Inkjet printing device

Abstract

To provide an inkjet printing device configured to prevent a tank from overflowing.SOLUTION: A control part controls an ink circulating part 5 so that an ink temperature adjusting part 39 can adjust a temperature of ink to a temperature in a printing optimum temperature range, while circulating the ink along a circulation passage 55, and controls an inkjet head 11. When the temperature of the ink at the time when the ink circulating part 5 starts to circulate the ink is less than a lower limit in a printing possible temperature range that is less than a lower limit in the printing optimum temperature range and normal operation of a pressurizing tank liquid level sensor 32 and a negative pressure tank liquid level sensor 37 is confirmed after the circulation of the ink is started and when a temperature of the ink at a time point when the operation is confirmed is in the printing possible temperature range, the control part controls the inkjet head 11 so that the head executes printing, while making the ink temperature adjusting part 39 adjust the temperature of the ink so that the temperature is in the printing possible temperature range.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to inkjet printing devices. [Background technology]

[0002] 2. Description of the Related Art Ink circulation type inkjet printing devices are known that perform printing by ejecting ink from an inkjet head while circulating the ink.

[0003] Among ink circulation type ink jet printing devices, there are those that circulate ink by applying positive pressure and negative pressure to a tank provided upstream and a tank provided downstream of the ink jet head, respectively.

[0004] In this inkjet printing device, ink is supplied from the upstream tank to the inkjet head by positive and negative pressures applied to the upstream tank and downstream tank, respectively, and ink not consumed by the inkjet head is collected in the downstream tank. Also, a pump transfers ink from the downstream tank to the upstream tank. In this way, printing is performed by the inkjet head while circulating ink between the upstream tank, the inkjet head, and the downstream tank.

[0005] In addition, in this inkjet printing device, the upstream tank and the downstream tank are each provided with a liquid level sensor that detects whether the liquid level of the ink stored in each tank is equal to or higher than a reference level. Also, an ink supply unit is provided that supplies ink to the downstream tank. Then, based on the logic (on, off) of each liquid level sensor, the operation of the pump and the ink supply operation by the ink supply unit are controlled.

[0006] However, in this inkjet printing device, if the liquid level sensor does not function properly due to a malfunction or the like, the ink circulation and replenishment operations will not be performed properly, and there is a risk that excessive ink will flow into the tank, causing an overflow.

[0007] In response to this, there is known a technique that determines that an error such as a malfunction has occurred in the liquid level sensor if there is no change in the logic of at least one of the liquid level sensors from the start of ink circulation until the timeout time has elapsed (see Patent Document 1). This makes it possible to reduce tank overflows caused by abnormalities in the liquid level sensor. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2017-164975 A Summary of the Invention [Problem to be solved by the invention]

[0009] In the above-mentioned inkjet printing apparatus, the temperature of the circulating ink is adjusted in order to maintain the ink temperature within a temperature range suitable for printing by the inkjet head.

[0010] Even if there is no abnormality in the liquid level sensor, when the circulating ink is heated, the increase in volume caused by the rise in ink temperature can cause the tank to overflow. In particular, in device configurations where the circulation path is relatively long and therefore the amount of circulating ink is relatively large, such tank overflows are likely to occur.

[0011] The present invention has been made in view of the above, and has an object to provide an inkjet printing apparatus that can prevent the tank from overflowing. [Means for solving the problem]

[0012] In order to achieve the above object, an inkjet printing apparatus of the present invention comprises an inkjet head, a tank for storing ink, a circulation path for circulating ink between the inkjet head and the tank, an ink circulation unit having a liquid level detection unit for detecting the liquid level of the ink in the tank, and an ink temperature adjustment unit for adjusting the temperature of the ink, and a control unit for circulating the ink along the circulation path, controlling the ink circulation unit to adjust the temperature of the ink to within an optimal printing temperature range using the ink temperature adjustment unit, and controlling the inkjet head, wherein when the temperature of the ink at the start of ink circulation is less than a lower limit of a printable temperature range that is less than a lower limit of the optimal printing temperature range, and normal operation of the liquid level detection unit is confirmed after ink circulation starts, and the temperature of the ink at the time of confirmation is within the printable temperature range, the control unit controls printing by the inkjet head while adjusting the ink temperature adjustment unit to maintain the temperature of the ink within the printable temperature range. Effect of the Invention

[0013] According to the inkjet printing apparatus of the present invention, it is possible to prevent the tank from overflowing. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a configuration of an inkjet printing apparatus according to an embodiment; [Diagram 2] 2 is a schematic configuration diagram of a transport section and a head unit of the inkjet printing apparatus shown in FIG. 1. [Diagram 3] 2 is a schematic configuration diagram of a maintenance unit of the inkjet printing apparatus shown in FIG. [Figure 4] 2 is a schematic configuration diagram of an ink circulation unit, an ink supply unit, and a pressure generation unit of the inkjet printing apparatus shown in FIG. 1. [Diagram 5] 2 is a flowchart for explaining the operation of the inkjet printing apparatus shown in FIG. [Figure 6]2 is a flowchart for explaining the operation of the inkjet printing apparatus shown in FIG. [Figure 7] FIG. 11 is an explanatory diagram of liquid level maintenance control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same or equivalent parts and components are denoted by the same or equivalent reference numerals throughout the drawings.

[0016] The following embodiments are examples of devices for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not limit the material, shape, structure, arrangement, etc. of each component to those described below. The technical idea of ​​the present invention can be modified in various ways within the scope of the claims.

[0017] FIG. 1 is a block diagram showing a configuration of an inkjet printing device according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a transport unit and a head unit of the inkjet printing device shown in FIG. 1. FIG. 3 is a schematic diagram of a maintenance unit of the inkjet printing device shown in FIG. 1. FIG. 4 is a schematic diagram of an ink circulation unit, an ink supply unit, and a pressure generation unit of the inkjet printing device shown in FIG. 1. Note that FIG. 4 is a diagram showing the head unit in a horizontal state. In the following description, the up / down, left / right, front / rear directions indicated by the arrows in FIG. 2 are defined as up / down, left / right, front / rear directions. The up / down direction is the vertical direction, and the left / right direction and front / rear direction are mutually orthogonal, and are all orthogonal to the up / down direction and parallel to the horizontal direction.

[0018] 1, an inkjet printing apparatus 1 according to this embodiment includes a transport section 2, a head unit 3, a maintenance section 4, ink circulation sections 5A-5D, ink supply sections 6A-6D, a pressure generation section (corresponding to a discharge section) 7, and a control section 8. Note that the alphabetical suffixes of the reference numerals of the ink circulation sections 5A-5D, etc. may be omitted to collectively denote the ink circulation sections.

[0019] The transport unit 2 transports the print medium 9. As the print medium 9, a three-dimensional object such as a cardboard box or a sheet-like object such as paper can be used.

[0020] The head unit 3 performs printing by ejecting ink onto the print medium 9 transported by the transport section 2. As shown in FIGS.

