JP2007015374A - Inkjet printer and method for removing bubble in inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printer of such a construction that bubbles generated in an upstream ink flow path of a filter can be certainly removed and thereby, a non-discharge or a discharge failure due to a decrease in the liquid droplet amount of a recording head can be avoided. <P>SOLUTION: This inkjet printer 1 comprises a recording head 7 with a nozzle 72 for discharging an ink, an ink tank 5 for storing the ink, an ink flow path 6 for supplying the ink to the recording head 7 from an ink tank 5, a valve 9 for opening/closing the ink flow path 6, a filter 62 installed in the ink flow path 6 between the valve 9 and the recording head 7, a suction cap 12 mounted on the recording head 7, covering a discharge aperture 73 when the ink is sucked from a discharge aperture 73 of a nozzle 72, and a suction pump 14 for sucking the ink from the discharge aperture 73 through the suction cap 12. In addition, an bubble storage part 61 for storing the prescribed amount of the bubbles K is provided in at least a part of the ink flow path 6 between the filter 62 and the recording head 7. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inkjet printer and a method for removing bubbles in an inkjet printer, and more particularly to an inkjet printer having a configuration for removing bubbles in an ink flow path and a method for removing bubbles in an inkjet printer.

  2. Description of the Related Art Conventionally, ink jet printers that record predetermined images by ejecting ink onto recording media such as paper and plastic thin plates have been proposed and put into practical use. The ink jet printer includes a recording head that discharges ink supplied from an ink tank through an ink flow path. For example, in a serial type ink jet printer, the recording head mounted on a carriage is moved in a predetermined scanning direction. In addition, a predetermined image is recorded on the recording medium by ejecting ink from the recording head toward the recording medium. In a line type ink jet printer, a predetermined image is recorded on a recording medium by ejecting ink from a line type recording head onto a recording medium conveyed in a predetermined conveying direction.

  By the way, in the above-described ink jet printer, as shown in FIG. 8, in order to remove foreign matters in the ink in the ink flow path 90 from the ink tank (not shown) to the pressure chamber 84 of the recording head 80. The filter 92 is often arranged. In the ink jet printer, the bubble K2 may enter the ink flow path 90. Among them, the bubble K2 that has entered the ink flow path 90 between the ink tank and the filter 92 is easily captured by the filter 92 and accumulates on the upstream side of the filter 92. The bubble K2 accumulated on the upstream side of the filter 92 closes the filter surface and becomes a flow path resistance, which causes ejection failure such as non-ejection in the recording head 80 and a drop in droplet amount.

  More specifically, when bubbles accumulate on the upstream side of the filter, a meniscus is formed in the mesh of the filter by the bubbles. For this reason, the area through which ink passes in the filter is reduced, the pressure due to the flow of ink from the ink flow path to the recording head is reduced, and as a result, the back pressure of the recording head is increased. When the back pressure of the recording head rises and exceeds a predetermined value, the meniscus formed at the nozzle ejection port in the recording head breaks, and bubbles enter the pressure chamber of the recording head from the ejection port. Due to the bubbles, the pressure required for ink ejection in the pressure chamber is lowered, and the ejection failure such as non-ejection and drop in droplet volume is caused in the recording head.

  Conventionally, it is said that bubbles accumulated on the upstream side of the filter pass through the filter and accumulate in the pressure chamber of the recording head, and the bubbles reduce the pressure required for ink ejection in the pressure chamber. However, since the bubbles passing through the filter are very small, it is considered that the bubbles are almost dissolved in the ink before reaching the pressure chamber. Therefore, in fact, as described above, it is considered that the pressure required for ink ejection in the pressure chamber is often reduced by the air bubbles entering from the ejection port that has been meniscus-breaked due to the increase in the back pressure, and this problem is solved. It is most important.

Further, conventionally, in order to remove the bubble K2 accumulated on the upstream side of the filter 92, a method is used in which the bubble K2 is sucked together with ink from the discharge port 83 of the nozzle 82 by the suction device, and the bubble K2 is sucked out from the discharge port. Yes. Here, a high pressure is required for the bubble K2 to pass through the filter 92. In order to generate this high pressure, a valve 95 is provided on the upstream side of the filter 92 in the ink flow path 90, and suction is performed by the suction device from the discharge port 83 of the nozzle 82 in a state in which the valve 95 is closed. A method has been proposed in which the flow rate of ink is increased by opening 95 to remove bubbles K2 (see, for example, Patent Document 1).
JP 2000-289225 A

  However, as described above, it is possible to perform suction with the suction device from the nozzle outlet while the valve provided upstream of the filter in the ink flow path is closed, and then open the valve. The pressure difference between the upstream side and the downstream side is high enough to cause a meniscus break, and unless the ink on the upstream side of the filter flows over the filter to the downstream side, the ink flow rate does not increase and bubbles are removed. The reality is that you can't.

Here, when the ink flow path downstream of the filter, that is, the ink flow path between the filter and the recording head is filled with ink and has no air bubbles, the liquid ink is sucked with the valve closed. However, the volume change with respect to pressure hardly occurs.
On the other hand, on the upstream side of the filter, bubbles are expanded by negative pressure by suctioning with the valve closed. However, as described above, there is almost no volume change on the downstream side of the filter. However, the meniscus does not break and air bubbles do not flow over the filter downstream.
For this reason, there have been cases in which bubbles remain in the ink flow path on the upstream side of the filter and the problem of ejection failure in the recording head cannot be resolved.

  Here, many of the recording heads in the conventional ink jet printer have a small number of nozzles, and since the flow passage cross-sectional area is small and the flow passage resistance is small, many of the filter areas are small. Even if the suction was performed without being conscious of the bubbles, it was possible to discharge the bubbles relatively easily. However, in recent years, particularly with the increase in the speed of image recording and the use of line heads, large recording heads with a large number of nozzles have been produced. As the recording head increases in size, the cross-sectional area of the flow path increases, and it is necessary to relatively increase the filter area in order to reduce the flow path resistance. For this reason, bubbles tend to remain on the upstream side of the filter, and when bubbles are removed using a valve in a large recording head, the flow rate is not simply increased, but the upstream and downstream sides of the filter consciously. Therefore, it is necessary to generate a large differential pressure that causes a meniscus break.

