Liquid ejection head and liquid ejection device

A liquid ejection head, including: first supply passages and first discharge passages extending in a first direction and arranged in a second direction intersecting the first direction; and a second supply passage extending in the second direction and communicating with the first supply passages to supply the liquid thereto and a second discharge passage extending in the second direction and communicating with the first discharge passages to discharge the liquid therefrom, wherein (A) a cross-sectional area of the second supply passage on a plane orthogonal to the second direction at a first portion thereof differs from that at a second portion thereof spaced apart from the first portion in the second direction and/or (B) a cross-sectional area of the second discharge passage on the plane at a first portion thereof differs from that at a second portion thereof spaced apart from the first portion in the second direction.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2018-183365, which was filed on Sep. 28, 2018, the disclosure of which is herein incorporated by reference in its entirety.

BACKGROUND

Technical Field

The following disclosure relates to a liquid ejection head configured to eject a liquid from nozzles and a liquid ejection device including the liquid ejection head.

Description of Related Art

A liquid ejection device configured to eject a liquid from nozzles is known. The known liquid ejection device includes a plurality of individual passages each of which includes an ejection hole, a pressurizing chamber, etc., and which are arranged in a D1 direction. The known liquid ejection device further includes a plurality of first supply passages each of which extends in the D1 direction and which are arranged in a D2 direction that intersects the D1 direction. A part of the individual passages are connected to a corresponding one of the first supply passages. End portions of the respective first supply passages that are located on one end side in the D1 direction are connected to each other by a second supply passage that extends in the D2 direction. Ink is supplied to the second supply passage through an opening formed at its end located on one end side in the D2 direction. The known liquid ejection device further includes a plurality of first discharge passages each of which extends in the D1 direction and which are arranged in the D2 direction. A part of the individual passages are connected to a corresponding one of the first discharge passages. End portions of the respective first discharge passages that are located on the other end side in the D1 direction are connected to each other by a second discharge passage that extends in the D2 direction. Ink in the second discharge passage is collected through an opening forming at its end located on the other end side in the D2 direction.

SUMMARY

In the liquid ejection device constructed as described above, the ink is supplied from the second supply passage to the first supply passages. However, the ink is supplied to the second supply passage through the opening formed at its one end located on the one end side in the D2 direction. In this arrangement, the ink is less prone to flow from the second supply passage into the first supply passages with an increase in a distance by which each first supply passage is distant from the opening toward the other end side in the D2 direction. Further, the ink is less prone to flow into the second discharge passage from the first discharge passages with an increase in the distance by which each first discharge passage is distant from the opening toward the other end side in the D2 direction.

Accordingly, one aspect of the present disclosure is directed to a liquid ejection head configured such that a liquid is supplied from one second supply passage to a plurality of first supply passages and the liquid is discharged from a plurality of first discharge passages to one second discharge passage, the liquid ejection head enabling the liquid to flow uniformly in the first supply passages and the first discharge passages. Another aspect of the present disclosure is directed to a liquid ejection device including the liquid ejection head.

In one aspect of the present disclosure, a liquid ejection head includes: a plurality of individual passages respectively including nozzles; a plurality of first supply passages each extending in a first direction so as to be connected to a part of the individual passages, the first supply passages being arranged in a second direction that intersects the first direction, a liquid being supplied to the part of the individual passages through a corresponding one of the first supply passages; a plurality of first discharge passages each extending in the first direction so as to be connected to a part of the individual passages, the first discharge passages being arranged in the second direction, the liquid being discharged from the part of the individual passages through a corresponding one of the first discharge passages; a second supply passage extending in the second direction and overlapping the first supply passages in a third direction that intersects a plane parallel to both the first direction and the second direction, the second supply passage communicating with the first supply passages to supply the liquid to the first supply passages, a second discharge passage extending in the second direction and overlapping the first discharge passages in the third direction, the second discharge passage communicating with the first discharge passages to discharge the liquid from the first discharge passages; wherein, where an area of a cross section of the second supply passage on a plane orthogonal to the second direction is defined as a cross-sectional area of the second supply passage and two portions of the second supply passage spaced apart from each other in the second direction are respectively defined as a first portion and a second portion, (A) the cross-sectional area of the second supply passage at the first portion differs from the cross-sectional area of the second supply passage at the second portion, and/or (B) where an area of a cross section of the second discharge passage on a plane orthogonal to the second direction is defined as a cross-sectional area of the second discharge passage and two portions of the second discharge passage spaced apart from each other in the second direction are respectively defined as a first portion and a second portion, the cross-sectional area of the second discharge passage at the first portion differs from the cross-sectional area of the second discharge passage at the second portion.

DETAILED DESCRIPTION OF THE EMBODIMENT

There will be hereinafter explained one embodiment of the present disclosure.

Overall Structure of Printer

As shown inFIG. 1, a printer1according to the present embodiment (as one example of “liquid ejection device”) includes an ink jet head2, a platen3, and conveyance rollers4,5.

As shown inFIGS. 1 and 2, the ink-jet head2includes four head units11(11a-11d) and a holder12. Each head unit11is one example of “liquid ejection head”. Each head unit11ejects ink from a plurality of nozzles10formed in its lower surface. Specifically, the nozzles10are arranged in a sheet width direction (as one example of “first direction”) so as to faun a nozzle row9. Each head unit11includes four nozzle rows9arranged in a sheet conveyance direction (as one example of “second direction”) orthogonal to the sheet width direction. Positions in the sheet width direction of the nozzles10in one of any two adjacent nozzle rows9are shifted with respect to those of the nozzles10in another one of the two adjacent nozzle rows9by a distance equal to a quarter of a nozzle pitch at which the nozzles10of each nozzle row9are arranged. It is noted that right and left sides are defined with respect to the sheet width direction as illustrated inFIG. 1. It is further noted that an upper side and a lower side inFIG. 1are respectively defined as an upstream side and a downstream side in the sheet conveyance direction.

The head unit11aand the head unit11care arranged in the sheet width direction, and the head unit11band the head unit11dare arranged in the sheet width direction. The head units11b,11dare positioned downstream of the head units11a,11cin the sheet conveyance direction orthogonal to the sheet width direction. The head units11b,11dare shifted to the right in the sheet width direction with respect to the head units11a,11c. In the thus constructed ink-jet head2, the nozzles10of the four head units11are arranged so as to extend over an entire dimension of a recording sheet P in the sheet width direction, namely, over an entire width of the recording sheet P. That is, the ink-jet head2is a line head. A detailed structure of the head units11will be later explained.

The holder12is a rectangular plate-like member whose longitudinal direction coincides with the sheet width direction. The four head units11are fixed to the holder12. Four rectangular through-holes12aare formed in the holder12so as to correspond to the four head units11. The nozzles10of each head unit11are downwardly exposed (toward the recording sheet P) from a corresponding one of the through-holes12a.

