WO2021183124A1

WO2021183124A1 - Recirculation bypass

Info

Publication number: WO2021183124A1
Application number: PCT/US2020/022105
Authority: WO
Inventors: Jacob M. LUM; Garrett E. CLARK
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-03-11
Filing date: 2020-03-11
Publication date: 2021-09-16

Abstract

A fluid ejection apparatus may include a first layer forming an inlet channel and an outlet channel, a fluid actuator supported by the first layer and a second layer. The second layer may include a recirculation passage and a bypass passage. The recirculation passage is associated with the fluid actuator to supply fluid for ejection by the fluid actuator through an ejection orifice and to circulate fluid across the fluid actuator from the inlet channel to the outlet channel. The bypass passage connects the inlet channel and the outlet channel. The bypass passage is not associated with any fluid actuator that ejects fluid through a corresponding ejection orifice.

Description

RECIRCULATION BYPASS

BACKGROUND

[0001] Fluid ejection apparatus are used to selectively eject droplets of fluid. Such fluid ejection apparatus may include a fluid actuator that displaces fluid through an ejection orifice. The fluid may be pumped to the fluid actuator from a fluid source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Figure 1 A is a bottom view illustrating portions of an example fluid ejection apparatus.

[0003] Figure 1 B is a sectional view of the fluid ejection apparatus of

Figure 1 A taken along line 1 B-1 B.

[0004] Figure 1C is a sectional view of the fluid ejection apparatus of

Figure 1A taken along line 1C-1C.

[0005] Figure 2 is a flow diagram of an example method for forming an example fluid ejection apparatus.

[0006] Figure 3 is a flow diagram of an example fluid ejection method.

[0007] Figure 4A is a perspective view illustrating portions of an example fluid ejection apparatus in section.

[0008] Figure 4B is a sectional view illustrating portions of the example fluid ejection apparatus of Figure 4A taken along line 4B-4B.

[0009] Figure 4C is a sectional view illustrating portions of the example fluid ejection apparatus of Figure 4A taken along line 4C-4C. [00010] Figure 5A is a top view illustrating portions of an example fluid ejection apparatus having recirculation passages and bypass passages between inlet and outlet channels.

[00011] Figure 5B is a perspective view of portions of the example fluid ejection apparatus of Figure 5A, omitting the fluids recirculation passages.

[00012] Figure 5C is an enlarged top view of portions of the example fluid ejection apparatus of 5A.

[00013] Figure 5D is an enlarged side view of portions of the example fluid ejection apparatus of Figure 5A.

[00014] Figure 6 is an enlarged top view of portions of an example fluid ejection apparatus.

[00015] Figure 7 is an enlarged top view of portions of an example fluid ejection apparatus.

[00016] Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The figures are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover, the drawings provide examples and/or implementations consistent with the description; however, the description is not limited to the examples and/or implementations provided in the drawings.

DETAILED DESCRIPTION OF EXAMPLES

[00017] Disclosed are fluid ejection apparatus and methods that utilize pumped fluid to reduce particle settling in the fluid and to cool the fluid ejection apparatus. Particles, such as ink pigments, within the fluid being supplied to the fluid actuator may settle. Such settling may block the ejection orifice or otherwise impair performance of the fluid ejection apparatus. The disclosed fluid ejection apparatus and methods recirculate the pumped fluid across the fluid actuator of a fluid ejector to reduce settling.

[00018] However, bulk fluid recirculation may result in a high pressure drop across the fluid actuator, reducing overall fluid flow. Such a reduction in the overall flow of fluid through the fluid ejection apparatus may result in a heat buildup which may also impair performance of the fluid ejection apparatus. The disclosed fluid ejection apparatus and methods provide additional fluid flow or fluid recirculation by allowing some of the pumped fluid to bypass the fluid actuator through a bypass passage. The additional fluid flow across the bypass passage provides enhanced cooling of the fluid ejection apparatus. The circulating flow rate of fluid may also facilitate a more uniform and constant temperature across the different fluid ejectors for more reliable and consistent fluid ejection or printing performance.

