WO2021145848A1

WO2021145848A1 - Bypass channel

Info

Publication number: WO2021145848A1
Application number: PCT/US2020/012506
Authority: WO
Inventors: Paul Richards; Tommy D. DESKINS; Alexander Govyadinov; Michael W. CUMBIE
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-01-15
Filing date: 2020-01-15
Publication date: 2021-07-22

Abstract

In various examples, a fluid ejection die may include a first chamber and a second chamber fluidly coupled at respective first ends with a fluid supply, a drop ejecting element positioned in the first chamber to cause fluid in the fluid ejection chamber to be ejected through a nozzle of the first chamber, a bypass channel fluidly coupled to the first and second chambers at respective second ends of the first and second chambers, a fluid recirculation channel fluidly coupled with the bypass channel and the fluid supply, and a fluid recirculating element to circulate fluid through the fluid recirculation channel and one or both of the first and second chambers. The bypass channel is to direct fluid flow from the first chamber to the second fluid chamber, bypassing the fluid recirculation channel, in response to energization of the drop ejecting element.

Description

BYPASS CHANNEL

Background

[0001] Fluid ejection devices, such as printheads or dies in inkjet printing systems, often use drop ejecting elements such as thermal resistors or piezoelectric material membranes within fluidic chambers to eject fluid drops (e.g., ink) from nozzles, such that properly sequenced ejection of ink drops from the nozzles causes characters or other images to be printed on a print medium as the printhead and the print medium move relative to each other. Holding ink within the fluidic chambers for prolonged periods of time without either firing or recirculating may be problematic because the water or other fluid in the ink may evaporate. In addition, when pigment-based inks are held in the fluidic chambers for prolonged periods of time, the pigment may separate from the fluid vehicle in which the pigment is mixed. These issues may result in altered drop trajectories, velocities, shapes and colors, all of which can negatively impact the print quality of a printed image.

Brief Description of the Drawings

[0002] Features of the present disclosure are illustrated by way of example and not limited in the following figure(s), in which like numerals indicate like elements.

[0003] FIG. 1 is a schematic plan view of a fluid ejection assembly without a fluid bypass channel, according to an example of the present disclosure.

[0004] FIG. 2 is a schematic plan view of a fluid ejection assembly with a fluid bypass channel, according to an example of the present disclosure. [0005] FIGS. 3A, 3B, and 3C are diagrams demonstrating the main operational phases of a fluid ejection assembly with a fluid bypass channel, according to an example of the present disclosure.

[0006] FIGS. 4A and 4B are diagrams demonstrating the main operational phases of a fluid ejection assembly with a fluid bypass channel, according to an example of the present disclosure.

[0007] FIGS. 4C and 4D are diagrams demonstrating the main operational phases of yet another fluid ejection assembly with a fluid bypass channel, according to an example of the present disclosure.

[0008] FIG. 5 is a schematic plan view of a plurality of fluid ejection assemblies with fluid bypass channels, according to an example of the present disclosure. [0009] FIG. 6 depicts a simplified block diagram of an inkjet printing system in which fluid ejection devices configured with selected aspects of the present disclosure can be deployed, according to an example of the present disclosure.

[0010] For simplicity and illustrative purposes, the present disclosure is described by referring mainly to an example thereof. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, the present disclosure may be practiced without limitation to these specific details. In other instances, some methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure.

[0011] The elements depicted in the accompanying figures may include additional components and that some of the components described in those figures may be removed and/or modified without departing from scopes of the elements disclosed herein. The elements depicted in the figures may not be drawn to scale and thus, the elements may have different sizes and/or configurations other than as shown in the figures.