[0021] The head unit 3 can rotate between a vertical state indicated by a solid line in Fig. 3 and a horizontal state indicated by a two-dot chain line. The vertical state of the head unit 3 is a state in which a nozzle surface 16a of a head module 16, which will be described later, is a vertical plane. When performing horizontal printing, the head unit 3 is in a vertical state. Horizontal printing is printing performed by ejecting ink horizontally onto the vertical surface of the printing medium 9.

[0022] The horizontal state of the head unit 3 is a state in which the nozzle surface 16a is a horizontal plane. When cleaning the inkjet head 11 using the maintenance unit 4 and when performing downward printing, the head unit 3 is in the horizontal state. Downward printing is printing performed by ejecting ink downward onto the horizontal surface of the print medium 9.

[0023] Here, the head unit 3 is capable of moving up and down, and when cleaning the inkjet head 11, it is placed in a higher position than when performing downward printing.

[0024] Inkjet heads 11A to 11D print images by ejecting ink onto print medium 9. Inkjet heads 11A to 11D eject ink of different colors (for example, black, cyan, magenta, and yellow). Inkjet heads 11A to 11D have the same configuration except for the colors of ink they eject.

[0025] The inkjet head 11 includes a plurality of head modules 16. In this embodiment, the inkjet head 11 includes six head modules 16. In the inkjet head 11, the head modules 16 are arranged in a staggered manner along the printing width direction. That is, in the inkjet head 11, the six head modules 16 arranged along the printing width direction are arranged with their positions alternately shifted in the front-rear direction perpendicular to the printing width direction. Here, the printing width direction is the up-down direction when the head unit 3 is in a vertical state, and is the left-right direction when the head unit 3 is in a horizontal state.

[0026] The head module 16 has a plurality of nozzles (not shown) arranged along the printing width direction, and ejects ink from the nozzles. The nozzles are open in a nozzle surface 16a of the head module 16.

[0027] The head holder 12 holds the inkjet heads 11A to 11D. A rotation shaft 17 extending in the front-rear direction is provided on the head holder 12. The head unit 3 is capable of rotating about the rotation shaft 17 between a vertical state and a horizontal state.

[0028] The maintenance unit 4 cleans the inkjet head 11. The maintenance unit 4 is movable between an extended position where it is positioned when cleaning the inkjet head 11, and a retracted position where it is retracted from the extended position. The extended position is the position of the maintenance unit 4 shown in Fig. 3, and is a position directly below the head unit 3 that is positioned horizontally at a predetermined height for cleaning. The maintenance unit 4 in the retracted position is not shown in the drawing.

[0029] As shown in FIG. 3, the maintenance unit 4 includes an ink receiving unit 21 and a wiper 22.

[0030] The ink receiving portion 21 receives the ink and the like that is removed from the nozzle surface 16a by wiping with the wiper 22 during maintenance of the inkjet head 11.

[0031] The wipers 22 wipe the nozzle surfaces 16a of the head modules 16 of the inkjet head 11 to remove ink and the like from the nozzle surfaces 16a. The maintenance unit 4 is provided with wipers 22 for wiping the front three head modules 16 of the six head modules 16 arranged in a staggered pattern for each of the inkjet heads 11A to 11D, and wipers 22 for wiping the rear three head modules 16. That is, the maintenance unit 4 is provided with eight wipers 22.

[0032] The ink circulation units 5A to 5D circulate the ink and supply it to the inkjet heads 11A to 11D, respectively. As shown in Fig. 4, the ink circulation unit 5 includes a pressurized tank (corresponding to a tank) 31, a pressurized tank liquid level sensor (corresponding to a liquid level detection unit) 32, an ink filter 33, a distributor 34, a collector 35, a negative pressure tank (corresponding to a tank) 36, a negative pressure tank liquid level sensor (corresponding to a liquid level detection unit) 37, an ink pump 38, an ink temperature adjustment unit 39, an ink temperature sensor 40, and ink circulation pipes 41 to 43.

[0033] The pressurized tank 31 stores the ink to be supplied to the inkjet head 11. The pressurized tank 31 is connected to the inkjet head 11 via an ink circulation pipe 41 and a distributor 34. An air layer 46 is formed on the ink surface inside the pressurized tank 31. The pressurized tank 31 is connected to a pressurized common air chamber 61 (described later) via a pressurized communication pipe 62 (described later). The pressurized tank 31 is disposed at a lower position (below) than the inkjet head 11.

[0034] The pressurized tank liquid level sensor 32 detects whether the ink level in the pressurized tank 31 has reached a predetermined reference level. When the ink level in the pressurized tank 31 is equal to or higher than the reference level, the pressurized tank liquid level sensor 32 outputs a signal indicating "ON." When the ink level in the pressurized tank 31 is lower than the reference level, the pressurized tank liquid level sensor 32 outputs a signal indicating "OFF."

[0035] The ink filter 33 removes dust and other particles from the ink. The ink filter 33 is disposed in the pressure tank 31.

[0036] The distributor 34 distributes the ink supplied from the pressurized tank 31 via the ink circulation pipe 41 to each head module 16 of the inkjet head 11 .

[0037] The collector 35 collects ink that has not been consumed by the inkjet head 11 from each head module 16. The ink collected by the collector 35 flows to the negative pressure tank 36 via an ink circulation pipe 42.

[0038] The negative pressure tank 36 receives and stores ink that has not been consumed by the inkjet head 11. The negative pressure tank 36 is connected to the inkjet head 11 via a collector 35 and an ink circulation pipe 42. The negative pressure tank 36 also stores ink that is supplied from an ink cartridge 56 of the ink supply unit 6, which will be described later. An air layer 47 is formed above the ink liquid surface inside the negative pressure tank 36. The negative pressure tank 36 is connected to a negative pressure common air chamber 68, which will be described later, via a negative pressure communication pipe 69, which will be described later. The negative pressure tank 36 is disposed at the same height as the pressurized tank 31.

[0039] The negative pressure tank liquid level sensor 37 is for detecting whether the ink level in the negative pressure tank 36 has reached a predetermined reference level. When the ink level in the negative pressure tank 36 is equal to or higher than the reference level, the negative pressure tank liquid level sensor 37 outputs a signal indicating "on." When the ink level in the negative pressure tank 36 is below the reference level, the negative pressure tank liquid level sensor 37 outputs a signal indicating "off."

[0040] The ink pump 38 sends ink from the negative pressure tank 36 to the pressurized tank 31. The ink pump 38 is provided midway along the ink circulation pipe 43.

[0041] The ink temperature adjustment unit 39 adjusts the temperature of the ink in the ink circulation unit 5. The ink temperature adjustment unit 39 is provided midway through the ink circulation tube 41. The ink temperature adjustment unit 39 includes a heater 51, a heater temperature sensor 52, a heat sink 53, and a cooling fan .

