Image forming device

Abstract

Provided is an image forming apparatus capable of arbitrarily adjusting the flow rate of ink flowing to multiple inkjet heads without increasing apparatus cost. The image forming apparatus includes an inkjet head, an ink reservoir, an ink that flows between the inkjet head and the ink reservoir, a pressure generating unit, and a first fluid resistance unit. The ink reservoir stores ink for circulation between the inkjet head and the ink reservoir; the pressure generating unit communicates with the ink reservoir and generates a first pressure to bring the internal pressure of the ink reservoir to the first pressure; and the first fluid resistance unit applies resistance to fluid flowing in a communication path between the ink reservoir and the pressure generating unit to bring the internal pressure of the ink reservoir to a second pressure different from the first pressure.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus. Background Art

[0002] Conventionally, there is known an inkjet image forming apparatus (hereinafter referred to as an image forming apparatus) that discharges ink from a plurality of nozzles provided in an inkjet head onto a recording medium transported by a transport device to form (record) an image on the recording medium.

[0003] Some image forming apparatuses include an ink supply mechanism that circulates ink between a supply tank for supplying ink, an inkjet head, and a recovery tank for recovering ink, and supplies ink to the inkjet head (see, for example, Patent Documents 1 and 2).

[0004] In the ink supply mechanism, a supply tank for supplying ink to the inkjet head is arranged above the inkjet head. The supply tank and the inkjet head are connected via an ink supply passage.

[0005] Negative pressure (negative pressure for meniscus) is applied to the supply tank, and this negative pressure is used to form an appropriate meniscus pressure at the discharge port of the inkjet head. By properly controlling the meniscus pressure, a meniscus of an appropriate shape can be formed at the discharge port of the inkjet head.

[0006] In the ink supply mechanism, a recovery tank, which collects ink from the inkjet head, is positioned above the inkjet head and lower than the supply tank. The recovery tank is also subjected to the same negative pressure as the supply tank. The difference in height (hydraulic head difference) between the supply tank and the recovery tank is utilized to guide the ink supplied to the inkjet head through the ink recovery passage to the recovery tank. The height difference between the supply tank and the recovery tank is used to adjust the flow rate of ink to the inkjet head.

[0007] Here, we describe a structure for applying the same negative pressure to the supply tank and the recovery tank. The supply tank and the recovery tank are connected to a pressure-reducing tank (buffer tank) configured to hold a predetermined volume of gas. A vacuum pump is connected to the pressure-reducing tank via a vacuum passage. The vacuum pump is then driven and controlled to reduce the pressure within the pressure-reducing tank to a predetermined pressure, thereby also reducing the pressure within the supply tank and the recovery tank connected to the pressure-reducing tank to a predetermined pressure (applying negative pressure).

[0008] The recovery tank and the supply tank are connected to each other via a circulation path provided with a pump. When a level sensor disposed in the supply tank detects that the ink level in the supply tank is lower than a specified level, the pump is driven to return the ink recovered in the recovery tank to the supply tank via the circulation path.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-962

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 2009-285845 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] However, in the above-mentioned ink supply mechanism, when the flow rate of ink flowing to the inkjet head is increased, although it is possible to cope with it by increasing the height difference between the supply tank and the recovery tank, in order to increase the height difference, the height position of the supply tank and the height position of the recovery tank need to be greatly separated, which has the problem of increasing the size of the device.

[0015] To address this issue, a possible solution is to eliminate the height difference between the supply tank and the recovery tank, apply different negative pressures to the supply tank and the recovery tank, and use the pressure difference (air pressure difference) between the supply tank and the recovery tank to guide the ink supplied to the inkjet head to the recovery tank. However, if multiple supply tanks and recovery tanks are provided for each of the multiple inkjet heads, the negative pressure generating source (decompression tank and vacuum pump) must be prepared for the same number of inkjet heads and supply tanks, which also increases the cost of the equipment.

[0016] An object of the present invention is to provide an image forming apparatus capable of arbitrarily adjusting the flow rate of ink flowing to a plurality of inkjet heads without increasing the cost of the apparatus.

[0017] Solutions to Problems

[0018] The image forming apparatus of the present invention comprises an inkjet head, an ink storage unit, a pressure generating unit, and a first fluid resistance unit.

[0019] The ink storage unit stores ink that flows between the inkjet head and the inkjet head.

[0020] The pressure generating portion is in communication with the ink storage portion and generates a first pressure so that the internal pressure of the ink storage portion becomes the first pressure.

[0021] The first fluid resistance portion applies resistance to the fluid flowing through the communication path between the ink storage portion and the pressure generating portion so that the internal pressure of the ink storage portion becomes a second pressure different from the first pressure.

[0022] Effects of the Invention

[0023] According to the present invention, the flow rate of ink flowing to a plurality of inkjet heads can be arbitrarily adjusted without increasing the cost of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1This is a diagram showing a schematic configuration of an inkjet image forming apparatus.

[0025] Figure 2 It is a schematic diagram showing the structure of an inkjet head unit.

[0026] Figure 3 This is a block diagram showing the main functional configuration of an inkjet image forming apparatus.

[0027] Figure 4 This is a diagram showing the structure of an ink supply mechanism that supplies ink to an inkjet head. DETAILED DESCRIPTION

[0028] Figure 1 1 is a diagram showing a schematic configuration of an inkjet image forming apparatus 1. The inkjet image forming apparatus 1 includes a paper feed unit 10, an image forming unit 20, a paper discharge unit 30, and a control unit 40 (see FIG. Figure 3 ).

