Patent ID: 12187048

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure are described below while referring to the drawings. The following drawings are schematic drawings. Therefore, details may be omitted. In addition, the dimensional proportions do not necessarily correspond to the actual dimensional proportions. The dimensional proportions do not necessarily match each other from drawing to drawing. Certain dimensions may be depicted as being larger than they are in reality, and certain shapes may be depicted in an exaggerated manner.

The drawings may include arrows representing directions D1 to D6. These directions are parallel to an ejection surface3a, which is described later. The directions D2 and D5 are, for example, parallel to a longitudinal direction of a head3, which is described later, and are so-called main scanning directions from another perspective. The directions D3 and D6 are perpendicular to the directions D2 and D5. The directions D1 and D4 are inclined with respect to the directions D3 and D6.

(Overall Configuration of Liquid Ejecting Device)

FIG.1is a diagram schematically illustrating the main configuration of a liquid ejecting device1(hereinafter, may be referred to as “ejecting device1”) according to an embodiment.

The ejecting device1is configured as a device that deposits a liquid onto a surface of an object101by ejecting droplets from the ejection surface3aof the head3towards the object101, such as an inkjet printer, for example. The ejection surface3amay face in any direction with respect to the vertical direction, but in the following description, for convenience, the direction in which the ejection surface3afaces is a downward direction and terms such as upper surface or lower surface may be used.

The specific type (intended use) of the ejecting device1may be any appropriate type. For example, the ejecting device1may be a device that prints characters and figures (or from another perspective, records information) by depositing ink onto a recording medium (for example, paper) serving as the object101. In other words, the ejecting device1may be a so-called printer. In addition, for example, the ejecting device1may be a device for decorating the body of an automobile by depositing paint onto the body of the automobile serving as the object101. In addition, for example, the ejecting device1may be a device that forms wiring by depositing a liquid containing conductive particles onto a circuit board serving as the object101.

Furthermore, unlike in the illustrated example, the ejecting device1does not have to be a device that deposits a liquid onto the object101. For example, the ejecting device1may be a device that ejects into a container a liquid chemical that reacts with a substance inside the container, or may be a device that sprays a disinfectant solution into the air.

As is clear from the above examples of specific types of the ejecting device1, the material, shape and dimensions of the object101may be chosen as appropriate. SinceFIG.1is a schematic diagram, the object101is illustrated as a rectangular parallelepiped. The material of the object101may be, for example, paper, cloth, resin, metal, ceramic, wood, or a combination of any of these materials. Types of the object101may include recording media (for example, paper rolls or sheets), circuit boards, clothing, beverage containers, storage containers, electronic equipment housings, and automobile bodies. The object101or the area of the object101onto which the liquid is to be deposited may be narrower or wider than the ejection surface3afrom which droplets are ejected.

As is clear from the above examples of specific types of the ejecting device1, the type of liquid may also be chosen as appropriate. For example, the types of liquids may include inks, paints, liquids containing conductive particles, chemicals, and disinfectants. Inks and paints may be distinguished from each other by the presence or absence of organic solvents and/or a function of protecting the surface of the object101. However, such distinctions do not need to be made. In the following description, paint may be read as ink as appropriate. The reverse is also true. A paint may contain a pigment for the purpose of providing a color or may be pigment-free (colorless) without having the purpose of providing a color (for example, for the sole purpose of adding gloss and/or protecting the object101).

The ejecting device1, for example, includes the head3that ejects droplets and a moving unit5that moves the head3relative to the object101. The head3has the ejection surface3ain which a plurality of nozzles (which are described later) for ejecting droplets is formed. The moving unit5, for example, maintains a state in which the ejection surface3aand the surface of the object101face each other and moves the ejection surface3aand the surface of the object101relative to each other along the ejection surface3aand the surface of the object101. The direction of relative movement is, for example, the direction D3 or D6. As can be understood from an inkjet printer, which is a specific example of the ejecting device1, droplets are deposited across a region having a larger area than the area of the region where the plurality of nozzles is arranged as a result of droplets being ejected from the ejection surface3ain synchronization with the relative movement described above.

The ejecting device1includes, for example, a tank7in which liquid is stored. The head3has a supply port3bfor allowing liquid to be supplied from the tank7to the head3and a collection port3cfor allowing liquid to be collected from the head3to the tank7. In other words, the liquid circulates through the head3and the tank7. Circulating the liquid in this way, for example, reduces the likelihood of the liquid stagnating inside the head3. This, in turn, reduces the likelihood of the stagnating liquid solidifying or components in the stagnating liquid precipitating. In addition, in this embodiment, the shear rate of the liquid can be adjusted, and therefore the viscosity of the liquid can be adjusted, as described below, by circulating the liquid.

The ejecting device1includes a circulation actuation unit9that applies pressure to the liquid so as to cause the liquid to circulate and a controller11that controls the various parts (for example, the head3, the moving unit5, and the circulation actuation unit9) of the ejecting device1. The combination of the circulation actuation unit9and the controller11may be regarded as a flow rate setting unit13used to set the flow rate of the liquid circulating through the head3(hereinafter, referred to as the “circulation flow rate”). The circulation flow rate may be regarded, for example, as being the same as the flow rate of the liquid flowing from the collection port3cto outside the head3.