The platen3is disposed below the ink jet head2and opposed to the nozzles10of the four head units11. The platen3is configured to support the recording sheet P from below. The conveyance roller4is disposed upstream of the ink-jet head2and the platen3in the sheet conveyance direction. The conveyance roller5is disposed downstream of the ink-jet head2and the platen3in the sheet conveyance direction. The conveyance rollers4,5convey the recording sheet P in the sheet conveyance direction.

The printer1performs printing on the recording sheet P such that the ink is ejected from the nozzles10of the four head units11onto the recording sheet P being conveyed by the conveyance rollers4,5in the sheet conveyance direction.

Head Unit

The head units11will be next explained. As shown inFIGS. 2, 3, 4A, and4B, each head unit11includes a nozzle plate31, a flow-passage member32, a vibration film33, a plurality of driving elements34, a protection plate35, and flow-passage plates36-39.

The nozzle plate31is formed of a synthetic rein, for instance. The nozzles10of the four nozzle rows9are formed in the nozzle plate31.

The flow-passage member32is formed of silicon (Si) and is disposed on an upper surface of the nozzle plate31. A plurality of pressure chambers40are formed in the flow-passage member32so as to correspond to the respective nozzles10. Each pressure chamber40overlaps, at a central portion thereof in the sheet conveyance direction, the corresponding nozzle10in an up-down direction (as one example of “third direction”). According to this configuration, there are formed, in the flow-passage member32, four pressure chamber rows8each of which is constituted by the pressure chambers40arranged in the sheet width direction. The four pressure chamber rows8are arranged in the sheet conveyance direction.

The vibration film33is disposed on an upper end portion of the flow-passage member32so as to cover the pressure chambers40. The vibration film33is formed of silicon dioxide (SiO2) or silicon nitride (SiN). The vibration film33is formed by oxidization or nitriding of the upper end portion of the flow-passage member32.

Inlet holes33aare formed in the vibration film33such that each inlet hole33aoverlaps, in the up-down direction, an upstream end portion of the corresponding pressure chamber40in the sheet conveyance direction. Outlet holes33bare formed in the vibration film33such that each outlet hole33boverlaps, in the up-down direction, a downstream end portion of the corresponding pressure chamber40in the sheet conveyance direction.

The driving elements34are provided for the respective pressure chambers40. Each driving element34is disposed at a portion of an upper surface of the vibration film33, which portion overlaps the corresponding pressure chamber40in the up-down direction. Each driving element34is a piezoelectric element including a piezoelectric member, electrodes, etc., for instance. The driving elements34have a known structure, and a detailed explanation thereof is dispensed with.

The protection plate35is formed of silicon (Si) and disposed on an upper surface of the flow-passage member32on which the vibration film33and the driving elements34are provided. Supply orifices35aare formed so as to extend through the protection plate35in the up-down direction at portions of the protection plate35athat overlap the corresponding inlet holes33ain the up-down direction. Discharge orifices35bare formed so as to extend through the protection plate35in the up-down direction at portions of the protection plate35that overlap the corresponding outlet holes33bin the up-down direction. In the present embodiment, one nozzle10, one pressure chamber40, one supply orifice35a, and one discharge orifice35bconstitute one individual passage20.

Recesses35care formed on the underside of the protection plate35at portions thereof that overlap the pressure chambers40of the pressure chamber rows8in the up-down direction. The driving elements34are disposed in the recesses35cso as to correspond to the pressure chamber rows8.

The flow-passage plate36is disposed on an upper surface of the protection plate35. There are formed, in the flow-passage plate36, four lower supply manifolds41(each as one example of “first supply passage”) and four lower discharge manifolds42(each as one example of “first discharge passage”).

The four lower supply manifolds41respectively correspond to the four pressure chamber rows8and are arranged in the sheet conveyance direction. Each lower supply manifold41extends in the sheet width direction throughout the pressure chambers40of a corresponding one of the four pressure chamber rows8and overlaps, in the up-down direction, the supply orifices35aconnected to the pressure chambers40. Each lower supply manifold41extends to the right, in the sheet width direction, of a region in which the corresponding pressure chamber row8is disposed. Each lower supply manifold41has a substantially constant dimension (e.g., about 1.0 mm) in the sheet conveyance direction throughout the sheet width direction.

The four lower discharge manifolds42respectively correspond to the four pressure chamber rows8and are arranged in the sheet conveyance direction. Each lower discharge manifold42extends in the sheet width direction throughout the pressure chambers40of a corresponding one of the four pressure chamber rows8and overlaps, in the up-down direction, the discharge orifices35bconnected to the pressure chambers40. Each lower discharge manifold42extends to the left, in the sheet width direction, of a region in which the corresponding pressure chamber row8is disposed. Each lower discharge manifold42has a substantially constant dimension (e.g., about 1.0 mm) in the sheet conveyance direction throughout the sheet width direction.

The flow-passage plate37is disposed on an upper surface of the flow-passage plate36. There are Ruined, in the flow-passage plate37, four supply connection openings46and four discharge connection openings47.

The four supply connection openings46respectively correspond to the four lower supply manifolds41. Each supply connection opening46overlaps, in the up-down direction, a right end portion of the corresponding lower supply manifold41in the sheet width direction. The four supply connection openings46are shaped like rectangles having mutually the same dimension in the sheet width direction and mutually the same dimension in the sheet conveyance direction, so that the four supply connection openings46have mutually the same cross-sectional area on a plane orthogonal to the up-down direction.

The four discharge connection openings47respectively correspond to the four lower discharge manifolds42. Each discharge connection opening47overlaps, in the up-down direction, a left end portion of the corresponding lower discharge manifold42in the sheet width direction. The four discharge connection openings47are shaped like rectangles having mutually the same dimension in the sheet width direction and mutually the same dimension in the sheet conveyance direction, so that the four discharge connection openings47have mutually the same cross-sectional area on the plane orthogonal to the up-down direction.

The flow-passage plate38is disposed on an upper surface of the flow-passage plate37. There are formed, in the flow-passage plate38, an upper supply manifold51(as one example of “second supply passage”) and an upper discharge manifold52(as one example of “second discharge passage”).

The upper supply manifold51extends in the sheet conveyance direction so as to be across the four lower supply manifolds41. The upper supply manifold51overlaps, in the up-down direction, the four supply connection openings46and the right end portions of the respective four lower supply manifolds41in the sheet width direction. The upper supply manifold51has a dimension in the sheet width direction that gradually increases toward the downstream side in the sheet conveyance direction, namely, a dimension in the sheet width direction that gradually increases with an increase in a distance from a supply opening56(which will be explained) in the sheet conveyance direction.