  Therefore, the problem of the present invention is that it has a configuration that can reliably remove bubbles generated in the ink flow path on the upstream side of the filter, and reliably eliminate ejection defects such as non-ejection and drop in droplet volume in the recording head. It is an object of the present invention to provide an ink jet printer that can be used and a method of removing bubbles in the ink jet printer.

The invention according to claim 1 is an inkjet printer,
A recording head having nozzles for ejecting ink;
An ink tank for storing ink;
An ink flow path for supplying ink from the ink tank to the recording head;
A valve for opening and closing the ink flow path;
A filter provided in an ink flow path between the valve and the recording head;
A suction cap attached to the recording head so as to cover the discharge port when ink is sucked from the discharge port of the nozzle;
A suction pump for sucking ink from the discharge port through the suction cap;
With
It is characterized in that at least a part of the ink flow path between the filter and the recording head is provided with a bubble storage part for storing a predetermined amount of bubbles.

As described above, according to the first aspect of the present invention, since the bubble storage section for storing a predetermined amount of bubbles is provided between the filter and the recording head, that is, at least a part of the ink flow path on the downstream side of the filter, Bubbles, which are gases accumulated in the bubble reservoir, expand by negative pressure by closing the valve and sucking from the nozzle outlet of the recording head, and then opening the valve will return the expanded bubbles to their original state. Shrink. At that time, a volume change corresponding to the amount of accumulated bubbles occurs. When a certain amount of pressure is applied to the filter due to such a volume change, a large pressure difference occurs between the upstream side and the downstream side of the filter, and ink or bubbles are generated from the upstream side to the downstream side of the filter at the moment when the valve is opened. Moves vigorously. The meniscus formed in the filter is broken by the momentum of the instantaneous movement of the ink and bubbles, and the ink on the upstream side of the filter flows over the filter to the downstream side. At the same time, bubbles on the upstream side of the filter also flow downstream through the filter. Then, some of the bubbles that flow downstream of the filter dissolve in the ink as they flow through the ink, and some of the bubbles merge with the bubbles accumulated in the bubble reservoir, and others are recorded. It is sucked out from the nozzle outlet of the head. In this way, bubbles generated in the ink flow path on the upstream side of the filter can be removed.
It should be noted that the volume change of the bubbles accumulated on the downstream side of the filter needs to be large enough to cause a meniscus break due to the generated differential pressure with respect to the volume change of the bubbles accumulated on the upstream side of the filter. .

The invention according to claim 2 is the inkjet printer according to claim 1,
It is characterized by comprising bubble injection means for sending bubbles to the bubble storage section.

  Thus, according to the second aspect of the present invention, since the bubble injection means for sending the bubbles to the bubble reservoir is provided, for example, the bubbles accumulated in the bubble reservoir of the ink flow path are discharged from the discharge port of the nozzle. Even if the air bubbles are lost, if the air bubbles are injected again, the air bubbles accumulated in the ink flow path on the upstream side of the filter can be easily returned to a state where they can be removed.

The invention according to claim 3 is the inkjet printer according to claim 2,
The bubble injection means is configured to inject bubbles into an ink flow path between the filter and the recording head and to send the bubbles into the bubble storage section.

The invention according to claim 4 is the inkjet printer according to claim 2,
The bubble injecting means is configured to inject bubbles from an ejection port of a nozzle of the recording head and to send the bubbles into the bubble storage unit.

The invention according to claim 5 is the inkjet printer according to claim 2,
The bubble injection means is configured to inject bubbles into the upstream side of the filter so as to cover the entire filter, transmit the bubbles to the downstream side of the filter, and send the bubbles to the bubble storage unit. It is said.

  As described above, in the inventions according to claims 3 to 5, a pattern having a specific configuration capable of sending air bubbles to the air bubble storage portion is defined.

The invention according to claim 6 is an inkjet printer,
A recording head having nozzles for ejecting ink;
An ink tank for storing ink;
An ink flow path for supplying ink from the ink tank to the recording head;
A valve for opening and closing the ink flow path;
Provided in an ink flow path between the valve and the recording head, a filter finer than the nozzle diameter of the nozzle;
A bubble injection means for injecting bubbles into the recording head;
Suction means for sucking ink in the recording head from the nozzle;
It is characterized by having.

  In this way, according to the invention described in claim 6, the bubbles injected by the bubble injection means expand with a negative pressure by sucking from the nozzle outlet of the recording head by closing the valve of the ink flow path, After that, the expanded bubble contracts to return to its original state by opening the valve. At that time, a volume change corresponding to the amount of bubbles occurs. When a certain amount of pressure is applied to the filter due to such a volume change, a large pressure difference occurs between the upstream side and the downstream side of the filter, and ink or bubbles are generated from the upstream side to the downstream side of the filter at the moment when the valve is opened. Moves vigorously. The meniscus formed in the filter is broken by the momentum of the instantaneous movement of the ink and bubbles, and the ink on the upstream side of the filter flows over the filter to the downstream side. At the same time, bubbles on the upstream side of the filter also flow downstream through the filter. Then, some of the bubbles that have flowed to the downstream side of the filter are dissolved in the ink as they flow through the ink, and others are sucked out from the nozzle outlets of the recording head. In this way, bubbles generated in the ink flow path on the upstream side of the filter can be removed.

The invention according to claim 7 is an inkjet printer,
A recording head having nozzles for ejecting ink;
An ink tank for storing ink;
An ink flow path for supplying ink from the ink tank to the recording head;
A valve for opening and closing the ink flow path;
Provided in an ink flow path between the valve and the recording head, a filter finer than the nozzle diameter of the nozzle;
A bubble injection means for injecting bubbles into the recording head;
Suction means for sucking ink in the recording head from the nozzle;
Controls the injection of bubbles into the recording head by the bubble injection means, the opening and closing of the valve, and the suction by the suction means so that the bubbles are transmitted from the upstream side to the downstream side of the filter and sent into the recording head. Control means to
It is characterized by having.