[00019] The disclosed hybrid fluid circulation across both recirculation passages and bypass passages offers benefits in printers that utilize high print flux duty cycles to meet print flux demands while providing marginal flow across fluid ejectors to inhibit remnant air bubble accumulation and viscous plug formation. The bypass circulation passages enhance fluid flow to provide enhanced convective cooling for isothermal printing at lower total pressure drops. As result, a fluid ejection apparatus may operate with high duty cycles while meeting print flux and nozzle health demands. For example, a print head designed to print high weight percent at lower duty cycles may benefit by apportioning a larger portion of the recirculation flow across the fluid ejectors (between the fluid actuators and associated ejection orifices) to reduce viscous plug formation in the bore or ejection orifice. The size, number and distribution of multiple bypass passages in parallel may be modulated to enhance flow uniformity across the fluid ejectors and to tune the fluid flow characteristics to a particular print application. [00020] Disclosed is an example fluid ejection apparatus that may include a first layer forming an inlet channel and an outlet channel, a fluid actuator supported by the first layer and a second layer. The second layer may include a recirculation passage and a bypass passage. The recirculation passage is associated with the fluid actuator to supply fluid for ejection by the fluid actuator through an ejection orifice and to circulate fluid across the fluid actuator from the inlet channel to the outlet channel. The bypass passage connects the inlet channel and the outlet channel. The bypass passage is not associated with any fluid actuator that ejects fluid through a corresponding ejection orifice.

[00021] Disclosed is an example fluid ejection method that may include circulating fluid from an inlet channel to an outlet channel of a first layer of a fluid ejection apparatus through a recirculation passage within a second layer of the fluid ejection apparatus and across a fluid actuator that is supported by the first layer, wherein the fluid actuator is to eject droplets of fluid from the recirculation passage through an ejection orifice. The example method may further include circulating fluid from the inlet channel to the outlet channel through a bypass passage within the second layer of the fluid ejection apparatus, wherein the bypass passage is not associated with any fluid actuator for ejecting droplets from the bypass passage through an ejection orifice.

[00022] Disclosed is an example method for forming a fluid ejection apparatus. The example method may include providing a first layer supporting a fluid actuator, the first layer forming an inlet channel and outlet channel. The example method may further include forming a second layer on the first layer, wherein the second layer may include a recirculation passage and a bypass passage. The recirculation passage is associated with the fluid actuator to supply fluid for ejection by the fluid actuator through an ejection orifice and to circulate fluid across the fluid actuator from the inlet channel to the outlet channel. The bypass passage connects the inlet channel and the outlet channel. The bypass passage is not associated with any fluid actuator for ejection fluid through a corresponding ejection orifice.

[00023] Figures 1A, 1B and 1C schematically illustrate portions of an example fluid ejection apparatus 20. Figure 1 A is a bottom view of fluid ejection apparatus 20. FIGURES 1B and 1C are sectional views of fluid ejection apparatus 20. Fluid ejection apparatus 20 utilizes pumped fluid to reduce particle settling in the fluid and to cool the fluid ejection apparatus 20. Fluid ejection apparatus 20 reduces settling by recirculating fluid across a fluid actuator of a fluid ejector while providing enhanced overall fluid flow by allowing some of the fluid to bypass the fluid actuator. Fluid ejection apparatus 20 comprises layer 24, fluid actuator 28 and layer 32.

[00024] Layer 24 comprises a layer or multiple layers of material that form an inlet channel 37 and an outlet channel 38. Inlet channel 37 may be directly or indirectly connected to a fluid source, a source of pressurized fluid. Pressurized fluid is supplied to fluid actuator 28 from the fluid source through inlet channel 37. Outlet channel 38 may be directly or indirectly connected to the fluid source to redirect fluid back to the fluid source.

[00025] In one implementation, layer 24 may comprise a layer or multiple layers of silicon. In yet other implementations, layer 24 may comprise other materials.

[00026] Fluid actuator 28 comprises a device that displaces fluid within an adjacent void or volume through an associated or corresponding ejection orifice 44. Fluid actuator 28 is supported by layer 24. In one implementation, electrically conductive traces, switches/transistors and other electronic componentry associated with the powering and control of fluid actuator 28 are also supported by layer 24.

[00027] In one implementation, fluid actuator 28 may comprise a thermal resistor which, upon receiving electrical current, heats to a temperature above the nucleation temperature of the fluid so as to vaporize a portion of the adjacent fluid to create a bubble which displaces the fluid through the associated orifice 44. In other implementations, the fluid actuator 28 may comprise other forms of fluid actuators. In other implementations, the fluid actuator may comprise a fluid actuator in the form of a piezo-membrane based actuator, an electrostatic membrane actuator, mechanical/impact driven membrane actuator, a magnetostrictive drive actuator, an electrochemical actuator, and external laser actuators (that form a bubble through boiling with a laser beam), other such microdevices, or any combination thereof.

