Inkjet recording apparatus

The controller of an inkjet recording apparatus supplies a recording medium onto the conveyor belt with a pair of registration rollers based on a detection result of the trailing edge of the recording medium by a first detection sensor and a detection result of an opening by a second detection sensor. The controller determines whether the recording medium is being placed on the conveyor belt coinciding with the opening that is moved due to the traveling of the conveyor belt, and based on the determination result, the controller controls the recording head to execute flushing and the pair of registration rollers to supply a subsequent recording medium onto the conveyor belt.

INCORPORATION BY REFERENCE

This application is based upon, and claims the benefit of priority from corresponding Japanese Patent Application No. 2020-069237 filed in the Japan Patent Office on Apr. 7, 2020, the entire contents of which are incorporated herein by reference.

BACKGROUND

Field of the Invention

The present disclosure relates to an inkjet recording apparatus that ejects ink onto a recording medium and records an image.

Description of Related Art

Conventionally, in an inkjet recording apparatus such as an inkjet printer, flushing (empty ejection) is performed by periodically ejecting ink from the nozzle in order to reduce or prevent clogging of the nozzle due to drying of the ink. Typically, an opening is provided in the conveyor belt that conveys the recording medium and when the opening comes to a position facing the recording head due to the traveling of the conveyor belt, ink is ejected from the nozzle of the recording head to clear the opening.

SUMMARY

The inkjet recording apparatus according to one aspect of the present disclosure includes a recording head, a pair of registration rollers, an endless conveyor belt, first and second detection sensors, and a controller that controls the recording head and the pair of registration rollers. The recording head has a plurality of nozzles that eject ink. The endless conveyor belt conveys a recording medium to a position facing the recording head, and has a plurality of openings in a conveyance direction of the recording medium, through which the ink passes when in positions facing the recording head when the recording head executes flushing by ejecting ink at a time different from the time that contributes to image formation on the recording medium. The pair of registration rollers supply the recording medium onto the conveyor belt. The first detection sensor detects a recording medium, by being positioned on an upstream side of the pair of registration rollers in a supply direction of the recording medium, and the second detection sensor detects a position of an opening of the conveyor belt. The controller determines whether the recording medium supplied onto the conveyor belt by the pair of registration rollers is placed on the conveyor belt coinciding with the opening that is moved due to the traveling of the conveyor belt based on a detection result of the trailing edge of the recording medium by the first detection sensor and a detection result of the opening by the second detection sensor and controls the execution of flushing by the recording head and controls supply of a subsequent recording medium by the pair of registration rollers onto the conveyor belt based on the determination.

DETAILED DESCRIPTION

1. Configuration of Inkjet Recording Apparatus

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.FIG.1is an explanatory diagram illustrating a schematic configuration of a printer100as an inkjet recording apparatus according to an embodiment of the present disclosure. The printer100includes a paper feed cassette2which is a paper storage unit. The paper feed cassette2is arranged in the lower inside portion of the printer main body1. Paper P, which is an example of a recording medium, is stored inside the paper feed cassette2.

The paper feeder3is arranged on the downstream side of the paper feed cassette2in the paper conveyance direction, that is, above the right side of the paper feed cassette2inFIG.1. The paper feeder3, separates and sends out the paper P sheet by sheet toward the upper right side of the paper feed cassette2inFIG.1.

The printer100includes a first paper conveyance path4ainside the printer100. The first paper conveyance path4ais positioned on the upper right side of the paper feed cassette2in the paper feed direction. The paper P sent out from the paper feed cassette2is conveyed vertically upward along the side surface of the printer main body1by the first paper conveyance path4a.

A pair of registration rollers13are provided at the downstream end of the first paper conveyance path4ain the paper conveyance direction. Further, the first conveyance unit5and the recording unit9are arranged in the immediate vicinity of the pair of registration rollers13on the downstream side in the paper conveyance direction. The paper P sent out from the paper feed cassette2reaches the pair of registration rollers13through the first paper conveyance path4a. The pair of registration rollers13correct tilt of the paper P during sending, measure the timing of the ink ejection operation executed by the recording unit9, and send the paper P toward the first conveyance unit5.

The paper P sent to the first conveyance unit5is conveyed by the first conveyor belt8to a position facing the recording unit9(particularly, the recording heads17ato17cdescribed later). An image is recorded on the paper P by ink ejected from the recording unit9onto the paper P. At this time, the ink ejection in the recording unit9is controlled by the controller110inside the printer100. The controller110is composed of, for example, a central processing unit (CPU), and has functions including a calculator to perform necessary calculations and a clock that measures time.

In the paper conveyance direction, the second conveyance unit12is arranged on the downstream side (left side inFIG.1) of the first conveyance unit5. The paper P, on which the image is recorded by the recording unit9is sent to the second conveyance unit12. The ink ejected onto the surface of the paper P dries while passing through the second conveyance unit12.

In the paper conveyance direction, a decurling section14is provided on the downstream side of the second conveyance unit12and near the left side surface of the printer main body1. The paper P whose ink has been dried by the second conveyance unit12is sent to the decurling section14, and the curl that has occurred on the paper P is corrected.

A second paper conveyance path4bis provided on the downstream side (upward inFIG.1) of the decurling section14in the paper conveyance direction. When double-sided recording is not performed, the paper P that has passed through the decurling section14passes through the second paper conveyance path4band is discharged to the paper discharge tray15provided on the outer left side surface of the printer100.

A reverse conveyance path16for double-sided recording is provided above the recording unit9and the second conveyance unit12in the upper part of the printer main body1. When double-sided recording is performed, after the recording on one side (the first side) of the paper P is completed, the paper P that has passed through the second conveyance unit12and the decurling section14passes through the second paper conveyance path4band is sent to the reverse conveyance path16.

The conveyance direction of the paper P sent to the reverse conveyance path16is subsequently turned over for recording on the other side (the second side) of the paper P. Then, the paper P passes through the upper part of the printer main body1and is sent toward the right side, and is sent to the first conveyance unit5again through the pair of registration rollers13in a state where the second side is facing upward. In the first conveyance unit5, the paper P is conveyed to a position facing the recording unit9, and an image is recorded on the second surface by ink ejected from the recording unit9. After double-sided recording, the paper P is discharged to the paper discharge tray15by going through the second conveyance unit12, the decurling section14, and the second paper conveyance path4bin order.

A maintenance unit19and a cap unit20are arranged below the second conveyance unit12. The maintenance unit19moves horizontally below the recording unit9when purging is executed, wipes the ink pushed out from the ink ejection port of the recording head, and collects the wiped ink. Purging refers to an operation of forcibly pushing out ink from the ink ejection port of the recording head in order to discharge thickened ink, foreign matter, and air bubbles from the ink ejection port. When capping the ink ejection surface of the recording head, the cap unit20moves horizontally below the recording unit9, then moves upward to mount to the lower surface of the recording head.

FIG.2is a plan view of the recording unit9. The recording unit9includes a head housing10and line heads11Y,11M,11C, and11K. The line heads11Y to11K are held in the head housing10and are formed to have a specific interval of height (for example, 1 mm) with respect to the conveyance surface of the endless first conveyor belt8stretched on a plurality of rollers including the drive roller6a, the driven roller6b, and the other rollers7aand7b. The driving of the drive roller6ais controlled by the controller110.

