets of paper S at a constant interval). The continuous printing on a plurality of sheets of paper S of the same size sequentially conveyed with an interval by the conveyor belt 30 corresponds to "continuous printing", and in the following description, it is simply referred to as "continuous printing".

[0055] Here, during continuous printing, a flushing process is performed on each recording head 40. The control unit 6 controls the flushing process performed by each recording head 40. The ink ejected during the flushing process does not contribute to printing. Therefore, the control unit 6 controls the ink ejected during the flushing process to pass through the opening 310. That is, the control unit 6 causes the ink to be ejected from each nozzle 4N at a timing when it faces the opening 310 that does not overlap with the paper S.

[0056] To perform such control, the control unit 6 recognizes the size of the paper S conveyed by the conveyance belt 30. Also, the control unit 6 detects the reference position of the conveyance belt 30. Then, the control unit 6 measures the conveyance start timing of the paper S from the registration roller pair 11 to the conveyance belt 30 so that the flushing area 31 appears between papers at a fixed cycle. In other words, the control unit 6 adjusts the space between the preceding paper S and the succeeding paper S by controlling the conveyance of the paper S from the registration roller pair 11 to the conveyance belt 30. The control unit 6 changes the conveyance start timing of the paper S from the registration roller pair 11 to the conveyance belt 30 according to the size of the paper S conveyed by the conveyance belt 30. Before executing the print job, the control unit 6 recognizes the size of the paper S (the paper S conveyed by the conveyance belt 30) used in the print job based on the print data of the print job to be executed this time.

[0057] The positional relationship between the paper S conveyed by the conveyance belt 30 and the flushing area 31 is shown in FIG. 7. The circumferential direction (the conveyance direction of the paper S) of the conveyance belt 30 in FIG. 7 is the direction from the right to the left of the paper surface. In FIG. 7, the flushing area 31 is shown by hatching, and the opening 310 is omitted. Also, in FIG. 7, the symbol of the paper S is omitted, and instead, the size of the paper S is noted inside the figure showing the paper S. For the sake of convenience, FIG. 7 shows a plurality of papers S of different sizes together.

[0058] Here, referring to FIG. 8, a detailed description will be given focusing on the A4 vertical size. In FIG. 8, the circumferential direction of the conveyance belt 30 (the conveyance direction of the sheet S) is the direction from the bottom to the top of the paper surface. In FIG. 8, for the sake of convenience, three sheets of paper S are illustrated, and numbers 1 to 3 indicating the conveyance order are attached to the symbols of each sheet S.

[0059] When the size of the sheet S is A4 vertical 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 of the sheets S2 and S3 at all. Although not shown, the flushing area 31 does not appear between the third sheet S3 and the fourth sheet S, and the flushing area 31 appears between the fourth sheet S and the fifth sheet S.

[0060] <Flushing Process> Hereinafter, regarding the control of the flushing process by each recording head 40, an explanation will be given focusing on one of the recording heads 40. The same control as that of the recording head 40 is also performed for the other recording heads 40. For this reason, the explanation of the control of the other recording heads 40 will be omitted.

[0061] The control unit 6 sets the period from when the leading edge of the sheet S (the first sheet S) printed first in the continuous printing for a plurality of sheets of the same size reaches the printing position of the recording head 40 (the position facing the recording head 40) to when the last printed sheet S (the final sheet S) in the continuous printing passes through the printing position of the recording head 40 (the position facing the recording head 40) as the control period of the flushing process in the continuous printing. In the example shown in FIG. 8, assuming that the first sheet in the continuous printing is the sheet S1, the time when the leading edge of the sheet S1 reaches the printing position of the recording head 40 becomes the starting point of the control period.

[0062] During the execution of continuous printing (during the control period of the flushing process), when the flushing area 31 that does not overlap with the paper S at all faces the recording head 40, the control unit 6 causes the recording head 40 to perform the flushing process. Each time the flushing area 31 that does not overlap with the paper S at all faces the recording head 40, the control unit 6 causes the recording head 40 to perform a process of discharging ink from each nozzle 4N toward the opening 310 as the flushing process. On the other hand, during the execution of continuous printing, even when a flushing area 31 that at least partially overlaps with the paper S faces the recording head 40, the control unit 6 does not cause the recording head 40 to perform the flushing process. This will be specifically described below.