[00028] Layer 32 is coupled to layer 24. Layer 32 forms recirculation passage 48 and bypass passage 50. Recirculation passage 48 is associated with fluid actuator 28 to supply fluid for ejection by fluid actuator 28 through ejection orifice 44. Recirculation passage 48 extends directly below or adjacent to fluid actuator 28, between fluid actuator 28 and ejection orifice 44. In addition to supplying fluid for ejection by fluid actuator 28, recirculation passage 48 also circulates fluid across the fluid actuator 28 from inlet channel 37 to outlet channel 38. Such recirculation reduces settling of particles suspended within the fluid, such as ink pigments. Although schematically illustrated as having a uniform width and height, it should be appreciated that recirculation passage 48 may vary along its width and/or height. In some implementations, recirculation passage 48 may have a different shape or size between fluid actuator 28 and ejection orifice 44 so as to form an ejection chamber.

[00029] Bypass passage 50 connects inlet channel 37 and outlet channel 38. In some implementations, bypass passage 50 is connected to inlet channel 37 and outlet channel 38 by fluid holes. In other implementations, bypass passage 50 is connected to inlet channel 37 and outlet channel 38 by slots or channels. In some implementations, bypass passage 50 may extend adjacent to a vent or other opening. In some implementations, bypass passage 50 may extend adjacent to a fluid actuator that forms an inertial pump. In contrast to recirculation passage 48, bypass passage 50 is not associated with any fluid actuator that is provided for ejecting fluid through a corresponding ejection orifice. Bypass passage 50 allows some of the fluid supplied to inlet channel 37 to bypass fluid actuator 28, increasing the overall flow of fluid between the inlet channel 37 and outlet channel 38. This overall increase in the flow of fluid between inlet channel 37 and outlet channel 38 may likewise increase the flow of fluid through such channels and may assist in cooling fluid ejection apparatus 20.

[00030] In some implementations, layer 32 is formed from a photo- imageable epoxy. In some implementations, layer 32 is formed from SU8. In some implementations, layer 32 may be formed from other materials or combination of materials.

[00031] Figure 2 is a flow diagram of an example method 100 that may be used to form a fluid ejection apparatus, such as the example fluid ejection apparatus 20 shown in Figures 1A, 1 B and 1C. As indicated by block 104, a first layer supporting a fluid actuator, such as layer 24 supporting fluid actuator 28, is provided. The first layer forms an inlet channel 37 and outlet channel 38. Layer 24 may be molded to form channels 37 and 38 or may undergo material removal processes, such as sawing, etching and the like to form channels 37 and 38. A fluid actuator may be bonded to or encapsulated within layer 24. Portions of the electronic circuitry associated with the fluid actuator may likewise be formed within or on layer 24.

[00032] As indicated by block 108, a second layer, such as layer 32 is formed. The second layer is formed so as to have a recirculation passage, such as recirculation passage 48, and a bypass passage, such as bypass passage 50. The recirculation passage is associated with the fluid actuator so as to supply fluid for ejection by the fluid actuator through an ejection orifice and to circulate fluid across the fluid actuator from the inlet channel to the outlet channel. The bypass passage connects the inlet channel and the outlet channel. The bypass passage is not associated with any fluid actuator for ejecting fluid through a corresponding ejection orifice.

[00033] In some implementations, the second layer may be molded so as to form the recirculation passage and the bypass passage. In some implementations, the second layer may undergo material removal processes or patterning processes such as photolithography and etching to form the recirculation passage and the bypass passage. For example, in implementations where the second layer is formed from a photo-imageable epoxy, masking and etching processes may be applied to form the recirculation passage and the bypass passage. In yet other implementations, a combination of different processes may be used to form the recirculation passage and the bypass passage.

[00034] Figure 3 is a flow diagram of an example fluid ejection method 200. Method 200 reduces settling of particles within the fluid being ejected by recirculate fluid across a fluid actuator, between the fluid actuator and a corresponding ejection orifice. Method 200 additionally enhances the overall flow of fluid through a fluid ejection apparatus by allowing a portion of the fluid to bypass the fluid actuator, enhancing the cooling of the fluid ejection apparatus.

[00035] As indicated by block 204, fluid is circulated from an inlet channel to an outlet channel of a first layer of a fluid ejection apparatus through a recirculation passage within a second layer of the fluid ejection apparatus and across a fluid actuator that is supported by the first layer. The fluid actuator is to eject drops of fluid from the recirculation passage through an ejection orifice.

[00036] As indicated by block 208, fluid is also circulated from the inlet channel to the outlet channel through a bypass passage within the second layer of the fluid ejection apparatus. The bypass passage is not associated with any fluid actuator for ejecting droplets from the bypass passage through a corresponding ejection orifice.