The line heads11Y to11K each have a plurality of (three in this example) recording heads17ato17c. The recording heads17ato17care arranged in a staggered manner along the paper width direction (the direction of arrow BB′), which is orthogonal to the paper conveyance direction (the direction of arrow A). The recording heads17ato17chave a plurality of ink ejection ports18(nozzles). The ink ejection ports18are arranged side by side at equal intervals in the width direction of the recording head, that is, in the paper width direction (the direction of arrow BB′). The line heads11Y to11K eject inks of each color of yellow (Y), magenta (M), cyan (C), and black (K) through the ink ejection ports18of the recording heads17ato17cand toward the paper P conveyed by the first conveyor belt8.

FIG.3schematically illustrates the configuration around the conveyance path of the paper P from the paper feed cassette2to the second conveyance unit12via the first conveyance unit5. Further,FIG.4is a block diagram illustrating a hardware configuration of a main part of the printer100. In addition to the above configuration, the printer100further includes a registration sensor21, a first paper sensor22, a second paper sensor23, and belt sensors24and25.

The registration sensor21detects the paper P that is conveyed from the paper feed cassette2by the paper feeder3and sent to the pair of registration rollers13. The registration sensor21is a first detection sensor that detects the paper P at a position on the upstream side of the pair of registration rollers13in the supply direction of the paper P. The controller110can control the rotational start time of the pair of registration rollers13based on the detection result of the registration sensor21. For example, based on the detection result of the registration sensor21, the controller110can control the supply time of the paper P to the first conveyor belt8after skew (tilt) correction by the pair of registration rollers13.

The first paper sensor22is a sensor that detects the position in the width direction of the paper P sent from the pair of registration rollers13to the first conveyor belt8. Based on the detection result of the first paper sensor22, from among the ink ejection ports18corresponding to the recording heads17ato17cof the line heads11Y to11K, the controller110can cause ink to be ejected from the ink ejection ports18in the width of the paper P thereby an image can be recorded on the paper P.

The second paper sensor23is a sensor that detects the passage of the paper P supplied to the first conveyor belt8by the pair of registration rollers13. That is, the second paper sensor23detects the position of the paper P conveyed by the first conveyor belt8in the conveyance direction. The second paper sensor23is positioned on the upstream side of the recording unit9and on the downstream side of the first paper sensor22in the paper conveyance direction. Based on the detection result of the second paper sensor23, the controller110controls the ink ejection timing with respect to the paper P reaching a position facing the line heads11Y to11K (recording heads17ato17c) by the first conveyor belt8.

The belt sensors24and25are second detection sensors provided on the first conveyor belt8to detect the positions of a plurality of opening groups82or openings80(seeFIG.5), which will be described later. That is, the belt sensors24and25detect the passage of at least one of the opening groups82due to the traveling of the first conveyor belt8. The belt sensor24is positioned on the downstream side of the recording unit9in the paper conveyance direction (traveling direction of the first conveyor belt8). The belt sensor25is positioned on the upstream side in the paper conveyance direction with respect to the driven roller6bon which the first conveyor belt8is stretched. Therefore, the belt sensor25may be positioned between the driven roller6band the other roller7b, or may be positioned between the roller7aand the roller7b. The driven roller6bis positioned on the upstream side in the traveling direction of the first conveyor belt8with respect to the recording unit9. The belt sensor24also has the same function as the second paper sensor23. Based on the detection result of the belt sensors24or25, the controller110can control the pair of registration rollers13so as to supply the paper P to the first conveyor belt8at a specific time.

Further, the position of the paper is detected by a plurality of sensors (second paper sensor23, belt sensor24), and the position of the opening group82of the first conveyor belt8is detected by the plurality of sensors (belt sensors24and25), so that it is possible to correct the error of the detected position and detect an abnormality.

The first paper sensor22, the second paper sensor23, and the belt sensors24and25described above may be configured as transmissive or reflective optical sensors, or contact image sensors (CIS sensors). Further, a mark corresponding to the position of the opening group82may be formed at an end of the first conveyor belt8in the width direction, and the belt sensors24and25may detect the position of the opening group82by detecting this mark.

In addition, the printer100may be provided with a meandering detection sensor that detects meandering of the first conveyor belt8, and may be configured to correct the meandering of the first conveyor belt8based on the detection result.

The printer100further includes an operation panel27, a storage unit28, and a communication unit29.

The operation panel27is an operation unit for receiving various setting inputs by the user. For example, the user can operate the operation panel27to input information on the size the size of the paper P to be set in the paper feed cassette2, that is, the size of the paper P to be conveyed by the first conveyor belt8.

The storage unit28is a memory device that stores the operation program of the controller110along with various information, and is configured by including read only memory (ROM), random access memory, (RAM), a non-volatile memory, and the like. The information set by the operation panel27(for example, the size information of the paper P) is stored in the storage unit28.

The communication unit29is a communication interface for transmitting and receiving information to and from an external device (for example, a personal computer (PC)). For example, when a user operates a PC and sends a print command together with image data to the printer100, the image data and the print command are input to the printer100via the communication unit29. In the printer100, the controller110controls the recording heads17ato17cbased on the image data to eject ink so that the image can be recorded on the paper P.

Further, as illustrated inFIG.3, the printer100has ink receptacles31Y,31M,31C, and31K on the inner peripheral surface side of the first conveyor belt8. When flushing is executed by the recording heads17ato17c, the ink receptacles31Y to31K receive and collect the ink discharged from the recording heads17ato17cand passed through the opening80of the first conveyor belt8. Therefore, the ink receptacles31Y to31K are provided at positions facing the recording heads17ato17cof the line heads11Y to11K via the first conveyor belt8. The ink collected by the ink receptacles31Y to31K is sent to, for example, a waste ink tank and discarded, or the ink may be reused without being discarded.

Here, flushing means ink ejection from the ink ejection port18. at a time different from the time that contributes to image formation (image recording) on the paper P, for the purpose of reducing or preventing clogging of the ink ejection port18due to drying of the ink. The execution of flushing in the recording heads17ato17cis controlled by the controller110.

The above-mentioned second conveyance unit12includes a second conveyor belt12aand a dryer12b. The second conveyor belt12ais stretched on two driving rollers12cand a driven roller12d. The paper P is conveyed by the first conveyance unit5, an image is recorded on the paper by ink ejection by the recording unit9, the paper P is conveyed by the second conveyor belt12a, dried by the dryer12bduring conveyance, and conveyed to the decurling section14described above.

2. Details of the First Conveyor Belt

2-1. Example of Configuration of the First Conveyor Belt

Next, the details of the first conveyor belt8of the first conveyance unit5will be described.FIG.5is a plan view illustrating an example of a configuration of the first conveyor belt8. In the present embodiment, a negative pressure suction method is used in which the paper P is conveyed by attraction to the first conveyor belt8through negative pressure suction. Therefore, the first conveyor belt8is provided with innumerable suction holes8athat allow passage of the suctioned air generated by the negative pressure suction.

