LIQUID DISCHARGE UNIT, DEVICE FOR DISCHARGING LIQUID, AND MAINTENANCE METHOD - Patent application

Abstract

To suppress volumes of air bubble in liquid from increasing excessively, in performing maintenance operation of drawing liquid in a nozzle into a pressure chamber side.SOLUTION: A liquid discharge unit comprises a liquid discharge head 100 that makes a pressure chamber communicating with a nozzle for discharging liquid cause pressure fluctuation, and a liquid circulating mechanism 200 that circulates liquid ejected through ejection passages 282 and 292 from the pressure chamber so that the liquid returns to the pressure chamber through supply passages 281 and 291, where a branch part that branches into another passage part 402 which is different from the passage part 292 for circulation communicating with the pressure chamber is provided in the ejection passage. The unit further comprises liquid current generating means 400 that generates liquid currents for drawing liquid in the nozzle into the pressure chamber side, by suctioning liquid in the ejection passages from the branch part to the another passage part, and flow passage switching means 401 that switches flow passage for liquid passing through the branch part to the passage part for circulation or the another passage part.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a liquid ejection unit, a device for ejecting liquid, and a maintenance method. [Background technology]

[0002] Conventionally, there is known a liquid ejection unit that has a liquid ejection head that generates pressure fluctuations in a pressure chamber that communicates with a nozzle that ejects liquid using a pressure generating means, and a liquid circulation mechanism that returns liquid discharged from the pressure chamber through a discharge passage to the pressure chamber through a supply passage.

[0003] For example, Patent Document 1 discloses an inkjet head (liquid ejection head) equipped with a circulation mechanism (liquid circulation mechanism) that returns ink (liquid) discharged from a pressure chamber through a circulation path (discharge passage) to the pressure chamber through an injection path (supply passage). This inkjet head is equipped with a pressure control means that applies negative pressure to the circulation path communicating with the pressure chamber to discharge the ink in the pressure chamber to the circulation path. In this inkjet head, a maintenance operation is performed to draw the ink in the nozzle to the pressure chamber side and break the meniscus once in order to avoid ejection defects due to particle settling and increased viscosity (thickening) of the ink (liquid) in the nozzle. During this maintenance operation, the pressure control means of the liquid circulation mechanism used for circulating the ink is used to generate a negative pressure in the circulation path that is greater than that during ink circulation, thereby drawing the ink in the nozzle to the pressure chamber side. Summary of the Invention [Problem to be solved by the invention]

[0004] However, when performing a maintenance operation to draw the liquid in the nozzle into the pressure chamber, outside air is sucked in through the nozzle and trapped in the liquid as air bubbles, causing the number of air bubbles in the circulating liquid to increase over time, resulting in malfunctions. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides a liquid ejection unit comprising: a liquid ejection head including a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, and a pressure generating means for generating a pressure fluctuation in the pressure chamber; and a liquid circulation mechanism for circulating liquid so that liquid discharged from the pressure chamber through a discharge passage returns to the pressure chamber through a supply passage, wherein the discharge passage is provided with a branch portion which branches off from a circulation passage portion communicating with the pressure chamber to another passage portion different from the circulation passage portion communicating with the pressure chamber, and the liquid ejection unit is characterized in that the liquid ejection unit comprises: a liquid flow generating means for generating a liquid flow that draws liquid in the nozzle toward the pressure chamber by sucking the liquid in the discharge passage from the branch portion to the other passage portion; and a flow path switching means for switching the flow path of liquid passing through the branch portion to the circulation passage portion or the other passage portion. Effect of the Invention

[0006] According to the present invention, when a maintenance operation is performed in which the liquid in the nozzle is drawn into the pressure chamber, the amount of air bubbles in the circulated liquid can be prevented from becoming excessive, thereby preventing the occurrence of problems. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of an image forming system according to an embodiment. [Diagram 2] 4 is an explanatory diagram for explaining the configuration of the head unit in the image forming system when the head unit is viewed from a normal direction of a sheet surface of a continuous sheet facing the head unit. FIG. [Diagram 3] FIG. 2 is an external perspective view illustrating a liquid ejection head in the image forming system. [Figure 4] FIG. 2 is a cross-sectional explanatory diagram perpendicular to the nozzle row direction of the liquid ejection head. [Diagram 5] 3A and 3B are explanatory diagrams for explaining the configuration and operation of a liquid circulating mechanism in the image forming system. [Figure 6] 4 is an explanatory diagram showing the positional relationship between a plurality of liquid ejection heads provided in one head array and non-image regions on a continuous sheet in the image forming system. FIG. [Figure 7]FIG. 2 is an explanatory diagram showing the positional relationship between a head unit having four head arrays and non-image areas on a continuous sheet in the image forming system. [Figure 8] 10 is a flowchart showing an example of the flow of a meniscus recovery operation in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment will be described in which the present invention is applied to an image forming system including an image forming apparatus formed of an inkjet printer, which is a device that ejects liquid.

[0009] FIG. 1 is a schematic diagram showing an example of an image forming system 1000 according to the present embodiment. The image forming system 1000 of this embodiment includes an unwinding device 1 that transports a continuous sheet 10, which is a continuous body serving as a recording material, an image forming device 5 that forms an image by ejecting liquid onto the continuous sheet 10 transported by the unwinding device 1, and a winding device 9 that discharges the continuous sheet 10 on which the image has been formed. The image forming device 5 includes a transport section 3 that transports the continuous sheet 10 transported by the unwinding device 1 to a head unit 50, a drying section 7 that dries the continuous sheet 10 on which the image has been formed, and the like.

[0010] The continuous sheet 10 is sent out from a sheet roll 11 of the unwinding device 1, transported by the rollers of the unwinding device 1, the transport section 3, the drying section 7, and the winding device 9, and taken up by a print roll 91 of the winding device 9. The continuous sheet 10 is transported opposite to the head unit 50 in the image forming device 5, and an image is formed by liquid ejected from the head unit 50.