[0042] The heater 51 heats the ink in the ink circulation pipe 41. The heater temperature sensor 52 detects the temperature of the heater 51. The heat sink 53 cools the ink in the ink circulation pipe 41 by dissipating heat. The cooling fan 54 sends cooling air to the heat sink 53.

[0043] The ink temperature sensor 40 detects the temperature of the ink in the ink circulation unit 5. The ink temperature sensor 40 is provided midway through the ink circulation tube 41.

[0044] The ink circulation pipe 41 connects the pressurized tank 31 and the distributor 34. A part of the ink circulation pipe 41 branches into a part that passes through the heater 51 and a part that passes through the heat sink 53. Ink flows from the pressurized tank 31 to the distributor 34 in the ink circulation pipe 41. The ink circulation pipe 42 connects the collector 35 and the negative pressure tank 36. Ink flows from the collector 35 to the negative pressure tank 36 in the ink circulation pipe 42. The ink circulation pipe 43 connects the negative pressure tank 36 and the pressurized tank 31. Ink flows from the negative pressure tank 36 to the pressurized tank 31 in the ink circulation pipe 43. The ink circulation pipes 41 to 43, the distributor 34, and the collector 35 form a circulation path 55 for circulating ink between the pressurized tank 31, the inkjet head 11, and the negative pressure tank 36.

[0045] Here, in the inkjet printing device 1, the head unit 3 and the ink circulation units 5A-5D are disposed at a relatively large distance from each other. Therefore, the ink circulation pipes 41, 42 are relatively long. In other words, the path between the pressurized tank 31 and the inkjet head 11 and the path between the inkjet head 11 and the negative pressure tank 36 in the circulation path 55 are relatively long.

[0046] The ink supply units 6A to 6D supply ink to the ink circulation units 5A to 5D, respectively. As shown in FIG.

[0047] The ink cartridge 56 contains ink used for printing by the inkjet head 11. The ink in the ink cartridge 56 is supplied to the negative pressure tank 36 of the ink circulation unit 5 via an ink supply pipe 58.

[0048] The ink supply valve 57 opens and closes the ink flow path in the ink supply pipe 58. When ink is supplied to the negative pressure tank 36, the ink supply valve 57 is opened.

[0049] The ink supply pipe 58 connects the ink cartridge 56 and the negative pressure tank 36. Ink flows through the ink supply pipe 58 from the ink cartridge 56 toward the negative pressure tank 36.

[0050] The pressure generating unit 7 generates pressure for circulating ink in the pressurized tank 31 and the negative pressure tank 36 of each ink circulating unit 5. As shown in Fig. 4, the pressure generating unit 7 includes a pressurized common air chamber 61, four pressurized communication tubes 62, a pressurized atmosphere release valve 63, a pressurized atmosphere release tube 64, a pressurized pressure adjustment valve 65, a pressurized pressure adjustment tube 66, a pressurized pressure sensor 67, a negative pressure common air chamber 68, four negative pressure communication tubes 69, a negative pressure atmosphere release valve 70, a negative pressure atmosphere release tube 71, a negative pressure pressure adjustment valve 72, a negative pressure pressure adjustment tube 73, a negative pressure sensor 74, an air pump 75, an air pump pipe 76, a junction tube 77, an air filter 78, an overflow pan 79, an overflow ball 80, and an overflow liquid level sensor 81.

[0051] The pressurized common air chamber 61 is an air chamber for equalizing the pressures of the pressurized tanks 31 of each ink circulation unit 5. The pressurized common air chamber 61 is in communication with the air spaces 46 of the pressurized tanks 31 of the ink circulation units 5A to 5D via four pressurized communicating pipes 62. As a result, the pressurized tanks 31 of the ink circulation units 5A to 5D are in communication with each other via the pressurized common air chamber 61 and the pressurized communicating pipes 62.

[0052] The pressurized communicating tubes 62 communicate between the pressurized common air chamber 61 and the air space 46 of the pressurized tank 31. The four pressurized communicating tubes 62 are provided corresponding to the ink circulation units 5A to 5D, one each. One end of the pressurized communicating tubes 62 is connected to the pressurized common air chamber 61, and the other end is connected to the air space 46 of the pressurized tank 31.

[0053] The pressurized atmosphere release valve 63 opens and closes the air flow path in the pressurized atmosphere release pipe 64 in order to switch the pressurized tank 31 between a sealed state (a state cut off from the atmosphere) and an atmosphere open state (a state connected to the atmosphere) via the pressurized common air chamber 61. The pressurized atmosphere release valve 63 is provided midway along the pressurized atmosphere release pipe 64.

[0054] The pressurized atmosphere release pipe 64 forms an air flow path for releasing the pressurized tank 31 to the atmosphere via the pressurized common air chamber 61. One end of the pressurized atmosphere release pipe 64 is connected to the pressurized common air chamber 61, and the other end is connected to the junction pipe 77.

[0055] The pressurized pressure adjustment valve 65 opens and closes the air flow path in the pressurized pressure adjustment pipe 66 in order to adjust the pressure in the pressurized common air chamber 61 and the pressurized tank 31. The pressurized pressure adjustment valve 65 is provided midway through the pressurized pressure adjustment pipe 66.

[0056] The pressurized pressure adjustment pipe 66 forms an air flow path for adjusting the pressure of the pressurized common air chamber 61 and the pressurized tank 31. The pressurized pressure adjustment pipe 66 is made up of a pipe thinner than the pressurized atmosphere release pipe 64, the negative pressure atmosphere release pipe 71, and the junction pipe 77. One end of the pressurized pressure adjustment pipe 66 is connected to the pressurized common air chamber 61, and the other end is connected to the junction pipe 77.

[0057] The pressurized pressure sensor 67 detects the pressure in the pressurized common air chamber 61. The pressure in the pressurized common air chamber 61 is equal to the pressure in the pressurized tank 31 of the ink circulation units 5A to 5D. This is because the pressurized common air chamber 61 and the air layer 46 of the pressurized tank 31 of the ink circulation units 5A to 5D are in communication with each other.

[0058] The negative pressure common air chamber 68 is an air chamber for equalizing the pressure of the negative pressure tanks 36 of each ink circulation unit 5. The negative pressure common air chamber 68 is in communication with the air layers 47 of the negative pressure tanks 36 of the ink circulation units 5A to 5D via four negative pressure communicating pipes 69. As a result, the negative pressure tanks 36 of the ink circulation units 5A to 5D are in communication with each other via the negative pressure common air chamber 68 and the negative pressure communicating pipes 69.

[0059] The negative pressure communicating tubes 69 communicate between the negative pressure common air chamber 68 and the air layer 47 of the negative pressure tank 36. The four negative pressure communicating tubes 69 are provided corresponding to the ink circulation units 5A to 5D, one each. One end of the negative pressure communicating tubes 69 is connected to the negative pressure common air chamber 68, and the other end is connected to the air layer 47 of the negative pressure tank 36.