[0029] The inkjet image forming apparatus 1 (functioning as the "image forming apparatus" of the present invention) conveys a recording medium P accommodated in a paper feed unit 10 to an image forming unit 20 under the control of a control unit 40. The image forming unit 20 forms an image on the recording medium P, and the recording medium P with the image formed thereon is conveyed to a paper discharge unit 30. The recording medium P may be various media, such as plain paper and coated paper, or other media capable of fixing ink deposited thereon, such as fabric or sheet-like resin, in addition to paper.

[0030] The paper feed unit 10 includes a paper feed tray 11 for storing recording media P and a medium supply unit 12 for conveying and supplying recording media P from the paper feed tray 11 to the image forming unit 20. The medium supply unit 12 includes an endless belt supported by two rollers. The rollers rotate while the recording medium P is placed on the belt, thereby conveying the recording medium P from the paper feed tray 11 to the image forming unit 20.

[0031] The image forming section 20 includes a conveying section 21 , a delivery unit 22 , a heating section 23 , an inkjet head unit 24 , a fixing section 25 , a paper delivery section 28 , and the like.

[0032] The transport unit 21 holds the recording medium P placed on the transport surface 211a (mounting surface) of the cylindrical transport roller 211, and moves the transport roller 211 in the X direction (with respect to the X direction). Figure 1 The transport roller 211 rotates around a rotation axis (cylindrical axis) extending in a direction perpendicular to the paper surface and moves in a circumferential direction, thereby performing a transport operation of transporting the recording medium P on the transport roller 211 along the transport direction (Y direction).

[0033] The transport roller 211 includes claws (not shown) and an air intake (not shown) for holding the recording medium P on its transport surface 211a. The claws press the ends of the recording medium P, while the air intake draws the recording medium P toward the transport surface 211a, thereby holding the recording medium P on the transport surface 211a. The transport unit 21 is connected to a transport roller motor (not shown) that rotates the transport roller 211. The transport roller 211 rotates at an angle proportional to the rotation of the transport roller motor.

[0034] The handover unit 22 delivers the recording medium P fed by the medium supply unit 12 of the paper feed unit 10 to the conveying unit 21. The handover unit 22 is located between the medium supply unit 12 of the paper feed unit 10 and the conveying unit 21. It uses a swing arm 221 to hold and pick up one end of the recording medium P fed from the medium supply unit 12 and delivers it to the conveying unit 21 via a handover roller 222.

[0035] The heating unit 23 is provided between the position where the transfer roller 222 is arranged and the position where the inkjet head unit 24 is arranged, and heats the recording medium P conveyed by the conveying unit 21 to a temperature within a predetermined temperature range. The heating unit 23 includes, for example, an infrared heater, and is controlled by the control unit 40 (see Figure 3 ) supplies a control signal to energize the infrared heater, causing it to generate heat.

[0036] The inkjet head unit 24 discharges ink onto the recording medium P from nozzle openings provided on an ink discharge surface facing the conveying surface 211 a of the conveying roller 211 at appropriate timing corresponding to the rotation of the conveying roller 211 holding the recording medium P, thereby forming an image. The inkjet head unit 24 is arranged so that the ink discharge surface and the conveying surface 211 a are separated by a predetermined distance.

[0037] In the inkjet image forming device 1 in this embodiment, four inkjet head units 24 corresponding to four colors of ink, namely white (W), yellow (Y), magenta (M), cyan (C), and black (K), are arranged in parallel at prescribed intervals in the order of W, Y, M, C, and K from the upstream side of the conveying direction of the recording medium P.

[0038] Figure 2 Schematic diagram showing the structure of the inkjet head unit 24. Here, the surface of the inkjet head unit 24 that faces the transport surface 211a of the transport roller 211 is shown.

[0039] The inkjet head unit 24 includes four inkjet heads 242 mounted on a mounting member 244. Each inkjet head 242 is equipped with multiple image forming elements (recording elements), each of which includes a nozzle 243, a pressure chamber for storing ink, and a piezoelectric element mounted on the wall of the pressure chamber. When a drive signal that causes the piezoelectric element to deform is input to the image forming element, the deformation of the piezoelectric element causes the pressure chamber to deform, causing the pressure within the pressure chamber to change, and ink is discharged from the nozzle connected to the pressure chamber.

[0040] The inkjet head 242 is provided with two nozzle rows consisting of nozzles 243 arranged at equal intervals along a direction intersecting the conveyance direction of the recording medium P (in this embodiment, the direction perpendicular to the conveyance direction, i.e., the X direction). The two nozzle rows are arranged so that the arrangement positions of the nozzles 243 are offset from each other along the X direction by half the arrangement interval of the nozzles 243 in each nozzle row.

[0041] The four inkjet heads 242 are arranged in a staggered grid pattern, with the nozzle rows seamlessly connected across their X-direction arrangement range. The nozzles 243 included in the inkjet head unit 24 are arranged in the X-direction to cover the X-direction width of the area on the recording medium P being transported by the transport unit 21, where the image is to be formed. During image formation, the inkjet head unit 24 is fixedly positioned relative to the rotation axis of the transport roller 211. Specifically, the inkjet head unit 24 comprises a linear inkjet head capable of ejecting ink across the X-direction width of the recording medium P, allowing for image formation. The inkjet image forming apparatus 1 is a single-path type inkjet image forming apparatus.

[0042] The number of nozzle rows included in the inkjet head 242 may not be two, but may be one or three or more. The number of inkjet heads 242 included in the inkjet head unit 24 may not be four, but may be three or less, or five or more.

