JP6697914B2 - Inkjet printer - Google Patents

Description

  The present invention relates to an ink circulation type ink jet printing apparatus.

  Ink circulation type inkjet printing in which ink is ejected from an inkjet head for printing while ink is circulated between the tank disposed upstream of the inkjet head, the inkjet head, and the tank disposed downstream thereof. The device is known.

  In such an ink circulation type inkjet printing apparatus, the upstream tank and the downstream tank of the inkjet head may be disposed above the nozzle surface of the inkjet head (see, for example, Patent Document 1).

  With such a configuration, it is necessary to keep the tank on the upstream side and the tank on the downstream side of the inkjet head in a hermetically sealed state during standby without ink circulation. This is to prevent ink from flowing from the tank to the inkjet head and leaking from the nozzle.

JP, 2010-76206, A

  However, if the upstream tank and the downstream tank of the inkjet head are closed during standby, the meniscus of the ink in the nozzle may be destroyed due to environmental changes, and there is a risk that ink leakage from the nozzle or air intake may occur. is there.

  For example, when an inkjet printing apparatus that has moved to a standby state in lowland is moved to highland, the nozzle pressure with respect to atmospheric pressure increases due to the decrease in atmospheric pressure. As a result, the meniscus of the ink in the nozzle may be destroyed and ink may leak. On the contrary, when the inkjet printing apparatus is moved from the highland to the lowland, the nozzle pressure with respect to the atmospheric pressure decreases due to the increase in the atmospheric pressure, the meniscus may be destroyed, and air may be sucked from the nozzle. ..

  The present invention has been made in view of the above, and an object of the present invention is to provide an inkjet printing apparatus that can reduce ink leakage and air suction from nozzles during standby.

  In order to achieve the above object, a first feature of an inkjet printing apparatus according to the present invention is an inkjet head having a nozzle surface in which nozzles for ejecting ink are opened, and a first tank for storing ink to be supplied to the inkjet head. A second tank for receiving ink not consumed by the inkjet head, a circulation path for circulating ink among the first tank, the inkjet head, and the second tank; and a circulation path in the circulation path. A third tank that is directly or indirectly connected to the path from the second tank to the first tank and stores ink, and the first tank and the second tank are in a sealed state in which they are shielded from the atmosphere. A sealing means, wherein the first tank and the second tank are closed by the sealing means during a standby without ink circulation, and the third tank is open to the atmosphere during a standby. That is

  A second feature of the inkjet printing apparatus according to the present invention further includes a switching unit that switches the third tank between a closed state and an atmosphere open state, and the third tank includes the first tank to the first tank. The third tank is arranged on the path to the tank, and when the ink is circulated, the third tank is closed by the switching unit and a negative pressure for sending the ink from the second tank to the third tank. In the standby state, the third tank is opened to the atmosphere by the switching means.

  A third characteristic of the inkjet printing apparatus according to the present invention is that the third tank is connected to the first tank via a connection path connected to a path from the second tank to the first tank. It is connected indirectly to the path to the tank.

  A fourth characteristic of the inkjet printing apparatus according to the present invention is that the third tank is arranged on a path from the second tank to the first tank and is open to the atmosphere during ink circulation and standby. A pump that sends ink from the second tank to the third tank is provided on the path from the second tank to the third tank, and a bypass path that bypasses the pump is provided. A detour opening/closing means for opening/closing a flow path of ink in the detour path is provided in the path, and the detour opening/closing means is closed during ink circulation, and the bypass tank opens and closes the second tank. Ink is sent to the third tank, and the detour opening/closing means is opened during standby.

  A fifth characteristic of the inkjet printing apparatus according to the present invention is that the third tank is arranged below the nozzle surface.

  A sixth feature of the inkjet printing apparatus according to the present invention is that the first tank and the second tank are connected via a valve that is in an open state when not energized, and a positive pressure during ink circulation is the above-mentioned. When the valve is opened in the state where the negative pressure is generated in the first tank and the negative pressure is generated in the second tank, the positive pressure of the first tank and the negative pressure of the second tank cancel each other out. is there.

  A seventh feature of the inkjet printing apparatus according to the present invention is that each of the third tanks is provided with a plurality of the inkjet heads, the first tank, the second tank, and the circulation path.

  According to the first aspect of the inkjet printing apparatus of the present invention, the third tank is directly or indirectly connected to the path from the second tank to the first tank in the circulation path. Then, during standby without ink circulation, the first tank and the second tank are sealed by the sealing means, and the third tank is open to the atmosphere. As a result, the nozzle pressure of the inkjet head during standby is determined by the height difference between the nozzle surface and the liquid surface of the third tank opened to the atmosphere. Therefore, even if the atmospheric pressure fluctuates due to environmental changes, the fluctuation of the nozzle pressure can be suppressed, so that it is possible to prevent the meniscus from being destroyed and ink leakage or air suction from the nozzles. Therefore, it is possible to reduce ink leakage and air suction from the nozzles during standby.

  According to the second feature of the inkjet printing apparatus of the present invention, the third tank is arranged on the path from the second tank to the first tank, and is closed by the switching means during ink circulation. At the same time, a negative pressure for sending the ink from the second tank to the third tank is applied. During standby, the third tank is opened to the atmosphere by the switching means. Thus, with the configuration in which the third tank is arranged on the circulation path, the ink is sent from the second tank to the third tank by the negative pressure of the third tank when the ink is circulated, and the liquid level of the third tank is increased during standby. The nozzle pressure can be determined by the difference in height from the nozzle surface.

  According to the third aspect of the inkjet printing apparatus of the present invention, the third tank is indirectly connected to the path from the second tank to the first tank via the connection path. Accordingly, with the configuration in which the third tank is arranged outside the circulation path, the nozzle pressure during standby can be determined by the height difference between the liquid surface of the third tank and the nozzle surface.

  According to the fourth aspect of the inkjet printing apparatus of the present invention, the third tank is arranged on the path from the second tank to the first tank, and is open to the atmosphere during ink circulation and standby. During ink circulation, the bypass opening/closing means is closed and ink is sent from the second tank to the third tank by the pump. During standby, the detour opening/closing means is opened so that the second tank and the third tank are communicated with each other via the detour path. Accordingly, in the configuration in which the third tank is arranged on the circulation path, the decrease in the flow rate due to the influence of the pressure loss in the path from the second tank to the third tank during the ink circulation is suppressed, and the nozzle pressure in the standby state is reduced. It can be determined by the height difference between the liquid surface of the three tanks and the nozzle surface.

  According to the fifth aspect of the inkjet printing apparatus of the present invention, since the third tank is arranged below the nozzle surface, the nozzle pressure during standby can be made negative. As a result, ink leakage during standby can be further reduced.

  According to the sixth aspect of the inkjet printing apparatus of the present invention, the first tank and the second tank are connected via a valve that is opened when not energized. Then, when the valve is opened in the state where the positive pressure during the ink circulation is generated in the first tank and the negative pressure is generated in the second tank, the positive pressure of the first tank and the negative pressure of the second tank become Offset. Therefore, even when the power is cut off during ink circulation, the pressure in the first tank and the second tank can be released by opening the valve.

  According to the seventh feature of the inkjet printing apparatus of the present invention, each of the third tanks includes a plurality of inkjet heads, a first tank, a second tank, and a circulation path. Accordingly, it is possible to realize a configuration in which a plurality of inkjet heads are provided for one color while suppressing the complexity of the device configuration.

FIG. 3 is a block diagram showing the configuration of the inkjet printing apparatus according to the first embodiment. FIG. 3 is a schematic configuration diagram of a printing unit and a pressure generation unit of the inkjet printing apparatus according to the first embodiment. 6 is a flowchart for explaining the operation of the inkjet printing apparatus in the first embodiment. (A)-(c) is explanatory drawing of the liquid level maintenance control in 1st Embodiment. (A), (b) is explanatory drawing of the pressure control in 1st Embodiment. FIG. 7 is a diagram illustrating a modification example of a printing unit according to the first embodiment. It is a schematic block diagram of the printing part and the pressure generation part in 2nd Embodiment. 7 is a flowchart for explaining the operation of the inkjet printing apparatus in the second embodiment. (A), (b) is explanatory drawing of the liquid level maintenance control in 2nd Embodiment arrangement. It is explanatory drawing of the pressure control in 2nd Embodiment. It is a figure which shows the example of a change of the printing part in 2nd Embodiment. It is a schematic block diagram of the printing part and pressure generation part in 3rd Embodiment. 9 is a flowchart for explaining the operation of the inkjet printing apparatus in the third embodiment. (A)-(c) is explanatory drawing of the liquid level maintenance control in 3rd Embodiment. It is a figure which shows the example of a change of the printing part in 3rd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts or components are designated with the same or equivalent reference numerals.

  The embodiments described below exemplify devices and the like for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, arrangement, etc. of each component. Is not specified below. The technical idea of the present invention can be modified in various ways within the scope of the claims.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of an inkjet printing apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a printing unit and a pressure generation unit of the inkjet printing apparatus according to the first embodiment. Note that the up-down direction in the following description is the vertical direction, and the up-down direction of the paper surface in FIG. 2 is the up-down direction.

  As shown in FIG. 1, the inkjet printing apparatus 1 according to the first embodiment includes four printing units 2, a pressure generation unit 3, a conveyance unit 4, and a control unit 5.

  The printing unit 2 circulates the ink and ejects the ink onto the sheet conveyed by the conveying unit 4 to print an image. The four printing units 2 eject ink of different colors (for example, black, cyan, magenta, and yellow). The four printing units 2 have the same configuration except that the colors of the ejected inks are different.

  As shown in FIG. 2, the printing unit 2 includes an inkjet head 11, an ink circulation unit 12, and an ink supply unit 13.

  The inkjet head 11 ejects the ink supplied by the ink circulation unit 12. The inkjet head 11 has a plurality of head modules 16.

  The head module 16 has an ink chamber (not shown) for storing ink, a plurality of nozzles (not shown) for ejecting ink, and a nozzle surface 16a in which the nozzles are opened. A piezo element (not shown) is arranged in the ink chamber. Ink is ejected from the nozzle by driving the piezo element. The nozzle surface 16a is the lower surface of the head module 16 that faces the sheet conveyed by the conveying section 4.

  The head module 16 is held by the head holder 17. The head holder 17 holds the head module 16 of the inkjet head 11 of each printing unit 2, and houses a distributor 22 and a collector 23, which will be described later, inside.

  The ink circulation unit 12 supplies ink to the inkjet head 11 while circulating the ink. The ink circulation unit 12 includes a pressure tank (corresponding to the first tank in claims) 21, a distributor 22, a collector 23, a negative pressure tank (corresponding to the second tank in claims) 24, and a recovery tank. (Equivalent to the third tank in the claims) 25, ink circulation pipes 26 to 29, an ink recovery valve 30, an ink circulation pump 31, a heat sink 32, and a heater 33.