[0060] The negative pressure air release valve 70 opens and closes the air flow path in the negative pressure air release pipe 71 in order to switch the negative pressure tank 36 between a sealed state and an open-to-atmosphere state via the negative pressure common air chamber 68. The negative pressure air release valve 70 is provided midway along the negative pressure air release pipe 71.

[0061] The negative pressure atmosphere release pipe 71 forms an air flow path for releasing the negative pressure tank 36 to the atmosphere via the negative pressure common air chamber 68. One end of the negative pressure atmosphere release pipe 71 is connected to the negative pressure common air chamber 68, and the other end is connected to the junction pipe 77.

[0062] The negative pressure adjustment valve 72 opens and closes the air flow path in the negative pressure adjustment pipe 73 in order to adjust the pressure in the negative pressure common air chamber 68 and the negative pressure tank 36. The negative pressure adjustment valve 72 is provided midway through the negative pressure adjustment pipe 73.

[0063] The negative pressure adjustment pipe 73 forms an air flow path for adjusting the pressure of the negative pressure common air chamber 68 and the negative pressure tank 36. The negative pressure adjustment pipe 73 is made up of a pipe thinner than the pressurized atmosphere release pipe 64, the negative pressure atmosphere release pipe 71, and the junction pipe 77. One end of the negative pressure adjustment pipe 73 is connected to the negative pressure common air chamber 68, and the other end is connected to the junction pipe 77.

[0064] The negative pressure sensor 74 detects the pressure in the negative pressure common chamber 68. The pressure in the negative pressure common chamber 68 is equal to the pressure in the negative pressure tank 36 of the ink circulation units 5A to 5D. This is because the negative pressure common chamber 68 and the air layer 47 of the negative pressure tank 36 of the ink circulation units 5A to 5D are in communication with each other.

[0065] The air pump 75 sucks air from the negative pressure tanks 36 of the ink circulation units 5A to 5D through the negative pressure common air chamber 68, and sends air to the pressurized tanks 31 of the ink circulation units 5A to 5D through the pressurized common air chamber 61. The air pump 75 is provided midway along the air pump piping 76.

[0066] The air pump piping 76 forms a flow path for air sent from the negative pressure common air chamber 68 to the pressurized common air chamber 61 by the air pump 75. One end of the air pump piping 76 is connected to the pressurized common air chamber 61, and the other end is connected to the negative pressure common air chamber 68.

[0067] One end of the junction pipe 77 is connected to an overflow pan 79, and the other end (upper end) is connected to the atmosphere via an air filter 78. The end of the junction pipe 77 on the overflow pan 79 side is normally closed by an overflow ball 80 described below. The pressurized atmosphere release pipe 64, the pressurized pressure adjustment pipe 66, the negative pressure atmosphere release pipe 71, and the negative pressure adjustment pipe 73 are connected to the junction pipe 77. As a result, the pressurized atmosphere release pipe 64, the pressurized pressure adjustment pipe 66, the negative pressure atmosphere release pipe 71, and the negative pressure adjustment pipe 73 are communicated with the atmosphere.

[0068] The air filter 78 prevents dust and other particles in the air from entering the junction pipe 77. The air filter 78 is disposed at the upper end of the junction pipe 77.

[0069] The overflow pan 79 receives the ink flowing through the junction pipe 77 when ink overflows from at least one of the pressurized tank 31 and the negative pressure tank 36 and further when ink overflows from the pressurized common air chamber 61 and the negative pressure common air chamber 68.

[0070] When there is no ink in overflow pan 79, overflow ball 80 closes the end of junction pipe 77 that opens to the bottom of overflow pan 79, preventing outside air from flowing into junction pipe 77. When ink flows from junction pipe 77 into overflow pan 79, overflow ball 80 floats up, allowing ink to flow into overflow pan 79.

[0071] The overflow liquid level sensor 81 detects whether or not the ink level in the overflow pan 79 has reached a predetermined level. When the overflow liquid level sensor 81 turns on, ink is discharged from the overflow pan 79 to a waste liquid tank (not shown).

[0072] The control unit 8 controls the operation of each unit of the inkjet printing apparatus 1. The control unit 8 includes a CPU, a RAM, a ROM, a hard disk, and the like.

[0073] When printing, the control unit 8 controls the ink circulation unit 5 so as to circulate the ink along the circulation path 55 and adjust the ink temperature to a temperature within a predetermined optimum temperature range for printing using the ink temperature adjustment unit 39. The control unit 8 also controls the inkjet head 11 so as to eject ink to print.

[0074] If the ink temperature at the start of ink circulation in the ink circulation unit 5 is below the lower limit of the specified printable temperature range, and normal operation of the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 is confirmed after ink circulation starts, and the ink temperature at the time of confirmation is within the printable temperature range, the control unit 8 controls the ink temperature adjustment unit 39 to adjust the ink temperature to maintain it within the printable temperature range, while controlling printing to be performed by the inkjet head 11.

[0075] Here, the optimal printing temperature range of the ink is a temperature range suitable for ejecting the ink from the inkjet head 11. Moreover, the printable temperature range of the ink is a temperature range from a predetermined lower limit value lower than the lower limit value of the optimal printing temperature range to the lower limit value of the optimal printing temperature range, and is a temperature range in which the inkjet head 11 can eject the ink.

[0076] Next, the operation of the inkjet printing apparatus 1 will be described with reference to the flowcharts of FIGS.

[0077] Unless otherwise specified, the processing in the flowcharts of FIGS. 5 and 6 is performed for each combination of the inkjet head 11, the ink circulation unit 5, and the ink supply unit 6 for each ink color.

[0078] When a print job is input, the control unit 8 starts ink circulation in the ink circulation unit 5 in step S1 of FIG.

[0079] Specifically, the control unit 8 closes the pressurized atmosphere release valve 63 and the negative pressure atmosphere release valve 70. As a result, the pressurized tank 31 is sealed via the pressurized common air chamber 61, and the negative pressure tank 36 is sealed via the negative pressure common air chamber 68. Here, while the inkjet printing device 1 is on standby, the pressurized atmosphere release valve 63 and the negative pressure atmosphere release valve 70 are open, and the pressurized pressure adjustment valve 65 and the negative pressure adjustment valve 72 are closed. Next, the control unit 8 starts driving the air pump 75. As a result, the negative pressure common air chamber 68 and the negative pressure tank 36 are depressurized, and the pressurized common air chamber 61 and the pressurized tank 31 are pressurized. As a result, a flow of ink is generated from the pressurized tank 31 toward the negative pressure tank 36 via the inkjet head 11, and ink circulation begins.

[0080] Here, since the pressure generating unit 7 is common to the ink circulation units 5A to 5D, the ink circulation starts simultaneously in the ink circulation units 5A to 5D.