[0043] The ink ejected from the nozzles 243 of the image forming element is a pigmented ink, particularly white ink containing titanium dioxide, for example. Alternatively, the ink ejected from the nozzles 243 of the image forming element is a gel ink. This gel ink contains a gelling agent, undergoes a phase transition to a gel or sol depending on temperature, and solidifies upon exposure to energy rays such as ultraviolet light. In this embodiment, gel ink is used as the ink ejected from the nozzles 243 of the image forming element.

[0044] The inkjet head unit 24 includes an ink heating portion (not shown) that heats the ink stored in the inkjet head unit 24. The ink heating portion operates under the control of the control portion 40 and heats the ink to a temperature at which the ink becomes a sol state.

[0045] The inkjet head 242 discharges heated sol-like ink. When the sol-like ink is discharged onto the recording medium P, the ink droplets naturally cool after landing on the recording medium P, whereby the ink quickly turns into a gel and solidifies on the recording medium P.

[0046] The fixing section 25 includes a light-emitting section arranged across the width of the transport section 21 in the X direction. The light-emitting section irradiates the recording medium P placed on the transport section 21 with energy rays such as ultraviolet rays, thereby curing and fixing the ink (gel ink) discharged onto the recording medium P. The light-emitting section of the fixing section 25 is arranged to face the transport surface 211a along the transport direction, between the position where the inkjet head unit 24 is arranged and the position where the delivery roller 281 of the paper delivery section 28 is arranged.

[0047] The paper receiving section 28 has a transfer roller 281 and a belt ring 282. The transfer roller 281 is cylindrical and transfers the recording medium P from the conveying section 21 to the belt ring 282. The belt ring 282 has an annular belt supported by two rollers on the inner side. The belt ring 282 is used to transport the recording medium P transferred from the conveying section 21 to the belt ring 282 by the transfer roller 281 and send the recording medium P to the paper discharging section 30.

[0048] The paper discharge section 30 includes a plate-shaped paper discharge tray 31 on which the recording medium P fed from the image forming section 20 by the paper delivery section 28 is placed.

[0049] Figure 3 This is a block diagram showing the main functional configuration of the inkjet image forming apparatus 1. The inkjet image forming apparatus 1 includes a heating unit 23, an inkjet head driving unit 241 and inkjet head 242, a fixing unit 25, a control unit 40, a transport driving unit 51, an operation display unit 52, and an input / output interface 53.

[0050] The inkjet head driving unit 241 supplies a driving signal to deform the piezoelectric element to the image forming element of the inkjet head 242 at an appropriate timing according to the image data, thereby discharging ink in an amount corresponding to the pixel value of the image data from the nozzles 243 of the inkjet head 242 .

[0051] The control unit 40 includes a CPU 41 (Central Processing Unit), a RAM 42 (Random Access Memory), a ROM 43 (Read Only Memory), and a storage unit 44 .

[0052] The CPU 41 reads various control programs and setting data stored in the ROM 43 and stores them in the RAM 42 , and executes the programs to perform various calculations. The CPU 41 also comprehensively controls the overall operation of the inkjet image forming apparatus 1 .

[0053] The RAM 42 provides a working memory space for the CPU 41 and temporarily stores data. The RAM 42 may also include a nonvolatile memory.

[0054] The ROM 43 stores various control programs and setting data executed by the CPU 41. In place of the ROM 43, a rewritable nonvolatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used.

[0055] The storage unit 44 stores print jobs (image formation commands) input from the external device 2 via the input / output interface 53, as well as image data associated with the print jobs. In addition to information specifying the image data associated with the image to be formed, the print jobs also include information regarding the type of recording medium P on which the image will be formed (e.g., the size and thickness of the recording medium P). For example, an HDD (Hard Disk Drive) is used as the storage unit 44, and a DRAM (Dynamic Random Access Memory) may also be used in combination.

[0056] The conveyance driving unit 51 supplies a driving signal to the conveyance roller motor of the conveyance roller 211 based on the control signal supplied from the control unit 40 , thereby rotating the conveyance roller 211 at a predetermined speed and timing.

[0057] In addition, the conveying drive unit 51 supplies a drive signal to the motor for operating the medium supply unit 12, the delivery unit 22 and the paper delivery unit 28 based on the control signal supplied from the control unit 40, thereby supplying and discharging the recording medium P to and from the conveying unit 21.

[0058] The operation display unit 52 includes a display device such as a liquid crystal display or an organic EL (electroluminescence) display, and input devices such as operation keys and a touch panel superimposed on the display screen. The operation display unit 52 displays various information on the display device and converts user input to the input device into operation signals, which are then output to the control unit 40.

[0059] The input / output interface 53 mediates data transmission and reception between the external device 2 and the control unit 40. For example, the input / output interface 53 is configured using any one of various serial interfaces and various parallel interfaces, or a combination of these interfaces.

[0060] The external device 2 is, for example, a personal computer, and supplies a print job, image data, and the like to the control unit 40 via the input / output interface 53 .

[0061] Next, refer to Figure 4 The structure of the ink supply mechanism 60 that supplies ink to the inkjet head 242 in the inkjet image forming apparatus 1 will be described. The ink supply mechanism 60 circulates ink between the inkjet head, a supply tank that supplies ink, and a recovery tank that recovers ink, and supplies ink to the inkjet head.

[0062] like Figure 4 As shown, the ink supply mechanism 60 includes a pressure reducing tank 61, a vacuum pump 62, an opening and closing valve 64, a pressure detecting unit 65, a first supply tank 80, an opening and closing valve 83, a first recovery tank 90, an opening and closing valve 93, a second supply tank 100, an opening and closing valve 103 and a second recovery tank 110, etc.