The upper discharge manifold52extends in the sheet conveyance direction so as to be across the four lower discharge manifolds42. The upper discharge manifold52overlaps, in the up-down direction, the four discharge connection openings47and the left end portions of the respective four lower discharge manifolds42in the sheet width direction. The upper discharge manifold52has a dimension in the sheet width direction that gradually increases toward the downstream side in the sheet conveyance direction, namely, a dimension in the sheet width direction that gradually increases with an increase in the distance away from the supply opening56in the sheet conveyance direction.

The flow-passage plate39is disposed on an upper surface of the flow-passage plate38. There are formed, in the flow-passage plate39, the supply opening56and a discharge opening57. The supply opening56overlaps, in the up-down direction, an upstream end of the upper supply manifold51in the sheet conveyance direction. The discharge opening57overlaps, in the up-down direction, an upstream end of the upper discharge manifold52in the sheet conveyance direction.

The supply opening56and the discharge opening57are connected to an ink tank60via respective flow passages not shown. A pump61is provided in the flow passage between the supply opening56and the ink tank60. The pump61delivers the ink in a direction from the ink tank60toward the supply opening56. That is, the pump61delivers the ink toward the upper supply manifold51.

When the ink is delivered by the pump61, the ink in the ink tank60flows into the head unit11through the supply opening56. In the head unit11, the ink flows through the upper supply manifold51, the supply connection openings46, and the lower supply manifolds41, so as to flow into the individual passages20via the corresponding supply orifices35a. Further, the ink in the individual passages20flows out of the corresponding discharge orifices35binto the lower discharge manifolds42, so as to return to the ink tank60via the lower discharge manifolds42, the discharge connection openings47, the upper discharge manifold52, and the discharge opening57. In this way, the ink is circulated between the ink tank60and the head unit11.

Here, a case is considered in which the upper supply manifold51has a cross-sectional area on a plane orthogonal to the sheet conveyance direction that is substantially constant throughout the sheet conveyance direction, unlike the upper supply manifold51in the present embodiment. In this case, the ink flow resistance is substantially the same among four joint portions of the upper supply manifold51at which the upper supply manifold51is joined to the respective four lower supply manifolds41, namely, among four portions of the upper supply manifold51that overlap the respective four supply connection openings46in the up-down direction. Further, the ink flow resistance is substantially the same among four joint portions of the upper discharge manifold52at which the upper discharge manifold52is joined to the respective four lower discharge manifolds42, namely, among four portions of the upper discharge manifold52that overlap the respective four discharge connection openings47in the up-down direction.

In the above case, there are considered degrees of ease of flow of the ink in the four lower supply manifolds41and in the four lower discharge manifolds42when the ink is delivered toward the upper supply manifold51by the pump61connected to the supply opening56. The degree of ease of flow of the ink from the upper supply manifold51into the four lower supply manifolds41decreases with an increase in a distance by which each lower supply manifold41is distant from the supply opening56in the sheet conveyance direction toward the downstream side. In other words, when focusing on any two of the four lower supply manifolds41, the ink is less prone to flow from the upper supply manifold51into one of the two lower supply manifolds41than into the other of the two lower supply manifolds41, the one of the two lower supply manifolds being located more downstream, namely, located farther from the supply opening56, in the sheet conveyance direction than the other of the two lower supply manifolds41. This may cause a large difference, among the four lower supply manifolds41, in the degree of ease of flow of the ink from the upper supply manifold51. Similarly, the degree of ease of flow of the ink into the upper discharge manifold52from the four lower discharge manifolds42decreases with an increase in a distance by which each lower discharge manifold42is distant from the supply opening56in the sheet conveyance direction toward the downstream side. In other words, when focusing on any two of the four lower discharge manifolds42, the ink is less prone to flow into the upper discharge manifold52from one of the two lower discharge manifolds42than from the other of the two lower discharge manifolds42, the one of the two lower discharge manifolds42being located more downstream, namely, located farther from the supply opening56, in the sheet conveyance direction than the other of the two lower discharge manifolds42. This may cause a large difference, among the four lower discharge manifolds42, in the degree of ease of flow of the ink into the upper discharge manifold52.

In the present embodiment, therefore, the upper supply manifold51is constructed such that the dimension thereof in the sheet width direction increases toward the downstream side in the sheet conveyance direction, whereby the cross-sectional area thereof on the plane orthogonal to the sheet conveyance direction increases toward the downstream side in the sheet conveyance direction. In other words, the dimension of the upper supply manifold51in the sheet width direction increases so as to be larger at a portion thereof farther from the supply opening56in the sheet conveyance direction (as one example of “second portion of the second supply passage”) than at a portion thereof closer to the supply opening56in the sheet conveyance direction (as one example of “first portion of the second supply passage”), whereby the cross-sectional area of the upper supply manifold51increases so as to be larger at the portion farther from the supply opening56in the sheet conveyance direction than at the portion closer to the supply opening56in the sheet conveyance direction. In other words, the cross-sectional area of the second supply passage at the first portion differs from the cross-sectional area of the second supply passage at the second portion. In the thus constructed upper supply manifold51, the ink flow resistance at four joint portions thereof (at which the upper supply manifold51is joined to the respective four lower supply manifolds41) decreases with an increase in a distance by which each joint portion is distant from the supply opening56in the sheet conveyance direction toward the downstream side. As a result, the degree of ease of flow of the ink from the upper supply manifold51can be made uniform among the lower supply manifolds41.

Further, in the present embodiment, the upper discharge manifold52is constructed such that the dimension thereof in the sheet width direction increases toward the downstream side in the sheet conveyance direction, whereby the cross-sectional area thereof on the plane orthogonal to the sheet conveyance direction increases toward the downstream side in the sheet conveyance direction. In other words, the dimension of the upper discharge manifold52in the sheet width direction increases so as to be larger at a portion thereof farther from the supply opening56in the sheet conveyance direction (as one example of “second portion of the second discharge passage”) than at a portion thereof closer to the supply opening56in the sheet conveyance direction (as one example of “first portion of the second discharge passage”), whereby the cross-sectional area of the upper discharge manifold52increases so as to be larger at the portion farther from the supply opening56in the sheet conveyance direction than at the portion closer to the supply opening56in the sheet conveyance direction. In other words, the cross-sectional area of the second discharge passage at the first portion differs from the cross-sectional area of the second discharge passage at the second portion. In the thus constructed upper discharge manifold52, the ink flow resistance at four joint portions thereof (at which the upper discharge manifold52is joined to the respective four lower discharge manifolds42) decreases with an increase in a distance by which each joint portion is distant from the supply opening56in the sheet conveyance direction toward the downstream side. As a result, the degree of ease of flow of the ink into the upper discharge manifold52can be made uniform among the lower discharge manifolds42.

