Inkjet printing equipment

Abstract

To provide an inkjet printing apparatus that can reduce the amount of foreign matter sucked into the nozzle. [Solution] The inkjet head 11 has nozzles for ejecting ink. The pressure generation unit 7 applies pressure to the inkjet head 11. The control unit 8 performs a purge by pressurizing the inkjet head 11 to discharge ink from the nozzles, then adjusts the nozzle pressure to a slightly positive pressure within the wiping nozzle pressure range where no ink is discharged, and then controls the pressure generation unit 7 to maintain the nozzle pressure within the wiping nozzle pressure range by pressurizing the inkjet head 11 before the nozzle pressure drops below the lower limit of the wiping nozzle pressure range, until wiping of the nozzle surface of the inkjet head 11 is completed.

Description

[[Technical Field]]

[0001] The present invention relates to an inkjet printing apparatus. [[Background Art]]

[0002] As an operation for cleaning an inkjet head in an inkjet printing apparatus, an operation is known in which after performing purging to forcibly discharge ink from nozzles of the inkjet head, the nozzle surface is wiped with a wiper. This removes foreign matter such as dust attached to the nozzle surface together with the ink discharged from the nozzles and attached to the nozzle surface.

[0003] Further, in the above-described operation, a technique is known in which in order to prevent foreign matter from being sucked into the nozzles, wiping is performed with a slightly positive nozzle pressure after purging (see Patent Document 1). [[Prior Art Literature]] [[Patent Literature]]

[0004] [[Patent Document 1]] Japanese Unexamined Patent Publication No. 2009-269361 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0005] However, with the above-described technique, the nozzle pressure may not be maintained at a slightly positive pressure until wiping is completed due to air bleeding in a mechanism that applies pressure to the inkjet head, for example. If the nozzle pressure is not maintained at a slightly positive pressure until wiping is completed, there is a risk that foreign matter may be sucked into the nozzles.

[0006] 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 capable of reducing the suction of foreign matter into the nozzles. [[Means for Solving the Problem]]

[0007] To achieve the above objective, the present invention provides an inkjet printing apparatus comprising: an inkjet head having nozzles for ejecting ink; a pressure application unit for applying pressure to the inkjet head; and a control unit that controls the pressure application unit to perform nozzle pressure maintenance adjustment, which involves purging the inkjet head by pressurizing it to discharge ink from the nozzles, adjusting the nozzle pressure to a predetermined range of slightly positive pressure where no ink is discharged, and then pressurizing the inkjet head to maintain the nozzle pressure within the predetermined range before the nozzle pressure drops below the lower limit of the predetermined range until wiping of the nozzle surface of the inkjet head where the nozzles open is completed. [Effects of the Invention]

[0008] According to the inkjet printing apparatus of the present invention, the amount of foreign matter drawn into the nozzle can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram showing the configuration of an inkjet printing apparatus according to an embodiment. [Figure 2] This is a schematic diagram of the transport and printing sections. [Figure 3] This is a schematic diagram of the maintenance department. [Figure 4] This is a schematic diagram of the ink circulation unit, ink replenishment unit, and pressure generation unit. [Figure 5] This is a diagram illustrating the general process of cleaning an inkjet print head. [Figure 6] This is a flowchart illustrating the operation during inkjet head cleaning. [Figure 7] This figure shows an example of the pressure changes in a pressurized tank. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals.

[0011] The embodiments shown below illustrate devices and the like that embody the technical concept of this invention, and the technical concept of this invention does not specify the material, shape, structure, arrangement, etc., of each component as described below. The technical concept of this invention can be modified in various ways within the scope of the claims.

[0012] Figure 1 is a block diagram showing the configuration of an inkjet printing apparatus according to an embodiment of the present invention. Figure 2 is a schematic diagram of the transport section and printing section of the inkjet printing apparatus shown in Figure 1. Figure 3 is a schematic diagram of the maintenance section of the inkjet printing apparatus shown in Figure 1. Figure 4 is a schematic diagram of the ink circulation section, ink replenishment section, and pressure application section of the inkjet printing apparatus shown in Figure 1. Note that Figure 4 shows the printing section in a horizontal position. In the following description, the up, down, left, right, front, and back directions indicated by the arrows in Figure 2 will be referred to as the up, down, left, right, front, and back directions. The up and down direction is the vertical direction, and the left and right directions and front and back directions are mutually orthogonal, and both are orthogonal to the up and down direction and parallel to the horizontal direction.

[0013] As shown in Figures 1 to 4, the inkjet printing apparatus 1 according to this embodiment comprises a transport unit 2, a printing unit 3, a maintenance unit 4, ink circulation units 5A to 5D, ink replenishment units 6A to 6D, a pressure generation unit (corresponding to a pressure application unit) 7, and a control unit 8. Note that the alphabetical subscripts in the symbols such as ink circulation units 5A to 5D may be omitted and the overall representation may be simplified.

[0014] The transport unit 2 transports the printing medium 9. The printing medium 9 can be a three-dimensional object such as a cardboard box or a sheet of paper.

[0015] The printing unit 3 performs printing by ejecting ink onto a print medium 9 conveyed by the conveyance unit 2. As shown in FIGS. 1 to 4, the printing unit 3 includes inkjet heads 11A to 11D and a head holder 12.

[0016] The printing unit 3 is manually rotatable 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 printing unit 3 refers to a state where a nozzle surface 17a of a head module 16, which will be described later, is a vertical surface. When performing horizontal-direction printing, the printing unit 3 is placed in the vertical state. Horizontal-direction printing is printing performed by ejecting ink in the horizontal direction onto the vertical surface of the print medium 9.

[0017] The horizontal state of the printing unit 3 refers to a state where the nozzle surface 17a is a horizontal surface. When cleaning the inkjet head 11 using the maintenance unit 4 and when performing downward printing, the printing unit 3 is placed in the horizontal state. Downward printing is printing performed by ejecting ink downward onto the horizontal surface of the print medium 9.