[00037] Figures 4A, 4B and 4C illustrate portions of an example fluid ejection apparatus 320. Figure 4A is a perspective view illustrating a cross- section of portions an example fluid ejection apparatus 320. Figures 4B and 4C are enlarged views of portions of the fluid ejection apparatus 320 of Fig. 4A. As with the above described apparatus 20, apparatus 320 reduces particle settling by using recirculation channels and enhances cooling by using bypass passages. Fluid ejection apparatus 320 comprises body 400, layer 422, layer 424, fluid actuators 428, layer 432 and layer 434.

[00038] Body 400 supports layers 422, 424, 432 and 434 while providing fan-out fluid passages 433-1 and 433-2 (collectively referred to as passages 433). In the example illustrated, passage 433-1 receives fluid from a pressurized fluid source 322. Passage 433-2 directs fluid back to the pressurized fluid source 322 for recirculation. In one implementation, body 400 comprises a single unitary polymeric body is formed from an epoxy mold compound. In other implementations, body 400 may be formed from other polymers. In one implementation, body 400 is molded to form fan-out fluid passages 433. In other implementations, body 400 may be formed from other materials.

[00039] Layer 422 comprises a layer of material extending between body 400 and layer 424. Layer 422 forms an outlet 435 for fluid passage 433- 1 and an inlet 436 for fluid passage 433-2. In one implementation, outlet 435 and inlet 436 comprise fluid holes. In another implementation, outlet 435 and inlet 436 comprise slots or channels.

[00040] Layer 424 comprises a layer or multiple layers of material forming inlet channel 437 and outlet channel 438. Inlet channel 437 extends within layer 424 from outlet 435 of layer 422. Outlet channel 438 extends within layer 424 from inlet 436. Inlet channel 437 and outlet channel 438 are separated by an intervening rib 440 of layer 424. Rib 440 supports fluid actuators 428, which are each similar to fluid actuator 28 described above. Layer 424 may additionally support electrically conductive traces, switches or other electronic componentry associated with the fluid actuators 428.

[00041] Although illustrated as two separate layers, in some implementations, layers 422 and 424 may comprise a single unitary or monolithic layer. In some implementations, both of layers 422 and 424 are formed from silicon. In other implementations, layers 422 and 424 may be formed from different materials. In some implementations, layer 424 may be formed from silicon while layer 422 is formed from other materials such as polymers, ceramics, glass and the like. In some implementations, layer 424 may be formed from materials other than silicon.

[00042] Layer 432 comprises a layer or multiple layers of a material or materials joined to an underside of layer 424 and forming recirculation passages 448 (shown in Figure 4B) and bypass passages 450 (shown in Figure 4C). Recirculation passages 448 comprise fluid passages that extend between and provide for fluid flow from channel 437 to channel 438 between an associated fluid actuator 428 and an ejection orifice 444 associated with the particular fluid actuator 428. In the example illustrated, each of recirculation passages 448 has a ceiling provided by layer 424, internal sides provided by layer 432 and a floor provided by layer 434.

[00043] Recirculation passages 448 each receive fluid from channel 437 through an inlet 452 and discharge fluid to channel 438 through an outlet 454. In one implementation, each of inlets 452 and outlets 454 comprise fluid holes formed in layer 424. In other implementations, inlet 452 and outlets 454 may be partially formed within layer 432. In some implementations, inlets 452 and outlets 454 may each comprise multiple fluid holes or an array of fluid holes.

In some implementations, inlets 452 and outlets 454 may comprise slots or channels. [00044] Recirculation passages 448 supply their respective fluid actuators 428 with fluid for ejection through the corresponding ejection orifice 444. Recirculation passages 448 additionally circulate fluid across their respective fluid actuators 428 from channel 437 to channel 438 to reduce settling.

[00045] Bypass passages 450 comprise fluid passages that extend between and provide for fluid flow from channel 437 to channel 438 without passing a fluid actuator that is to eject fluid through a corresponding ejection orifice. In the example illustrated, each of bypass passages 450 has a ceiling provided by layer 424, internal sides provided by layer 432 and a floor provided by layer 434. In other implementations, bypass passages 450 may be wholly contained within layer 432.

[00046] Bypass passages 450 each receive fluid from channel 437 through an inlet 462 and discharge fluid to channel 438 through an outlet 464. In some implementations, the recirculation passages 448 and the bypass passages 450 form all outlets from the inlet channel 437and wherein the recirculation passages 448 and the bypass passages 450 form all inlets to the outlet channel 438. In one implementation, each of inlets 462 and outlets 464 comprise fluid holes formed in layer 424. In other implementations, inlet 462 and outlets 464 may be partially formed within layer 432. In some implementations, inlets 462 and outlets 464 may each comprise multiple fluid holes or an array of fluid holes. In some implementations, inlets 462 and outlets 464 may comprise slots or channels.