[0063] Furthermore, the first supply tank 80, the first recovery tank 90, the second supply tank 100, and the second recovery tank 110 function as the "ink storage unit" of the present invention, storing ink that circulates between the inkjet head and the inkjet head. Furthermore, the on-off valves 83, 93, and 103 function as the "on-off unit" of the present invention.

[0064] The first supply tank 80 stores ink to be supplied to the inkjet head 242A (functioning as the "first inkjet head" of the present invention) via the ink supply path 75. In the present embodiment, the first supply tank 80 is arranged above the inkjet head 242A.

[0065] Although not shown, the first supply tank 80, the first recovery tank 90, and the inkjet head 242A are provided to correspond to the four colors of ink: yellow (Y), magenta (M), cyan (C), and black (K). The inkjet head 242A discharges the yellow (Y), magenta (M), cyan (C), or black (K) ink supplied from the first supply tank 80.

[0066] For example, a negative pressure of -2.5 kPa (negative meniscus pressure) is applied to the first supply tank 80. This negative pressure creates an appropriate meniscus pressure at the discharge port of the inkjet head 242A. By properly controlling the meniscus pressure, a meniscus of an appropriate shape can be formed at the discharge port of the inkjet head 242A.

[0067] An atmospheric communication passage 82 (atmospheric opening pipe) capable of communicating with the atmosphere is connected to the first supply tank 80. An on-off valve 83 (e.g., a solenoid valve) is controlled by the control unit 40 to open and close the atmospheric communication passage 82. By adjusting the amount of atmospheric air drawn into the first supply tank 80 through the atmospheric communication passage 82, the pressure in the first supply tank 80 is adjusted toward atmospheric pressure (the pressure in the first supply tank 80 is increased).

[0068] The first recovery tank 90 stores ink recovered from the inkjet head 242A via the ink recovery passage 76. In this embodiment, a metal container with a capacity of approximately 40 liters is used as the first recovery tank 90. In this embodiment, the first recovery tank 90 is arranged above the inkjet head 242A and at a position lower than the first supply tank 80.

[0069] The same negative pressure as that of the first supply tank 80 (e.g., -2.5 kPa) is applied to the first recovery tank 90, and the height difference between the first supply tank 80 and the first recovery tank 90 ( Figure 4 The ink supplied from the first supply tank 80 to the inkjet head 242A is guided to the first recovery tank 90 via the ink recovery passage 76 (the head difference indicated by H in FIG). The flow rate of the ink flowing to the inkjet head 242A is adjusted by the height difference between the first supply tank 80 and the first recovery tank 90.

[0070] An atmospheric communication passage 92 (atmospheric opening pipe) capable of communicating with the atmosphere is connected to the first recovery tank 90. An on-off valve 93 (e.g., a solenoid valve) is controlled by the control unit 40 to open and close the atmospheric communication passage 92, thereby adjusting the amount of atmospheric air drawn into the first recovery tank 90 through the atmospheric communication passage 92, thereby adjusting the pressure in the first recovery tank 90 toward atmospheric pressure (increasing the pressure in the first recovery tank 90).

[0071] The first supply tank 80 and the first recovery tank 90 are connected to each other via a circulation passage (not shown) equipped with a pump. When a level sensor disposed in the first supply tank 80 detects that the ink level in the first supply tank 80 falls below a predetermined level, the pump is activated to return the ink recovered in the first recovery tank 90 to the first supply tank 80 via the circulation passage.

[0072] The second supply tank 100 stores ink supplied to the inkjet head 242B (functioning as the "second inkjet head" in the present invention) via the ink supply passage 77. In this embodiment, the second supply tank 100 is positioned above the inkjet head 242B. The inkjet head 242B discharges white (W) ink supplied from the second supply tank 100.

[0073] For example, a negative pressure of -2.5 kPa (negative meniscus pressure) is applied to the second supply tank 100. This negative pressure creates an appropriate meniscus pressure at the discharge port of the inkjet head 242B. By properly controlling the meniscus pressure, a meniscus of an appropriate shape can be formed at the discharge port of the inkjet head 242B.

[0074] An atmospheric communication passage 102 (atmospheric opening pipe) capable of communicating with the atmosphere is connected to the second supply tank 100. An on-off valve 103 (e.g., a solenoid valve) is controlled by the control unit 40 to open and close the atmospheric communication passage 102, thereby adjusting the amount of atmospheric air drawn into the second supply tank 100 through the atmospheric communication passage 102, thereby adjusting the pressure within the second supply tank 100 toward atmospheric pressure (increasing the pressure within the second supply tank 100).

[0075] The second recovery tank 110 stores ink recovered from the inkjet head 242B via the ink recovery passage 78. In this embodiment, a metal container with a capacity of approximately 40 liters is used as the second recovery tank 110. In this embodiment, the second recovery tank 110 is arranged above the inkjet head 242B and at the same height as the second supply tank 100.

[0076] A negative pressure different in magnitude (e.g., -14.5 kPa) from that applied to the second supply tank 100 is applied to the second recovery tank 110. The ink supplied from the second supply tank 100 to the inkjet head 242B is guided to the second recovery tank 110 via the ink recovery passage 78 by utilizing the difference in negative pressure applied to each of the second supply tanks 100 and the second recovery tank 110. The flow rate of ink flowing to the inkjet head 242B is adjusted by utilizing the difference in negative pressure applied to each of the second supply tanks 100 and the second recovery tank 110.

[0077] The second supply tank 100 and the second recovery tank 110 are connected to each other via a circulation passage (not shown) equipped with a pump. When a level sensor disposed in the second supply tank 100 detects that the ink level in the second supply tank 100 falls below a predetermined level, the pump is activated to return the ink recovered in the second recovery tank 110 to the second supply tank 100 via the circulation passage.