Accordingly, the configuration described above enables an amount of circulation of the ink to be uniform among the plurality of individual passages20.

While the embodiment of the present disclosure has been described above, it is to be understood that the present disclosure is not limited to the details of the illustrated embodiment, but may be embodied with various changes without departing from the scope of the disclosure.

In the illustrated embodiment, the upper supply manifold51and the upper discharge manifold52are constructed such that only the dimensions thereof in the sheet width direction are increased toward the downstream side in the sheet conveyance direction, whereby the respective cross-sectional areas of the upper supply manifold51and the upper discharge manifold52on the plane orthogonal to the sheet conveyance direction are increased toward the downstream side in the sheet conveyance direction. The present disclosure is not limited to this configuration. For instance, each of the upper supply manifold51and the upper discharge manifold52may be constructed such that only the dimension thereof in the up-down direction increases toward the downstream side in the sheet conveyance direction or both the dimension thereof in the sheet width direction and the dimension thereof in the up-down direction increase toward the downstream side in the sheet conveyance direction, whereby the cross-sectional area of each of the upper supply manifold51and the upper discharge manifold52on the plane orthogonal to the sheet conveyance direction may be increased toward the downstream side in the sheet conveyance direction.

In the illustrated embodiment, the upper supply manifold51is constructed such that the dimension thereof in the sheet width direction increases toward the downstream side in the sheet conveyance direction, and the upper discharge manifold52is constructed such that the dimension thereof in the sheet width direction increases toward the downstream side in the sheet conveyance direction. The present disclosure is not limited to this configuration. For instance, one of the upper supply manifold51and the upper discharge manifold52may be constructed such that the dimension thereof in the sheet width direction is substantially constant throughout the sheet conveyance direction.

In the illustrated embodiment, the four supply connection openings46have the same size, the same shape, and the same cross-sectional area on the plane orthogonal to the up-down direction, and the four discharge connection openings47have the same size, the same shape, and the same cross-sectional area on the plane orthogonal to the up-down direction. The present disclosure is not limited to this configuration.

In a first modification shown inFIG. 5, the dimensions of four supply connection openings101in the sheet width direction increase with an increase in a distance by which each supply connection opening101is distant from the supply opening56in the sheet conveyance direction toward the downstream side, whereby cross-sectional areas of the respective four supply connection openings101on the plane orthogonal to the up-down direction accordingly increase. In other words, when focusing on any two of the four supply connection openings101, one of the two supply connection openings101has the dimension in the sheet width direction larger than that of the other of the two supply connection openings101, the one of the two supply connection openings101being located more downstream, namely, located farther from the supply opening56, in the sheet conveyance direction than the other of the two supply connection openings101. Thus, the one of the two supply connection openings101has the cross-sectional area on the plane orthogonal to the up-down direction larger than that of the other of the two supply connection openings101. For instance, the most downstream one of the four supply connection openings101in the sheet conveyance direction has a dimension Wi2in the sheet width direction that is equal to about 0.6 mm whereas the most upstream one of the four supply connection openings101in the sheet conveyance direction has a dimension Wi1in the sheet width direction that is not less than 0.2 mm and not greater than 0.5 mm. Each of the four supply connection openings101has a dimension in the sheet conveyance direction that is not less than 0.1 mm and not greater than 1.0 mm.

In the first modification ofFIG. 5, the dimensions of four discharge connection openings102in the sheet width direction increase with an increase in a distance by which each discharge connection opening102is distant from the supply opening56in the sheet conveyance direction toward the downstream side, whereby cross-sectional areas of the respective four discharge connection openings102on the plane orthogonal to the up-down direction accordingly increase. In other words, when focusing on any two of the four discharge connection openings102, one of the two discharge connection openings102has the dimension in the sheet width direction larger than that of the other of the two discharge connection openings102, the one of the two discharge connection openings102being located more downstream, namely, located farther from the supply opening56, in the sheet conveyance direction than the other of the two discharge connection openings102. Thus, the one of the two discharge connection openings102has the cross-sectional area on the plane orthogonal to the up-down direction larger than that of the other of the two discharge connection openings102. For instance, the most downstream one of the four discharge connection openings102in the sheet conveyance direction has a dimension Wo2in the sheet width direction that is equal to about 0.6 mm whereas the most upstream one of the four discharge connection openings102in the sheet conveyance direction has a dimension Wo1in the sheet width direction that is not less than 0.2 mm and not greater than 0.5 mm Each of the four discharge connection openings102has a dimension in the sheet conveyance direction that is not less than 0.1 mm and not greater than 1.0 mm.

In the first modification, the dimensions of the four supply connection openings101in the sheet width direction increase with an increase in the distance by which each supply connection opening101is distant from the supply opening56in the sheet conveyance direction toward the downstream side, whereby the cross-sectional areas of the four supply connection openings101on the plane orthogonal to the up-down direction accordingly increase. According to this configuration, the ink flow resistance in the four supply connection openings101decreases with an increase in the distance by which each supply connection opening101is distant from the supply opening56in the sheet conveyance direction toward the downstream side. As a result, the degree of ease of flow of the ink from the upper supply manifold51into the four lower supply manifolds41can be made uniform among the four lower supply manifolds41.

In the first modification, the dimensions of the four discharge connection openings102in the sheet width direction increase with an increase in the distance by which each discharge connection opening102is distant from the supply opening56in the sheet conveyance direction toward the downstream side, whereby the cross-sectional areas of the four discharge connection openings102on the plane orthogonal to the up-down direction accordingly increase. According to this configuration, the ink flow resistances in the four discharge connection openings102decrease with an increase in the distance by which each discharge connection opening102is distant from the supply opening56in the sheet conveyance direction toward the downstream side. As a result, the degree of ease of flow of the ink into the upper discharge manifold52from the four lower discharge manifolds42can be made uniform among the four lower discharge manifolds42.

In the first modification, both the supply connection openings101and the discharge connection openings102are constructed such that the supply connection openings101and the discharge connection openings102located more downstream have larger dimensions in the sheet width direction so as to have larger cross-sectional areas on the plane orthogonal to the up-down direction. The present disclosure is not limited to this configuration. For instance, only the four supply connection openings101or only the four discharge connection openings102may have a constant dimension in the sheet width direction.

In the first modification, the dimension of the supply connection openings101in the sheet width direction and the dimension of the discharge connection openings102in the sheet width direction are not limited to those described above. For instance, the dimension Wi2in the sheet width direction of the most downstream supply connection opening101in the sheet conveyance direction may be greater than or less than 0.6 mm. Further, the dimension Wi1in the sheet width direction of the most upstream supply connection opening101in the sheet conveyance direction may be less than 0.2 mm or greater than 0.5 mm provided that the dimension Wi1is less than the dimension Wi2. Similarly, the dimension Wo2in the sheet width direction of the most downstream discharge connection opening102in the sheet conveyance direction may be greater than or less than 0.6 mm. Further, the dimension Wo1in the sheet width direction of the most upstream discharge connection opening102in the sheet conveyance direction may be less than 0.2 mm or greater than 0.5 mm provided that the dimension Wo1is less than the dimension Wo2.

