Printer and method for cleaning nozzle

Abstract

The present invention is a method for cleaning a nozzle of a printer which performs printing by discharging ink from the nozzle, which is provided to a print head, while circulating the ink between a supply tank, the print head and a recovery tank. When a discharge port of the nozzle is wiped by a cleaning member, an ink flow path passing through the nozzle is closed, a circulation flow path which connects the supply tank and the recovery tank without passing through the nozzle is formed, and the ink is heated by a heater provided along the circulation flow path while circulating the ink in the circulation flow path.

Description

Printing apparatus and nozzle cleaning method

[0001] The present invention relates to a printing apparatus that performs printing by ejecting ink from a print head and a cleaning method for nozzles of the printing apparatus. In particular, the present invention relates to a technique for performing printing in a state where ink is heated.

[0002] In a printing apparatus that performs printing by ejecting ink from a print head, an ink circulation system that circulates ink in a flow path may be employed for the purposes of suppressing drying of nozzles that eject ink and preventing aggregation of ink. For example, in the technique described in Patent Document 1, ink is circulated when a certain period of time has elapsed since the previous operation, thereby removing bubbles in the ink and resolving sedimentation of ink components.

[0003] In this technique, as ink circulation flow paths, a flow path that passes through the print head and a bypass flow path that does not pass through the print head are selectively used depending on the situation. Specifically, when the time from the completion of the previous printing process to restoration is relatively short, ink circulation is performed through the flow path passing through the print head. On the other hand, when the operation stop period becomes long, circulation using the bypass flow path is performed. This is because the bypass flow path can have lower flow path resistance than an ink flow path passing through a print head provided with fine nozzles, and is suitable for circulating a large amount of ink in a short time.

[0004] Furthermore, Patent Document 1 also describes cleaning of a nozzle surface. Specifically, as processing for cleaning the nozzle surface and adjusting it to a state suitable for printing, it describes purge processing for sucking ink remaining in nozzles, feeding cleaning liquid into a cap while the nozzle surface is covered with the cap, and wiping the nozzle surface with a wiper. In addition, Patent Document 2, which was previously disclosed by the applicant of the present application, also describes operations for protecting and cleaning nozzles using a cap.

[0005] Japanese Patent Application Laid-Open No. 2021-160283 Japanese Patent Application Laid-Open No. 2023-120490

[0006] Although not specifically considered in the conventional technologies described above, in this type of printing apparatus, the ink is sometimes heated to reduce its viscosity before being used for printing. In this case, stopping the flow of ink would lead to a drop in temperature, so it is basically necessary to keep the ink circulating at all times in order to maintain the temperature.

[0007] When accessing the nozzles for cleaning, it is necessary to temporarily stop the circulation to prevent ink leakage from the nozzles. On the other hand, in cases where ink temperature adjustment is required, stopping the circulation leads to a decrease in ink temperature, creating a conflicting demand to avoid stopping circulation as much as possible. However, the technology described in Patent Document 1 only allows ink circulation in a capped state, and Patent Document 2 does not mention ink circulation.

[0008] Thus, in systems that circulate ink while simultaneously regulating temperature, the crucial challenge lies in how to reconcile cleaning operations with ink circulation, but no solution has yet been demonstrated.

[0009] This invention has been made in view of the above problems, and aims to provide a cleaning technology for a printing apparatus that circulates ink while adjusting the temperature, which can prevent ink leakage from the nozzles while also preventing a drop in the ink temperature.

[0010] One aspect of the printing apparatus according to the present invention is a printing apparatus comprising: a print head having a nozzle for ejecting ink; a maintenance unit having a cleaning member for wiping the nozzle outlet; a supply tank for storing the ink supplied to the print head; a recovery tank for storing the ink recovered from the print head; a circulation channel forming unit that forms a circulation channel including a first channel for transporting the ink from the supply tank to the recovery tank and a second channel for returning the ink from the recovery tank to the supply tank; a branch channel forming unit that branches off from the first channel midway through the first channel and rejoins the first channel via the print head; a heater inserted in the second channel for heating the ink; and a control unit that controls the flow of the ink in the circulation channel and the branch channel.

[0011] Here, the branched channel forming unit has a control valve for opening and closing the branched channel, and when the maintenance unit wipes the discharge port with the cleaning member, the control unit closes the control valve and heats the ink with the heater while circulating the ink in the circulation channel that does not go through the branched channel.

[0012] Another aspect of this invention is a method for cleaning a nozzle in a printing apparatus that performs printing by circulating ink between a supply tank, a print head, and a recovery tank, and ejecting the ink from a nozzle provided on the print head. In this method, when the nozzle outlet is wiped with a cleaning member, the ink flow path through the nozzle is closed, while a circulation path is formed that connects the supply tank and the recovery tank without passing through the nozzle. The ink is then heated by a heater provided on the circulation path while the ink is circulated through it.

[0013] In this configuration, ink can be circulated and heated through a circulation channel that does not involve a print head, while the discharge port is wiped by a cleaning member. Since the ink channel that goes through the print head is closed, leakage of ink from the discharge port is prevented. Furthermore, since the ink can be circulated and heated during this time, a drop in the ink temperature can also be prevented.

[0014] As described above, according to the present invention, ink is circulated in a circulation channel that does not pass through the print head, heating the ink while the discharge port is wiped by a cleaning member. Therefore, it is possible to prevent ink leakage from the nozzle while also preventing a drop in the ink temperature.

[0015] The aforementioned and other purposes and novel features of this invention will become more fully apparent upon reading the following detailed description with reference to the accompanying drawings. However, the drawings are for illustrative purposes only and do not limit the scope of this invention.

[0016] This is a diagram showing the configuration of an inkjet printing apparatus according to the first embodiment. This is a diagram conceptually showing the configuration of the ink supply unit and the head unit. This is a perspective view showing a part of the head unit and the ink supply unit. This is a schematic bottom view showing the configuration of the head unit. This is a schematic perspective view showing the configuration of the maintenance unit. This is a block diagram showing the electrical configuration of this inkjet printing apparatus. This is a diagram schematically showing the piping system involved in ink circulation. This is a diagram showing the flow of ink in the first circulation mode. This is a diagram showing the flow of ink in the second circulation mode. This is a diagram showing the flow of ink in the second circulation mode. This is a flowchart showing the cleaning operation of this embodiment. This is a diagram schematically showing the movement of the head unit and the maintenance unit. This is a diagram schematically showing the movement of the head unit and the maintenance unit. This is a diagram schematically showing the movement of the head unit and the maintenance unit. This is a diagram schematically showing the movement of the head unit and the maintenance unit. This is a diagram schematically showing the movement of the head unit and the maintenance unit. This is a diagram schematically showing the movement of the head unit and the maintenance unit. This is a diagram schematically showing the movement of the head unit and the maintenance unit. This is a diagram schematically showing the movement of the head unit and the maintenance unit. This is a diagram schematically showing the movement of the head unit and the maintenance unit. This is a diagram showing the flow of ink in the circulation mode of the second embodiment. This is a diagram showing the ink flow in the circulation mode of the second embodiment. This is a diagram showing the ink flow in the circulation mode of the second embodiment. This is a diagram showing the ink flow in the circulation mode of the third embodiment. This is a diagram showing the ink flow in the circulation mode of the third embodiment. This is a diagram showing the ink flow in the circulation mode of the third embodiment.

[0017] Hereinafter, several embodiments of the present invention will be described with reference to the attached drawings. Note that the components described in these embodiments are merely illustrative and are not intended to limit the scope of the present invention to them alone. In the drawings, for ease of understanding, the dimensions and number of parts may be exaggerated or simplified as needed.

[0018] <First Embodiment> Figure 1 is a diagram showing the configuration of an inkjet printing apparatus according to the first embodiment. The inkjet printing apparatus 1 is an inkjet type printer that records characters and images on the surface of a continuous paper 10 by transporting a long strip of continuous paper 10 and ejecting ink droplets from a plurality of head units 35 toward the continuous paper 10. The continuous paper 10 is an example of a printing medium. The printing medium may be single sheets of paper, plastic film, corrugated cardboard, metal foil, or a glass substrate. In addition, the ink ejected by the head unit 35 in the inkjet printing apparatus 1 is, for example, water-based ink. However, the ink ejected by the head unit 35 may be oil-based ink or UV ink, etc.

[0019] As shown in Figure 1, the inkjet printing apparatus 1 comprises an unwinding roller 11, a winding roller 12, a transport unit 2, a printing unit 3, a drying unit 5, and a control unit 9.