[0018] Here, the printing unit 3 can be manually lifted and lowered, and is disposed at a higher position when cleaning the inkjet head 11 than when performing downward printing.

[0019] The inkjet heads 11A to 11D eject ink onto the print medium 9 to print an image. The inkjet heads 11A to 11D eject inks of respectively different colors (for example, black, cyan, magenta, and yellow). The inkjet heads 11A to 11D have the same configuration except for the color of the ejected ink.

[0020] The inkjet head 11 includes a plurality of head modules 16. In the present embodiment, the inkjet head 11 includes six head modules 16. In the inkjet head 11, the head modules 16 are arranged in a staggered pattern along the print width direction. That is, in the inkjet head 11, six head modules 16 arranged along the print width direction are disposed with their positions alternately shifted in the front-rear direction perpendicular to the print width direction. Here, the print width direction is the vertical direction when the printing unit 3 is in the vertical orientation, and is the horizontal direction when the printing unit 3 is in the horizontal orientation.

[0021] The head module 16 includes a nozzle plate 17 and a plurality of nozzles 18 (see FIG. 5).

[0022] The nozzle plate 17 is a member in which the nozzles 18 are formed. The surface of the nozzle plate 17 that faces a print medium 9 during printing serves as a nozzle surface 17a where the nozzles 18 open.

[0023] The nozzles 18 eject ink supplied to the head module 16. In the head module 16, the plurality of nozzles 18 are arranged along the print width direction.

[0024] A head holder 12 holds the inkjet heads 11A to 11D. The head holder 12 is provided with a rotating shaft 19 extending in the front-rear direction. With the rotating shaft 19 as a center, the printing unit 3 is rotatable between a vertical orientation and a horizontal orientation.

[0025] A maintenance unit 4 performs cleaning of the inkjet head 11. The maintenance unit 4 is manually movable between a deployed position, which is the position adopted when cleaning the inkjet head 11, and a retracted position, where the maintenance unit 4 is retracted from the deployed position. The deployed position is the position of the maintenance unit 4 shown in FIG. 3, which is located directly below the printing unit that is placed horizontally at a predetermined height for cleaning. An illustration of the maintenance unit 4 in the retracted position is omitted.

[0026] As shown in Figure 3, the maintenance unit 4 includes an ink receiving unit 21 and a wiper 22.

[0027] The ink receiving section 21 receives ink and other substances removed from the nozzle surface 17a by wiping with the wiper 22 during cleaning of the inkjet head 11.

[0028] The wiper 22 wipes the nozzle surface 17a of the head module 16 to remove ink and other substances from the nozzle surface 17a. The maintenance unit 4 is provided with two wipers 22 for each of the inkjet heads 11A to 11D: one for the front three head modules 16 of the six head modules 16 arranged in a staggered pattern, and another for the rear three head modules 16. In other words, the maintenance unit 4 is provided with eight wipers 22. The wipers 22 are moved left and right (in the direction of the nozzle arrangement 18) by manually operating a handle (not shown).

[0029] The ink circulation units 5A to 5D circulate the ink and supply it to the inkjet heads 11A to 11D, respectively. As shown in Figure 4, the ink circulation unit 5 includes a pressurized tank (equivalent to a tank) 31, a pressurized tank liquid level sensor 32, an ink filter 33, a distributor 34, a collector 35, a negative pressure tank 36, a negative pressure tank liquid level sensor 37, an ink pump 38, an ink temperature adjustment unit 39, an ink temperature sensor 40, and ink circulation pipes 41 to 43.

[0030] The pressurized tank 31 stores the ink supplied to each head module 16 of the inkjet head 11. The pressurized tank 31 is connected to each head module 16 of the inkjet head 11 via an ink circulation pipe 41 and a distributor 34. An air layer 46 is formed above the liquid surface of the ink inside the pressurized tank 31. The pressurized tank 31 is connected to a pressurized common air chamber 61, which will be described later, via a pressurized communication pipe 62, which will be described later. The pressurized tank 31 is positioned lower (below) the inkjet head 11.

[0031] The pressurized tank liquid level sensor 32 detects whether the liquid level of the ink in the pressurized tank 31 has reached a predetermined reference height. If the liquid level of the ink in the pressurized tank 31 is at or above the reference height, the pressurized tank liquid level sensor 32 outputs a signal indicating "ON". If the liquid level of the ink in the pressurized tank 31 is below the reference height, the pressurized tank liquid level sensor 32 outputs a signal indicating "OFF".

[0032] The ink filter 33 removes dust and other debris from the ink. The ink filter 33 is installed inside the pressurized tank 31.

[0033] 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.

[0034] The collector 35 collects ink that was not 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 the ink circulation pipe 42.

[0035] The negative pressure tank 36 receives and stores ink that is not consumed by the inkjet head 11. The negative pressure tank 36 is connected to each head module 16 of the inkjet head 11 via the collector 35 and the ink circulation pipe 42. The negative pressure tank 36 also stores ink supplied from the ink cartridge 56 of the ink supply unit 6, which will be described later. An air layer 47 is formed above the liquid surface of the ink inside the negative pressure tank 36. The negative pressure tank 36 is connected to the negative pressure common air chamber 68, which will be described later, via the negative pressure communication pipe 69, which will be described later. The negative pressure tank 36 is positioned at the same height as the pressurized tank 31.

[0036] The negative pressure tank liquid level sensor 37 is used to detect whether the liquid level of the ink in the negative pressure tank 36 has reached a predetermined reference height. The negative pressure tank liquid level sensor 37 outputs an "ON" signal if the liquid level of the ink in the negative pressure tank 36 is at or above the reference height. The negative pressure tank liquid level sensor 37 also outputs an "OFF" signal if the liquid level of the ink in the negative pressure tank 36 is below the reference height.