  The pressure tank 21 stores the ink supplied to the inkjet head 11. The ink in the pressure tank 21 is supplied to the inkjet head 11 via the ink circulation pipe 26 and the distributor 22. That is, the pressure tank 21 is arranged on the upstream side of the inkjet head 11 in the ink circulation direction. In the pressure tank 21, an air layer 36 is formed on the ink surface. The pressurizing tank 21 is connected to a pressurizing common air chamber 51, which will be described later, via a pressurizing communication pipe 52, which will be described later. The pressure tank 21 is arranged in the vicinity of the inkjet head 11 and at a position higher (above) than the nozzle surface 16a.

  The pressure tank 21 is provided with a pressure tank liquid level sensor 37 and an ink filter 38.

  The pressure tank liquid level sensor 37 is for detecting whether or not the liquid level of the ink in the pressure tank 21 has reached the reference height. The pressurized tank liquid level sensor 37 outputs a signal indicating "ON" when the liquid level in the pressurized tank 21 is equal to or higher than the reference height, and outputs "OFF" when it is less than the reference height. It outputs the indicated signal.

  The ink filter 38 removes dust and the like in the ink.

  The distributor 22 distributes the ink supplied from the pressure tank 21 via the ink circulation pipe 26 to each head module 16 of the inkjet head 11.

  The aggregator 23 collects the ink not consumed by the inkjet head 11 from each head module 16. The ink collected by the collector 23 flows to the negative pressure tank 24 via the ink circulation pipe 27.

  The negative pressure tank 24 receives the ink not consumed by the inkjet head 11 from the collector 23 and stores it. That is, the negative pressure tank 24 is arranged on the downstream side of the inkjet head 11 in the ink circulation direction. In the negative pressure tank 24, an air layer 39 is formed on the ink surface. The negative pressure tank 24 is connected to a negative pressure common air chamber 56 described later via a negative pressure communication pipe 57 described later. The negative pressure tank 24 is arranged in the vicinity of the inkjet head 11 and the pressure tank 21 and at the same height as the pressure tank 21.

  The negative pressure tank 24 is provided with a negative pressure tank liquid level sensor 40. The negative pressure tank liquid level sensor 40 is for detecting whether or not the liquid surface height of the ink in the negative pressure tank 24 has reached the reference height. The negative pressure tank liquid level sensor 40 outputs a signal indicating “ON” when the liquid level in the negative pressure tank 24 is equal to or higher than the reference height, and outputs “OFF” when it is less than the reference height. It outputs the indicated signal.

  The recovery tank 25 stores the ink supplied to the pressure tank 21. The recovery tank 25 receives the ink supplied from the ink supply unit 13 and stores the supplied ink. Further, the recovery tank 25 receives and stores the ink from the negative pressure tank 24. The recovery tank 25 is connected to the pressure tank 21 via an ink circulation pipe 29, and is connected to the negative pressure tank 24 via an ink circulation pipe 28. As a result, the recovery tank 25 is arranged on the path from the negative pressure tank 24 to the pressure tank 21 in the ink circulation path. In other words, the recovery tank 25 is directly connected to the path from the negative pressure tank 24 to the pressure tank 21 in the ink circulation path. In the recovery tank 25, an air layer 41 is formed on the liquid surface of the ink. The recovery tank 25 is connected to a recovery common air chamber 63 described later via a recovery communication pipe 64 described below. The recovery tank 25 is arranged at a position lower (lower) than the nozzle surface 16 a of the head module 16 of the inkjet head 11.

  The recovery tank 25 is provided with a recovery tank liquid level sensor 42. The recovery tank liquid level sensor 42 is for detecting whether or not the liquid level of the ink in the recovery tank 25 has reached the reference height. The recovery tank liquid level sensor 42 outputs a signal indicating “ON” when the liquid level in the recovery tank 25 is equal to or higher than the reference height, and outputs a signal indicating “OFF” when the liquid level is less than the reference height. Is output.

  The ink circulation pipe 26 connects the pressure tank 21 and the distributor 22. Ink flows through the ink circulation pipe 26 from the pressure tank 21 toward the distributor 22. The ink circulation pipe 27 connects the collector 23 and the negative pressure tank 24. Ink flows from the collector 23 to the negative pressure tank 24 in the ink circulation pipe 27. The ink circulation pipe 28 connects the negative pressure tank 24 and the recovery tank 25. Ink flows through the ink circulation pipe 28 from the negative pressure tank 24 toward the recovery tank 25. The ink circulation pipe 29 connects the recovery tank 25 and the pressure tank 21. Ink flows through the ink circulation pipe 29 from the recovery tank 25 toward the pressure tank 21. The ink circulation pipes 26 to 29, the distributor 22, and the collector 23 constitute a circulation path for circulating ink among the pressure tank 21, the inkjet head 11, the negative pressure tank 24, and the recovery tank 25. It

  The ink recovery valve 30 opens and closes the ink flow path in the ink circulation pipe 28. The ink recovery valve 30 is provided in the middle of the ink circulation pipe 28. The ink recovery valve 30 is a normally open solenoid valve that is closed when energized and opened when not energized.

  The ink circulation pump 31 feeds ink from the recovery tank 25 to the pressure tank 21. The ink circulation pump 31 is provided in the middle of the ink circulation pipe 29.

  The heat sink 32 cools the ink circulated in the ink circulation unit 12. The heat sink 32 is provided in the middle of the ink circulation tube 28.

  The heater 33 heats the ink circulated in the ink circulation unit 12. The heater 33 is provided in the middle of the ink circulation tube 29.

  The ink supply unit 13 supplies ink to the ink circulation unit 12. The ink supply unit 13 includes an ink cartridge 46, an ink supply valve 47, and an ink supply pipe 48.

  The ink cartridge 46 contains ink used for printing by the inkjet head 11. The ink in the ink cartridge 46 is supplied to the recovery tank 25 of the ink circulation unit 12 via the ink supply pipe 48.

  The ink supply valve 47 opens and closes the ink flow path in the ink supply pipe 48. The ink supply valve 47 is provided in the middle of the ink supply pipe 48. The ink supply valve 47 is a normally open solenoid valve.

  The ink supply pipe 48 connects the ink cartridge 46 and the recovery tank 25. When the ink supply valve 47 is opened during the ink circulation, the negative pressure generated in the recovery tank 25 causes the ink to flow from the ink cartridge 46 toward the recovery tank 25 in the ink supply pipe 48.

  The pressure generation unit 3 generates a pressure for ink circulation in the pressure tank 21, the negative pressure tank 24, and the recovery tank 25 of each printing unit 2. As shown in FIG. 2, the pressure generation unit 3 includes a pressurization common air chamber 51, four pressurization communication pipes 52, a pressurization pressure adjustment valve 53, a pressurization pressure adjustment pipe 54, and a pressurization pressure. The sensor 55, the negative pressure common air chamber 56, the four negative pressure communication pipes 57, the negative pressure pressure adjustment valve 58, the negative pressure pressure adjustment pipe 59, the negative pressure pressure sensor 60, and the pressurization pressure communication valve. 61, pressurization/negative pressure communication pipe 62, recovery common air chamber 63, four recovery communication pipes 64, recovery pressure adjusting valve 65, recovery pressure adjusting pipe 66, recovery atmosphere opening valve 67, recovery atmosphere An open pipe 68, an air filter 69, a recovery pressure sensor 70, an air pump 71, an air pump pipe 72, a negative pressure introducing valve 73, and a negative pressure introducing pipe 74 are provided.

  The pressurized common air chamber 51 is an air chamber for equalizing the pressures of the pressure tanks 21 of the respective printing units 2. The pressurized common air chamber 51 communicates with the air layers 36 of the pressure tanks 21 of the four printing units 2 via the four pressure communication pipes 52. As a result, the pressure tanks 21 of the respective printing units 2 are communicated with each other via the pressure common air chamber 51 and the pressure communication pipe 52.

  The pressurizing communication pipe 52 connects the pressurizing common air chamber 51 and the air layer 36 of the pressurizing tank 21. The four pressurizing communication tubes 52 are provided corresponding to each of the printing units 2. The pressurizing communication pipe 52 has one end connected to the pressurizing common air chamber 51 and the other end connected to the air layer 36 of the pressurizing tank 21.

  The pressurization pressure adjustment valve 53 opens and closes the air passage in the pressurization pressure adjustment pipe 54 in order to adjust the pressures of the pressurization common air chamber 51 and the pressurization tank 21. The pressurizing pressure adjusting valve 53 is provided in the middle of the pressurizing pressure adjusting pipe 54. The pressurizing pressure adjusting valve 53 is a normally closed solenoid valve that is opened when energized and closed when not energized. The pressurizing pressure adjusting valve 53 corresponds to a part of the sealing means in the claims.

  The pressurization pressure adjustment pipe 54 forms an air flow path for adjusting the pressures of the pressurization common air chamber 51 and the pressurization tank 21. The pressurization pressure adjustment pipe 54 has one end connected to the pressurization common air chamber 51 and the other end connected to the recovery atmosphere open pipe 68.

  The pressurization pressure sensor 55 detects the pressure in the pressurization common air chamber 51. The pressure in the pressurized common air chamber 51 is equal to the pressure in the pressure tank 21 of each printing unit 2. This is because the pressurization common air chamber 51 and the air layer 36 of the pressurization tank 21 of each printing unit 2 communicate with each other.

  The negative pressure common air chamber 56 is an air chamber for equalizing the pressures of the negative pressure tanks 24 of the respective printing units 2. The negative pressure common air chamber 56 communicates with the air layer 39 of the negative pressure tanks 24 of the four printing units 2 via the four negative pressure communication pipes 57. As a result, the negative pressure tanks 24 of the respective printing units 2 are communicated with each other via the negative pressure common air chamber 56 and the negative pressure communication pipe 57.

  The negative pressure communication pipe 57 connects the negative pressure common air chamber 56 and the air layer 39 of the negative pressure tank 24. The four negative pressure communication tubes 57 are provided corresponding to each printing unit 2. The negative pressure communication pipe 57 has one end connected to the negative pressure common air chamber 56 and the other end connected to the air layer 39 of the negative pressure tank 24.

  The negative pressure adjusting valve 58 opens and closes the air passage in the negative pressure adjusting pipe 59 in order to adjust the pressures of the negative common air chamber 56 and the negative tank 24. The negative pressure adjusting valve 58 is provided in the middle of the negative pressure adjusting tube 59. The negative pressure adjusting valve 58 is a normally closed solenoid valve. The negative pressure adjusting valve 58 corresponds to a part of the sealing means in the claims.

  The negative pressure adjusting pipe 59 forms an air flow path for adjusting the pressures of the negative pressure common air chamber 56 and the negative pressure tank 24. The negative pressure adjusting pipe 59 has one end connected to the negative pressure common air chamber 56 and the other end connected to the recovery atmosphere opening pipe 68.