[0020] The unwinding roller 11 holds the continuous paper 10 wound into a roll. The unwinding roller 11 rotates to unwind the continuous paper 10 and supply it to the transport unit 2. The take-up roller 12 winds the continuous paper 10 into a roll. In the inkjet printing apparatus 1, the continuous paper 10 is transported roll-to-roll by the unwinding roller 11 and the take-up roller 12.

[0021] The conveying unit 2 conveys the continuous paper 10 supplied from the unwinding roller 11 to the take-up roller 12. The conveying unit 2 has a drive roller 21, a nip roller 23, and a plurality of conveying rollers 25. The drive roller 21 is connected to a motor (not shown) and rotates actively by the power of the motor. The nip roller 23 grips the continuous paper 10 together with the drive roller 21. The nip roller 23 presses against the drive roller 21 via the continuous paper 10, thereby generating a gripping force for the drive roller 21 to convey the continuous paper 10. The plurality of conveying rollers 25 rotate passively. At least some of the plurality of conveying rollers 25 may be configured to rotate actively.

[0022] The printing unit 3 has four head units 35 and four ink supply units 4. The four head units 35 have similar structures to each other, and the four ink supply units 4 have similar structures to each other.

[0023] The four head units 35 are arranged spaced apart from each other in the transport direction. Each of the four head units 35 ejects droplets of ink from a nozzle 83 (Figure 2) toward the surface of the continuous paper 10. The four head units 35 each record a monochrome image on the surface of the continuous paper 10 by ejecting ink of different colors (e.g., cyan, magenta, yellow, and black). A multicolor image is formed on the upper surface of the continuous paper 10 by superimposing the four monochrome images.

[0024] The printed continuous paper 10 is then sent to the drying section 5. In the drying section 5, the ink ejected onto the continuous paper 10 is heated and dried. Heating for drying may be done by radiant heat from a heater, or by blowing hot air. These may be used in combination. After drying, the continuous paper 10 is wound into a roll by the winding roller 12.

[0025] Figure 2 is a conceptual diagram showing the configuration of the ink supply unit and the head unit. In this embodiment, each head unit 35 has a plurality of ejection heads 80. In this example, each head unit 35 has five ejection heads 80. The plurality of ejection heads 80 have the same structure as each other. In Figure 2, only one ejection head 80 is shown in detail, while the remaining four ejection heads 80 are shown in a simplified manner. As shown in Figure 2, the ejection head 80 has a housing 81, an internal tank 82, and a plurality of nozzles 83.

[0026] The housing 81 forms the outer frame of the discharge head 80. The internal tank 82 is located inside the housing 81 and is capable of temporarily storing ink. Multiple nozzles 83 are arranged at equal intervals from each other in the transport direction and width direction of the continuous paper 10 at the lower part of the housing 81. Each of the multiple nozzles 83 communicates with the internal tank 82. Each nozzle 83 also has a piezoelectric element 831, an ink chamber 832, and a discharge port 830. The piezoelectric element 831 is a pressure generating element. The ink chamber 832 communicates with the internal tank 82.

[0027] The ink in the internal tank 82 flows down into the ink chamber 832. Then, the ink in the ink chamber 832 is pressurized by the piezoelectric element 831, causing ink droplets to be ejected from the ejection port 830. The ink ejection method may also be a so-called thermal method, which uses a heater as the pressure generating element.

[0028] The ink supply unit 4 is a device that circulates ink by supplying ink to the head unit 35 and recovering any ink that is not discharged from the head unit 35. The structure of the four ink supply units 4 is the same as that of the others.

[0029] As shown in Figure 2, the ink supply unit 4 includes a supply tank 51, a recovery tank 52, a replenishment tank 53, a supply-side manifold 61, a plurality (five in this embodiment) of supply-side branch pipes 62, a plurality (five in this embodiment) of recovery-side branch pipes 63, a recovery-side manifold 64, a connecting pipe 65, a replenishment pipe 66, a circulation pump 71, a replenishment pump 72, a backflow prevention on / off valve 73, a heater 74, a first filter 75, a second filter 76, and a degassing unit 77. In Figure 2, the supply-side manifold 61 and the recovery-side manifold 64 are shown with thick lines to distinguish them from other pipes.

[0030] The supply tank 51 is a container for temporarily storing ink supplied to the head unit 35. The supply tank 51 has an internal chamber 510, which is capable of temporarily storing ink.

[0031] Figure 3 is a perspective view showing a part of the head unit and ink supply section. The supply-side manifold 61 and five supply-side branch pipes 62 connect the supply tank 51 to the five discharge heads 80 of one head unit 35. Note that in Figure 3, only one of the five discharge heads 80 of the head unit 35 is shown. Similarly, only one of the five supply-side branch pipes 62 connected to the supply-side manifold 61 is shown, and only one of the five recovery-side branch pipes 63 connected to the recovery-side manifold 64 is shown.

[0032] As shown in Figures 2 and 3, the upstream end of the supply-side manifold 61 is connected to the internal chamber of the supply tank 51. The supply-side branch pipes 62 branch off from the supply-side manifold 61. The supply-side manifold 61 is a thicker pipe than the supply-side branch pipes 62. The upstream end of each supply-side branch pipe 62 is connected to the internal passage of the supply-side manifold 61. The downstream end of each supply-side branch pipe 62 is connected to the internal tank 82 of the discharge head 80. As will be described later, a solenoid valve 621 is interposed in the supply-side branch pipe 62. Furthermore, a filter may be provided in the supply-side branch pipe 62.

[0033] The five recovery-side branch pipes 63 and the recovery-side manifold 64 connect the five discharge heads 80 of one head unit 35 to the recovery tank 52. As shown in Figures 2 and 3, the recovery-side branch pipes 63 are thin pipes that branch off from the recovery-side manifold 64. The upstream end of each recovery-side branch pipe 63 is connected to the internal tank 82 of the discharge head 80. The downstream end of each recovery-side branch pipe 63 is connected to the internal passage of the recovery-side manifold 64. The downstream end of the recovery-side manifold 64 is connected to the internal chamber of the recovery tank 52. The recovery-side manifold 64 is a thicker pipe than the recovery-side branch pipes 63. As will be described later, a solenoid valve 631 is interposed in the recovery-side branch pipe 63. Furthermore, a filter may be provided in the recovery-side branch pipe 63.

[0034] The recovery tank 52 temporarily stores the ink recovered from the head unit 35. The recovery tank 52 has an internal chamber 520 for storing the ink.

[0035] As shown in Figure 3, the supply-side manifold 61 extends horizontally directly from the lower side of the supply tank 51, that is, without piping, and their internal spaces are in communication with each other. On the other hand, the recovery-side manifold 64 extends horizontally directly from the lower side of the recovery tank 52, and their internal spaces are in communication with each other.

[0036] The extension direction D1 from the supply tank 51 to the supply-side manifold 61 and the extension direction D2 from the recovery tank 52 to the recovery-side manifold 64 are parallel to each other and in opposite directions. In addition, the supply-side manifold 61 and the recovery-side manifold 64 are located close together in the horizontal direction perpendicular to the extension directions D1 and D2, that is, in the direction perpendicular to the plane of the paper. In the vertical direction, the supply-side manifold 61 and the recovery-side manifold 64 can be at the same height. That is, the supply-side manifold 61 and the recovery-side manifold 64 are located at a certain distance from each other in the horizontal direction.

[0037] As shown in Figure 2, the ink supply unit 4 has a pressure difference forming unit 55. The pressure difference forming unit 55 is connected to the supply tank 51 and the recovery tank 52. The pressure difference forming unit 55 forms a pressure difference between the internal chamber 510 of the supply tank 51 and the internal chamber 520 of the recovery tank 52 by adjusting the pressure (internal pressure) of the internal chamber 510 of the supply tank 51 and the internal chamber 520 of the recovery tank 52.

[0038] In detail, the pressure difference forming unit 55 has a pressurizing unit 56 and a depressurizing unit 57. The pressurizing unit 56 and the depressurizing unit 57 are controlled by the control unit 9. The pressurizing unit 56 makes the internal pressure of the supply tank 51 a positive pressure greater than atmospheric pressure by supplying gas to the internal chamber 510 of the supply tank 51. The depressurizing unit 57 makes the internal pressure of the recovery tank 52 a negative pressure less than atmospheric pressure by sucking gas from the internal chamber 520 of the recovery tank 52.

[0039] The pressurized section 56 includes a pressure tank 561 that stores air inside, a pipe 562 that connects the pressure tank 561 and the supply tank 51, and a tank valve 563 inserted in the pipe 562. When the tank valve 563 is opened by a control command from the control unit 9, the pressure tank 561 and the supply tank 511 are connected via the pipe 562, and their internal pressures become equal. When the control unit 9 closes the tank valve 563, the connection between the pressure tank 561 and the supply tank 51 is severed.