[0081] Also, in step S1, when the ink circulation starts, the control unit 8 causes the ink temperature adjustment unit 39 to start adjusting the ink temperature so that the ink temperature falls within the optimal printing temperature range. Specifically, if the ink temperature detected by the ink temperature sensor 40 at the start of the ink circulation is lower than the lower limit of the optimal printing temperature range, the control unit 8 causes the ink temperature adjustment unit 39 to start heating the ink. Also, if the ink temperature detected by the ink temperature sensor 40 at the start of the ink circulation is higher than the upper limit of the optimal printing temperature range, the control unit 8 causes the ink temperature adjustment unit 39 to start cooling the ink.

[0082] Here, after the ink circulation starts in step S1, the control unit 8 controls the operation of the air pump 75 and the opening and closing of the pressurized pressure adjustment valve 65 and the negative pressure adjustment valve 72 based on the detection values ​​of the pressurized pressure sensor 67 and the negative pressure sensor 74 so that the pressures in the pressurized tank 31 and the negative pressure tank 36 reach and are maintained at their respective set pressures.

[0083] The set pressures of the pressurized tank 31 and the negative pressure tank 36 are preset as pressure values ​​for circulating the ink while maintaining the nozzle pressure of the head module 16 of the inkjet head 11 at an appropriate value. The set pressure of the pressurized tank 31 is a positive pressure, and the set pressure of the negative pressure tank 36 is a negative pressure.

[0084] Furthermore, while the ink is circulating in the ink circulation unit 5, the control unit 8 performs liquid level maintenance control. The liquid level maintenance control is control of the ink pump 38 and the ink supply valve 57 according to the liquid level heights in the pressurized tank 31 and the negative pressure tank 36, in order to maintain the liquid levels in the pressurized tank 31 and the negative pressure tank 36 at reference heights.

[0085] 7, when the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 are both on, the control unit 8 turns off the ink pump 38 and closes the ink supply valve 57. Similarly, when the pressurized tank liquid level sensor 32 is on and the negative pressure tank liquid level sensor 37 is off, the control unit 8 turns off the ink pump 38 and closes the ink supply valve 57.

[0086] When the pressurized tank liquid level sensor 32 is off and the negative pressure tank liquid level sensor 37 is on, the control unit 8 turns on the ink pump 38 and closes the ink supply valve 57 .

[0087] When both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 are in the OFF state, the control unit 8 turns off the ink pump 38 and opens the ink supply valve 57 .

[0088] That is, when the pressurized tank liquid level sensor 32 is OFF and the negative pressure tank liquid level sensor 37 is ON, the ink level maintenance control causes the ink pump 38 to send ink from the negative pressure tank 36 to the pressurized tank 31. When both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 are OFF, the ink level maintenance control causes ink to be replenished from the ink cartridge 56 to the negative pressure tank 36. In this way, the ink circulation is performed while the liquid levels in the pressurized tank 31 and the negative pressure tank 36 are maintained.

[0089] Returning to FIG. 5, in step S2, the control unit 8 determines whether the temperature of the ink in the ink circulation unit 5 detected by the ink temperature sensor 40 at the start of ink circulation is equal to or higher than the lower limit of the printable temperature range.

[0090] If it is determined that the ink temperature at the start of ink circulation is equal to or higher than the lower limit of the printable temperature range (step S2: YES), then in step S3, the control unit 8 sets the timeout time to the normal timeout time.

[0091] Here, the timeout time is a threshold time during which the logic (on / off) of the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 does not change, in order to determine whether or not these level sensors are operating normally. If there is no logic change in at least one of the two level sensors (pressurized tank liquid level sensor 32 and negative pressure tank liquid level sensor 37) from the start of ink circulation until the timeout time has elapsed, it is determined that a timeout error has occurred. A timeout error is an error caused by an abnormal operation due to a malfunction or the like in at least one of the two level sensors.

[0092] After the ink circulation starts, as described above, the ink flows from the pressurized tank 31 to the negative pressure tank 36 via the inkjet head 11, and the liquid level maintenance control causes fluctuations in the liquid level in the pressurized tank 31 and the negative pressure tank 36. Therefore, when the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 are operating normally, both the on and off states can be detected by both the liquid level sensors. In other words, a logical change can be detected by both the liquid level sensors.

[0093] For example, if the pressurized tank liquid level sensor 32 is on and the negative pressure tank liquid level sensor 37 is off at the start of ink circulation, and ink flows from the pressurized tank 31 to the negative pressure tank 36, causing the pressurized tank liquid level sensor 32 to turn off and the negative pressure tank liquid level sensor 37 to turn on, then both liquid level sensors will have detected both on and off.

[0094] Also, for example, if the liquid levels of the pressurized tank 31 and the negative pressure tank 36 are both at the reference level and the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 are both on when ink circulation starts, when the pressurized tank liquid level sensor 32 turns off and the negative pressure tank liquid level sensor 37 turns on as ink flows from the pressurized tank 31 to the negative pressure tank 36, the ink pump 38 starts to be driven by the liquid level maintenance control. As a result, when the negative pressure tank liquid level sensor 37 turns off as ink is sent from the negative pressure tank 36 to the pressurized tank 31, this means that both the on and off states have been detected by both liquid level sensors.

[0095] Here, during the period until a logical change is detected by both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 and normal operation of both liquid level sensors is confirmed, even if the pressurized tank liquid level sensor 32 turns on after the ink pump 38 starts to drive and before the negative pressure tank liquid level sensor 37 turns off, the ink pump 38 will be driven until the negative pressure tank liquid level sensor 37 turns off, unlike the liquid level maintenance control in Figure 7.

[0096] The normal timeout time is a timeout time used when the ink temperature at the start of the ink circulation is equal to or higher than the lower limit of the printable temperature range. The normal timeout time can be set to a predetermined time equal to or higher than the theoretical time from the start of the ink circulation until both the liquid level sensors detect a logical change when, for example, the ink temperature at the start of the ink circulation is a predetermined temperature equal to or higher than the lower limit of the printable temperature range, the liquid levels in the pressurized tank 31 and the negative pressure tank 36 are both at the reference height at the start of the ink circulation, and both the liquid level sensors are on at the start of the ink circulation.

[0097] Next, in step S4, the control unit 8 determines whether or not a logic change has been detected in both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37.

[0098] If it is determined that a logical change has not been detected by at least one of the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 (step S4: NO), the control unit 8 determines in step S5 whether the normal timeout time has elapsed since the start of ink circulation. If it is determined that the normal timeout time has not elapsed (step S5: NO), the control unit 8 returns to step S4.

[0099] When it is determined that the normal timeout period has elapsed (step S5: YES), in step S6, the control unit 8 determines that a timeout error has occurred.

[0100] Next, in step S7, the control unit 8 ends the ink circulation and the ink temperature adjustment in the ink circulation unit 5. This ends a series of processes.

[0101] Here, when a timeout error occurs in at least one of the ink circulation units 5A to 5D, the control unit 8 ends the ink circulation and the ink temperature adjustment in all of the ink circulation units 5A to 5D.

