JP2017030154A - Printer, and cleaning method of discharge head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of performing pressure purge without using compressed air.SOLUTION: A printer comprises: a discharge head 32 which includes a plurality of nozzles; a main tank 51 which stores ink; a sub-tank 53 which is arranged between the main tank 51 and the discharge head 32; a supply pump 52 which feeds ink from the main tank 51 to the sub-tank 53; a meniscus control unit 64 which decompresses the inside of the sub-tank 53; a pressure adjustment unit 60 which controls the meniscus pressure in the discharge head 32; a pressure adjustment control valve 62 which is arranged between the sub-tank 53 and the pressure adjustment unit 60; and a purge control unit which controls pressure purge for compressing the inside of the discharge head 32 to discharge ink. The purge control unit compresses the inside of the sub-tank 53 by driving the supply pump 52 while closing the pressure adjustment control valve 62 and executes the pressure purge to the discharge head 32.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a printing apparatus and a discharge head cleaning method.

  Conventionally, a printing apparatus having an ejection head that ejects ink onto a recording medium has been used. A conventional printing apparatus is described in Patent Document 1, for example.

  In an ejection head having a plurality of nozzles, if ink is not ejected for a long time, the ink solvent evaporates from the ink surface in the nozzles, and the ink aggregates or the viscosity of the ink increases. As a result, there is a risk that ink ejection from the nozzles may be defective. Therefore, as described in Patent Document 1, it is known that in this type of printing apparatus, so-called pressure purge is performed in which the inside of the ejection head is pressurized and ink is ejected from the nozzles.

JP2012-11668A

  In the printing apparatus described in Patent Literature 1, by supplying compressed air to a back pressure tank disposed between the main tank and the discharge nozzle, the discharge nozzle is pressurized through the back pressure tank to be discharged from the nozzle. Ink is ejected and pressure purge is performed.

  However, in such a configuration, if dust or moisture is contained in the air, aggregates and precipitates are generated in the ink, which may clog the nozzle. Therefore, when pressurizing a tank for storing ink using compressed air, it is necessary to use clean and dry air. That is, it is necessary to prepare an expensive and large-sized apparatus for supplying clean and dry air.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique capable of performing a pressure purge without using compressed air.

  In order to solve the above-described problems, a first invention of the present application includes an ejection head including a plurality of nozzles that eject ink onto a recording medium, a main tank that stores the ink, the main tank, and the ejection head. A meniscus pressure adjusting unit for controlling the meniscus pressure in the discharge head, including a sub tank disposed between the main tank, a liquid feeding means for sending the ink from the main tank to the sub tank, and a pressure reducing mechanism for reducing the pressure in the sub tank. And a purge control unit that controls a pressure purge that pressurizes the inside of the discharge head to discharge the ink, and the purge control unit. Pressurizes the inside of the sub-tank by driving the liquid feeding means while keeping the inside of the sub-tank in an air-tight state by the air-tight transition section. The executes pressure purged to the ejection head is a printing device.

  A second invention of the present application is the printing apparatus according to the first invention, further comprising a head opening / closing valve disposed between the sub tank and the discharge head, wherein the purge control unit is configured to perform the pressure purge. Then, after pressurizing the inside of the sub-tank which is in an airtight state with the head opening / closing valve closed, the head opening / closing valve is opened to discharge the ink from the discharge head.

  A third invention of the present application is the printing apparatus according to the second invention, further comprising pressure measuring means for measuring a pressure inside the sub-tank, wherein the purge control unit is configured to perform the pressure purge when the pressure purge is performed. After the pressure in the sub tank measured by the measuring means reaches a predetermined pressure, the head opening / closing valve is opened.

  A fourth invention of the present application is the printing apparatus according to any one of the first to third inventions, wherein the plurality of heads are disposed between the plurality of ejection heads, the sub tank, and the ejection heads. And the purge control unit is capable of executing partial purge for performing the pressure purge only on a part of the discharge heads of the plurality of discharge heads. In the partial purge, The purge control unit opens the head opening / closing valve disposed between the ejection head to be purged and the sub tank, and the head opening / closing valve disposed between the other ejection head and the sub tank. The pressure purge is executed in a state where is closed.

  A fifth invention of the present application is the printing apparatus according to any one of the first to fourth inventions, wherein the meniscus pressure adjusting unit has one end connected to the sub-tank and one end connected to the main pipe. An air release pipe that communicates with the end and the other end of which is open to the atmosphere; an air release control valve that is inserted into the air release pipe; an exhaust pipe that has one end communicating with the other end of the main pipe; and An exhaust pump that is connected to the other end and exhausts gas in the exhaust pipe; and an exhaust control valve that is inserted into the exhaust pipe, and the airtight transition is controlled by a pressure adjustment control valve that is inserted into the main pipe. The pressure reducing mechanism is configured by the exhaust pipe, the exhaust pump, and the exhaust control valve.

  A sixth invention of the present application is a cleaning method for cleaning an ejection head having a plurality of nozzles in a printing apparatus that ejects ink onto a recording medium, wherein a) the main tank stores the ink, and the main tank stores the ink. And a step of pressurizing the inside of the sub-tank, and b) communicating the pressurized sub-tank and the ejection head through the inside of the ejection head. Pressurizing and ejecting the ink from the ejection head to perform a pressure purge.