Further, the first conveyor belt8is also provided with an opening group82. The opening group82is a set of openings80which allow passage of ink ejected from each nozzle (ink ejection port18) of the recording heads17ato17cduring flushing. The opening area of one opening80is larger than the opening area of one suction hole8a. The first conveyor belt8has, in one cycle, a plurality of opening groups82in the conveyance direction (A direction) of the paper P, and the present embodiment has six groups. Note that one cycle refers to a time period or distance in which the first conveyor belt8makes one revolution. When the opening groups82are distinguished from each other, the six opening groups82are referred to as opening groups82A to82F from the downstream side in the A direction. The suction holes8aare positioned between each opening group82and the adjacent opening group82in the A direction. This means that in the first conveyor belt8, the suction holes8aare not formed in a region (around the opening80) coinciding with an opening group82.

The opening groups82are irregularly positioned in the A direction in one cycle of the first conveyor belt8. That is, in the A direction, the interval between an opening group82and an adjacent opening group82is not constant but variable (there are at least two types of the above intervals). At this time, the maximum distance between the two opening groups82adjacent to each other in the A direction (for example, the distance between the opening group82A and the opening group82B inFIG.5) is longer than the length of the paper P of the minimum printable size (for example, A4 size (horizontally placed)) in the A direction when it is placed on the first conveyor belt8.

The opening group82has an opening row81. The opening row81is configured by arranging a plurality of openings80in the belt width direction (paper width direction, BB′ direction) orthogonal to the A direction. One opening group82has at least one opening row81in the A direction, and in the present embodiment, has two opening rows81. To distinguish the two opening rows81from each other, one row is referred to as the opening row81aand the other row is referred to as the opening row81b.

In one opening group82, the openings80of any opening row81(for example, opening row81a) are positioned to be offset in the BB′ direction with respect to the openings80of the other opening row81(for example, opening row81b), and are positioned to coincide with a part of the opening80of another opening row81(for example, opening row81b) when viewed in the A direction. Further, in each opening row81, the plurality of openings80are positioned at equal intervals in the BB′ direction.

By arranging the plurality of opening rows81in the A direction to form one opening group82as described above, the width of the opening group82in the BB′ direction is longer than the width of the recording heads17ato17cin the BB′ direction. Therefore, the opening group82covers the entire ink ejection region of the recording heads17ato17cin the BB′ direction, and the ink ejected from all the ink ejection ports18of the recording heads17ato17cduring flushing passes through any opening80of the opening group82.

2-2. Pattern of Opening Groups Used when Flushing

In the present embodiment, the controller110drives the recording heads17ato17cto record an image on the paper P based on the image data transmitted from the outside (for example, a PC) while the first conveyor belt8conveys the paper P. At that time, by causing the recording heads17ato17cto perform flushing (flushing between sheets) between the conveyed paper P and the subsequent paper P clogging of the ink ejection port18is reduced or prevented.

Here, in the present embodiment, the controller110determines a pattern (combination) of a plurality of opening groups82, in the A direction, used for flushing in one cycle of the first conveyor belt8, according to the size of the paper P to be used. The size of the paper P to be used can be recognized by the controller110based on the information stored in the storage unit28(the size information of the paper P input by the operation panel27a). Note that the pattern of the opening group82is worded differently from the placement pattern of the paper P described later.

FIGS.6to9each illustrate an example of a pattern of the opening group82for each paper P having a different size. For example, when the paper P to be used is A4 size (horizontally placed) or letter size (horizontally placed), the controller110selects the pattern of the opening group82shown inFIG.6. That is, out of the six opening groups82shown inFIG.5, the controller110selects the opening groups82A,82C, and82F as the opening groups82to be used for flushing. When the paper P to be used is A4 size (vertically placed) or letter size (vertically placed), out of the six opening groups82, the controller110selects the opening groups82A and82D as the opening groups82to be used for flushing, as shown inFIG.7. When the paper P to be used is A3 size, B4 size, or legal size (all vertically placed), out of the six opening groups82, the controller110selects the opening groups82A,82B,82E as the opening groups82to be used for flushing, as shown inFIG.8. When the paper P to be used has a size of 13 inches×19.2 inches, out of the six opening groups82, the controller110selects groups82A and82D as the opening groups82to be used for flushing, as shown inFIG.9. Note that in each drawing, the opening80of the opening group82belonging to the above pattern is shown in black for convenience.

Then, the controller110causes the recording heads17ato17cto execute flushing at the time when the opening group82, positioned in the determined pattern, faces the recording heads17ato17cdue to the traveling of the first conveyor belt8. Here, the traveling speed of the first conveyor belt8(paper conveyance speed), the interval between the opening groups82A to82E, and the positions of the recording heads17ato17cwith respect to the first conveyor belt8are all known. Therefore, if the belt sensor24or25detects that an opening group82(for example, the opening group82A), serving as a reference, has passed due to the traveling of the first conveyor belt8, it is possible to know after how many seconds from the time of detection the opening groups82A to82E will pass through positions that face the recording heads17ato17c. Therefore, based on the detection result of the belt sensors24or25, the controller110causes the recording heads17ato17cto execute flushing at the time when the opening group82, positioned in the pattern determined above, faces the recording heads17ato17c.

Further, the controller110controls the supply of the paper P to the first conveyor belt8so as to be offset in the A direction with respect to the opening group82, which is positioned in the determined pattern. That is, the controller110supplies the paper P using the pair of registration rollers13between the plurality of opening groups82arranged in the A direction in the above pattern on the first conveyor belt8.

For example, when the paper P to be used is A4 size (horizontally placed) or letter size (horizontally placed), as shown inFIG.6, the controller110controls the pair of registration rollers13to supply the paper P at specific supply timing onto the first conveyor belt8, to place two sheets of paper between opening group82A and opening group82C, to place two sheets of paper between opening group82C and the opening group82F, and to place one sheet of paper between opening group82F and opening group82A (in the next cycle), on the first conveyor belt8. At this time, the controller110controls the pair of registration rollers13to supply the paper P onto the first conveyor belt8so each paper P can be arranged at a position separated by a specific distance or more in the A direction (including both the upstream side and the downstream side) from the opening groups82A,82C, and82F, which are positioned in a pattern on the first conveyor belt8. The specific distance is set to 10 mm as an example.

Here, the supply timing of the paper P by the pair of registration rollers13can be determined by the controller110based on the detection result of the belt sensor24or25. For example, when the belt sensor25detects that an opening group82(for example, the opening group82A), serving as a reference, has passed due to the traveling of the first conveyor belt8, the controller110can determine how many seconds from the time of detection the paper P should be supplied to the first conveyor belt8by the pair of registration rollers13to arrange the paper P at each position shown inFIG.6. Therefore, the controller110determines the supply timing of the paper P based on the detection result of the belt sensor25, and controls the pair of registration rollers13so that the paper P is supplied at the determined supply timing. As a result, the paper P can be arranged at each position shown inFIG.6on the first conveyor belt8at approximately equal intervals. In the example inFIG.6, five sheets of paper P can be conveyed in one cycle of the first conveyor belt8, and 150 ipm (images per minute) can be achieved as a number of prints (productivity) on paper P per minute.