[0063] In the following description, a symbol "A" is attached to the flushing area 31 that does not overlap with the paper S at all and is referred to as the non-overlapping flushing area 31A, and a symbol "B" is attached to the flushing area 31 that at least partially overlaps with the paper S and is referred to as the overlapping flushing area 31B. The plurality of flushing areas 31 are classified into either the non-overlapping flushing area 31A or the overlapping flushing area 31B.

[0064] To control the flushing process by the recording head 40, the control unit 6 detects the reference position of the conveyor belt 30 (detects the position of the flushing area 31 in the circumferential direction). Also, the control unit 6 recognizes the position of the paper S on the conveyor belt 30 that has been conveyed from the registration roller pair 11 to the conveyor belt 30. For example, the control unit 6 recognizes the position of the paper S on the conveyor belt 30 that has been conveyed from the registration roller pair 11 to the conveyor belt 30 by detecting the arrival of the leading edge of the paper S at the detection position of the paper sensor 62. Also, for example, the control unit 6 recognizes the position of the paper S on the conveyor belt 30 that has been conveyed from the registration roller pair 11 to the conveyor belt 30 based on the reading data obtained by reading by the paper sensor 62 (CIS). Also, for example, the control unit 6 recognizes the position of the paper S on the conveyor belt 30 based on the elapsed time from the start of conveyance of the paper S by the registration roller pair 11.

[0065] Based on the reference position of the conveyor belt 30 (the position in the circumferential direction of the flushing area 31) and the position of the sheet S on the conveyor belt 30, the control unit 6 recognizes the positional relationship between the sheet S on the conveyor belt 30 and the flushing area 31. Then, the control unit 6 recognizes the flushing area 31 that does not overlap with the sheet S at all as the non-overlapping flushing area 31A, and the flushing area 31 that at least partially overlaps with the sheet S as the overlapping flushing area 31B.

[0066] In the example shown in FIG. 8, from the drawing surface, the first and fourth flushing areas 31 are recognized as the non-overlapping flushing area 31A, and the second, third, and fifth flushing areas 31 are recognized as the overlapping flushing area 31B.

[0067] The non-overlapping flushing area 31A appears between the sheets. However, the non-overlapping flushing area 31A does not necessarily appear between all the sheets. Depending on the size of the sheet S in the conveying direction, the non-overlapping flushing area 31A appears between all the sheets. Also, depending on the size of the sheet S in the conveying direction, all the flushing areas 31 become the non-overlapping flushing area 31A. It is impossible for all the flushing areas 31 to become the overlapping flushing area 31B.

[0068] When the sheet S used for continuous printing is a standard size (such as A4 size), as shown in FIG. 7, the conveyance control of the sheet S is performed so that the positional relationship between the sheet S and the flushing area 31 becomes a predetermined pattern. The pattern of the positional relationship between the sheet S and the flushing area 31 is predetermined for each size of the sheet S. The control unit 6 recognizes the pattern corresponding to the size of the sheet S used for continuous printing, and controls the conveyance of the sheet S so that the positional relationship between the sheet S and the flushing area 31 becomes the pattern. Therefore, when the sheet S used for continuous printing is a standard size, ideally, the positional relationship between the sheet S and the flushing area 31 becomes the positional relationship shown in FIG. 7.

[0069] In the example shown in FIG. 8, that is, in the case of A4 portrait size, the non-overlapping flushing area 31A reaches the printing position of the recording head 40 once every time the overlapping flushing area 31B passes through the printing position of the recording head 40 twice. In other words, a cycle in which the non-overlapping flushing area 31A reaches the printing position of the recording head 40 after the overlapping flushing area 31B passes through the printing position of the recording head 40 twice in a row is repeated. Therefore, in the case of A4 portrait size, the flushing process is performed once while the flushing area 31 passes through the printing position of the recording head 40 three times.

[0070] As another example, in the case of A4 landscape size (the second size from the bottom in the drawing of FIG. 7), all the flushing areas 31 become non-overlapping flushing areas 31A. Therefore, in the case of A4 landscape size, the flushing process is performed every time the flushing area 31 reaches the printing position of the recording head 40.

