Inkjet recording device and method for detecting abnormality in flow path part of inkjet head

Abstract

The present invention detects an abnormality in a flow path part of an inkjet head at an early stage. This inkjet recording device comprises: a pressure control part that controls the operation of a pressure adjustment part such that the pressure inside an inlet is gradually reduced while the difference between the pressure inside the inlet and the pressure inside an outlet is maintained constant; and a pressure determination part that determines whether or not an air bubble entrainment pressure, which is the pressure inside the inlet when the nozzle of an inkjet head starts to entrain air bubbles due to a meniscus break, is within the normal air bubble entrainment pressure range.

Description

Inkjet recording apparatus and method for detecting abnormality in flow path portion of inkjet head

[0001] The present invention relates to an inkjet recording apparatus and a method for detecting an abnormality in a flow path portion of an inkjet head.

[0002] An inkjet head of an inkjet recording apparatus has an inlet for introducing ink as a liquid and an outlet for导出 the ink to the outside. Further, a plurality of nozzles for ejecting ink are formed at the tip of the inkjet head. The inkjet head has a flow path portion inside thereof for circulating ink between the inlet and the outlet (see Patent Document 1).

[0003] Further, in order to suppress an increase in the viscosity of the ink in the nozzle and stabilize the ejection operation of the nozzle, the inkjet recording apparatus described in Patent Document 1 includes an ink circulation apparatus for circulating ink between the inkjet head and the outside.

[0004] Japanese Patent Application Laid-Open No. 2022-51512

[0005] By the way, when an abnormality occurs in the flow path portion of the inkjet head, for example, due to混入 of foreign matter, the flow performance of the flow path portion of the inkjet head deteriorates, which may cause image defects in the inkjet recording apparatus. On the other hand, in the inkjet recording apparatus described in Patent Document 1, there is no means for detecting the presence or absence of an abnormality in the flow path portion of the inkjet head, and the abnormality in the flow path portion of the inkjet head cannot be discovered early.

[0006] Therefore, an object of the present invention is to provide an inkjet recording apparatus and a method for detecting an abnormality in a flow path portion of an inkjet head that can early discover an abnormality in the flow path portion of the inkjet head.

[0007] One aspect of the inkjet recording apparatus of the present invention includes: a pressure adjustment unit for adjusting the pressure inside the inlet and outlet of an inkjet head; a pressure control unit for controlling the operation of the pressure adjustment unit so as to gradually decrease the pressure inside the inlet while maintaining a constant differential pressure between the pressure inside the inlet and the pressure inside the outlet; and a pressure determination unit for determining whether the bubble entrapment pressure, which is the pressure inside the inlet at which the nozzle of the inkjet head begins to entrap bubbles due to meniscus breakage as the pressure inside the inlet decreases, is within the range of normal bubble entrapment pressure that would be expected if the flow path for circulating liquid between the inlet and the outlet in the inkjet head were functioning correctly.

[0008] One aspect of the method for detecting abnormalities in the flow path of an inkjet head according to the present invention comprises: a pressure reduction step of gradually decreasing the pressure in the inlet while maintaining a constant differential pressure between the pressure in the inlet and the pressure in the outlet of the inkjet head; and a pressure determination step of determining whether the bubble entrapment pressure, which is the pressure in the inlet at which the nozzle of the inkjet head begins to entrap bubbles due to meniscus breakage as the pressure in the inlet decreases, is within the range of normal bubble entrapment pressure that would be expected if the flow path for circulating liquid between the inlet and the outlet of the inkjet head were functioning correctly.

[0009] According to the present invention, abnormalities in the flow path of an inkjet head can be detected early.

[0010] Figure 1 is a schematic front view of the inkjet recording apparatus according to this embodiment. Figure 2 is a schematic bottom view of the head unit according to this embodiment, showing a state in which multiple inkjet heads are mounted on a carriage. Figure 3 is a schematic front view of the inkjet head according to this embodiment, showing a state in which the inkjet head is mounted on a carriage. Figure 4 is a schematic cross-sectional view of the flow path section of the inkjet head according to this embodiment. Figure 5 is a schematic perspective view showing the relationship between the wiring board, the channel board, and the nozzle plate. Figure 6 is a schematic plan view of the nozzle plate. Figure 7 is an enlarged cross-sectional view along line II in Figure 4, showing how a meniscus is formed inside the nozzle. Figure 8 is an enlarged cross-sectional view along line II in Figure 4, showing how the nozzle entrains air bubbles due to a break in the meniscus. Figure 9 is a schematic diagram showing the ink circulation device and related configurations according to this embodiment. Figure 10 is a control block diagram of the inkjet recording apparatus according to this embodiment. Figure 11 is a flowchart illustrating the abnormality detection method for the flow path section of the inkjet head according to this embodiment. Figure 12 is an enlarged cross-sectional view along line II in Figure 4, showing how ink leaks from the nozzle due to a meniscus break. Figure 13 is a schematic diagram showing an ink circulation device and related configurations according to a modified example of this embodiment. Figure 14 is a control block diagram of an inkjet recording device according to a modified example of this embodiment. Figure 15 is a flowchart illustrating a method for setting the pressure in the inlet of an inkjet head according to a modified example of this embodiment.

[0011] The following description of this embodiment will be made with reference to the drawings. In this embodiment, the transport direction is the direction in which the recording medium is transported. The flow direction is the direction in which the ink as a liquid flows. In this embodiment, the X-axis direction is the main scanning direction, which is perpendicular to the transport direction. The Y-axis direction is the sub-scanning direction, which is the transport direction.

[0012] The overall configuration of the inkjet recording apparatus 10 according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a schematic front view of the inkjet recording apparatus 10 according to this embodiment. Figure 2 is a schematic bottom view of the head unit 42 according to this embodiment, showing a state in which a plurality of inkjet heads 46 are mounted on the carriage 44.

[0013] As shown in Figure 1, the inkjet recording apparatus 10 according to this embodiment is a recording apparatus that forms a color image on a recording medium P by injecting four colors of liquid ink toward the recording medium P at appropriate timings while moving the recording medium P in the transport direction. In addition to paper such as plain paper and coated paper, various media that can fix the ink that lands on the surface can be used as the recording medium P, such as cloth and resin film. The inkjet recording apparatus 10 uses liquid ink that changes phase between gel and sol (liquid) depending on the temperature. For example, energy ray irradiation type ink such as UV ink, which is gel-like at room temperature, changes to a sol when heated, and solidifies when irradiated with energy rays during image formation, can be used.

[0014] The inkjet recording device 10 includes a device body 12 that extends in the left-right direction in Figure 1. The device body 12 has a center frame 14, a first side frame 16 located on one side of the center frame 14, and a second side frame 18 located on the other side of the center frame 14.

[0015] The first side frame 16 is provided with a paper feeding unit 20 for feeding recording media P. The paper feeding unit 20 has a plate-shaped paper feeding tray 22 for placing recording media P, and the paper feeding tray 22 is mounted on the first side frame 16 so as to be movable in the vertical direction. The paper feeding tray 22 is configured to move up and down according to the amount of recording media P to be placed on it, and the uppermost recording media P is held at a predetermined height position.