[00047] Bypass passages 450 allow a portion of the fluid being supplied by channel 437 to bypass recirculation passages 448 and their respective fluid actuators 428. As a result, flow between channels 437 and 438 is increased. The increased flow of fluid may assist in absorbing and carrying away excess heat to provide convective cooling for fluid ejection apparatus 320. [00048] Layer 434 comprises a layer of material or multiple layers of material joined to layer 432 and forming ejection orifices 444. In some implementations, layer 434 is formed from the same material as layer 432.

For example, in some implementations, layers 432 and layer 434 both formed from a photo-imageable epoxy. In some implementations, layer 434 is formed from a different material as layer 432. In some implementations, layers 424, 432 and 434 are formed as a single fluid ejection die which is joined to body 400 by layer 422. In some implementations, layers 422, 424, 432 and 434 are formed as a single fluid ejection die which is otherwise joined to body 400.

[00049] Figures 5A, 5B, 5C and 5D illustrate internal fluid regions of an example fluid ejection apparatus 520 through which fluid flows. For ease of illustration, such figures illustrate the boundaries of the internal fluid regions with the layers that define such boundaries being transparently shown.

Figures 5A, 5B and 5C illustrate one example arrangement of recirculation passages and bypass passages along a fluid ejection apparatus in which the recirculation passages and the bypass passages are isolated from one another within the layer forming such passages.

[00050] As shown by Figure 5D, apparatus 520 comprises layers 522, 524, 532 and 534 which substantially correspond to layers 422, 424, 432 and 434, respectively of apparatus 320. Layer 522 extends between body 400 (shown in Figure 4A) and layer 524. In the example illustrated, layer 522 comprises three outlets 535-1 , 535-2, 535-3 (collectively referred to as outlets 535) and two inlets 536-1 and 536-2 (collectively referred to as inlets 536). Outlets 535 deliver fluid from a pressurized fluid source 322 through a supply passage such as passage 433-1 shown in Figure 4A. Inlets 536 deliver fluid to the pressurized fluid source 322 through a passage such as passage 433-2 shown in Figure 4A.

[00051] Layer 524 forms a series of alternating inlet and outlet channels, wherein the inlet channels are individually connected to outlets 535 of supply passage 433-1 (shown in Figure 4A) and wherein the outlet channels are individually connected to inlets 536 of discharge passage 433-2 (shown in Figure 4A) . Figure 5B illustrates three example inlet channels 537-1 , 537-2 and 537-3 and two example outlet channels 538-1 and 538-2. Inlet channels 537-1 , 527-2 and 537-3 receive pressurized fluid through outlets 535-1 , 525-2 and 535-3, respectively, of layer 522 while outlet channels 538-1 and 538-2 discharge fluid through outlets 536-1 and 536-2, respectively, of layer 522. Similar to channels 437 and 438 of apparatus 320, channels 537 and 538 are separated by intervening walls or ribs 540 (shown in Figure 5A) which support fluid actuators 528 (shown in Figure 5C) generally opposite to an ejection orifice 544. In the example illustrated, each of channels 537 and 538 is Chevron -shaped, facilitating a staggering offset relationship between different ejection orifices 544 of different fluid ejectors arranged between the channels 537, 538.

[00052] In one implementation, layer 524 may comprise a layer or multiple layers of silicon. In yet other implementations, layer 524 may comprise other materials.

[00053] Layer 532 extends over layer 524 between layer 524 and layer 534. Layer 532 forms a two-dimensional array of recirculation passages 548 and bypass passages 550. As shown by Figures 5A and 5C, recirculation passages 548 connect adjacent inlet channels 537 and outlet channels 538.

In the example illustrated, recirculation passages 548 are arranged in sets 560-1 , 560-2, 560-3 and 560-4 and sets 562-1 , 562-2, 562-3 and 562-4. Sets 560-1 and 562-1 are arranged opposite ends of channels 537-1 and 538-1 , interconnecting channels 537-1 and 538-1. Sets 560-2 and 562-2 are arranged opposite ends of channels 537-2 and 538-1 , interconnecting channels 537-2 and 538-1. Sets 560-3 and 562-3 are arranged opposite ends of channels 537-2 and 538-2, interconnecting channels 537-2 and 538-2. Sets 560-4 and 562-4 are arranged opposite ends of channels 537-3 and 538-2, interconnecting channels 537-3 and 538-2. [00054] As indicated by arrows 563-1, sets 560-1 and 562-1 direct the flow of fluid from channel 537-1 , across associated fluid actuators and ejection orifices, to channel 538-1. As indicated by arrows 563-2, sets 560-2 and 562-2 direct the flow of fluid from channel 537-2, across associated fluid actuators 528 and ejection orifices 544, to channel 538-1. As indicated by arrows 563-3, sets 560-3 and 562-3 flow from channel 537-2, across associated fluid actuators 528 and ejection orifices 544, to channel 538-2. As indicated by arrows 563-4, sets 560-4 and 562-4 direct the flow of fluid from channel 537-3, across associated fluid actuators 528 and ejection orifices 544, to channel 538-2.