  A seventh invention of the present application is the cleaning method of the sixth invention, wherein the step b) is performed after the pressure in the sub tank reaches a predetermined pressure in the step a).

  An eighth invention of the present application is the cleaning method according to the sixth invention or the seventh invention, wherein the printing apparatus includes a plurality of ejection heads, a plurality of sub-tanks, and a plurality of ejection heads disposed between the ejection heads. In the step b), the pressurized sub tank and the discharge head to be purged are communicated with each other, and the communication between the sub tank and the other discharge heads is blocked. Only some of the ejection heads are pressurized and purged.

  According to the first to eighth inventions of the present application, the inside of the sub-tank is pressurized by liquid feeding from the main tank to the sub-tank, so that the inside of the discharge head can be pressurized to perform the pressure purge. Thereby, pressure purge can be performed without using compressed air.

  In particular, according to the second and seventh inventions of the present application, it is possible to perform a pressure purge on the discharge head after the pressure in the sub-tank has been raised in advance. Thereby, a high pressure can be applied to the ejection head from the start of the pressure purge. Therefore, the purge time can be shortened and the ink consumption can be suppressed.

  In particular, according to the fourth and eighth inventions of the present application, only a part of the ejection heads that need to be cleaned can be pressurized and purged. Thereby, ink consumption can be suppressed.

1 is a diagram conceptually illustrating a configuration of a printing apparatus according to an embodiment. It is a bottom view of the head unit concerning one embodiment. It is the figure which showed notionally the structure of the ink supply system of the printing apparatus which concerns on one Embodiment. It is the block diagram which showed the control system of the printing apparatus which concerns on one Embodiment. It is a flowchart which shows the flow of the cleaning process which concerns on one Embodiment. It is a flowchart which shows the flow of the cleaning process which concerns on a modification.

  Embodiments of the present invention will be described below with reference to the drawings. Hereinafter, the direction in which the printing paper 9 is transported is referred to as “transport direction”, and the horizontal direction orthogonal to the transport direction is referred to as “width direction”.

<1. Configuration of printing device>
FIG. 1 is a diagram conceptually showing the configuration of a printing apparatus 1 according to an embodiment of the present invention. FIG. 2 is a bottom view of the head unit 30. FIG. 3 is a diagram conceptually illustrating the configuration of the ink supply system of the printing apparatus 1.

  The printing apparatus 1 ejects ink droplets from the plurality of ejection heads 32 of the head unit 30 onto the printing paper 9 while conveying the printing paper 9 that is a long belt-like recording medium, thereby forming a color image on the printing paper 9. Is an ink jet printing apparatus. As shown in FIGS. 1 to 3, the printing apparatus 1 includes a transport mechanism 20, four head units 30, a UV lamp 40, an ink supply unit 50, a pressure adjustment unit 60, an ink discharge unit 70, a control unit 10, and an operation unit. 100.

  The transport mechanism 20 is a mechanism for transporting the printing paper 9 in the transport direction, which is the longitudinal direction of the print paper 9. The transport mechanism 20 according to the present embodiment includes an unwinding unit 21, a plurality of transport rollers 22, and a winding unit 23.

  A motor (not shown) serving as a power source is connected to the unwinding unit 21, the plurality of transport rollers 22, and the winding unit 23. When the control unit 10 drives the motor, the unwinding unit 21, the plurality of transport rollers 22, and the winding unit 23 rotate. Note that a part or all of the transport roller 22 may be a driven roller that is not connected to the motor and rotates according to the movement of the printing paper 9.

  The plurality of transport rollers 22 constitute a transport path for the printing paper 9. Each conveyance roller 22 guides the printing paper 9 to the downstream side of the conveyance path by rotating about the horizontal axis. Further, when the printing paper 9 comes into contact with the plurality of conveying rollers 22, tension is applied to the printing paper 9. In this manner, the printing paper 9 is fed out from the unwinding unit 21 and conveyed to the winding unit 23 along the conveyance path constituted by the plurality of conveyance rollers 22. The conveyed printing paper 9 is collected to the winding unit 23.

  The four head units 30 are arranged above the conveyance path of the printing paper 9 with an interval in the conveyance direction. The four head units 30 respectively eject cyan (C), magenta (M), yellow (Y), and black (K) ink droplets onto the upper surface of the printing paper 9. In the printing apparatus 1 of the present embodiment, UV curable UV ink is used.

  The printing apparatus 1 according to the present embodiment ejects ink droplets from each head unit 30 while the printing paper 9 passes only under each head unit 30 once, thereby causing a desired image pattern on the printing paper 9. Is a so-called one-pass type recording apparatus. Since the structures of the four head units 30 are substantially the same, the structure of one head unit 30 will be described below.

  As shown in FIG. 2, the head unit 30 includes a housing 31 and a plurality of ejection heads 32 attached to the housing 31. Each discharge head 32 has a discharge surface exposed on the lower surface of the housing 31. A plurality of nozzles 33 are two-dimensionally arranged on the ejection surface, which is the lower surface of the ejection head 32. The individual nozzles 33 are arranged with their positions shifted in the width direction, and one nozzle 33 is assigned to an area of 1 pixel width on the printing paper 9.