[0011] In the head unit 50, for example, full line type head arrays 51K, 51C, 51M, and 51Y for four colors are arranged in order from the upstream side in the sheet conveying direction, and liquid circulation mechanisms 200K, 200C, 200M, and 200Y corresponding to the head arrays 51K, 51C, 51M, and 51Y, respectively. Each of the head arrays 51K, 51C, 51M, and 51Y includes one or more liquid ejection heads, and ejects black (K), cyan (C), magenta (M), and yellow (Y) liquids onto the continuous sheet 10 being conveyed.

[0012] FIG. 2 is an explanatory diagram illustrating the configuration of the head unit 50, when the head unit 50 is viewed from the normal direction of the sheet surface of the continuous sheet 10 facing the head unit 50. As shown in FIG. 2, each of the head arrays 51K, 51C, 51M, and 51Y of this embodiment has liquid ejection heads 100 arranged in a staggered pattern on the base member 52. More specifically, the liquid ejection heads 100 arranged in each of the head arrays 51K, 51C, 51M, and 51Y are arranged so that the nozzle row direction coincides with the sheet width direction (direction perpendicular to the sheet conveying direction). The sheet conveying direction positions of adjacent liquid ejection heads 100 are shifted alternately, and the sheet width direction positions of the nozzle rows of adjacent liquid ejection heads 100 are arranged so that they partially overlap each other.

[0013] FIG. 3 is an explanatory perspective view showing the appearance of the liquid ejection head 100 according to this embodiment. FIG. 4 is a cross-sectional explanatory diagram perpendicular to the nozzle row direction of the liquid ejection head 100 in this embodiment. The liquid ejection head 100 of this embodiment includes a structural portion in which a nozzle plate 101, a flow path plate 102, and a vibration plate member 103 are laminated and joined together. The liquid ejection head 100 also includes a piezoelectric actuator 111 as a pressure generating means for displacing a vibration region (vibration plate) 130 of the vibration plate member 103, a common liquid chamber member 120 that also serves as a frame member of the liquid ejection head 100, and a cover 129. The portion formed by the flow path plate 102 and the vibration plate member 103 is referred to as a flow path member 140.

[0014] The nozzle plate 101 is formed with a plurality of nozzles 104 for ejecting liquid.

[0015] The flow path plate 102 is formed with an individual liquid chamber 106 as a pressure chamber communicating with the nozzle 104 via a nozzle communication passage 105, a supply-side fluid resistance portion 107 communicating with the individual liquid chamber 106, and a through hole or groove portion serving as a liquid introduction portion 108 communicating with the supply-side fluid resistance portion 107. The nozzle communication passage 105 is a flow path communicating with each of the nozzle 104 and the individual liquid chamber 106. In addition, the liquid introduction portion 108 communicates with a supply-side common liquid chamber 110 via an opening 109 in the vibration plate member 103.

[0016] The diaphragm member 103 has a deformable vibration region 130 that forms the wall surface of the individual liquid chamber 106 of the flow path plate 102. The diaphragm member 103 has, for example, a two-layer structure (not limited to this), and is composed of a first layer that forms a thin portion and a second layer that forms a thick portion from the flow path plate 102 side, and the deformable vibration region 130 is formed in the first layer in a portion corresponding to the individual liquid chamber 106.

[0017] On the opposite side of the vibration plate member 103 from the individual liquid chamber 106, a piezoelectric actuator 111 including an electromechanical conversion element is disposed as a driving means (actuator means, pressure generating means) for deforming the vibration region 130 of the vibration plate member 103. The piezoelectric actuator 111 is, for example, formed by groove processing a piezoelectric member bonded onto a base member 113 by half-cut dicing to form a required number of columnar piezoelectric elements 112 in a comb shape at specified intervals. The piezoelectric elements 112 are bonded to protruding portions 130a which are island-shaped thick portions formed in the vibration region 130 of the vibration plate member 103. A flexible wiring member 115 is connected to the piezoelectric elements 112.

[0018] A supply side common liquid chamber 110 and a discharge side common liquid chamber 150 are formed in the common liquid chamber member 120. The supply side common liquid chamber 110 communicates with a supply port 171, and the discharge side common liquid chamber 150 communicates with a discharge port 181. The common liquid chamber member 120 is constituted by, for example, a first common liquid chamber member 121 and a second common liquid chamber member 122, and the first common liquid chamber member 121 is joined to the vibration plate member 103 side of the flow path member 140, and the second common liquid chamber member 122 is laminated and joined to the first common liquid chamber member 121.

[0019] The first common liquid chamber member 121 forms a downstream common liquid chamber 110A which is a part of the supply side common liquid chamber 110 which communicates with the liquid introduction portion 108, and a discharge side common liquid chamber 150 which communicates with a discharge flow path 151. The second common liquid chamber member 122 forms an upstream common liquid chamber 110B which is the remaining part of the supply side common liquid chamber 110. The flow path plate 102 is formed with a discharge flow path 151 which extends along the surface direction of the flow path plate 102 and communicates with each individual liquid chamber 106 via a nozzle communication path 105. The discharge flow path 151 communicates with the discharge side common liquid chamber 150.

[0020] In the liquid ejection head 100 of this embodiment, for example, by lowering the voltage applied to the piezoelectric element 112 from a reference potential (intermediate potential), the piezoelectric element 112 contracts, the vibration area 130 of the diaphragm member 103 is pulled, and the volume of the individual liquid chamber 106 expands. As a result, liquid flows into the individual liquid chamber 106. On the other hand, by increasing the voltage applied to the piezoelectric element 112 to expand the piezoelectric element 112 in the stacking direction and deform the vibration area 130 of the diaphragm member 103 in a direction toward the nozzle 104, the volume of the individual liquid chamber 106 contracts. As a result, the liquid in the individual liquid chamber 106 is pressurized, and the liquid is ejected from the nozzle 104.

[0021] The liquid in the individual liquid chamber 106 that is not ejected from the nozzle 104 is discharged from the discharge flow path 151 to the discharge side common liquid chamber 150, and is then supplied again from the discharge side common liquid chamber 150 to the supply side common liquid chamber 110 through an external circulation path. Note that the method of driving the head is not limited to the above example (pull-push shot), and pull shots, push shots, etc. can also be performed depending on the applied drive waveform.