[0102] In step S4, when it is determined that a logical change has been detected in both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 (step S4: YES), the control unit 8 proceeds to step S8.

[0103] Here, the determination in step S4 is "YES" if a logical change is detected in both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 from the start of ink circulation until the normal timeout time has elapsed. The fact that a logical change is detected in both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 from the start of ink circulation until the normal timeout time has elapsed means that normal operation of both liquid level sensors has been confirmed.

[0104] In step S8, the control unit 8 determines whether or not the ink temperature is within the optimum printing temperature range at the time when a logical change is detected by the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 (the time when normal operation of both liquid level sensors is confirmed). If it is determined that the ink temperature is not within the optimum printing temperature range (step S8: NO), the control unit 8 repeats step S8.

[0105] Here, if the ink temperature at the start of ink circulation is above the lower limit of the printable temperature range (step S2: YES), ink temperature adjustment is performed from the start of ink circulation with the aim of bringing the ink temperature within the optimal printing temperature range.

[0106] If it is determined in step S8 that the ink temperature is within the optimum printing temperature range (step S8: YES), in step S9, the control unit 8 starts printing based on the print job. Specifically, the control unit 8 starts ejecting ink from the inkjet head 11 based on the print job.

[0107] When all of inkjet heads 11A to 11D are ready to print, control unit 8 causes inkjet heads 11A to 11D to start printing.

[0108] A printable state for the inkjet head 11 means that when the ink temperature at the start of ink circulation in the ink circulation section 5 corresponding to the inkjet head 11 is equal to or higher than the lower limit of the printable temperature range, normal operation of the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 is confirmed (step S4: YES), and the ink temperature is within the optimal temperature range for printing (step S8: YES).

[0109] Furthermore, if the ink temperature at the start of ink circulation in the ink circulation section 5 corresponding to the inkjet head 11 is below the lower limit of the printable temperature range, then the inkjet head 11 is in a printable state when normal operation of the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 is confirmed (step S13: YES described below) and the ink temperature at this confirmed point is equal to or higher than the lower limit of the printable temperature range (step S15: NO described below).

[0110] Next, in step S10, the control unit 8 determines whether or not printing based on the print job has finished. If it is determined that printing has not finished (step S10: NO), the control unit 8 repeats step S10.

[0111] When it is determined that printing has ended (step S10: YES), the control unit 8 proceeds to step S7 and ends the ink circulation and ink temperature adjustment in the ink circulation unit 5. This ends a series of processes.

[0112] Here, when printing has been completed in all of the inkjet heads 11A to 11D, the control unit 8 ends the ink circulation and ink temperature adjustment in all of the ink circulation units 5A to 5D.

[0113] In step S2, if it is determined that the ink temperature at the start of ink circulation is below the lower limit of the printable temperature range (step S2: NO), in step S11 of FIG. 6, the control unit 8 sets the timeout time to a low temperature timeout time.

[0114] Here, the low temperature timeout period is a timeout period that is used when the ink temperature at the start of ink circulation is below the lower limit of the printable temperature range.

[0115] The lower the ink temperature, the higher the viscosity, and the slower the ink circulates in the ink circulation unit 5. For this reason, the lower the ink temperature, the longer the time from the start of ink circulation until the logic of the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 changes. For this reason, it is appropriate to make the timeout period longer the lower the ink temperature.

[0116] For this reason, the low temperature timeout time is longer than the normal timeout time. For example, the low temperature timeout time can be set to a predetermined time longer than the theoretical time required for the ink temperature to rise from the start of ink circulation to the lower limit of the printable temperature range by adjusting the ink temperature using the ink temperature adjustment unit 39. In this case, the low temperature timeout time is a time that corresponds to the ink temperature at the start of ink circulation, and the lower the ink temperature at the start of ink circulation, the longer the low temperature timeout time.

[0117] Next, in step S12, the control unit 8 starts ink supply control for low temperatures. The ink supply control for low temperatures differs from the ink supply control included in the liquid level maintenance control of Fig. 7 in that when the duration during which both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 remain in the off state reaches a predetermined supply standby time, a specified amount of ink is supplied by the ink supply unit 6.

[0118] Here, the ink supply control included in the liquid level maintenance control in Figure 7 is a control that opens the ink supply valve 57 to start ink supply when the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 are both in the OFF state, and closes the ink supply valve 57 to end ink supply when the negative pressure tank liquid level sensor 37 turns ON.

[0119] The above-mentioned refill waiting time is shorter than the low temperature timeout time. The refill waiting time can be set, for example, as a theoretical time from the start of ink circulation until both liquid level sensors detect a logical change when the ink temperature at the start of ink circulation is equal to or lower than the lower limit of the printable temperature range, the liquid levels in the pressurized tank 31 and the negative pressure tank 36 are both at the reference height at the start of ink circulation, and both liquid level sensors are on at the start of ink circulation. In this case, the refill waiting time is a time according to the ink temperature at the start of ink circulation, and the lower the ink temperature at the start of ink circulation, the longer the refill waiting time.

[0120] When the ink temperature at the start of ink circulation is at a low temperature below the lower limit of the printable temperature range, even if both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 are in the OFF state, the increase in volume caused by the rise in ink temperature may cause both liquid level sensors to change from the OFF state. For this reason, in this case, low-temperature ink supply control prevents ink from being replenished immediately even if both liquid level sensors are in the OFF state, thereby preventing excessive replenishment of ink.

[0121] The above-mentioned specified amount is preset as an amount that does not result in excessive ink supply. The amount of ink supplied by the ink supply unit 6 can be controlled by the opening time of the ink supply valve 57. The opening time of the ink supply valve 57 for supplying the specified amount varies depending on the temperature of the ink. In low-temperature ink supply control, if the negative pressure tank liquid level sensor 37 turns on before the amount of ink supply reaches the specified amount, the control unit 8 closes the ink supply valve 57 at that point in time to end ink supply.

[0122] Next, in step S13, the control unit 8 determines whether or not a logic change has been detected in both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37.

[0123] If it is determined that a logical change has not been detected by at least one of the liquid level sensors (step S13: NO), the control unit 8 determines in step S14 whether or not the low temperature timeout time has elapsed since the start of ink circulation. If it is determined that the low temperature timeout time has not elapsed (step S14: NO), the control unit 8 returns to step S13.

[0124] When it is determined that the low temperature timeout period has elapsed (step S14: YES), the control unit 8 proceeds to step S6 in FIG. 5 and determines that a timeout error has occurred.

[0125] Next, in step S7, the control unit 8 ends the ink circulation and the ink temperature adjustment in the ink circulation unit 5. This ends a series of processes.

[0126] In step S13, when it is determined that a logical change has been detected in both of the liquid level sensors (step S13: YES), the control unit 8 proceeds to step S15.

[0127] Here, the determination in step S13 is "YES" if a logical change is detected in both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 from the start of ink circulation until the low temperature timeout time has elapsed. The fact that a logical change is detected in both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 from the start of ink circulation until the low temperature timeout time has elapsed means that normal operation of both liquid level sensors has been confirmed.