[0037] The ink pump 38 delivers ink from the negative pressure tank 36 to the pressurized tank 31. The ink pump 38 is located in the middle of the ink circulation pipe 43.

[0038] 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 located in the middle of the ink circulation pipe 41. The ink temperature adjustment unit 39 includes a heater 51, a heater temperature sensor 52, a heat sink 53, and a cooling fan 54.

[0039] The heater 51 heats the ink in the ink circulation tube 41. The heater temperature sensor 52 detects the temperature of the heater 51. The heat sink 53 cools the ink in the ink circulation tube 41 by dissipating heat. The cooling fan 54 blows cooling air onto the heat sink 53.

[0040] The ink temperature sensor 40 detects the temperature of the ink in the ink circulation section 5. The ink temperature sensor 40 is located in the middle of the ink circulation pipe 41.

[0041] The ink circulation pipe 41 connects the pressurized tank 31 and the distributor 34. Part of the ink circulation pipe 41 is branched into a section that passes through the heater 51 and a section that passes through the heat sink 53. Ink flows through the ink circulation pipe 41 from the pressurized tank 31 to the distributor 34. The ink circulation pipe 42 connects the collector 35 and the negative pressure tank 36. Ink flows through the ink circulation pipe 42 from the collector 35 to the negative pressure tank 36. The ink circulation pipe 43 connects the negative pressure tank 36 and the pressurized tank 31. Ink flows through the ink circulation pipe 43 from the negative pressure tank 36 to the pressurized tank 31. The ink circulation pipes 41-43, the distributor 34 and the collector 35 constitute a circulation path for circulating ink between the pressurized tank 31, the inkjet head 11 and the negative pressure tank 36.

[0042] In this inkjet printing apparatus 1, the printing unit 3 and the ink circulation units 5A to 5D are located relatively far apart. Therefore, the ink circulation pipes 41 and 42 are relatively long. Specifically, the ink path consisting of the ink circulation pipe 41 and the distributor 34 that connects the pressurized tank 31 and the inkjet head 11, and the ink path consisting of the ink circulation pipe 42 and the collector 35 that connects the inkjet head 11 and the negative pressure tank 36 are relatively long.

[0043] The ink supply units 6A to 6D each supply ink to the ink circulation units 5A to 5D. As shown in Figure 4, the ink supply unit 6 comprises an ink cartridge 56, an ink supply valve 57, and an ink supply pipe 58.

[0044] The ink cartridge 56 contains the 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 the ink supply pipe 58.

[0045] The ink supply valve 57 opens and closes the ink flow path in the ink supply pipe 58. When supplying ink to the negative pressure tank 36, the ink supply valve 57 is opened.

[0046] The ink supply tube 58 connects the ink cartridge 56 to the negative pressure tank 36. Ink flows from the ink cartridge 56 to the negative pressure tank 36 through the ink supply tube 58.

[0047] The pressure generation unit 7 generates pressure for ink circulation in the pressurized tank 31 and negative pressure tank 36 of each ink circulation unit 5. In addition, when the inkjet head 11 is being cleaned, the pressure generation unit 7 applies pressure (purging pressure Pp) to the pressurized tank 31 of each ink circulation unit 5 for purging, which involves pressurizing the inkjet head 11 to discharge ink from the nozzles 18.

[0048] As shown in Figure 4, the pressure generating unit 7 includes a pressurized common air chamber 61, four pressurized connecting pipes 62, a pressurized atmospheric release valve 63, a pressurized atmospheric release pipe 64, a pressurized pressure regulating valve 65, a pressurized pressure regulating pipe 66, a pressurized pressure sensor 67, a negative pressure common air chamber 68, four negative pressure connecting pipes 69, a negative pressure atmospheric release valve 70, a negative pressure atmospheric release pipe 71, a negative pressure regulating valve 72, a negative pressure regulating pipe 73, a negative pressure sensor 74, an air pump 75, piping for the air pump 76, a junction pipe 77, an air filter 78, an overflow pan 79, an overflow ball 80, and an overflow liquid level sensor 81.

[0049] The common pressurized air chamber 61 is an air chamber for equalizing the pressure in the pressurized tanks 31 of each ink circulation unit 5. The common pressurized air chamber 61 is connected to the air layer 46 of the pressurized tanks 31 of the ink circulation units 5A to 5D via four pressurized connecting pipes 62. As a result, the pressurized tanks 31 of the ink circulation units 5A to 5D are connected to each other via the common pressurized air chamber 61 and the pressurized connecting pipes 62.

[0050] The pressurized connecting pipe 62 connects the pressurized common air chamber 61 to the air layer 46 of the pressurized tank 31. There are four pressurized connecting pipes 62, one for each of the ink circulation sections 5A to 5D. One end of the pressurized connecting pipe 62 is connected to the pressurized common air chamber 61, and the other end is connected to the air layer 46 of the pressurized tank 31.

[0051] The pressurized atmospheric release valve 63 opens and closes the airflow path in the pressurized atmospheric release pipe 64 in order to switch the pressurized tank 31 between a sealed state (isolated from the atmosphere) and an open state (connected to the atmosphere) via the pressurized common air chamber 61. The pressurized atmospheric release valve 63 is installed in the middle of the pressurized atmospheric release pipe 64.

[0052] The pressurized atmospheric vent pipe 64 forms an air passage for venting the pressurized tank 31 to the atmosphere via the pressurized common air chamber 61. One end of the pressurized atmospheric vent pipe 64 is connected to the pressurized common air chamber 61, and the other end is connected to the confluence pipe 77.

[0053] The pressurizing valve 65 opens and closes the air passage in the pressurizing pipe 66 to adjust the pressure in the pressurized common air chamber 61 and the pressurized tank 31. The pressurizing valve 65 is located in the middle of the pressurizing pipe 66.