[0078] Next, a specific configuration for applying negative pressure to the first supply tank 80 , the first recovery tank 90 , the second supply tank 100 , and the second recovery tank 110 will be described.

[0079] The first supply tank 80 is connected to the pressure-reducing tank 61 (buffer tank) via communication passages 70 and 71. Furthermore, the first recovery tank 90 is connected to the pressure-reducing tank 61 via communication passages 70 and 72. Furthermore, the second supply tank 100 is connected to the pressure-reducing tank 61 via communication passages 70 and 73. Furthermore, the second recovery tank 110 is connected to the pressure-reducing tank 61 via communication passages 70 and 74.

[0080] The pressure reducing tank 61 is configured to accommodate a predetermined volume of gas. The vacuum pump 62 is connected to the pressure reducing tank 61 via a vacuum passage 63. The vacuum pump 62 is controlled by the control unit 40 and sucks the air in the pressure reducing tank 61 via the vacuum passage 63 to reduce the pressure (air pressure) in the pressure reducing tank 61. The pressure detecting unit 65 detects the pressure in the pressure reducing tank 61 and outputs it to the control unit 40. Under the control of the control unit 40, the opening and closing valve 64 (e.g., a solenoid valve) opens and closes the vacuum passage 63 according to the detection result of the pressure detecting unit 65 to adjust the amount of air sucked into the vacuum pump 62 so that the pressure in the pressure reducing tank 61 becomes a predetermined pressure (e.g., -14.5 kPa).

[0081] The control unit 40 controls the vacuum pump 62 and the on-off valve 64 to reduce the pressure within the pressure-reducing tank 61 to a predetermined pressure (corresponding to the "first pressure" of the present invention). This control also reduces the pressure within the first supply tank 80, the first recovery tank 90, the second supply tank 100, and the second recovery tank 110, which are connected to the pressure-reducing tank 61, to the predetermined pressure (applying negative pressure). Furthermore, the control unit 40, the pressure-reducing tank 61, the vacuum pump 62, the on-off valve 64, and the pressure detecting unit 65 function as the "pressure generating unit" of the present invention, which generates the first pressure so that the internal pressures of the first supply tank 80, the first recovery tank 90, the second supply tank 100, and the second recovery tank 110 reach the first pressure.

[0082] In addition, in the previous ink supply mechanism, when the flow rate of ink flowing in the inkjet head is increased, although it is possible to cope with it by increasing the height difference (head difference) between the supply tank and the recovery tank, in order to increase the height difference, the height position of the supply tank and the height position of the recovery tank need to be greatly separated, which leads to the problem of increasing the size of the device.

[0083] To address this issue, a possible solution is to eliminate the height difference between the supply tank and the recovery tank, apply different negative pressures to the supply tank and the recovery tank, and use the pressure difference (air pressure difference) between the supply tank and the recovery tank to guide the ink supplied to the inkjet head to the recovery tank. However, if multiple supply tanks and recovery tanks are provided for each of the multiple inkjet heads, the negative pressure generating source (decompression tank and vacuum pump) must be prepared for the same number of inkjet heads and supply tanks, which also increases the cost of the equipment.

[0084] Therefore, in this embodiment, the ink supply mechanism 60 is configured to arbitrarily adjust the flow rate of ink flowing to the plurality of inkjet heads without increasing the cost of the device.

[0085] Specifically, a first fluid resistance portion 81 is provided in the communication passage 71. This first fluid resistance portion 81 applies resistance to the fluid (e.g., air) flowing in the communication passage 71, that is, generates pressure loss, thereby causing the internal pressure of the first supply tank 80 to be a desired pressure (e.g., -2.5 kPa, corresponding to the "second pressure" of the present invention) different from the pressure within the pressure reduction tank 61 (e.g., -14.5 kPa). More specifically, when the first supply tank 80 is open to the atmosphere, the first fluid resistance portion 81 applies resistance to the fluid flowing in the communication passage 71, thereby causing the difference between the pressure within the pressure reduction tank 61 and the internal pressure of the first supply tank 80 to be greater than a predetermined pressure (e.g., 1 kPa).

[0086] In the present embodiment, the first fluid resistance portion 81 is an element that suppresses pressure fluctuations within the first supply tank 80 due to pressure fluctuations within the pressure reducing tank 61 caused by the control of the vacuum pump 62 and the on-off valve 64, and is composed of, for example, an orifice. For example, by adjusting the throttling diameter of the orifice, the fluid resistance value of the first fluid resistance portion 81 can be arbitrarily adjusted. In other words, if the first fluid resistance portion 81 is not provided, after the pressure within the pressure reducing tank 61 begins to fluctuate, pressure fluctuations similar to those within the pressure reducing tank 61 will occur within the first supply tank 80 over time. However, by providing the first fluid resistance portion 81, the internal pressure of the first supply tank 80 can be adjusted to a desired pressure (e.g., -2.5 kPa).

[0087] In addition, in a case where it is difficult to adjust the internal pressure of the first supply tank 80 to the desired pressure using only the first fluid resistance portion 81 (for example, when the pressure in the pressure reducing tank 61 or even the negative pressure applied to the first supply tank 80 is very large), the control portion 40 may also control the opening and closing valve 83 to adjust the amount of air in the atmosphere that is sucked into the first supply tank 80 through the atmosphere connecting passage 82, thereby adjusting the pressure in the first supply tank 80.