  As shown in FIG. 2, the plurality of ejection heads 32 are arranged in a staggered manner (alternatingly in an oblique manner) along the width direction. That is, the plurality of ejection heads 32 includes a first ejection head row 301 arranged in the width direction and a second ejection head row 302 arranged in the width direction at a position downstream of the first ejection head row 301. And have. The ejection heads 32 of the first ejection head row 301 and the ejection heads 32 of the second ejection head row 302 are alternately arranged in the width direction. As described above, the plurality of ejection heads 32 are arranged in a staggered manner, so that the plurality of ejection heads 32 are arranged at a high density in the width direction.

  As shown in FIG. 3, each ejection head 32 includes a casing 321, an ink storage chamber 322 and a plurality of ink chambers 323 provided in the casing 321, an ink supply port 324, and a plurality of nozzles 33.

  The ink storage chamber 322 is primarily filled with ink supplied from the outside of the ejection head 32 via the ink supply port 324. The ink storage chamber 322 and each of the plurality of ink chambers 323 communicate with each other via a communication port 325. Accordingly, when the pressure in the ink chamber 323 decreases, ink is supplied from the ink storage chamber 322 to the ink chamber 323.

  The ink chamber 323 is secondarily filled with ink in the ejection head 32. In FIG. 3, six ink chambers 323 are shown for convenience, but in the actual ejection head 32, ink chambers 323 are provided for each of a large number of nozzles 33.

  A nozzle 33 is provided at each lower end of the ink chamber 323. The nozzle 33 is a small hole that communicates the ink chamber 323 with the external space. When ink is not ejected, the ink surface forms a meniscus inside the nozzle 33. The lower end portion of the nozzle 33 is disposed so as to be exposed on the lower surface of the casing 321.

  A pressure generating element 326 is disposed on each wall surface of the ink chamber 323. The pressure generating element 326 is an in-head pressurizing mechanism that pressurizes ink stored in the ink chamber 323.

  The discharge head 32 of this embodiment is a so-called piezo-type discharge head. Therefore, a piezoelectric element is used for the pressure generating element 326 of the present embodiment. When an ejection signal that is an electrical signal is sent from the control unit 10 to the pressure generating element 326, the pressure generating element 326 is deformed and pressure is applied to the ink filled in the ink chamber 323. When the pressure in the ink chamber 323 increases, the ink in the ink chamber 323 is ejected from the nozzle 33 as droplets.

  The ejection head of the present invention is not limited to the piezo method. For example, a so-called thermal-type ejection head that uses a heater as the pressure generating element to heat the liquid in the pressure chamber to generate bubbles to increase the pressure in the pressure chamber may be used.

  The UV lamp 40 irradiates ultraviolet rays on the upper surface side of the printing paper 9 conveyed by the conveyance mechanism 20 on the downstream side of the four head units 30. The ink droplets ejected on the printing paper 9 are cured by irradiation with ultraviolet rays. As a result, the image is fixed on the printing paper 9.

  As shown in FIG. 3, the ink supply unit 50 includes a main tank 51, a supply pump 52, a sub tank 53, and a pipe 54. The pipe 54 includes a first supply pipe 541 that connects the main tank 51 and the sub tank 53, a second supply pipe 542 that connects the sub tank 53 and the plurality of discharge heads 32, and a plurality of branch pipes 543.

  The main tank 51 is a container for storing ink before supply. One end of the first supply pipe 541 is connected to the inside of the main tank 51 in the vicinity of the lower end portion of the main tank 51. The other end of the first supply pipe 541 is connected to the inside of the sub tank 53.

  The supply pump 52 is liquid feeding means for sending ink from the main tank 51 to the sub tank 53. The supply pump 52 is inserted in the first supply pipe 541. The supply pump 52 generates an ink flow from the main tank 51 toward the sub tank 53 in the first supply pipe 541 in accordance with an operation signal from the control unit 10. As a result, the ink stored in the main tank 51 is supplied to the sub tank 53 via the first supply pipe 541.

  A first on-off valve 544 and a filter 545 are inserted in the first supply pipe 541. The first on-off valve 544 is disposed between the main tank 51 and the supply pump 52. The filter 545 is disposed between the supply pump 52 and the sub tank 53.

  When the first on-off valve 544 is in a closed state, the communication of the first supply pipe 541 is blocked. That is, when the first on-off valve 544 is in the closed state, the communication between the main tank 51 and the sub tank 53 is blocked. On the other hand, when the 1st on-off valve 544 is an open state, the communication of the 1st supply piping 541 is ensured. The first on-off valve 544 is normally closed, and is opened only when the supply pump 52 is operated to supply ink from the main tank 51 to the sub tank 53. Thereby, it is possible to prevent the pressure fluctuation in the sub tank 53 from affecting the main tank 51.

  The filter 545 removes solid components and foreign matters of ink that passes through the first supply pipe 541. Thereby, it is suppressed that solid components and foreign matters are mixed in the ink supplied to the sub tank 53 and the ejection head 32. The filter 545 may be disposed at a place other than between the supply pump 52 and the sub tank 53 as long as the filter 545 is interposed in the first supply pipe 541.