[0054] The pressurized pressure regulating pipe 66 forms an air passage for regulating the pressure of the pressurized common air chamber 61 and the pressurized tank 31. The pressurized pressure regulating pipe 66 consists of a pipe narrower than the pressurized atmospheric vent pipe 64, the negative pressure atmospheric vent pipe 71, and the confluence pipe 77. One end of the pressurized pressure regulating pipe 66 is connected to the pressurized common air chamber 61, and the other end is connected to the confluence pipe 77.

[0055] 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 tanks 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 tanks 31 of the ink circulation units 5A to 5D are in communication.

[0056] The negative pressure common air chamber 68 is an air chamber for equalizing the pressure in the negative pressure tanks 36 of each ink circulation unit 5. The negative pressure common air chamber 68 is connected to the air layer 47 of the negative pressure tanks 36 of the ink circulation units 5A to 5D via four negative pressure connecting pipes 69. As a result, the negative pressure tanks 36 of the ink circulation units 5A to 5D are connected to each other via the negative pressure common air chamber 68 and the negative pressure connecting pipes 69.

[0057] The negative pressure communication pipe 69 connects the negative pressure common air chamber 68 with the air layer 47 of the negative pressure tank 36. There are four negative pressure communication pipes 69, one for each of the ink circulation sections 5A to 5D. One end of each negative pressure communication pipe 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.

[0058] The negative pressure atmospheric release valve 70 opens and closes the air passage in the negative pressure atmospheric release pipe 71 in order to switch the negative pressure tank 36 between a sealed state and an open state to the atmosphere via the negative pressure common air chamber 68. The negative pressure atmospheric release valve 70 is installed in the middle of the negative pressure atmospheric release pipe 71.

[0059] The negative pressure atmospheric release pipe 71 forms an air passage for releasing the negative pressure tank 36 to the atmosphere via the negative pressure common air chamber 68. One end of the negative pressure atmospheric release pipe 71 is connected to the negative pressure common air chamber 68, and the other end is connected to the confluence pipe 77.

[0060] The negative pressure regulating valve 72 opens and closes the air passage in the negative pressure regulating pipe 73 to regulate the pressure in the negative pressure common air chamber 68 and the negative pressure tank 36. The negative pressure regulating valve 72 is located in the middle of the negative pressure regulating pipe 73.

[0061] The negative pressure regulating pipe 73 forms an air passage for regulating the pressure of the negative pressure common air chamber 68 and the negative pressure tank 36. The negative pressure regulating pipe 73 consists of a pipe narrower than the pressurized atmospheric vent pipe 64, the negative pressure atmospheric vent pipe 71, and the confluence pipe 77. One end of the negative pressure regulating pipe 73 is connected to the negative pressure common air chamber 68, and the other end is connected to the confluence pipe 77.

[0062] The negative pressure sensor 74 detects the pressure in the negative pressure common air chamber 68. The pressure in the negative pressure common air chamber 68 is equal to the pressure in the negative pressure tanks 36 of the ink circulation sections 5A to 5D. This is because the negative pressure common air chamber 68 and the air layer 47 of the negative pressure tanks 36 of the ink circulation sections 5A to 5D are in communication.

[0063] The air pump 75 draws air from the negative pressure tanks 36 of the ink circulation sections 5A to 5D via the negative pressure common air chamber 68, and also sends air to the pressurized tanks 31 of the ink circulation sections 5A to 5D via the pressurized common air chamber 61. The air pump 75 is installed in the middle of the air pump piping 76.

[0064] The air pump piping 76 forms a passage for air sent by the air pump 75 from the negative pressure common air chamber 68 to the pressurized common air chamber 61. 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.

[0065] One end of the confluence pipe 77 is connected to the overflow pan 79, and the other end (upper end) is open to the atmosphere via the air filter 78. The end of the confluence pipe 77 on the overflow pan 79 side is normally closed by the overflow ball 80, which will be described later. The confluence pipe 77 is connected to a pressurized atmospheric outlet pipe 64, a pressurized pressure regulating pipe 66, a negative pressure atmospheric outlet pipe 71, and a negative pressure regulating pipe 73. As a result, the pressurized atmospheric outlet pipe 64, the pressurized pressure regulating pipe 66, the negative pressure atmospheric outlet pipe 71, and the negative pressure regulating pipe 73 are open to the atmosphere.

[0066] The air filter 78 prevents dust and other particles from entering the confluence pipe 77. The air filter 78 is installed at the upper end of the confluence pipe 77.

[0067] The overflow pan 79 receives ink flowing through the confluence pipe 77 when ink overflows from at least one of the pressurized tank 31 and the negative pressure tank 36, and ink also overflows from the pressurized common air chamber 61 and the negative pressure common air chamber 68.

[0068] The overflow ball 80 closes the end of the confluence pipe 77, which opens to the bottom of the overflow pan 79, when there is no ink in the overflow pan 79, preventing outside air from entering the confluence pipe 77. When ink flows from the confluence pipe 77 to the overflow pan 79, the overflow ball 80 floats up, allowing ink to flow into the overflow pan 79.

[0069] The overflow liquid level sensor 81 detects whether the ink level in the overflow pan 79 has reached a predetermined height. When the overflow liquid level sensor 81 is turned on, ink is discharged from the overflow pan 79 into a waste liquid tank (not shown).

[0070] The control unit 8 controls the operation of each part of the inkjet printing device 1. The control unit 8 is composed of a CPU, RAM, ROM, hard disk, etc.

[0071] During cleaning of the inkjet head 11, the control unit 8 controls the pressure generation unit 7 to pressurize the inkjet head 11 and perform a purge to discharge ink from each nozzle 18. After that, it adjusts the nozzle pressure of each nozzle 18 to a set nozzle pressure during wiping within a predetermined wiping nozzle pressure range (corresponding to a predetermined range). Subsequently, until wiping of the nozzle surface 17a is completed, the control unit 8 controls the pressure generation unit 7 to pressurize the inkjet head 11 before the nozzle pressure drops below the lower limit of the wiping nozzle pressure range, thereby maintaining the nozzle pressure within the wiping nozzle pressure range.