[0012] The pigment suspension and fluid evaporation issues noted previously may be resolved to some extent by periodically recirculating fluid through various channels and/or chambers to prevent viscous plugs, ink void of pigment, and/or similar issues. For example, fluid recirculation elements such as pumps, resistors, piezoelectric material membranes, etc., may be energized/actuated at various intervals to circulate fluid through various arrangements of fluid recirculation channels in order to avoid some of these issues. However, these techniques may lead to remnant air bubbles forming and/or coalescing in various locations, such as in those recirculation channels, at fluid recirculation elements, at fluid ejection elements, and so forth. These air bubbles may cause various print defects and/or may damage fluid ejection elements,

[0013] Examples are described herein for fluid ejection devices and/or systems that include “bypass” channels that are positioned, shaped, and/or designed to prevent air from entering other areas, particularly the fluid recirculation channels described above, and/or from migrating to undesired locations such as the backside of a silicon die and/or fluid slot. In some examples, a bypass channel may fluidly couple together first and second chambers, one or both which may be fluid ejection chambers, at first ends of those chambers. Second, opposite ends of the first and second chambers may be fluidly coupled to a fluid source, e.g., by way of fluid feed hole that is fluidly coupled with an underlying fluid reservoir (e.g., in a different silicon layer) and/or a fluid feed slot. And in some examples, a fluid recirculation channel that is used at various intervals to recirculate fluid without ejecting it may be operably coupled with the bypass channel. For instance, in some examples, the fluid recirculation channel may bisect the bypass channel.

[0014] When a drop ejecting element such as a thermal resistor or piezoelectric material membrane in one of the first and second chambers is energized or actuated, it may cause a droplet of fluid to be ejected through a nozzle or bore in that same chamber. When that happens, e.g., when a thermal resistor is used to create a bubble within the chamber, that bubble displaces fluid within the chamber. Consequently, some of that fluid leaves the chamber as a droplet ejected through the nozzle.

[0015] However, other fluid that is not ejected through the nozzle may be forced along other path(s). With examples described herein, the most probable path may be the bypass channel that fluidly couples the first and second chambers. For example, the bypass channel may direct fluid flow caused by the bubble-induced fluid displacement from the drop-ejecting chamber to the other chamber. This is in contrast to the fluid being directed into the fluid recirculation path described previously, which may cause air bubbles to migrate to and/or coalesce at undesirable locations. In some examples, fluid in the distinct fluid recirculation path may actually be pulled into the bypass channel at the same time, which may further clear the fluid recirculation channel of air bubbles.

[0016] The examples discussed hereinafter will focus on the implementation of the hereinafter-described apparatus and techniques within printing applications. However, it will be appreciated that the apparatus and techniques may also be used in connection with other applications in different technology fields.

[0017] FIG. 1 depicts a fluid ejection assembly 100 without a fluid bypass channel. In some examples as shown in FIG. 1, fluid ejection assembly 100 may include a fluid ejection chamber 102 and a corresponding first drop ejecting element 104 formed in, provided within, or communicated with fluid ejection chamber 102. Fluid ejection chamber 102 and first drop ejecting element 104 may be formed on a substrate 108, which also defines a first fluid feed hole 108 that fluidly couples fluid ejection chamber 102 with a fluid (e.g., ink) reservoir (not depicted). First fluid feed hole 108 feeds to fluid ejection chamber 102 through a first end 118 of fluid ejection chamber 102. In some examples, first fluid feed hole 108 may be a fluid feed slot instead. Substrate 106 may be formed, for example, of silicon, glass, a stable polymer, or the like. In some examples, a plurality of fluid ejection assemblies similar to fluid ejection assembly 100 depicted in FIG. 1 may be provided on a fluid ejection device such as a fluid ejection die.

[0018] First drop ejecting element 104 may be any device that is to eject fluid drops through a nozzle 110. Nozzle 110 may be of a circular, non-circular, or other shapes, such as the two-iobed shape depicted in FIG. 1. Examples of suitable first drop ejecting element 104 may include thermal resistors and piezoelectric actuators. A thermal resistor, as an example of a drop ejecting element, may be formed on a surface of substrate 106, and may include a thin- fiim stack including an oxide layer, a metal layer, and a passivation layer such that, when activated, heat from the thermal resistor vaporizes a thin layer of fluid interfacing with the thin film resistor in fluid ejection chamber 102, thereby causing a bubble that ejects a drop of fluid through nozzle 110. A piezoelectric actuator, as an example of first drop ejecting element 104, may include a piezoelectric material provided on a moveable membrane communicated with fluid ejection chamber 102 such that, when activated, the piezoelectric material causes deflection of the membrane relative to fluid ejection chamber 102, thereby generating a pressure pulse that ejects a drop of fluid through nozzle 110.