  The sub tank 53 temporarily stores ink to be supplied to the ejection head 32. The sub tank 53 includes a liquid level sensor 531, a pressure adjustment pipe 532, and a pressure sensor 533. Ink is stored in the lower part of the sub tank 53, and the upper part of the sub tank 53 is filled with clean air.

  The liquid level sensor 531 is a sensor that detects the liquid level height of the ink stored in the sub tank 53. Based on the signal from the liquid level sensor 531, the control unit 10 detects the liquid level of the ink in the sub tank 53 and determines whether or not to supply ink to the sub tank 53. When supplying ink to the sub tank 53, the control unit 10 opens the first opening / closing valve 544 and operates the supply pump 52. When the supply of ink to the sub tank 53 is stopped, the control unit 10 stops the supply pump 52 and closes the first on-off valve 544.

  The sub tank 53 is connected to each discharge head 32 via a second supply pipe 542 and a branch pipe 543. One end of the second supply pipe 542 is connected to the inside of the sub tank 53 in the vicinity of the lower end portion of the sub tank 53. The other end of the second supply pipe 542 is connected to one end of the plurality of branch pipes 543. The other end of the branch pipe 543 is connected to the ink supply port 324 of the ejection head 32.

  A second on-off valve 546 is inserted in each branch pipe 543. That is, each second on-off valve 546 is a head on-off valve disposed between the sub tank 53 and each discharge head 32. Therefore, when the second on-off valve 546 is opened, the sub-tank 53 and the discharge head 32 connected to the branch pipe 543 through which the second on-off valve 546 is inserted communicate with each other. Accordingly, the ink stored in the sub tank 53 is supplied to the ink storage chamber 322 of the ejection head 32 via the second supply pipe 542, the branch pipe 543, and the ink supply port 324. On the other hand, when the second on-off valve 546 is closed, the communication between the sub tank 53 and the discharge head 32 connected to the branch pipe 543 through which the second on-off valve 546 is inserted is blocked.

  As described above, the sub tank 53 is indirectly connected to the ink storage chamber 322 and the ink chamber 323 of the discharge head 32 via the second supply pipe 542 and the branch pipe 543. Therefore, if the second on-off valve 546 is opened, the pressure in the discharge head 32 can be adjusted by adjusting the pressure in the sub tank 53.

  One end of the pressure adjustment pipe 532 is connected to the upper part of the sub tank 53. A pressure sensor 533 is provided at the other end of the pressure adjustment pipe 532. The pressure in the pressure adjusting pipe 532 is substantially the same as the pressure of the gas filled in the upper part of the sub tank 53. Therefore, the pressure sensor 533 serves as a pressure measurement unit that measures the pressure inside the sub tank 53 in a purge operation described later.

  The pressure adjustment unit 60 controls the pressure in the ejection head 32. The pressure adjustment unit 60 includes a main pipe 61, a pressure adjustment control valve 62, an air release unit 63, and a meniscus control unit 64. The atmosphere release unit 63 includes an atmosphere release pipe 631 and an atmosphere release control valve 632. The meniscus control unit 64 includes an exhaust pipe 641, an exhaust pump 642, an exhaust control valve 643, a buffer tank 644, and a pressure sensor 645.

  One end of the main pipe 61 is connected in communication with the pressure adjustment pipe 532 in the middle thereof. One end of the atmosphere opening pipe 631 and one end of the exhaust pipe 641 are connected to the other end of the main pipe 61. In other words, the atmosphere opening portion 63 and the meniscus control portion 64 are connected to the other end of the main pipe 61. A pressure adjustment control valve 62 and a buffer tank 644 are interposed in the main pipe 61.

  The pressure adjustment control valve 62 is an on-off valve that controls communication of the main pipe 61. When the pressure adjustment control valve 62 is open, the sub tank 53 and the buffer tank 644 communicate with each other. Further, when the pressure adjustment control valve 62 is closed, the communication between the sub tank 53 and the buffer tank 644 is blocked.

  One end of the atmosphere opening pipe 631 is connected to the other end of the main pipe 61 in communication. Further, the other end of the air release pipe 631 is open to the atmosphere. An air release control valve 632 is interposed in the air release pipe 631. When the atmosphere release control valve 632 is in the open state, the main pipe 61 is opened to the atmosphere. That is, when both the pressure adjustment control valve 62 and the atmosphere release control valve 632 are open, the sub tank 53 and the buffer tank 644 are opened to the atmosphere. Further, when the atmosphere release control valve 632 is in a closed state, the main pipe 61 and the outside air are blocked.

  Therefore, when the pressure in the sub tank 53 is to be lowered when the pressure in the buffer tank 644 is higher than the atmospheric pressure, the control unit 10 opens both the pressure adjustment control valve 62 and the atmosphere release control valve 632. State. Then, the pressure in the sub tank 53 and the buffer tank 644 can be quickly reduced to the atmospheric pressure.

  One end of the exhaust pipe 641 is connected in communication with the other end of the main pipe 61. Further, an exhaust pump 642 is connected to the other end of the exhaust pipe 641. The exhaust pump 642 is connected to the other end of the exhaust pipe 641 and discharges the gas in the exhaust pipe 641. An exhaust control valve 643 is inserted in the exhaust pipe 641. When the exhaust control valve 643 is in the open state, the main pipe 61 and the exhaust pump 642 communicate with each other. Further, when the exhaust control valve 643 is in a closed state, the communication between the main pipe 61 and the exhaust pump 642 is blocked.