[0071] Thus, the appearance frequency of the non-overlapping flushing area 31A changes according to the size in the paper S conveyance direction. That is, according to the size in the paper S conveyance direction, the number of passes of the non-overlapping flushing area 31A (i.e., the number of passes of the overlapping flushing area 31B) passing through the printing position of the recording head 40 changes.

[0072] Therefore, for example, when the number of printed sheets for continuous printing using A4 portrait size paper S and continuous printing using A4 landscape size paper S are the same, in the continuous printing using A4 portrait size paper S, the number of flushing processes performed during the continuous printing does not become less than that in the continuous printing using A4 landscape size paper S. In other words, in the continuous printing using A4 portrait size paper S, the period from when the flushing process is performed at a certain timing until the next time it is performed becomes longer than that in the continuous printing using A4 landscape size paper S.

[0073] If the ink discharge amount of each nozzle 4N in one flushing process is the same when using paper S in the vertical A4 size and when using paper S in the horizontal A4 size, the total discharge amount of the individual inks of the nozzles 4N in the flushing process is less when using paper S in the vertical A4 size than when using paper S in the horizontal A4 size. Therefore, during continuous printing, ink discharge failure (clogging of the nozzles 4N) due to an increase in the viscosity of the ink in the nozzles 4N is likely to occur. The longer the period from when a flushing process is performed until the next flushing process is performed (the period when the flushing process is not performed), the easier it is for the ink in the nozzles 4N to dry (there is a risk that the ink viscosity will increase and discharge failure will easily occur).

[0074] Therefore, when causing the recording head 40 to perform a flushing process during continuous printing, the control unit 6 increases the discharge amount of the individual inks of the nozzles 4N in the current flushing process as the non-flushing period (the period when the flushing process is not performed) from the previous flushing process to the current flushing process is longer. That is, when causing the recording head 40 to perform a flushing process during continuous printing, the control unit 6 increases the discharge amount of the individual inks of the nozzles 4N in the current flushing process as the number of times the overlapping flushing area 31B passes through the printing position of the recording head 40 (the position facing the recording head 40) during the non-flushing period from the previous flushing process to the current flushing process is larger.

[0075] Hereinafter, the ink discharge amount in the flushing process will be described by taking the case of using paper S of the first size and the case of using paper of the second size as examples.

[0076] Note that the first size is a reference size. The reference size is a size equal to or less than the length corresponding to the predetermined interval FG shown in FIG. 5. For example, the reference size corresponds to the length in the conveyance direction (the circumferential direction of the conveyance belt 30) of the paper S in the horizontal A4 size.

[0077] On the other hand, the second size is larger than the length corresponding to the predetermined interval FG shown in FIG. 5. Therefore, when using the paper S of the second size, the paper S cannot be placed within the range between one flushing area 31 and the other flushing area 31 adjacent to each other in the circumferential direction of the conveyance belt 30. In other words, the paper S cannot be placed without protruding from the said range. For this reason, when using the paper S of the second size, each paper S will necessarily overlap with one of the flushing areas 31.

[0078] When using the paper S of the first size (reference size) for continuous printing, the control unit 6 causes the resist rollers pair 11 to convey the paper S from the registration position to the conveyance belt 30 at a timing when the flushing area 31 appears between all the sheets of the plurality of sheets of paper S conveyed by continuous printing without overlapping with the paper S. Therefore, when the size of the paper S used for continuous printing in the conveyance direction is the first size, all the flushing areas 31 become non-overlapping flushing areas 31A, and the overlapping flushing area 31B does not appear.

[0079] Also, when using the paper S of the first size for continuous printing, the control unit 6 sets the discharge amount of each individual ink of the nozzles 4N in one flushing process to a predetermined reference amount. That is, the control unit 6 causes the recording head 40 to perform, as one flushing process, a process of discharging the reference amount of ink from each nozzle 4N when the recording head 40 and the non-overlapping flushing area 31A are facing each other.

[0080] For example, the discharge amount of each individual ink of the nozzles 4N becomes the reference amount by performing ink discharges of a predetermined reference number of times (ink discharges for a predetermined number of lines). Therefore, when using the paper S of the first size for continuous printing, the control unit 6 causes each nozzle 4N to perform ink discharges of the reference number of times in one flushing process.