  Thus, according to the seventh aspect of the present invention, the air bubbles injected by the air bubble injecting means are expanded by negative pressure by sucking from the nozzle outlet of the recording head by closing the valve of the ink flow path, After that, the expanded bubble contracts to return to its original state by opening the valve. At that time, a volume change corresponding to the amount of bubbles occurs. When a certain amount of pressure is applied to the filter due to such a volume change, a large pressure difference occurs between the upstream side and the downstream side of the filter, and ink or bubbles are generated from the upstream side to the downstream side of the filter at the moment when the valve is opened. Moves vigorously. The meniscus formed in the filter is broken by the momentum of the instantaneous movement of the ink and bubbles, and the ink on the upstream side of the filter flows over the filter to the downstream side. At the same time, bubbles on the upstream side of the filter also flow downstream through the filter. Then, some of the bubbles that have flowed to the downstream side of the filter are dissolved in the ink as they flow through the ink, and others are sucked out from the nozzle outlets of the recording head. In this way, bubbles generated in the ink flow path on the upstream side of the filter can be removed.

The invention according to claim 8 is the inkjet printer according to claim 6 or 7,
It is characterized in that at least a part of the ink flow path between the filter and the recording head is provided with a bubble storage part for storing a predetermined amount of bubbles.

  Thus, according to the eighth aspect of the present invention, since the air bubble storage portion in which a predetermined amount of air bubbles are accumulated is provided, pressure is applied to the filter by the air bubbles accumulated in the air bubble storage portion, and the upstream side and the downstream side of the filter. A large pressure difference can be generated between them.

The invention according to claim 9 is the ink jet printer according to claim 8,
The bubble injection means is configured to inject bubbles into an ink flow path between the filter and the recording head and to send the bubbles into the bubble storage section.

The invention according to claim 10 is the ink jet printer according to claim 8,
The bubble injecting means is configured to inject bubbles from an ejection port of a nozzle of the recording head and to send the bubbles into the bubble storage unit.

The invention according to claim 11 is the inkjet printer according to claim 8,
The bubble injection means is configured to inject bubbles into the upstream side of the filter so as to cover the entire filter, transmit the bubbles to the downstream side of the filter, and send the bubbles to the bubble storage unit. It is said.

  As described above, in the inventions according to the ninth to eleventh aspects, a pattern of a specific configuration capable of sending air bubbles to the air bubble storing portion is defined.

The invention described in claim 12 is a method for removing bubbles in an ink jet printer.
A method of removing air bubbles in a filter finer than a nozzle diameter of the nozzle provided between an ink tank for storing ink and a recording head having a nozzle for discharging ink,
A bubble injection step of injecting bubbles into the recording head;
A valve closing operation step of closing a valve provided between the ink tank and the filter after injection of the bubbles;
An ink suction step for attaching a suction cap to a nozzle for discharging ink of the recording head, and sucking ink inside the recording head; and
A valve opening operation step of opening the valve after suction of the ink;
It is characterized by having.

  Thus, according to the twelfth aspect of the present invention, the air bubbles injected into the inside of the recording head are expanded by a negative pressure by sucking from the nozzle outlet of the recording head by closing the valve of the ink flow path. Thereafter, the expanded bubble is shrunk to return to its original state by opening the valve. At that time, a volume change corresponding to the amount of bubbles occurs. When a certain amount of pressure is applied to the filter due to such a volume change, a large pressure difference occurs between the upstream side and the downstream side of the filter, and ink or bubbles are generated from the upstream side to the downstream side of the filter at the moment when the valve is opened. Moves vigorously. The meniscus formed in the filter is broken by the momentum of the instantaneous movement of the ink and bubbles, and the ink on the upstream side of the filter flows over the filter to the downstream side. At the same time, bubbles on the upstream side of the filter also flow downstream through the filter. Then, some of the bubbles that have flowed to the downstream side of the filter are dissolved in the ink as they flow through the ink, and others are sucked out from the nozzle outlets of the recording head. In this way, bubbles generated in the ink flow path on the upstream side of the filter can be removed.

  According to the first aspect of the present invention, since bubbles generated in the ink flow path upstream of the filter can be removed, ejection failures such as non-ejection and drop in droplet volume in the recording head are surely eliminated. And a good image can be formed.

  According to the second to fifth aspects of the present invention, even if the air bubbles accumulated in the air bubble storage portion of the ink flow path are discharged from the discharge port of the nozzle, if the air bubbles are injected again, the filter Since it is possible to easily return the bubbles accumulated in the upstream ink flow path to a removable state, it is possible to more reliably eliminate ejection defects such as non-ejection and drop in droplet volume in the recording head. A good image can be formed.

  According to the sixth aspect of the present invention, since bubbles generated in the ink flow path upstream of the filter can be removed, ejection defects such as non-ejection and a drop in droplet volume in the recording head are surely eliminated. And a good image can be formed.

  According to the seventh aspect of the present invention, since bubbles generated in the ink flow path upstream of the filter can be removed, ejection defects such as non-ejection and a drop in droplet volume in the recording head are surely eliminated. And a good image can be formed.

  According to the eighth aspect of the present invention, the pressure is applied to the filter by the air bubbles accumulated in the air bubble storage portion, and a large pressure difference is generated between the upstream side and the downstream side of the filter, so that the moment when the valve is opened. In addition, the meniscus formed on the filter can be broken by the momentum of ink and bubbles moving from the upstream side to the downstream side of the filter.

  According to the ninth to eleventh aspects of the present invention, even if the air bubbles accumulated in the air bubble storage portion of the ink flow path are discharged from the discharge port of the nozzle, if the air bubbles are injected again, the filter Since it is possible to easily return the bubbles accumulated in the upstream ink flow path to a removable state, it is possible to more reliably eliminate ejection defects such as non-ejection and drop in droplet volume in the recording head. A good image can be formed.

  According to the twelfth aspect of the present invention, since bubbles generated in the ink flow path upstream of the filter can be removed, ejection defects such as non-ejection and drop in droplet volume in the recording head can be surely eliminated. And a good image can be formed.

  Hereinafter, embodiments of an inkjet printer according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the illustrated example.

  First, the configuration of an ink jet printer according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram showing the entire inkjet printer according to an embodiment of the present invention.