[0019] As shown in FIG. 1, fluid ejection assembly 100 may further include a fluid recirculation channel 112 and a fluid circulating element 114 formed in, provided within, or communicated with fluid recirculation channel 112. Fluid recirculation channel 112 may include a second end 128 that is open to and in fluid communication with a second fluid feed hole 120. Fluid recirculation channel 112 is also open to and in fluid communication at an opposite end 122 to fluid ejection chamber 102.

[0020] Fluid circulating element 114 in FIG. 1 (and similar fluid circulating elements described elsewhere herein) may form or represent an actuator to pump or circulate (or recirculate) fluid through fluid recirculation channel 112. Fluid circulating element 114 may thus be, for instance, a thermal resistor or a piezoelectric actuator. The thermal resistors may be, for example, a single resistor, a split resistor, a comb resistor, or multiple resistors. A variety of other devices, however, may also be used to implement first drop ejecting element 104 and fluid circulating element 114 including, for example, a piezoelectric actuator, an electrostatic membrane, a mechanical/impact driven membrane, a voice coil, a magneto-strictive drive, and so on.

[0021] Fluid ejection assembly 100 is depicted as including a single fluid ejection chamber 102 with nozzle 110 and one fluid circulating element 114 in FIG. 1. In this regard, fluid ejection assembly 100 is depicted as having a 1:1 nozzle-to-pump ratio, in which fluid circulating element 114 is referred to as a "pump" that induces fluid flow through fluid recirculation channel 112, With a 1:1 nozzle-to-pump ratio, circulation is provided for fluid ejection chamber 102 by fluid circulating element 114, It should be noted that other nozzle-to-pump ratios (e.g., 2:1, 3:1, 4:1, etc.) are also possible, where fluid circulating element 114 may induce fluid flow through fluid recirculation channel 112 communicated with multiple fluid ejection chambers and, therefore, multiple nozzle openings or orifices.

[0022] With the design of fluid ejection assembly 100 as shown in FIG. 1 , fluid recirculation channel 112 may form a fluid circulation (or recirculation) loop between first fluid feed hole 108 and second fluid feed hole 120. For example, a fluid circulation (or recirculation) loop may be formed between first fluid feed hole 108 and second fluid feed hole 120, through fluid ejection chamber 102 and fluid recirculation channel 112.

[0023] As shown in FIG. 1 , fluid circulating element 114 may be formed in, provided within, or communicated with a channel portion 124 of fluid recirculation channel 112. Channel portion 124 forms an asymmetry to fluid recirculation channel 112 whereby a fluid flow distance between fluid circulating element 114 and first fluid feed hole 108 is less than a fluid flow distance between fluid circulating element 114 and second fluid feed hole 120. Consequently, when fluid circulating element 114 is actuated or"fired^", fluid may circulate from first fluid feed hole 108, through fluid ejection chamber 102 and fluid recirculation channel 112, to second fluid feed hole 120, as indicated by an arrow 126. This is not meant to be limiting, however, and it should be noted that fluid recirculation channel 112 may have other shapes that impose fluid flow in the opposite direction.

[0024] Circulating (or recirculating) fluid through fluid recirculation channel 112 may help to reduce ink blockage and/or clogging in nozzle 110 as well as to keep the fluid in fluid ejection chamber 102 fresh, e.g., reduce or minimize pigment separation, ink stagnation, viscous plug formation, etc. However, with the design as shown in FIG, 1, firing first drop ejecting element 104 or fluid circulating element 114 may lead to remnant air bubbles coalescing in various locations, such as in fluid recirculation channel 112, at fluid circulating element 114, at drop ejecting element 104, and so forth. The coalesced remnant air bubbles may interfere with the operation of fluid circulating element 114 or drop ejecting element 104 thus interfering the subsequent drop ejection. In addition, the coalesced remnant air bubbles may also migrate to interfere with second fluid feed hole 120.

[0025] Other examples are described herein for a micro-recirculation design that includes a bypass channel to prevent these remnant air bubbles from entering the pump channel, such as fluid recirculation channel 112.