[0081] Here, when causing the recording head 40 to perform a flushing process during continuous printing, if the overlapping flushing area 31B appears during the non-flushing period from the previous flushing process to the current one, the control unit 6 increases the discharge amount of each ink of the nozzles 4N in the current flushing process to be more than the reference amount. Note that if the overlapping flushing area 31B does not appear during the non-flushing period, the control unit 6 sets the discharge amount of each ink of the nozzles 4N in the current flushing process to the reference amount.

[0082] When the size of the paper S used for continuous printing is the first size (reference size), the overlapping flushing area 31B does not appear. For this reason, the discharge amount of each ink of the nozzles 4N in the flushing process is set to the reference amount each time (the discharge amount of the ink is small). However, when the size of the paper S used for continuous printing is the first size, since all the flushing areas 31 become non-overlapping flushing areas 31A, each time the printing position of the recording head 40 passes through the flushing area 31, the flushing process is performed.

[0083] On the other hand, when the size of the paper S used for continuous printing is the second size, both the non-overlapping flushing area 31A and the overlapping flushing area 31B appear. That is, during the non-flushing period, the overlapping flushing area 31B passes through the printing position of the recording head 40 at least once.

[0084] When the second size is the A4 vertical size, as shown in FIG. 8, the overlapping flushing area 31B passes through the printing position of the recording head 40 twice during the non-flushing period. When the second size is the A3 size, as shown in FIG. 9, the overlapping flushing area 31B passes through the printing position of the recording head 40 once during the non-flushing period. Thereby, in the example shown in FIG. 8 and the example shown in FIG. 9, the discharge amount of each ink of the nozzles 4N in one flushing process becomes more than the reference amount.

[0085] Incidentally, the longer the non-flushing period during which the overlapping flushing area 31B passes through the printing position of the recording head 40, the longer the non-flushing period becomes. The longer the non-flushing period, the easier it is for the ink in the nozzle 4N to dry. Therefore, it is preferable to increase the discharge amount of each ink in the nozzle 4N in one flushing process as the number of times the overlapping flushing area 31B passes through the printing position of the recording head 40 during the non-flushing period increases.

[0086] Therefore, when causing the recording head 40 to perform the flushing process during continuous printing, the control unit 6 sets the discharge amount of each ink in the nozzle 4N in the current flushing process based on the number of times the overlapping flushing area 31B passes through the printing position of the recording head 40 during the non-flushing period. The discharge amount of each ink in the nozzle 4N in one flushing process increases as the number of times the overlapping flushing area 31B passes through the printing position of the recording head 40 during the non-flushing period increases. That is, the discharge amount of each ink in the nozzle 4N in one flushing process increases as the non-flushing period becomes longer.

[0087] Specifically, when setting the discharge amount of each ink in the nozzle 4N in one flushing process, the control unit 6 recognizes the number of passes of the overlapping flushing area 31B through the printing position of the recording head 40 during the non-flushing period from the previous flushing process to the current one. Further, the control unit 6 obtains an adjustment value obtained by adding 1 to the number value indicating the recognized number of passes.

[0088] In the example shown in FIG. 8, the overlapping flushing area 31B passes through the printing position of the recording head 40 twice during the non-flushing period. Therefore, the adjustment value is 3 (=2 + 1). In the example shown in FIG. 9, the overlapping flushing area 31B passes through the printing position of the recording head 40 once during the non-flushing period. Therefore, the adjustment value is 2 (=1 + 1).

[0089] Further, the control unit 6 obtains the number of times obtained by multiplying the reference number of times by the adjustment value. Then, the control unit 6 sets the number of discharges of each ink of the nozzles 4N in the current flushing process to the number of times obtained by multiplying the reference number of times by the adjustment value. By performing such a setting, the longer the non-flushing period is (the larger the number of times the overlapping flushing area 31B passes through the printing position of the recording head 40 during the non-flushing period), the larger the number of discharges of each ink of the nozzles 4N in the current flushing process becomes. That is, the longer the non-flushing period is, the larger the discharge amount of each ink of the nozzles 4N in the current flushing process becomes.

[0090] An example of the control of the flushing process is shown in FIG. 10. FIG. 10 shows each control when using a sheet S of the first size (A4 landscape size) as the reference size, when using a sheet S of the second size, A4 portrait size, and when using a sheet S of the second size, A3 size.