When the paper P to be used is A4 size (vertically placed) or letter size (vertically placed), the controller110controls the pair of registration rollers13to supply the paper P at a specific supply timing onto the first conveyor belt8to place two sheets of paper P between an opening group82A and an opening group82D, and to place two sheets of paper P between the opening group82D and the opening group82A (in the next cycle), on the first conveyor belt8, as shown inFIG.7. In the example inFIG.7, four sheets of paper P can be conveyed in one cycle of the first conveyor belt8, and a productivity of 120 ipm can be achieved.

When the paper P to be used is A3 size, B4 size, or legal size (all vertically placed), as shown inFIG.8, the controller110controls the pair of registration rollers13to supply the paper P at specific supply timing onto the first conveyor belt8, to place one sheet of paper P between the opening82A and the opening group82B, one sheet of paper P between the opening group82B and the opening group82E, and one sheet of paper P between the opening group82E and the opening group82A (in the next cycle), on the first conveyor belt8. In the example inFIG.8, three sheets of paper P can be conveyed in one cycle of the first conveyor belt8, and a productivity of 90 ipm can be achieved.

When the paper P to be used has a size of 13 inches×19.2 inches, as shown inFIG.9, the controller110controls the pair of registration rollers13to supply the paper P at specific supply timing onto the first conveyor belt8to place one sheet between the opening group82A and the opening group82D, and to place one sheet of paper P between the opening group82D and the opening group82A (in the next cycle), on the first conveyor belt8. In the example inFIG.9, two sheets of paper P can be conveyed in one cycle of the first conveyor belt8, and a productivity of 60 ipm can be achieved.

That is, as shown inFIGS.6to9, the pattern of the opening group82used for flushing is determined according to the size of the paper P to be used and the placement pattern of the positioned paper P is determined which is offset from the opening group82in the A direction. From this, the placement pattern of the paper P placed on the first conveyor belt8can be said to be determined according to the size of the paper P to be used. Further, the flushing time can be said to be determined by the size of the paper P, the productivity, and the position of the opening group82(opening80) in the A direction.

3. Basic Concept of Flushing Control and Paper Supply Control to the First Conveyor Belt

Normally, by supplying the paper P to the first conveyor belt8and placing the paper P as shown inFIGS.6to9, the opening group82(opening80) determined according to the size of the paper P can be used for flushing.

However, if a slip of the paper P or the like occurs during the conveyance of the paper P and the supply of the paper P is delayed, the paper P may be placed coinciding with the opening group82of the first conveyor belt8.FIG.10schematically illustrates the placement positions of the sheets of paper P1to P3(for example, A3 size) on the first conveyor belt8when the sheets of paper P1to P3are sequentially supplied to the first conveyor belt8and a conveyance delay occurs for the second and subsequent sheets of paper P2and P3. As shown in the figure, due to the conveyance delay, the second sheet of paper P2is placed on the first conveyor belt8so as to coincide with the opening group82E used for flushing. In this case, if the recording heads17ato17care caused to execute flushing at the time of facing opening group82E, the ink ejected at the time of flushing adheres to the paper P2, and the image quality of the image formed on the paper P2deteriorates. Therefore, it is necessary to stop the flushing. However, when flushing using the opening group82E is stopped, since flushing does not occur before image formation on the third sheet of paper P3(between the sheets between the second sheet of paper P2and the third sheet of paper P3), there is a possibility that clogging due to drying of the ink may occur at any of the ink ejection ports18before the image is formed on the paper P3. As a result, it may not be possible to satisfactorily form an image on the paper P3.

FIG.11schematically illustrates a state in which a paper P1, longer in the conveyance direction than a set size (for example, A3 size) is supplied and arranged on the first conveyor belt8. As shown in the figure, when the size of the paper P1actually supplied to the first conveyor belt8is larger than the set size (for example, A3 size), since the paper P1is placed so as to cover the opening group82B for flushing, which is determined according to the set size, it is necessary to stop flushing using the opening group82B in order to avoid deterioration of the image quality of the paper P1. If the flushing is stopped, before the image is formed on the subsequent paper, clogging may occur at one of the ink ejection ports18due to drying of the ink and the image formation on the subsequent paper may not be performed satisfactorily.

Therefore, in the present embodiment, based on the detection result of the trailing edge of the paper P by the registration sensor21and the detection result of the opening group82(opening80) by the belt sensor25, the controller110determines whether the paper P, supplied to the first conveyor belt8by the pair of registration rollers13, coincides with the opening group82for flushing that moves due to the traveling of the first conveyor belt8when placed on the first conveyor belt8. Note that the trailing edge of the paper P is the edge on the upstream side in the conveyance direction of the paper P (A direction, supply direction). On the other hand, the leading edge of the paper P is the edge on the downstream side in the conveyance direction of the paper P.

Then, for example, as shown inFIGS.6to9, when the paper P does not coincide with the opening80for flushing when placed on the first conveyor belt8, that is, when the flushing opening80is positioned after the trailing edge of the preceding paper P (on the upstream side), and the controller110causes the recording heads17ato17cto perform flushing using the opening80. Since the paper P does not coincide with the opening80for flushing, even if the opening80is used to perform flushing, the ink for flushing does not adhere to the paper P, and it is possible to avoid deterioration of the image quality of the recorded image of the paper P. Further, by performing flushing, good quality ink can be ejected from the recording heads17ato17cin image formation onto the subsequent paper P, and the image formation can be performed satisfactorily. When the paper P does not coincide with the flushing opening80when placed on the first conveyor belt8, the supply of the subsequent paper P to the first conveyor belt8may be delayed, as will be described later (see, for example, 4-1-2b).

On the other hand, when the paper P is placed on the first conveyor belt8coinciding with the opening80for flushing, that is, the flushing opening80is positioned before (the downstream side of) the trailing edge of the preceding paper P, the controller110stops flushing using the opening80and controls the pair of registration rollers13to delay the supply of the subsequent paper P to the first conveyor belt8.

FIG.12schematically illustrates the placement position when the supply of the subsequent P3to P5to the first conveyor belt8is delayed when, for example, the conveyance of the sheet of paper P2to the first conveyor belt8is delayed during conveyance due to slipping or the like, and the sheet of paper P2coincides with the opening group82E for flushing. In the example of the figure, so that the leading edge of the subsequent paper P3is positioned after the opening group82F (upstream side) in the first cycle of the first conveyor belt8, based on the detection result of the opening group82F of the belt sensor25, the pair of registration rollers13are controlled to supply the subsequent paper P3to the first conveyor belt8. Further, with respect to the subsequent sheets P4and P5, the pair of registration rollers13are controlled to supply the subsequent sheets P4and P5onto the first conveyor belt8based on the detection results of the groups82B and82E by the belt sensor25so that the respective leading edges of the sheets P4and P5are positioned after the opening groups82B and82E in the second cycle of the first conveyor belt8.