[0022] FIG. 5 is an explanatory diagram for explaining the configuration and operation of the liquid circulation mechanism 200 in this embodiment. Although the liquid circulation mechanism 200 is provided for each of the head arrays 51K, 51C, 51M, and 51Y, the configuration and operation thereof are substantially the same.

[0023] The liquid circulation mechanism 200 includes a main tank 201, a supply side sub-tank 211, a discharge side sub-tank 221, and an intermediate sub-tank 231 as means for storing the liquid discharged from the liquid discharge head 100. Each of the sub-tanks 211, 221, 231 is configured so that an interface between gas and liquid (gas-liquid interface) 210 is generated inside. The intermediate sub-tank 231 is open to the atmosphere, and is disposed between the supply side sub-tank 211 and the discharge side sub-tank 221.

[0024] The liquid circulation mechanism 200 also includes, as liquid sending means for generating a liquid flow for circulating the liquid, a supply pump 202 that sends liquid from the intermediate sub-tank 231 to the supply side sub-tank 211, a discharge pump 203 that sends liquid from the discharge side sub-tank 221 to the intermediate sub-tank 231, and a refill pump 204 that sends liquid from the main tank 201 to the intermediate sub-tank 231. The liquid circulation mechanism 200 also includes a supply side manifold 241 and a discharge side manifold 251 that communicate with a plurality of liquid ejection heads 100 provided in the head array 51 to which the liquid circulation mechanism 200 is connected.

[0025] Furthermore, the liquid circulation mechanism 200 includes a degassing device 270 between the supply side sub-tank 211 and the supply side manifold 241, as a degassing means for removing dissolved gas (air bubbles, etc.) from the liquid.

[0026] The intermediate sub-tank 231 receives liquid from the main tank 201 via the supply passage filter 205 and the supply passage by the liquid sending operation of the supply pump 204. The supply pump 204 performs a liquid sending operation so that the liquid level in the intermediate sub-tank 231 is maintained at a predetermined height based on the detection result of a liquid level detection means 232 that detects the liquid level position (liquid level height) in the intermediate sub-tank 231.

[0027] The intermediate sub-tank 231 and the supply side sub-tank 211 are connected through a supply passage 281, and a supply pump 202 is provided in the supply passage 281. The intermediate sub-tank 231 and the discharge side sub-tank 221 are connected through a discharge passage 282, and a discharge pump 203 is provided in the discharge passage 282 as a second liquid flow generating means.

[0028] The supply side sub-tank 211 is connected to a supply side manifold 241 through a supply passage 291 including a degassing device 270 and a supply passage filter 271. The supply side manifold 241 is connected to the supply port 171 side of the liquid ejection head 100 through a head supply passage 242. The supply side manifold 241 is also provided with a supply pressure sensor 274 as a detection means for detecting the pressure inside the supply side manifold 241. The supply passage of this embodiment is mainly composed of supply passages 281, 291, the supply side manifold 241, and the head supply passage 242.

[0029] The discharge side sub-tank 221 is connected to the discharge side manifold 251 through a discharge passage 292. The discharge side manifold 251 is connected to the discharge port 181 side of the liquid ejection head 100 through a head discharge passage 252. The discharge side manifold 251 is provided with a discharge pressure sensor 276 as a detection means for detecting the pressure inside the discharge side manifold 251. Note that instead of the discharge pressure sensor 276, a detection means for detecting the liquid flow speed inside the discharge side manifold 251 may be provided. The discharge passage of this embodiment is mainly composed of the discharge passages 282, 292, the discharge side manifold 251, and the head discharge passage 252.

[0030] In this embodiment, liquid circulates through a circulation path that runs from the intermediate sub-tank 231, through the supply passage 281, the supply side sub-tank 211, the supply passage 291, the degassing device 270, the supply side manifold 241, the head supply passage 242, the liquid ejection head 100, the head discharge passage 252, the discharge side manifold 251, the discharge passage 292, the discharge side sub-tank 221, the discharge passage 282, and back to the intermediate sub-tank 231.

[0031] In this embodiment, the control unit 500 that controls the head unit 50 controls the liquid sending operation by independent feedback control of the supply pump 202 and the discharge pump 203 based on the detection results of the supply pressure sensor 274 and the discharge pressure sensor 276. This controls the flow rate of the liquid flowing through the supply passage and the discharge passage, and circulates the liquid so as to obtain a predetermined meniscus pressure.

[0032] Next, the exhaust passage pressure reducing mechanism 400 in this embodiment will be described. 5, in the middle of the discharge passage 292, a branch portion is provided which branches into a suction passage 402 as a separate passage portion different from the circulation passage portion (discharge passage 292) which leads to the discharge side sub-tank 221. This branch portion is provided with a flow path switching means 401 which switches the flow path of the liquid passing through the branch portion to the discharge passage 292 or the suction passage 402. The discharge passage pressure reduction mechanism 400 of this embodiment is connected to the branch portion of the discharge passage 292 via the suction passage 402. The discharge passage pressure reduction mechanism 400 may be provided individually for each of the liquid circulation mechanisms 200K, 200C, 200M, and 200Y of each color, or may be provided in common to some or all of the liquid circulation mechanisms 200K, 200C, 200M, and 200Y.

[0033] The discharge passage pressure reduction mechanism 400 functions as a liquid flow generating means for generating a liquid flow that draws the liquid in the nozzle 104 of the liquid ejection head 100 toward the individual liquid chamber 106 by sucking the liquid in the discharge passage 292 from the branching portion into the suction passage 402. The discharge passage pressure reduction mechanism 400 of this embodiment includes a discharge tank 410 as a liquid storage portion, an air pressure adjustment means 411, an air pump 412 as a negative pressure generating means, and an air pressure sensor 414.

[0034] Upon receiving a flow path switching signal from the control unit 500, the flow path switching means 401 performs a switching operation to a flow path corresponding to the flow path switching signal.