[0088] Furthermore, a first fluid resistance portion 91 is provided in the communication passage 72. This first fluid resistance portion 91 applies resistance to the fluid (e.g., air) flowing in the communication passage 72, that is, generates pressure loss, thereby causing the internal pressure of the first recovery tank 90 to be a desired pressure (e.g., -2.5 kPa, corresponding to the "second pressure" of the present invention) different from the pressure (e.g., -14.5 kPa) within the pressure reduction tank 61. More specifically, when the first recovery tank 90 is open to the atmosphere, the first fluid resistance portion 91 applies resistance to the fluid flowing in the communication passage 72, thereby causing the difference between the pressure within the pressure reduction tank 61 and the internal pressure of the first recovery tank 90 to be greater than a predetermined pressure (e.g., 1 kPa).

[0089] In the present embodiment, the first fluid resistance portion 91 is an element that suppresses pressure fluctuations in the first recovery tank 90 due to pressure fluctuations in the pressure reducing tank 61 caused by the control of the vacuum pump 62 and the on-off valve 64, and is composed of, for example, a throttle hole. For example, by adjusting the throttle diameter of the throttle hole, the fluid resistance value of the first fluid resistance portion 91 can be arbitrarily adjusted. In other words, if the first fluid resistance portion 91 is not provided, after the pressure in the pressure reducing tank 61 begins to fluctuate, as time passes, pressure fluctuations similar to the pressure fluctuations in the pressure reducing tank 61 will occur in the first recovery tank 90. However, by providing the first fluid resistance portion 91, the internal pressure of the first recovery tank 90 can be adjusted to a desired pressure (e.g., -2.5 kPa).

[0090] In addition, in a case where it is difficult to adjust the internal pressure of the first recovery tank 90 to the desired pressure using only the first fluid resistance part 91 (for example, when the pressure in the pressure reducing tank 61 or even the negative pressure applied to the first recovery tank 90 is very large), the control part 40 can also control the opening and closing valve 93 to adjust the amount of air in the atmosphere that is sucked into the first recovery tank 90 through the atmosphere communication path 92, thereby adjusting the pressure in the first recovery tank 90.

[0091] Furthermore, a first fluid resistance portion 101 is provided in the communication passage 73. This first fluid resistance portion 101 applies resistance to the fluid (e.g., air) flowing in the communication passage 73 so as to maintain the internal pressure of the second supply tank 100 at a desired pressure (e.g., -2.5 kPa, corresponding to the "second pressure" of the present invention) different from the pressure within the pressure reduction tank 61 (e.g., -14.5 kPa). More specifically, when the second supply tank 100 is exposed to the atmosphere, the first fluid resistance portion 101 applies resistance to the fluid flowing in the communication passage 73 so as to maintain the difference between the pressure within the pressure reduction tank 61 and the internal pressure of the second supply tank 100 at or above a predetermined pressure (e.g., 1 kPa).

[0092] In the present embodiment, the first fluid resistance section 101 is an element that suppresses pressure fluctuations in the second supply tank 100 due to pressure fluctuations in the pressure reducing tank 61 caused by the control of the vacuum pump 62 and the on-off valve 64, and is composed of, for example, a throttle hole. For example, by adjusting the throttle diameter of the throttle hole, the fluid resistance value of the first fluid resistance section 101 can be arbitrarily adjusted. In other words, if the first fluid resistance section 101 is not provided, after the pressure in the pressure reducing tank 61 begins to fluctuate, the same pressure fluctuations as those in the pressure reducing tank 61 will occur in the second supply tank 100 over time. However, by providing the first fluid resistance section 101, the internal pressure of the second supply tank 100 can be adjusted to a desired pressure (e.g., -2.5 kPa).

[0093] In addition, in a case where it is difficult to adjust the internal pressure of the second supply tank 100 to the desired pressure using only the first fluid resistance part 101 (for example, when the pressure in the pressure reducing tank 61 or even the negative pressure applied to the second supply tank 100 is very large), the control part 40 can also control the opening and closing valve 103 to adjust the amount of air in the atmosphere that is sucked into the second supply tank 100 through the atmosphere connecting passage 102, thereby adjusting the pressure inside the second supply tank 100.

[0094] In addition, there is no first fluid resistance portion in the connecting passage 74 that applies resistance to the fluid (e.g., air) flowing in the connecting passage 74, that is, generates pressure loss. After the pressure in the pressure reducing tank 61 begins to change, the internal pressure of the second recovery tank 110 becomes the same as the pressure in the pressure reducing tank 61 (e.g., -14.5 kPa) over time.

[0095] In addition, a second fluid resistance portion 84 is provided in the atmospheric communication passage 82, which applies resistance to the fluid (e.g., air) flowing in the atmospheric communication passage 82, that is, generates pressure loss so that the internal pressure of the first supply tank 80 becomes a desired pressure (e.g., -2.5 kPa) that is different from the pressure in the pressure reducing tank 61 (e.g., -14.5 kPa).

[0096] Thus, when the amount of atmospheric air drawn into the first supply tank 80 via the atmosphere communication passage 82 is adjusted by opening and closing the on-off valve 83, the pressure fluctuation within the first supply tank 80 caused by this adjustment can be suppressed, making it easier to adjust the pressure within the first supply tank 80. If the on-off valve 83 is not provided, in cases where it would be difficult to adjust the internal pressure of the first supply tank 80 to a desired pressure using only the first fluid resistance portion 81 (for example, when the pressure within the pressure reduction tank 61 or even the negative pressure applied to the first supply tank 80 is extremely large), the provision of the second fluid resistance portion 84 allows the amount of atmospheric air drawn into the first supply tank 80 via the atmosphere communication passage 82 to be adjusted, thereby adjusting the pressure within the first supply tank 80 to a desired pressure.