As described above, by stopping the flushing using the opening80(first opening) of the opening group82E coinciding with the preceding paper P2, it is possible to avoid deterioration of the image quality of the recorded image of the preceding paper P2due to ink ejected by the flushing adhering to the preceding paper P2. Further, by controlling the pair of registration rollers13to delay the supply of the subsequent sheets P3to P5to the first conveyor belt8, the subsequent sheets of paper P3to P5can be placed after another opening80(on the upstream side) as a second opening on the first conveyor belt8(for example, the opening80of the opening groups82F,82B or82E). The second opening is an opening80detected after the first opening by the belt sensor25. As a result, it is possible to perform flushing using the other opening80before forming an image on the subsequent sheets P3to P5and image formation on the subsequent sheets P3to P5can be performed satisfactorily. As a result, it becomes possible to realize consistent image quality for all the printed sheets of paper P1to P5.

That is, even when the preceding paper P is, for some reason, placed so as to coincide with the opening80of the first conveyor belt8, by appropriately controlling the execution of the flushing by the recording heads17ato17cand the supply of the subsequent paper P by the pair of registration rollers13to the first conveyor belt, deterioration of the image quality of the recorded image of the preceding paper P can be avoided, and an opportunity to perform flushing before forming an image on the subsequent paper P is secured without fail, so the image formation on the subsequent paper P can be performed satisfactorily.

Further, even when the preceding paper P and the flushing opening80coincide, it is not necessary to end the image formation on the subsequent sheets of paper P3to P5for the reason that the flushing cannot be executed, and productivity can be ensured by continuing image formation on the subsequent sheets of paper P3to P5. Moreover, by the pair of registration rollers13controlling the supply of the sheets of paper P3to P5so that the leading edges of the sheets of paper P3to P5are each positioned after the other openings80, deterioration in production due to delay in the supply of the sheets of paper P3to P5can be minimized.

In particular, when the controller110determines that the preceding paper P2coincides with the opening80(first opening) of the opening group82E for flushing when placed on the first conveyor belt8, the controller stops the execution of flushing by the recording heads17ato17cat the time when facing the opening80due to the traveling of the first conveyor belt8, and the controller110causes the pair of registration rollers13to supply the subsequent paper P3to the first conveyor belt8, so that the subsequent paper P3is placed in the upstream side of the opening80(second opening) of the other opening group82F which is detected by the belt sensor25after detection of the first opening and moves by the traveling of the first conveyor belt8. Then, at the time when facing the second opening due to the traveling of the first conveyor belt8, the flushing by recording heads17ato17cis executed.

By stopping the flushing using the opening80coinciding with the preceding paper P2, it is possible to avoid deterioration of the image quality of the recorded image of the paper P2due to flushing. Further, since an opportunity to perform flushing using the second opening is secured before image formation on the subsequent paper P3, the above flushing can be executed to perform favorable image formation on the subsequent paper P3.

FIG.13schematically illustrates a placement state in which paper P1, longer in the conveyance direction than the set size (for example, A3 size), is placed on the first conveyor belt8so as to cover the opening80of the opening group82B according to the set size, and the placement when the supply of the subsequent sheets of paper P2and P3onto the first conveyor belt8is delayed. In the example of the figure, so that the leading edge of the subsequent paper P2is positioned after the opening group82E (upstream side) in the first cycle of the first conveyor belt8, based on the detection result of the opening group82E of the belt sensor25, the pair of registration rollers13is controlled to supply the subsequent paper P2to the first conveyor belt8. Further, by controlling the pair of registration rollers13based on the detection result of the opening group82B by the belt sensor25, the subsequent paper P3is supplied to the first conveyor belt8so that the leading edge of the subsequent paper P3is positioned after the opening group82B in the second cycle of the first conveyor belt8.

In this way, when the paper P1larger than the set size is placed on the first conveyor belt8, even if the opening80(first opening) of the opening group82B used for flushing of that set size is covered by the paper P1, by controlling the supply of the subsequent sheets of paper P2and P3as described above, it is possible to avoid deterioration of the image quality of the recorded image of the preceding paper P1. Before image formation on the subsequent sheets of paper P2and P3, by performing flushing using the opening80(second opening) from the other opening groups82E and82B, the image formation on subsequent sheets of paper P2and P3can be performed satisfactorily, and effects similar to the above can be obtained.

4. Specific Control of Flushing and Paper Supply

Hereinafter, specific control of flushing of the recording heads17ato17cand supply of the paper P to the first conveyor belt8will be described. Here, a first detection sensor that detects the paper P by being positioned on the upstream side of the pair of registration rollers13in the supply direction of the paper P is described as a registration sensor21, but the first detection sensor may be any sensor that is arranged between the paper feeder3and the pair of registration rollers13to detect the paper P, and is not limited to the above-mentioned registration sensor21.

In the following, among the openings80of the different opening groups82of the first conveyor belt8detected by the belt sensor25, an opening80detected first is also referred to as the first opening80a, and an opening80detected later is also referred to as a second opening80b. Therefore, in the first conveyor belt8, the second opening80bis positioned on the upstream side of the first opening80ain the belt traveling direction. The second opening80bmay be an opening80that appears first in the upstream side of the first opening80a, or may be an opening80that appears second or later.

FIG.14schematically shows an example of the positional relationship between the pair of registration rollers13, the registration sensor21, and the belt sensor25. For convenience of explanation below, the point where the paper P supplied toward the first conveyor belt8by the pair of registration rollers13merges with the first conveyor belt8is set as the merging position Q (illustrated by a star mark). Then, the conveyance distance of the paper P from the pair of registration rollers13to the merging position Q is A (mm), the conveyance distance of the paper P from the detection position of the registration sensor21to the merging position Q is B (mm), and the conveyance distance of the first conveyor belt8from the detection position of the belt sensor25the merge position Q to, that is, movement distance of the opening80(first opening80aor second opening80b) from the detection position to the merging position Q due to the travel of the first conveyor belt8is C (mm). It is assumed all of these are known. Further, the traveling speed of the first conveyor belt8is also known, and it is assumed that the traveling speed is equal to the supply speed of the paper P supplied from the paper feeder3to the first conveyor belt8via the pair of registration rollers13.

As shown in the figure, when the pair of registration rollers13, the registration sensor21and the belt sensor25are arranged so as to have an A<B<C relationship, the flushing control and the paper P supply control are classified into three cases as follows.

4-1-1. Detection of the Trailing Edge of the Preceding Paper, Leading Edge of the Subsequent Paper Reaches Pair of Registration Rollers

FIG.15schematically illustrates a state in which the registration sensor21has already detected the trailing edge of the preceding paper Pa, and when the belt sensor25has detected the first opening80afor flushing, the leading edge of the subsequent paper Pb has reached the pair of registration rollers13. It is assumed that the pair of registration rollers13are stopped. As described above, since the conveyance distances A and B are known, the conveyance distance of the paper Pb from the registration sensor21to the pair of registration rollers13can be obtained. Since the conveyance speed of the paper Pb by the paper feeder3or the like is also known, the controller110can determine how many seconds after the registration sensor21detects the leading edge of the paper Pb the leading edge of the paper Pb will reach the pair of registration rollers13.