The ejecting device1may include only one head3(and tank7) as in the case of a monochrome printer, or may include multiple heads3(and multiple tanks7) that eject different liquids from each other like in the case of a color printer. The ejecting device1may also include multiple heads3that eject the same liquid as each other. There are advantages to providing a plurality of heads3that eject the same liquid such as, for example, a reduction in the time taken to deposit liquid on a certain area and an improvement in dot density. In the following description, only one head3will be referred to for convenience.

(Moving Unit)

The moving unit5can, for example, move the object101relative to the head3in at least one out of the directions D3 and D6. As has already been mentioned, this direction is the direction of movement when ejecting droplets and is a so-called sub-scanning direction. The moving unit5may be able to realize relative movement between the head3and the object101in directions other than the directions D3 and D6. Other directions in which relative movement may be realized include, for example, the directions D2 and D5, which are perpendicular to the directions D3 and D6, and directions perpendicular to the ejection surface3a(a direction in which the head3and the object101are brought closer together and a direction in which the head3and the object101are moved away from each other). The moving unit5may also be capable of realizing relative rotation between the head3and the object101.

The moving unit5may move only the object101, the head3, or both the object101and the head3in an absolute coordinate system. The specific configuration of the moving unit5may be appropriately decided upon in accordance with the specific type of the ejecting device1.

For example, in the case where the ejecting device1is a so-called line printer, the moving unit5may be configured as a device for conveying a recording medium (for example, paper) as the object101. The device may, for example, include a plurality of rollers that generates a frictional force by contacting the recording medium and an electric motor that causes the plurality of rollers to rotate. In the case where the ejecting device1is a so-called serial printer, for example, the moving unit5may include a device for conveying the recording medium as the object101in a prescribed conveyance direction and a device for moving the head3in a direction perpendicular to the conveyance direction and along the recording medium.

For example, the ejecting device1may include a conveyor belt that conveys any type of object101. For example, the ejecting device1may include a movable table on which any type of object101is placed. For example, the ejecting device1may include an industrial robot that moves any type of object101and/or an industrial robot that moves the head3. Examples of industrial robots may include vertical articulated robots (articulated robots in a narrow sense), SCARA robots, Cartesian robots, and parallel link robots.

(Tank and Circulation Actuation Unit)

The tank7and circulation actuation unit9may be, for example, the same as or similar to a tank and a circulation actuation unit used in known inkjet printers that circulate liquids, or may be components to which such known tanks and circulation actuation units have been applied.

For example, the tank7may be configured to store the liquid to be supplied to the head3and the liquid collected from the head3in the same space. The tank7may also be configured to store the liquid to be supplied to the head3and the liquid collected from the head3in separate spaces and allow the liquid to flow from the latter space to the former space. In this case, the tank7may include two spaces realized by partitioning one tank with a partition wall or may include two spaces realized by including two tanks connected to each other by flow paths. The inside of the tank7(the space mentioned above) may be open to the atmosphere or sealed. In the latter case, the pressure inside the tank7may be adjusted to a suitable pressure using a valve or vacuum pump, for example. The tank7may include a main tank and a sub-tank having a smaller capacity than the main tank. The sub-tank functions as an intermediary between the main tank and the head3.

In the illustrated example, the circulation actuation unit9includes a pump15that pumps the liquid from the tank7to the head3, a pressure sensor17A that detects the pressure of the liquid on the side near the supply port3b, and a pressure sensor17B that detects the pressure of the liquid on the side near the collection port3c. The controller11, for example, performs feedback control on the pump15so that the pressure difference between the supply port3band the collection port3cconverges at a prescribed target value on the basis of the values detected by the pressure sensors17A and17B. Thus, the circulation flow rate is subjected to feedback control so that the circulation flow rate becomes the target flow rate.

Unlike in the illustrated example, a pump15that pumps the liquid from the collection port3cto the tank7may be provided instead of or in addition to the pump15on the side near the supply port3b. Instead of or in addition to the pump15pumping the liquid, liquid flow may be generated by controlling the pressure inside the tank7by using a vacuum pump or the like. Liquid flow may be generated by raising the liquid level in the tank containing the liquid to be supplied so as to be higher than the liquid level in the tank storing the collected liquid.

Instead of or in addition to the pressure sensors17A and17B, flow rate sensors may be provided in order to detect the flow rate of the liquid supplied to the head3and/or the flow rate of the liquid collected from the head3and may be used in control of the circulation flow rate. As is understood from the various ways in which the liquid flow may be generated described above, instead of or in addition to these sensors, a sensor that detects the air pressure inside the tank7may be provided and used in control of the circulation flow rate. Open-loop control may be used without performing sensor-based feedback control. In other words, sensors do not have to be provided.