[0072] Here, the nozzle pressure setting during wiping described above is set as the value of the nozzle pressure that results in a slightly positive pressure during wiping. The nozzle pressure range during wiping is the range of slightly positive pressure in which ink is not discharged from nozzle 18.

[0073] Next, we will explain the operation of the inkjet printer 1 during printing.

[0074] When a print job is input, the control unit 8 starts the ink circulation in the ink circulation unit 5.

[0075] Specifically, the control unit 8 closes the pressurized atmospheric release valve 63 and the negative pressure atmospheric release valve 70. This seals the pressurized tank 31 via the pressurized common air chamber 61 and the negative pressure tank 36 via the negative pressure common air chamber 68. When the inkjet printing device 1 is in standby mode, the pressurized atmospheric release valve 63 and the negative pressure atmospheric release valve 70 are open, and the pressurized pressure regulating valve 65 and the negative pressure regulating valve 72 are closed. Next, the control unit 8 starts driving the air pump 75. This reduces the pressure in the negative pressure common air chamber 68 and the negative pressure tank 36, and pressurizes the pressurized common air chamber 61 and the pressurized tank 31. This creates an ink flow from the pressurized tank 31 through the inkjet head 11 to the negative pressure tank 36, and ink circulation begins.

[0076] After ink circulation begins, the control unit 8 controls the operation of the air pump 75 and the opening and closing of the pressure regulating valve 65 and the pressure regulating valve 72 based on the detected values ​​of the pressure sensor 67 and the pressure regulating valve 74, so that the pressure in the pressure tank 31 and the pressure regulating valve 36 reaches and is maintained at their respective set pressures.

[0077] The set pressures of the pressurized tank 31 and the negative pressure tank 36 are predetermined as pressure values ​​necessary to circulate the ink while maintaining the correct nozzle pressure of the inkjet head 11. The set pressure of the pressurized tank 31 is positive pressure, and the set pressure of the negative pressure tank 36 is negative pressure.

[0078] When the pressures in the pressurized tank 31 and the negative pressure tank 36 reach their respective set pressures, the control unit 8 starts executing the print job. Specifically, the control unit 8 controls the transport unit 2 to transport the print medium 9 and to print an image onto the print medium 9 by ejecting ink from each head module 16 of each inkjet head 11.

[0079] During the execution of a print job, ink is supplied from the pressurized tank 31 to the inkjet head 11, and any ink not consumed by the inkjet head 11 is recovered into the negative pressure tank 36. 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 drives the ink pump 38. This causes ink to be sent from the negative pressure tank 36 to the pressurized tank 31. When the pressurized tank liquid level sensor 32 turns on, the control unit 8 stops the ink pump 38. In this way, ink is circulated and printing is performed.

[0080] Furthermore, when both the pressurized tank liquid level sensor 32 and the negative pressure tank liquid level sensor 37 are turned off, the control unit 8 opens the ink supply valve 57. This allows ink to be supplied from the ink cartridge 56 to the negative pressure tank 36. When the negative pressure tank liquid level sensor 37 is turned on, the control unit 8 closes the ink supply valve 57.

[0081] Furthermore, the control unit 8 controls the ink temperature adjustment unit 39 to adjust the ink temperature so that the temperature detected by the ink temperature sensor 40 remains within an appropriate temperature range.

[0082] When printing based on a print job is completed, the control unit 8 opens the pressurized atmospheric release valve 63 and the negative pressure atmospheric release valve 70, and closes the pressurized pressure regulating valve 65 and the negative pressure regulating valve 72. This stops the ink circulation. The control unit 8 also stops the ink temperature adjustment by the ink temperature adjustment unit 39. This completes the series of operations.

[0083] Next, we will briefly describe the cleaning process for the inkjet head 11 in the inkjet printing device 1.

[0084] As shown in Figure 5, before cleaning, ink may adhere to the nozzle surface 17a of the head module 16 of the inkjet head 11 due to the accumulation of ink mist generated during printing. In addition, foreign matter such as dust may adhere to the nozzle surface 17a.

[0085] When cleaning the inkjet head 11, ink is first discharged from each nozzle 18 by purging. At least a portion of the discharged ink adheres to the nozzle surface 17a.

[0086] After purging, the nozzle pressure of each nozzle 18 is adjusted to a slightly positive pressure, set nozzle pressure for wiping. In this state, the nozzle surface 17a is wiped by the wiper 22. Wiping removes foreign matter along with the ink adhering to the nozzle surface 17a. Here, as will be described later, nozzle pressure maintenance adjustment is performed to maintain the nozzle pressure of each nozzle 18 within the wiping nozzle pressure range until wiping of the nozzle surface 17a of each head module 16 is completed.

[0087] Next, the operation of the inkjet head 11 in the inkjet printing device 1 during cleaning will be explained with reference to the flowchart in Figure 6.

[0088] When the maintenance unit 4 is positioned in the deployed position and the printing unit 3 is positioned horizontally at the cleaning height, in step S1 of Figure 6, the control unit 8 controls the pressure generation unit 7 to generate a purging pressure Pp in the pressurized tank 31.

[0089] Specifically, the control unit 8 first closes the pressurized atmospheric release valve 63. This seals the pressurized tank 31 via the pressurized common air chamber 61. Next, the control unit 8 starts driving the air pump 75. This causes the pressurized tank 31 to start pressurizing. When the value detected by the pressurized pressure sensor 67 reaches the purging pressure Pp, the control unit 8 stops the air pump 75.

[0090] When a purging pressure Pp is generated in the pressurized tank 31, a predetermined purging pressure (positive pressure) is applied to each head module 16 of the inkjet head 11, causing ink to be discharged from each nozzle 18. At least a portion of the ink discharged from each nozzle 18 adheres to the nozzle surface 17a.