[0091] Also, in FIG. 10, periods T1, T2, T3, and T4 are periods during which the flushing area 31 faces the recording head 40. In other words, the flushing area 31 passes through the printing position of the recording head 40 during this period. In this period, the non-overlapping flushing area 31A may pass through the printing position of the recording head 40, or the overlapping flushing area 31B may pass through the printing position of the recording head 40.

[0092] When the sheet S is A4 landscape size, the non-overlapping flushing area 31A faces the recording head 40 in all of the periods T1, T2, T3, and T4. And the flushing process is performed in all of the periods T1, T2, T3, and T4. In the flushing process in this case, ink of a reference amount is discharged from each nozzle 4N. That is, ink discharge of the reference number of times is performed at each nozzle 4N. Here, it is assumed that ink discharge for n1 lines (n1 times of ink discharge) is performed at each nozzle 4N. For example, n1 lines are 10 lines. That is, the reference number of times is 10 times.

[0093] When the paper S is in the A4 landscape size, during the non-flushing period from the previous flushing process to the current one, the overlapping flushing area 31B does not pass through the printing position of the recording head 40 (the number of times is 0). Therefore, the adjustment value is 1 (= the number of times + 1). The number of times obtained by multiplying the reference number of times (= 10 times) by the adjustment value (= 1) is 10 times. As a result, in the flushing process, ink ejection for 10 lines (10 times of ink ejection) is performed at each nozzle 4N.

[0094] When the paper S is in the A4 portrait size, during each of the periods T1, T2, and T4, the overlapping flushing area 31B passes through the printing position of the recording head 40. And in the period T3, the non-overlapping flushing area 31A faces the recording head 40. Therefore, the flushing process is performed in the period T3. Here, it is assumed that ink ejection for n2 lines (n2 times of ink ejection) is performed at each nozzle 4N.

[0095] When the paper S is in the A4 portrait size, during the non-flushing period from the previous flushing process to the current one, the overlapping flushing area 31B passes through the printing position of the recording head 40 twice (the number of times is 2). Therefore, the adjustment value is 3 (= the number of times + 1). The number of times obtained by multiplying the reference number of times (= 10 times) by the adjustment value (= 3) is 30 times. As a result, in the flushing process, ink ejection for 30 lines (30 times of ink ejection) is performed at each nozzle 4N. That is, n2 lines are 30 lines.

[0096] When the paper S is in the A3 size, in the period T1, the overlapping flushing area 31B passes through the printing position of the recording head 40. And in the next period T2, the non-overlapping flushing area 31A faces the recording head 40, and the flushing process is performed. Here, it is assumed that ink ejection for n3 lines (n3 times of ink ejection) is performed at each nozzle 4N. In the subsequent period T3, the overlapping flushing area 31B passes through the printing position of the recording head 40. Also, in the period T4, the non-overlapping flushing area 31A passes through the printing position of the recording head 40 (flushing process for n3 lines is performed).

[0097] When the paper S is A3 size, during the non-flushing period from the previous flushing process to the current one, the overlapping flushing area 31B passes through the printing position of the recording head 40 once (the number of times is 1). Therefore, the adjustment value is 2 (= the number of times + 1). The number of times obtained by multiplying the reference number of times (= 10 times) by the adjustment value (= 2) is 20 times. As a result, in the flushing process, ink ejection for 20 lines (20 times of ink ejection) is performed at each nozzle 4N. That is, n2 lines are 20 lines.

[0098] In the present embodiment, as described above, when the control unit 6 causes the recording head 40 to perform the flushing process during continuous printing, the longer the non-flushing period from the previous flushing process to the current one, the larger the individual ink ejection amount of the nozzles 4N in the current flushing process. That is, the control unit 6 changes the individual ink ejection amount of the nozzles 4N in one flushing process according to the size of the paper S in the conveyance direction used for continuous printing.

[0099] In this configuration, when it is possible to control so that the non-overlapping flushing area 31A appears between all sheets of the plurality of sheets of paper S conveyed in continuous printing (when the non-flushing period is the shortest), the individual ink ejection amount of the nozzles 4N in one flushing process becomes the minimum (reference amount). When it is not possible to control so that the non-overlapping flushing area 31A appears between all sheets of the plurality of sheets of paper S conveyed in continuous printing, the individual ink ejection amount of the nozzles 4N in one flushing process becomes larger than the reference amount.