Therefore, when the controller110determines that the leading edge of the subsequent paper Pb has reached the pair of registration rollers13, based on the detection of the leading edge of the subsequent paper Pb by the registration sensor21when the trailing edge of the preceding paper Pa has already been detected by the registration sensor21and at the point in time when the belt sensor25detects the first opening80afor flushing, the controller110causes the pair of registration rollers13to supply the subsequent paper Pb to the first conveyor belt8(starting the second paper supply), and causes the recording heads17ato17cto execute flushing at the time when facing the first opening80adue to the traveling of the first conveyor belt8, after the first opening80ahas moved the distance of (C−A) due to the traveling of the first conveyor belt8.

When the subsequent paper Pb is supplied to the first conveyor belt8at the above time, the traveling of the first conveyor belt8can cause the first opening80afor flushing of the first conveyor belt8, to be positioned between the preceding paper Pa and the subsequent paper Pb. Therefore, by using the first opening80ato perform flushing, since the ink ejected at the time of flushing does not adhere to the preceding paper Pa, it is possible to avoid deterioration of the image quality of the recorded image of the preceding paper Pa. Further, by performing flushing using the first opening80abefore forming an image on the subsequent paper Pb, image formation on the subsequent paper Pb can be performed satisfactorily.

4-1-2. Detection of the Trailing Edge of the Preceding Paper, when the Leading Edge of the Subsequent Paper has not Reached the Pair of Registration Rollers

FIG.16schematically illustrates a state in which the registration sensor21has already detected the trailing edge of the preceding paper Pa, and at the time when the belt sensor25has detected the first opening80afor flushing, the leading edge of the subsequent paper Pb has not reached the pair of registration rollers13. When it is assumed that the leading edge of the subsequent paper Pb reaches the pair of registration rollers13t seconds after the registration sensor21detects the leading edge of the subsequent paper Pb, when less than t seconds have passed since the registration sensor21detected the leading edge of the subsequent paper Pb, the controller110determines that the leading edge of the subsequent paper Pb has not reached the pair of registration rollers13. The flushing control in this case and the supply control of the subsequent paper Pb to the first conveyor belt8are further classified into the following two cases.

4-1-2a. When the Movement Amount D of the Opening is (C−A) or Less when the Leading Edge of the Subsequent Paper Reaches the Pair of Registration Rollers

FIG.17schematically illustrates a state in which when the leading edge of the subsequent paper Pb has reached the pair of registration rollers13, the movement amount D of the first opening80afor flushing, due to the traveling of the first conveyor belt8, detected by the belt sensor25, is (C−A) or less.

When the trailing edge of the preceding paper Pa has already been detected by the registration sensor21, based on the detection of the leading edge of the subsequent paper Pb by the registration sensor21, after it is determined that the leading edge of the subsequent paper Pb has not reached the pair of registration rollers13, as shown inFIG.17, at a later point in time when the leading edge of the subsequent paper Pb reaches the pair of registration rollers13, when the movement amount D of the first opening80afrom the detection position of the belt sensor25due to the traveling of the first conveyor belt8, is (C−A) or less, the controller110performs the following control. That is, until the movement amount D of the first opening80aexceeds (C−A) due to the traveling of the first conveyor belt8, the controller110stops the supply of the subsequent paper Pb by the pair of registration rollers13, and when the movement amount D exceeds (C−A), the controller110supplies the subsequent paper Pb to the first conveyor belt8by the pair of registration rollers13, and at the time when the first opening80afaces the recording heads17ato17c, the controller110causes the recording heads17ato17cto execute flushing. The movement amount D can be obtained from the product of the traveling speed of the first conveyor belt8and the elapsed time from when the belt sensor25detects the first opening80auntil the subsequent paper Pb reaches the pair of registration rollers13.

In such a supply control of the subsequent paper Pb, after the first opening80afor flushing has passed the merging position Q due to the traveling of the first conveyor belt8, the subsequent paper Pb can be merged and placed onto the first conveyor belt8. As a result, by performing flushing using the first opening80abefore forming an image on the subsequent paper Pb, image formation on the subsequent paper Pb can be performed satisfactorily.

4-1-2b. When the Movement Amount D of the Opening Exceeds (C−A) when the Leading Edge of the Subsequent Paper Reaches the Pair of Registration Rollers

FIG.18schematically illustrates a state in which the movement amount D of the first opening80afor flushing detected by the belt sensor25exceeds (C−A) due to the traveling of the first conveyor belt8, when the leading edge of the subsequent paper Pb reaches the pair of registration rollers13.

When the trailing edge of the preceding paper Pa has already been detected by the registration sensor21, based on the detection of the leading edge of the subsequent paper Pb by the registration sensor21, when it is determined that the leading edge of the subsequent paper Pb has not reached the pair of registration rollers13, the controller110later performs the following control, when, as shown inFIG.18, at the point in time when the leading edge of the subsequent paper Pb reaches the pair of registration rollers13, when the movement amount D of the first opening80a, from the detection position of the belt sensor25due to the traveling of the first conveyor belt8exceeds (C−A). That is, after the second opening80bof the other opening group82is detected by the belt sensor25, until the second opening80bmoves the distance (C−A) due to the traveling of the first conveyor belt8the controller stops the supply of the subsequent paper Pb by the pair of registration rollers13, and after the movement amount exceeds (C−A), the controller110causes the pair of registration rollers13to supply the subsequent paper Pb to the first conveyor belt8by, and at the time when the second opening80bfaces the recording heads17ato17c, causes the recording heads17ato17cto execute flushing.

For example, when, at the point in time when the leading edge of the subsequent paper Pb reaches the pair of registration rollers13, the movement amount D of the first opening80afor flushing, due to the traveling of the first conveyor belt8, detected by the belt sensor25, exceeds (C−A), it is possible to place the first opening80anear the merging position Q. In such a case, when the supply of the subsequent paper Pb to the first conveyor belt8(second paper supply) by the pair of registration rollers13is started, the interval between the first opening80aand the subsequent paper in the first conveyor belt8is too wide, so even if flushing is performed using the first opening80a, the ink in the ink ejection port18may dry in the time period until the next image formation on the subsequent paper Pb, and the effect of flushing may be reduced.

When the movement amount D of the first opening80a, which is detected first, exceeds (C−A), after the second opening80bis detected by the belt sensor25and the distance (C−A) is moved due to the traveling of the first conveyor belt8, the subsequent paper Pb is supplied onto the first conveyor belt8by the pair of registration rollers13, so that the subsequent paper Pb can be placed on the upstream side of and immediately after the second opening80bin the first conveyor belt8. As a result, by performing flushing using the second opening80bimmediately before forming an image on the subsequent paper Pb, image formation on the subsequent paper Pb can be performed satisfactorily. Further, in the first conveyor belt8, by narrowing the distance between the second opening80band the subsequent paper Pb, the interval between the opening80and the paper P is set to be easily constant for any paper80and it becomes easier to keep the time of flushing using the opening P and the time of image formation on the paper P constant. As a result, ink ejection control for the recording heads17ato17cbecomes easier

The control of the controller110in 4-1-2a and 4-1-2b described above can be summarized as follows. That is, when the controller110determines that the preceding paper Pa is placed on the first conveyor belt8without coinciding with the first opening80a(offset in the conveyance direction), based on the position of the first opening80aat the point in when the leading edge of the subsequent paper Pb reaches the pair of registration rollers13(based on whether the movement amount D of the first opening80ais (C−A) or less), the controller determines whether the paper Pb is to be placed on the upstream side of the first opening80aor on the upstream side of the second opening80b, and at a time based on the determination result, causes the pair of registration rollers13to supply subsequent paper Pb onto the first conveyor belt8, and between first opening80aand second opening80b, causes the recording heads17ato17cto perform flushing at a time when facing the opening80closest to the subsequent paper Pb placed on the first conveyor belt8. Since flushing can be performed using the first opening80aor the second opening80bimmediately before image formation on the subsequent paper Pb, a state having the maximum effect of flushing is maintained, and image formation on the subsequent paper Pb can be performed satisfactorily.