[0128] In step S15, the control unit 8 determines whether the ink temperature at the time when a logical change is detected in the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 (the time when normal operation of both liquid level sensors is confirmed) is less than the lower limit of the printable temperature range.

[0129] If it is determined that the ink temperature is below the lower limit of the printable temperature range (step S15: YES), then in step S16, the control unit 8 executes cleaning of the inkjet head 11. This cleaning is performed to reduce the amount of ink in the ink circulation unit 5 by purging, which will be described later.

[0130] Here, the maintenance unit 4 is common to the inkjet heads 11A to 11D. Therefore, if the ink temperature at the time when the logical change is detected by the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 in at least any of the ink circulation units 5A to 5D is less than the lower limit of the printable temperature range (step S15: YES), the control unit 8 executes cleaning of all of the inkjet heads 11A to 11D.

[0131] Specifically, first, the control unit 8 opens the pressurized atmosphere release valve 63 and the negative pressure atmosphere release valve 70, and closes the pressurized pressure adjustment valve 65 and the negative pressure adjustment valve 72. This stops the ink circulation. The control unit 8 also stops the ink temperature adjustment by the ink temperature adjustment unit 39.

[0132] When the maintenance section 4 is placed in the deployed position and the head unit 3 is placed horizontally at a height position for cleaning, the control section 8 executes a purge to forcibly expel some of the ink in the ink circulation section 5 from the nozzles of the inkjet head 11.

[0133] Specifically, the control unit 8 closes the pressurized atmosphere release valve 63. This causes the pressurized tank 31 to be sealed via the pressurized common air chamber 61. Next, the control unit 8 pressurizes the pressurized tank 31 by driving the air pump 75. This causes ink to be discharged from each nozzle of each head module 16 of each inkjet head 11. At least a portion of the ink discharged from the nozzle adheres to the nozzle surface 16a.

[0134] Here, the control unit 8 sets the amount of ink to be discharged from the inkjet head 11 by purging (amount of purged ink) according to the difference between the ink temperature at the time when both liquid level sensors detect a logical change and the lower limit of the printable temperature range in the ink circulation unit 5 where the ink temperature at the time when both liquid level sensors detect a logical change is determined to be below the lower limit of the printable temperature range. Specifically, the larger this difference is, the larger the amount of purged ink is set.

[0135] In addition, if it is determined simultaneously in multiple ink circulation units 5 that the ink temperature at the time a logical change is detected by both liquid level sensors is less than the lower limit of the printable temperature range, the amount of ink to be purged can be set according to the difference between the minimum or average ink temperature at the time a logical change is detected by both liquid level sensors in those ink circulation units 5 and the lower limit of the printable temperature range.

[0136] The amount of ink purged in the cleaning performed in step S16 may be greater than the amount of ink purged in normal cleaning, which is performed, for example, every time a predetermined number of sheets are printed.

[0137] Furthermore, during purging in the cleaning performed in step S16, the control unit 8 does not perform ink supply to the ink circulation unit 5 by low-temperature ink supply control. That is, even if both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 are turned off, the control unit 8 does not perform ink supply by the ink supply unit 6.

[0138] After purging, the control unit 8 controls the maintenance unit 4 to wipe the nozzle surface 16a of each head module 16 of each inkjet head 11 with each wiper 22. This removes ink adhering to the nozzle surface 16a as well as dust and other debris on the nozzle surface 16a. As a result, the maintenance of the inkjet head 11 is completed.

[0139] Next, in step S17, the control unit 8 resumes ink circulation and ink temperature adjustment in the ink circulation unit 5. That is, similar to step S1 in Fig. 5 described above, the control unit 8 starts ink circulation in the ink circulation unit 5 and starts ink temperature adjustment by the ink temperature adjustment unit 39 so that the ink temperature falls within the optimum printing temperature range. After this, the control unit 8 returns to step S11.

[0140] In step S15, if it is determined that the ink temperature is equal to or higher than the lower limit of the printable temperature range (step S15: NO), in step S18, the control unit 8 ends the low-temperature ink supply control, whereby thereafter, the ink supply control is performed according to the liquid level maintenance control of FIG.

[0141] Next, in step S19, the control unit 8 determines whether the ink temperature at the time when the pressure tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 detect a logic change is below the upper limit of the printable temperature range.

[0142] If it is determined that the ink temperature is below the upper limit of the printable temperature range, i.e., within the printable temperature range (step S19: YES), then in step S20, the control unit 8 starts ink temperature adjustment by the ink temperature adjustment unit 39 to maintain the ink temperature within the printable temperature range. After this, the control unit 8 proceeds to step S9 in Fig. 5 and starts printing based on the print job.

[0143] In step S19, if it is determined that the ink temperature is equal to or higher than the upper limit of the printable temperature range (step S19: NO), the control unit 8 proceeds to step S9 in FIG. 5 and starts printing based on the print job.

[0144] Here, if the ink temperature is equal to or higher than the upper limit of the printable temperature range at the time when the logical change is detected by the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37, the ink temperature is within the optimum printing temperature range. In this case, the ink temperature adjustment to maintain the ink temperature within the optimum printing temperature range continues.

[0145] As described above, in the inkjet printing device 1, if the ink temperature at the start of ink circulation in the ink circulation unit 5 is below the lower limit of the printable temperature range, and normal operation of the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 is confirmed after ink circulation starts, and the ink temperature at the time of confirmation is within the printable temperature range, the control unit 8 controls the ink temperature adjustment unit 39 to adjust the ink temperature to maintain a temperature within the printable temperature range, while controlling printing by the inkjet head 11.

[0146] In this way, when the ink temperature at the start of ink circulation is below the lower limit of the printable temperature range, if the ink temperature is within the printable temperature range when normal operation of both liquid level sensors is confirmed and printing can begin, the ink is not heated to the optimal printing temperature range and printing is performed while maintaining the ink within the printable temperature range, thereby suppressing the increase in volume due to a rise in ink temperature and preventing overflow of the pressurized tank 31 and negative pressure tank 36.

[0147] As described above, in the inkjet printing device 1, the path between the pressurized tank 31 and the inkjet head 11 and the path between the inkjet head 11 and the negative pressure tank 36 in the circulation path 55 are relatively long. Therefore, the amount of ink circulating in the ink circulation unit 5 is relatively large. As a result, the increase in the volume of the ink due to the temperature rise is relatively large. In addition, when the normal operation of both liquid level sensors is confirmed, the ink is stored in the pressurized tank 31 and the negative pressure tank 36 up to the vicinity of the reference height. Therefore, if the ink is heated from the point when the normal operation of both liquid level sensors is confirmed, there is a risk that the increase in the volume of the ink will cause the pressurized tank 31 and the negative pressure tank 36 to overflow. In contrast, in the inkjet printing device 1, as described above, the increase in the volume of the ink due to the temperature rise can be suppressed, and the overflow of the pressurized tank 31 and the negative pressure tank 36 can be suppressed.