[0100] When it is impossible to control so that the non-overlapping flushing area 31A appears between all of the sheets of the plurality of sheets of paper S conveyed by continuous printing, the number of executions per unit time of the flushing process is less than when it is possible to control so that the non-overlapping flushing area 31A appears between all of the sheets of the plurality of sheets of paper S conveyed by continuous printing. Therefore, it is preferable to increase the discharge amount of each ink of the nozzles 4N in one flushing process. Thereby, drying of the ink in the nozzles 4N (clogging of the nozzles 4N) can be suppressed. That is, a decrease in image quality can be suppressed. On the other hand, when it is possible to control so that the non-overlapping flushing area 31A appears between all of the sheets of the plurality of sheets of paper S conveyed by continuous printing, since the number of executions per unit time of the flushing process is the maximum, even if the discharge amount of each ink of the nozzles 4N in one flushing process is minimized (reference amount), drying of the ink in the nozzles 4N (clogging of the nozzles 4N) can be suppressed.

[0101] As described above, by changing the discharge amount of each ink of the nozzles 4N in the flushing process according to the positional relationship between the sheets of the plurality of sheets of paper S conveyed by the conveyor belt 30 and the flushing area 31 (that is, the size in the conveyance direction of the paper S), it is possible to reduce the consumption amount of the ink in the flushing process while suppressing a decrease in image quality.

[0102] Further, in the present embodiment, as described above, when the size in the conveyance direction of the paper S used for continuous printing is a reference size equal to or less than the predetermined interval FG, the control unit 6 causes the resist roller pair 11 to convey the paper S from the registration position to the conveyor belt 30 at a timing when the non-overlapping flushing area 31A appears between all of the sheets of the plurality of sheets of paper S conveyed by continuous printing. Thereby, when the size in the conveyance direction of the paper S used for continuous printing is equal to or less than the predetermined interval FG, the number of executions per unit time of the flushing process can be increased.

[0103] Also, in the present embodiment, as described above, when the control unit 6 causes the recording head 40 to perform the flushing process during continuous printing, if the overlapping flushing area 31B appears during the non-flushing period from the previous flushing process to the current one, the discharge amount of each ink of the nozzles 4N in the current flushing process is made larger than the reference amount. Here, the fact that the overlapping flushing area 31B appears during the non-flushing period means that the non-flushing period is longer than that in continuous printing using the paper S of the reference size. Therefore, when the overlapping flushing area 31B appears during the non-flushing period, it is preferable to make the discharge amount of each ink of the nozzles 4N in the flushing process larger than the reference amount.

[0104] In addition, when the size of the paper S is a standard size, the positional relationship between the paper S and the flushing area 31 becomes any of the patterns shown in FIG. 7. That is, when the size of the paper S is a standard size, based on the size of the paper S, the length of the non-flushing period can be recognized in advance. However, when the size of the paper S is a non-standard size, the length of the non-flushing period cannot be recognized in advance.

[0105] Also, for example, as shown in FIG. 11, even when the size of the paper S is a standard size, if a misregistration occurs in any of the papers S, the paper S overlaps the flushing area 31 that would not originally overlap the paper S. In FIG. 11, the upper part shows the normal state where no misregistration of the paper S occurs, and the lower part shows the state where misregistration of the paper S occurs. In this example, originally, the flushing process is performed when the flushing area 31 in the figure faces the recording head 40. However, due to the occurrence of misregistration of the paper S, the flushing process is not performed even when the flushing area 31 in the figure faces the recording head 40. As a result, the non-flushing period becomes longer than expected.

[0106] Therefore, in the present embodiment, as described above, when the control unit 6 causes the recording head 40 to perform the flushing process during continuous printing, the control unit 6 recognizes the number of times the overlapping flushing area 31B has passed through the position facing the recording head during the non-flushing period from the previous flushing process to the current flushing process. The larger the recognized number of passes, the larger the ejection amount of each ink from the nozzle 4N in the current flushing process. Thereby, it is ensured that the longer the non-flushing period from the previous flushing process to the current flushing process, the larger the ejection amount of each ink from the nozzle 4N in the flushing process can be made.