[0097] In addition, a second fluid resistance portion 94 is provided in the atmospheric communication passage 92, which applies resistance to the fluid (e.g., air) flowing in the atmospheric communication passage 92, that is, generates pressure loss so that the internal pressure of the first recovery tank 90 becomes a desired pressure (e.g., -2.5 kPa) different from the pressure in the pressure reduction tank 61 (e.g., -14.5 kPa).

[0098] Thus, when the amount of atmospheric air drawn into the first recovery tank 90 via the atmosphere communication passage 92 is adjusted by opening and closing the on-off valve 93, the pressure fluctuation within the first recovery tank 90 caused by this adjustment can be suppressed, making it easier to adjust the pressure within the first recovery tank 90. If the on-off valve 93 is not provided, in cases where it would be difficult to adjust the internal pressure of the first recovery tank 90 to a desired pressure using only the first fluid resistance portion 91 (for example, when the pressure within the pressure reduction tank 61 or even the negative pressure applied to the first recovery tank 90 is extremely large), the provision of the second fluid resistance portion 94 allows the amount of atmospheric air drawn into the first recovery tank 90 via the atmosphere communication passage 92 to be adjusted, thereby adjusting the pressure within the first recovery tank 90 to a desired pressure.

[0099] In addition, a second fluid resistance portion 84 is provided in the atmosphere communication passage 102. The second fluid resistance portion 84 applies resistance to the fluid (e.g., air) flowing in the atmosphere communication passage 102, that is, generates pressure loss, so that the internal pressure of the second supply tank 100 becomes a desired pressure (e.g., -2.5 kPa) different from the pressure (e.g., -14.5 kPa) in the pressure reduction tank 61.

[0100] Thus, when the amount of atmospheric air drawn into the second supply tank 100 via the atmosphere communication passage 102 is adjusted by opening and closing the on-off valve 103, the pressure fluctuation within the second supply tank 100 resulting from this adjustment can be suppressed, making it easier to adjust the pressure within the second supply tank 100. If the on-off valve 103 were not provided, in situations where it would be difficult to adjust the internal pressure of the second supply tank 100 to a desired pressure using only the first fluid resistance portion 101 (for example, when the pressure within the pressure reduction tank 61 or even the negative pressure applied to the second supply tank 100 is extremely large), the provision of the second fluid resistance portion 104 allows the amount of atmospheric air drawn into the second supply tank 100 via the atmosphere communication passage 102 to be adjusted, thereby adjusting the pressure within the second supply tank 100 to a desired pressure.

[0101] As described in detail above, the inkjet image forming apparatus 1 (image forming apparatus) includes inkjet heads 242A, 242B, a first supply tank 80, a first recovery tank 90, a second supply tank 100, and a second recovery tank 110 (ink storage unit), a pressure generating unit (control unit 40, a pressure reducing tank 61, a vacuum pump 62, an on-off valve 64, and a pressure detecting unit 65), and first fluid resistance units 81, 91, and 101. The second supply tank 100 and the second recovery tank 110 store ink supplied or recovered (circulated) between the inkjet heads 242A and 242B. The above-mentioned pressure generating part is connected to the ink storage part, generating a first pressure so that the internal pressure of the ink storage part becomes the first pressure. The above-mentioned first fluid resistance part 81, 91, 101 applies resistance to the fluid flowing in the communication path between the ink storage part and the pressure generating part, so that the internal pressure of the ink storage part becomes a second pressure different from the first pressure.

[0102] With this configuration, by providing the first fluid resistance portions 81, 91, and 101 and adjusting their fluid resistance values, the internal pressures of the first supply tank 80, the first recovery tank 90, and the second supply tank 100 can be arbitrarily adjusted to desired pressures different from the pressure generated by a single negative pressure generating source (the pressure within the pressure reduction tank 61). Therefore, when multiple supply tanks (the first supply tank 80 and the second supply tank 100) and recovery tanks (the first recovery tank 90 and the second recovery tank 110) are provided for each of the multiple inkjet heads (the inkjet heads 242A and 242B), it is not necessary to prepare a negative pressure generating source (the pressure reduction tank and the vacuum pump) for each of the multiple inkjet heads, or even for each of the multiple supply tanks and recovery tanks. This allows the flow rate of ink flowing to each of the multiple inkjet heads to be arbitrarily adjusted without increasing the cost of the device.

[0103] In the above embodiment, the ink supply mechanism 60 is described as an example of a structure in which the multiple inkjet heads 242A and 242B are driven under different internal pressure conditions, such as the internal pressure difference between the first supply tank 80 and the first recovery tank 90 (0 kPa = -2.5 - (-2.5)) and the internal pressure difference between the second supply tank 100 and the second recovery tank 110 (12 kPa = -2.5 - (-14.5)). In other words, the multiple inkjet heads 242A and 242B are driven under different pressure difference conditions between the supply tanks and the recovery tanks. However, the present invention is not limited to this. For example, the ink supply mechanism 60 may also be configured to drive the multiple inkjet heads 242A and 242B under a single pressure difference condition, such as the internal pressure difference between the first supply tank 80 and the first recovery tank 90 and the internal pressure difference between the second supply tank 100 and the second recovery tank 110.

[0104] Furthermore, in the above embodiment, an example is described in which the ink supply mechanism 60 is provided with a first fluid resistance portion. This ink supply mechanism 60 circulates ink between the inkjet head, a supply tank for supplying ink, and a recovery tank for recovering ink, thereby supplying ink to the inkjet head. However, the present invention is not limited to this embodiment. For example, the first fluid resistance portion may be provided in an ink supply mechanism such that the internal pressure of the supply tank is arbitrarily adjusted to a desired pressure different from that of a negative pressure generating source. This ink supply mechanism supplies ink from the supply tank to the inkjet head without circulating ink between the inkjet head, the supply tank, and the recovery tank.