  The ink jet printer 1 is a serial type ink jet printer, which ejects ink onto a recording medium P and records an image on the recording medium P. The ink jet printer 1 is provided with a recording medium transport mechanism 41 (shown in FIG. 4). The recording medium transport mechanism 41 is formed in a flat plate shape and records on the platen 2 that supports the recording medium P from the non-recording surface. The medium P is transported in a transport direction orthogonal to the main scanning direction A while passing through the recording area Y in FIG.

Above the platen 2, a guide rail 3 extending along the main scanning direction A is disposed. A carriage 4 is supported on the guide rail 3, and the carriage 4 is mounted with a recording head 7 that ejects ink onto the recording medium P, and is moved along the guide rail 3 by a carriage driving mechanism 42 to a home position. From the area X to the maintenance area Z, it reciprocates in the main scanning direction A.
Further, as shown in FIG. 2, ejection ports 73 of a number of nozzles 72 for ejecting ink are disposed on the ejection surface 71 of the recording head 7 facing the recording medium P.

  In the inkjet printer 1 according to the present embodiment, a total of four recording heads 7 are arranged on the carriage so that four colors of ink of black (K), yellow (Y), magenta (M), and cyan (C) can be ejected. 4 is installed. In the present embodiment, four recording heads 7 are arranged in a line in the main scanning direction A. The ink used in the ink jet printer is not limited to this, and for example, colors such as light yellow (LY), light magenta (LM), and light cyan (LC) can be used. In this case, the recording head 7 corresponding to each color is mounted on the carriage 4.

  Each of these recording heads 7 is connected to an ink tank 5 for storing black, yellow, magenta, and cyan inks via an ink flow path 6 such as an ink supply pipe as shown in FIG. Yes. That is, the ink in the ink tank 5 is supplied to each recording head 7 by the ink flow path 6. Further, the ink flow path 6 between the ink tank 5 and the recording head 7 is provided with a damper 8 that is a shock absorber for the vertical movement of the carriage 4 and a flow path control valve 9 that opens and closes the ink flow path 6. Yes. Further, as shown in FIG. 2, a filter for removing foreign matters in the ink is provided in the ink flow path 6 between the flow path control valve 9 and the pressure chamber 74 for ejecting ink in the recording head 7. 62 is installed. Further, at least a part of the ink flow path 6 between the filter 62 and the pressure chamber 74 of the recording head 7 is provided with a bubble storage portion in which a predetermined amount of bubbles K are accumulated. In the present embodiment, a bubble reservoir 61 is specially formed in a part of the ink passage 6 having a normal diameter as the bubble reservoir. Note that the amount of bubbles stored in the bubble storage unit is determined appropriately in consideration of various conditions such as the type of ink and the shape of the ink flow path.

  Moreover, in this embodiment, the bubble 43 is sent with respect to the sensor 43 which detects the bubble K which exists in the bubble reservoir 61 as the said bubble reservoir, or detects the amount of bubbles, and the bubble reservoir 61 as the said bubble reservoir. Bubble injection means 44. Then, by detecting the bubble K or the amount of bubbles by the sensor 43, the differential pressure necessary for the bubble K of the bubble reservoir 61 to suck the bubble K2 (shown in FIG. 6) accumulated on the upstream side of the filter 62 is generated. When it is determined that the number of bubbles has been reduced to such an extent that it cannot be performed, the bubble injection means 44 sends a necessary amount of bubbles K to the bubble reservoir 61. The bubble injection means may be a mechanical device or mechanism for sending bubbles to the bubble reservoir (bubble reservoir) with a pump or the like. ) May be communicated to inject bubbles.

Also, the bubble injection means 44 of this embodiment injects bubbles K into the ink flow path 6 between the filter 62 and the recording head 7 as shown in FIG. Although it is the structure which sends in a bubble, it is not restricted to this.
For example, the bubble injecting means may be configured to inject bubbles from the nozzle discharge port of the recording head and to send the bubbles into the bubble storage section. Specifically, bubble injection means having the following configuration can be mentioned.
In this case, the suction device 11 to be described later can be operated so as to reverse the suction operation, that is, so that the fluid flows backward from the suction cap 12 to the recording head 7. Then, with the suction cap 12 covering the ejection surface 71 of the recording head 7, pressure is applied from the suction device 11 to break the meniscus of the ejection port 73 of the recording head 7, thereby causing air (bubbles K) to flow. The bubble K is fed into the bubble reservoir 61 which is a bubble reservoir through the recording head 7. Further, as another example, the suction device 11 or another device is configured to be able to give an impact to the recording head 7, and by applying an impact to the recording head 7, the meniscus of the discharge port 73 is configured. The bubble K may be injected into the recording head 7 from the discharge port 73, and the bubble K may be sent to the bubble reservoir 61, which is a bubble storage portion, via the recording head 7.

Further, the bubble injection means may be configured to inject bubbles into the upstream side of the filter so as to cover the entire filter, transmit the bubbles to the downstream side of the filter, and send the bubbles to the bubble storage unit. Specifically, bubble injection means having the following configuration can be mentioned.
In this case, bubble injecting means such as a compressor or an air valve for injecting bubbles into the upstream side of the filter 62, that is, between the ink tank 5 and the filter 62 is provided. Further, the bubble injection means is configured to inject the bubble K so as to cover not the part of the upstream side of the filter 62 but the entire filter. Then, the bubble K is injected so as to cover the entire filter 62, the discharge cap 71 of the suction device 11 covers the ejection surface 71 of the recording head 7, and the bubble K passes through the filter 62, and the bubble storage unit. The bubble K can be sent to and stored in the bubble reservoir 61.
Note that bubbles K2 (see FIG. 6) that cause ejection failure in the recording head 7 accumulate in a part of the upstream side of the filter 62, but if the bubbles K are injected so as to cover the entire filter in this way, the filter 62 Therefore, the meniscus of the filter 62 can be easily broken, and the bubbles K can pass through the filter 62 with a small pressure. The above example utilizes this fact to allow the bubbles K to pass through the filter 62 with a small pressure, and to send the bubbles to the bubble storage section.
Further, as a configuration for injecting bubbles to the upstream side of the filter 62, a configuration in which the bubbles K are sent together with ink from the ink tank 5 can be cited in addition to the above-described configuration.