[0148] Furthermore, in the inkjet printing device 1, if the ink temperature at the start of ink circulation in the ink circulation unit 5 is below the lower limit of the printable temperature range, and normal operation of the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 is confirmed after ink circulation starts and the ink temperature at the time of confirmation is below the lower limit of the printable temperature range, the control unit 8 stops the ink circulation in the ink circulation unit 5 and the ink temperature adjustment by the ink temperature adjustment unit 39 and discharges some of the ink in the ink circulation unit 5 from the inkjet head 11 by purging during cleaning. Thereafter, the control unit 8 controls the ink circulation unit 5 to resume the ink circulation and the ink temperature adjustment by the ink temperature adjustment unit 39.

[0149] Here, if the temperature of the ink is below the lower limit of the printable temperature range when normal operation of both liquid level sensors is confirmed and printing can begin, heating the ink to above the lower limit of the printable temperature range in order to print may increase the volume of the ink and cause overflow in the pressurized tank 31 and negative pressure tank 36. By purging as described above to discharge some of the ink in the ink circulation unit 5, overflow in the pressurized tank 31 and negative pressure tank 36 can be prevented.

[0150] Furthermore, the control unit 8 sets the amount of purged ink in the above-mentioned purge in accordance with the difference between the ink temperature at the time when normal operation of the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 is confirmed and the lower limit of the printable temperature range. This prevents a shortage of the amount of purged ink, thereby further preventing overflow of the pressurized tank 31 and the negative pressure tank 36. Also, the frequency of cleaning (purging) to prevent overflow of the pressurized tank 31 and the negative pressure tank 36 can be reduced.

[0151] The amount of purged ink in the above-mentioned purge may be set according to the ink characteristics. For example, the amount of purged ink may be set to be larger as the volume change rate per unit temperature of the ink is larger. The amount of purged ink may also be set according to the difference between the ink temperature and the lower limit of the printable temperature range at the time when the normal operation of the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 is confirmed, and the ink characteristics.

[0152] The present invention is not limited to the above-described embodiment, and the components can be modified and embodied in the implementation stage without departing from the gist of the invention. In addition, various inventions can be formed by appropriately combining the multiple components disclosed in the above-described embodiment. For example, some components may be deleted from all the components shown in the embodiment.

[0153] [Note] This application discloses the following inventions.

[0154] (Appendix 1) An inkjet head; an ink circulation unit including a tank for storing ink, a circulation path for circulating ink between the inkjet head and the tank, a liquid level detection unit for detecting the liquid level of the ink in the tank, and an ink temperature adjustment unit for adjusting the temperature of the ink; a control unit that controls the ink circulation unit so that the ink temperature adjustment unit adjusts the temperature of the ink to within an optimum printing temperature range while circulating the ink along the circulation path, and also controls the inkjet head; The control unit controls the inkjet printing device to perform printing using the inkjet head while adjusting the ink temperature using the ink temperature adjustment unit to maintain the ink temperature within the printable temperature range when the ink temperature at the start of ink circulation is below the lower limit of a printable temperature range, which is below the lower limit of the optimal printing temperature range, and when normal operation of the liquid level detection unit is confirmed after ink circulation starts and the ink temperature at the time of confirmation is within the printable temperature range.

[0155] (Appendix 2) a discharge unit that discharges the ink from the ink circulation unit through the inkjet head, The inkjet printing device described in Appendix 1, characterized in that, when the temperature of the ink at the start of ink circulation is below a lower limit of the printable temperature range, and normal operation of the liquid level detection unit is confirmed after ink circulation starts and the temperature of the ink at the time of confirmation is below the lower limit of the printable temperature range, the control unit controls the ink circulation unit to stop ink circulation in the ink circulation unit and adjustment of the ink temperature by the ink temperature adjustment unit, to discharge a portion of the ink in the ink circulation unit from the inkjet head by the discharge unit, and then to resume ink circulation and adjustment of the ink temperature by the ink temperature adjustment unit.

[0156] (Appendix 3) The inkjet printing device described in Appendix 2, characterized in that the control unit sets the amount of ink to be discharged from the inkjet head by the discharge unit in accordance with at least one of the difference between the temperature of the ink at the time when normal operation of the liquid level detection unit is confirmed and the lower limit of the printable temperature range, and the ink characteristics. [Explanation of symbols]

[0157] 1 Inkjet printing device 2. Conveyor section 3 Head Unit 4. Maintenance Department 5,5A~5D Ink Circulation Section 6,6A~6D Ink supply unit 7 Pressure generating section 8. Control Unit 11, 11A to 11D Inkjet head 12 Head holder 31 Pressurized Tank 32 Pressurized tank liquid level sensor 33 Ink Filter 34 Distributor 35 Collector 36 Negative Pressure Tank 37 Negative pressure tank liquid level sensor 38 Ink Pump 39 Ink temperature adjustment unit 40 Ink temperature sensor 41~43 Ink circulation pipe 55 Circulation Route

Claims

1. An inkjet head; an ink circulation unit including a tank for storing ink, a circulation path for circulating ink between the inkjet head and the tank, a liquid level detection unit for detecting the liquid level of the ink in the tank, and an ink temperature adjustment unit for adjusting the temperature of the ink; a control unit that controls the ink circulation unit so that the ink temperature adjustment unit adjusts the temperature of the ink to within an optimum printing temperature range while circulating the ink along the circulation path, and also controls the inkjet head; The control unit controls the inkjet printing device to perform printing using the inkjet head while adjusting the ink temperature using the ink temperature adjustment unit to maintain the ink temperature within the printable temperature range when the ink temperature at the start of ink circulation is below the lower limit of a printable temperature range, which is below the lower limit of the optimal printing temperature range, and when normal operation of the liquid level detection unit is confirmed after ink circulation starts and the ink temperature at the time of confirmation is within the printable temperature range.

2. a discharge unit that discharges the ink from the ink circulation unit through the inkjet head, 2. The inkjet printing device according to claim 1, wherein, when the temperature of the ink at the start of ink circulation is less than a lower limit of the printable temperature range, and normal operation of the liquid level detection unit is confirmed after ink circulation starts and the temperature of the ink at the time of confirmation is less than the lower limit of the printable temperature range, the control unit controls the ink circulation unit to stop ink circulation in the ink circulation unit and adjustment of the ink temperature by the ink temperature adjustment unit, to discharge a portion of the ink in the ink circulation unit from the inkjet head by the discharge unit, and then to resume ink circulation and adjustment of the ink temperature by the ink temperature adjustment unit.

3. The inkjet printing device according to claim 2, characterized in that the control unit sets the amount of ink to be discharged from the inkjet head by the discharge unit in accordance with at least one of the difference between the temperature of the ink at the time when normal operation of the liquid level detection unit is confirmed and the lower limit of the printable temperature range, and the ink characteristics.

Images