  Therefore, when both the pressure adjustment control valve 62 and the exhaust control valve 643 are opened and the exhaust pump 642 is driven, the gas in the sub tank 53 and the buffer tank 644 becomes the pressure adjustment pipe 532, the main pipe 61, and the exhaust pipe 641. It is discharged through. As a result, the pressure in the sub tank 53 can be reduced to a negative pressure. That is, the meniscus control unit 64 constitutes a pressure reducing mechanism that reduces the pressure in the sub tank 53 based on the pressure value of the pressure sensor 645.

  In the printing process and standby time, excluding the purge operation in the cleaning process, the pressure in the ink chamber 323 is adjusted to a pressure at which an ink meniscus is formed in the nozzle 33 (hereinafter referred to as a meniscus pressure). In the present embodiment, since the ink chamber 323 is disposed below the ink storage chamber 322, it is necessary to set the pressure in the sub tank 53 so that the pressure in the ink storage chamber 322 becomes negative. When the pressure in the ink chamber 323 is higher than the meniscus pressure, the control unit 10 drives the exhaust pump 642 with both the pressure adjustment control valve 62 and the exhaust control valve 643 open, thereby adjusting the pressure in the sub tank 53. Reduce to meniscus pressure.

  In the printing apparatus 1, as described above, the main pipe 61, the atmosphere release unit 63, and the meniscus control unit 64 constitute a meniscus pressure adjusting unit that controls the meniscus pressure in the ejection head 32. In addition, the pressure adjustment control valve 62 constitutes an airtight transition that enables the subtank 53 to be transitioned to an airtight state. Here, the airtight state refers to a state in which the gas in the sub tank 53 is not communicated with the outside of the sub tank 53.

  The ink discharge unit 70 includes a plurality of caps 71, a cap moving mechanism 72, a discharge pipe 73, and an ink discharge mechanism 74.

  Each of the caps 71 covers the surface of the ejection head 32 having the nozzles 33 during a period when the ejection head 32 does not record on the printing paper 9. This suppresses evaporation of the ink solvent from the meniscus surface of the ink formed in the nozzle 33 during the period when recording on the printing paper 9 is not performed, and solidification or aggregation of the ink near the nozzle 33.

  During a period when the ejection head 32 does not record on the printing paper 9, the cap moving mechanism 72 arranges the cap 71 at a nozzle facing position (position indicated by a solid line in FIG. 3) that covers the lower surface of the ejection head 32. On the other hand, when the ejection head 32 performs printing on the printing paper 9, the cap moving mechanism 72 is in a standby position (a position indicated by a broken line in FIG. 3) where the cap 71 does not overlap the ejection head 32 vertically before the start of the printing process. Move to. Then, when the printing process is completed, the cap moving mechanism 72 moves the cap 71 to the nozzle facing position again. In FIG. 3, the cap 71 does not cover the entire lower surface of the ejection head 32, but the cap 71 may cover the entire lower surface of the ejection head 32.

  In the present embodiment, the cap 71 is disposed so that no gap is formed between the surface of the ejection head 32 and the cap 71 at the nozzle facing position, but the present invention is not limited to this. When using ink that is unlikely to cause evaporation from the meniscus surface, the cap 71 may not completely cover the nozzle 33. In the present embodiment, a pressure purge is performed as the purge operation, and therefore a gap may be interposed between the surface of the ejection head 32 and the cap 71. However, when the printing apparatus 1 can select suction purge as well as pressure purge as the purge operation, it is necessary to arrange the cap 71 so that there is no gap between the cap 71 and the lower surface of the ejection head 32. is there.

  Each cap 71 is connected to an ink discharge mechanism 74 via a discharge pipe 73. The ink discharge mechanism 74 is a mechanism for discharging ink from the cap 71. The ink discharge mechanism 74 is constituted by, for example, a suction pump. When ink is discharged from the discharge head 32 to the cap 71, the ink is discharged from the inside of the cap 71 through the discharge pipe 73 and the ink discharge mechanism 74. Thereby, ink can be ejected from the nozzle 33 in a state where the cap 71 covers the nozzle 33.

  When the printing apparatus 1 performs a printing process, ink droplets are ejected from the plurality of ejection heads 32 of each head unit 30 onto the upper surface of the printing paper 9 while the printing paper 9 is conveyed by the conveyance mechanism 20. Each head unit 30 is provided with a plurality of nozzles 33 for ejecting ink droplets at positions opposed to substantially the entire width of the upper surface of the printing paper 9. For this reason, each head unit 30 can eject ink droplets over substantially the entire width of the upper surface of the printing paper 9.

  A color pattern is formed on the upper surface of the printing paper 9 by sequentially performing such ink droplet ejection processing in the four head units 30 in charge of each color.