  In addition to the specially formed bubble reservoir 61 as shown in FIG. 2, as the bubble reservoir, the diameter of the ink flow path 6A as shown in FIG. 5 is slightly increased on the downstream side of the filter 62A. 61A may be provided, or a bubble storage part according to another form may be provided. In FIG. 5, the same parts as those shown in FIG. 2 are denoted by the same reference numerals and description thereof is omitted.

  In some cases, a large-capacity main ink tank and a small-capacity sub-ink tank are provided as ink tanks for storing ink. At this time, ink is supplied from the main ink tank to the sub ink tank, the ink is temporarily stored in the sub ink tank, and then the ink is supplied from the sub ink tank to the recording head. At this time, the filter is provided at least between the sub ink tank and the recording head.

  The outer end of the recording area Y in which the carriage 4 is movable and the platen 2 is provided is a maintenance area Z, and a maintenance unit for performing head maintenance on the recording head 7 in the maintenance area Z. 10 is provided. The maintenance unit 10 is provided with a suction device 11 that sucks ink from the discharge port 73 of the nozzle 72, a cleaning blade 16, an ink receiver 17, and the like.

  The suction device 11 is provided with four suction caps 12 corresponding to the number of recording heads 7 that cover the ejection surface 71 of the recording head 7. In addition, an ink communication tube 13 that communicates with the inside of the suction cap 12 is provided on the bottom surface of the suction cap 12. A suction pump 14 is provided in the middle of the ink communication pipe 13, and a waste ink tank 15 for receiving the sucked ink is provided at the lower end of the ink communication pipe 13.

An ink receiver 17 is provided near one end of the suction cap 12 to receive ink ejected when ink is ejected from the ejection port 73 of the recording head 7, adjacent to the ink receiver 17. A blade 16 that wipes off the ink adhering to the ejection surface 71 is provided.
The suction pump 14 includes a cylinder pump and a tube pump, and operates with the suction cap 12 covering the discharge surface 71, whereby ink inside the recording head 7 is discharged from the discharge port 73 together with foreign matter and bubbles. A suction force for suction is generated.

Instead of the blade 16 in the maintenance unit 10, an ink absorbing device that plays a role of sucking ink adhering to the ejection surface 71 of the recording head 7 may be provided.
As the ink absorbing device, for example, a sheet-shaped ink absorber, a roll shaft provided at both ends of the ink absorber for winding the ink absorber, and the lower surface side of the ink absorber between the two roll shafts And a heater configured to warm the ink absorber and a roll shaft driving mechanism.

  A position opposite to the maintenance area Z across the platen 2 at the other end of the movement range of the carriage 4 is a home position area X. In the home position area X, the recording head 7 is placed. A moisturizing unit 20 for moisturizing is provided. The moisturizing unit 20 is provided with four moisturizing caps 21 that moisturize the ink of the recording head 7 by covering the ejection surface 71 when the recording head 7 is in a standby state. These four moisturizing caps 21 are arranged corresponding to the arrangement of the recording heads 7 so as to simultaneously cover the ejection surfaces 71 of the four recording heads 7.

Next, the control configuration in the present embodiment will be described with reference to FIG.
In the present embodiment, as shown in FIG. 4, the inkjet printer 1 includes a carriage drive mechanism 42, a recording medium transport mechanism 41, a recording head 7, a maintenance unit 10, a moisturizing unit 20, a flow path control valve 9, a sensor 43, A control unit 30 for controlling the bubble injection means 44 and the like is provided. The control unit 30 includes a CPU 31, a RAM 32, a ROM 33, and the like. The control unit 30 includes a carriage drive mechanism 42, a recording medium transport mechanism 41, a recording head 7, and a maintenance unit 10 via an interface (not shown). The moisturizing unit 20, the flow path control valve 9, the sensor 43, the bubble injection means 44, the input unit 45, and the like are connected.

  The control unit 30 reciprocates the carriage 4 in the main scanning direction A, repeats conveyance and stop of the recording medium P in accordance with the operation of the carriage 4, and intermittently conveys the recording medium P in the conveyance direction. The operations of the carriage drive mechanism 42 and the recording medium transport mechanism 41 are controlled.

  Further, the control unit 30 is connected with an input unit 45 and a recording head 7 including a host computer and a scanner for inputting image information, a keyboard for inputting image recording conditions, and the like. The recording head 7 is operated based on the input predetermined signal and ink is ejected onto the recording medium P to record a predetermined image.

The control unit 30 operates the maintenance unit 10 and the flow path control valve 9 to perform head maintenance when a predetermined maintenance start condition is met, every time a predetermined time elapses after the power is turned on, and by manual operation. So that it is controlled.
Further, the control unit 30 controls the moisturizing unit 20 to perform a moisturizing operation by the moisturizing cap 21 in a standby state that is not during image formation or head maintenance.

  In addition, the control unit 30 monitors the presence or absence or amount of bubbles in the bubble storage unit such as the bubble reservoir 61 by the sensor 43, and detects that the bubble K has decreased or disappeared by the sensor 43. In this case, the bubble injection means 44 is operated so as to send a predetermined amount of bubbles to the bubble storage unit.

  Next, the operation of the inkjet printer 1 configured as described above will be described.

  First, in the present embodiment, the carriage 4 on which the recording head 7 is mounted is in a standby state on the moisturizing unit 20 at a time other than image recording and head maintenance, and the moisturizing unit 20 is provided with the moisturizing unit 20. By covering the discharge port 73 of the nozzle 72 in the recording head 7 with the cap 21, the discharge port 73 of the nozzle 72 is protected.

Next, the operation at the time of image recording will be described.
When the user sets the recording medium P in the ink jet printer 1 and turns on the power of the ink jet printer 1, power is supplied to each part of the ink jet printer 1. When image information is sent from the input unit 45 to the control unit 30 of the ink jet printer 1 and setting information for various image recording conditions is sent, the control unit 30 starts image recording and moves the recording head 7. The mounted carriage 4 moves above the platen 2. At that time, the moisturizing unit 20 is lowered to remove the moisturizing cap 21 from the recording head 7.

  When the carriage 4 reaches a predetermined position, the recording medium transport mechanism 41 transports the recording medium P in the transport direction, and simultaneously the carriage 4 reciprocates along the main scanning direction A. Here, the recording medium conveyance mechanism 41 repeats conveyance and conveyance stop in order, and conveys the recording medium P intermittently.