[0040] The pressurizing unit 56 includes an introduction pipe 564 for introducing compressed air supplied from the outside into the pressure tank 561, and a pressurizing valve 565 attached to the introduction pipe 564. When the control unit 9 opens the pressurizing valve 565, compressed air is introduced from the introduction pipe 564 into the pressure tank 561, and the air inside the pressure tank 561 is pressurized. This allows positive pressure to be applied to the supply tank 52 via the pipe 562. When the control unit 9 closes the pressurizing valve 565, the introduction of compressed air from the introduction pipe 564 into the pressure tank 561 is prohibited. Furthermore, the pressurizing unit 56 includes an introduction pipe 566 for introducing atmospheric pressure into the pressure tank 561, and an opening valve 567 attached to the introduction pipe 566. When the control unit 9 opens the opening valve 567, the pressure tank 561 is opened to atmospheric pressure via the introduction pipe 566. When the control unit 9 closes the opening valve 567, the pressure tank 561 is cut off from atmospheric pressure.

[0041] Furthermore, the pressurizing unit 56 has a pressure detector 568 attached to the piping 562 between the pressure tank 561 and the tank valve 563. This pressure detector 568 detects the pressure in the piping 562, i.e., the pressure in the pressure tank 561, and outputs it to the control unit 9. With the tank valve 563 open and the supply tank 51 and the pressure tank 561 in communication, the control unit 9 controls the opening and closing of the pressurizing valve 565 and the atmospheric release valve 567 based on the pressure detected by the pressure detector 568. In this way, the pressure P1 applied to the gas-liquid interface L1 of the supply tank 51 can be adjusted.

[0042] The pressure reducing unit 57 includes a pressure tank 571 that stores air, a pipe 572 connecting the pressure tank 571 and the recovery tank 52, and a tank valve 573 interposed in the pipe 572. When the control unit 9 opens the tank valve 573, the pressure tank 571 and the recovery tank 52 communicate with each other via the pipe 572, so that the respective internal pressures of the two tanks become equal. When the control unit 9 closes the tank valve 573, communication between the pressure tank 571 and the recovery tank 52 is blocked.

[0043] The pressure reducing unit 57 includes an exhaust pump 579, an exhaust pipe 574 connecting the exhaust pump 579 and the pressure tank 571, and an exhaust valve 575 attached to the exhaust pipe 574. When the control unit 100 opens the exhaust valve 575, the exhaust pump 579 exhausts air from the pressure tank 571 via the exhaust pipe 574. Accordingly, the pressure inside the recovery tank 52 is reduced, that is, a negative pressure is applied to the interior of the recovery tank 52. When the control unit 9 closes the exhaust valve 575, exhaust through the exhaust pipe 574 by the exhaust pump 579 is prohibited. Furthermore, the pressure reducing unit 57 includes an introduction pipe 576 that introduces atmospheric pressure into the pressure tank 571, and an open valve 577 attached to the introduction pipe 576. When the control unit 9 opens the open valve 577, the pressure tank 571 is opened to atmospheric pressure via the introduction pipe 576. When the control unit 9 closes the open valve 577, the pressure tank 571 is blocked from atmospheric pressure.

[0044] In addition, the pressure reducing unit 57 includes a pressure detector 578 attached to the pipe 572 between the pressure tank 571 and the tank valve 573. The pressure detector 578 detects the pressure in the pipe 572, that is, the pressure in the pressure tank 571, and outputs the detected pressure to the control unit 9. The control unit 9 controls the opening and closing of the exhaust valve 575 and the open valve 577 based on the pressure detected by the pressure detector 578, in a state where the tank valve 573 is opened to bring the recovery tank 52 and the pressure tank 571 into communication while causing the exhaust pump 579 to perform exhaust. By this configuration, the pressure P2 applied to the gas-liquid interface L2 of the recovery tank 52 can be adjusted.

[0045] As described above, in the pressure difference forming section 55, a pressurizing section 56 applies positive pressure to a supply tank 51 as needed, while a pressure reducing section 57 applies negative pressure to a recovery tank 52 as needed. As a result, a pressure difference (differential pressure) in which the supply tank 51 has a higher pressure is generated between the supply tank 51 and the recovery tank 52. This differential pressure causes ink to flow in an ink flow path formed by connecting the supply tank 51 and the recovery tank 52. Each of the valves provided in the pressurizing section 56 and the pressure reducing section 57 is a solenoid valve that operates in accordance with a control command from a control section 9.

[0046] More specifically, due to the differential pressure formed by the pressure difference forming section 55, the ink stored in the supply tank 51 is sent to the internal tank 82 of each discharge head 80 via the supply-side manifold 61 and each supply-side branch pipe 62. Further, due to the differential pressure formed by the pressure difference forming section 55, ink that has not been discharged from each discharge head 80 is sent to the recovery tank 52 via each recovery-side branch pipe 63 and the recovery-side manifold 64.

[0047] The supply tank 51 is provided with a liquid level sensor 511 for detecting the liquid amount of ink stored in the tank. On the other hand, the recovery tank 52 is provided with a liquid level sensor 521 for detecting the liquid amount of ink stored in the tank. The control section 9 grasps the ink storage amounts of the supply tank 51 and the recovery tank 52 based on output signals from these liquid level sensors 511 and 521, and controls each section of the ink supply section 4 to maintain these amounts within an appropriate range.

[0048] The connection pipe 65 communicably connects an internal chamber 510 of the supply tank 51 and an internal chamber 520 of the recovery tank 52. As shown in FIG. 2, the upstream end of the connection pipe 65 is communicatively connected to the internal chamber 520 of the recovery tank 52. Further, the downstream end of the connection pipe 65 is communicatively connected to the internal chamber 510 of the supply tank 51. A circulation pump 71, a check on-off valve 73, a heater 74, a second filter 76, and a deaeration unit 77 are attached to the connection pipe 65. Note that a replenishment pipe 66 is connected to a connection point 655 between the check on-off valve 73 and the heater 74 in the connection pipe 65.

[0049] The circulation pump 71 performs a liquid transfer operation to send ink from the recovery tank 52 to the supply tank 51. The circulation pump 71 generates an ink flow from the recovery tank 52 to the supply tank 51 in the internal passage of the connecting pipe 65. Preferably, the circulation pump 71 is a diaphragm pump that is less likely to generate foreign matter such as dust when operated. The flow rate of the circulation pump 71 is changed in multiple stages by a control signal output by the control unit 9.

[0050] The backflow prevention valve 73 is located in the connecting pipe 65 downstream of the circulation pump 71 and upstream of the connection point 655. When the backflow prevention valve 73 is closed, the connecting pipe 65 is shut off. In other words, when the backflow prevention valve 73 is closed, backflow of ink from the connection point 655 to the circulation pump 71 is prevented. When the backflow prevention valve 73 is opened, the connecting pipe 65 is opened.

[0051] The heater 74 heats the ink passing through the connecting pipe 65. The heater 74 is located in the connecting pipe 65 between the connection point 655 and the supply tank 51. The heater 74 has a temperature sensor 741. The temperature sensor 741 measures the temperature of the ink flowing into the heater 74. The temperature sensor 741 may also measure the temperature of the ink that has passed through the heater 74. The heater 74 is electrically connected to the control unit 9. The heater 74 outputs data indicating the temperature measured by the temperature sensor 741 to the control unit 9. The control unit 9 controls the heater 74 based on the temperature measured by the temperature sensor 741.

[0052] The second filter 76 is located between the connection point 655 and the supply tank 51 in the connecting pipe 65. The second filter 76 filters the ink flowing through the connecting pipe 65 and removes foreign matter contained in the ink. The filtration diameter (mesh size) of the second filter 76 is, for example, 4 to 6 μm.

[0053] The degassing unit 77 is located between the connection point 655 and the supply tank 51 in the connecting pipe 65. In this embodiment, the degassing unit 77 is, for example, a hollow fiber membrane degassing module. The degassing unit 77 removes air bubbles from the ink flowing through the connecting pipe 65.

[0054] The replenishment tank 53 stores the ink that is to be replenished to the supply tank 51. The replenishment tank 53 has an internal chamber capable of storing ink. The replenishment tank 53 is located outside the ink circulation path that circulates between the supply tank 51 and the recovery tank 52.