[0091] Next, in step S2, the control unit 8 determines whether a predetermined purge pressure maintenance time has elapsed since generating the purging pressure Pp in the pressurized tank 31. If it determines that the purge pressure maintenance time has not elapsed (step S2: NO), the control unit 8 repeats step S2.

[0092] If the control unit 8 determines that the purge pressure maintenance time has elapsed (step S2: YES), in step S3, the control unit 8 controls the pressure generation unit 7 to adjust the pressure in the pressurized tank 31 to the wiping pressure Pw.

[0093] Specifically, the control unit 8 opens the pressure adjustment valve 65. This causes the pressure in the pressurized tank 31 to begin to decrease. When the value detected by the pressure sensor 67 drops to the pressure Pw required for wiping, the control unit 8 closes the pressure adjustment valve 65. Here, the pressure Pw required for wiping is the pressure in the pressurized tank 31 at which the nozzle pressure of each nozzle 18 of the inkjet head 11 becomes the aforementioned set nozzle pressure for wiping.

[0094] In step S3 described above, when the pressure in the pressurized tank 31 is adjusted to the wiping pressure Pw, the nozzle pressure is adjusted to the set nozzle pressure for wiping, and the operator manually starts wiping the nozzle surface 17a with the wiper 22. That is, wiping of the nozzle surface 17a starts with the nozzle pressure of each nozzle 18 being slightly positive.

[0095] Next, in step S4, the control unit 8 determines whether or not wiping of the nozzle surfaces 17a of all head modules 16 of the inkjet head 11 has been completed. At this point, if the operator who performed the manual wiping confirms the completion of wiping on an operation panel (not shown), the control unit 8 determines that wiping has been completed.

[0096] If it is determined that wiping is not complete (step S4: NO), in step S5, the control unit 8 determines whether the pressure in the pressurized tank 31, i.e., the value detected by the pressurized pressure sensor 67, is below a specified value. Here, the specified value is set to a value equal to or greater than the pressure in the pressurized tank 31 at which the nozzle pressure becomes the lower limit of the nozzle pressure range during wiping.

[0097] If the control unit 8 determines that the pressure in the pressurized tank 31 is below a specified value (step S5: YES), in step S6, the control unit 8 controls the pressure generation unit 7 to pressurize the pressurized tank 31 to the adjustment pressure Pc. Specifically, the control unit 8 starts driving the air pump 75, and when the value detected by the pressurized pressure sensor 67 reaches the adjustment pressure Pc, it stops the air pump 75. After this, the control unit 8 returns to step S4.

[0098] Here, the adjustment pressure Pc mentioned above is the pressure in the pressurized tank 31 at which the nozzle pressure is within the wiping nozzle pressure range and is higher than the set nozzle pressure during wiping.

[0099] If, in step S5, it is determined that the pressure in the pressurized tank 31 exceeds a specified value (step S5: NO), then in step S7, the control unit 8 determines whether a specified time has elapsed since the most recent pressurization of the pressurized tank 31 to the adjustment pressure Pc. Here, if the pressurized tank 31 has not been pressurized even once since adjusting the pressure in the pressurized tank 31 to the wiping pressure Pw in step S3, the control unit 8 determines whether a specified time has elapsed since the time the pressure was adjusted to the wiping pressure Pw in step S3.

[0100] Here, the specified time mentioned above is set to a value less than or equal to the time it takes for the nozzle pressure to decrease from the set nozzle pressure during wiping to the lower limit of the nozzle pressure range during wiping, as determined experimentally.

[0101] If it is determined that the specified time has not elapsed (step S7: NO), the control unit 8 returns to step S4.

[0102] If the control unit 8 determines that the specified time has elapsed (step S7: YES), it proceeds to step S6 and controls the pressure generation unit 7 to pressurize the pressure in the pressurized tank 31 to the adjustment pressure Pc. After this, the control unit 8 returns to step S4.

[0103] In step S4, if the control unit 8 determines that wiping is complete (step S4: YES), the series of operations ends.

[0104] As mentioned above, in the inkjet printing apparatus 1, the ink path, consisting of an ink circulation pipe 41 and a distributor 34 connecting the pressure tank 31 and the inkjet head 11, is relatively long. Therefore, a relatively high pressure is required as the wiping pressure Pw generated in the pressure tank 31 in order to set the nozzle pressure to the nozzle pressure set for wiping.

[0105] The higher the pressure generated in the pressurized tank 31, the easier it is for air to escape from the pressurized atmospheric release valve 63 and the pressurized pressure adjustment valve 65, etc., which can easily cause a decrease in the pressure of the pressurized tank 31. When the pressure in the pressurized tank 31 decreases, the nozzle pressure of the inkjet head 11 decreases. For this reason, in an inkjet printing device 1 in which the ink path connecting the pressurized tank 31 and the inkjet head 11 is relatively long, if the pressure in the pressurized tank 31 is not adjusted after the nozzle pressure has been adjusted to the nozzle pressure set for wiping, the time in which the nozzle pressure can be maintained within the wiping nozzle pressure range is relatively short.

[0106] However, in inkjet printing apparatus 1, wiping is performed manually by the operator, so it is necessary to maintain the nozzle pressure within the wiping nozzle pressure range for a relatively long period of time.

[0107] Therefore, in the inkjet printing apparatus 1, after adjusting the nozzle pressure to the nozzle pressure set for wiping using the flowchart in Figure 6 described above, a nozzle pressure maintenance adjustment is performed to maintain the nozzle pressure within the wiping nozzle pressure range until wiping is completed.

[0108] Specifically, the control unit 8 performs a first control according to steps S5 and S6 in Figure 6, and a second control according to steps S7 and S6, to pressurize the inkjet head 11 before the nozzle pressure drops below the lower limit of the wiping nozzle pressure range, thereby maintaining the nozzle pressure within the wiping nozzle pressure range.