In the first modification, only the dimension in the sheet width direction of the supply connection openings101and only the dimension in the sheet width direction of the discharge connection openings102are changed so as to change the cross-sectional areas thereof on the plane orthogonal to the up-down direction. The present disclosure is not limited to this configuration. Only the dimension in the sheet conveyance direction of the supply connection openings101and only the dimension in the sheet conveyance direction of the discharge connection openings102may be changed so as to change the cross-sectional areas thereof on the plane. Alternatively, both the dimension in the sheet width direction and the dimension in the sheet conveyance direction of the supply connection openings101and both the dimension in the sheet width direction and the dimension in the sheet conveyance direction of the discharge connection openings102may be changed so as to change the cross-sectional areas thereof on the plane.

In the illustrated embodiment, each lower supply manifold41has the dimension in the sheet conveyance direction that is substantially constant throughout the sheet width direction, and each lower discharge manifold42has the dimension in the sheet conveyance direction that is substantially constant throughout the sheet width direction. The present disclosure is not limited to this configuration.

In a second modification shown inFIG. 6, each lower supply manifold111is constructed such that its dimension in the sheet conveyance direction gradually increases toward the left side in the sheet width direction away from the corresponding supply connection opening46, whereby a cross-sectional area of each lower supply manifold111on a plane orthogonal to the sheet width direction gradually increases toward the left side in the sheet width direction away from the corresponding supply connection opening46. In other words, each lower supply manifold111has the dimension in the sheet conveyance direction that increases so as to be larger at a portion of each lower supply manifold111farther from the corresponding supply connection opening46in the sheet width direction (as one example of “second portion of the first supply passage”) than at a portion thereof closer to the corresponding supply connection opening46in the sheet width direction (as one example of “first portion of the first supply passage”), whereby the cross-sectional area of each lower supply manifold111on the plane increases so as to be larger at the portion thereof farther from the corresponding supply connection opening46in the sheet width direction than at the portion thereof closer to the corresponding supply connection opening46in the sheet width direction. In other words, the cross-sectional area of each of the first supply passages at the first portion differs from the cross-sectional area of each of the first supply passages at the second portion. For instance, the dimension in the sheet conveyance direction at each portion of the lower supply manifold111falls within a range from not less than 0.5 mm to not greater than 1.0 mm. Specifically, each lower supply manifold111has a dimension Wi3in the sheet conveyance direction at a right end thereof in the sheet width direction that is equal to about 0.5 mm and a dimension Wi4in the sheet conveyance direction at a left end thereof in the sheet width direction that is equal to about 1.0 mm.

Similarly, each lower discharge manifold112is constructed such that its dimension in the sheet conveyance direction gradually increases toward the left side in the sheet width direction away from the corresponding supply connection opening46, whereby a cross-sectional area of each lower discharge manifold112on the plane orthogonal to the sheet width direction gradually increases toward the left side in the sheet width direction away from the corresponding supply connection opening46. In other words, each lower discharge manifold112has the dimension in the sheet conveyance direction that increases so as to be larger at a portion of each lower discharge manifold112farther from the corresponding supply connection opening46in the sheet width direction (as one example of “second portion of the first discharge passage”) than at a portion thereof closer to the corresponding supply connection opening46in the sheet width direction (as one example of “first portion of the first discharge passage”), whereby the cross-sectional area of each lower discharge manifold112on the plane increases so as to be larger at the portion thereof farther from the corresponding supply connection opening46in the sheet width direction than at the portion thereof closer to the corresponding supply connection opening46in the sheet width direction. In other words, the cross-sectional area of each of the first discharge passages at the first portion differs from the cross-sectional area of each of the first discharge passages at the second portion. Here, the corresponding supply connection opening46refers to one supply connection opening46from which the ink that flows through the lower discharge manifold112in question is supplied. For instance, the dimension in the sheet conveyance direction at each portion of the lower discharge manifold112falls within a range from not less than 0.5 mm to not greater than 1.0 mm Specifically, each lower discharge manifold112has a dimension Wo3in the sheet conveyance direction at a right end thereof in the sheet width direction that is equal to about 0.5 mm and a dimension Wo4in the sheet conveyance direction at a left end thereof in the sheet width direction that is equal to about 1.0 mm.

Here, a case is considered in which the ink flow resistance is uniform among a plurality of joint portions of each lower supply manifold111at which the lower supply manifold111is connected to the respective supply orifices35a, in contrast to the second modification. In this case, when the ink is delivered toward the upper supply manifold51by the pump61connected to the supply opening56, the ink is less prone to flow into the individual passages20(the supply orifices35a) from the corresponding lower supply manifold111with an increase in a distance by which each individual passage20(each supply orifice35a) is distant from the corresponding supply connection opening46in the sheet width direction. Similarly, a case is considered in which the ink flow resistance is uniform at a plurality of joint portions of each lower discharge manifold112at which the lower discharge manifold112is connected to the respective discharge orifices35b, in contrast to the second modification. In this case, the ink is less prone to flow from the individual passages20(the discharge orifices35b) into the corresponding lower discharge manifold112with an increase in a distance by which each individual passage20(each discharge orifice35b) is distant from the corresponding supply connection opening46in the sheet width direction.

In the second modification, the dimension in the sheet conveyance direction of each lower supply manifold111increases toward the left side in the sheet width direction away from the corresponding supply connection opening46, whereby the cross-sectional area of the lower supply manifold111on the plane orthogonal to the sheet width direction increases toward the left side in the sheet width direction away from the corresponding supply connection opening46. According to this configuration, the ink flow resistance at the joint portions of each lower supply manifold111to the respective supply orifices35adecreases with an increase in the distance by which each joint portion is distant from the corresponding supply connection opening46in the sheet width direction. As a result, the degree of ease of flow of the ink from each lower supply manifold111can be made uniform among the corresponding individual passages20.

In the second modification, the dimension in the sheet conveyance direction of each lower discharge manifold112increases toward the left side in the sheet width direction away from the corresponding supply connection opening46, whereby the cross-sectional area of the lower discharge manifold112on the plane orthogonal to the sheet width direction increases toward the left side in the sheet width direction away from the corresponding supply connection opening46. According to this configuration, the ink flow resistance at the joint portions of each lower discharge manifold112to the respective discharge orifices35bdecreases with an increase in the distance by which each joint portion is distant from the corresponding supply connection opening46in the sheet width direction. As a result, the degree of ease of flow of the ink into each lower discharge manifold112can be made uniform among the corresponding individual passages20.