[0026] An example of a fluid ejection assembly 200 with a bypass channel is shown in FIG. 2. In addition to the components of fluid ejection assembly 100 depicted in FIG. 1, fluid ejection assembly 200 also includes a bypass channel 236 which is indicated within the dashed outline in FIG. 2. Bypass channel 236 is fluidly coupled with a first fluid feed hole 208 through a first bypass end 232, fluidly coupled with a fluid recirculation channel 212 through a second bypass end 234, and fluidly coupled with a fluid ejection chamber 202 through a third bypass end 222 as shown in FIG. 2. Fluid ejection assembly 200 still has a 1 :1 nozzie-to-pump ratio as there is a single a fluid circulating element 214 and a single nozzle 210, but other configurations/ratios are contemplated.

[0027] With the example shown in FIG. 2, when a drop ejecting element 204 in fluid ejection chamber 202 is fired to eject the fluid (e.g. ink), the fluid may also circulate from the ejection chamber 202, through the second bypass end 234 and bypass channel 236, through first end 216 and back to ejection chamber 202. The reason for such a fluid flow direction is that as the chamber 202 refills, the bypass channel 236 may be designed to provide additional fluid volume from fluid recirculation channel 212 which includes fluid from the chamber 202 and ink feed hole 220.

[0628] In addition, fluid from second fluid feed hole 220 may flow as indicated by an arrow 226 through bypass channel 236 towards first fluid feed hole 208,

In this way, remnant air bubbles may be prevented from entering fluid recirculation channel 212, and instead may remain small and be ejected through nozzle 210 during subsequent drop ejections. [0029] In various examples, component(s) of a fluid ejection assembly may be dimensioned and/or shaped relative to one another in order to impose particular fluid flows as described herein. Non-limiting examples of dimensions of components of fluid ejection assembly 200, such as fluid recirculation channel 212, fluid ejection chamber 202, bypass channel 236, fluid circulating element 214, and a first end 216 of fluid ejection chamber 202, are shown in FIG. 2. These dimensions are merely examples, and other dimensions are contemplated.

[0030] As shown in FIG. 2, the width of fluid recirculation channel 212 in some examples may be 10 micrometers (pm). The width of first end 216 of fluid ejection chamber 202 may be 10 pm, and the width of fluid ejection chamber 202 may be more than 10 pm. The distance between second bypass end 234 and third bypass end 222 may be 20 pm. The distance between the end of fluid circulating element 114 that is closer to fluid ejection chamber 202, and second bypass end 234 may be 15 pm. The length and width of the left leg of bypass channel 236 fluidly coupled with fluid ejection chamber 202 may each be 8 pm. The width of the other longer leg of bypass channel 236 leading back to fluid feed hole 208 may be 6 pm.

[0031] Accordingly, the width of fluid recirculation channel 212 (10 pm) is larger than the widths of both legs of bypass channel 236. In addition, the width of the left leg connected with fluid ejection chamber 202 (8 pm) is larger than the width (6 pm) of the longer right leg channel. In addition, providing a narrowed leg portion between fluid circulating element 214 and fluid ejection chamber 202 may help to “de-couple” fluid circulating element 214 from fluid ejection chambers 202, which also may mitigate cross-talk between fluid circulating element 214 and fluid ejection chambers 202.

[0032] An example of fluid ejection assembly 300 having a 2:1 nozzle-to- pump ratio is shown in FIGS. 3A, 3B, and 3C, In addition to the components of fluid ejection assembly 200 depicted in FIG. 2, fluid ejection assembly 300 may also include a second nozzle 324 with a second drop ejecting element 322 in a second fluid ejection chamber 318. With a 2:1 nozzle-to-pump ratio, circulation may be provided for both a first fluid ejection chamber 302 and a second fluid ejection chamber 318 by a single fluid circulating element 314 in a fluid recirculation channel 312.

[0033] In FIGS. 3A, 3B, and 3C, a first nozzle 310 in first fluid ejection chamber 302 and second nozzle 324 in second fluid ejection chamber 318 may eject different drop weights. First nozzle 310 in first fluid ejection chamber 302 may be a high drop weight (HDW) nozzle that ejects relatively higher drop weights of jettable material as compared to second nozzle 324 in second fluid ejection chamber 318, which may be a low drop weight (LOW) nozzle. For example, first nozzle 310 in first fluid ejection chamber 302 may eject an amount of jettable material that has a drop weight of between 7 and 11 nanograms (ng), while second nozzle 324 in second fluid ejection chamber 318 may eject an amount of jettable material that has a drop weight of between 2 and 7 ng. These examples are merely illustrative, and other drop weights are contemplated.