4-1-3. When the Trailing Edge of the Preceding Paper is not Detected

FIG.19schematically illustrates a state in which the registration sensor21does not detect the trailing edge of the preceding paper Pa at the time when the belt sensor25detects the opening80. The flushing control in this case is further classified into the following two cases.

4-1-3a. When the Movement Amount E of the Opening is Less than (C−B) when the Trailing Edge of the Preceding Paper Reaches the Registration Sensor

FIG.20schematically illustrates a state in which, when the trailing edge of the preceding paper Pa reaches the registration sensor21, the movement amount E of the first opening80afor flushing, due to the traveling of the first conveyor belt8, and which is detected by the belt sensor25is less than (C−B).

After the controller110determines that the trailing edge of the preceding paper Pa has not been detected by the registration sensor21, at a later point in time when the trailing edge of the preceding paper Pa is detected by the registration sensor21, when the movement amount E of the first opening80afrom the detection position of the belt sensor25due to traveling of the first conveyor belt8is less than (C−B), so the subsequent paper is placed on the upstream side of the first opening80a, the controller110causes the pair of registration rollers13to supply the subsequent paper Pb onto the first conveyor belt8, and at the time when the first opening80bfaces the recording heads17ato17c, causes the recording heads17ato17cto execute flushing. The movement amount E can be obtained from the product of the traveling speed of the first conveyor belt8and the elapsed time from when the belt sensor25detects the first opening80auntil the trailing edge of the preceding paper Pa is detected by the registration sensor21.

In this case, even after the registration sensor21detects the trailing edge, if the preceding paper Pa moves by the distance B, the first opening80adoes not catch up with the preceding paper Pa, and therefore, the preceding paper Pa will not be positioned coinciding with the first opening80aon the first conveyor belt8. Therefore, by using the first opening80ato cause the recording heads17ato17cto execute flushing, it is possible to avoid deterioration of the image quality of the recorded image of the preceding paper Pa. Further, since flushing is executed using the first opening80abefore the image formation on the subsequent paper Pb, image formation on the subsequent paper Pb can be performed satisfactorily.

4-1-3b. When the Movement Amount E of the Opening is (C−B) or More when the Trailing Edge of the Preceding Paper Reaches the Registration Sensor

FIG.21schematically illustrates a state when, when the trailing edge of the preceding paper Pa reaches the registration sensor21, the movement amount E of the first opening80afor flushing due to the traveling of the first conveyor belt8detected by the belt sensor25is (C−B) or more.

After the controller110determines that the trailing edge of the preceding paper Pa has not been detected by the registration sensor21, at the point in time when the trailing edge of the preceding paper Pa is detected by the registration sensor21, when the movement amount E of the first opening80afrom the detection position of the belt sensor25due to traveling of the first conveyor belt8is (C−B) or more, at the time when the first opening80A is facing the recording heads17ato17c, the controller110stops the execution of flushing by the recording heads17ato17c. Then, the controller110causes the pair of registration rollers13to supply the subsequent paper Pb onto the first conveyor belt8so that the subsequent paper Pb is placed on the upstream side of the second opening80bdetected by the belt sensor25, and at the time when facing the second opening80bdue to the traveling of the first conveyor belt8, the controller110causes the recording heads17ato17cto execute flushing.

Under the above conditions, when the preceding paper Pa merges the traveling first conveyor belt8, the preceding paper Pa is placed by coinciding with the first opening80a. Therefore, by using the first opening80ato stop the flushing of the recording heads17ato17c, it is possible to avoid deterioration of the image quality of the recorded image of the preceding paper Pa. Further, since flushing is executed using the second opening80bbefore the image formation on the subsequent paper Pb, image formation on the subsequent paper Pb can be performed satisfactorily.

FIG.22schematically illustrates another example of the positional relationship between the pair of registration rollers13, the registration sensor21, and the belt sensor25. As shown in the figure, when the pair of registration rollers13, the registration sensor21and the belt sensor25are arranged so as to have an A<C<B relationship, the flushing control and the paper P supply control are classified into three cases as follows.

4-2-1. Detection of the Trailing Edge of the Leading Paper, Reaching of the Leading Edge of the Trailing Paper to the Pair of Registration Rollers

FIG.23schematically illustrates a state in which the registration sensor21has already detected the trailing edge of the preceding paper Pa and at the point in time when the belt sensor25has detected the first opening80afor flushing, the leading edge of the subsequent paper Pb reaches the pair of registration rollers13. It is assumed that the pair of registration rollers13is stopped. In this case, after the first opening80ahas moved the distance (C−A) due to the traveling of the first conveyor belt8, the controller110and causes the pair of registration rollers13to supply the subsequent paper Pb onto the first conveyor belt8(starting the second paper supply), and causes the recording heads17ato17cto execute flushing at the time when facing the first opening80adue to the traveling of the first conveyor belt8.

When the subsequent paper Pb is supplied to the first conveyor belt8at the above time, the traveling of the first conveyor belt8can cause the first opening80afor flushing of the first conveyor belt8, to be positioned between the preceding paper Pa and the subsequent paper Pb. Therefore, by using the first opening80ato perform flushing, since the ink ejected at the time of flushing does not adhere to the preceding paper Pa, it is possible to avoid deterioration of the image quality of the recorded image of the preceding paper Pa. Further, by performing flushing using the first opening80abefore forming an image on the subsequent paper Pb, image formation on the subsequent paper Pb can be performed satisfactorily.

4-2-2. Detection of the Trailing Edge of the Leading Paper when the Leading Edge of the Subsequent Paper has not Reached the Pair of Registration Rollers

FIG.24schematically illustrates a state in which, the registration sensor21has already detected the trailing edge of the preceding paper Pa and at the point in time when the belt sensor25has detected the first opening80afor flushing, the leading edge of the subsequent paper Pb has not reached the pair of registration rollers13. The flushing control in this case and the supply control of the subsequent paper Pb to the first conveyor belt8are further classified into the following two cases.

4-2-2a. When the Movement Amount D of the Opening is (C−A) or Less when the Leading Edge of the Subsequent Paper has Reached the Pair of Registration Rollers

FIG.25schematically illustrates a state in which, when the leading edge of the subsequent Paper Pb has reached the registration rollers13, the movement amount D of the first opening80afor flushing, due to the traveling of the first conveyor belt8, detected by the belt sensor25is (C−A) or less.