In the second modification, the dimension in the sheet conveyance direction at each portion of the lower supply manifold111and the dimension in the sheet conveyance direction at each portion of the lower discharge manifold112both fall within the range from not less than 0.5 mm to not greater than 1.0 mm. The present disclosure is not limited to this configuration. In each of the lower supply manifolds111and the lower discharge manifolds112, the smallest dimension in the sheet conveyance direction may be less than 0.5 mm, and the largest dimension in the sheet conveyance direction may be greater than 1.0 mm.

In the second modification, only the dimension in the sheet conveyance direction of each lower supply manifold111and only the dimension in the sheet conveyance direction of each lower discharge manifold112are changed, whereby the cross-sectional areas thereof on the plane orthogonal to the sheet width direction are changed. The present disclosure is not limited to this configuration. The cross-sectional areas of each lower supply manifold111and each lower discharge manifold112may be changed by changing only the dimension in the up-down direction or by changing both the dimension in the sheet conveyance direction and the dimension in the up-down direction.

In the second modification, the dimension in the sheet conveyance direction increases toward the left side in the sheet width direction for both the lower supply manifolds111and the lower discharge manifolds112. The present disclosure is not limited to this configuration. Only one of: the lower supply manifolds111; and the lower discharge manifolds112may have the dimension in the sheet conveyance direction that is substantially constant throughout the sheet width direction.

In the illustrated embodiment, the supply opening56is connected to the upstream end of the upper supply manifold51in the sheet conveyance direction, and the discharge opening57is connected to the upstream end of the upper discharge manifold52in the sheet conveyance direction. That is, the supply opening56and the discharge opening57are respectively connected to the upper supply manifold51and the upper discharge manifold52on the same side, i.e., on the upstream side, in the sheet conveyance direction. The present disclosure is not limited to this configuration.

In a third modification shown inFIG. 7, an upper discharge manifold121extends downstream in the sheet conveyance direction beyond a region thereof in which the upper discharge manifold121is connected to the four discharge connection openings47. A discharge opening122overlaps, in the up-down direction, a downstream end of the upper discharge manifold121in the sheet conveyance direction. The upper discharge manifold121has a dimension in the sheet width direction that gradually increases toward the downstream side in the sheet conveyance direction, namely, a dimension in the sheet width direction that gradually increases with an increase in a distance from the supply opening56in the sheet conveyance direction, whereby its cross-sectional area on the plane orthogonal to the sheet conveyance direction gradually increases toward the downstream side in the sheet conveyance direction.

According to this configuration, the upper discharge manifold121has the dimension in the sheet width direction that increases toward the downstream side in the sheet conveyance direction, whereby its cross-sectional area on the plane orthogonal to the sheet conveyance direction increases toward the downstream side in the sheet conveyance direction. Thus, the degree of ease of flow of the ink into the upper discharge manifold121can be made uniform among the four lower discharge manifolds42.

In the embodiment and the modifications illustrated above, the pump61configured to deliver the ink toward the upper supply manifold51is disposed in the flow passage between the supply opening56and the ink tank60. The present disclosure is not limited to this configuration.

In a fourth modification shown inFIG. 8, the pump is not disposed between the supply opening56and the ink tank60, in contrast to the third modification. Instead, a pump130is disposed in a flow passage between the discharge opening122and the ink tank60. The pump130is configured to deliver the ink in a direction from the discharge opening122toward the ink tank60. That is, the pump130is configured to deliver the ink in a direction in which the ink is discharged from an upper discharge manifold132.

In the thus constructed fourth modification, an upper supply manifold131has a dimension in the sheet width direction that gradually increases toward the upstream side in the sheet conveyance direction, namely, a dimension in the sheet width direction that gradually increases with an increase in a distance from the discharge opening122in the sheet conveyance direction, whereby its cross-sectional area on the plane orthogonal to the sheet conveyance direction gradually increases toward the upstream side in the sheet conveyance direction. In other words, the cross-sectional area of the upper supply manifold131increases so as to be larger at a portion thereof farther from the discharge opening122in the sheet conveyance direction (as one example of “second portion of the second supply passage”) than at a portion thereof closer to the discharge opening122in the sheet conveyance direction (as one example of “first portion of the second supply passage”). In other words, the cross-sectional area of the second supply passage at the first portion differs from the cross-sectional area of the second supply passage at the second portion. Further, an upper discharge manifold132has a dimension in the sheet width direction that gradually increases toward the upstream side in the sheet conveyance direction, namely, a dimension in the sheet width direction that gradually increases with an increase in a distance from the discharge opening122in the sheet conveyance direction, whereby its cross-sectional area on the plane orthogonal to the sheet conveyance direction gradually increases toward the upstream side in the sheet conveyance direction. In other words, the cross-sectional area of the upper discharge manifold132increases so as to be larger at a portion thereof farther from the discharge opening122in the sheet conveyance direction (as one example of “second portion of the second supply passage”) than at a portion thereof closer to the discharge opening122in the sheet conveyance direction ((as one example of “first portion of the second supply passage”). In other words, the cross-sectional area of the second discharge passage at the first portion differs from the cross-sectional area of the second discharge passage at the second portion.

Here, a case is considered in which the dimension in the sheet width direction of the upper supply manifold131and the dimension in the sheet width direction of the upper discharge manifold132are substantially constant throughout the sheet conveyance direction, in contrast to the fourth modification. In this case, the ink flow resistance is substantially the same among four joint portions of the upper supply manifold131at which the upper supply manifold131is joined to the respective four lower supply manifolds41, namely, among four portions of the upper supply manifold131that overlap the respective supply connection openings46in the up-down direction. Further, the ink flow resistance is substantially the same among four joint portions of the upper discharge manifold132at which the upper discharge manifold132is joined to the respective lower discharge manifolds42, namely, among four portions of the upper discharge manifold132that overlap the respective four supply connection openings46in the up-down direction.

In the above case, there are considered degrees of ease of flow of the ink in the four lower supply manifolds41and in the four lower discharge manifolds42when the ink is delivered by the pump130connected to the discharge opening122in the direction in which the ink is discharged from the upper discharge manifold132. The degree of ease of flow of the ink from the upper supply manifold131into the four lower supply manifolds41decreases with an increase in a distance by which each lower supply manifold41is distant from the discharge opening122in the sheet conveyance direction toward the upstream side. In other words, when focusing on any two of the four lower supply manifolds41, the ink is less prone to flow from the upper supply manifold131into one of the two lower supply manifolds41than into the other of the two lower supply manifolds41, the one of the two lower supply manifolds41being located more upstream, namely, located farther from the discharge opening122, in the sheet conveyance direction than the other of the two lower supply manifolds41. This may cause a large difference, among the four lower supply manifolds41, in the degree of ease of flow of the ink from the upper supply manifold131. Similarly, the degree of ease of flow of the ink into the upper discharge manifold132from the four lower discharge manifolds42decreases with an increase in a distance by which each lower discharge manifold42is distant from the discharge opening122in the sheet conveyance direction toward the upstream side. In other words, when focusing on any two of the four lower discharge manifolds42, the ink is less prone to flow into the upper discharge manifold132from one of the two lower discharge manifolds42than from the other of the two lower discharge manifolds42, the one of the two lower discharge manifolds42being located more upstream, namely, located farther from the discharge opening122, in the sheet conveyance direction than the other of the two lower discharge manifolds42. This may cause a large difference, among the four lower discharge manifolds42, in the degree of ease of flow of the ink into the upper discharge manifold132.