[0034] FIGS. 3A, 3B, and 3G also respectively depict three main operational phases of fluid ejection assembly 300. In the first operational phase shown in FIG. 3A, firing first HDW nozzle 310 creates a net fluid flow in a bypass channel 336 (shown as the channel section within the dashed outline), from first fluid ejection chamber 302 to second fluid ejection chamber 318, as indicated by an arrow 338. Flow direction is the result of chamber 302 refilling after drop ejection. The bypass channel 336 may provide additional fluid volume from fluid recirculation channel 312 which includes fluid from chamber 302 and fluid feed hole 320. As the chamber refills fluid flows past particle tolerance pillars 332, through chamber 318 from the bypass channel 336.

[0035] In the second operational phase as shown in FIG. 3B, firing second LDW nozzle 324 creates a net fluid flow in bypass channel 336, from second fluid ejection chamber 318 to first fluid ejection chamber 302. After drop ejection chamber 318 refills drawing fluid from bypass channel 336, through chamber 302 via particle tolerance pillars 332.

[0036] In the third operational phase as shown in FIG. 3C, firing fluid circulating element 314 may create a net fluid flowing from first and second fluid ejection chambers 302 and 318 to second fluid feed hole 320 through fluid recirculation channel 312, The flow direction is indicated by arrows 342. In this situation, the remnant air bubbles may not flow into locations of first fluid ejection chamber 302 or second fluid ejection chamber 318. The potential harm to the performance of first drop ejecting element 304, second drop ejecting element 322, first nozzle 310, or second nozzle 324 may be thus avoided. Additionally or alternatively, in some examples, firing fluid circulating element 314 may create a net fluid flow in the opposite direction of arrows 342.

[0037] There are a variety of size and/or shape selections that can be made to change the fluidic resistance of flow channels. For example, the desired fluidic resistance of fluid recirculation channel 312 may be achieved by increasing the length or decreasing the width of fluid recirculation channel 312. The small fluidic resistance of bypass channel 336 may be achieved by increasing the width of bypass channel 336, decreasing the length of bypass channel 336, and/or increasing a fluidic gap of the particle tolerance pillars 332, [0038] In some examples, narrowing the width of bypass channel 336 between first fluid ejection chamber 302 and second fluid ejection chamber 318 may help to “de-couple” first fluid ejection chamber 302 and second fluid ejection chamber 318, and mitigate potential cross-talk between first fluid ejection chamber 302 and second fluid ejection chamber 318. In addition, providing a narrowed bypass channel 336 between fluid circulating element 314 and first and second fluid ejection chambers 302 and 318 may help to “decouple” fluid circulating element 314 from first and second fluid ejection chambers 302 and 318, and mitigate potential cross-talk between fluid circulating element 314 and first and second fluid ejection chambers 302 and 318.

[0039] Fluid ejection assembly 300 may also include, as a manifold structure 330, particle tolerant architectural features between first and second fluid ejection chambers 302 and 318 and first fluid feed hole 308. Particle tolerant architecture size and location can affect flowrates between first and second fluid feed holes (308 and 320) during refill. Increasing resistance of the first fluid feed hole 308 while decreasing resistance between first fluid ejection chamber 302 and second fluid ejection chamber 318 allows increased flow from second fluid feed hole 320 via the recirculation channel 312 and bypass channel 338. Particle tolerant architectural features may be, for example, a pillar, a column, a post, or other structure (or structures). In this particular example, each particle tolerant architectural feature fakes the form of a triangular particle tolerance pillar 332. It should be noted that particle tolerance pillar 332 may be also of circular, square, or other shapes.

[0040] Particle tolerance pillar 332 may form an “island” which may allow the fluid to flow past while preventing objects, such as air bubbles or particles (e.g., dust, fibers), from flowing into first and second fluid ejection chambers 302 and 318 from first fluid feed hole 308, Such objects, if allowed to enter into first fluid ejection chamber 302 or second fluid ejection chamber 318, may affect the performance of fluid ejection assembly 300, for example, the performance of first drop ejecting element 304 or second drop ejecting element 322. Particle tolerance pillars 332 may be formed during the fabrication of fluid ejection assembly 300.