  The negative pressure sensor 60 detects the pressure in the negative common air chamber 56. The pressure in the negative pressure common air chamber 56 is equal to the pressure in the negative pressure tank 24 of each printing unit 2. This is because the negative pressure common air chamber 56 and the air layer 39 of the negative pressure tank 24 of each printing unit 2 communicate with each other.

  The pressurization/negative pressure communication valve 61 opens/closes an air flow path in the pressurization/pressure communication pipe 62 in order to switch between communication and interruption between the pressurization common air chamber 51 and the negative pressure common air chamber 56. The pressurizing/negative pressure communicating valve 61 is provided in the middle of the pressurizing/negative pressure communicating pipe 62. The pressurizing/negative pressure communicating valve 61 is a normally open type solenoid valve. Since the pressurizing/negative pressure communicating valve 61 is opened and the pressurizing common air chamber 51 and the negative pressure common air chamber 56 are communicated with each other, the pressurizing communicating pipe 52, the pressurizing common air chamber 51, and the pressurizing/negative pressure communicating pipe 62. The pressure tank 21 and the negative pressure tank 24 are communicated with each other via the negative pressure common air chamber 56 and the negative pressure communication pipe 57. That is, by opening/closing the pressurizing/pressurizing communication valve 61, communication between the pressurizing tank 21 and the negative pressure tank 24 can be switched. Therefore, it can be said that the pressurization tank 21 and the negative pressure tank 24 are connected via the pressurization/negative pressure communication valve 61. The pressurizing/negative pressure communicating valve 61 corresponds to the valve in the claims.

  The pressurization/negative pressure communication pipe 62 forms an air flow path for communicating the pressurization common air chamber 51 and the negative pressure common air chamber 56. The pressurization/negative pressure communication pipe 62 has one end connected to the pressurization common air chamber 51 and the other end connected to the negative pressure common air chamber 56.

  The recovery common air chamber 63 is an air chamber for equalizing the pressures of the recovery tanks 25 of the respective printing units 2. The recovery common air chamber 63 communicates with the air layers 41 of the recovery tanks 25 of the four printing units 2 via the four recovery communication tubes 64. As a result, the collection tanks 25 of the printing units 2 are communicated with each other via the collection common air chamber 63 and the collection communication pipe 64.

  The recovery communication pipe 64 connects the recovery common air chamber 63 and the air layer 41 of the recovery tank 25. The four recovery communication tubes 64 are provided for each printing unit 2 one by one. The recovery communication pipe 64 has one end connected to the recovery common air chamber 63 and the other end connected to the air layer 41 of the recovery tank 25.

  The recovery pressure adjusting valve 65 opens and closes the air passage in the recovery pressure adjusting pipe 66 in order to adjust the pressures of the recovery common air chamber 63 and the recovery tank 25. The recovery pressure adjusting valve 65 is provided in the middle of the recovery pressure adjusting pipe 66. The recovery pressure adjusting valve 65 is a normally closed solenoid valve.

  The recovery pressure adjusting pipe 66 forms an air flow path for adjusting the pressure of the recovery common air chamber 63 and the recovery tank 25. The recovery pressure adjusting pipe 66 has one end connected to the recovery common air chamber 63 and the other end connected to the recovery atmosphere open pipe 68.

  The recovery-atmosphere opening valve 67 is provided for switching the recovery common air chamber 63 and the recovery tank 25 between a closed state (a state in which the atmosphere is shut off) and an atmosphere-released state (a state in which the atmosphere is communicated). The air flow path in 68 is opened and closed. The recovery atmosphere release valve 67 is provided on the recovery atmosphere release pipe 68 near the recovery common air chamber 63. The recovery atmosphere release valve 67 is a normally open type solenoid valve. The recovery atmosphere release valve 67 corresponds to the switching means in the claims.

  The recovery atmosphere open pipe 68 forms an air flow path for opening the recovery common air chamber 63 and the recovery tank 25 to the atmosphere. One end of the recovery atmosphere open pipe 68 is connected to the recovery common air chamber 63, and the other end (upper end) communicates with the atmosphere via the air filter 69. A pressurization pressure adjustment pipe 54, a negative pressure adjustment pipe 59, and a recovery pressure adjustment pipe 66 are connected to the recovery atmosphere release pipe 68. As a result, the pressurizing pressure adjusting pipe 54, the negative pressure adjusting pipe 59, and the recovery pressure adjusting pipe 66 are communicated with the atmosphere. The pressurization pressure adjustment pipe 54, the negative pressure adjustment pipe 59, and the recovery pressure adjustment pipe 66 are connected to the recovery atmosphere release pipe 68 between the recovery atmosphere release valve 67 and the air filter 69.

  The air filter 69 prevents dust and the like in the air from entering the recovered atmosphere open pipe 68. The air filter 69 is installed at the upper end of the recovery atmosphere open pipe 68.

  The recovery pressure sensor 70 detects the pressure in the recovery common air chamber 63. The pressure in the recovery common air chamber 63 is equal to the pressure in the recovery tank 25 of each printing unit 2. This is because the recovery common air chamber 63 and the air layer 41 of the recovery tank 25 of each printing unit 2 are in communication with each other.

  The air pump 71 sucks air from the recovery common air chamber 63 and sends the air to the pressurized common air chamber 51. The air pump 71 is provided in the middle of the air pump pipe 72.

  The air pump pipe 72 forms a flow path of air sent from the recovery common air chamber 63 to the pressurized common air chamber 51 by the air pump 71. The air pump pipe 72 has one end connected to the recovery common air chamber 63 and the other end connected to the pressurized common air chamber 51.

  The negative pressure introducing valve 73 opens and closes the air flow path in the negative pressure introducing pipe 74 in order to reduce the pressure in the negative pressure common air chamber 56 by using the pressure in the recovery common air chamber 63. The negative pressure introducing valve 73 is provided in the middle of the negative pressure introducing pipe 74. The negative pressure introduction valve 73 is a normally closed solenoid valve. The negative pressure introducing valve 73 corresponds to a part of the sealing means in the claims.

  The negative pressure introducing pipe 74 forms a flow path of air for lowering the pressure in the negative pressure common air chamber 56 by using the pressure in the recovery common air chamber 63. The negative pressure introducing pipe 74 has one end connected to the recovery common air chamber 63 and the other end connected to the negative pressure common air chamber 56.

  Here, the air amount design of the pressurization system and the negative pressure system in the printing unit 2 and the pressure generation unit 3 will be described.

  As will be described later, in the inkjet printing apparatus 1, the pressurization/negative pressure communication valve 61 is opened at the end of ink circulation. At this time, the positive pressure of the pressure system including the pressure tank 21 and the common pressure chamber 51 and the negative pressure of the negative pressure system including the negative pressure tank 24 and the common pressure chamber 56 during the ink circulation are The amount of air in the pressurization system and the air in the negative pressure system are offset so that the pressures of the pressurization tank 21, the pressurization common air chamber 51, the negative pressure tank 24, and the negative pressure common air chamber 56 become equivalent to atmospheric pressure. Quantity is designed.

  Specifically, according to Boyle's law, the air amount Vk1 of the pressurizing system and the air amount Vf1 of the negative pressure system in the inkjet printing apparatus 1 are designed so that the following expression (1) is established. The pressure is gauge pressure.

Pks×Vk1+Pfs×Vf1=0 (1)
Here, Pks is a set pressure of the pressure tank 21 during ink circulation. Pfs is a set pressure of the negative pressure tank 24 during ink circulation. The set pressures Pks and Pfs are set as pressure values for making the nozzle pressure of the inkjet head 11 an appropriate value (negative pressure) while circulating the ink at a predetermined ink circulation flow rate in the ink circulation unit 12. .

  The air amount Vk1 of the pressurization system is an air amount of a portion which communicates with the pressurization tank 21 when the ink is circulated and becomes the set pressure Pks together with the pressurization tank 21. The air amount Vk1 of the pressurizing system is represented by the following equation (2).

Vk1=4×Vkt+Vkc+4×Vkr+Vkb+Vkn+Vkp (2)
Here, Vkt is the capacity of the air layer 36 in the pressure tank 21. Vkt corresponds to the volume of the space above the reference height of the liquid level in the pressure tank 21. Vkc is the capacity of the pressurized common air chamber 51. Vkr is the capacity of the pressure communication pipe 52. Vkb is the capacity of the portion of the pressurization pressure adjustment pipe 54 between the pressurization common air chamber 51 and the pressurization pressure adjustment valve 53. Vkn is a capacity of a portion of the pressurization/pressure communication pipe 62 between the pressurization common air chamber 51 and the pressurization/pressure communication valve 61. Vkp is the capacity of the portion of the air pump pipe 72 between the pressurized common air chamber 51 and the air pump 71.

  The air amount Vf1 of the negative pressure system is an air amount of a portion which communicates with the negative pressure tank 24 during the ink circulation and becomes the set pressure Pfs together with the negative pressure tank 24. The air amount Vf1 of the negative pressure system is expressed by the following equation (3).

Vf1=4×Vft+Vfc+4×Vfr+Vfb+Vfn+Vfi (3)
Here, Vft is the capacity of the air layer 39 in the negative pressure tank 24. Vft corresponds to the volume of the space above the reference height of the liquid level in the negative pressure tank 24. Vfc is the capacity of the negative pressure common air chamber 56. Vfr is the capacity of the negative pressure communication pipe 57. Vfb is the capacity of the portion of the negative pressure adjustment pipe 59 between the negative pressure common air chamber 56 and the negative pressure adjustment valve 58. Vfn is the capacity of the portion of the pressurization/pressure communication pipe 62 between the negative pressure common air chamber 56 and the pressurization/pressure communication valve 61. Vfi is the capacity of the portion of the negative pressure introducing pipe 74 between the negative pressure common air chamber 56 and the negative pressure introducing valve 73.

  Returning to FIG. 1, the transport unit 4 takes out a sheet from a paper feed table (not shown) and transports the sheet along the transport path. The transport unit 4 has a roller for transporting a sheet, a motor for driving the roller (neither is shown), and the like.

  The control unit 5 controls the operation of each unit of the inkjet printing apparatus 1. The control unit 5 includes a CPU, a RAM, a ROM, a hard disk, and the like.

  At the time of printing, the control unit 5 controls the printing unit 2 and the pressure generation unit 3 so that the ink circulation unit 12 circulates the ink and ejects the ink from the inkjet head 11. Further, the control unit 5 closes the pressurization pressure adjustment valve 53, the negative pressure pressure adjustment valve 58, and the negative pressure introduction valve 73 during standby without ink circulation to close the pressurization tank 21 and the negative pressure tank from the atmosphere. The closed state is shut off, and the recovery atmosphere opening valve 67 is opened to control the recovery tank 25 to be open to the atmosphere.