  While stopping in the intermittent conveyance, the carriage 4 moves forward in the main scanning direction A on the platen 2 and moves backward or reciprocates. As the carriage 4 moves, the plurality of recording heads 7 move together with the carriage 4, and these recording heads 7 eject ink from the ejection ports 73 of the ejection surface 71 toward the recording medium P during the movement. The ink droplets ejected and ejected as droplets land on the stopped recording medium P. By repeating this, a predetermined image is recorded on the recording medium P.

Next, operations during head maintenance will be described.
During head maintenance of the recording head 7, first, the carriage 4 moves along the guide rail 3 above the suction device 11 of the maintenance unit 10, and the discharge cap 73 of the recording head 7 is covered with the suction cap 12. Then, the flow path control valve 9 is closed, the suction pump 14 is operated, and suction is started. Then, as the negative pressure with respect to the ink flow path 6 increases, the bubbles on the upstream side of the filter 62 and the bubbles K on the downstream side of the filter 62 expand. At this time, the expansion of the bubble K on the downstream side of the filter is made larger than the expansion of the bubble on the upstream side of the filter. Thereafter, the flow path control valve 9 is opened with the suction pump 14 stopped and the suction cap 12 in close contact. Then, the air bubbles upstream and the downstream air bubbles of the filter 62 contract to return. At that time, since the volume change of the bubbles on the downstream side is made larger, a differential pressure with a magnitude causing a meniscus break is generated in the direction in which the ink flows to the ejection port 73, and the ink is discharged from the upstream side of the filter 62. At the same time, bubbles flow downstream. Then, some of the bubbles that have flowed downstream of the filter 62 are dissolved in the ink while flowing in the ink, and the other part are bubbles and bubbles accumulated in the bubble reservoir 61 (bubble reservoir). The other unity is sucked out from the discharge port 73 of the nozzle 72 in the recording head 7. By such a suction operation, bubbles generated in the ink flow path 6 on the upstream side of the filter 62 are removed. If all the bubbles on the upstream side of the filter cannot be removed by one suction operation, the same suction operation is repeated several times.

Thereafter, the maintenance operation such as separating the suction cap 12, moving the carriage 4 to the position of the blade 16, and wiping the discharge surface 71 with the blade 16 is performed.
Then, the blade 16 is separated and the carriage 4 is moved to the ink receiver 17 to perform idle ejection, and the head maintenance operation is completed.

  Here, an ink suction process for sucking ink from the recording head 7 will be described in detail with reference to FIG.

When the ink suction process is performed, first, the control unit 30 sends a bubble to the bubble reservoir 61 by performing a bubble injection process described later (step: S1). In addition, when bubbles naturally accumulate in the bubble reservoir 61, the following suction processing may be performed without performing the bubble injection processing separately.
Next, the control unit 30 keeps the flow path control valve 9 closed (step; S2), and brings the suction cap 12 into contact with the recording head 7 so as to cover the ejection port 73 of the recording head 7 (step; S3). ). When the suction cap 12 comes into contact with the recording head 7, the control unit 30 operates the suction pump 14 to start the suction operation (step; S4). As a result, the bubbles on the upstream side of the filter 62 and the bubbles K on the downstream side of the filter 62 expand as the negative pressure on the ink flow path 6 increases. At this time, the expansion of the bubble K on the downstream side of the filter is made larger than the expansion of the bubble on the upstream side of the filter.
Thereafter, the control unit 30 stops the suction pump 14 and opens the flow path control valve 9 with the suction cap 12 in close contact (Step S5). Thereby, the air bubbles upstream and the downstream air bubbles of the filter 62 contract to return. At this time, since the volume change is larger in the air bubbles on the downstream side of the filter as described above, a differential pressure having a magnitude that causes a meniscus break is generated in the direction in which the ink flows to the ejection port 73, and the filter 62. Bubbles flow into the downstream side together with ink from the upstream side.
Then, some of the bubbles that have flowed downstream of the filter 62 are dissolved in the ink while flowing in the ink, and the other part are bubbles and bubbles accumulated in the bubble reservoir 61 (bubble reservoir). The other unity is sucked out from the discharge port 73 of the nozzle 72 in the recording head 7. When bubbles generated in the ink flow path 6 on the upstream side of the filter 62 are removed by such a suction operation, the control unit 30 moves the suction cap 12 away from the recording head 7 (step; S6), and the ink The suction process is terminated.

  Next, the bubble injection process for sending bubbles to the bubble reservoir 61 (bubble storage part) will be described in detail with reference to FIGS. Various methods can be applied as the bubble injection process for sending the bubbles to the bubble reservoir 61. In this embodiment, the method using the bubble injection unit 44 (see FIG. 10) and the bubble injection unit 44 are not used. Next, a method of sending bubbles into the bubble reservoir 61 by the suction device 11 (see FIG. 11) will be described.

First, when the bubbles are sent into the bubble reservoir 61 using the bubble injection means 44, the control unit 30 opens the bubble injection means 44 as shown in FIG. 10 (step; S11). Thereby, the bubble K is inject | poured into the upstream of the filter 62 (step; S12). When the bubbles are injected, the control unit 30 closes the bubble injection means 44 (step; S13), and ends the bubble injection operation.
The bubble injecting means 44 may inject the bubbles K into the ink flow path 6 between the filter 62 and the recording head 7 and send the bubbles into the bubble reservoir 61. However, it is also possible to inject air bubbles so as to cover the entire filter on the upstream side of the filter, transmit the air bubbles to the downstream side of the filter, and send the air bubbles to the air bubble reservoir 61.

Next, when the bubbles are sent into the bubble reservoir 61 by the suction device 11 without using the bubble injection means 44, the control unit 30 first closes the flow path control valve 9, as shown in FIG. (Step; S21), the suction cap 12 is brought into contact with the recording head 7 so as to cover the ejection port 73 of the recording head 7 (Step; S22). When the suction cap 12 comes into contact with the recording head 7, the control unit 30 operates the suction pump 14 to perform an operation opposite to the suction operation, that is, an operation for causing the ink to flow backward from the suction cap 12 to the recording head 7 (step S23). As a result, pressure is applied from the suction device 11 toward the inside of the recording head 7 to break the meniscus of the ejection port 73 of the recording head 7 and inject air (bubbles K) into the ejection port 73 of the recording head 7. The bubble K is sent into the bubble reservoir 61 through the recording head 7.
When the bubbles are injected, the control unit 30 moves the suction cap 12 away from the recording head 7 (step; S24), and ends the bubble injection operation.