[0041] In some examples, manifold structure 330 may form an interface between the first ends of the first and second chambers 302 and 318 and the fluid supply. In some examples, manifold structure 330 and bypass channel 338 may be sized and/or shaped so that a loop formed with first and second chambers 302 and 318, bypass channel 336, and manifold structure 330 has a lower fluidic resistance than fluid recirculation channel 312. [0042] FIGS. 4A-D respectively depict main operational phases of two similar but different fluid ejection assemblies 400 and 450. In some examples, fluid ejection assemblies 400 and 450 may both have a single fluid slot 408 as the fluid source, and both have 1:1 nozzle-to-pump ratios. However, fluid ejection assembly 400 has a first drop ejecting element 404 and a first nozzle 410 in a first chamber 402 and no drop ejecting elements or nozzles in a smaller second chamber 418, while fluid ejection assembly 450 has a second drop ejecting element 422 and a second nozzle 424 in second chamber 418 and no drop ejecting elements or nozzles in first chamber 402. In some examples, such as that depicted in FIGs. 4A-D, first nozzle 410 is a HDW nozzle and second nozzle 424 is a LDW nozzle. However, this is not meant to be limiting, and other arrangements are contemplated.

[0043] As the fluid source (and sink) for fluid ejection assemblies 400 and 450, fluid slot 408 may provide a supply of fluid ( e.g . ink) to first chamber 402 and first ejecting element 404 for fluid ejection assembly 400, and to second chamber 418 and second drop ejecting element 422 for fluid ejection assembly 450. Fluid slot 408 may include, for example, a hole, passage, opening, convex geometry or other fluidic architecture formed in or through a substrate 406 by which or through which fluid may be supplied to first and second chambers 402 and 418. Fluid slot 408 may include one (e.g. , a single) or more than one (e.g. , a series of) such hole, passage, opening, convex geometry or other fluidic architecture that communicates fluid with one (e.g., a single) or more than one chamber, and may be of circular, non-circular, or other shape.

[0044] As shown in FIGS. 4A-D, fluid ejection assemblies 400 and 450 may further include a fluid recirculation channel 412 and a fluid circulating element 414 formed in, provided within, or communicated with fluid recirculation channel 412. Fluid recirculation channel 412 may include a section that is open to and in fluid communication at an end 428 with fluid slot 408. Fluid recirculation channel 412 may be also open to and in fluid communication at an opposite end 434 to a bypass channel 436.

[0045] In the first operational phase for fluid ejection assembly 400 as shown in FIG. 4A, firing first HDW nozzle 410 creates a net fluid flow in bypass channel 436, from first chamber 402 to second chamber 418, as indicated by an arrow 426. In some examples, bypass channel 436 and second chamber 418 in combination may be taken as a long bypass channel, and the long bypass channel may be fluidly coupled with fluid slot 408 through a first bypass end 432, and with first chamber 402 through a second bypass end 423.

[0046] In the second operational phase for fluid ejection assembly 400 as shown in FIG. 4B, firing fluid circulating element 414 creates a net fluid flow from fluid slot 408, through first and third bypass ends 432 and 416, first and second chambers 402 and 418, fluid recirculation channel 412, and end 428, back to fluid slot 408, as indicated by arrows 438. [0047] In the first operational phase for fluid ejection assembly 450 as shown in FIG. 4C, firing second LDW nozzle 424 creates a net fluid flow in bypass channel 436, from second chamber 418 to first chamber 402, as indicated by an arrow 440. Similar to fluid ejection assembly 400 in FIG. 4A, bypass channel 436 and first chamber 402 in combination may be taken as a long bypass channel, and the long bypass channel may be fluidly coupled with fluid slot 408 through a third bypass end 416, and with second chamber 418 through a fourth bypass end 420. In the second operational phase for fluid ejection assembly 450 as shown in FIG. 4D, firing fluid circulating element 414 creates a net fluid flow that is indicated by arrows 442,

[0048] FIG. 5 is a schematic plan view of a fluid ejection die 501 that includes plurality of fluid ejection assemblies 500. In some examples, each fluid ejection assembly 500 may have two separate fluid slots as the fluid source — a first fluid slot 508 and a second fluid slot 520. With a 2:1 nozzle-to-pump ratio, fluid ejection assembly 500 may include a first drop ejecting element 504 and a first nozzle 510 in a first fluid ejection chamber 502, and a second ejecting element 522 and a second nozzle 524 in a second fluid ejection chamber 518. First nozzle 510 may be a HDW nozzle, while second nozzle 524 may be a LOW nozzle. Other arrangements are contemplated. Separate fluid slots located as shown in FIG. 5 may save the space for more fluid ejection assemblies 500 in fluid ejection die 501.