[0035] The discharge tank 410 is a liquid storage section that stores the liquid sucked from the discharge passage 292 through the branching section into the suction passage 402. The discharge tank 410 is configured so that an interface between gas and liquid (gas-liquid interface) 210 is generated inside, and the gas in the discharge tank 410 is discharged to the outside from the gas discharge passage 403 by an air pump 412. The air pump 412 is connected to the discharge tank 410 via an air pressure adjustment means 411, and operates to continuously reduce the pressure inside the discharge tank 410. The air pressure adjustment means 411 adjusts the reduction in pressure by the air pump 412 so that the output value of an air pressure sensor 414 that detects the pressure inside the discharge tank 410 becomes a set value instructed by the control unit 500.

[0036] Next, a meniscus recovery operation as a maintenance operation in this embodiment will be described. The meniscus recovery operation of this embodiment is an operation to temporarily destroy the meniscus by drawing the liquid in the nozzle 104 of the liquid ejection head 100 toward the individual liquid chamber 106. By such an operation, the liquid in the nozzle where particles have settled or the viscosity has increased (thickened) can be replaced with normal liquid in the individual liquid chamber 106, and the meniscus can be restored to a state where normal ejection operation is possible.

[0037] When the liquid in the nozzle 104 is drawn into the individual liquid chamber 106, external air is sucked in from the nozzle 104 and taken in as air bubbles in the liquid. These air bubbles have the effect of improving the mixability between the liquid in the nozzle, whose particles have settled or whose viscosity has increased (thickened), and the other liquid in the individual liquid chamber 106, so a certain amount of air bubbles may be mixed in the liquid. However, if the amount of air bubbles in the liquid becomes too large, various problems will occur. For example, if the amount of air bubbles in the liquid becomes too large, the detection result of the discharge pressure sensor 276 that detects the pressure in the discharge passage will become unstable (detection value will fluctuate, etc.), making it difficult to properly control the supply pump 202 and the discharge pump 203, and making it impossible to properly control the liquid circulation.

[0038] In the conventional configuration, during this meniscus recovery operation, the discharge pump 203 used for circulating the liquid is used to generate a negative pressure in the discharge passage that is greater than that during liquid circulation, thereby drawing the liquid in the nozzle 104 into the individual liquid chamber 106. In this configuration, air bubbles caused by external air sucked in from the nozzle 104 are taken into the liquid and accumulate there each time a meniscus recovery operation is performed. As a result, the amount of air bubbles contained in the circulated liquid increases over time, causing an excess of air bubbles and resulting in the above-mentioned problems.

[0039] It is possible to reduce the amount of air bubbles in the circulated liquid by adopting a configuration (degassing configuration) in which the air-liquid interface 210 is generated inside each of the sub-tanks 211, 221, 231 in the circulation path, as in this embodiment, or by providing a degassing device 270 in the circulation path. However, unless the amount of air bubbles that can be reduced in this way exceeds the amount of air bubbles taken in during the meniscus recovery operation, the amount of air bubbles contained in the circulated liquid increases over time.

[0040] According to this embodiment, the discharge passage pressure reducing mechanism 400 is connected to a branching portion provided in the discharge passage, and during the meniscus recovery operation, the flow path switching means 401 switches to the suction passage 402, and the liquid in the discharge passage is sucked from the branching portion into the suction passage 402. This generates a liquid flow that draws the liquid in the nozzle 104 toward the individual liquid chamber 106, and the meniscus recovery operation can be performed. In this embodiment, during the meniscus recovery operation, the liquid in the discharge passage is sucked into the suction passage 402, which is different from the discharge passage that constitutes the circulation path, so that air bubbles contained in the liquid sucked into the suction passage 402 are removed from the circulating liquid. That is, according to this embodiment, air bubbles can be removed from the circulating liquid every time the meniscus recovery operation is performed. Therefore, even if air bubbles are taken into the circulating liquid by the air sucked from the nozzle 104 every time the meniscus recovery operation is performed, the amount of air bubbles in the circulating liquid can be prevented from becoming excessive, and the occurrence of the above-mentioned problems can be prevented.

[0041] To explain the meniscus recovery operation in detail, first, before the meniscus recovery operation, an operation of circulating the liquid along the circulation path is performed. In this circulation operation, the flow path switching means 401 is set to the flow path of the discharge passage 292 (the flow path from the discharge side manifold 251 to the discharge side sub-tank 221). Then, based on the detection results of the supply pressure sensor 274 and the discharge pressure sensor 276, the control unit 500 feedback-controls the supply pump 202 and the discharge pump 203 to circulate the liquid so as to obtain a predetermined meniscus pressure.

[0042] At this time, the control unit 500 instructs the air pressure adjustment means 411 to set a negative pressure greater than the detection value of the discharge pressure sensor 276 during stable circulation in the discharge passage. Therefore, the pressure of the discharge tank 410 in the discharge passage pressure reduction mechanism 400 is adjusted by the air pump 412, the air pressure adjustment means 411, and the air pressure sensor 414 to a negative pressure greater than the detection value of the discharge pressure sensor 276 during stable circulation in the discharge passage.

[0043] The control unit 500 controls the flow path switching means 401 at the start timing of the meniscus recovery operation to switch from the discharge passage 292 (flow path to the discharge side sub-tank 221) to the suction passage 402 (flow path to the discharge passage pressure reduction mechanism 400) for a predetermined operation time set in advance. By switching the flow path in this way, the discharge passage 292 is connected to the discharge passage pressure reduction mechanism 400, which is at a negative pressure greater than the pressure at this time (pressure during stable circulation), and a liquid flow is generated that draws the liquid in the nozzle 104 into the individual liquid chamber 106. As a result, the meniscus is destroyed, and the liquid in the nozzle, in which particles have settled or the viscosity has increased (thickened), is replaced with normal liquid in the individual liquid chamber 106.

[0044] Thereafter, after a preset operation time has elapsed, the flow path switching means 401 switches the flow path of the branching section from the suction passage 402 (flow path to the discharge passage pressure reduction mechanism 400) to the discharge passage 292 (flow path to the discharge side sub-tank 221) under the control of the control unit 500. As a result, the control unit 500 feedback controls the supply pump 202 and the discharge pump 203 based on the detection results of the supply pressure sensor 274 and the discharge pressure sensor 276, thereby returning the pressure in the discharge passage to the pressure during stable circulation at which a predetermined meniscus pressure is obtained. As a result, a meniscus that enables normal discharge operation is formed, and the circulation of the liquid is resumed.