In the fourth modification, therefore, the upper supply manifold131is constructed such that the dimension thereof in the sheet width direction increases toward the upstream side in the sheet conveyance direction, whereby the cross-sectional area thereof on the plane orthogonal to the sheet conveyance direction increases toward the upstream side in the sheet conveyance direction. In the thus constructed upper supply manifold131, the ink flow resistance at the four joint portions thereof (at which the upper supply manifold131is joined to the respective four lower supply manifolds41) decreases with an increase in the distance by which each joint portion is distant from the discharge opening122in the sheet conveyance direction toward the upstream side. As a result, the degree of ease of flow of the ink from the upper supply manifold51can be made uniform among the four lower supply manifolds41.

Further, in the fourth modification, the upper discharge manifold132is constructed such that the dimension thereof in the sheet width direction increases toward the upstream side in the sheet conveyance direction, whereby the cross-sectional area thereof on the plane orthogonal to the sheet conveyance direction increases toward the upstream side in the sheet conveyance direction. In the thus constructed upper discharge manifold132, the ink flow resistance at the four joint portions thereof (at which the upper discharge manifold132is joined to the respective four lower discharge manifolds42) decreases with an increase in the distance by which each joint portion is distant from the discharge opening122in the sheet conveyance direction toward the upstream side. As a result, the degree of ease of flow of the ink into the upper discharge manifold132can be made uniform among the four lower discharge manifolds42.

Accordingly, the configuration described above enables an amount of circulation of the ink to be uniform among the plurality of individual passages20.

In the embodiment and the modifications illustrated above, the pump is disposed in one of: the flow passage between the ink tank and the supply opening; and the ink passage between the ink tank and the discharge opening. The present disclosure is not limited to this configuration. For instance, the pump may be disposed in each of those flow passages.

In this case, depending on a relationship between amounts of the ink delivered from the respective two pumps per unit time, an ink flow resistance distribution at each portion in the flow passages in the head unit11, etc., the upper supply manifold and/or the upper discharge manifold is constructed such that the cross-sectional area thereof on the plane orthogonal to the sheet conveyance direction increases with an increase in the distance from the supply opening in the sheet conveyance direction or such that the cross-sectional area thereof on the plane orthogonal to the sheet conveyance direction increases with an increase in the distance from the discharge opening in the sheet conveyance direction, as in the illustrated embodiment and the first through third modifications. Accordingly, the configuration enables an amount of circulation of the ink to be uniform among the plurality of individual passages20.

Also in the case where the pump is disposed in one of: the flow passage between the ink tank and the supply opening; and the flow passage between the ink tank and the discharge opening, the upper supply manifold and/or the upper discharge manifold may be constructed as described above depending on the ink flow resistance at each portion in the flow passages in the head unit11. That is, the upper supply manifold and/or the upper discharge manifold may be constructed such that the cross-sectional area thereof on the plane orthogonal to the sheet conveyance direction increases with an increase in the distance from the supply opening in the sheet conveyance direction or such that the cross-sectional area thereof on the plane orthogonal to the sheet conveyance direction increases with an increase in the distance from the discharge opening in the sheet conveyance direction.

In the embodiment and the modifications illustrated above, the upper supply manifold and/or the upper discharge manifold is constructed such that the cross-sectional area thereof on the plane orthogonal to the sheet conveyance direction increases or decreases with an increase in the distance from the supply opening in the sheet conveyance direction. The present disclosure is not limited to this configuration. For instance, the upper supply manifold may have mutually different dimensions in the sheet width direction at only at least two portions thereof that overlap, in the up-down direction, the corresponding at least two of the supply connection openings. In this case, the dimension in the sheet width direction at other portion except the at least two portions may be substantially constant. Similarly, the upper discharge manifold may have mutually different dimensions in the sheet width direction at only at least two portions thereof that overlap, in the up-down direction, the corresponding at least two of the discharge connection openings. In this case, the dimension in the sheet width direction at other portion except the at least two portions may be substantially constant.

In the embodiment and modifications illustrated above, the cross-sectional area of each of the upper supply manifold and the upper discharge manifold on the plane orthogonal to the sheet conveyance direction is changed in accordance with the distance from the supply opening or the discharge opening in the sheet conveyance direction. The present disclosure is not limited to this configuration.

A fifth modification shown inFIG. 9differs from the second modification in that each of an upper supply manifold141and an upper discharge manifold142has a dimension in the sheet width direction that is substantially constant, namely, a cross-sectional area on the plane orthogonal to the sheet conveyance direction that is substantially constant.

In the fifth modification, the cross-sectional area of each of lower supply manifolds111on the plane orthogonal to the sheet width direction gradually increases toward the left side in the sheet width direction away from the corresponding supply connection opening46. In other words, the cross-sectional area of each lower supply manifold111increases so as to be larger at a portion thereof farther from the corresponding supply connection opening46in the sheet width direction (as one example of “second portion of the first supply passage”) than at a portion thereof closer to the corresponding supply connection opening46in the sheet width direction (as one example of “first portion of the first supply passage”). In other words, the cross-sectional area of each of the first supply passages at the first portion differs from the cross-sectional area of each of the first supply passages at the second portion. Thus, the degree of ease of flow of the ink from each lower supply manifold111can be made uniform among the corresponding individual passages20.

In the fifth modification, the cross-sectional area of each of lower discharge manifolds112on the plane orthogonal to the sheet width direction gradually increases toward the left side in the sheet width direction away from the corresponding supply connection opening46. In other words, the cross-sectional area of each lower discharge manifold112increases so as to be larger at a portion thereof farther from the corresponding supply connection opening46in the sheet width direction (as one example of “second portion of the first discharge passage”) than at a portion thereof closer to the corresponding supply connection opening46in the sheet width direction (as one example of “first portion of the first discharge passage”). In other words, the cross-sectional area of each of the first discharge passages at the first portion differs from the cross-sectional area of each of the first discharge passages at the second portion. Thus, the degree of ease of flow of the ink into each lower discharge manifold112can be made uniform among the corresponding individual passages20.