[0016] The paper feeding unit 20 has a transport unit 24 for transporting the recording medium P fed from the paper feeding tray 22 in the transport direction. The transport unit 24 is provided extending from the first side frame 16 to the center frame 14. The transport unit 24 has a plurality of rotatable support rollers 26 and an endless belt 28 that is wrapped around the plurality of support rollers 26. By causing the belt 28 to circulate through the rotation of the plurality of support rollers 26, the recording medium P fed from the paper feeding tray 22 is transported in the transport direction.

[0017] The center frame 14 is provided with an image forming unit 30 for ejecting ink onto a recording medium P to form an image. The image forming unit 30 has an image forming drum 32 that carries the recording medium P, and the image forming drum 32 is rotatably mounted on the center frame 14. With the recording medium P carried on the outer surface (conveying surface) of the image forming drum 32, the image forming drum 32 is rotated by driving a motor (not shown) for the image forming drum, thereby conveying the recording medium P in the conveying direction.

[0018] The image forming unit 30 has a transfer unit 34 for transferring the recording medium P from the transport unit 24 to the image forming drum 32. The transfer unit 34 is provided between the transport unit 24 and the image forming drum 32 in the center frame 14. The transfer unit 34 has a swing arm 36 that supports one end of the recording medium P transported by the transport unit 24, and a transfer drum 38 that transfers the recording medium P supported on the swing arm 36 to the image forming drum 32. By supporting one end of the recording medium P on the transport unit 24 with the swing arm 36 and transferring it to the transfer drum 38, the recording medium P is transferred from the transfer drum 38 to the image forming drum 32.

[0019] The image forming unit 30 has a medium heating unit 40 for heating the recording medium P supported on the image forming drum 32. The medium heating unit 40 is located on the downstream side of the transfer drum 38 in the transport direction on the center frame 14. The medium heating unit 40 is positioned opposite the outer circumferential surface of the image forming drum 32. The medium heating unit 40 has, for example, an infrared heater and heats the image forming drum 32 and the recording medium P so that the recording medium P transported by the image forming drum 32 reaches a temperature within a predetermined range.

[0020] As shown in Figures 1 and 2, the image forming unit 30 has a plurality of head units 42 that eject ink onto a recording medium P supported on an image forming drum 32 to form an image. The plurality of head units 42 are arranged downstream of the medium heating unit 40 in the transport direction. The plurality of head units 42 are units corresponding to four colors of ink: yellow (Y), magenta (M), cyan (C), and black (K). The plurality of head units 42 corresponding to the four colors of ink (Y, M, C, K) are arranged at intervals along the transport direction, starting from the upstream side in the transport direction.

[0021] Each head unit 42 is held in a carriage 44 that is mounted on the center frame 14 so as to be movable in the main scanning direction (X-axis direction). In other words, each head unit 42 is mounted on the center frame 14 so as to be movable in the X-axis direction via each carriage 44. Each head unit 42 moves in the X-axis direction between a printing position for printing (image formation) and a maintenance position for maintenance.

[0022] Each head unit 42 has a plurality of inkjet heads 46 that eject ink onto the recording medium P, and the plurality of inkjet heads 46 are mounted on a carriage 44 which serves as a mounting base. The plurality of inkjet heads 46 are arranged, for example, in a staggered pattern along the X-axis. In other words, each head unit 42 constitutes a line head including the plurality of inkjet heads 46. Figure 2 conceptually shows the plurality of inkjet heads 46.

[0023] As shown in Figure 1, the image forming unit 30 has a fixing unit 48 for fixing ink to the recording medium P, and the fixing unit 48 is provided on the downstream side in the transport direction of the plurality of head units 42 in the center frame 14. The fixing unit 48 is positioned opposite the outer circumferential surface of the image forming drum 32. The fixing unit 48 has a light-emitting unit that irradiates energy rays such as ultraviolet light. The light-emitting unit of the fixing unit 48 applies a predetermined amount of energy to the ink ejected onto the recording medium P, thereby curing the ink and fixing it to the recording medium P.

[0024] The image forming unit 30 has a delivery unit 50 that transports the recording medium P, which has been irradiated with energy rays, from the image forming drum 32 in the transport direction. The delivery unit 50 is provided extending from the center frame 14 to the second side frame 18. The delivery unit 50 has a plurality of rotatable support rollers 52, an endless belt 54 provided to wrap around the plurality of support rollers 52, and a transfer drum 56 that transfers the recording medium P from the image forming drum 32 to the belt 54. By causing the belt 54 to circulate through the rotation of the plurality of support rollers 52, the recording medium P sent out from the image forming drum 32 is transported in the transport direction.

[0025] The second side frame 18 is provided with a paper output section 58 for ejecting the image-formed recording medium P. The paper output section 58 has a plate-shaped paper output tray 60 for placing the image-formed recording medium P. The paper output section 58 stores the recording medium P until the user removes it from the paper output tray 60.

[0026] Next, the specific configuration of the inkjet head 46 according to this embodiment will be described with reference to Figures 3 to 8. Figure 3 is a schematic front view of the inkjet head 46 according to this embodiment, showing the inkjet head 46 mounted on the carriage 44. Figure 4 is a schematic cross-sectional view of the flow path section of the inkjet head 46 according to this embodiment. Figure 5 is a schematic perspective view showing the relationship between the wiring board 84, the channel board 86, and the nozzle plate 88. Figure 6 is a schematic plan view of the nozzle plate 88. Figures 7 and 8 are enlarged cross-sectional views along line II in Figure 4, where Figure 7 shows the formation of a meniscus within the nozzle 88n, and Figure 8 shows the nozzle 88n entrapping air bubbles due to a break in the meniscus.

[0027] As shown in Figures 3 and 4, the inkjet head 46 is mounted on a carriage 44 which serves as a mounting base, and covers a through-hole 44h formed in the carriage 44. The inkjet head 46 also has a housing 62, which is attached to the carriage 44 by a plurality of mounting bolts 64. The housing 62 has an opening 62a at its bottom (lower side). The housing 62 is made of a metal such as aluminum alloy. A box-shaped cover member 66 is provided on the upper side of the housing 62, and the cover member 66 is made of a metal such as resin or aluminum alloy.

[0028] An inlet 68 for introducing ink into the housing 62 from the outside is provided at one end of the upper surface of the housing 62 in the X-axis direction. An outlet 70 for guiding ink out of the housing 62 to the outside is provided at the other end of the upper surface of the housing 62 in the X-axis direction.

[0029] As shown in Figure 4, a manifold 72 extending in the X-axis direction is provided inside the housing 62, and the manifold 72 has an opening 72a at its bottom. The manifold 72 is made of a resin such as polyimide resin. A common ink chamber 72c for storing ink is formed inside the manifold 72, and the common ink chamber 72c extends from one end to the other in the X-axis direction of the manifold 72. Ink discharge chambers 72e for discharging ink to the outside of the manifold 72 are formed at both ends in the X-axis direction inside the manifold 72. The common ink chamber 72c and the ink discharge chambers 72e constitute part of the flow path for circulating liquid ink between the inlet 68 and the outlet 70 inside the inkjet head 46.