[0107] Also, in the present embodiment, as described above, when the control unit 6 causes the recording head 40 to perform the flushing process during continuous printing, the control unit 6 obtains an adjustment value obtained by adding 1 to the number value indicating the number of passes, and sets the number obtained by multiplying the reference number by the adjustment value as the number of ejection times of each ink from the nozzle 4N in the current flushing process. Thereby, it is easy to increase the ejection amount (the number of ejection times of ink) of each ink from the nozzle 4N in the flushing process as the non-flushing period is longer (the larger the number of passes).

[0108] The embodiment disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above embodiment but by the claims, and further includes all modifications within the meaning and scope equivalent to the claims.

Explanation of Reference Numerals

[0109] 4N Nozzle 6 Control Unit 11 Registration Roller Pair (Registration Unit) 30 Conveyor Belt 31 Flushing Area 31A Non-Overlapping Flushing Area 31B Overlapping Flushing Area 40 Recording Head 100 Printer (Inkjet Recording Device) 310 Aperture FG specified interval S paper (recording medium)

Claims

【Claim 1】 A conveyance belt that is rotatably supported and conveys a recording medium by rotating; A recording head that is disposed at a position facing the recording medium and has a plurality of nozzles arranged in a width direction orthogonal to the circumferential direction of the conveyance belt, and performs printing on the recording medium by discharging ink from the nozzles; A control unit that controls a flushing process by the recording head; and The conveyance belt has a flushing area in which an opening is formed; A plurality of the flushing areas are arranged at a predetermined interval from each other in the circumferential direction; During execution of continuous printing on a plurality of the recording media sequentially conveyed by the conveyance belt, each time a non-overlapping flushing area, which is a flushing area that does not overlap the recording medium, faces the recording head, the control unit causes the recording head to perform a process of discharging ink from the nozzles toward the opening as the flushing process, while even when an overlapping flushing area, which is a flushing area where at least a part overlaps the recording medium, faces the recording head, the control unit does not cause the recording head to perform the flushing process; When the control unit causes the recording head to perform the flushing process during execution of the continuous printing, the longer the period from the previous performance of the flushing process to the current performance of the flushing process, the larger the discharge amount of each individual ink of the nozzles in the current flushing process; A resist unit that conveys the recording medium from a resist position, which is a position upstream in the conveyance direction from the installation position of the conveyance belt, toward the conveyance belt; The control unit adjusts the paper gap, which is the interval between the previously conveyed recording medium and the next conveyed recording medium, by controlling the conveyance of the recording medium to the conveyance belt by the resist unit; When the size of the recording medium in the conveyance direction used in the continuous printing is equal to or less than a reference size of the predetermined interval, the control unit causes the resist unit to convey the recording medium from the resist position to the conveyance belt at a timing when the non-overlapping flushing area appears in all of the paper gaps of the plurality of the recording media conveyed in the continuous printing; When the size of the recording medium in the conveyance direction used in the continuous printing is equal to the reference size, the control unit sets the discharge amount of each individual ink of the nozzles in the flushing process to a predetermined reference amount; When the control unit causes the recording head to perform the flushing process during the execution of the continuous printing, if the overlapping flushing area appears during the period from the previous execution of the flushing process to the current execution, the inkjet recording apparatus increases the discharge amount of each ink of the nozzles in the current flushing process to be more than the reference amount. **Claim 2** When the control unit causes the recording head to perform the flushing process during the execution of the continuous printing, the control unit recognizes the number of times the overlapping flushing area has passed through the position facing the recording head during the period from the previous execution of the flushing process to the current execution. The greater the number of passes, the greater the discharge amount of each ink of the nozzles in the current flushing process. The inkjet recording apparatus according to claim 1. **Claim 3** The discharge amount of each ink of the nozzles becomes the reference amount by performing ink discharge a predetermined number of reference times. When the control unit causes the recording head to perform the flushing process during the execution of the continuous printing, the control unit obtains an adjustment value obtained by adding 1 to the number value indicating the number of passes, and sets the number obtained by multiplying the reference number by the adjustment value as the number of discharges of each ink of the nozzles in the current flushing process. The inkjet recording apparatus according to claim 2.

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