  Next, the operation of the inkjet printing apparatus 1 will be described.

  FIG. 3 is a flow chart for explaining the operation of the inkjet printing apparatus 1. The process of the flowchart of FIG. 3 starts when a print job is input to the inkjet printing apparatus 1.

  In step S1 of FIG. 3, the control unit 5 closes the pressurization/negative pressure communication valve 61 and the recovered atmosphere opening valve 67, and opens the negative pressure introduction valve 73. By closing the pressurization/negative pressure communication valve 61, the pressurization common air chamber 51 and the negative pressure common air chamber 56 are shut off from each other. Further, by opening the negative pressure introducing valve 73, the negative pressure common air chamber 56 and the recovery common air chamber 63 are communicated with each other. Further, by closing the recovery atmosphere opening valve 67, the recovery common air chamber 63 and the recovery tank 25 are shut off from the atmosphere.

  Note that during standby, the pressurization/negative pressure communication valve 61 and the recovery atmosphere release valve 67 are open, and the negative pressure introduction valve 73 is closed. Further, the pressurizing pressure adjusting valve 53, the negative pressure adjusting valve 58, and the recovery pressure adjusting valve 65 are closed. Further, the ink recovery valve 30 and the ink supply valve 47 are open.

  Next, in step S2, the control unit 5 starts the liquid level maintenance control. The liquid level maintenance control is a control for maintaining the liquid levels of the pressure tank 21, the negative pressure tank 24, and the recovery tank 25 near the reference height. In the liquid level maintenance control, the control unit 5 controls the ink circulation pump 31, the ink recovery valve 30, and the ink supply valve 47 according to the liquid level of the pressure tank 21, the negative pressure tank 24, and the recovery tank 25. Control.

  Specifically, as shown in FIG. 4A, when the pressure tank liquid level sensor 37 is off, the control unit 5 turns on (drives) the ink circulation pump 31. When the pressure tank liquid level sensor 37 is on, the control unit 5 turns off (stops) the ink circulation pump 31.

  Further, as shown in FIG. 4B, when the negative pressure tank liquid level sensor 40 is off, the control unit 5 closes the ink recovery valve 30. When the negative pressure tank liquid level sensor 40 is on, the control unit 5 opens the ink recovery valve 30.

  Further, as shown in FIG. 4C, when the recovery tank liquid level sensor 42 is off, the control unit 5 opens the ink supply valve 47. When the recovery tank liquid level sensor 42 is on, the control unit 5 closes the ink supply valve 47.

  Returning to FIG. 3, in step S3 following step S2, the control unit 5 starts pressure control. The pressure control is a control for generating and maintaining the set pressures Pks, Pfs, Prs in the pressurization tank 21, the negative pressure tank 24, and the recovery tank 25, respectively. Here, the set pressure Prs of the recovery tank 25 is a negative pressure smaller than the set pressure Pfs of the negative pressure tank 24 (the absolute value is large). The set pressure Prs of the recovery tank 25 is set as a pressure value for sending ink from the negative pressure tank 24 to the recovery tank 25 due to the pressure difference with the negative pressure tank 24.

  In the pressure control, the control unit 5 responds to the detected pressure Pk of the pressurizing tank 21, the pressure Pf of the negative pressure tank 24, and the pressure Pr of the recovery tank 25, the air pump 71, the pressurizing pressure adjusting valve 53, and the negative pressure adjusting valve 53. The pressure introduction valve 73, the negative pressure adjustment valve 58, and the recovery pressure adjustment valve 65 are controlled.

  Specifically, as shown in FIG. 5A, when Pk<Pks and |Pr|<|Prs|, the control unit 5 turns on (drives) the air pump 71 and sets the pressurization pressure adjustment valve 53 and The recovery pressure adjusting valve 65 is closed. As a result, the air pump 71 sucks air from the closed collection common air chamber 63, and the pressure in the collection tank 25 decreases (the absolute value of the negative pressure increases). In addition, the pressure of the pressurizing tank 21 is increased by sending air to the pressurized common air chamber 51 in the closed state by the air pump 71.

  When Pk<Pks and |Pr|≧|Prs|, the control unit 5 turns on the air pump 71, closes the pressurization pressure adjustment valve 53, and opens the recovery pressure adjustment valve 65. As a result, the air pump 71 sends air to the pressurized common air chamber 51 in a sealed state, so that the pressure in the pressure tank 21 rises. Further, when the recovery pressure adjusting valve 65 is opened, air flows into the recovery common air chamber 63 through the recovery pressure adjusting pipe 66, so that the pressure of the recovery tank 25 increases (the absolute value of the negative pressure is Smaller).

  When Pk≧Pks and |Pr|<|Prs|, the control unit 5 turns on the air pump 71, opens the pressurization pressure adjustment valve 53, and closes the recovery pressure adjustment valve 65. As a result, air is sucked from the collection common air chamber 63 in the closed state by the air pump 71, so that the pressure of the collection tank 25 decreases (the absolute value of the negative pressure increases). Further, when the pressurization pressure adjustment valve 53 is opened, air flows out from the pressurization common air chamber 51 via the pressurization pressure adjustment pipe 54, and the pressure in the pressurization tank 21 decreases.

  When Pk≧Pks and |Pr|≧|Prs|, the control unit 5 turns off (stops) the air pump 71, and opens the pressurization pressure adjustment valve 53 and the recovery pressure adjustment valve 65. As a result, air flows out from the pressurization common air chamber 51 via the pressurization pressure adjustment pipe 54, so that the pressure in the pressurization tank 21 decreases. In addition, the pressure of the recovery tank 25 increases (the absolute value of the negative pressure decreases) as air flows into the recovery common air chamber 63 via the recovery pressure adjusting pipe 66.

  Further, as shown in FIG. 5B, when |Pf|<|Pfs|, the control unit 5 opens the negative pressure introducing valve 73 and closes the negative pressure adjusting valve 58. As a result, air is sucked from the negative pressure common air chamber 56 in the closed state via the negative pressure introducing pipe 74, and the pressure in the negative pressure tank 24 decreases (the absolute value of the negative pressure increases).

  When |Pf|≧|Pfs|, the control unit 5 closes the negative pressure introducing valve 73 and opens the negative pressure adjusting valve 58. As a result, the air flows into the negative pressure common air chamber 56 through the negative pressure adjustment pipe 59, so that the pressure of the negative pressure tank 24 increases (the absolute value of the negative pressure decreases).

  Returning to FIG. 3, in step S4 following step S3, the control unit 5 determines whether or not the set pressures Pks, Pfs, Prs are generated in the pressurization tank 21, the negative pressure tank 24, and the recovery tank 25, respectively. To judge. When it is determined that the set pressure is not generated in at least one of the pressure tank 21, the negative pressure tank 24, and the recovery tank 25 (step S4: NO), the control unit 5 repeats step S4.

  When it is determined that the set pressures Pks, Pfs, and Prs are generated in the pressurization tank 21, the negative pressure tank 24, and the recovery tank 25 (step S4: YES), the control unit 5 executes the print job in step S5. Start execution. Specifically, the control unit 5 causes the ink jet head 11 to eject ink onto the sheet conveyed by the conveying unit 4 to print an image based on the print job.

  During execution of the print job, ink is supplied from the pressure tank 21 to the inkjet head 11, and the ink not consumed by the inkjet head 11 is collected in the negative pressure tank 24. When the pressure tank liquid level sensor 37 is turned off due to the outflow of ink from the pressure tank 21 to the inkjet head 11, the ink circulation pump 31 feeds the ink from the recovery tank 25 to the pressure tank 21 by the liquid level maintenance control. To do. When the negative pressure tank liquid level sensor 40 is turned on by the inflow of ink from the inkjet head 11 to the negative pressure tank 24, the ink recovery valve 30 is opened and the ink flows from the negative pressure tank 24 to the recovery tank 25. Printing is performed while the ink is circulated in this manner.

  Further, when the recovery tank liquid level sensor 42 is turned off by sending the ink from the recovery tank 25 to the pressure tank 21, the ink supply valve 47 is opened, and the ink is supplied from the ink cartridge 46 to the recovery tank 25.

  After the execution of the print job is started, in step S6, the control unit 5 determines whether the print job is completed. When determining that the print job is not completed (step S6: NO), the control unit 5 repeats step S6.

  When it is determined that the print job is completed (step S6: YES), the control unit 5 ends the pressure control in step S7. Here, when the air pump 71 is being driven, the control unit 5 stops it. Further, the control unit 5 closes and closes, if any, the pressurization pressure adjustment valve 53, the negative pressure pressure adjustment valve 58, the recovery pressure adjustment valve 65, and the negative pressure introduction valve 73 if they are opened. What is being done keeps it.

  Next, in step S8, the control unit 5 ends the liquid level maintenance control. Here, when the ink circulation pump 31 is being driven, the control unit 5 stops it. Further, when at least one of the ink recovery valve 30 and the ink supply valve 47 is opened, the control unit 5 closes the opened one.

  When the pressure control and the liquid level maintenance control are completed, the ink circulation in the ink circulation unit 12 is completed.

  Next, in step S9, the control unit 5 opens the pressurization/negative pressure communication valve 61. As described above, in the inkjet printing apparatus 1, since the pressurization system air amount Vk1 and the negative pressure system air amount Vf1 are designed so that the expression (1) is satisfied, the pressurization/negative pressure communication valve 61 is opened. Then, the positive pressure of the pressurizing system and the negative pressure of the negative pressure system cancel each other out. As a result, the pressures of the pressure tank 21 and the negative pressure tank 24 become atmospheric pressure.

  Next, in step S10, the control unit 5 opens the recovery air release valve 67, the ink recovery valve 30, and the ink supply valve 47. As a result, the series of operations is completed, and the inkjet printing apparatus 1 enters the standby state.

  When the inkjet printing apparatus 1 is in the standby state, the pressure tank 21 and the negative pressure tank 24 are in a hermetically sealed state in which they are shielded from the atmosphere. On the other hand, the recovery tank 25 is open to the atmosphere. Therefore, the nozzle pressure Pn of the inkjet head 11 in the standby state is a pressure corresponding to the height difference (water head difference) H between the liquid surface of the ink in the recovery tank 25 and the nozzle surface 16a. Specifically, the nozzle pressure Pn during standby is represented by the following equation (4).

Pn=-ρ×g×H (4)
Here, ρ is the density of the ink. g is the gravitational acceleration. The nozzle pressure Pn has a negative value (negative pressure) because the recovery tank 25 is disposed below the nozzle surface 16a.

  The recovery tank 25 is arranged at a height such that the standby nozzle pressure Pn does not exceed the meniscus breaking pressure. The meniscus breaking pressure is determined according to the diameter of the nozzle and the surface tension of the ink.