  The control unit 10 is a part for controlling the operation of each unit in the printing apparatus 1. As conceptually shown in FIG. 1, the control unit 10 of the present embodiment is configured by a computer having an arithmetic processing unit 11 such as a CPU, a memory 12 such as a RAM, and a storage unit 13 such as a hard disk drive. Yes. Further, as shown in FIG. 4, the control unit 10 includes the transport mechanism 20, the pressure generating elements 326 of the four head units 30, the UV lamp 40, the liquid level sensor 531 of the ink supply unit 50, and the pressure sensor. 533, a first on-off valve 544, a second on-off valve 546, a pressure adjustment control valve 62, an air release control valve 632, an exhaust pump 642, an exhaust control valve 643, a pressure sensor 645, a cap moving mechanism 72 of the ink discharge unit 70, and The ink discharge mechanism 74 and the operation unit 100 are electrically connected to each other.

  The control unit 10 temporarily reads the computer program 131 and data 132 stored in the storage unit 13 into the memory 12, and the arithmetic processing unit 11 performs arithmetic processing based on the computer program 131 and data 132. The operation of each unit in the printing apparatus 1 is controlled. Thereby, the printing process in the printing apparatus 1 and the cleaning process mentioned later progress. In addition, the control part 10 may be comprised with the electronic circuit.

  The control unit 10 includes a purge control unit 14 as a processing unit realized on software. That is, the purge control unit 14 is realized by the arithmetic processing unit 11, the memory 12, and the storage unit 13 described above. The purge control unit 14 controls the pressure purge in the cleaning process.

  The operation unit 100 includes a display unit 101 and an input unit 102. The display unit 101 displays information such as the operating status of the printing apparatus 1 input from the control unit 10. An operator can input a command from the input unit 102 to the control unit 10. As the display unit 101, for example, a liquid crystal display is used. For the input unit 102, for example, a keyboard or a mouse is used. In the operation unit 100 of the present embodiment, the display unit 101 and the input unit 102 are separate devices that are independent from the printing apparatus 1, respectively, but a touch panel type in which the display unit 101 and the input unit 102 are integrated. The operation unit 100 may be attached to the main body of the printing apparatus 1.

<2. About cleaning process>
Next, the cleaning process of the ejection head 32 in the printing apparatus 1 will be described with reference to FIG. FIG. 5 is a flowchart showing the flow of the cleaning process of the present embodiment. In the cleaning process of this embodiment, the ink in the ejection head 32 is pressurized from the outside of the ejection head 32, thereby discharging the ink from the ejection head 32 through the nozzle 33.

  In the cleaning process, first, the control unit 10 places the cap 71 at the nozzle facing position (step S101). Specifically, when the cap 71 is previously arranged at the nozzle facing position, the control unit 10 does not move the cap 71. On the other hand, when the cap 71 is disposed at the standby position, the control unit 10 drives the cap moving mechanism 72 to move the cap 71 from the standby position to the nozzle facing position.

  Next, the control unit 10 closes all the second on-off valves 546 and the pressure adjustment control valves 62 (step S102). That is, the control unit 10 closes the second open / close valve 546 and the pressure adjustment control valve 62 that are in the open state, and continues the closed state for the closed state.

  Subsequently, the control unit 10 opens the first on-off valve 544 and starts driving the supply pump 52 (step S103). As a result, ink is supplied from the main tank 51 into the sub tank 53. When the amount of ink in the sub tank 53 increases, the gas filled in the upper part of the sub tank 53 is compressed. As a result, the pressure in the sub tank 53 gradually increases.

  When it is determined that the pressure in the sub tank 53 has reached a predetermined pressure, the control unit 10 stops driving the supply pump 52 and closes the first on-off valve 544 (step S104). Here, whether or not the pressure in the sub tank 53 has reached a predetermined pressure may be determined based on whether or not the driving time of the supply pump 52 has reached a predetermined time. You may judge based on the pressure information signal sent. Further, whether or not the pressure in the sub tank 53 has reached a predetermined pressure is determined based on a signal from the liquid level sensor 531 where the liquid level of the ink in the sub tank 53 has reached a predetermined level or higher. You may judge by whether or not.

  The “predetermined pressure” that serves as a reference for stopping the driving of the supply pump 52 may be set according to the number of ejection heads 32 to be purged in step S105 described later.

  Thereafter, the control unit 10 opens the second on-off valve 546 (hereinafter referred to as the target second on-off valve 546) inserted in the branch pipe 543 communicating with the discharge head 32 to be purged for a predetermined time (step). S105). As a result, the discharge head 32 to be purged communicates with the pressurized sub tank 53, and the inside of the discharge head 32 is pressurized. Accordingly, so-called pressure purge is performed in which ink is continuously discharged from the inside of the discharge head 32 through the nozzle 33. After a predetermined time has elapsed, the control unit 10 closes the opened target second on-off valve 546.

  In the inkjet printing apparatus 1, if a printing process is performed for a long time, an ink component may stay in the ejection head 32, and ejection failure may occur in some of the nozzles 33. In addition, when printing is temporarily stopped, the ink attached to the nozzles 33 may solidify, resulting in ejection failure in some of the nozzles 33. At this time, if a cleaning operation is performed on all the ejection heads 32, a large amount of ink is consumed. Therefore, as in the present embodiment, it is desirable to perform a cleaning operation (partial purge) only on some of the ejection heads 32 that need to be cleaned. In this way, ink consumption can be suppressed.