[0055] The replenishment piping 66 connects the internal chamber 530 of the replenishment tank 53 to the connecting piping 65 so that they can communicate with each other. As shown in Figure 2, the replenishment piping 66 is connected to the internal chamber of the replenishment tank 53 at its upstream end. The replenishment piping 66 is also connected to the connecting piping 65 at a connection point 655 at its downstream end. The connection point 655 is located between the circulation pump 71 and the supply tank 51 in the connecting piping 65. The connection point 655 is located between the backflow prevention valve 73 and the supply tank 51 in the connecting piping 65. The replenishment piping 66 is also connected to the replenishment pump 72 and the first filter 75.

[0056] The replenishment pump 72 performs a liquid delivery operation, sending ink from the replenishment tank 53 to the connecting pipe 65. The replenishment pump 72 is, for example, a diaphragm pump. The flow rate of the replenishment pump 72 is changed to multiple stages by a control signal output by the control unit 9.

[0057] The first filter 75 is located in the replenishment piping 66 between the replenishment pump 72 and the connection point 655. The first filter 75 filters the ink flowing through the replenishment piping 66 and removes foreign matter contained in the ink. The filtration diameter of the first filter 75 (the size of the mesh of the first filter 75) is, for example, about 10 to 30 μm. That is, the filtration diameter of the first filter 75 is greater than or equal to the filtration diameter of the second filter 76. However, the filtration diameter of the first filter 75 may be less than the filtration diameter of the second filter 76.

[0058] A first bypass pipe 67 is provided to connect the supply tank 51 and the recovery manifold 64. A solenoid valve 671 is inserted into the first bypass pipe 67. On the other hand, a second bypass pipe 68 is provided to connect the supply manifold 61 and the recovery tank 52. A solenoid valve 681 is inserted into the second bypass pipe 68. The functions of these will be described later. Multiple (five in this embodiment) discharge heads 80 are associated with the supply manifold 61 and the recovery manifold 64. That is, the supply manifold 61 supplies ink to these five discharge heads 80, and the recovery manifold 64 recovers ink from these five discharge heads 80. Neither the first bypass pipe 67 nor the second bypass pipe 68 has any discharge heads 80 associated with the supply manifold 61 or the recovery manifold 64 inserted into it.

[0059] Figure 4 is a schematic bottom view showing the configuration of the head unit. Here, the XYZ coordinate system is introduced to uniformly indicate spatial directions in each of the following figures. The X direction is horizontal and parallel to the width direction of the continuous paper 10. The Y direction is horizontal and perpendicular to the X direction. The Z direction is perpendicular to both the X and Y directions and corresponds to the vertical direction.

[0060] The head unit 35 has a plurality of (five in this example) ejection heads 80. The plurality of ejection heads 80 are arranged in a so-called staggered arrangement in two rows in the X direction. In other words, a head row C1 consisting of three ejection heads 80 arranged parallel to the X direction and a head row C2 consisting of two ejection heads 80 arranged parallel to the X direction are provided at a predetermined interval in the Y direction. Each ejection head 80 has a plurality of ejection ports 830 arranged in a staggered pattern in the X direction, facing the continuous paper 10 from above. Each ejection port 830 ejects ink onto the continuous paper 10 using an inkjet method. In the head unit 35, each ejection head 80 is integrally held by a holding member 351 made of a non-elastic material such as metal or resin.

[0061] Therefore, the head unit 35 has a structure in which multiple discharge ports 830, each of the discharge heads 80, are arranged on its lower surface. In the head unit 35, it is desirable that the lower surface of each discharge head 80 and the lower surface of the holding member 351 form the same horizontal plane.

[0062] Below the head unit 35 configured in this way, the maintenance unit 36, which will be described next, is located. The maintenance unit 36 ​​is provided for each of the multiple head units 35, and each maintenance unit 36 ​​faces the corresponding head unit 35 from below. Since the multiple maintenance units 36 provided for the multiple head units 35 have a common configuration, we will describe one maintenance unit 36.

[0063] The configuration and operating principle of the maintenance unit 36 ​​described here are generally the same as those described in Patent Document 2 previously disclosed by the applicant. Therefore, only a brief explanation will be given here.

[0064] Figure 5 is a schematic perspective view showing the configuration of the maintenance unit. The maintenance unit 36 ​​has a base member 361 that is elongated in the X direction and has a rectangular parallelepiped shape. Box-shaped tubs 362 and 363 with open tops are attached to this base member 361 to receive ink and various processing liquids discharged from the head unit 35. Inside the larger tub 362, caps 364 are provided according to the number and position of the discharge heads 80 in the head unit 35. The tub 362 has a box-shaped tub body 362a that is rectangular in plan view and has an open top, and an elastic member 362b is attached around the entire circumference of the upper end of its side wall. The cap 364 has a structure in which a sealing member 364b is attached to the upper end of a cap body 364a that is formed in a box shape corresponding to the outer shape of the discharge head 80 and has an open top, so as to surround the opening. The sealing member 364b is a roughly rectangular annular part, for example, made of rubber.

[0065] When the maintenance unit 36 ​​is positioned below the head unit 35 as shown in Figure 4, the upper end of the bat 362 abuts against the lower surface of the head unit 35. In this way, the maintenance unit 36 ​​covers the lower surfaces of multiple ejection heads 80 collectively, shielding them from the outside space. In addition, each of the caps 364 covers the area around the ejection port 830 of the corresponding ejection head 80, shielding it from the outside space. This suppresses the evaporation and drying of ink at the ejection port 830.

[0066] Inside the smaller bat 363, there is a wiper blade 366 that is supported so as to be able to move up and down by a lifting mechanism 365 using an appropriate actuator. Two sets of the lifting mechanism 365 and wiper blade 366 are provided, corresponding to each of the two head rows C1 and C2.

[0067] The maintenance unit 36 ​​is movable in the (+X) direction, and as will be described later, when the maintenance unit 36 ​​moves below the head unit 35 in the (+X) direction with a predetermined gap between them, the upper end of the wiper blade 366 rubs against the lower surface of the head unit 35, that is, the lower surface of each discharge head 80. As a result, ink adhering to the area around the discharge port 830 provided on each discharge head 80 is wiped away by the wiper blade 366, and the nozzle 83 is cleaned.

[0068] The head unit 35 is movable up and down by a lifting mechanism (not shown), and moves closer to and further away from the maintenance unit 36 ​​in the vertical direction. That is, the distance between the head unit 35 and the maintenance unit 36 ​​in the vertical direction can be changed. By combining the vertical movement of the head unit 35 relative to the maintenance unit 36 ​​and the reciprocating movement of the maintenance unit 36 ​​in the X direction relative to the head unit 35, the head unit 35 and the maintenance unit 36 ​​can have various positional relationships.

[0069] Figure 6 is a block diagram showing the electrical configuration of this inkjet printing apparatus. The control unit 9 is an information processing device for controlling each part of the inkjet printing apparatus 1. As shown in Figure 1, the control unit 9 has a processor 91 such as a CPU, a memory 92 such as RAM, and a storage unit 93 such as a hard disk drive. The storage unit 93 stores a program 931 for executing the process of transporting continuous paper 10 and printing, and the process of supplying ink to the head unit 35. The storage unit 93 also stores print data 933 indicating the image to be printed on the continuous paper 10.

[0070] As shown in Figure 6, the control unit 9 is communicatively connected to the transport unit 2, each head unit 35, each ink supply unit 4, valves (e.g., backflow prevention on / off valve 73), pumps (circulation pump 71, replenishment pump 72, etc.), heater 74, sensors including temperature sensor 741, and pressure difference forming unit 55. The control unit 9 controls the operation of each of these units according to the program 931. As a result, the transport and printing of the continuous paper 10 proceeds, and ink is supplied to the internal tanks 82 of each ejection head 80.

[0071] In the inkjet printing apparatus 1 configured as described above, ink supplied from the ink supply unit 4 to the ejection head 80 is ejected from the ejection port 830 of the nozzle 83, and printing is performed on the continuous paper 10, which is the printing medium. As will be explained next, the viscosity of the ink is temperature-dependent, and it is necessary to heat the ink in order to maintain an ink viscosity suitable for printing.

[0072] The ink used in the inkjet printing apparatus 1 has the general property that its viscosity decreases as the temperature rises. In an inkjet printing apparatus that ejects ink droplets using the fluidity of the ink, it is required that the viscosity of the ink supplied to the ejection head 80 falls within a range suitable for printing. In the following description, the term "optimal printing temperature range" used in relation to ink temperature refers to the range of ink temperatures in which the ink can be maintained at a viscosity suitable for printing.