  As described above, the inkjet printing apparatus 1 includes the recovery tank 25. During standby, the control unit 5 closes the pressurization pressure adjustment valve 53, the negative pressure pressure adjustment valve 58, and the negative pressure introduction valve 73 to close the pressurization tank 21 and the negative pressure tank 24, and at the same time collects the collected atmosphere. The open valve 67 is opened to control the collection tank 25 to be open to the atmosphere.

  As a result, the nozzle pressure Pn of the inkjet head 11 in the standby state is determined by the height difference H between the liquid surface in the recovery tank 25 opened to the atmosphere and the nozzle surface 16a. Therefore, even if the atmospheric pressure fluctuates due to environmental changes, the fluctuation of the nozzle pressure Pn can be suppressed, so that it is possible to prevent the meniscus from being broken and ink leakage or air suction from the nozzles to occur. Therefore, according to the inkjet printing apparatus 1, it is possible to reduce ink leakage and air suction from the nozzles during standby.

  In the inkjet printing apparatus 1, the recovery tank 25 is arranged on the path from the negative pressure tank 24 to the pressure tank 21. When the ink is circulated, the recovery tank 25 is hermetically closed by closing the recovery atmosphere release valve 67, and a negative pressure is applied. During standby, the recovery tank 25 is opened to the atmosphere by opening the recovery atmosphere release valve 67. With this configuration, the recovery tank 25 is arranged on the circulation path, the ink is sent from the negative pressure tank 24 to the recovery tank 25 by the negative pressure of the recovery tank 25 during the ink circulation, and the liquid in the recovery tank 25 is in the standby state. The nozzle pressure can be determined by the height difference H between the surface and the nozzle surface 16a.

  In the inkjet printing apparatus 1, since the pressure tank 21 and the negative pressure tank 24 are arranged above the inkjet head 11, the pressure tank 21 and the negative pressure tank 24 do not protrude below the inkjet head 11. Therefore, the degree of freedom in layout of a maintenance mechanism (not shown) for cleaning the nozzle surface 16a of the inkjet head 11 or the like is increased.

  Further, in the inkjet printing apparatus 1, the heat sink 32 is arranged in the ink circulation pipe 28 between the negative pressure tank 24 and the recovery tank 25, and the heater 33 is disposed in the ink circulation pipe 29 between the pressure tank 21 and the recovery tank 25. Are arranged. Therefore, even if the head holder 17 is moved for maintenance of the inkjet head 11, it is possible to eliminate the need to move the heavy heat sink 32 and the heater 33.

  Further, in the inkjet printing apparatus 1, since the recovery tank 25 is disposed below the nozzle surface 16a, the standby nozzle pressure Pn can be set to a negative pressure. This makes it possible to suppress ink leakage from the nozzle even if the nozzle has scratches or the like. As a result, ink leakage during standby can be further reduced.

  Further, in the inkjet printing apparatus 1, the pressurizing tank 21 and the negative pressure tank 24 are connected via the pressurizing/negative pressure communicating valve 61 which is a normally open type electromagnetic valve. Then, the positive/negative pressure communication valve 61 is opened in a state where the positive pressure (set pressure Pks) during ink circulation is generated in the pressurization tank 21 and the negative pressure (set pressure Pfs) is generated in the negative pressure tank 24. Then, the positive pressure of the pressure tank 21 and the negative pressure of the negative pressure tank 24 cancel each other out. Therefore, even if the power is cut off during ink circulation, the pressure in the pressure tank 21 and the negative pressure tank 24 can be released by opening the normally open type pressurizing/negative pressure communicating valve 61.

  Note that the printing unit 2 may be configured to include a plurality of inkjet heads 11 and a plurality of units of the ink circulation unit 12 other than the recovery tank 25 for each recovery tank 25. For example, as shown in FIG. 6, for one recovery tank 25, the inkjet head 11, the pressure tank 21, the distributor 22, the collector 23, the negative pressure tank 24, the ink circulation pipes 26 to 29, and the ink recovery valve. It is also possible to have a configuration in which two 30, two ink circulation pumps 31, two heat sinks 32, and two heaters 33 are provided.

  In this way, by making one recovery tank 25 common to a plurality of inkjet heads 11, it is possible to realize a configuration in which a plurality of inkjet heads 11 are provided for one color while suppressing the complexity of the apparatus configuration.

  Even in this case, when the pressurizing/negative pressure communicating valve 61 is opened at the end of the ink circulation, the positive pressure of the pressurizing system and the negative pressure of the negative pressure system are canceled so that the air of the pressurizing system is canceled. And the amount of air in the negative pressure system are designed.

(Second embodiment)
Next, a second embodiment in which the printing unit and the pressure generating unit of the above-described first embodiment are changed will be described. FIG. 7 is a schematic configuration diagram of the printing unit and the pressure generation unit in the second embodiment.

  As shown in FIG. 7, in the printing unit 2A of the second embodiment, the ink circulation unit 12 and the ink supply unit 13 of the printing unit 2 of the first embodiment are replaced with an ink circulation unit 12A and an ink supply unit 13A, respectively. It is a composition.

  The ink circulation unit 12A is different from the ink circulation unit 12 in the first embodiment in that the ink circulation pipe 28 is replaced with an ink circulation pipe 76, the ink circulation pipe 29, the recovery tank 25, and the ink recovery valve 30 are omitted, and the sub tank ( The third tank 77 of the claims), a sub-tank valve 78, and a connecting pipe (corresponding to the connection path of the claims) 79 are provided.

  The ink circulation pipe 76 connects the pressure tank 21 and the negative pressure tank 24. In the ink circulation unit 12A, the ink circulation pipes 26, 27, 76, the distributor 22, and the collector 23 constitute an ink circulation path. The ink circulation pipe 76 constitutes a path from the negative pressure tank 24 to the pressure tank 21 in this circulation path.

  The ink circulation pump 76, the heat sink 32, and the heater 33 are installed in the ink circulation pipe 76. The ink circulation pump 31 sends ink from the negative pressure tank 24 to the pressure tank 21.

  The sub tank 77 stores ink to be supplied to the negative pressure tank 24. The sub tank 77 receives the ink supplied from the ink supply unit 13A and stores the supplied ink. The sub tank 77 is indirectly connected to the ink circulation pipe 76 via a connection pipe 79. In the sub tank 77, an air layer 80 is formed on the ink surface. The sub tank 77 is connected to a sub tank common air chamber 89, which will be described later, via a sub tank communication pipe 90, which will be described later. The sub tank 77 is arranged at a position (lower) lower than the nozzle surface 16a of the head module 16 of the inkjet head 11.

  The sub tank 77 is provided with a sub tank liquid level sensor 81. The sub tank liquid level sensor 81 is for detecting whether or not the liquid level of the ink in the sub tank 77 has reached the reference height. The sub tank liquid level sensor 81 outputs a signal indicating "ON" when the liquid level in the sub tank 77 is equal to or higher than the reference height, and outputs a signal indicating "OFF" when the liquid level is less than the reference height. To do.

  The sub-tank valve 78 opens and closes the ink flow path in the connection pipe 79 in order to switch communication and cutoff between the ink circulation pipe 76 and the sub-tank 77. The sub tank valve 78 is provided in the middle of the connecting pipe 79. The sub tank valve 78 is a normally open type solenoid valve.

  The connection pipe 79 forms an ink flow path for connecting the ink circulation pipe 76 and the sub tank 77. The connection pipe 79 has one end connected to a portion of the ink circulation pipe 76 between the negative pressure tank 24 and the ink circulation pump 31, and the other end connected to the sub tank 77.

  The ink supply unit 13A has a configuration in which an ink supply pump 82 is added to the ink supply unit 13 in the first embodiment.

  The ink supply pipe 48 of the ink supply unit 13A connects the ink cartridge 46 and the sub tank 77. The ink supply valve 47 of the ink supply unit 13A is a normally closed solenoid valve.

  The ink supply pump 82 sends ink from the ink cartridge 46 to the sub tank 77. The ink supply pump 82 is provided in the middle of the ink supply pipe 48.

  The pressure generation unit 3A generates pressure for ink circulation in the pressure tank 21 and the negative pressure tank 24 of each printing unit 2A. As shown in FIG. 7, the pressure generation unit 3A has a negative pressure atmosphere release valve 86 and a negative pressure atmosphere release pipe 87 added to the pressure generation unit 3 in the first embodiment, and an air pump pipe 72 and a recovery common gas are added. The chamber 63, the recovery communication pipe 64, and the recovery atmosphere opening pipe 68 are replaced with an air pump pipe 88, a sub tank common air chamber 89, a sub tank communication pipe 90, and a sub tank atmosphere opening pipe 91, respectively, and a recovery pressure adjusting valve 65 and a recovery pressure adjusting pipe. 66, the recovery atmosphere opening valve 67, the recovery pressure sensor 70, the negative pressure introducing valve 73, and the negative pressure introducing pipe 74 are omitted.

  The negative pressure atmosphere opening valve 86 opens and closes the air flow path in the negative pressure atmosphere opening pipe 87 in order to switch the negative pressure common air chamber 56 and the negative pressure tank 24 between the closed state and the atmosphere opened state. The negative pressure atmosphere release valve 86 is provided in the middle of the negative pressure atmosphere release pipe 87. The negative pressure atmosphere release valve 86 is a normally closed solenoid valve.

  The negative pressure atmosphere opening pipe 87 forms a flow path of air for opening the negative pressure common air chamber 56 and the negative pressure tank 24 to the atmosphere. The negative pressure atmosphere open pipe 87 has one end connected to the negative pressure common air chamber 56 and the other end connected to the sub tank atmosphere open pipe 91.

  Here, the negative pressure common air chamber 56 and the negative pressure tank 24 are opened to the atmosphere when purging for ejecting ink from the nozzles for maintenance of the inkjet head 11. In this case, the negative pressure atmosphere open valve 86 is opened, and the pressurization pressure adjustment valve 53 and the pressurization/negative pressure communication valve 61 are closed, and the air pump 71 moves the negative pressure common air chamber 56 to the pressurized common air chamber 51. Air is sent. As a result, the pressure tank 21 is pressurized, and the ink is pushed out from the nozzle of the inkjet head 11.

  The air pump pipe 88 forms a flow path of air sent from the negative pressure common air chamber 56 to the pressurized common air chamber 51 by the air pump 71. The air pump pipe 88 has one end connected to the negative pressure common air chamber 56 and the other end connected to the pressurized common air chamber 51. An air pump 71 is provided in the middle of the air pump pipe 88.

  The sub tank common air chamber 89 is a common air chamber for opening the sub tank 77 of each printing unit 2A to the atmosphere. The sub-tank common air chamber 89 is always open to the atmosphere via a sub-tank atmosphere open pipe 91. The sub-tank common air chamber 89 is communicated with the air layers 80 of the sub-tanks 77 of the four printing units 2A via the four sub-tank communication pipes 90. As a result, the sub tank 77 of each printing unit 2A is always open to the atmosphere.