  In the present embodiment, the pressure in the sub-tank 53 is increased to a predetermined pressure in advance, and then the second on-off valve 546 is opened, so that the discharge head 32 is pressurized and purged at a desired pressure. it can. As a result, a high pressure can be applied to the ejection head 32 from the start point of the pressure purge. Accordingly, since the purge time can be shortened, the ink consumption can be further suppressed.

  In the present embodiment, the target second on-off valve 546 is opened and the pressure purge is performed in a state where the liquid feeding by the supply pump 52 is stopped, but the present invention is not limited to this. In step S <b> 105, the target second on-off valve 546 may be opened while liquid supply by the supply pump 52 is being performed. By doing so, the pressure drop in the sub tank 53 and the discharge head 32 during the pressure purge is suppressed. Therefore, a decrease in the ink ejection speed from the nozzle 33 during the pressure purge is suppressed, and the ejection failure is more easily improved.

  After the pressurization purge in step S105 is completed, the controller 10 depressurizes the sub tank 53 and adjusts the pressure in the ink chamber 323 to the meniscus pressure (step S106). Specifically, first, the control unit 10 opens the pressure adjustment control valve 62 and the atmosphere release control valve 632 to release the sub tank 53 to the atmosphere. At this time, the exhaust control valve 643 is closed. As a result, the pressure in the sub tank 53 decreases to near atmospheric pressure. Thereafter, the controller 10 closes the atmosphere release control valve 632 and opens the exhaust control valve 643 to start driving the exhaust pump 642. As a result, the pressure in the sub tank 53 is further reduced, and the pressure in the ink chamber 323 is adjusted to the meniscus pressure.

  When the decompression in the sub-tank 53 is completed, the control unit 10 opens all the second on-off valves 546 that are in the closed state, and opens them (step S107). Further, the controller 10 drives the cap moving mechanism 72 to move the cap 71 disposed at the nozzle facing position to the standby position. Then, wiping is performed on the nozzle 33 of the ejection head 32 that has been subjected to the pressure purge (step S108). Specifically, the control unit 10 moves a wiping blade (not shown) to wipe the surface having the nozzle 33 of the ejection head 32 that has been pressurized and purged. Thereby, the ink ejected by pressure purge and adhering to the vicinity of the nozzle 33 can be removed. Note that the wiping in step S108 may be performed before the opening of the second on-off valve 546 in step S107.

  As described above, in the printing apparatus 1, the inside of the sub tank 53 is pressurized by feeding the liquid from the main tank 51 to the sub tank 53, thereby pressurizing the ink chamber 323 in the pressure purge. Thereby, pressure purge can be performed without using compressed air.

<3. Modification>
Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

  FIG. 6 is a flowchart showing the flow of the cleaning process according to the modification. In the cleaning process of the example of FIG. 6, first, similarly to step S101 of the above embodiment, the control unit 10 places the cap 71 at the nozzle facing position (step S201).

  Next, the control unit 10 closes the pressure adjustment control valve 62 to a closed state. Further, the second on-off valve 546 inserted in the branch pipe 543 communicating with the discharge head 32 to be purged is opened to be opened, and the other second on-off valve 546 is closed to be closed. (Step S202).

  Subsequently, the control unit 10 opens the first on-off valve 544 and starts driving the supply pump 52 (step S203). Accordingly, ink is supplied from the main tank 51 into the sub tank 53, and the pressure in the sub tank 53 increases. Accordingly, the discharge head 32 in which the corresponding second on-off valve 546 is in the open state is in communication with the sub tank 53, so that the inside is pressurized. Accordingly, so-called pressure purge is performed in which ink is continuously discharged from the inside of the discharge head 32 through the nozzle 33.

  After a predetermined time has elapsed, the control unit 10 stops driving the supply pump 52 (step S204). Thereafter, the controller 10 reduces the pressure in the sub tank 53 and adjusts the pressure in the ink chamber 323 to the meniscus pressure, similarly to step S106 in the above embodiment (step S205).

  When the decompression in the sub-tank 53 is completed, the control unit 10 opens all the second on-off valves 546 that are in the closed state (step S206). Further, the controller 10 drives the cap moving mechanism 72 to move the cap 71 disposed at the nozzle facing position to the standby position. Then, wiping is performed on the nozzle 33 of the ejection head 32 that has been subjected to the pressure purge (step S207). Note that the wiping in step S207 may be performed before the opening of the second on-off valve 546 in step S206.

  As shown in the example of FIG. 6, with the second on-off valve 546 corresponding to the discharge head 32 to be purged opened, the inside of the sub tank 53 is pressurized by liquid feeding from the main tank 51 to the sub tank 53. Pressurization in the ink chamber 323 in the pressure purge may be performed. Even in this case, the pressure purge can be performed without using compressed air.

  In the above-described embodiment, the pressure adjustment control valve 62 is provided to make the sub-tank 53 changeable into an airtight state. However, the present invention is not limited to this. The pressure adjustment control valve 62 may be omitted, and an airtight transition portion may be configured by both the atmosphere release control valve 632 and the exhaust control valve 643. In that case, when the purge operation is performed, the inside of the sub tank 53 can be made airtight by closing both the air release control valve 632 and the exhaust control valve 643.