[0109] The first control described above is a control that pressurizes the pressurized tank 31 by the pressure generation unit 7 when the pressure in the pressurized tank 31 falls below a specified value. The second control is a control that pressurizes the pressurized tank 31 by the pressure generation unit 7 when a specified time has elapsed since the time when the nozzle pressure was first adjusted to the wiping pressure Pw after purging (the start of nozzle pressure maintenance adjustment), and when a specified time has elapsed since the most recent pressurization of the pressurized tank 31.

[0110] In addition, in the second control, the most recent time when the pressurized tank 31 is pressurized includes the time when the pressurized tank 31 is pressurized by the first control. Furthermore, in the second control, if the pressurized tank 31 is pressurized by the first control before the specified time has elapsed from the start of nozzle pressure maintenance adjustment, the pressurized tank 31 will not be pressurized at the time when the specified time has elapsed from the time the nozzle pressure is adjusted to the wiping pressure Pw.

[0111] If only the first control is performed and the second control is not, the nozzle pressure may drop to a pressure lower than the lower limit of the nozzle pressure range during wiping. The reason for this is as follows.

[0112] In the inkjet printer 1, the ink path connecting the pressure tank 31 and the inkjet head 11 is relatively long, so it takes some time for a constant pressure to be applied to the entire ink path after pressurizing the pressure tank 31. As a result, the nozzle pressure may be lower than the pressure in the pressure tank 31. Consequently, even if the nozzle pressure has dropped to the value that would occur if the pressure in the pressure tank 31 had dropped to a specified value, the pressure in the pressure tank 31 detected by the pressure sensor 67 may be higher than the specified value, and the pressure tank 31 may not be pressurized. As a result, the nozzle pressure may drop to a pressure lower than the lower limit of the nozzle pressure range during wiping.

[0113] Furthermore, if only the second control is performed and the first control is not performed, it will not be feedback control, which may result in the nozzle pressure reaching an unexpected value.

[0114] Therefore, the inkjet printing device 1 combines the first control and the second control.

[0115] Here, the specified value in the first control and the specified time in the second control are set according to the length of the ink path, which consists of an ink circulation pipe 41 and a distributor 34 connecting the pressurized tank 31 and the inkjet head 11.

[0116] In the first control, the specified value is set to a larger value the longer the ink path. Also, in the second control, the specified time is set to a shorter time the longer the ink path. This is because the longer the ink path, the longer the time from when the pressure tank 31 is pressurized until the inkjet head 11 is pressurized, so the pressure tank 31 is pressurized earlier.

[0117] Figure 7 shows an example of the pressure changes in the pressurized tank 31 due to the processing of the flowchart in Figure 6 described above.

[0118] At time t1 in Figure 7, a purging pressure Pp is generated in the pressurized tank 31 (step S1 in Figure 6). Subsequently, the pressurized tank 31 gradually depressurizes due to the reduction of ink in the pressurized tank 31 as a result of purging.

[0119] From time t1 to time t2, after the purge pressure maintenance period, the pressure in the pressurizing tank 31 is adjusted to the wiping pressure Pw, and at time t3, the pressure in the pressurizing tank 31 becomes the wiping pressure Pw (step S3 in Figure 6). At this time t3, nozzle pressure maintenance adjustment begins.

[0120] As described above, the pressure in the pressurized tank 31 gradually decreases from time t3 as air escapes from the pressurized atmospheric release valve 63 and the pressurized pressure adjustment valve 65, etc. At time t4, pressurization of the pressurized tank 31 to the adjustment pressure Pc begins when the pressure in the pressurized tank 31 falls below the specified value due to the decrease in pressure, or when the specified time has elapsed since the start of nozzle pressure maintenance adjustment (time t3). Then, at time t5, the pressure in the pressurized tank 31 becomes the adjustment pressure Pc (step S6 in Figure 6).

[0121] Subsequently, at times t6 and t8, pressurization of the pressurized tank 31 to the adjustment pressure Pc begins either because the pressure in the pressurized tank 31 falls below the specified value or because the specified time has elapsed since the most recent pressurization of the pressurized tank 31, and at times t7 and t9, the pressure in the pressurized tank 31 becomes the adjustment pressure Pc (step S6 in Figure 6).

[0122] By adjusting the pressure in the pressurized tank 31 in this way, the nozzle pressure is maintained within the wiping nozzle pressure range until the wiping is completed at time t10.

[0123] As described above, in the inkjet printing apparatus 1, when cleaning the inkjet head 11, the control unit 8 controls the pressure generation unit 7 to pressurize the inkjet head 11 and perform a purge to discharge ink from each nozzle 18, and then adjusts the nozzle pressure of each nozzle 18 to the set nozzle pressure during wiping within the nozzle pressure range during wiping. Subsequently, the control unit 8 controls the pressure generation unit 7 to perform nozzle pressure maintenance adjustment, which involves pressurizing the inkjet head 11 before the nozzle pressure drops below the lower limit of the nozzle pressure range during wiping until wiping of the nozzle surface 17a is completed, thereby maintaining the nozzle pressure within the nozzle pressure range during wiping. This reduces the possibility of a slight positive pressure not being maintained at the nozzle until wiping is completed, thus reducing the chance of foreign matter being sucked into the nozzle 18.

[0124] Specifically, the control unit 8 performs a first control, in which the pressure generation unit 7 pressurizes the pressurized tank 31 when the pressure in the pressurized tank 31 falls below a specified value, and a second control, in which the pressure generation unit 7 pressurizes the pressurized tank 31 when a specified time has elapsed from the start of nozzle pressure maintenance adjustment and when a specified time has elapsed from the most recent pressurization of the pressurized tank 31. This pressurizes the inkjet head 11 before the nozzle pressure drops below the lower limit of the wiping nozzle pressure range, thereby maintaining the nozzle pressure within the wiping nozzle pressure range. As a result, the nozzle pressure can be maintained within the wiping nozzle pressure range with high precision.