[0049] Fluid ejection assembly 500 may further include a fluid recirculation channel 512 and a fluid circulating element 514 formed in, provided within, or communicated with fluid recirculation channel 512. Fluid recirculation channel 512 may include a section that is open to and in fluid communication at end 528 with second fluid slot 520. Fluid recirculation channel 512 may be also open to and in fluid communication at an opposite end 534 to a bypass channel 536. To prevent the fluid from entering fluid recirculation channel 512, bypass channel 536 may be designed to increase refill volume from second fluid slot 520 via recirculation channel 512. The main operational phases shown in FIGS. 4A,

4B, and 4G for fluid ejection assembly 400 with two separate fluid feed holes 408 and 420 may be applied here for fluid ejection assembly 500 with two separate fluid slots 508 and 520.

[0050] As described, above, accumulation of remnant air bubbles may be overcome by fluidly coupling a bypass channel with a fluid recirculation channel. FIG. 6 schematically illustrates how the bypass channel may be incorporated into a printing system, to illustrate one non-limiting example of the role a bypass channel may play within an entire system. It should be noted that fluid ejection die and/or devices that include bypass channels as described may be applicable in other areas, such as various types of microelectromechanical ( "EMS" ) devices that may be deployed in various domains such as healthcare and/or life sciences, and/or chemical analysis (e.g., titrations).

[0051] FIG. 6 depicts a block diagram of a fluid ejection device 650 including a fluid ejection assembly 600 that may share various characteristics with fluid ejection assemblies 100, 200, 300, 400, 450, and/or 500, according to one example of the principles described herein. The fluid ejection device 650 includes an electronic controller 670 and the fluid ejection assembly 600 within at least one printhead 668. The fluid ejection assembly 600 may be any example fluid ejection assembly described, illustrated, and/or contemplated by the present disclosure. The fluid ejection assembly 600 may include a fluid recirculation channel 612 that shares various characteristics with fluid recirculation channels 112, 212, 312, 412, and 512 described herein. The fluid ejection assembly 600 may also include a bypass channel 636 that shares various characteristics with bypass channels 236, 336, 436, and 536 described herein.

[0052] The electronic controller 670 may include a processor, firmware, and other electronics for communicating with and controlling integrated circuitry (not depicted) that in turn operates fluid ejection assembly 600 in order to eject fluid droplets in a precise manner. The electronic controller 670 receives data from a host system (not depicted), such as a computer. The data represents, for example, a document and/or file to be printed and forms a print job that includes at least one print job commands and/or command parameters. From the data, the electronic controller 670 defines a pattern of drops to eject which form characters, symbols, and/or other graphics or images.

[0053] In one example, the fluid ejection device 650 may be an inkjet printing device. In this example, the fluid ejection device 650 may further include a fluidically coupled jettable material reservoir 672 fluidically coupled to the fluid recirculation channel 612 and bypass channel 636 of the fluid ejection assembly 600 to supply jettable material thereto.

[0054] A media transport assembly 674 may be included in the fluid ejection device 650 to provide media for the fluid ejection device 650 in order to create images on the media via ejection of the jettable material. The fluid ejection device 650 may further include a power supply 676 to power the various electronic elements of the fluid ejection device 650.

[0055] Although described specifically throughout the entirety of the instant disclosure, representative examples of the present disclosure have utility over a wide range of applications, and the above discussion is not intended and should not be construed to be limiting, but is offered as an illustrative discussion of aspects of the disclosure,

[0056] What has been described and illustrated herein is an example of the disclosure along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration and are not meant as limitations. Many variations are possible within the scope of the disclosure, which is intended to be defined by the following claims - and their equivalents - in which all terms are meant in their broadest reasonable sense unless otherwise indicated.