[0045] FIG. 6 is an explanatory diagram showing the positional relationship between a plurality of liquid ejection heads 100 provided in one head array 51 and non-image regions 10b on the continuous sheet 10. As shown in FIG. FIG. 7 is an explanatory diagram showing the positional relationship between the head unit 50 including the four head arrays 51K, 51C, 51M, and 51Y and the non-image area 10b on the continuous sheet 10. As shown in FIG.

[0046] The meniscus recovery operation of this embodiment is an operation that once destroys the meniscus of the nozzle 104, and therefore cannot be performed during an image forming operation in which an image forming operation is being performed in which liquid is discharged from the nozzle 104 of the liquid ejection head 100 onto the continuous sheet 10 based on image information. Therefore, the meniscus recovery operation of this embodiment is performed during a non-image forming operation in which an image forming operation is not being performed. Examples of periods of non-image forming operation include a period before a print job is started, a period after a print job is completed, and a period in which the image forming operation is temporarily halted due to some factor.

[0047] In this embodiment, the meniscus recovery operation can be performed during a non-image forming operation during a continuous image forming operation in which images based on image information are continuously formed on the continuous sheet 10. In this case, the meniscus recovery operation is performed during a period in which a non-image area portion 10b between image area portions 10a (areas where images are formed by liquid ejection) on the continuous sheet 10 exists in the facing area (liquid ejection area) of the target head array 51. The meniscus recovery operation may be performed every time a non-image area portion 10b on the continuous sheet 10 exists in the facing area (liquid ejection area) of the target head array 51, or may be performed at predetermined intervals.

[0048] The execution time of the meniscus recovery operation (the length of the period during which the flow path of the branching portion is switched to the suction passage 402 side (predetermined operation time)) is limited by the time for the non-image area 10b on the continuous sheet 10 to pass through the opposing area of ​​the target head array 51. Specifically, for example, as shown in FIG. 6, it is set shorter than the time from the point when the downstream side (leading end side) of the non-image area 10b in the sheet conveying direction passes through the downstream side (leading end side) of the nozzle surface range (sheet conveying direction range) 100a in the sheet conveying direction of all the liquid ejection heads 100 connected to the same discharge passage pressure reducing mechanism 400 to the point when the upstream side (rear end side) of the non-image area 10b in the sheet conveying direction passes through the upstream side (rear end side) of the nozzle surface range 100a in the sheet conveying direction. The length of the continuous sheet 10 in the sheet conveying direction corresponding to this operation time is indicated by the reference symbol 10c in FIG. 6.

[0049] FIG. 8 is a flowchart showing an example of the flow of the meniscus recovery operation in this embodiment. When the image forming system 1000 is powered on (S1), the control unit 500 first performs an initialization process (S2) such as controlling the flow path switching means 401 to switch the flow path of the branch to the discharge passage 292 (the flow path from the discharge side manifold 251 to the discharge side sub-tank 221). After that, the control unit 500 reads / inputs setting information for the meniscus recovery operation (S3).

[0050] Examples of this setting information include the operation timing of the meniscus recovery operation (non-image forming operation period), the operation frequency of the meniscus recovery operation (how many pages it is performed on, how many jobs it is performed on, the time interval between meniscus recovery operations during standby, etc.), and image creation settings (the page length of the job (the length of the image area 10a in the sheet conveying direction), the length of the non-image area 10b between the image area 10a in the sheet conveying direction, etc.).

[0051] Next, the control unit 500 starts feedback control of the supply pump 202 and the discharge pump 203 based on the detection results of the supply pressure sensor 274 and the discharge pressure sensor 276, and starts circulating the liquid to the liquid ejection head 100 (S4). Meanwhile, the control unit 500 controls the discharge passage pressure reduction mechanism 400 to operate the air pump 412 to reduce the pressure in the discharge tank 410 (S5). When the pressure in the discharge tank 410 detected by the air pressure sensor 414 reaches the set pressure for the meniscus recovery operation (a set value that is a negative pressure greater than the detection value of the discharge pressure sensor 276 during stable circulation in the discharge passage) (Yes in S6), the system transitions to a printable standby state (S7).

[0052] During this standby state, if a time period equivalent to a predetermined meniscus recovery operation time interval has elapsed without an instruction to start printing being given (without starting an image forming operation), the meniscus recovery operation is executed (S8).

[0053] Furthermore, when a user issues an instruction to start printing, such as by pressing a print start button (S9), the control unit 500 confirms that the image forming system 1000, including the drying unit 7, is ready to print, and then starts conveying the continuous sheet 10 (S10). Then, when the control unit 500 confirms that the continuous sheet 10 is in a constant speed conveying state at a target speed based on the output value of the encoder 3b provided on the roller 3a of the conveying unit 3 (S11), it determines that the continuous sheet 10 is in an image forming ready state so that an image forming operation can be started.

[0054] After determining that the image formation is possible, the control unit 500 performs a pre-printing meniscus recovery operation before starting a liquid ejection operation (image formation operation) based on the image data (image information) of the job (S12). In this pre-printing meniscus recovery operation, the meniscus recovery operation is performed on all the nozzles 104 of all the liquid ejection heads 100 for the head arrays 51K, 51C, 51M, and 51Y of all the colors (K, C, M, and Y).

[0055] After the pre-printing meniscus recovery operation is completed, the control unit 500 starts the image forming operation (S13), and ejects liquid according to the image data from the liquid ejection heads 100 of the head arrays 51K, 51C, 51M, and 51Y in order from the upstream side in the sheet conveying direction. As a result, images according to the image data are sequentially formed in the image area 10a of the continuous sheet 10.