  In the above embodiment, the cap is moved to change the positional relationship between the ejection head and the cap, but the present invention is not limited to this. The positional relationship between the ejection head and the cap may be changed by fixing the position of the cap and moving the head unit.

  Moreover, although the printing apparatus of the above embodiment has four head units, the number of head units may be 1 to 3, or 5 or more.

  Moreover, although the ultraviolet curable UV ink was used in the printing apparatus of the above embodiment, the present invention is not limited to this. Instead of the UV ink, other types of ink such as oil-based ink or water-based ink dried by hot air may be used. In that case, the printing apparatus may not have a UV lamp.

  Further, the printing apparatus of the above-described embodiment prints an image on printing paper as a recording medium. However, the printing apparatus of the present invention may print a pattern such as an image on a sheet-like recording medium (for example, a resin film) other than general paper.

  Moreover, you may combine suitably each element which appeared in said embodiment and modification in the range which does not produce inconsistency.

DESCRIPTION OF SYMBOLS 1 Printing apparatus 9 Printing paper 10 Control part 32 Discharge head 33 Nozzle 40 UV lamp 50 Ink supply part 51 Main tank 52 Supply pump 53 Sub tank 60 Pressure adjustment part 62 Pressure adjustment control valve 63 Atmospheric release part 64 Meniscus control part 531 Liquid level sensor 533 Pressure sensor 541 First supply pipe 542 Second supply pipe 544 First on-off valve 546 Second on-off valve 632 Atmospheric release control valve 641 Exhaust pipe 642 Exhaust pump 643 Exhaust control valve

Claims (8)

An ejection head having a plurality of nozzles for ejecting ink to a recording medium;
A main tank for storing the ink;
A sub tank disposed between the main tank and the discharge head;
Liquid feeding means for feeding the ink from the main tank to the sub tank;
A pressure reducing mechanism for reducing the pressure in the sub tank, and a meniscus pressure adjusting unit for controlling the meniscus pressure in the discharge head;
An airtight transition portion that enables the interior of the sub-tank to be transformed into an airtight state;
A purge control unit for controlling a pressure purge for pressurizing the inside of the ejection head and ejecting the ink;
Have
The purge control unit pressurizes the sub-tank by driving the liquid feeding unit while the sub-tank is in an airtight state by the airtight transition unit, and executes the pressure purge on the discharge head. Printing device. The printing apparatus according to claim 1,
A head opening / closing valve disposed between the sub tank and the discharge head;
The purge control unit pressurizes the inside of the sub-tank that is in an airtight state with the head opening / closing valve closed when performing the pressure purge, and then opens the head opening / closing valve to open the head from the discharge head. A printing device that ejects ink. The printing apparatus according to claim 2,
A pressure measuring means for measuring the pressure inside the sub tank;
The printing apparatus, wherein the purge control unit opens the head opening / closing valve after the pressure in the sub tank measured by the pressure measuring unit reaches a predetermined pressure when the pressure purge is performed. The printing apparatus according to any one of claims 1 to 3,
A plurality of the ejection heads;
A plurality of head opening / closing valves disposed between the sub tank and each of the ejection heads;
Have
The purge control unit is capable of executing a partial purge for performing the pressure purge only on a part of the plurality of ejection heads.
In the partial purge, the purge control unit opens the head opening / closing valve disposed between the discharge head to be purged and the sub tank, and is disposed between the other discharge heads and the sub tank. A printing apparatus that executes the pressure purge while the head opening / closing valve is closed. The printing apparatus according to any one of claims 1 to 4,
The meniscus pressure adjusting unit is
A main pipe having one end connected to the sub tank;
One end communicates with the other end of the main pipe, and the other end of the main pipe is opened to the atmosphere.
An atmosphere release control valve interposed in the atmosphere release pipe;
An exhaust pipe having one end communicating with the other end of the main pipe;
An exhaust pump connected to the other end of the exhaust pipe and exhausting the gas in the exhaust pipe;
An exhaust control valve interposed in the exhaust pipe;
Have
The airtight transition portion is constituted by a pressure adjustment control valve inserted in the main pipe,
The printing apparatus, wherein the pressure reducing mechanism is configured by the exhaust pipe, the exhaust pump, and the exhaust control valve. In a printing apparatus that ejects ink to a recording medium, a cleaning method for cleaning an ejection head including a plurality of nozzles,
a) supplying liquid from a main tank storing the ink to a sub tank disposed between the main tank and the ejection head, and pressurizing the sub tank;
b) communicating the pressurized subtank with the ejection head to pressurize the inside of the ejection head, ejecting the ink from the ejection head, and performing a pressure purge;
A cleaning method. The cleaning method according to claim 6, wherein
The cleaning method, wherein the step b) is performed after the pressure in the sub tank reaches a predetermined pressure in the step a). The cleaning method according to claim 6 or 7, wherein
The printing apparatus includes:
A plurality of the ejection heads;
A plurality of head opening / closing valves disposed between the sub tank and each of the ejection heads;
Have
In the step b), the pressurized sub-tank and the ejection head to be purged are communicated with each other, and the communication between the sub-tank and the other ejection heads is blocked to apply only to some of the ejection heads. A cleaning method that performs pressure purge.

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