[0073] In the ink supply unit 4, the ink temperature is maintained within the appropriate printing temperature range by heating the low-temperature ink with the heater 74 while circulating it. However, the supply-side branch pipe 62 and the recovery-side branch pipe 63, which are directly connected to the ejection head 80, are particularly narrow pipes and may be made of, for example, resin tubing. For this reason, they are not suitable for pressurizing high-viscosity ink, and ink aggregation may occur in the tubing, or the tubing may be damaged or detached. Also, because the ink flow rate is small, it takes a long time to circulate the ink.

[0074] Thus, the circulation of ink through the ejection head 80 is undesirable because it may damage the device and requires a long time for the ink to heat up. Therefore, in this embodiment, as has been done in the prior art, an ink circulation channel is formed that bypasses the ejection head 80.

[0075] Figure 7 is a schematic diagram showing the piping system involved in ink circulation. More specifically, Figure 7 is a schematic diagram that extracts and illustrates the components of the ink flow path shown in Figures 2 and 3 that are involved in ink circulation. In Figure 7, the supply tank 51, supply-side manifold 61, recovery tank 52, and recovery-side manifold 64 are shown as cross-sectional views of their horizontal cross-sections viewed from above. Here, in order to show the piping around the discharge head 80, the supply-side manifold 61 and the recovery-side manifold 64 are shown spaced apart in the vertical direction. However, as mentioned above, in the actual device, these are arranged adjacent to each other in the horizontal direction.

[0076] As shown in Figure 7, the internal spaces of the supply tank 51 and the supply-side manifold 61 are directly connected without the need for piping, and the internal space of the supply-side manifold 61 extends to the right in the figure. In other words, the internal space of the supply-side manifold 61 is connected to the supply tank 51 at its left end. Similarly, the internal spaces of the recovery tank 52 and the recovery-side manifold 64 are directly connected without the need for piping, and the internal space of the recovery-side manifold 64 extends to the left in the figure. In other words, the internal space of the recovery-side manifold 64 is connected to the recovery tank 52 at its right end.

[0077] Furthermore, the supply tank 51 and the left end of the recovery-side manifold 64, that is, the end opposite to the recovery tank 52, are connected by a first bypass pipe 67 into which a solenoid valve 671 is inserted. In addition, the right end of the supply-side manifold 61, that is, the end opposite to the supply tank 51, and the recovery tank 52 are connected by a second bypass pipe 68 into which a solenoid valve 681 is inserted.

[0078] Both the first bypass pipe 67 and the second bypass pipe 68 have the function of bypassing the ejection head 80 from the ink flow path that normally passes through the ejection head 80. In other words, by using the first bypass pipe 67 and the second bypass pipe 68, a circulation flow path that does not pass through the ejection head 80 (hereinafter referred to as the "bypass flow path") can be formed.

[0079] Since the first bypass pipe 67 and the second bypass pipe 68 are provided to form a bypass flow path, their flow path cross-sectional area can be determined arbitrarily. It is desirable to increase the flow path cross-sectional area in order to ensure a sufficient ink flow rate in the bypass flow path. This makes it possible to raise the ink temperature to the appropriate printing temperature range in a short time.

[0080] Furthermore, in the actual device, the supply-side manifold 61 and the recovery-side manifold 64 are located in close proximity. Therefore, the lengths of the first bypass pipe 67 and the second bypass pipe 68 can be made extremely short. This shortens the flow path length of the bypass pipes, further reducing the time required to heat the ink to the appropriate printing temperature range.

[0081] In this embodiment, the ink supply unit 4 can selectively execute two operating modes for achieving ink circulation: a "first circulation mode" in which ink is circulated through all ejection heads 80, and a "second circulation mode" in which ink is circulated without passing through all ejection heads 80. Specific examples of these circulation modes will be described in detail below.

[0082] Figure 8 shows the flow of ink in the first circulation mode. In Figure 8 and the later Figures 9A and 9B, a solid black solenoid valve indicates that it is closed. Any other white solenoid valves indicate that they are open. Solid arrows represent the flow of ink, and dashed arrows represent the flow of gas.

[0083] As shown in Figure 8, in the first circulation mode, the solenoid valve 671 on the first bypass pipe 67 and the solenoid valve 681 on the second bypass pipe 68 are closed, while the solenoid valve 621 on the supply-side branch pipe 62 and the solenoid valve 631 on the recovery-side branch pipe 63, which are connected to each of the discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64, are all opened.

[0084] Furthermore, in the pressure difference forming section 55 (pressurizing section 56, depressurizing section 57), the tank valves 563 and 573 are opened. Pressurized gas flows in from the pressure tank 561 of the pressurizing section 56, applying a positive pressure higher than atmospheric pressure to the ink in the supply tank 51. On the other hand, a negative pressure is formed in the pressure tank 571 of the depressurizing section 57, so the gas in the recovery tank 52 flows into the pressure tank 571, applying a negative pressure lower than atmospheric pressure to the ink in the recovery tank 52.

[0085] In this way, a pressure difference is formed between the supply tank 51 and the recovery tank 52, causing the ink in the supply tank 51 to be pumped to the discharge heads 80 via the supply-side manifold 61 and the supply-side branch pipe 62. As a result, the ink flows from the supply-side manifold 61 through each discharge head 80 to the recovery-side manifold 64. The circulation pump 71 operates, causing the ink to recirculate from the recovery tank 52 back to the supply tank 51. A heater 74 installed in this recirculation path adjusts the temperature of the ink flowing into the supply tank 51 to the appropriate temperature range for printing.

[0086] Thus, in the first circulation mode, ink that has been temperature-adjusted to the optimal printing temperature range circulates within the circulation channel 6 via the ejection head 80. Therefore, the control unit 9 can control the ejection head 80 to eject ink with a viscosity suitable for printing. This allows for obtaining high-quality printing results. In this specification, the circulation channel 6 at this time, that is, the channel that starts from the supply tank 51 and returns to the supply tank 51 via the supply-side manifold 61, supply-side branch pipe 62, ejection head 80, recovery-side manifold 64, recovery tank 52, and connecting pipe 65, is sometimes referred to as the "first circulation channel."

[0087] Figures 9A and 9B show the flow of ink in the second circulation mode. As shown in Figure 9A, in one example of the second circulation mode, the solenoid valve 671 on the first bypass pipe 67 and the solenoid valve 681 on the second bypass pipe 68 are opened, while the solenoid valve 621 on the supply-side branch pipe 62 and the solenoid valve 631 on the recovery-side branch pipe 63, which are connected to each of the discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64, are all closed.

[0088] Furthermore, the tank valve 563 on the piping 562 connecting the supply tank 51 and the pressurizing unit 56 is closed. As a result, communication between the pressure tank 561 of the pressurizing unit 56 and the supply tank 51 is cut off, and the application of positive pressure to the ink in the supply tank 51 is stopped. Similarly, the tank valve 573 on the piping 572 connecting the recovery tank 52 and the depressurizing unit 57 is also closed. As a result, communication between the pressure tank 571 of the depressurizing unit 57 and the recovery tank 52 is cut off, and the application of negative pressure to the ink in the recovery tank 52 is stopped. Consequently, the ink circulates in a sealed flow path without external pressure.

[0089] Considering the supply tank 51 as the starting point, the ink in the supply tank 51 flows through two bypass channels, as shown by the solid arrows: one from the first bypass pipe 67 via the recovery-side manifold 64 to the recovery tank 52, and the other from the supply-side manifold 61 via the second bypass pipe 68 to the recovery tank 52, both of which flow into the recovery tank 52. The ink flowing out of the recovery tank 52 is sent to the heater 74 by the connecting pipe 65 and the circulation pump 71 inserted in the middle of it.

[0090] If the heater 74 is turned on at this time, the ink is heated and returned to the supply tank 51 via the connecting pipe 65. By heating and circulating the ink in this way, the ink temperature can be raised. There is no need to circulate low-temperature ink to the ejection head 80, and a circulation channel 7a with a large flow rate and short channel length can be formed. Therefore, it is possible to raise the ink temperature from a relatively low initial ink temperature to the appropriate printing temperature range in a short time.

[0091] In this specification, the circulation path in the second circulation mode may be referred to as the "second circulation path." In this case, the second circulation path 7a consists of two parallel paths that start from the supply tank 51 and reach the recovery tank 52. Specifically, the second circulation path 7a is composed of a path from the supply-side manifold 61 via the second bypass pipe 68, a path from the first bypass pipe 67 via the recovery-side manifold 61, and a connecting path 65.