[0125] Furthermore, in the inkjet printing apparatus 1, the specified value in the first control and the specified time in the second control are set according to the length of the ink path connecting the pressure tank 31 and the inkjet head 11. This makes it possible to maintain the nozzle pressure within the wiping nozzle pressure range with high precision while suppressing excessive frequency of pressurization during nozzle pressure maintenance adjustment.

[0126] In the embodiment described above, each inkjet head 11 is shown to eject one color of ink, but a configuration in which one inkjet head ejects multiple colors of ink is also possible. In this case, it is possible to reduce the chance of other colored inks being drawn into the nozzle and causing ink mixing within the nozzle.

[0127] Furthermore, although the above-described embodiment combines the first and second controls, only one of the controls may be performed. Even in this case, it is possible to reduce the likelihood that the nozzle pressure will not be maintained within the wiping nozzle pressure range until wiping is completed.

[0128] Furthermore, while the above-described embodiment shows a configuration in which pressure is applied to the inkjet head 11 by applying pressure to the pressurized tank 31, the invention is not limited to this, and any method that can apply pressure to the inkjet head is acceptable.

[0129] Furthermore, in the embodiment described above, the specified value in the first control and the specified time in the second control were set according to the length of the ink path connecting the pressurized tank 31 and the inkjet head 11. However, the invention is not limited to this, and a common specified value and specified time may be set for different ink path lengths.

[0130] The present invention is not limited to the embodiments described above, and the components can be modified and implemented in practice without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiments.

[0131] [Note] This application discloses the following invention:

[0132] (Note 1) An inkjet head having nozzles for ejecting ink, A pressure application unit that applies pressure to the inkjet head, After purging by pressurizing the inkjet head to discharge ink from the nozzles, the control unit controls the pressure application unit to adjust the nozzle pressure to a predetermined range of slightly positive pressure where no ink is discharged, and then, until wiping of the nozzle surface where the nozzles of the inkjet head open is completed, pressurize the inkjet head to maintain the nozzle pressure within the predetermined range before the pressure drops below the lower limit of the predetermined range, thereby performing nozzle pressure maintenance adjustment. An inkjet printing apparatus characterized by comprising the following features.

[0133] (Note 2) The aforementioned inkjet head is connected to an ink storage tank via an ink path, The pressure application unit applies pressure to the inkjet head by applying pressure to the tank, The inkjet printing apparatus according to Appendix 1, characterized in that the control unit maintains the nozzle pressure within the predetermined range by controlling, in the nozzle pressure maintenance adjustment, the pressure application unit to pressurize the tank when the pressure in the tank falls below a predetermined value, and the pressure application unit to pressurize the tank when a predetermined time has elapsed from the start of the nozzle pressure maintenance adjustment and when a predetermined time has elapsed from the most recent pressurization of the tank.

[0134] (Note 3) The inkjet printing apparatus according to Appendix 2, characterized in that the specified value and the specified time are set according to the length of the ink path. [Explanation of symbols]

[0135] 1. Inkjet printing device 2. Conveying section 3 Printing Department 4. Maintenance Department 5,5A~5D Ink circulation section 6, 6A~6D Ink Refill Section 7 Pressure generation unit 8 Control Unit 9 Print media 11, 11A~11D Inkjet Heads 12 Head holders 16 Head Modules 17 Nozzle Plate 17a Nozzle surface 18 nozzles 19. Rotating shaft 21 Ink receiving section 22 wipers 31 Pressurized tank 32 Pressurized tank liquid level sensor 33 Ink Filter 34 Distributor 35 Collector 36. Vacuum Tank 37. Vacuum Tank Liquid Level Sensor 38 Ink pump 39 Ink temperature adjustment section 40. Ink temperature sensor 41-43 Ink circulation tube 51 Heater 52 Heater temperature sensor 53 Heatsink 54 Cooling fan 56 Ink Cartridges 57 Ink refill valve 58 Ink Refill Tube 61 Pressurized common air chamber 62 Pressurized connecting pipe 63 Pressurized atmospheric release valve 64 Pressurized atmospheric vent pipe 65 Pressure Regulating Valve 66 Pressurized pressure regulating tube 67 Pressure Sensor 68 Negative pressure common air chamber 69. Negative pressure communication pipe 70. Negative pressure atmospheric release valve 71. Negative pressure atmospheric release pipe 72. Negative pressure regulating valve 73. Negative pressure regulating pipe 74. Negative pressure sensor 75 Air pump 76 Piping for air pumps 77 Confluence pipe 78 Air filter 79 Overflow Pan 80 Overflow Balls 81 Overflow liquid level sensor

Claims

1. An inkjet head having nozzles for ejecting ink, A pressure application unit that applies pressure to the inkjet head, After purging by pressurizing the inkjet head to discharge ink from the nozzles, the control unit controls the pressure application unit to adjust the nozzle pressure to a predetermined range of slightly positive pressure where no ink is discharged, and then, until wiping of the nozzle surface where the nozzles of the inkjet head open is completed, pressurize the inkjet head to maintain the nozzle pressure within the predetermined range before the pressure drops below the lower limit of the predetermined range, thereby performing nozzle pressure maintenance adjustment. An inkjet printing apparatus characterized by comprising the following features.

2. The aforementioned inkjet head is connected to an ink storage tank via an ink path, The pressure application unit applies pressure to the inkjet head by applying pressure to the tank, The inkjet printing apparatus according to claim 1, characterized in that the control unit maintains the nozzle pressure within the predetermined range by controlling, in the nozzle pressure maintenance adjustment, the pressure application unit to pressurize the tank when the pressure in the tank falls below a predetermined value, and the pressure application unit to pressurize the tank when a predetermined time has elapsed from the start of the nozzle pressure maintenance adjustment and when a predetermined time has elapsed from the most recent time the tank has been pressurized.

3. The inkjet printing apparatus according to claim 2, characterized in that the specified value and the specified time are set according to the length of the ink path.

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