[00055] In the example illustrated, layer 532 additionally forms a pair of spaced pillars 545 on opposite sides of each fluid actuator 528 and ejection orifice 544. Pillars 545 are spaced to allow fluid flow therebetween and passed such pillars. Pillars 545 serve to filter the fluid flowing across the fluid actuator 528 and its associated ejection orifice 544. In some implementations, other arrangements of pillars 545 or other filtering mechanisms may be employed. In other implementations, pillars 545 may be omitted.

[00056] Similar to recirculation passages 548, bypass passages 550 extend between and fluidly interconnect adjacent channels 537 and 538. However, unlike recirculation patches 548, bypass passages 550 are not associated with any fluid ejector fluid actuator; bypass passages do not extend across any fluid actuator that is provided for ejecting fluid through a corresponding ejection orifice. In the example illustrated, bypass passages 550 omit any such pillars to lessen restriction of fluid flow. In some implementations, layer 532 may form pillars within bypass passages 550 additionally filter the fluid flowing through bypass passages 550.

[00057] As shown by Figure 5A, bypass passages 550 are evenly spread or distributed amongst the fluid ejection orifices to provide more even flow across apparatus 520. In the example illustrated, each of sets 560 and 562 of recirculation passages 548 is bordered on opposite ends by a bypass passage 550. In the example illustrated, each of sets 560 and 562 is further bifurcated by an intermediate bypass passage 550. The end and intermediate locations of the bypass passages 550 provide enhanced uniformity of the fluid flow across the recirculation passages 548.

[00058] As indicated by arrows 565-1, those bypass passages 550 interconnecting channels 537-1 and 538-1 direct the flow of fluid from channel 537-12 channel 538-1 , bypassing the fluid actuators associated with recirculation passages 548 of sets 560-1 and 562-1. As indicated by arrows 565-2, those bypass passages 550 interconnecting channels 537-2 and 538-1 direct the flow of fluid from channel 537-2 to channel 538-1 , bypassing the fluid actuators associated with recirculation passages 548 of sets 560-2 and 562-2. As indicated by arrows 565-3, those bypass passages 550 interconnecting channels 537-2 and 538-2 direct the flow of fluid from channel 537-2 to channel 538-2, bypassing the fluid actuators associated with recirculation passages 548 of sets 560-3 and 562-3. As indicated by arrows 565-4, those bypass passages 550 interconnecting channels 537-3 and 538-2 direct the flow of fluid from channel 537-3 to channel 538-2, bypassing the fluid actuators associated with recirculation passages 548 of sets 560-4 and 562-4.

[00059] As shown by Figures 5B (which omits the illustration of recirculation passages 548) and Figure 5C, each of recirculation passages 548 and bypass passages 550 is fluidically isolated from other recirculation passages 548 and other bypass passages within layer 534. Each of recirculation passages 548 has one end directly connected to an associated channel 537 and another end directly connected to an associated channel 538 by an individual fluid hole. By way of example, Figure 5C illustrates a first recirculation passage 548-1 of set 560-2 connected to channel 538-2 by a first fluid hole 570 and connected to channel 537-2 by fluid hole 572.

Recirculation passages 548 extend across differently sized fluid actuators 528 having differently sized ejection orifices 544 which provide different drop weights for the fluid droplets being ejected.

[00060] Similar to recirculation passages 548, each of bypass passages 550 has one end directly connected to an associated channel 537 and another and directly connected to an associated channel 538 by an individual fluid hole. By way of example, Figure 5C illustrates an example bypass passage 550-1 extending between and connecting channel 53-2 and 537-2. Bypass passage 550-1 is connected to channel 538-2 by a first fluid hole 580 and connected to channel 537-2 by second different fluid hole 582. Bypass passages 550 allow a portion of the fluid to bypass recirculation passages 548 and their respective fluid actuators 528. As a result, flow between channels 537 and 538 is increased. The increased flow of fluid may assist in absorbing and carrying away excess heat to provide convective cooling for fluid ejection apparatus 520.