  The sub tank communication pipe 90 connects the sub tank common air chamber 89 and the air layer 80 of the sub tank 77. The four sub-tank communication pipes 90 are provided one for each printing unit 2A. One end of the sub tank communication pipe 90 is connected to the sub tank common air chamber 89, and the other end is connected to the air layer 80 of the sub tank 77.

  The sub tank atmosphere opening pipe 91 connects the sub tank common air chamber 89 to the atmosphere. One end of the sub tank atmosphere opening pipe 91 is connected to the sub tank common air chamber 89, and the other end communicates with the atmosphere through the air filter 69. A pressurized pressure adjusting pipe 54, a negative pressure adjusting pipe 59, and a negative pressure atmosphere releasing pipe 87 are connected to the sub tank atmosphere releasing pipe 91.

  Here, the air amount design of the pressurization system and the negative pressure system in the printing unit 2A and the pressure generation unit 3A will be described.

  Also in the second embodiment, as in the above-described first embodiment, when the pressurization/negative pressure communication valve 61 is opened at the end of ink circulation, the positive pressure of the pressurization system and the negative pressure of the negative pressure system are The air amount of the pressurizing system and the air amount of the negative pressure system are designed so as to cancel each other out.

  Specifically, according to Boyle's law, the pressurization system air amount Vk2 and the negative pressure system air amount Vf2 in the printing unit 2A and the pressure generation unit 3A are designed so that the following expression (5) is established. ..

Pks×Vk2+Pfs×Vf2=0 (5)
The air amount Vk2 of the pressurization system is expressed by the following equation (6).

Vk2=4×Vkt+Vkc+4×Vkr+Vkb+Vkn+Vkq (6)
Here, Vkq is the capacity of the portion of the air pump pipe 88 between the pressurized common air chamber 51 and the air pump 71. Vkt, Vkc, Vkr, Vkb, and Vkn are included in the above equation (2), respectively.

  The air amount Vf2 of the negative pressure system is expressed by the following equation (7).

Vf2=4×Vft+Vfc+4×Vfr+Vfb+Vfn+Vfq+Vfh (7)
Here, Vfq is the capacity of the portion of the air pump pipe 88 between the negative pressure common air chamber 56 and the air pump 71. Vfh is the capacity of the portion of the negative pressure atmosphere open pipe 87 between the negative pressure common air chamber 56 and the negative pressure atmosphere open valve 86. Vft, Vfc, Vfr, Vfb, and Vfn are included in the above equation (3), respectively.

  Next, the operation of the inkjet printing apparatus according to the second embodiment will be described.

  FIG. 8 is a flow chart for explaining the operation of the inkjet printing apparatus in the second embodiment. The process of the flowchart of FIG. 8 starts when a print job is input to the inkjet printing apparatus.

  In step S11 of FIG. 8, the control unit 5 closes the pressurization/negative pressure communication valve 61 and the sub tank valve 78. By closing the pressurization/negative pressure communication valve 61, the pressurization common air chamber 51 and the negative pressure common air chamber 56 are shut off from each other. Further, by closing the sub tank valve 78, the ink circulation pipe 76 and the sub tank 77 are shut off from each other.

  During the standby, the pressurizing/negative pressure communicating valve 61 and the sub tank valve 78 are open. Further, the pressurizing pressure adjusting valve 53, the negative pressure adjusting valve 58, the negative pressure atmosphere opening valve 86, and the ink supply valve 47 are closed.

  Next, in step S12, the control unit 5 starts the liquid level maintenance control. The liquid level maintenance control in the second embodiment is a control for maintaining the liquid levels of the pressure tank 21, the negative pressure tank 24, and the sub tank 77 near the reference height. In the liquid level maintenance control, the control unit 5 controls the sub tank valve 78 and the ink circulation pump 31 according to the liquid level of the pressurizing tank 21 and the negative pressure tank 24. The control unit 5 also controls the ink supply valve 47 and the ink supply pump 82 according to the liquid level of the sub tank 77.

  Specifically, as shown in FIG. 9A, when both the pressure tank liquid level sensor 37 and the negative pressure tank liquid level sensor 40 are off, the control unit 5 opens the sub tank valve 78 and the ink is discharged. The circulation pump 31 is turned off.

  When the pressurized tank liquid level sensor 37 is on and the negative pressure tank liquid level sensor 40 is off, the control unit 5 closes the sub tank valve 78 and turns off the ink circulation pump 31. Similarly, when both the pressurized tank liquid level sensor 37 and the negative pressure tank liquid level sensor 40 are on, the control unit 5 closes the sub tank valve 78 and turns off the ink circulation pump 31.

  When the pressure tank liquid level sensor 37 is off and the negative pressure tank liquid level sensor 40 is on, the control unit 5 closes the sub tank valve 78 and turns on the ink circulation pump 31.

  Further, as shown in FIG. 9B, when the sub tank liquid level sensor 81 is off, the control unit 5 opens the ink supply valve 47 and turns on the ink supply pump 82. When the sub tank liquid level sensor 81 is on, the control unit 5 closes the ink supply valve 47 and turns off the ink supply pump 82.

  Returning to FIG. 8, in step S13 following step S12, the control unit 5 starts pressure control. The pressure control in the second embodiment is control for generating and maintaining the set pressures Pks and Pfs in the pressurization tank 21 and the negative pressure tank 24, respectively. In the pressure control, the control unit 5 controls the air pump 71, the pressurizing pressure adjusting valve 53, and the negative pressure adjusting valve 58 according to the detected pressure Pk of the pressurizing tank 21 and the detected pressure Pf of the negative pressure tank 24. To do.

  Specifically, as shown in FIG. 10, when Pk<Pks and |Pf|<|Pfs|, the control unit 5 closes the pressurizing pressure adjusting valve 53 and the negative pressure adjusting valve 58, and the air pump 71. To turn on. As a result, the air is sucked by the air pump 71 from the closed negative pressure tank 24, and the pressure in the negative pressure tank 24 decreases (the absolute value of the negative pressure increases). Further, the pressure of the pressure tank 21 is increased by sending air by the air pump 71 to the pressure tank 21 in the sealed state.

  When Pk≧Pks and |Pf|<|Pfs|, the control unit 5 opens the pressurization pressure adjustment valve 53 and closes the negative pressure pressure adjustment valve 58. The control unit 5 also turns on the air pump 71. As a result, the air flows out of the pressure tank 21 via the pressure adjustment pipe 54, and the pressure in the pressure tank 21 decreases. Further, since the air pump 71 sucks air from the negative pressure tank 24 in a closed state, the pressure in the negative pressure tank 24 decreases (the absolute value of the negative pressure increases).

  When Pk<Pks and |Pf|≧|Pfs|, the control unit 5 closes the pressurization pressure adjustment valve 53 and opens the negative pressure pressure adjustment valve 58. The control unit 5 also turns on the air pump 71. As a result, air is sent by the air pump 71 to the pressure tank 21 in a sealed state, so that the pressure of the pressure tank 21 rises. Further, the air flows into the negative pressure tank 24 through the negative pressure adjusting pipe 59, so that the pressure in the negative pressure tank 24 increases (the absolute value of the negative pressure decreases).

  When Pk≧Pks and |Pf|≧|Pfs|, the controller 5 opens the pressurization pressure adjustment valve 53 and the negative pressure adjustment valve 58, and turns off the air pump 71. As a result, air flows out from the pressure tank 21 via the pressure adjustment pipe 54, and the pressure in the pressure tank 21 decreases. Further, the air flows into the negative pressure tank 24 through the negative pressure adjusting pipe 59, so that the pressure in the negative pressure tank 24 increases (the absolute value of the negative pressure decreases).

  Returning to FIG. 8, in step S14 following step S13, the control unit 5 determines whether or not the set pressures Pks and Pfs are generated in the pressurization tank 21 and the negative pressure tank 24, respectively. When it is determined that the set pressure is not generated in at least one of the pressure tank 21 and the negative pressure tank 24 (step S14: NO), the control unit 5 repeats step S14.

  When it is determined that the set pressures Pks and Pfs are generated in the pressure tank 21 and the negative pressure tank 24 (step S14: YES), the control unit 5 starts execution of the print job in step S15.

  During execution of the print job, ink is supplied from the pressure tank 21 to the inkjet head 11, and the ink not consumed by the inkjet head 11 is collected in the negative pressure tank 24. When the pressure tank liquid level sensor 37 is turned off and the negative pressure tank liquid level sensor 40 is turned on, the ink circulation pump 31 feeds ink from the negative pressure tank 24 to the pressure tank 21 by the liquid level maintenance control. . Printing is performed while the ink is circulated in this manner.

  When the pressure tank liquid level sensor 37 and the negative pressure tank liquid level sensor 40 are both turned off due to the ink consumption decreasing due to the consumption of the ink, the sub tank valve 78 is opened by the liquid level maintenance control. As a result, ink is sent from the sub tank 77 to the negative pressure tank 24 due to the pressure difference between the negative pressure tank 24 to which the negative pressure is applied and the sub tank 77 that is open to the atmosphere.

  When the sub tank liquid level sensor 81 is turned off by supplying ink from the sub tank 77 to the negative pressure tank 24, the ink level maintenance control opens the ink supply valve 47 and drives the ink supply pump 82. As a result, ink is supplied from the ink cartridge 46 to the sub tank 77.

  After the execution of the print job is started, in step S16, the control unit 5 determines whether the print job is completed. When it is determined that the print job is not completed (step S16: NO), the control unit 5 repeats step S16.

  When it is determined that the print job is completed (step S16: YES), the control unit 5 ends the pressure control in step S17. Here, when the air pump 71 is being driven, the control unit 5 stops it. When at least one of the pressurization pressure adjustment valve 53 and the negative pressure adjustment valve 58 is opened, the control unit 5 closes the opened one.

  Next, in step S18, the control unit 5 ends the liquid level maintenance control. Here, when the ink circulation pump 31 is being driven, the control unit 5 stops it. Further, the control unit 5 closes the sub tank valve 78 when it is open. Further, when the ink supply valve 47 is opened and the ink supply pump 82 is being driven, the control unit 5 closes the ink supply valve 47 and stops the ink supply pump 82.

  Next, in step S19, the control unit 5 opens the pressurization/negative pressure communication valve 61. As described above, in the second embodiment, since the pressurization system air amount Vk2 and the negative pressure system air amount Vf2 are designed so that the equation (5) is satisfied, the pressurization/negative pressure communication valve 61 is opened. Then, the positive pressure of the pressurizing system and the negative pressure of the negative pressure system cancel each other out. As a result, the pressures of the pressure tank 21 and the negative pressure tank 24 become atmospheric pressure.

  Next, in step S20, the control unit 5 opens the sub tank valve 78. As a result, the series of operations is completed, and the inkjet printing apparatus enters a standby state.