[0030] One end of the ink supply channel 74 is connected to one end of the common ink chamber 72c in the X-axis direction, and the other end of the ink supply channel 74 is connected to the inlet 68. The common ink chamber 72c is in communication with the inlet 68 via the ink supply channel 74. The ink supply channel 74 is located upstream in the ink flow direction within the inkjet head 46. A filter (not shown) for removing impurities from the ink is placed in the middle of the ink supply channel 74. Alternatively, the filter may be placed in the common ink chamber 72c instead of in the middle of the ink supply channel 74. The ink supply channel 74 and the filter constitute a part of the flow path section of the inkjet head 46.

[0031] One end of the first ink discharge channel 76 is connected to the other end of the common ink chamber 72c in the X-axis direction. One end of each second ink discharge channel 78 is connected to each ink discharge chamber 72e. The other end of the first ink discharge channel 76 and the other end of each second ink discharge channel 78 are connected by a merging section 80. One end of the third ink discharge channel 82 is connected to the merging section 80, and the other end of the third ink discharge channel 82 is connected to the outlet 70.

[0032] The common ink chamber 72c is connected to the outlet 70 via the first ink discharge channel 76, the confluence section 80, and the third ink discharge channel 82. Each ink discharge chamber 72e is connected to the outlet 70 via each second ink discharge channel 78, the confluence section 80, and the third ink discharge channel 82. The first ink discharge channel 76, each second ink discharge channel 78, the confluence section 80, and the third ink discharge channel 82 are located on the downstream side in the ink flow direction within the inkjet head 46. The first ink discharge channel 76, the second ink discharge channel 78, the confluence section 80, and the third ink discharge channel 82 constitute a part of the flow path section of the inkjet head 46.

[0033] As shown in Figures 4 and 5, a wiring board 84 extending in the X-axis direction is provided on the lower side of the manifold 72 so as to close the opening 72a, and the wiring board 84 is, for example, a glass substrate. Multiple first through holes 84h are formed on the wiring board 84 at intervals in the X-axis direction, and the arrangement of the multiple first through holes 84h is in multiple rows (for example, two rows) in the Y-axis direction. Second through holes 84b are formed on both ends of the wiring board 84 in the X-axis direction. A wiring pattern (not shown) is also formed on the wiring board 84, and the wiring pattern is connected to a power supply circuit (not shown) via a flexible circuit board (not shown). The first through holes 84h and the second through holes 84b constitute a part of the flow path of the inkjet head 46.

[0034] A channel board 86 extending in the X-axis direction is provided on the underside of the wiring board 84. The channel board 86 has ink channels (pressure chambers) 86c and dummy channels (pseudo-pressure chambers) 86d alternately formed in the X-axis direction. The arrangement of the ink channels 86c and dummy channels 86d is in multiple rows (for example, two rows) in the Y-axis direction. Each ink channel 86c communicates with a common ink chamber 72c via a corresponding first through-hole 84h. Each dummy channel 86d is a sealed air chamber and does not communicate with the common ink chamber 72c.

[0035] The walls of each ink channel 86c in the X-axis direction are each composed of piezoelectric elements. The piezoelectric elements of each ink channel 86c undergo shear deformation when a voltage is applied from the power supply circuit via the wiring patterns of the flexible circuit board and the wiring board 84. The shear deformation of the piezoelectric elements of each ink channel 86c causes pressure fluctuations within each ink channel 86c. Note that the configuration of the channel board 86 may be modified to omit the multiple dummy channels 86d.

[0036] Discharge channels 86e are formed at both ends of the channel substrate 86 in the X-axis direction, and each discharge channel 86e communicates with each ink discharge chamber 72e via a second through hole 84b. The ink channel 86c, dummy channel 86d, and discharge channel 86e constitute a part of the flow path of the inkjet head 46.

[0037] As shown in Figures 4 to 6, a nozzle plate 88 extending in the X-axis direction is provided on the lower side of the channel substrate 86, and the nozzle plate 88 is positioned inside the opening 62a of the housing 62. The nozzle plate 88 is made of a metal such as stainless steel or nickel alloy. Multiple nozzles 88n for ejecting (discharging) ink are formed on the channel substrate 86 at intervals in the X-axis direction, and the arrangement of the multiple nozzles 88n is in multiple rows (for example, two rows) in the Y-axis direction. Each nozzle 88n communicates with a corresponding ink channel 86c and is configured to eject ink by pressure fluctuations within the corresponding ink channel 86c.

[0038] As shown in Figures 4 to 8, a pair of return channels 88r are formed near each nozzle 88n on the upper surface of the nozzle plate 88 to return a portion of the ink supplied to each ink channel 86c back to the outlet 70. Each pair of return channels 88r communicates with the corresponding ink channel 86c. The nozzles 88n and return channels 88r constitute a part of the flow path section of the inkjet head 46.

[0039] Multiple common return channels 90 extending in the X-axis direction are formed between the channel substrate 86 and the nozzle plate 88, and these multiple common return channels 90 are spaced apart in the Y-axis direction. Each common return channel 90 communicates with multiple return channels 88r and discharge channels 86e. The common return channels 90 constitute a part of the flow path section of the inkjet head 46.

[0040] With the above configuration, a portion of the ink supplied from the common ink chamber 72c to the ink channel 86c via the first through-hole 84h flows into the discharge channel 86e via the return flow path 88r and the common return flow path 90 without being ejected from the nozzle 88n. The ink that flows into the discharge channel 86e flows into the ink discharge chamber 72e via the second through-hole 84b.

[0041] As shown in Figure 9, the inkjet recording device 10 is equipped with an ink circulation device 92 that circulates ink between a plurality of inkjet heads 46 and the outside. Figure 9 is a schematic diagram showing the ink circulation device 92 and related configuration according to this embodiment. In Figure 9, only one ink circulation device 92 is shown, but the inkjet recording device 10 is equipped with a plurality of ink circulation devices 92 that circulate the four colors of ink: Y, M, C, and K. The specific configuration of the ink circulation device 92 is as follows.

[0042] The carriage 44 is equipped with an ink tank (sub-tank) 94 for storing ink. One end of the first main channel 96 is connected to the ink tank 94, and the first main channel 96 has a plurality of branched channels 96b on the other end. The tip of each branched channel 96b is connected to the inlet 68 of each inkjet head 46.

[0043] In the middle of the first main flow path 96, a first pump 98 for feeding the ink in the ink tank 94 to the inlet 68 side of the plurality of ink jet heads 46 is disposed. Near the first pump 98 in the middle of the first main flow path 96, a first pressure control valve 100 that can be opened to the atmosphere is disposed. The first pump 98 and the first pressure control valve 100 correspond to a first pressure adjustment unit that adjusts the pressure in the inlet 68 of the plurality of ink jet heads 46. The first pressure adjustment unit is not limited to the first pump 98 and the first pressure control valve 100, and other configurations other than the first pump 98 and the first pressure control valve 100 may be used.