[0056] In this embodiment, the control unit 500 counts the output signal of the encoder 3b, starting from the liquid ejection start timing of the black head array 51K, for example. The control unit 500 calculates the encoder count value at the start and end of the passage of the operation time corresponding portion 10c of the non-image area 10b through the opposing area of ​​each head array, based on the page length of the job set before printing and the length of the non-image area 10b in the sheet conveying direction. Then, according to the calculated encoder count value, the meniscus recovery operation timing set before printing, frequency, and other setting information, the meniscus recovery operation for all nozzles of each color (K, C, M, Y) is performed independently for each head array 51K, 51C, 51M, 51Y.

[0057] In this specification, the liquid to be ejected may have a viscosity and surface tension that allows it to be ejected from the head, and is not particularly limited, but is preferably one whose viscosity becomes 30 [mPa·s] or less at room temperature and normal pressure, or by heating or cooling. More specifically, the liquid may be a solution, suspension, emulsion, etc., containing a solvent such as water or an organic solvent, a colorant such as a dye or pigment, a functionalizing material such as a polymerizable compound, a resin, or a surfactant, a biocompatible material such as DNA, amino acids, proteins, calcium, or an edible material such as a natural dye, etc., and these can be used for applications such as inkjet ink, surface treatment liquid, a liquid for forming a component of an electronic element or a light-emitting element, an electronic circuit resist pattern, a material liquid for three-dimensional modeling, etc.

[0058] The "liquid ejection unit" is a liquid ejection head integrated with functional parts and mechanisms, and includes a collection of parts related to ejecting liquid. For example, the "liquid ejection unit" includes the liquid circulation mechanism 200 and the discharge passage pressure reduction mechanism 400, as well as at least one of the following components: a head tank, a carriage, a supply mechanism, a maintenance and recovery mechanism, and a main scanning movement mechanism, combined with a liquid ejection head.

[0059] Here, integration includes, for example, a liquid ejection head, a functional part, and a mechanism that are fixed to each other by fastening, bonding, engaging, etc., and one is held movably relative to the other. Also, the liquid ejection head, the functional part, and the mechanism may be configured to be detachable from each other.

[0060] For example, there are liquid ejection units in which the liquid ejection head and the head tank are integrated together, and there are also liquid ejection units in which the liquid ejection head and the head tank are integrated together by being connected to each other by a tube, etc. Here, a unit including a filter can be added between the head tank and the liquid ejection head of these liquid ejection units.

[0061] Furthermore, there is a liquid ejection unit in which the liquid ejection head and the carriage are integrated.

[0062] In some liquid ejection units, the liquid ejection head is movably supported by a guide member that constitutes a part of the scanning movement mechanism, and the liquid ejection head and the scanning movement mechanism are integrated together, and in some liquid ejection units, the liquid ejection head, the carriage, and the main scanning movement mechanism are integrated together.

[0063] Furthermore, there is a liquid ejection unit in which a cap member, which is part of the maintenance and recovery mechanism, is fixed to a carriage on which the liquid ejection head is attached, thereby integrating the liquid ejection head, carriage, and maintenance and recovery mechanism.

[0064] In addition, some liquid ejection units have a head tank or a liquid ejection head to which a flow path component is attached, and a tube is connected to the liquid ejection head, integrating the liquid ejection head with a supply mechanism. Liquid is supplied from a liquid storage source to the liquid ejection head via this tube.

[0065] The main scanning movement mechanism includes the guide member alone, and the supply mechanism includes the tube alone and the loading unit alone.

[0066] The term "liquid ejection device" includes devices that have a liquid ejection head or a liquid ejection unit and eject liquid by driving the liquid ejection head. Liquid ejection devices include not only devices that can eject liquid onto objects to which the liquid can adhere, but also devices that eject liquid into air or liquid.

[0067] This "liquid ejecting device" can also include means for feeding, transporting, and discharging items onto which liquid can be attached, as well as pre-processing devices and post-processing devices.

[0068] For example, examples of "devices that eject liquid" include image forming devices that eject ink to form an image on paper, and three-dimensional modeling devices that eject modeling liquid onto a powder layer formed by layering powder in order to create a three-dimensional object (a three-dimensional model).

[0069] In addition, the term "liquid ejection device" is not limited to devices that use ejected liquid to visualize meaningful images such as letters and figures. For example, it also includes devices that form patterns that have no meaning in themselves and devices that create three-dimensional images.

[0070] The above-mentioned "material to which a liquid can adhere" means material to which a liquid can adhere at least temporarily, and material to which the liquid adheres and sticks, material to which the liquid adheres and penetrates, etc. Specific examples include media such as paper, recording paper, film, cloth, and other recording media, electronic substrates, electronic components such as piezoelectric elements, powder layers, organ models, and test cells, and unless otherwise specified, all materials to which a liquid can adhere are included.

[0071] The material of the "material to which a liquid can adhere" may be any material to which a liquid can adhere even temporarily, such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, and ceramics.

[0072] Furthermore, the "liquid ejection device" may be a device in which a liquid ejection head and an object to which liquid can be attached move relatively, but is not limited to this. Specific examples include a serial type device in which a liquid ejection head moves, a line type device in which a liquid ejection head does not move, etc.

[0073] Other examples of "liquid ejecting devices" include a treatment liquid application device that ejects a treatment liquid onto paper to apply the treatment liquid to the surface of the paper for purposes such as modifying the surface of the paper, and an injection granulation device that ejects a composition liquid in which raw materials are dispersed through a nozzle to granulate fine particles of the raw materials.

[0074] In the present application, the terms image formation, recording, printing, imprinting, printing, modeling, and the like are all synonymous.