  When the inkjet printing apparatus is in the standby state, the pressure tank 21 and the negative pressure tank 24 are in a sealed state in which they are shielded from the atmosphere. Since the sub-tank valve 78 is open, the ink in the sub-tank 77 that is open to the atmosphere is connected to the ink in the ink circulation pipe 76 via the connection pipe 79.

  Therefore, the nozzle pressure Pn of the inkjet head 11 in the standby state is a pressure corresponding to the height difference (water head difference) H between the liquid surface of the ink in the sub tank 77 and the nozzle surface 16a. That is, the nozzle pressure Pn in the standby state is represented by the above equation (4).

  The sub-tank 77 is arranged at a height such that the standby nozzle pressure Pn does not exceed the meniscus breaking pressure, like the recovery tank 25 of the first embodiment.

  As described above, in the second embodiment, the control unit 5 closes the pressurization pressure adjustment valve 53, the negative pressure pressure adjustment valve 58, and the negative pressure atmosphere release valve 86 in the standby state to close the pressurization tank 21 and The negative pressure tank 24 is hermetically closed, and the sub tank valve 78 is opened to connect the sub tank 77 and the ink circulation pipe 76 which are open to the atmosphere.

  As a result, the nozzle pressure Pn during standby is determined by the height difference H between the liquid surface in the sub tank 77 and the nozzle surface 16a. Therefore, similar to the first embodiment, even if the atmospheric pressure changes due to environmental changes, the change in the nozzle pressure Pn can be suppressed. Therefore, also in the second embodiment, it is possible to reduce ink leakage and air suction from the nozzles during standby.

  Further, since the sub tank 77 is indirectly connected to the ink circulation pipe 76 via the connection pipe 79, the sub tank 77 is arranged outside the circulation path, and the nozzle pressure Pn during standby is the liquid in the sub tank 77. It can be determined by the height difference H between the surface and the nozzle surface 16a.

  Note that the printing unit 2A may be configured such that one sub-tank 77 includes a plurality of inkjet heads 11 and a plurality of parts of the ink circulation unit 12A other than the sub-tank 77. For example, as shown in FIG. 11, for one sub-tank 77, the inkjet head 11, the pressure tank 21, the distributor 22, the collector 23, the negative pressure tank 24, the ink circulation pipes 26, 27, 76, the sub-tank valve are provided. 78, the connection pipe 79, the ink circulation pump 31, the heat sink 32, and the heater 33 may be provided in pairs, respectively.

  In this way, by making one sub-tank 77 common to a plurality of inkjet heads 11, it is possible to realize a configuration in which a plurality of inkjet heads 11 are provided for one color while suppressing the complexity of the device configuration.

  Even in this case, when the pressurizing/negative pressure communicating valve 61 is opened at the end of the ink circulation, the positive pressure of the pressurizing system and the negative pressure of the negative pressure system are canceled so that the air of the pressurizing system is canceled. And the amount of air in the negative pressure system are designed.

(Third Embodiment)
Next, a third embodiment in which the printing unit of the second embodiment described above is changed will be described. FIG. 12 is a schematic configuration diagram of the printing unit and the pressure generating unit in the third embodiment.

  As shown in FIG. 12, the printing unit 2B in the third embodiment has a configuration in which the ink circulation unit 12A of the printing unit 2A in the second embodiment is replaced with an ink circulation unit 12B.

  The ink circulation unit 12B is different from the ink circulation unit 12 in the first embodiment in that the recovery tank 25 and the ink circulation pipe 28 are replaced with a sub-tank (corresponding to the third tank in the claims) 96 and an ink circulation pipe 97, respectively. A configuration in which the valve 30 is omitted and an ink return pump (corresponding to a pump in claims) 98, a bypass pipe (corresponding to a bypass path in claims) 99, and a bypass valve (corresponding to bypass opening/closing means in claims) 100 are provided. Is.

  The sub tank 96 stores the ink to be supplied to the pressure tank 21. The sub tank 96 receives the ink supplied from the ink supply unit 13A and stores the supplied ink. Further, the sub tank 96 receives and stores the ink from the negative pressure tank 24. The sub tank 96 is connected to the pressure tank 21 via the ink circulation pipe 29, and is connected to the negative pressure tank 24 via the ink circulation pipe 97. Accordingly, the sub tank 96 is arranged on the path from the negative pressure tank 24 to the pressurization tank 21 in the ink circulation path. In other words, the sub tank 96 is directly connected to the path from the negative pressure tank 24 to the pressure tank 21 in the ink circulation path. The sub tank 96 is arranged at a position lower (lower) than the nozzle surface 16 a of the head module 16 of the inkjet head 11.

  An air layer 101 is formed on the liquid surface of the ink in the sub tank 96. The air layer 101 is connected to the sub tank common air chamber 89 via the sub tank communication pipe 90 of the pressure generation unit 3A. As a result, the sub tank 96 is always open to the atmosphere.

  The sub tank 96 is provided with a sub tank liquid level sensor 102. The sub tank liquid level sensor 102 is for detecting whether or not the liquid level of the ink in the sub tank 96 has reached the reference height. The sub-tank liquid level sensor 102 outputs a signal indicating “ON” when the liquid level inside the sub-tank 96 is equal to or higher than the reference height, and outputs a signal indicating “OFF” when it is lower than the reference height. To do.

  The ink circulation pipe 97 connects the negative pressure tank 24 and the sub tank 96. In the ink circulation unit 12B, the ink circulation pipes 26, 27, 97, 29, the distributor 22, and the collector 23 constitute an ink circulation path.

  The ink return pump 98 sends ink from the negative pressure tank 24 to the sub tank 96. The ink return pump 98 is provided in the middle of the ink circulation pipe 97.

  The bypass pipe 99 constitutes a path that bypasses the ink return pump 98. One end of the bypass pipe 99 is connected to a portion of the ink circulation pipe 97 between the negative pressure tank 24 and the ink return pump 98, and the other end thereof is a portion of the ink circulation pipe 97 between the ink return pump 98 and the sub tank 96. It is connected to the.

  The bypass valve 100 opens and closes the ink flow path in the bypass tube 99. The bypass valve 100 is provided in the middle of the bypass pipe 99. The bypass valve 100 is a normally open solenoid valve.

  The air amount design of the pressurizing system and the negative pressure system in the printing unit 2B and the pressure generating unit 3A of the third embodiment is performed by the pressurizing system and the negative pressure system in the printing unit 2A and the pressure generating unit 3A of the second embodiment described above. It is similar to the air amount design of. That is, also in the third embodiment, the air amount Vk2 of the pressurizing system and the air amount Vf2 of the negative pressure system in the printing unit 2B and the pressure generating unit 3A are designed so that the above-described equation (5) is established.

  Next, the operation of the inkjet printing apparatus according to the third embodiment will be described.

  FIG. 13 is a flow chart for explaining the operation of the inkjet printing apparatus in the third embodiment. The process of the flowchart of FIG. 13 starts when a print job is input to the inkjet printing apparatus.

  In step S21 of FIG. 13, the control unit 5 closes the pressurization/negative pressure communication valve 61 and the bypass valve 100. By closing the pressurization/negative pressure communication valve 61, the pressurization common air chamber 51 and the negative pressure common air chamber 56 are shut off from each other. Further, by closing the bypass valve 100, the ink flow path in the bypass pipe 99 is closed.

  During the standby, the pressurization/negative pressure communication valve 61 and the bypass valve 100 are opened. Further, the pressurizing pressure adjusting valve 53, the negative pressure adjusting valve 58, the negative pressure atmosphere opening valve 86, and the ink supply valve 47 are closed.

  Next, in step S22, the control unit 5 starts liquid level maintenance control. The liquid level maintenance control in the third embodiment is a control for maintaining the liquid levels of the pressure tank 21, the negative pressure tank 24, and the sub tank 96 near the reference height. In the liquid level maintenance control, the control unit 5 controls the ink circulation pump 31 according to the liquid level height of the pressure tank 21. The controller 5 also controls the ink return pump 98 according to the liquid level of the negative pressure tank 24. The control unit 5 also controls the ink supply valve 47 and the ink supply pump 82 according to the liquid level of the sub tank 96.

  Specifically, as shown in FIG. 14A, the control unit 5 turns on the ink circulation pump 31 when the pressure tank liquid level sensor 37 is off. When the pressure tank liquid level sensor 37 is on, the control unit 5 turns off the ink circulation pump 31.

  Further, as shown in FIG. 14B, when the negative pressure tank liquid level sensor 40 is in the off state, the control section 5 turns off the ink feedback pump 98. When the negative pressure tank liquid level sensor 40 is on, the control unit 5 turns on the ink feedback pump 98.

  Further, as shown in FIG. 14C, when the sub-tank liquid level sensor 102 is off, the control unit 5 opens the ink supply valve 47 and turns on the ink supply pump 82. When the sub tank liquid level sensor 102 is on, the control unit 5 closes the ink supply valve 47 and turns off the ink supply pump 82.

  Returning to FIG. 13, following step S22, the control unit 5 starts pressure control in step S23. The pressure control in the third embodiment is similar to the pressure control in the second embodiment described above.

  Next, in step S24, the control unit 5 determines whether or not the set pressures Pks and Pfs are generated in the pressurization tank 21 and the negative pressure tank 24, respectively. When it is determined that the set pressure is not generated in at least one of the pressure tank 21 and the negative pressure tank 24 (step S24: NO), the control unit 5 repeats step S24.

  When it is determined that the set pressures Pks and Pfs are generated in the pressure tank 21 and the negative pressure tank 24 (step S24: YES), the control unit 5 starts execution of the print job in step S25.

  During execution of the print job, ink is supplied from the pressure tank 21 to the inkjet head 11, and the ink not consumed by the inkjet head 11 is collected in the negative pressure tank 24. When the pressure tank liquid level sensor 37 is turned off by the outflow of ink from the pressure tank 21 to the inkjet head 11, the ink circulation pump 31 feeds the ink from the sub tank 96 to the pressure tank 21 by the liquid level maintenance control. . When the negative pressure tank liquid level sensor 40 is turned on by the inflow of ink from the inkjet head 11 into the negative pressure tank 24, the ink return pump 98 sends the ink from the negative pressure tank 24 to the sub tank 96. Printing is performed while the ink is circulated in this manner.

  When the sub tank liquid level sensor 102 is turned off by supplying ink from the sub tank 96 to the pressure tank 21, the ink supply valve 47 is opened and the ink supply pump 82 is driven. As a result, ink is supplied from the ink cartridge 46 to the sub tank 96.

  After the execution of the print job is started, in step S26, the control unit 5 determines whether the print job is completed. When determining that the print job is not completed (step S26: NO), the control unit 5 repeats step S26.

  When it is determined that the print job is completed (step S26: YES), the control unit 5 ends the pressure control in step S27. Here, when the air pump 71 is being driven, the control unit 5 stops it. When at least one of the pressurization pressure adjustment valve 53 and the negative pressure adjustment valve 58 is opened, the control unit 5 closes the opened one.