When the trailing edge of the preceding paper Pa has already been detected by the registration sensor21, and based on the detection of the leading edge of the subsequent paper Pb by the registration sensor21, when it is determined that the leading edge of the subsequent paper Pb has not reached the pair of registration rollers13, as shown inFIG.25, at a later point in time when the leading edge of the subsequent paper Pb reaches the pair of registration rollers13, when the movement amount D of the first opening80a, from the detection position of the belt sensor25due to the traveling of the first conveyor belt8, is (C−A) or less, the controller110performs the following control. That is, until the movement amount D of the first opening80aexceeds (C−A) due to the traveling of the first conveyor belt8, the controller110stops the supply of the subsequent paper Pb by the pair of registration rollers13, and when the movement amount D exceeds (C−A), the controller110causes the pair of registration rollers13to supply the subsequent paper Pb onto the first conveyor belt8, and at the time when the first opening80afaces the recording heads17ato17c, the controller110causes the recording heads17ato17cto execute flushing.

In such a supply control of the subsequent paper Pb, after the first opening80afor flushing has passed the merging position Q due to the traveling of the first conveyor belt8, the subsequent paper Pb can be merged and placed onto the first conveyor belt8. As a result, by performing flushing using the first opening80abefore forming an image on the subsequent paper Pb, image formation on the subsequent paper Pb can be performed satisfactorily.

4-2-2b. When the Movement Amount D of the Opening Exceeds (CA) when the Leading Edge of the Subsequent Paper Reaches the Pair of Registration Rollers

FIG.26, schematically illustrates a state in which, when the leading edge of the subsequent paper Pb reaches the pair of registration rollers13, the movement amount D of the first opening80afor flushing detected by the belt sensor25, due to the traveling of the first conveyor belt8, exceeds (C−A).

When the trailing edge of the preceding paper Pa has already been detected by the registration sensor21, and based on the detection of the leading edge of the subsequent paper Pb by the registration sensor21, when it is determined that the leading edge of the subsequent paper Pb has not reached the pair of registration rollers13, as shown inFIG.26, at a later point in time when the leading edge of the subsequent paper Pb reaches the pair of registration rollers13, when the movement amount D of the first opening80a, from the detection position of the belt sensor25due to the traveling of the first conveyor belt8, exceeds (C−A), the controller110performs the following control. That is, after the second opening80bof the other opening group82is detected by the belt sensor25, until the second opening80bmoves the distance (C−A) due to the traveling of the first conveyor belt8, the controller stops the supply of the subsequent paper Pb by the pair of registration rollers13, and after the movement amount exceeds (C−A), the controller110causes the pair of registration rollers13to supply the subsequent paper Pb to the first conveyor belt8, and at the time when the second opening80bfaces the recording heads17ato17c, causes the recording heads17ato17cto execute flushing.

When the first opening80a, first detected by the belt sensor25, is positioned near the merging position Q due to the traveling of the first conveyor belt8, if the supply of the subsequent paper Pb by the pair of registration rollers13to the first conveyor belt8is started (second paper supply), the interval between the first opening80aand the subsequent paper Pb in the first conveyor belt8is too wide, so even if the first opening80ais used to perform flushing, the ink in the ink ejection port18may dry in the time period until the next image formation on the subsequent paper Pb, and the effect of flushing will be reduced.

When the movement amount D of the first opening80aexceeds (C−A), after the second opening80bis detected by the belt sensor25and then after moving the distance of (C−A) due to the traveling of the first conveyor belt8, the subsequent paper Pb is supplied onto the first conveyor belt8by the pair of registration rollers13, so that the subsequent paper Pb can be placed immediately after the second opening80bin the first conveyor belt8. As a result, by performing flushing using the second opening80bimmediately before forming an image on the subsequent paper Pb, image formation on the subsequent paper Pb can be performed satisfactorily. Further, in the first conveyor belt8, by narrowing the distance between the second opening80band the subsequent paper Pb, the interval between the opening80and the paper P can be made constant for any paper80and it becomes easier to keep the time of flushing using the opening P and the time of image formation on the paper P constant. As a result, ink ejection control for the recording heads17ato17cbecomes easier.

4-2-3. Trailing Edge of Preceding Paper not Detected

FIG.27schematically illustrates a state in which the registration sensor21does not detect the trailing edge of the preceding paper Pa when the belt sensor25detects the first opening80a. In this case, the controller110stops the execution of flushing by the recording heads17ato17cat the time when the first opening80afaces the recording heads17ato17c, causes the pair of registration rollers13to supply the subsequent paper Pb onto the first conveyor belt8so that the subsequent paper Pb is placed to the upstream side of the second opening80b(for example, after the belt sensor25detects the second opening80band after the second opening80btravels the distance (C−A)), and causes the recording heads17ato17cto execute flushing at the time of facing the second opening80bdue to the traveling of the first conveyor belt8.

If the registration sensor21does not detect the trailing edge of the preceding paper Pa at the point in time when the belt sensor25detects the first opening80a, the preceding paper Pa is placed on the first conveyor belt8to coincide with the first opening80a(the first opening80adoes not completely pass through the merging position Q). Therefore, by stopping the flushing of the recording heads17ato17cusing the first opening80a, it is possible to avoid deterioration of the image quality of the recorded image of the preceding paper Pa. Further, since flushing is executed using the second opening80bbefore the image formation on the subsequent paper Pb, image formation on the subsequent paper Pb can be performed satisfactorily.

In the present embodiment, the first conveyor belt8has opening groups82irregularly positioned in the conveyance direction. When such a first conveyor belt8is used, the paper P is placed on the opening group82positioned in a pattern corresponding to the size of the paper P so as to be offset in the conveyance direction, to form an image on the paper P, and flushing can be performed using the opening group82. However, when the preceding paper Pa coincides with the opening group82(opening80) positioned in the above pattern due to a conveyance delay from slipping or the like, it becomes difficult to expose the other opening80used for flushing between the preceding paper Pa and the subsequent paper Pb, and it becomes difficult to secure a flushing opportunity before forming an image on the subsequent paper Pb. Therefore, the control of the present embodiment, in which the flushing opportunity can be secured before the image formation on the subsequent paper Pb, is particularly effective when using the first conveyor belt8having the opening groups82irregularly positioned in the conveyance direction.

The first conveyor belt8is not limited to the configuration in which the opening groups82are irregularly positioned in the conveyance direction as described above. For example, the first conveyor belt8may have a configuration in which the opening groups82are positioned at equal intervals in the conveyance direction.

In the above, the case where the paper P is attracted to the first conveyor belt8by negative pressure suction and conveyed has been described. However, the first conveyor belt8may be charged and the paper P may be electrostatically attached to the first conveyor belt8and conveyed (electrostatic attachment method).

In the above, an example of using a color printer that records a color image using four color inks as an inkjet recording apparatus has been described, but even when a monochrome printer that records a monochrome image using black ink is used, it is possible to apply control of supply of the paper P as described in the present embodiment.

The present disclosure can be applied to an inkjet recording apparatus that ejects ink onto a recording medium to record an image.