[0044] A first pressure sensor 102 as a first pressure detection unit for detecting the pressure in the inlet 68 is provided at or near the inlet 68 of each ink jet head 46. Further, in the middle of each branch flow path 96b, a flow rate sensor 104 for detecting the flow rate of the ink flowing into the inlet 68 of each ink jet head 46 is disposed. Instead of disposing the flow rate sensor 104 in the middle of each branch flow path 96b, the flow rate sensor 104 may be disposed in a portion upstream of the branch portion in the flow direction in the first main flow path 96.

[0045] A main tank (not shown) for storing ink is provided at a position separated from the carriage 44. One end of a second main flow path 106 is connected to the ink tank 94, and the other end of the second main flow path 106 is connected to the main tank. In the middle of the second main flow path 106, a second pump 108 for feeding the ink in the main tank to the ink tank 94 side is disposed.

[0046] One end (not shown) of a third main flow path 110 is connected to the main tank. In other words, one end of the third main flow path 110 is connected to the main tank. One end of the third main flow path 110 may be connected to the main tank via a recovery side sub-tank (not shown). Further, the other end side of the third main flow path 110 has a plurality of branched flow paths 110b. The tip of each branch flow path 110b is connected to the outlet 70 of each ink jet head 46.

[0047] In the middle of the third main flow path 110, a third pump 112 for sending ink from the outlet 70 side of the plurality of inkjet heads 46 to the main tank side is disposed. Near the third pump 112 in the middle of the third main flow path 110, an atmospheric pressure releasable second pressure control valve 114 is disposed. The third pump 112 and the second pressure control valve 114 correspond to a second pressure adjustment unit that adjusts the pressure in the outlet 70 of the plurality of inkjet heads 46. The second pressure adjustment unit is not limited to the third pump 112 and the second pressure control valve 114, and a configuration other than the third pump 112 and the second pressure control valve 114 may be used. A second pressure sensor 116 as a second pressure detection unit for detecting the pressure in the outlet 70 is provided at or near the outlet 70 of each inkjet head 46.

[0048] Near each branch flow path 110b, an ultrasonic sensor 118 as a bubble detection unit for detecting the presence or absence of bubbles in the ink discharged from the outlet 70 of each inkjet head 46 is provided. Each ultrasonic sensor 118 detects the presence or absence of bubbles in the ink based on a change in the reception intensity. Instead of providing the ultrasonic sensor 118 near each branch flow path 110b, the ultrasonic sensor 118 may be provided near a portion on the downstream side in the flow direction from the branch portion in the third main flow path 110. The ink circulation device 92 may include a photosensor that detects the presence or absence of bubbles in the ink based on a change in the amount of received light instead of the ultrasonic sensor 118 as the bubble detection unit.

[0049] Referring to FIGS. 7, FIG. 8, and FIG. 10, the control configuration of the inkjet recording apparatus 10 according to the present embodiment will be described. FIG. 10 is a control block diagram of the inkjet recording apparatus 10 according to the present embodiment.

[0050] As shown in Figure 10, the inkjet recording device 10 includes a control unit 120 that controls the paper feeding unit 20, the image forming unit 30, and the ink circulation device 92, etc. The control unit 120 is responsible for controlling the entire inkjet recording device 10. The control unit 120 has a CPU 122 (Central Processing Unit), ROM 124 (Read Only Memory), RAM 126 (Random Access Memory), and a storage unit 128. An input / output interface 130 is connected to the control unit 120, and an external device 132 is connected to the input / output interface 130.

[0051] The CPU 122 provides overall control over the operation of the inkjet recording device 10. The CPU 122 reads various control programs and setting data stored in the ROM 124, stores them in the RAM 126, and executes the programs to perform various calculations. The RAM 126 also provides the CPU 122 with a working memory space and stores temporary data. The RAM 126 may also include non-volatile memory.

[0052] ROM 124 stores various control programs and setting data executed by the CPU 122. Alternatively, a rewritable non-volatile memory such as EEPROM (Electrically Erasable Programmable Read Only Memory) or flash memory may be used instead of ROM 124. The storage unit 128 stores print jobs and image data related to those print jobs, which are input from the external device 132 via the input / output interface 130. For example, an HDD (Hard Disk Drive) may be used as the storage unit 128, or DRAM (Dynamic Random Access Memory) may be used in combination.

[0053] The input / output interface 130 mediates the transmission and reception of data between the external device 132 and the control unit 120. The input / output interface 130 is composed of, for example, various serial interfaces, various parallel interfaces, or a combination thereof. The external device 132 is, for example, a personal computer, which supplies print jobs and image data, etc., to the control unit 120 via the input / output interface 130.

[0054] The control unit 120 (CPU 122) executes various control programs and functions as a "pressure control unit," "pressure acquisition unit," and "pressure determination unit" as defined in the claims, as follows. The main components of the control unit 120 are as follows.

[0055] As shown in Figures 7 and 10, the control unit 120, acting as a pressure control unit, controls the operation of the first pump 98 and the first pressure control valve 100, which act as a first pressure adjustment unit, and also controls the operation of the third pump 112 and the second pressure control valve 114, which act as a second pressure adjustment unit. The control unit 120 controls the operation of the first pump 98, etc., so as to apply pressure to the inlet 68 and outlet 70 under conditions that the meniscus in the nozzle 88n does not break (destroy). The meniscus refers to the interface between the ink (liquid) and the outside air inside the nozzle 88n. The operation of the first pump 98, etc. refers to the operation of the first pump 98, the first pressure control valve 100, the third pump 112, and the second pressure control valve 114. As mentioned above, Figure 7 shows the state in which a meniscus has been formed inside the nozzle 88n.

[0056] The control unit 120 controls the operation of the first pump 98 and the like so as to maintain a constant differential pressure between the pressure in the inlet 68 and the pressure in the outlet 70, based on the detection results from each first pressure sensor 102 and each second pressure sensor 116. The control unit 120 controls the operation of the first pump 98 and the like so as to gradually decrease the pressure in the inlet 68 by a predetermined value (for example, 0.1 kPa) while maintaining a constant differential pressure between the pressure in the inlet 68 and the pressure in the outlet 70 (a predetermined differential pressure).

[0057] As shown in Figures 7, 8, and 10, the control unit 120, acting as a pressure acquisition unit, monitors the detection results from multiple ultrasonic sensors 118. The control unit 120 detects the timing at which one of the nozzles 88n begins to entrain bubbles due to meniscus breakage as the pressure inside the inlet 68 decreases. While monitoring the detection results from the multiple ultrasonic sensors 118, the control unit 120 acquires the pressure inside the inlet 68 at the moment when one of the nozzles 88n begins to entrain bubbles due to meniscus breakage as the bubble entrainment pressure. As mentioned above, Figure 8 shows how the nozzle 88n entrains bubbles due to meniscus breakage.