[00061] As indicated by arrows 567, fluid not flowing through the sets 560 of recirculation passages 548 or the bypass passages 550 amongst sets 560 flows further along inlet channels 537 to the other end of such channels where the fluid may circulate to outlet channels 538 across the sets 562 of recirculation passages 548 or across the bypass passages 550 distributed amongst such sets 562 of recirculation passages 548. In some implementations, the recirculation passages 548 and the bypass passages 550 form all outlets from the inlet channels 537and wherein the recirculation passages 548 and the bypass passages 550 form all inlets to the outlet channels 538. In the example illustrated, 50 to 80% of the fluid supplied to inlet channels 537 is circulated across the fluid actuators and ejection orifices. The apportionment of flow across the recirculation passages 548 relative to across the bypass passages 550 may be varied by varying the size, number and location of recirculation passages 548 as well as size, number and location of bypass passages 550. [00062] In some implementations, layer 532 is formed from a photo- imageable polymer, such as a photo-imageable epoxy. In some implementations, layer 532 is formed from SU8. In some implementations, layer 532 may be formed from other materials or combination of materials. [00063] Layer 534 comprise a layer of material or multiple layers of material joined to layer 532 and forming ejection orifices 544. In some implementations, layer 534 is formed from the same material as layer 532.

For example, in some implementations, layers 532 and layer 534 both formed from a photo-imageable epoxy. In some implementations, layer 534 is formed from a different material as layer 532. In some implementations, layers 524, 532 and 534 are formed as a single fluid ejection die which is joined to body 400 by layer 522. In some implementations, layers 522, 524, 532 and 534 are formed as a single fluid ejection die which is otherwise joined to body 400.

[00064] Figure 6 illustrates portions of an example fluid ejection apparatus 620. Apparatus 620 is similar to apparatus 520 described above except that apparatus 620 additionally comprises manifold passages 687-1 ,

687-2, 687-3, 687-4 (collectively referred to as passages 687), 688-1 , 688-2

688-3 and 688-4 (collectively referred to as passages 688). Those remaining components of apparatus 620 which correspond to components of apparatus 520 are numbered similarly in Figure 6 and/or are shown in Figures 5A-5D. Figure 6 illustrates how the multiple fluid holes 570, 572 of recirculation passages 548 and the multiple fluid holes 580, 582 of bypass passages 550 may be fluidically connected to one another within layer 534 to provide enhanced flow uniformity.

[00065] Manifold passages 687 and 688 each comprise passages molded or otherwise formed in layer 534 so as to extend along the recirculation patches 548 and bypass passages 550 while interconnecting the various fluid holes. Manifold passages 687 connect the fluid holes 572 of recirculation passages 548 through which fluid is supplied to the recirculation passages 548. Manifold passages 687 further connect the fluid holes 582 of bypass passages 550 through which fluid is supplied to such bypass passages 550. In the example illustrated, manifold passages 687 connect fluid holes 572 to fluid holes 582.

[00066] Manifold passages 688 connect the fluid holes 570 of recirculation passages 548 through which fluid is discharged from the recirculation passages 548. Manifold passages 688 further connect the fluid holes 580 of bypass passages 550 through which fluid is discharged from such bypass passages 550. In the example illustrated, manifold passages 688 connect fluid holes 570 to fluid holes 580.

[00067] Figure 7 illustrates portions of an example fluid ejection apparatus 720. Apparatus 720 is similar to apparatus 620 except that apparatus 720 comprises a different arrangement of recirculation passages 548 and bypass passages 550. Those remaining components of apparatus 720 which correspond to components of apparatus 620 are numbered similarly in Figure 7 and/or are shown in Figures 5A-5D or Figure 6. Figure 7 illustrates how different fluid ejection apparatus may have different patterns or layouts of recirculation passages 548 and bypass passages 550 to achieve particular cooling and recirculation flow characteristics or flow objectives.

[00068] As shown by Figure 7, fluid ejection apparatus 720 comprises a pattern of alternating recirculation passages and bypass passages along the alternating inlet channels 537 and outlet channels 538. The larger number of recirculation passages 548 and bypass passages 550 may provide a higher fluid flow rate in enhanced convective cooling. The interspersal of bypass passages 550 amongst the recirculation passages 548 in the alternating pattern may provide enhanced uniformity of fluid flow through the fluid ejection apparatus 620.

[00069] Although the present disclosure has been described with reference to example implementations, workers skilled in the art will recognize that changes may be made in form and detail without departing from disclosure. For example, although different example implementations may have been described as including features providing various benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example implementations or in other alternative implementations. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example implementations and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements. The terms “first”, “second”, “third” and so on in the claims merely distinguish different elements and, unless otherwise stated, are not to be specifically associated with a particular order or particular numbering of elements in the disclosure.