Next, an experiment for demonstrating the effect of the present invention will be described.
Here, a part of the ink jet printer 1 of the present embodiment is used to vary the amount of bubbles accumulated in the bubble storage section, and then suction is performed by the suction device 11 of the maintenance unit 10, and the filter 62 at that time is used. The relationship between the differential pressure before and after and the volume of bubbles passing through the filter 62 was investigated. Details will be described below.

First, as shown in FIG. 6, a sufficient amount of air bubbles K2 is injected into the upstream side (ink tank 5 side) of the filter 62 provided in the ink flow path 6 in order to remove foreign matters in the ink. Further, the bubble injection means 44 (in this experiment, an air valve communicating with the outside to directly inject bubbles into the bubble reservoir 61 provided in the ink flow path 6 between the filter 62 and the recording head 7) is controlled. In this case, the air valve communicating with the outside is controlled to be opened and closed, and a predetermined amount of bubbles K are stored in the bubble reservoir 61 which is a bubble reservoir.
Then, the ejection port 73 of the recording head 7 is covered with the suction cap 12 of the suction device 11 of the maintenance unit 10. Then, the flow path control valve 9 is closed and the suction pump 14 is operated to start suction. The differential pressure before and after the filter 62 at this time is measured with a pressure gauge 46 attached in advance. When the differential pressure reaches a predetermined pressure, the suction pump 14 is stopped and the suction cap 12 is in close contact with the flow path. The control valve 9 is opened. Here, if the differential pressure is a pressure that causes the meniscus break in the filter 62, the bubble K <b> 2 passes through the meniscus break of the filter 62 with the ink vigorously downstream. At this time, the volume of the bubble K2 that has passed through the downstream side of the filter 62 together with the ink is measured. This was repeated by changing the differential pressure, and the relationship between the differential pressure and the volume of the bubble K2 passing through the filter 62 was investigated. Further, the amount of bubbles K to be reserved in the bubble reservoir ^61, the case where the ^{0mm 3, 20mm 3, 40mm 3} , 60mm 3, to investigate the relationship between the volume of bubbles K2 passing through the differential pressure and the filter 62, respectively, The results are shown in the graph of FIG. In the filter 62 and ink used here, the meniscus break value is about 0.1 atm. In the case of a normal filter and ink, the meniscus break value is often 0.3 atm or less.

These results, the amount of bubbles K to be reserved in the bubble reservoir ^61, in the case of 20mm ^3, 40mm ^3, 60mm ^3, the predetermined amount of air bubbles K2 is passed through the filter 62 when respectively applying a predetermined pressure difference. On the other hand, when the amount of the bubble K stored in the bubble reservoir 61 is 0 mm ³ , the bubble K2 does not pass through the filter 62 even if any differential pressure is applied. From this, it was found that the bubble K2 passes through the filter 62 due to the presence of the bubble K in the bubble reservoir 61.

  It was also found that the bubble K2 passes through the filter 62 when the differential pressure exceeds the meniscus break value of the filter 62 (here, 0.1 atm). Furthermore, at a predetermined differential pressure (here, 0.3 atm) or more, the volume of the bubble K2 that passes through does not change, and the upper limit of the bubble K2 that passes through is almost the same as the amount of the bubble K stored in the bubble reservoir 61. I understood it.

As described above, according to the ink jet printer of the present embodiment, the bubble storage unit that stores a predetermined amount of bubbles is provided between the filter and the recording head, that is, at least a part of the ink flow path on the downstream side of the filter. The bubble, which is the gas accumulated in the bubble reservoir, expands with a negative pressure by closing the valve and sucking it from the nozzle outlet of the recording head, and then the expanded bubble is restored by opening the valve. Shrinks with wax. At that time, a volume change corresponding to the amount of accumulated bubbles occurs. On the other hand, the air bubbles accumulated on the upstream side of the filter are expanded by a negative pressure by sucking from the nozzle outlet of the recording head with the valve closed, and then the expanded air bubbles are restored by opening the valve. The volume contracts according to the amount of air bubbles accumulated during the contraction. The difference in volume between the two causes a differential pressure between the upstream side and the downstream side of the filter. When the differential pressure is high enough to break the meniscus formed on the filter, the ink on the upstream side of the filter flows downstream beyond the filter. At the same time, bubbles on the upstream side of the filter also flow downstream through the filter. Some of the bubbles that have flowed to the downstream side of the filter are dissolved in the ink as they flow through the ink, and others are sucked out from the discharge ports of the nozzles in the recording head. In this way, bubbles generated in the ink flow path on the upstream side of the filter can be removed.
As a result, ink curing on the nozzle surface can be reduced and a normal image recording state can be maintained.
It should be noted that the volume change of the bubbles accumulated on the downstream side of the filter needs to be large enough to cause a meniscus break due to the generated differential pressure with respect to the volume change of the bubbles accumulated on the upstream side of the filter. .

Further, in the present embodiment, since there is provided a bubble injection means for sending bubbles into the bubble reservoir by injecting bubbles between the filter and the recording head, that is, in the ink channel on the downstream side of the filter, Even if the air bubbles accumulated in the air bubble storage section are discharged from the nozzle outlet, if the air bubbles are injected again, the air bubbles accumulated in the ink flow path on the upstream side of the filter can be easily returned to a removable state. be able to.
As a result, ejection failures such as non-ejection and a drop in the amount of droplets in the recording head can be more reliably eliminated, and a better image can be formed.
When the bubble injection means is configured to inject bubbles from the discharge port of the nozzle of the recording head and send the bubbles to the bubble storage section, or so that the bubble injection means covers the entire filter upstream of the filter. The same effect is also obtained when the bubbles are injected, the bubbles are permeated downstream of the filter, and the bubbles are sent to the bubble storage part.