[0058] The control unit 120, acting as a pressure determination unit, determines whether the acquired bubble entrapment pressure is within the normal range of bubble entrapment pressure. Here, the normal range of bubble entrapment pressure refers to the range of bubble entrapment pressure expected when the flow path of the inkjet head 46 is functioning correctly. The normal range of bubble entrapment pressure is set based on the design value of the pressure loss from the inlet 68 to the nozzle 88n, the dimensional tolerances of the components constituting the flow path of the inkjet head 46, and the allowable amount of clogging in the flow path of the inkjet head 46. If a water-repellent coating or other water-repellent treatment is applied to the lower surface of the nozzle plate 88, the normal range of bubble entrapment pressure is set taking into account the state of that water-repellent treatment.

[0059] The control unit 120, acting as a pressure determination unit, determines that the flow paths of the multiple inkjet heads 46 are normal if the bubble entrapment pressure is within the normal range of bubble entrapment pressure. The control unit 120 determines that there is an abnormality in the flow path of one of the inkjet heads 46 if the bubble entrapment pressure is outside the normal range of bubble entrapment pressure. The control unit 120 may also determine the degree of abnormality in the flow path state of one of the inkjet heads 46 according to the degree to which the bubble entrapment pressure deviates from the normal range of bubble entrapment pressure.

[0060] As shown in Figures 9 and 10, the control unit 120 performs a cleaning process on the lower surfaces of the nozzle plates 88 of the multiple inkjet heads 46. Specifically, the control unit 120 performs the cleaning process by driving a known air blow device (not shown), for example, as shown in Japanese Patent Application Publication No. 2022-28185, to blow compressed air onto the lower surfaces of the nozzle plates 88 of the multiple inkjet heads 46. Alternatively, instead of using the air blow device to perform the cleaning process, the control unit 120 may use a known wipe unit (not shown), for example, as shown in Japanese Patent Application Publication No. 2020-609.

[0061] The control unit 120 performs a de-bubbling process in the flow channels of the multiple inkjet heads 46. Specifically, the control unit 120 controls the operation of the first pump 98 and the like to maintain a high pressure difference between the pressure in the inlet 68 and the pressure in the outlet 70, under the condition that the meniscus in the nozzle 88n does not break. Alternatively, the control unit 120 may perform a purging process instead of maintaining the high pressure difference between the pressure in the inlet 68 and the pressure in the outlet 70, under the condition that the meniscus in the nozzle 88n does not break. If the control unit 120 performs a purging process, it performs a cleaning process following the purging process.

[0062] Referring to Figures 10 and 11, a method for detecting abnormalities in the flow path of an inkjet head according to this embodiment will be described. Figure 11 is a flowchart illustrating the method for detecting abnormalities in the flow path of an inkjet head according to this embodiment.

[0063] The method for detecting abnormalities in the flow channels of an inkjet head according to this embodiment is a method for detecting whether or not there are abnormalities in the flow channels of a plurality of inkjet heads 46. The method for detecting abnormalities in the flow channels of an inkjet head according to this embodiment includes a cleaning and foam removal step, a pressure reduction step, a pressure acquisition step, and a pressure determination step. The specific details of each step in the method for detecting abnormalities in the flow channels of an inkjet head according to this embodiment are as follows.

[0064] (Cleaning and foam removal process) As shown in Figures 10 and 11, the control unit 120 performs a cleaning process on the lower surface of the nozzle plate 88 of the multiple inkjet heads 46, as described above. Subsequently, the control unit 120 performs a foam removal process on the flow path of the multiple inkjet heads 46, as described above (step S101). The cleaning and foam removal process is performed in a room temperature environment.

[0065] (Pressure Reduction Process) After the cleaning and foam removal process is completed, the control unit 120 controls the operation of the first pump 98, etc., to apply pressure to the inlet 68 and outlet 70 under conditions that the meniscus in the nozzle 88n does not break (step S102). Next, the control unit 120 controls the operation of the first pump 98, etc., to reduce the pressure in the inlet 68 by a predetermined value while keeping the pressure difference between the pressure in the inlet 68 and the pressure in the outlet 70 constant (step S103).

[0066] The control unit 120 then determines, based on the detection results from the multiple ultrasonic sensors 118, whether or not air bubbles are being trapped in any of the nozzles 88n due to a meniscus break (step S104). If it is determined that no air bubbles are being trapped in any of the nozzles 88n (the case of NO in step S104), the control unit 120 returns to step S103. The pressure reduction process is performed under normal temperature conditions.

[0067] (Pressure acquisition process, pressure determination process) If it is determined that air bubbles are being drawn into any of the nozzles 88n (if the answer is YES in step S104), the control unit 120 acquires the pressure inside the inlet 68 at the time when air bubbles begin to be drawn in as the air bubble entrainment pressure (step S105). The control unit 120 then determines whether the acquired air bubble entrainment pressure is within the normal range of air bubble entrainment pressure (step S106).

[0068] If the bubble entrapment pressure is within the normal range (YES in step S106), the control unit 120 determines that the flow paths of the multiple inkjet heads 46 are normal (step S107). On the other hand, if the bubble entrapment pressure is outside the normal range (NO in step S106), the control unit 120 determines that there is an abnormality in the flow path of one of the inkjet heads 46 (step S108). If the bubble entrapment pressure is outside the normal range, the control unit 120 may notify the user to perform a recovery operation, such as replacing the filter. The control unit 120 may also determine the degree of abnormality in the flow path state of one of the inkjet heads 46 according to the degree to which the bubble entrapment pressure deviates from the normal range.

[0069] Furthermore, the cleaning and foam removal steps may be omitted from the configuration of the abnormality detection method for the flow channel of the inkjet head according to this embodiment.

[0070] The entity that performs each step of the abnormality detection method for the flow channel of the inkjet head according to this embodiment is not limited to the control unit 120, but may be an operator. In other words, the abnormality detection method for the flow channel of the inkjet according to this embodiment may be used to detect whether or not there is an abnormality in the flow channel of the inkjet head 46 at the stage before the inkjet recording device 10 is shipped. In this case, a non-volatile inspection liquid that does not contain pigment may be used as the liquid used in the pressure increase process instead of ink.

[0071] According to the configuration of the inkjet recording apparatus 10 in this embodiment, the control unit 120 has the functions of a pressure control unit and a pressure determination unit, as described above. Specifically, the control unit 120 as a pressure control unit controls the operation of the first pump 98, etc., so as to maintain a constant differential pressure between the pressure in the inlet 68 and the pressure in the outlet 70, while gradually decreasing the pressure in the inlet 68. The control unit 120 as a pressure determination unit determines whether the bubble entrapment pressure, which is the pressure in the inlet 68 when any of the nozzles 88n begins to entrap bubbles B, is within the normal range of bubble entrapment pressure. Therefore, if the pressure loss from the inlet 68 to the nozzle 88n increases significantly more than the design value and the bubble entrapment pressure is higher than the normal range of bubble entrapment pressure, it can be determined that there is an abnormality in the flow path of any of the inkjet heads 46. Also, if the pressure loss from the inlet 68 to the nozzle 88n decreases significantly more than the design value and the bubble entrapment pressure is lower than the normal range of bubble entrapment pressure, it can be determined that there is an abnormality in the flow path of any of the inkjet heads 46.