Claims

CLAIMS What is claimed is:

1. A fluid ejection assembly comprising: a first chamber and a second chamber fluidly coupled at respective first ends with a fluid supply; a drop ejecting element positioned in the first chamber to cause fluid in the first chamber to be ejected through a nozzle of the first chamber; a bypass channel fluidly coupled to the first and second chambers at respective second ends of the first and second chambers; a fluid recirculation channel fluidly coupled with the bypass channel and the fluid supply; and a fluid recirculating element to circulate fluid through the fluid recirculation channel and one or both of the first and second chambers; wherein the bypass channel is to direct fluid flow from the first chamber to the second fluid chamber, bypassing the fluid recirculation channel, in response to energization of the drop ejecting element.

2. The fluid ejection assembly of claim 1 , wherein the drop ejecting element comprises a first drop ejecting element, and the fluid ejection die includes a second drop ejecting element positioned in the second chamber to cause fluid in the second chamber to be ejected through a nozzle of the second chamber.

3. The fluid ejection assembly of claim 2, wherein the bypass channel is to direct fluid flow from the second chamber to the first fluid chamber, bypassing the fluid recirculation channel, in response to energization of the second drop ejecting element.

4. The fluid ejection assembly of claim 3, wherein the first chamber comprises a high drop weight chamber and the second chamber comprises a low drop weight chamber.

5. The fluid ejection assembly of claim 1 , wherein the first ends of the first and second chambers are fluidly coupled with a first fluid source, and the fluid recirculation channel is fluidly coupled, at an opposite end of the fluid recirculation channel from the bypass channel, to a second fluid source.

6. The fluid ejection assembly of claim 5, wherein the fluid recirculation channel directs fluid from the second fluid source into the bypass channel in response to energization of the drop ejecting element.

7. The fluid ejection assembly of claim 1 , wherein a fluid flow distance between the fluid recirculating element and a first fluid source is less than a fluid flow distance between the fluid recirculating element and a second fluid source.

8. The fluid ejection assembly of claim 1 , comprising a manifold that forms an interface between the first ends of the first and second chambers and the fluid supply.

9. A fluid ejection device comprising: a fluid ejection die comprising: a fluid ejection chamber having a nozzle, a drop ejecting element to cause fluid to be ejected from the fluid ejection chamber through the nozzle, a fluid recirculation channel in communication with the fluid ejection chamber, a fluid recirculating element to recirculate fluid between the fluid recirculation channel and the fluid ejection chamber, and a bypass channel in communication with the fluid ejection chamber and the fluid recirculation channel, wherein in response to actuation of the drop ejecting element, the bypass channel is to direct fluid flow to bypass the fluid recirculation channel; and circuitry to selectively actuate the drop ejecting element to eject fluid through the nozzle or actuate the fluid recirculating element to circulate fluid through the fluid recirculation channel.

10. The fluid ejection device of claim 9, wherein the fluid recirculation channel receives fluid from both the fluid ejection chamber and the bypass channel in response to actuation of the fluid recirculation element.

11. The fluid ejection device of claim 9, wherein fluid recirculation element is positioned with the fluid recirculation channel and comprises a pump or a resistor.

12. The fluid ejection device of claim 9, wherein the fluid recirculation channel has a dimension that is selected so that the fluid recirculation channel directs fluid into the bypass channel in response to actuation of the drop ejecting element.

13. The fluid ejection device of claim 12, wherein the dimension comprises a width or length of the fluid recirculation channel.

14. A fluid ejection die comprising: a plurality of fluid ejection assemblies, each fluid ejection assembly comprising: a plurality of drop ejection channels that are fluidly coupled to each other via a bypass channel; a respective plurality of drop ejection elements incorporated into the drop ejection channels; a pump channel that is fluidly coupled to the plurality of drop ejection channels; a pump incorporated into the pump channel; and a controller to activate the drop ejection elements to generate fluid displacements within the drop ejection channels to drive a flow of fluid through the bypass channel past the pump channel.

15. The fluid ejection device of claim 14, wherein the pump drives fluid through the plurality of drop ejection channels into the pump channel In response to actuation of the pump by the controller.