[0092] On the other hand, another example of the second circulation mode shown in Figure 9B differs from the example shown in Figure 9A in that the solenoid valve 671 on the first bypass piping 67 is closed. Therefore, ink circulation does not occur through the first bypass piping 67. Ink circulates only through the path from the supply tank 51 to the recovery tank 52 via the supply-side manifold 61 and the second bypass piping 68. In this case, the second circulation path 7b is composed of the supply-side manifold 61, the second bypass piping 68, the recovery tank 52, and the connecting path 65, starting from the supply tank 51.

[0093] In terms of circulating all the ink in the flow path, the circulation path 7a shown in Figure 9A is advantageous. On the other hand, the circulation path 7b shown in Figure 9B circulates a smaller total amount of ink than the circulation path 7a shown in Figure 9A. For example, when raising the temperature of cooled ink to the appropriate printing temperature range, a smaller amount of circulating ink can shorten the required time. Therefore, this circulation path 7b can be used, for example, to shorten the waiting time from standby to the start of printing.

[0094] Thus, in this embodiment, as a second circulation mode that does not go through the discharge head 80, there is a circulation path 7a (Figure 9A) that uses two bypass passages in parallel, and a circulation path 7b (Figure 9B) that uses only the bypass passage including the second bypass pipe 68. These two circulation paths 7a and 7b can be used appropriately depending on the purpose.

[0095] Next, the cleaning operation in this inkjet printing apparatus 1 will be described. The nozzle cleaning operation required periodically in an inkjet printing apparatus is described, for example, in Patent Documents 1 and 2. However, there is no disclosure regarding cleaning operations in systems that involve ink circulation and require ink temperature control, as in this embodiment.

[0096] When cleaning around the nozzle 83, ink circulation via the ejection head 80 may be suspended to prevent ink leakage from the nozzle. However, stopping ink circulation causes the temperature of the ink in the flow path to drop. This increases the time it takes for the ink temperature to recover to the appropriate printing temperature range after the cleaning operation is completed. The cleaning operation of this embodiment is configured to resolve these problems.

[0097] Figure 10 is a flowchart showing the cleaning operation of this embodiment. Figures 11A to 11D and 12A to 12D schematically show the movement of the head unit and the maintenance unit during the cleaning operation. The cleaning operation shown in Figure 10 is realized by the control unit 9 executing a pre-prepared program 931 to cause each part of the device to perform predetermined operations. Examples of timings in which the cleaning operation should be performed include: when the device is started up, before a new printing operation is performed after a predetermined time has elapsed since the completion of the previous printing operation, when the head unit is replaced or attached / detached, when any problem occurs with the print quality, and when the user gives an instruction to perform a cleaning operation.

[0098] If a cleaning operation is required, ink circulation in a second circulation mode using the bypass channel is selected (step S101). As a result, ink circulation through the ejection head 80 is not performed. In addition, ink circulation in the second circulation mode helps to maintain the temperature of the ink in the circulation channel. Next, the cap 364 that covered the bottom surface of the ejection head 80 to prevent the nozzle 83 from drying out during standby is removed (uncapping; step S102).

[0099] Figure 11A schematically shows the positional relationship between the head unit 35 and the cleaning unit 36 ​​during capping. In this state, the head unit 35 and the cleaning unit 36 ​​are in close contact via the elastic member 362b, and the cap 364 is also in close contact with the lower surface of the ejection head 80. As a result, the ejection port 830 provided on the ejection head 80 is isolated from the outside space, and evaporation and drying / solidification of the ink in the nozzle 83 are suppressed.

[0100] Although not shown in the diagrams until now, the head unit 35 is provided with a cleaning roller 368 and a cleaning fluid nozzle 369 at its (+X) end as a configuration for performing a cleaning operation. The cleaning roller 368 is a roller member having a surface layer made of an elastic material, such as foamed resin.

[0101] Figure 11B shows the uncapped state. As the head unit 35 moves upward as indicated by the arrow, the cap 364 covering the lower surface of the discharge head 80 is released. From this state, as indicated by the arrow in Figure 11C, the maintenance unit 36 ​​moves from the position directly below the head unit 35 in the (+X) direction. Finally, as shown in Figure 11D, the maintenance unit 36 ​​reaches a "retracted position" where it has moved laterally from below the head unit 35 (step S103).

[0102] At this time, as shown in Figures 11C and 11D, cleaning fluid is discharged from the cleaning fluid nozzle 369, and the cleaning fluid is stored in the cap 364 of the maintenance section 36, which passes below the cleaning fluid nozzle 369. This cleaning fluid is used to clean the cap 364, as well as to clean the discharge port 830 of the discharge head 80 in the capped state.

[0103] Subsequently, as indicated by the arrow in Figure 11D, the maintenance unit 36 ​​moves in the (-X) direction and returns to its position directly below the head unit 35 (step S104). At this time, as shown in Figure 12A, the head unit 35 has not descended as far as the capping state shown in Figure 11A, and is only lightly pressed against the maintenance unit 36. Therefore, the cap 364 does not cover the discharge head 80.

[0104] From this state, the liquid level is adjusted to optimize the amount of ink stored in the supply tank 51 (step S105). This process ensures that sufficient ink is stored in the supply tank 51 in preparation for the subsequent printing operation after the purging discharge and cleaning are completed. Specifically, based on the detection result of the liquid level sensor 511, the amount of ink discharged by the circulation pump 71 that sends ink to the supply tank 51, and the opening degrees of the solenoid valves 671 and 681 provided in the ink output path from the supply tank 51 are adjusted. In this way, the amount of ink stored in the supply tank 51 can be adjusted to an appropriate value.

[0105] Next, the ink circulation mode is changed to the first circulation mode, that is, circulation via the ejection head 80 (step S106). Then, the solenoid valve 621 provided in the supply channel leading to the ejection head 80 is opened, and the ink remaining in the nozzle 83 is pushed out by positive pressure (purge ejection; step S107). Here, the residual ink in the nozzle 83 is discharged to the outside by applying positive pressure, but as described in Patent Document 1, a purging operation in which the residual ink is drawn into the ejection head by applying negative pressure may also be used. During purge ejection, the maintenance unit 36 ​​covers the lower part of the head unit 35, so that the ejected ink does not leak to the outside.

[0106] After purging, the ink circulation is switched to the second circulation mode (step S108). In order to perform purging, it is necessary to temporarily open the ink flow path connected to the nozzle 83. On the other hand, this is not necessary at times other than purging, and in fact, it would be detrimental. The reason is as follows: For example, if a cleaning operation becomes necessary due to some irregular situation, there is a high possibility that the ink meniscus in the nozzle 83 is damaged. If ink is pressure-fed to the ejection head 80 in this state, ink will drip from the nozzle 83.

[0107] In particular, if such ink leakage occurs while the cartridge is uncapped, the leaked ink will scatter throughout the device. To avoid this, it is preferable that ink does not flow into the ejection head 80 except for the minimum period necessary for purging. Therefore, ink circulation is performed in a second circulation mode that does not go through the ejection head 80, immediately before and after purging.

[0108] With the ink circulating in the second circulation mode, the wiper blade 366 wipes the discharge port 830 (step S109). That is, as shown in Figure 12B, the height of the head unit 35 is set so that the upper end of the wiper blade 366 contacts the lower surface of the discharge head 80, and in this state, the maintenance unit 36 ​​moves in the (+X) direction. As a result, the wiper blade 366 rubs against the lower surface of the discharge head 80, wiping away ink and other dirt adhering to the area around the discharge port 830.

[0109] Finally, as shown in Figure 12C, the maintenance unit 36 ​​moves in the (+X) direction until the upper end of the wiper blade 366 contacts the cleaning roller 368. This cleans the wiper blade 366, which has scraped off dirt from the discharge head 80 (wiper cleaning; step S110). After that, the maintenance unit 36 ​​returns to the position directly below the head unit 35.

[0110] If necessary (YES in step S111), steps S104 to S110 of the above process are repeated. If repetition is not necessary (NO in step S111), the head unit 35 descends to cap the nozzle 83 as shown in Figure 12D (step S112), and the cleaning operation ends.

[0111] As described above, in this embodiment, when performing a cleaning operation on the nozzle 83, ink circulation is performed in a second circulation mode that does not go through the ejection head 80, except during purge ejection when it is necessary to pressurize the ink in the nozzle 83. Therefore, ink circulation is achieved even during the cleaning operation, and the ink temperature can be continuously adjusted by operating the heater 74 on the circulation path.

[0112] Therefore, printing can be started immediately after the cleaning operation is completed, significantly reducing waiting time. In particular, by using the bypass channel for circulation, it is possible to circulate ink at a larger flow rate and higher flow rate than through the circulation channel via the ejection head 80. As a result, temperature adjustment can be performed in a short time. Furthermore, aggregation caused by ink stagnation can be prevented.