[0072] Therefore, according to the inkjet recording apparatus 10 of this embodiment, abnormalities in the flow path of the inkjet head 46 can be detected early.

[0073] Furthermore, according to the configuration of the inkjet recording apparatus 10 in this embodiment, the control unit 120 has the function of a pressure acquisition unit, as described above. Specifically, the control unit 120, as a pressure acquisition unit, monitors the detection results from a plurality of ultrasonic sensors 118 and acquires the pressure inside the inlet 68 when any of the nozzles 88n begin to entrain bubbles as the bubble entrainment pressure. As a result, the control unit 120 can acquire the bubble entrainment pressure in the flow path of the inkjet head 46 with high accuracy.

[0074] Therefore, according to the inkjet recording apparatus 10 of this embodiment, abnormalities in the flow path of the inkjet head 46 can be accurately detected.

[0075] Furthermore, according to the configuration of the inkjet recording apparatus 10 of this embodiment, as described above, a first pressure sensor 102 for detecting the pressure inside the inlet 68 is provided in or near the inlet 68 of each inkjet head 46. A second pressure sensor 116 for detecting the pressure inside the outlet 70 is provided in or near the outlet 70 of each inkjet head 46. The control unit 120, acting as a pressure control unit, controls the operation of the first pump 98 and the like to maintain a constant differential pressure between the pressure inside the inlet 68 and the pressure inside the outlet 70 based on the detection results from each first pressure sensor 102 and each second pressure sensor 116. Therefore, the control unit 120 can control the differential pressure between the pressure inside the inlet 68 and the pressure inside the outlet 70 with high precision.

[0076] Therefore, according to the inkjet recording apparatus 10 of this embodiment, abnormalities in the flow path of the inkjet head 46 can be accurately detected.

[0077] Furthermore, according to the configuration of the inkjet recording device 10 in this embodiment, as described above, the flow path of the inkjet head 46 has a return flow path 88r for returning a portion of the ink supplied to each ink channel 86c back to the outlet 70 side. Therefore, by circulating ink from the inlet 68 side to the outlet 70 side, ink can be circulated to each ink channel 86c.

[0078] Therefore, according to the inkjet recording apparatus 10 of this embodiment, it is possible to detect whether or not there is an abnormality in substantially the entire area of ​​the flow path of the inkjet head 46.

[0079] According to the configuration of the method for detecting abnormalities in the flow path of an inkjet head according to this embodiment, in the pressure reduction step, the pressure in the inlet 68 is gradually reduced while maintaining a constant differential pressure between the pressure in the inlet 68 and the pressure in the outlet 70. In the pressure determination step, it is determined whether the bubble entrapment pressure, which is the pressure in the inlet 68 when any of the nozzles 88n begins to entrap bubbles B, is within the normal range of bubble entrapment pressure. Therefore, if the pressure loss from the inlet 68 to the nozzle 88n increases significantly more than the design value, and the bubble entrapment pressure is higher than the normal range of bubble entrapment pressure, it can be determined that there is an abnormality in the flow path of any of the inkjet heads 46. Also, if the pressure loss from the inlet 68 to the nozzle 88n decreases significantly more than the design value, and the bubble entrapment pressure is lower than the normal range of bubble entrapment pressure, it can be determined that there is an abnormality in the flow path of any of the inkjet heads 46.

[0080] Therefore, according to the method for detecting abnormalities in the flow channel of the inkjet head according to this embodiment, abnormalities in the flow channel of the inkjet head 46 can be detected at an early stage.

[0081] Furthermore, according to the configuration of the abnormality detection method for the flow channel of the inkjet head according to this embodiment, the pressure acquisition step monitors the detection results from multiple ultrasonic sensors 118. In other words, the pressure acquisition step monitors for the presence or absence of air bubbles in the ink discharged from the outlets 70 of multiple inkjet heads 46. While monitoring for the presence or absence of air bubbles in the ink, the pressure inside the inlet 68 when any of the nozzles 88n begin to entrap air bubbles is acquired as the air bubble entrapment pressure. Therefore, the air bubble entrapment pressure can be acquired with high accuracy in the flow channel of the inkjet head 46.

[0082] Therefore, according to the method for detecting abnormalities in the flow channel of an inkjet head according to this embodiment, abnormalities in the flow channel of the inkjet head 46 can be accurately detected.

[0083] Furthermore, according to the configuration of the abnormality detection method for the flow channel of the inkjet head according to this embodiment, as described above, the pressure reduction process is performed in a room temperature environment. Therefore, the temperature difference across all nozzles 88n can be reduced, and viscosity variations of the ink at each nozzle 88n can be suppressed.

[0084] Therefore, according to the method for detecting abnormalities in the flow channel of an inkjet head according to this embodiment, abnormalities in the flow channel of the inkjet head 46 can be accurately detected.

[0085] Furthermore, according to the configuration of the abnormality detection method for the flow path of the inkjet head according to this embodiment, a non-volatile inspection liquid that does not contain pigment may be used as the liquid used for the pressure reduction treatment. In this case, the viscosity of the ink can be sufficiently stabilized in all nozzles 88n.

[0086] Therefore, according to the method for detecting abnormalities in the flow channel of an inkjet head according to this embodiment, abnormalities in the flow channel of the inkjet head 46 can be detected more accurately.

[0087] A modified version of this embodiment of the inkjet recording device 10A will be described with reference to Figures 7 and 12 to 14. Figure 12 is an enlarged cross-sectional view along line II in Figure 4, showing how ink has leaked from the nozzle 88n due to a meniscus break. Figure 13 is a schematic diagram showing the ink circulation device 92A and related configurations according to a modified version of this embodiment. Figure 14 is a control block diagram of the modified version of the inkjet recording device 10A according to this embodiment.

[0088] As shown in Figure 13, the inkjet recording device 10A according to a modified example of this embodiment has the same configuration as the inkjet recording device 10 according to this embodiment (see Figure 9). The differences in the configuration of the inkjet recording device 10A according to a modified example of this embodiment compared to the configuration of the inkjet recording device 10 according to this embodiment will be explained. For the sake of convenience of explanation, the same reference numerals are used for components that have the same function as those described in this embodiment, and their descriptions will not be repeated.

[0089] A modified version of this embodiment of the ink circulation device 92A includes a camera 134 as an imaging unit provided at an appropriate position on the center frame 14 (see Figure 1). The camera 134 images all nozzles 88n of a plurality of inkjet heads 46 located at the maintenance position. The camera 134 may be movable in the X-axis direction relative to the center frame 14. Multiple cameras 134 may be arranged at intervals in the X-axis direction.