[0075] The above description is merely an example, and each of the following aspects provides unique effects. [First aspect] The first aspect is a liquid ejection head 100 including a nozzle 104 for ejecting liquid, a pressure chamber (e.g., an individual liquid chamber 106) communicating with the nozzle, and a pressure generating means (e.g., a piezoelectric actuator 111) for generating a pressure fluctuation in the pressure chamber, and a liquid ejection unit (e.g., a head array 51 or a head unit 52) ​​including a liquid circulation mechanism 200 for circulating liquid such that liquid discharged from the pressure chamber through a discharge passage (e.g., discharge passages 282, 292, etc.) returns to the pressure chamber through a supply passage (e.g., supply passages 281, 291, etc.). 0), the discharge passage is provided with a branch portion which branches off to another passage portion (e.g., a suction passage 402) different from a circulation passage portion (e.g., a discharge passage 292) which leads to the pressure chamber, and the nozzle is provided with a liquid flow generating means (e.g., a discharge passage pressure reducing mechanism 400) which generates a liquid flow which draws the liquid in the nozzle into the pressure chamber by sucking the liquid in the discharge passage from the branch portion to the other passage portion, and a flow path switching means 401 which switches the flow path of the liquid passing through the branch portion to the circulation passage portion or the other passage portion. When performing a maintenance operation to draw the liquid in the nozzle into the pressure chamber, external air is sucked in from the nozzle and taken into the liquid as air bubbles. These air bubbles have the effect of improving the mixability of the liquid in the nozzle, which has undergone particle settling or increased viscosity (thickening), with other liquid in the pressure chamber, so a certain amount of air bubbles may be mixed into the liquid. However, if the amount of air bubbles in the liquid becomes too large, various problems may occur. For example, in the case where the liquid circulation is controlled based on the detection results of the liquid flow velocity or pressure in the discharge passage, if the amount of air bubbles in the liquid becomes too large, the detection results become unstable, making it difficult to properly control the liquid circulation. In the conventional configuration, during this maintenance operation, the liquid circulation mechanism used for circulating the liquid is used to generate a negative pressure in the discharge passage that is greater than that during liquid circulation, so that the liquid in the nozzle is drawn into the pressure chamber. With this configuration, air bubbles caused by external air sucked in from the nozzle are taken into the liquid and accumulate there each time a maintenance operation is performed. As a result, the amount of air bubbles contained in the circulating liquid increases over time, causing an excess of air bubbles and various problems. In this aspect, a branch portion is provided in the discharge passageway, which is a circulation passageway leading to the pressure chamber and another passageway connected to the liquid flow generating means, and a flow path switching means is provided at this branch portion. As a result, when the branch portion is switched to the circulation passageway side by the flow path switching means, the liquid can be circulated by the liquid circulation mechanism. On the other hand, when the branch portion is switched to the other passageway side by the flow path switching means, the liquid flow generating means sucks the liquid in the discharge passageway from the branch portion to the other passageway, and generates a liquid flow that draws the liquid in the nozzle into the pressure chamber, thereby allowing a maintenance operation to be performed. In this aspect, during the maintenance operation, the liquid in the discharge passage is sucked into another passage portion different from the circulation passage portion, so that air bubbles contained in the liquid sucked into the other passage portion are removed from the circulated liquid. That is, according to this aspect, air bubbles can be removed from the circulated liquid every time a maintenance operation is performed. Therefore, even if air bubbles are taken into the circulated liquid by the air sucked from the nozzle every time a maintenance operation is performed, it is possible to prevent the amount of air bubbles in the circulated liquid from becoming excessive, and the occurrence of various problems can be prevented.

[0076] [Second aspect] The second aspect is characterized in that in the first aspect, the liquid flow generating means has a liquid storage section (e.g., discharge tank 410) for storing the liquid sucked into the other passage section, and negative pressure generating means (e.g., air pump 412) for generating negative pressure in the liquid storage section for sucking the liquid in the discharge passage from the branch section into the other passage section. According to this, the liquid sucked into the separate passage can be stored in the liquid storage section. The liquid stored in the liquid storage section may be discarded, or may be returned to the circulation path after air bubbles in the liquid have been sufficiently removed.

[0077] [Third aspect] A third aspect is the second aspect, characterized in that the negative pressure generating means sucks in gas in the liquid storage portion to generate the negative pressure in the liquid storage portion. According to this, gas (air bubbles) that has escaped from the liquid stored in the liquid storage portion can be discharged from the liquid storage portion by the negative pressure generating means.

[0078] [Fourth aspect] A fourth aspect is characterized in that, in any of the first to third aspects, the liquid circulation mechanism further comprises a detection means (e.g., a discharge pressure sensor 276) for detecting a liquid flow velocity or pressure in the discharge passage, and a second liquid flow generating means (e.g., a discharge pump 203) for generating a liquid flow in the discharge passage according to a detection result of the detection means, within a range in which the liquid in the nozzle is not drawn into the pressure chamber when the liquid in the discharge passage is caused to flow from the branch portion to the circulation passage portion. In such a liquid circulation mechanism, if the amount of bubbles in the liquid becomes too large, the detection result of the detection means that detects the pressure in the discharge passage becomes unstable (the detection value fluctuates, etc.), making it difficult to appropriately control the second liquid flow generating means and therefore difficult to appropriately control the liquid circulation. Therefore, for a liquid discharge unit equipped with such a liquid circulation mechanism, the effect of being able to suppress the amount of bubbles in the circulated liquid from becoming excessive is particularly beneficial.

[0079] [Fifth aspect] The fifth aspect is an apparatus for discharging liquid (for example, the image forming apparatus 5 or the image forming system 1000), which is characterized in that it comprises the liquid discharging unit according to any one of the first to fourth aspects. According to this aspect, when performing a maintenance operation to draw the liquid in the nozzle into the pressure chamber, it is possible to prevent the amount of air bubbles in the circulated liquid from becoming excessive, thereby providing a device for ejecting liquid that can prevent the occurrence of malfunctions.

[0080] [Sixth aspect] The sixth aspect is characterized in that, in the fifth aspect, during a non-image forming operation in which an image forming operation is not being performed in which liquid is ejected from the nozzles of the liquid ejection head onto a recording material (e.g., a continuous sheet 10) based on image information, the flow path of the liquid passing through the branching portion is switched to the other passage portion by the flow path switching means, a liquid flow is generated by the liquid flow generating means to draw the liquid in the nozzles into the pressure chamber, and then the flow path of the liquid passing through the branching portion is switched to the circulation passage portion by the flow path switching means. According to this, it is possible to perform a maintenance operation for drawing the liquid inside the nozzles into the pressure chambers without affecting the image forming operation.

[0081] [Seventh aspect] A seventh aspect is the sixth aspect, characterized in that, when the image forming operations are performed consecutively, the control means performs the control during a non-image forming operation between the image forming operations. According to this, even during the execution of continuous image forming operations, a maintenance operation can be performed to draw the liquid inside the nozzles into the pressure chambers.