Claims

WHAT IS CLAIMED IS:

1. A fluid ejection apparatus comprising: a first layer forming an inlet channel and an outlet channel; a fluid actuator supported by the first layer; and a second layer forming: a recirculation passage associated with the fluid actuator to supply fluid for ejection by the fluid actuator through an ejection orifice and to circulate fluid across the fluid actuator from the inlet channel to the outlet channel; and a bypass passage connecting the inlet channel and the outlet channel, the bypass passage not being associated with any fluid actuator for ejecting fluid through a corresponding ejection orifice.

2. The fluid ejection apparatus of claim 1 further comprising: a first fluid hole connecting the inlet channel to the recirculation passage on a first side of the fluid actuator; and a second fluid hole connecting the outlet channel to the recirculation passage on a second side of the fluid actuator. 3. The fluid ejection apparatus of claim 2 further comprising: a third fluid hole connecting the inlet channel to the bypass passage; and 4 a fourth fluid hole connecting the outlet channel to the

5 bypass passage.

1 4. The fluid ejection apparatus of claim 3 further comprising a second

2 bypass passage connecting the inlet channel and the outlet channel, the second

3 bypass passage not being associated with any fluid actuator.

1 5. The fluid ejection apparatus of claim 4 further comprising a

2 manifold passage formed in the second layer and connecting the bypass

3 passage and the second bypass passage.

1 6. The fluid ejection apparatus of claim 5, wherein the manifold

2 passage further connects the recirculation passage to the bypass passage in the

3 second bypass passage.

1 7. The fluid ejection apparatus of claim 1 , wherein a third layer forms

2 the ejection orifice. i 8. The fluid ejection apparatus of claim 1 further comprising:

2 a second fluid actuator supported by the first layer; and

3 a second recirculation passage formed in the second layer,

4 the second recirculation passage associated with the fluid actuator to supply fluid for ejection by the second fluid actuator through a

6 second ejection orifice and to circulate fluid across the second fluid

7 actuator from the inlet channel to the outlet channel.

1 9. The fluid ejection apparatus of claim 8 comprising:

2 a first manifold passage connected to the inlet channel and

3 formed in the second layer, the first manifold passage connected to the recirculation passage and the second recirculation passage; and a second manifold passage connected to the outlet channel and formed in the second layer, the second manifold passage connected to the recirculation passage and the second recirculation passage, wherein the bypass passage connects the first manifold passage and the second manifold passage. 10. The fluid ejection apparatus of claim 1 comprising recirculation passages and bypass passages connected to the inlet channel, wherein the recirculation passages and the bypass passages form all outlets from the inlet channel and wherein the recirculation passages and the bypass passages form all inlets to the outlet channel. 11. The fluid ejection apparatus of claim 1 , when the first layer comprises silicon and wherein the second layer comprises a photo-imageable polymer. 12. A fluid ejection method comprising: circulating fluid from an inlet channel to an outlet channel of a first layer of a fluid ejection apparatus through a recirculation passage within a second layer of the fluid ejection apparatus and across a fluid actuator that is supported by the first layer, the fluid actuator is to eject droplets of fluid from the recirculation passage through an ejection orifice; and circulating fluid from the inlet channel to the outlet channel through a bypass passage within the second layer of the fluid 0 ejection apparatus, the bypass passage not being associated with1 any fluid actuator for ejecting droplets from the bypass passage2 through an ejection orifice.

1 13. The fluid ejection method of claim 12 directing fluid from the bypass

2 passage to a second bypass passage within the second layer across a manifold

3 passage within the second layer. i 14. A method for forming a fluid ejection apparatus, the method

2 comprising:

3 providing a first layer supporting a fluid actuator, the first

4 layer forming an inlet channel and outlet channel;

5 forming a second layer on the first layer, the second layer

6 comprising:

7 a recirculation passage associated with the

8 fluid actuator to supply fluid for ejection by the fluid 9 actuator through an ejection orifice and to circulate0 fluid across the fluid actuator from the inlet channel to1 the outlet channel; and 2 a bypass passage connecting the inlet channel3 and the outlet channel, the bypass passage not being associated4 with any fluid actuator for ejection fluid through a corresponding5 ejection orifice.

1 15. The method of claim 14 further comprising:

2 forming a second bypass passage in the second layer, the

3 second bypass passage connecting the inlet channel and the outlet

4 channel and not being associated with any fluid actuator; and forming a manifold passage in the second layer, the manifold passage connecting the bypass passage and the second bypass passage.