[0090] As shown in Figures 7, 13, and 14, the control unit 120, acting as a pressure control unit, controls the operation of the first pump 98 and the like to apply pressure to the inlet 68 and outlet 70 under conditions where the meniscus in the nozzle 88n does not break. Based on the detection results from each first pressure sensor 102 and each second pressure sensor 116, the control unit 120 controls the operation of the first pump 98 and the like to maintain a constant differential pressure between the pressure in the inlet 68 and the pressure in the outlet 70. While maintaining a constant differential pressure between the pressure in the inlet 68 and the pressure in the outlet 70, the control unit 120 controls the operation of the first pump 98 and the like to gradually increase the pressure in the inlet 68. As mentioned above, Figure 7 shows the state in which a meniscus has been formed in the nozzle 88n.

[0091] As shown in Figures 7 and 12 to 14, the control unit 120, acting as a pressure acquisition unit, monitors the meniscus within all nozzles 88n of the multiple inkjet heads 46 from the captured images taken by the camera 134. While monitoring the meniscus within all nozzles 88n, the control unit 120 acquires the pressure in the inlet 68 as the overflow pressure when ink begins to overflow from any of the nozzles 88n due to a meniscus break as the pressure in the inlet 68 increases. As mentioned above, Figure 12 shows how ink leaks from a nozzle 88n due to a meniscus break.

[0092] As shown in Figures 13 and 14, the control unit 120, acting as a pressure setting unit, sets the pressure inside the inlet 68 during image formation based on the acquired overflow pressure and the acquired bubble entrapment pressure. Specifically, the control unit 120 sets the pressure inside the inlet 68 during image formation based on the overflow pressure and bubble entrapment pressure to suppress ink overflow from the nozzle 88n due to meniscus breakage and bubble entrapment. The pressure inside the inlet 68 during image formation is set using the bubble entrapment pressure and overflow pressure as parameters, taking into account variations in pressure control, pressure changes inside the nozzle 88n during ink ejection, and the negative pressure to be applied to the meniscus. If a water-repellent coating or other water-repellent treatment is applied to the lower surface of the nozzle plate 88, the pressure inside the inlet 68 during image formation is set taking into account the treatment status of that water-repellent treatment.

[0093] Referring to Figures 14 and 15, a method for setting the pressure inside the inkjet head inlet according to a modified example of this embodiment will be described. Figure 15 is a flowchart illustrating the method for setting the pressure inside the inkjet head inlet according to a modified example of this embodiment.

[0094] The modified version of this embodiment provides a method for setting the pressure inside the inlet of an inkjet head. This modified version includes a cleaning and foam removal step, a pressure increase step, a first pressure acquisition step, a pressure decrease step, a second pressure acquisition step, and a pressure setting step. The specific details of each step in the modified version of this embodiment provide are as follows.

[0095] (Cleaning and foam removal process) As shown in Figures 14 and 15, the control unit 120 performs a cleaning process on the lower surface of the nozzle plate 88 of the multiple inkjet heads 46, as described above. Subsequently, the control unit 120 performs a foam removal process on the flow path of the multiple inkjet heads 46, as described above (step S201). The cleaning and foam removal process is performed in a room temperature environment.

[0096] (Pressure Increase Process) After the cleaning and foam removal process is completed, the control unit 120 controls the operation of the first pump 98 and the like to apply pressure to the inlet 68 and outlet 70 under conditions that the meniscus in the nozzle 88n does not break (step S202). Next, the control unit 120 controls the operation of the first pump 98 and the like to increase the pressure in the inlet 68 by a predetermined value while keeping the differential pressure between the pressure in the inlet 68 and the pressure in the outlet 70 constant (step S203).

[0097] The control unit 120 then monitors the meniscus within all nozzles 88n from the captured images taken by the camera 134 and determines whether or not ink overflow has occurred in any of the nozzles 88n due to a meniscus break (step S204). If it is determined that no ink overflow has occurred in any of the nozzles 88n (the case of NO in step S204), the control unit 120 returns to step S203. The pressure increase process is performed under normal temperature conditions.

[0098] (First pressure acquisition step) If it is determined that ink is overflowing from any of the nozzles 88n (if the answer to step S204 is YES), the control unit 120 acquires the pressure inside the inlet 68 at the time the ink begins to overflow as the overflow pressure (step S205).

[0099] (Pressure Reduction Process) After the completion of the first pressure acquisition process, the control unit 120 controls the operation of the first pump 98, etc., to apply pressure to the inlet 68 and outlet 70 under conditions that the meniscus in the nozzle 88n does not break (step S206). Next, the control unit 120 controls the operation of the first pump 98, etc., to reduce the pressure in the inlet 68 by a predetermined value while keeping the differential pressure between the pressure in the inlet 68 and the pressure in the outlet 70 constant (step S207).

[0100] The control unit 120 then determines, based on the detection results from the multiple ultrasonic sensors 118, whether or not air bubbles are being trapped in any of the nozzles 88n due to a meniscus break (step S208). If it is determined that no air bubbles are being trapped in any of the nozzles 88n (the case of NO in step S208), the control unit 120 returns to step S207. The pressure reduction process is performed under normal temperature conditions.

[0101] (Second pressure acquisition step, pressure setting step) If it is determined that air bubbles are being drawn into any of the nozzles 88n (if the answer to step S208 is YES), the control unit 120 acquires the pressure inside the inlet 68 at the time when air bubbles begin to be drawn in as the air bubble drawing pressure (step S209). Then, based on the air bubble drawing pressure and the overflow pressure, the control unit 120 sets the pressure inside the inlet 68 during image formation to suppress ink overflow from the nozzles 88n due to meniscus breakage and air bubble drawing (step S210).

[0102] According to the configuration of the inkjet recording device 10A in a modified example of this embodiment, the control unit 120 has the functions of a pressure acquisition unit and a pressure setting unit, as described above. Specifically, the control unit 120 as a pressure acquisition unit monitors the meniscus in all nozzles 88n and acquires the pressure in the inlet 68 when ink begins to overflow from any of the nozzles 88n as the overflow pressure. The control unit 120 as a pressure acquisition unit monitors the detection results from a plurality of ultrasonic sensors 118 and acquires the pressure in the inlet 68 when any of the nozzles 88n begins to entrain bubbles as the bubble entrainment pressure. The control unit 120 as a pressure setting unit sets the pressure in the inlet 68 during image formation based on the overflow pressure and the bubble entrainment pressure. As a result, ink overflow from the nozzles 88n due to meniscus breakage and bubble entrainment become less likely to occur during image formation.

[0103] Therefore, according to the modified inkjet recording apparatus 10A of this embodiment, an image can be stably formed on the recording medium P (see Figure 1).

[0104] According to the configuration of the pressure setting method in the inlet of the inkjet head according to a modified example of this embodiment, as described above, in the first pressure acquisition step, the pressure in the inlet 68 when ink begins to overflow from any of the nozzles 88n is acquired as the overflow pressure. In the second pressure acquisition step, the pressure in the inlet 68 when any of the nozzles 88n begins to entrain bubbles is acquired as the bubble entrainment pressure. In the pressure setting step, the pressure in the inlet 68 during image formation is set based on the bubble entrainment pressure and the overflow pressure. As a result, ink overflow from the nozzles 88n due to meniscus breakage and bubble entrainment become less likely to occur during image formation.