[0113] In particular, in this embodiment, a supply pipe 62 and a recovery pipe 63 are provided, connected to the discharge head 80, so as to connect a supply-side manifold section 61 directly connected to the supply tank 51 and a recovery-side manifold section 64 directly connected to the recovery tank 52. Therefore, the supply pipe 62 branches off in the middle of the supply-side manifold section 61, and the recovery pipe 63 joins in the middle of the recovery-side manifold section 64. The supply-side manifold section 61 and the recovery-side manifold section 64 each form part of a bypass flow path.

[0114] Therefore, the ink flow within the supply-side manifold 61 and the recovery-side manifold 64 remains almost unchanged between the first circulation mode and the second circulation mode. Consequently, after the cleaning operation is completed, appropriately temperature-controlled ink can be quickly supplied to the ejection head 80.

[0115] The second circulation mode, which is performed in parallel with the cleaning operation, can be implemented using either of the two circulation channels shown in Figures 9A and 9B. For example, if it is necessary to adjust the temperature of a large amount of ink in a short time, the circulation channel 7a, which uses the two bypass channels shown in Figure 9A in parallel, is advantageous. On the other hand, if the objective is to minimize the time from when the ink temperature is low until printing is possible, such as when the device is started up, it is preferable to use the circulation channel 7b shown in Figure 9B to reduce the total amount of circulating ink. In this case, the other bypass channel should be opened only after the temperature of the ink circulating in circulation channel 7b has risen sufficiently.

[0116] Furthermore, during the cleaning operation, the first circulation mode (step S108) during purge ejection does not need to be performed exclusively with the second circulation mode. That is, in step S108, it is sufficient that an ink flow path is formed via the ejection head 80 to enable ink ejection from the nozzle 83, and it is not necessary for the bypass flow path to be closed. Therefore, these flow paths may exist in parallel. However, since the flow resistance of the bypass flow path is usually sufficiently low, there is a risk that the supply of ink to the ejection head 80, which has a higher flow resistance, may be delayed. To avoid this, the flow resistance of the bypass flow path may be increased to guide some of the ink towards the ejection head 80.

[0117] <Second Embodiment> Figures 13A to 13C illustrate the flow of ink in the first and second circulation modes of the second embodiment. In describing the second embodiment, components having the same or corresponding structure and operation as those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and detailed descriptions are omitted. The main differences between the piping system of the first embodiment and the piping system of the second embodiment are as follows. In other words, in the piping system of the first embodiment, the bypass piping that bypasses all discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 consists of a first bypass pipe 67 connecting the recovery-side manifold 64 and the supply tank 51, and a second bypass pipe 68 connecting the supply-side manifold 61 and the recovery tank 52.

[0118] In contrast, in the piping system of the second embodiment, as shown in Figure 13A, the bypass piping that bypasses all discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 is composed of a third bypass pipe 600 that connects the supply-side manifold 61 and the recovery-side manifold 64. More specifically, the third bypass pipe 600 connects the downstream end 61a of the supply-side manifold 61 and the upstream end 64a of the recovery-side manifold 64 in the ink flow direction. A solenoid valve 601 is interposed in the third bypass pipe 600.

[0119] Figure 13B illustrates the first circulation mode in the second embodiment. The first circulation mode is an ink circulation mode mainly performed during printing. In the first circulation mode, all solenoid valves 621 and 631 corresponding to each of the discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 are opened. Also, solenoid valve 601 is closed and the heater 74 is turned on. In this state, a pressure difference is formed between the supply tank 51 and the recovery tank 52. As a result, the ink in the supply tank 51 passes through the supply-side manifold 61, through all the supply-side branch pipes 62, discharge heads 80 and recovery-side branch pipes 63 associated with the supply-side manifold 61 and the recovery-side manifold 64, and is recovered into the recovery-side manifold 64. The ink recovered in the recovery-side manifold 64 is returned to the supply tank 51 by the operation of the circulation pump 71, passing through the connection pipe 65 from the recovery tank 52, and after its temperature is adjusted by the heater 74.

[0120] Figure 13C illustrates the second circulation mode in the second embodiment. The second circulation mode is an ink circulation mode mainly performed during head maintenance, excluding purge dispensing. In the second circulation mode, all solenoid valves 621 and 631 corresponding to each of the dispensing heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 are closed. Also, solenoid valve 601 is opened and the heater 74 is turned on. The magnitude of the pressure difference between the supply tank 51 and the recovery tank 52 is adjusted as appropriate. In this state, the circulation pump 71 is driven. As a result, the ink in the supply tank 51 passes through the supply-side manifold 61, bypasses all the dispensing heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64, and is recovered to the recovery-side manifold 64 through the third bypass pipe 600. The ink recovered in the recovery-side manifold 64 is returned to the supply tank 51 by the operation of the circulation pump 71, passing through the recovery tank 52 and connecting pipe 65, and after its temperature is adjusted by the heater 74.

[0121] <Third Embodiment> Figures 14A to 14C illustrate the flow of ink in the first and second circulation modes of the third embodiment. In describing the third embodiment, components having the same or corresponding structure and operation as those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and detailed descriptions are omitted. The main differences between the piping system of the first embodiment and the piping system of the third embodiment are as follows. In other words, in the piping system of the first embodiment, the bypass piping that bypasses all discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 consists of a first bypass pipe 67 connecting the recovery-side manifold 64 and the supply tank 51, and a second bypass pipe 68 connecting the supply-side manifold 61 and the recovery tank 52.

[0122] In contrast, in the piping system of the third embodiment, as shown in Figure 14A, a bypass pipe that bypasses all discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 is made up of a fourth bypass pipe 700 that connects the supply tank 51 and the recovery tank 52. More specifically, the fourth bypass pipe 700 connects the vicinity of the bottom surface of the supply tank 51 and the vicinity of the bottom surface of the recovery tank 52. A solenoid valve 701 is interposed in the fourth bypass pipe 700.

[0123] Figure 14B illustrates the first circulation mode in the third embodiment. The first circulation mode is an ink circulation mode mainly performed during printing. In the first circulation mode, all solenoid valves 621 and 631 corresponding to each of the discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 are opened. Also, the solenoid valve 701 is closed and the heater 74 is turned on. In this state, a pressure difference is formed between the supply tank 51 and the recovery tank 52. As a result, the ink in the supply tank 51 passes through the supply-side manifold 61, through all the supply-side branch pipes 62, discharge heads 80 and recovery-side branch pipes 63 associated with the supply-side manifold 61 and the recovery-side manifold 64, and is recovered into the recovery-side manifold 64. The ink recovered in the recovery-side manifold 64 is returned to the supply tank 51 by the operation of the circulation pump 71, passing through the connection pipe 65 from the recovery tank 52, and after its temperature is adjusted by the heater 74.

[0124] Figure 14C illustrates the second circulation mode in the third embodiment. The second circulation mode is an ink circulation mode mainly performed during head maintenance, excluding purge dispensing. In the second circulation mode, all solenoid valves 621 and 631 corresponding to each of the dispensing heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 are closed. Also, the solenoid valve 701 is opened and the heater 74 is turned on. The magnitude of the pressure difference between the supply tank 51 and the recovery tank 52 is adjusted as appropriate. In this state, the circulation pump 71 is driven. As a result, the ink in the supply tank 51 bypasses all the dispensing heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 without passing through the supply-side manifold 61, and is recovered to the recovery tank 52 through the fourth bypass pipe 700. The ink recovered in the recovery tank 52 is returned to the supply tank 51 by the operation of the circulation pump 71, passing through the connecting pipe 65, and after its temperature is adjusted by the heater 74.

[0125] <Other> As described above, the inkjet printing apparatus 1 of the above embodiment corresponds to one embodiment of the "printing apparatus" of the present invention. In this embodiment, the discharge head 80, supply tank 51, recovery tank 52, and heater 74 function as the "printing head," "supply tank," "recovery tank," and "heater" of the present invention, respectively. In addition, the cap 364 and wiper blade 366 function as the "cap" and "cleaning member" of the present invention, respectively, and the maintenance section 36 including these corresponds to the "maintenance section" of the present invention.

[0126] Furthermore, in the above embodiment, the first bypass pipe 67 and the second bypass pipe 68 correspond to the "bypass pipes" of the present invention. The pair of the supply-side manifold section 61 and the second bypass pipe 68, and the pair of the first bypass pipe 67 and the recovery-side manifold section 64, each form the "first flow path" of the present invention. In other words, in the above embodiment, two sets of first flow paths exist in parallel. These, along with the connecting pipe 65 that forms the "second flow path" of the present invention, together correspond to the "circulation flow path forming section" of the present invention.