In the fifth modification, only one of: the lower supply manifolds111; and the lower discharge manifolds112may have the dimension in the sheet conveyance direction that is substantially constant throughout the sheet width direction.

A sixth modification shown inFIG. 10differs from the fourth modification in that each of an upper supply manifold151and an upper discharge manifold152has a dimension in the sheet width direction that is substantially constant throughout the sheet conveyance direction. The sixth modification further differs from the fourth modification in that each of lower supply manifolds156and each of lower discharge manifolds157have a dimension in the sheet conveyance direction that gradually increases toward the right side in the sheet width direction away from the corresponding discharge connection opening47, whereby a cross-sectional area of each lower supply manifold156and a cross-sectional area of each lower discharge manifold157on the plane orthogonal to the sheet width direction gradually increase toward the right side in the sheet width direction away from the corresponding discharge connection opening47. Here, the corresponding discharge connection opening47refers to one discharge connection opening47into which the ink that flows through the lower discharge manifold157in question is discharged.

In the sixth modification, the cross-sectional area of each lower supply manifold156on the plane orthogonal to the sheet width direction increases toward the right side in the sheet width direction away from the corresponding discharge connection opening47. In other words, the cross-sectional area of each lower supply manifold156increases so as to be larger at a portion thereof farther from the corresponding discharge connection opening47in the sheet width direction (as one example of “second portion of the first supply passage”) than at a portion thereof closer to the corresponding discharge connection opening47in the sheet width direction (as one example of “first portion of the first supply passage”). In other words, the cross-sectional area of each of the first supply passages at the first portion differs from the cross-sectional area of each of the first supply passages at the second portion. Thus, the degree of ease of flow of the ink from each lower supply manifold156can be made uniform among the corresponding individual passages20.

In the sixth modification, the cross-sectional area of each lower discharge manifold157on the plane orthogonal to the sheet width direction increases toward the right side in the sheet width direction away from the corresponding discharge connection opening47. In other words, the cross-sectional area of each lower discharge manifold157increases so as to be larger at a portion thereof farther from the corresponding discharge connection opening47in the sheet width direction (as one example of “second portion of the first discharge passage”) than at a portion thereof closer to the corresponding discharge connection opening47in the sheet width direction (as one example of “first portion of the first discharge passage”). In other words, the cross-sectional area of each of the first discharge passages at the first portion differs from the cross-sectional area of each of the first discharge passages at the second portion. Thus, the degree of ease of flow of the ink into each lower discharge manifold157can be made uniform among the corresponding individual passages20.

In the sixth modification, only one of: the lower supply manifolds156; and the lower discharge manifolds157may have the dimension in the sheet conveyance direction that is substantially constant throughout the sheet width direction.

In the illustrated embodiment, each supply connection opening46overlaps, in the up-down direction, the right end portion of the corresponding lower supply manifold41, and each discharge connection opening47overlaps, in the up-down direction, the left end portion of the corresponding lower discharge manifold42. The present disclosure is not limited to this configuration. Each supply connection opening46may overlap, in the up-down direction, some mid portion of the corresponding lower supply manifold41in the sheet width direction, and the corresponding pressure chamber row8and the corresponding nozzle row9may extend on both sides of the supply connection opening46in the sheet width direction. Similarly, each discharge connection opening47may overlap, in the up-down direction, some mid portion of the corresponding lower discharge manifold42in the sheet width direction, and the corresponding pressure chamber row8and the corresponding nozzle row9may extend on both sides of the discharge connection opening47in the sheet width direction.

In the illustrated embodiment, the lower supply manifolds41and the lower discharge manifolds42are formed through the single flow-passage plate36in the head unit11. The present disclosure is not limited to this configuration. The lower supply manifolds41and the lower discharge manifolds42may be formed through two or more flow-passage plates stacked on each other.

In the illustrated embodiment, the upper supply manifold51and the upper discharge manifold52are formed in the single flow-passage plate38in the head unit11. The present disclosure is not limited to this configuration. The upper supply manifold51and the upper discharge manifold52may be formed through two or more flow-passage plates stacked on each other.

In the illustrated embodiment, the supply connection openings46and the discharge connection openings47are formed in the single flow-passage plate37in the head unit11. The present disclosure is not limited to this configuration. The supply connection openings46and the discharge connection openings47may be formed through two or more flow-passage plates stacked on each other. In this case, as long as each supply connection opening46and each discharge connection opening47formed through at least one of the two or more flow-passage plates have the respective sizes described above, the size of each supply connection opening46may differ among the two or more flow-passage plates and the size of each discharge connection opening47may differ among the two or more flow-passage plates.

In the illustrated embodiment, the supply opening56and the discharge opening57are formed through the single flow-passage plate39in the head unit11. The present disclosure is not limited to this configuration. The supply opening56and the discharge opening57may be forming through two or more flow-passage plates stacked on each other. In this case, as long as the supply opening56and the discharge opening57formed through at least one of the two or more flow-passage plates have the respective sizes described above, the size of the supply opening56may differ among the two or more flow-passage plates and the size of the discharge opening57may differ among the two or more flow-passage plates.

In the illustrated embodiment, the dimension of the upper supply manifold51in the sheet width direction continuously increases toward the downstream side in the sheet conveyance direction. The present disclosure is not limited to this configuration. The dimension of the upper supply manifold51in the sheet width direction may increase stepwise toward the downstream side in the sheet conveyance direction such that the side walls of the upper supply manifold51are shaped like stairs, for instance. In this case, the dimension of the upper supply manifold51in the sheet width direction may change in two steps, three steps, or four or more steps.

In the illustrated embodiment, the dimension of the upper discharge manifold52in the sheet width direction continuously increases toward the downstream side in the sheet conveyance direction. The present disclosure is not limited to this configuration. The dimension of the upper discharge manifold52in the sheet width direction may increase stepwise toward the downstream side in the sheet conveyance direction such that the side walls of the upper discharge manifold52are shaped like stairs, for instance. In this case, the dimension of the upper discharge manifold52in the sheet width direction may change in two steps, three steps, or four or more steps.

In the embodiment and the modifications illustrated above, the ink flow direction may be inverse. That is, the flow passages used for discharging the ink from the plurality of individual passages20into the ink tank60may be used as flow passages for supplying the ink from the ink tank60into the plurality of individual passages, and the flow passages used for supplying the ink from the ink tank60into the plurality of individual passages20may be used as flow passages for discharging the ink from the plurality of individual passages20into the ink tank60.

While the present disclosure is applied to the ink jet head configured to eject the ink from the nozzles and the printer including the ink-jet head, the present disclosure may be applied to a liquid ejection head configured to eject, from the nozzles, a liquid other than the ink and a liquid ejection device including such a liquid ejection head.