[0105] Therefore, according to the pressure setting method in the inlet of the inkjet head according to a modified example of this embodiment, an image can be stably formed on the recording medium P (see Figure 1).

[0106] Although this embodiment has been described in detail above, the present invention is not limited to the specific embodiments described above. Various modifications and changes are possible to the specific examples described in the above embodiments within the scope of the gist of the present invention as described in the claims.

[0107] The present invention is useful as an inkjet recording device that can detect abnormalities in the flow path of an inkjet head at an early stage.

[0108] All disclosures in the specification, drawings, and abstract contained in the Japanese application No. 2024-175681, filed on October 7, 2024, are incorporated herein by reference.

[0109] 10 Inkjet recording device 10A Inkjet recording device 12 Device body 14 Center frame 16 First side frame 18 Second side frame 20 Paper feeding section 22 Paper feeding tray 24 Transport section 26 Support roller 28 Belt 30 Image forming section 32 Image forming drum 34 Transfer unit 36 ​​Swing arm 38 Transfer drum 40 Media heating section 42 Head unit 44 Carriage 44h Through hole 46 Inkjet head 48 Fixing section 50 Delivery section 52 Support roller 54 Belt 56 Transfer drum 58 Paper discharge section 60 Paper discharge tray 62 Housing 62a Opening 64 Mounting bolt 66 Cover member 68 Inlet 70 Outlet 72 Manifold 72a Opening 72c Common ink chamber 72e Ink discharge chamber 74 Ink supply channel 76 First ink discharge channel 78 Second ink discharge channel 80 Confluence 82 Third ink discharge channel 84 Wiring board 84h First through hole 84b Second through hole 86 Channel board 86c Ink channel (pressure chamber) 86d Dummy channel (simulated pressure chamber) 86e Discharge channel 88 Nozzle plate 88n Nozzle 88r Return channel 90 Common return channel 92 Ink circulation device 92A Ink circulation device 94 Ink tank (sub-tank) 96 First main channel 96b Branch channel 98 First pump (first pressure adjustment unit) 100 First pressure control valve (first pressure adjustment unit) 102 First pressure sensor (first pressure detection unit) 104 Flow sensor 106 Second main channel 108 Second pump 110 Third main channel 110b Branch channel 112 Third pump (second pressure adjustment unit) 114 Second pressure control valve (second pressure adjustment unit) 116 Second pressure sensor (second pressure detection unit) 118 Ultrasonic sensor (bubble detection unit) 120 Control unit (pressure control unit, pressure acquisition unit, pressure determination unit, pressure setting unit) 122 CPU 124 ROM 126 RAM 128 Storage unit 130 Input / output interface 132 External device 134 Camera (imaging unit) P Recording medium

Claims

1. An inkjet recording apparatus comprising: a pressure adjustment unit for adjusting the pressure inside the inlet and outlet of an inkjet head; a pressure control unit for controlling the operation of the pressure adjustment unit so as to gradually decrease the pressure inside the inlet while maintaining a constant differential pressure between the pressure inside the inlet and the pressure inside the outlet; and a pressure determination unit for determining whether the bubble entrapment pressure, which is the pressure inside the inlet at which the nozzle of the inkjet head begins to entrap bubbles due to meniscus breakage as the pressure inside the inlet decreases, is within the range of normal bubble entrapment pressure expected when the flow path for circulating liquid between the inlet and the outlet in the inkjet head is functioning correctly.

2. An inkjet recording apparatus according to claim 1, comprising: a bubble detection unit for detecting the presence or absence of bubbles in the liquid discharged from the outlet; and a pressure acquisition unit that monitors the detection results from the bubble detection unit and acquires the pressure in the inlet as the pressure in the inlet decreases, at which point the nozzle begins to entrain bubbles due to a meniscus break, as the bubble entrainment pressure, wherein the pressure determination unit determines whether the bubble entrainment pressure acquired by the pressure acquisition unit is within the range of the normal bubble entrainment pressure.

3. The inkjet recording apparatus according to claim 1, wherein the pressure determination unit determines that the flow path of the inkjet head is normal if the bubble entrapment pressure is within the normal range, and determines that there is an abnormality in the flow path of the inkjet head if the bubble entrapment pressure is outside the normal range.

4. The inkjet recording apparatus according to claim 1, comprising: a first pressure detection unit provided in or near the inlet for detecting the pressure inside the inlet; and a second pressure detection unit provided in or near the outlet for detecting the pressure inside the outlet, wherein the pressure control unit controls the operation of the pressure adjustment unit to maintain a constant differential pressure between the pressure inside the inlet and the pressure inside the outlet based on the detection results from the first pressure detection unit and the second pressure detection unit.

5. The inkjet recording apparatus according to claim 1, wherein the flow channel section has a return channel for returning a portion of the liquid supplied to the liquid channel communicating with the nozzle back to the outlet side.

6. The inkjet recording apparatus according to claim 1, wherein the pressure control unit controls the operation of the pressure adjustment unit to gradually increase the pressure in the inlet while maintaining a constant differential pressure between the pressure in the inlet and the pressure in the outlet, and includes a pressure setting unit that sets the pressure in the inlet during image formation based on the overflow pressure, which is the pressure in the inlet when liquid begins to overflow from the nozzle due to a meniscus break as the pressure in the inlet increases, and the bubble entrapment pressure.

7. A method for detecting abnormalities in the flow path of an inkjet head, comprising: a pressure reduction step of gradually decreasing the pressure in the inlet while maintaining a constant differential pressure between the pressure in the inlet and the pressure in the outlet of the inkjet head; and a pressure determination step of determining whether the bubble entrapment pressure, which is the pressure in the inlet at which the nozzle of the inkjet head begins to entrap bubbles due to meniscus breakage as the pressure in the inlet decreases, is within the range of normal bubble entrapment pressure expected when the flow path for circulating liquid between the inlet and the outlet of the inkjet head is functioning correctly.

8. A method for detecting abnormalities in the flow path of an inkjet head according to claim 7, comprising a pressure acquisition step of acquiring the pressure in the inlet at the time when the nozzle begins to entrain bubbles due to a meniscus break as the pressure in the inlet decreases, the pressure determination step of determining whether the bubble entrainment pressure acquired in the pressure acquisition step is within the range of the normal bubble entrainment pressure.

9. The method for detecting an abnormality in the flow channel of an inkjet head according to claim 7, wherein in the pressure determination step, if the bubble entrapment pressure is within the range of the normal bubble entrapment pressure, it is determined that the flow channel of the inkjet head is normal, and if the bubble entrapment pressure is not within the normal range, it is determined that there is an abnormality in the flow channel of the inkjet head.

10. The method for detecting abnormalities in the flow path of an inkjet head according to claim 7, wherein the pressure reduction process is performed in a room temperature environment.

11. The method for detecting abnormalities in the flow path of an inkjet head according to claim 7, wherein the liquid used in the pressure reduction process is a non-volatile inspection liquid that does not contain pigment.

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