[0105] In the above embodiment, a single-path inkjet image forming apparatus 1 is described as an example. However, the present invention can also be applied to an inkjet image forming apparatus that records an image while scanning with an inkjet head unit. Furthermore, the present invention can also be applied to an inkjet image forming apparatus in which a single nozzle is provided in the inkjet head unit.

[0106] In addition, the above-mentioned embodiments are merely examples of embodiments of the present invention and should not be construed as limiting the scope of the present invention. That is, the present invention can be implemented in various forms without departing from the gist of the present invention or its main features.

[0107] Description of Reference Numerals

[0108] 1. Inkjet image forming apparatus; 2. External device; 10. Paper feed unit; 11. Paper feed tray; 12. Medium supply unit; 20. Image forming unit; 21. Conveyor unit; 211. Conveyor roller; 211a. Conveyor surface; 22. Handover unit; 23. Heating unit; 24. Inkjet head unit; 241. Inkjet head drive unit; 242, 242A, 242B, Inkjet head; 243. Nozzle; 244. Mounting member; 25. Fixing unit; 28. Paper delivery unit; 30. Paper discharge unit; 31. Paper discharge tray; 40. Control unit; 41. CPU; 42. RAM; 43. ROM; 44. Storage unit; 51. Conveyor drive unit; 5 2. Operation display unit; 53. Input / output interface; 60. Ink supply mechanism; 61. Pressure reducing tank; 62. Vacuum pump; 63. Vacuum passage; 64, 83, 93, 103. Open / close valve; 65. Pressure detection unit; 70, 71, 72, 73, 74. Communication passage; 75, 77. Ink supply passage; 76, 78. Ink recovery passage; 80. First supply tank; 81, 91, 101. First fluid resistance unit; 82, 92, 102. Atmosphere communication passage; 84, 94, 104. Second fluid resistance unit; 90. First recovery tank; 100. Second supply tank; 110. Second recovery tank; L. Ink; P. Recording medium.

Claims

1. An image forming apparatus, wherein: The image forming apparatus includes an inkjet head, an ink storage unit, a pressure generating unit, a first fluid resistance unit, an atmosphere communication path, and a second fluid resistance unit. The ink storage unit stores ink that flows between the inkjet head and the inkjet head. The pressure generating portion is in communication with the ink storage portion and generates a first pressure so that the internal pressure of the ink storage portion becomes the first pressure. The first fluid resistance portion applies resistance to the fluid flowing in the communication path between the ink storage portion and the pressure generating portion so that the internal pressure of the ink storage portion becomes a second pressure different from the first pressure. The atmosphere communication passage is connected to the ink storage portion and can communicate with the atmosphere. The second fluid resistance portion applies resistance to the fluid flowing through the atmosphere communication passage.

2. The image forming apparatus according to claim 1, wherein The image forming device includes an opening and closing portion, The opening and closing portion opens and closes the atmosphere communication path.

3. The image forming apparatus according to claim 1 or 2, wherein: When the ink storage portion is open to the atmosphere, the first fluid resistance portion applies resistance to the fluid flowing through the communication path so that the difference between the first pressure and the internal pressure of the ink storage portion becomes equal to or greater than a predetermined pressure.

4. The image forming apparatus according to claim 1 or 2, wherein: The inkjet head includes a first inkjet head and a second inkjet head. The ink storage unit includes a first supply tank, a first recovery tank, a second supply tank, and a second recovery tank. The first supply tank stores ink supplied to the first inkjet head, the first recovery tank stores ink recovered from the first inkjet head, the second supply tank stores ink supplied to the second inkjet head, and the second recovery tank stores ink recovered from the second inkjet head. The internal pressure difference between the first supply tank and the first recovery tank is the same as the internal pressure difference between the second supply tank and the second recovery tank.

5. The image forming apparatus according to claim 3, wherein The inkjet head includes a first inkjet head and a second inkjet head. The ink storage unit includes a first supply tank, a first recovery tank, a second supply tank, and a second recovery tank. The first supply tank stores ink supplied to the first inkjet head, the first recovery tank stores ink recovered from the first inkjet head, the second supply tank stores ink supplied to the second inkjet head, and the second recovery tank stores ink recovered from the second inkjet head. The internal pressure difference between the first supply tank and the first recovery tank is the same as the internal pressure difference between the second supply tank and the second recovery tank.

6. The image forming apparatus according to claim 1 or 2, wherein: The inkjet head includes a first inkjet head and a second inkjet head. The ink storage unit includes a first supply tank, a first recovery tank, a second supply tank, and a second recovery tank. The first supply tank stores ink supplied to the first inkjet head, the first recovery tank stores ink recovered from the first inkjet head, the second supply tank stores ink supplied to the second inkjet head, and the second recovery tank stores ink recovered from the second inkjet head. The internal pressure difference between the first supply tank and the first recovery tank is different from the internal pressure difference between the second supply tank and the second recovery tank.

7. The image forming apparatus according to claim 3, wherein: The inkjet head includes a first inkjet head and a second inkjet head. The ink storage unit includes a first supply tank, a first recovery tank, a second supply tank, and a second recovery tank. The first supply tank stores ink supplied to the first inkjet head, the first recovery tank stores ink recovered from the first inkjet head, the second supply tank stores ink supplied to the second inkjet head, and the second recovery tank stores ink recovered from the second inkjet head. The internal pressure difference between the first supply tank and the first recovery tank is different from the internal pressure difference between the second supply tank and the second recovery tank.

Images