  The ink jet printer according to the present invention is not limited to the above-described embodiment, and various improvements and design changes may be made without departing from the spirit of the present invention.

For example, the recording head is not limited to a configuration including a piezoelectric element, and may include a heater, for example.
Further, although the ink jet printer of the present embodiment includes four recording heads, the present invention is not limited thereto, and an appropriate number of recording heads may be provided.

  Further, in the present embodiment, the ink jet printer according to the present invention causes the recording head mounted on the carriage to reciprocate in the scanning direction and ejects ink from the recording head while transporting the recording medium in the transport direction. Although it is a serial type ink jet printer that forms an image, it can also be applied to a line type ink jet printer that forms an image by ejecting ink from a recording head fixed to the printer body and transporting a recording medium. It is.

1 is a diagram illustrating a schematic configuration of an inkjet printer according to an embodiment of the present invention. It is the schematic which shows the ink flow path near the filter in the inkjet printer of this embodiment. FIG. 2 is a schematic diagram illustrating a configuration between an ink tank and a recording head in the ink jet printer according to the embodiment. It is a control block diagram which shows the main control structures in the inkjet printer of this embodiment. It is the schematic which shows the ink flow path near the filter in the inkjet printer of other embodiment. It is the schematic which shows the mode of the experiment which demonstrates the effect of this invention. It is a graph which shows the experimental result of the experiment which demonstrates the effect of this invention. It is the schematic which shows the ink flow path near the filter in the conventional inkjet printer. It is a flowchart explaining the process of the suction process of the bubble removal method in the inkjet printer which concerns on one Embodiment of this invention. It is a flowchart explaining the process of the bubble injection | pouring process of the bubble removal method in the inkjet printer which concerns on one Embodiment of this invention. It is a flowchart explaining the modification of the process of the bubble injection | pouring process shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet printer 3 Guide rail 4 Carriage 5 Ink tank 6, 6A Ink flow path 7 Recording head 9 Flow path control valve (valve)
DESCRIPTION OF SYMBOLS 10 Maintenance unit 11 Suction apparatus 12 Suction cap 14 Suction pump 20 Moisturizing unit 30 Control part 43 Sensor 44 Bubble injection means 61 Bubble accumulation (bubble accumulation part)
61A Enlarged part (bubble storage part)
62, 62A Filter 71 Discharge surface 72 Nozzle 73 Discharge port 74 Pressure chamber A Main scanning direction K Bubble (bubble collected in bubble reservoir)
K2 bubbles (bubbles accumulated on the upstream side of the filter)
P Recording medium

Claims (12)

A recording head having nozzles for ejecting ink;
An ink tank for storing ink;
An ink flow path for supplying ink from the ink tank to the recording head;
A valve for opening and closing the ink flow path;
A filter provided in an ink flow path between the valve and the recording head;
A suction cap attached to the recording head so as to cover the discharge port when ink is sucked from the discharge port of the nozzle;
A suction pump for sucking ink from the discharge port through the suction cap;
With
An ink jet printer, comprising: a bubble storage portion in which a predetermined amount of bubbles are accumulated in at least a part of an ink flow path between the filter and the recording head.   The inkjet printer according to claim 1, further comprising a bubble injecting unit that feeds bubbles into the bubble storage unit.   The inkjet according to claim 2, wherein the bubble injecting means is configured to inject bubbles into an ink flow path between the filter and the recording head, and to send the bubbles into the bubble storage section. Printer.   The inkjet printer according to claim 2, wherein the bubble injecting unit is configured to inject bubbles from an ejection port of a nozzle of the recording head and to send the bubbles into the bubble storage unit.   The bubble injection means is configured to inject bubbles into the upstream side of the filter so as to cover the entire filter, transmit the bubbles to the downstream side of the filter, and send the bubbles to the bubble storage unit. The inkjet printer according to claim 2. A recording head having nozzles for ejecting ink;
An ink tank for storing ink;
An ink flow path for supplying ink from the ink tank to the recording head;
A valve for opening and closing the ink flow path;
Provided in an ink flow path between the valve and the recording head, a filter finer than the nozzle diameter of the nozzle;
A bubble injection means for injecting bubbles into the recording head;
Suction means for sucking ink in the recording head from the nozzle;
An ink jet printer comprising: A recording head having nozzles for ejecting ink;
An ink tank for storing ink;
An ink flow path for supplying ink from the ink tank to the recording head;
A valve for opening and closing the ink flow path;
Provided in an ink flow path between the valve and the recording head, a filter finer than the nozzle diameter of the nozzle;
A bubble injection means for injecting bubbles into the recording head;
Suction means for sucking ink in the recording head from the nozzle;
Controls the injection of bubbles into the recording head by the bubble injection means, the opening and closing of the valve, and the suction by the suction means so that the bubbles are transmitted from the upstream side to the downstream side of the filter and sent into the recording head. Control means to
An ink jet printer comprising:   8. The ink jet printer according to claim 6, further comprising: a bubble storage unit that stores a predetermined amount of bubbles in at least a part of an ink flow path between the filter and the recording head.   9. The ink jet according to claim 8, wherein the bubble injecting means is configured to inject bubbles into an ink flow path between the filter and the recording head and to send the bubbles into the bubble storage section. Printer.   9. The ink jet printer according to claim 8, wherein the bubble injecting unit is configured to inject bubbles from an ejection port of a nozzle of the recording head and to send the bubbles into the bubble storage unit.   The bubble injection means is configured to inject bubbles into the upstream side of the filter so as to cover the entire filter, transmit the bubbles to the downstream side of the filter, and send the bubbles to the bubble storage unit. An ink jet printer according to claim 8. A method of removing air bubbles in a filter finer than a nozzle diameter of the nozzle provided between an ink tank for storing ink and a recording head having a nozzle for discharging ink,
A bubble injection step of injecting bubbles into the recording head;
A valve closing operation step of closing a valve provided between the ink tank and the filter after injection of the bubbles;
An ink suction step for attaching a suction cap to a nozzle for discharging ink of the recording head, and sucking ink inside the recording head; and
A valve opening operation step of opening the valve after suction of the ink;
A method of removing bubbles in an ink jet printer, comprising:

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