[0127] Furthermore, the supply pipe 62 and the recovery pipe 63 function as the "branching channel forming section" of the present invention, and the control valves 621 and 631 correspond to the "control valves" of the present invention. Also, the purge discharge (step S107) in the above embodiment corresponds to the "purge operation" of the present invention.

[0128] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. For example, in the above embodiment, the temperature sensor 741 is integrated with the heater 74, but these may be configured as separate units and each inserted into the recirculation piping. Also, multiple sets of heaters and temperature sensors may be connected in series.

[0129] Furthermore, in the above embodiment, the supply-side manifold section 61 and the recovery-side manifold section 64 form two parallel "first flow paths." This increases the cross-sectional area of ​​the flow paths, enabling circulation at a high flow rate. Alternatively, the supply-side manifold section and the recovery-side manifold section may be connected in series to form a "first flow path." That is, the first bypass pipe 67 and the second bypass pipe 65 in the above embodiment may be eliminated, and instead, the supply-side manifold section 61 and the recovery-side manifold section 64 may be connected by piping. Even with such a configuration, it is possible to form an ink circulation path that does not pass through the print head.

[0130] Furthermore, in the descriptions of the first to third embodiments described above, the pressure difference forming unit 55 includes a pressurizing unit 56 that sets the internal pressure of the supply tank 51 to a positive pressure greater than atmospheric pressure, and a depressurizing unit 57 that sets the internal pressure of the recovery tank 52 to a negative pressure less than atmospheric pressure. However, the pressure difference forming unit 55 may also include a first depressurizing unit that sets the internal pressure of the supply tank 51 to a first negative pressure less than atmospheric pressure, and a second depressurizing unit that sets the internal pressure of the recovery tank 52 to a second negative pressure less than the first negative pressure.

[0131] Furthermore, each of the solenoid valves in the above embodiment functions as an on / off valve that switches the ink flow on and off. However, at least some of them may be equipped with a flow rate control function.

[0132] As described above with examples of specific embodiments, in the printing apparatus according to the present invention, for example, the maintenance unit has a cap that isolates the discharge port from the outside space, and wiping the discharge port with the cleaning member may be performed with the cap retracted from the discharge port. By providing a cap, ink leaking from the discharge port is prevented from scattering into the surroundings, but the cap must be retracted when wiping with the cleaning member. Even in this case, by circulating the ink through a circulation channel that does not go through the print head, it is possible to prevent ink from leaking out with the cap retracted.

[0133] For example, the control unit may be configured to perform a purging operation to remove ink remaining in the nozzle prior to wiping the discharge port with a cleaning member, and to open the control valve while the purging operation is being performed, while closing the control valve before and after the purging operation. With such a configuration, an ink flow path is formed through the print head when the purging operation is performed, so that ink remaining in the nozzle can be effectively removed. On the other hand, since the control valve is closed before and after the purging operation, ink leakage from the print head can be prevented.

[0134] Alternatively, for example, a supply-side manifold section may be connected to the supply tank, the internal space of which communicates with the internal space of the supply tank and forms part of the first flow path, and the branch flow path may branch off from the supply-side manifold section. With such a configuration, the ink flow path from the supply tank to the branching point of the branch flow path is common to both circulation via the print head and circulation without the print head. Therefore, when supplying ink to the print head after cleaning is complete, the ink, which has already been sufficiently heated, can be quickly delivered.

[0135] In this case, the circulation channel forming section may also have a bypass pipe connecting the supply-side manifold section and the recovery tank. This bypass pipe can constitute a part of the first channel from the supply tank to the recovery tank.

[0136] Alternatively, for example, the recovery tank may be connected to a recovery-side manifold section whose internal space communicates with the internal space of the recovery tank and forms part of the first flow path, and the branch flow path may merge with the recovery-side manifold section. With such a configuration, even when ink circulation is performed via the print head, ink flows within the recovery-side manifold section, thus preventing ink aggregation due to convection.

[0137] In this case, the circulation channel forming section may also have a bypass pipe connecting the supply tank and the recovery side manifold section. This bypass pipe can constitute a part of the first channel from the supply tank to the recovery tank.

[0138] Alternatively, the control unit may be configured to adjust the amount of ink stored in the supply tank to a predetermined value by controlling the ratio of the amount of ink flowing out of the supply tank to the amount of ink flowing into the supply tank while circulating the ink through a circulation channel that does not use a branching channel. With such a configuration, the amount of ink in the supply tank can be optimized while wiping is being performed by the cleaning member. As a result, printing can be performed immediately after the wiping operation is completed.

[0139] Although the invention has been described above in accordance with specific embodiments, this description is not intended to be interpreted restrictively. As with other embodiments of the invention, various modifications of the disclosed embodiments will be apparent to those familiar with the art by referring to the description of the invention. Therefore, the appended claims are intended to include such modifications or embodiments without departing from the true scope of the invention.

[0140] This invention can be applied to all printing apparatuses that use ink for printing, and is particularly suitable for printing apparatuses that heat the ink while circulating it.

[0141] 1 Inkjet printing apparatus 9 Control unit 36 ​​Maintenance unit 51 Supply tank 52 Recovery tank 61 Supply side manifold unit (first flow path, circulation flow path forming unit) 64 Recovery side manifold unit (first flow path, circulation flow path forming unit) 62 Supply piping (branch flow path forming unit) 63 Recovery piping (branch flow path forming unit) 65 Connecting flow path (second flow path, circulation flow path forming unit) 67 First bypass piping (bypass piping, first flow path, circulation flow path forming unit) 68 Second bypass piping (bypass piping, first flow path, circulation flow path forming unit) 74 Heater 80 Discharge head (printing head) 364 Cap 366 Wiper blade (cleaning member) 621, 631 Solenoid valve

Claims

1. A printing apparatus comprising: a print head having a nozzle for ejecting ink; a maintenance unit having a cleaning member for wiping the nozzle outlet; a supply tank for storing the ink supplied to the print head; a recovery tank for storing the ink recovered from the print head; a circulation channel forming unit that forms a circulation channel including a first channel for transporting the ink from the supply tank to the recovery tank and a second channel for returning the ink from the recovery tank to the supply tank; a branch channel forming unit that branches off from the first channel midway through the first channel and rejoins the first channel via the print head; a heater inserted in the second channel for heating the ink; and a control unit that controls the flow of the ink in the circulation channel and the branch channel, wherein the branch channel forming unit has a control valve for opening and closing the branch channel, and when the maintenance unit wipes the nozzle outlet with the cleaning member, the control unit closes the control valve and heats the ink with the heater while circulating the ink in the circulation channel that does not go through the branch channel.

2. The printing apparatus according to claim 1, wherein the maintenance unit has a cap that isolates the discharge port from the outside space, and the discharge port is wiped with the cleaning member while the cap is retracted from the discharge port.

3. The printing apparatus according to claim 1, wherein the control unit performs a purging operation to remove the ink remaining in the nozzle prior to wiping the discharge port with the cleaning member, and opens the control valve while performing the purging operation, while closing the control valve before and after the purging operation.

4. The printing apparatus according to any one of claims 1 to 3, wherein a supply-side manifold section is connected to the supply tank, the internal space of which communicates with the internal space of the supply tank and forms part of the first flow path, and the branch flow path branches off from the supply-side manifold section.

5. The printing apparatus according to claim 4, wherein the circulation channel forming section has a first bypass pipe connecting the supply-side manifold section and the recovery tank.

6. The printing apparatus according to claim 4, wherein a recovery-side manifold section is connected to the recovery tank, the internal space of which communicates with the internal space of the recovery tank and forms part of the first flow path, and the branch flow path merges with the recovery-side manifold section.

7. The printing apparatus according to claim 6, wherein the circulation channel forming section has a second bypass pipe connecting the supply tank and the recovery side manifold section.

8. The printing apparatus according to any one of claims 1 to 3, wherein the control unit circulates the ink in the circulation channel without passing through the branch channel, and controls the ratio of the amount of ink flowing out of the supply tank to the amount of ink flowing into the supply tank to adjust the amount of ink stored in the supply tank to a predetermined value.

9. A method for cleaning a nozzle in a printing apparatus that performs printing by discharging ink from a nozzle provided on a print head while circulating ink between a supply tank, a print head, and a recovery tank, wherein when the discharge port of the nozzle is wiped with a cleaning member, the ink flow path passing through the nozzle is closed, while a circulation flow path connecting the supply tank and the recovery tank is formed without passing through the nozzle, and the ink is heated by a heater provided on the circulation flow path while the ink is circulated in the circulation flow path.

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