[0082] [Eighth aspect] An eighth aspect is a maintenance method for a liquid ejection unit including a liquid ejection head having a nozzle for ejecting liquid, a pressure chamber connected to the nozzle, and a pressure generating means for generating pressure fluctuations in the pressure chamber, and a liquid circulation mechanism for circulating liquid so that liquid discharged from the pressure chamber through a discharge passage returns to the pressure chamber through a supply passage, characterized in that a flow path switching means for switching the flow path of liquid passing through a branching portion of the discharge passage switches from a circulation passage portion leading to the pressure chamber to another passage portion different from the circulation passage portion, and then the liquid in the discharge passage is sucked from the branching portion to the other passage portion, thereby drawing the liquid in the nozzle toward the pressure chamber. According to this aspect, when a maintenance operation is performed in which the liquid in the nozzle is drawn into the pressure chamber, the amount of air bubbles in the circulated liquid can be prevented from becoming excessive, thereby preventing the occurrence of problems. [Explanation of symbols]

[0083] 1: Unwinding device 3: Transport section 3a: Lola 3b: Encoder 5: Image forming device 7:Drying section 9: Winding device 10: Continuous sheet 10a: Image area section 10b: Non-image area part 10c: Operating time corresponding part 11: Sheet roll 50: Head unit 51: Head array 52: Base material 91: Printing roll 100: Liquid ejection head 101: Nozzle plate 102: Flow path plate 103: Diaphragm member 104: Nozzle 105: Nozzle connection passage 106: Individual liquid chamber 107: Supply side fluid resistance section 108: Liquid introduction section 109 :Aperture 110: Supply side common liquid chamber 111: Piezoelectric actuator 112: Piezoelectric element 113: Base material 115: Flexible wiring materials 120: Common liquid chamber member 121: First common liquid chamber member 122: Second common liquid chamber member 129: Cover 130: Vibration area 140: Flow path member 150:Discharge side common liquid chamber 151: Discharge flow path 171: Supply port 181: Discharge port 200:Liquid circulation mechanism 201: Main tank 202: Supply pump 203: Discharge pump 204: Supply pump 205: Supply passage filter 210:Air-liquid interface 211: Supply side subtank 221: Discharge side subtank 231: Intermediate sub-tank 232: Liquid level detection means 241: Supply manifold 242: Head supply passage 251: Discharge manifold 252: Head discharge passage 270: Deaeration device 271: Supply passage filter 274: Supply pressure sensor 276: Discharge pressure sensor 281,291: Supply passage 282,292:Discharge passage 400: Exhaust passage pressure reducing mechanism 401: Flow path switching means 402: Intake passage 403: Gas exhaust passage 410: Discharge tank 411: Air pressure adjustment means 412: Air pump 414: Barometric pressure sensor 500: Control section 1000: Image forming system [Prior art documents] [Patent documents]

[0084] [Patent Document 1] JP 2018-202768 A

Claims

1. a liquid ejection head including a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, and a pressure generating means for generating a pressure fluctuation in the pressure chamber; a liquid circulation mechanism that circulates liquid such that liquid discharged from the pressure chamber through the discharge passage returns to the pressure chamber through the supply passage, the exhaust passage is provided with a branch portion that branches off into another passage portion different from the circulation passage portion that communicates with the pressure chamber, a liquid flow generating means for sucking the liquid in the discharge passage from the branch portion to the other passage portion, thereby generating a liquid flow that draws the liquid in the nozzle toward the pressure chamber; A liquid discharge unit comprising: a flow path switching means for switching a flow path of liquid passing through the branch portion between the circulation path portion and the other path portion.

2. The liquid ejection unit according to claim 1 , A liquid ejection unit characterized in that the liquid flow generating means has a liquid storage section that stores the liquid sucked into the other passage section, and a negative pressure generating means that generates a negative pressure within the liquid storage section to suck the liquid in the discharge passage from the branch section into the other passage section.

3. The liquid ejection unit according to claim 2, The liquid discharge unit, wherein the negative pressure generating means sucks in gas within the liquid storage portion to generate the negative pressure within the liquid storage portion.

4. The liquid ejection unit according to claim 1 , The liquid circulation mechanism is a liquid ejection unit characterized in that it has a detection means for detecting a liquid flow velocity or pressure in the discharge passage, and a second liquid flow generating means for generating a liquid flow in the discharge passage according to a detection result of the detection means, within a range in which the liquid in the nozzle is not drawn into the pressure chamber when the liquid in the discharge passage is caused to flow from the branch portion to the circulation passage portion.

5. A liquid ejection device comprising the liquid ejection unit according to claim 1 .

6. 6. The liquid ejection device according to claim 5, a control means for controlling a flow path of the liquid passing through the branching portion to be switched to the other passage portion by the flow path switching means during a non-image forming operation in which an image forming operation is not being performed in which liquid is ejected from the nozzles of the liquid ejection head onto a recording material based on image information, and then a liquid flow generating means for generating a liquid flow that draws the liquid in the nozzles into the pressure chamber, and then a control means for controlling a flow path of the liquid passing through the branching portion to be switched to the circulation passage portion by the flow path switching means.

7. 7. The liquid ejection device according to claim 6, The liquid ejecting device, wherein, when the image forming operations are performed successively, the control means executes the control during a non-image forming operation between the image forming operations.

8. A maintenance method for a liquid ejection unit including a liquid ejection head including a nozzle that ejects liquid, a pressure chamber that communicates with the nozzle, and a pressure generating means that generates a pressure fluctuation in the pressure chamber, and a liquid circulation mechanism that circulates liquid such that liquid discharged from the pressure chamber through a discharge passage returns to the pressure chamber through a supply passage, comprising: a flow path switching means for switching the flow path of liquid passing through a branched portion of the discharge passage from a circulation passage portion leading to the pressure chamber to another passage portion different from the circulation passage portion, and then the liquid in the discharge passage is sucked from the branched portion to the other passage portion, thereby drawing the liquid in the nozzle toward the pressure chamber.

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