  Next, in step S28, the control unit 5 ends the liquid level maintenance control. Here, when the ink circulation pump 31 is being driven, the control unit 5 stops it. Further, the control unit 5 stops the ink return pump 98 when it is being driven. Further, when the ink supply valve 47 is opened and the ink supply pump 82 is being driven, the control unit 5 closes the ink supply valve 47 and stops the ink supply pump 82.

  Next, in step S29, the control unit 5 opens the pressurization/negative pressure communication valve 61. When the pressurization/negative pressure communication valve 61 is opened, the positive pressure of the pressurization system and the negative pressure of the negative pressure system are offset. As a result, the pressures of the pressure tank 21 and the negative pressure tank 24 become atmospheric pressure.

  Next, in step S30, the control unit 5 opens the bypass valve 100. As a result, the series of operations is completed, and the inkjet printing apparatus enters a standby state.

  When the inkjet printing apparatus is in the standby state, the pressure tank 21 and the negative pressure tank 24 are in a sealed state in which they are shielded from the atmosphere. Further, since the bypass valve 100 is in the open state, the negative pressure tank 24 and the sub tank 96 in the atmosphere open state are communicated with each other via the bypass pipe 99.

  Therefore, the nozzle pressure Pn of the inkjet head 11 in the standby state is a pressure corresponding to the height difference (water head difference) H between the liquid surface of the ink in the sub tank 96 and the nozzle surface 16a. That is, the nozzle pressure Pn in the standby state is represented by the above equation (4).

  Similar to the recovery tank 25 of the first embodiment, the sub tank 96 is arranged at a height such that the standby nozzle pressure Pn does not exceed the meniscus breaking pressure.

  As described above, in the third embodiment, the control unit 5 closes the pressurization pressure adjustment valve 53, the negative pressure pressure adjustment valve 58, and the negative pressure atmosphere release valve 86 in the standby state to close the pressurization tank 21 and The negative pressure tank 24 is closed, and the bypass valve 100 is opened so that the negative pressure tank 24 and the sub tank 96 open to the atmosphere are communicated with each other.

  As a result, the nozzle pressure Pn during standby is determined by the height difference H between the liquid surface in the sub tank 96 and the nozzle surface 16a. Therefore, similar to the first embodiment, even if the atmospheric pressure changes due to environmental changes, the change in the nozzle pressure Pn can be suppressed. Therefore, also in the third embodiment, it is possible to reduce ink leakage and air suction from the nozzles during standby.

  In the third embodiment, the sub tank 96 is arranged on the path from the negative pressure tank 24 to the pressure tank 21, and is opened to the atmosphere during ink circulation and standby. At the time of ink circulation, the bypass valve 100 is closed and ink is sent from the negative pressure tank 24 to the sub tank 96 by the ink return pump 98. By using the ink return pump 98, the path from the negative pressure tank 24 to the sub tank 96 is different from the configuration in which ink is sent from the negative pressure tank 24 to the recovery tank 25 by the negative pressure of the recovery tank 25 as in the first embodiment. It is possible to suppress the decrease in the flow rate due to the influence of the pressure loss in. During standby, the bypass valve 100 is opened, so that the negative pressure tank 24 and the sub tank 96 are communicated with each other via the bypass pipe 99.

  Accordingly, in the configuration in which the sub-tank 96 is arranged on the circulation path, the decrease in the flow rate in the path from the negative pressure tank 24 to the sub-tank 96 during ink circulation is suppressed, and the nozzle pressure Pn during standby is the liquid level in the sub-tank 96. And the height difference H between the nozzle surface 16a and the nozzle surface 16a.

  Note that the printing unit 2B may have a configuration in which each sub-tank 96 is provided with a plurality of inkjet heads 11 and each part of the ink circulation unit 12B other than the sub-tank 96. For example, as shown in FIG. 15, for one sub-tank 96, the inkjet head 11, the pressure tank 21, the distributor 22, the collector 23, the negative pressure tank 24, the ink circulation pipes 26, 27, 97, 29, The ink return pump 98, the bypass pipe 99, the bypass valve 100, the ink circulation pump 31, the heat sink 32, and the heater 33 may be provided in pairs, respectively.

  In this way, by making one sub-tank 96 common to a plurality of inkjet heads 11, it is possible to realize a configuration in which a plurality of inkjet heads 11 are provided for one color while suppressing the complexity of the device configuration.

  Even in this case, when the pressurizing/negative pressure communicating valve 61 is opened at the end of the ink circulation, the positive pressure of the pressurizing system and the negative pressure of the negative pressure system are canceled so that the air of the pressurizing system is canceled. And the amount of air in the negative pressure system are designed.

  The present invention is not limited to the above-described embodiments as they are, and constituent elements can be modified and embodied without departing from the scope of the invention in an implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments. For example, some components may be deleted from all the components shown in the embodiment.

  For example, in the above-described first embodiment, the recovery tank 25 is arranged below the nozzle surface 16a of the inkjet head 11. However, the recovery tank 25 may be arranged above the nozzle surface 16a as long as the standby nozzle pressure Pn does not exceed the meniscus breaking pressure. Similarly in the second embodiment, the sub tank 77 may be arranged above the nozzle surface 16a as long as the nozzle pressure Pn during standby does not exceed the meniscus breaking pressure. Further, similarly in the third embodiment, the sub tank 96 may be arranged above the nozzle surface 16a as long as the nozzle pressure Pn during standby is within the range not exceeding the meniscus breaking pressure.

DESCRIPTION OF SYMBOLS 1 Inkjet printing device 2, 2A, 2B Printing part 3, 3A Pressure generation part 4 Conveying part 5 Control part 11 Inkjet head 12, 12A, 12B Ink circulation part 13, 13A Ink supply part 16 Head module 16a Nozzle surface 21 Pressurized tank 22 Distributor 23 Aggregator 24 Negative Pressure Tank 25 Recovery Tank 26-29,76,97 Ink Circulation Pipe 30 Ink Recovery Valve 31 Ink Circulation Pump 32 Heat Sink 33 Heater 51 Pressurized Common Air Chamber 52 Pressurized Communication Pipe 53 Pressurized Pressure Adjusting valve 54 Pressurizing pressure adjusting pipe 56 Negative pressure common air chamber 57 Negative pressure communicating pipe 58 Negative pressure pressure adjusting valve 59 Negative pressure pressure adjusting pipe 61 Positive/negative pressure communicating valve 62 Positive/negative pressure communicating pipe 63 Recovery Common air chamber 64 Recovery Communication pipe 65 Recovery pressure adjustment valve 66 Recovery pressure adjustment pipe 67 Recovery atmosphere release valve 68 Recovery atmosphere release pipe 71 Air pump 72,88 Air pump piping 73 Negative pressure introduction valve 74 Negative pressure introduction pipe 77,96 Sub tank 78 Sub tank valve 79 Connection pipe 82 Ink supply pump 89 Sub-tank common air chamber 90 Sub-tank communication pipe 91 Sub-tank atmosphere open pipe 98 Ink return pump 99 Detour pipe 100 Detour valve

Claims (7)

An inkjet head having a nozzle surface with nozzles for ejecting ink,
A first tank for storing ink to be supplied to the inkjet head;
A second tank for receiving ink not consumed by the inkjet head;
A circulation path for circulating ink among the first tank, the inkjet head, and the second tank;
A third tank for storing ink, which is directly or indirectly connected to a path from the second tank to the first tank in the circulation path;
A sealing means for sealing the first tank and the second tank from the atmosphere,
The first tank and the second tank are sealed by the sealing means during standby without ink circulation,
It said third tank, in standby, a shall be opened to the atmosphere state, characterized in that the nozzle pressure of the nozzle waiting is disposed at a height that does not exceed the meniscus breakdown pressure jet Printing device. An inkjet head having a nozzle surface with nozzles for ejecting ink,
A first tank for storing ink to be supplied to the inkjet head;
A second tank for receiving ink not consumed by the inkjet head;
A circulation path for circulating ink among the first tank, the inkjet head, and the second tank;
A third tank which is arranged on the path from the second tank to the first tank in the circulation path and stores ink;
Sealing means for bringing the first tank and the second tank into a sealed state in which they are shielded from the atmosphere;
And a switching means for switching the third tank between a sealed state and the atmosphere open state,
The first tank and the second tank are sealed by the sealing means during standby without ink circulation,
At the time of ink circulation, the third tank is closed by the switching means, and a negative pressure for sending ink from the second tank to the third tank is applied,
During standby, the third tank, features and be Louis inkjet printing apparatus to be opened to atmosphere state by the switching means. An inkjet head having a nozzle surface with nozzles for ejecting ink,
A first tank for storing ink to be supplied to the inkjet head;
A second tank for receiving ink not consumed by the inkjet head;
A circulation path for circulating ink among the first tank, the inkjet head, and the second tank;
A second storage tank that is indirectly connected to a path from the second tank to the first tank via a connection path connected to a path from the second tank to the first tank in the circulation path , and stores ink. 3 tanks,
A sealing means for sealing the first tank and the second tank from the atmosphere,
The first tank and the second tank are sealed by the sealing means during standby without ink circulation,
The inkjet printing apparatus is characterized in that the third tank is open to the atmosphere during standby . An inkjet head having a nozzle surface with nozzles for ejecting ink,
A first tank for storing ink to be supplied to the inkjet head;
A second tank for receiving ink not consumed by the inkjet head;
A circulation path for circulating ink among the first tank, the inkjet head, and the second tank;
A third tank which is arranged on the path from the second tank to the first tank in the circulation path and stores ink;
Sealing means for bringing the first tank and the second tank into a sealed state in which they are shielded from the atmosphere;
A pump that is provided on the path from the second tank to the third tank and that sends ink from the second tank to the third tank;
A bypass route provided on the route from the second tank to the third tank and bypassing the pump;
A bypass opening/closing means for opening/closing the ink flow path in the bypass path;
The first tank and the second tank are sealed by the sealing means during standby without ink circulation,
The third tank is opened to the atmosphere during ink circulation and standby,
At the time of ink circulation, the bypass opening/closing means is closed, and ink is sent from the second tank to the third tank by the pump,
During standby, the bypass switching means, wherein the to Louis inkjet printing apparatus that is opened.   The inkjet printing apparatus according to claim 1, wherein the third tank is arranged below the nozzle surface.   The first tank and the second tank are connected via a valve that is opened when not energized, a positive pressure during ink circulation is generated in the first tank, and a negative pressure is generated in the second tank. The positive pressure of the first tank and the negative pressure of the second tank cancel each other out when the valve is opened in the state of being generated in the above. The inkjet printing apparatus described.   7. The plurality of inkjet heads, the first tank, the second tank, and the circulation path are respectively provided for one of the third tanks, and the circulation path is provided. Inkjet printing device.