For example, the tank7and the circulation actuation unit9are not moved in an absolute coordinate system by the moving unit5. Therefore, for example, in a mode in which the moving unit5moves the head3in the absolute coordinate system, the head3moves relative to the tank7and the circulation actuation unit9. In this case, the head3, the tank7, and the circulation actuation unit9may be connected to each other by flow paths consisting of, for example, flexible tubing. In a mode in which the moving unit5does not move the head3in the absolute coordinate system, the head3is fixed in place with respect to the tank7and the circulation actuation unit9. In this case, the configuration of the flow paths connecting the head3, the tank7, and the circulation actuation unit9to each other may be chosen as appropriate. Unlike in the above description, all or part of the tank7and/or the circulation actuation unit9may move together with the head3.

(Controller)

The controller11consists of, for example, a computer, a Field Programmable Gate Array (FPGA), an Application Specific Integrated Circuit (ASIC), any other forms of circuitry, etc. Although not specifically illustrated, the computer includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an external storage device. The head3, the moving unit5, and the circulation actuation unit9are controlled by executing programs stored in the ROM and/or external storage device.

(Head)

FIG.2Ais an exploded perspective view of the head3.

The head3includes a flow path member19(reference symbol appears inFIG.1), which has a flow path along which the liquid flows, an actuator21that applies pressure to the liquid in the flow path member19, and signal transmission members23for inputting drive signals to the actuator21(not illustrated inFIG.1). The flow path member19includes a first flow path member25having the ejection surface3aand a second flow path member27including the supply port3band the collection port3c. The surface of the first flow path member25on the opposite side from the ejection surface3amay be referred to as a pressurized surface25a.

The first flow path member25and the second flow path member27are formed in roughly flat plate like shapes and together form the roughly flat plate-shaped flow path member19when stacked one on top of the other. Liquid supplied to the supply port3bis supplied from the second flow path member27to the first flow path member25and is then ejected from the ejection surface3a. The remaining liquid that is not ejected flows from the first flow path member25to the second flow path member27and is collected from the collection port3c.

The controller11outputs a control signal on the basis of prescribed data such as image data. The control signal is input, for example, via the signal transmission members23, to a driver, which is not illustrated, mounted on the signal transmission members23. The driver generates a drive signal having a predetermined waveform on the basis of the input control signal. The drive signal is input to the actuator21via the signal transmission members23. The actuator21applies pressure to the liquid inside the flow path member19with a pressure waveform corresponding to the waveform of the drive signal. As a result, the liquid inside the flow path member19is ejected from the ejection surface3a. The division of roles between the controller11and the driver may be decided upon as appropriate, and the driver may be regarded as being part of the controller11.

(Second Flow Path Member, Supply Reservoir, and Collection Reservoir)

FIG.2Bis a perspective view of the second flow path member27. More precisely, this figure is a view of the second flow path member27from the side where the first flow path member25is located, and the upper side of the sheet inFIG.2Bcorresponds to the lower side of the sheet inFIGS.1and2A.FIG.3Ais a planar see-through view of the head3seen from the opposite side from the side where the ejection surface3ais located. In this figure, the shape of the second flow path member27and the actuator21are illustrated.

As illustrated inFIG.2B, the second flow path member27has two grooves (refer to reference symbols29and31) formed in the surface on the side where the first flow path member25is located. These two grooves are blocked by the first flow path member25and form a supply reservoir29and a collection reservoir31illustrated inFIGS.2B and3A. The supply reservoir29leads to the supply port3band is a flow path that supplies liquid supplied to the supply port3bto the flow path of the first flow path member25. The collection reservoir31leads to the collection port3cand is a flow path that collects liquid from the flow path of the first flow path member25and guides the collected liquid to the collection port3c.

The supply reservoir29and the collection reservoir31include, for example, portions (main portions29aand31a) that extend in a straight line along the longitudinal direction (directions D2 and D5) of the head3. The main portions29aand31ahave, for example, lengths that span the length, in the longitudinal directions (directions D2 and D5), of the region in which a plurality of nozzles (described later) is arranged (refer to the arrangement region of the actuator21inFIG.3A). The main portion29aand31aare located on opposite sides from each other in the lateral direction of the head3(directions D3 and D6) with respect to the arrangement region of the plurality of nozzles. In the description of the embodiments, for convenience, the shapes, dimensions, and so forth of the supply reservoir29and the collection reservoir31may be described while focusing only on the main portions29aand31a.

The supply port3b, for example, leads to one end (the end in the direction D2) of the supply reservoir29. The other end (the end in the direction D5) of the supply reservoir29is a dead end (in other words, closed). The liquid in the supply reservoir29flows in the direction from the one end to the other end (in the direction D5). The collection port3c, for example, leads to one end (in the direction D5) of the collection reservoir31. The other end of the collection reservoir31(the end in the direction D2) is a dead end (in other words, closed). The liquid in the collection reservoir31flows in the direction from the other end to the one end (in the direction D5). The direction in which the liquid in the supply reservoir29flows and the direction in which the liquid in the collection reservoir31flows are identical to each other in the illustrated example. However, these directions may instead be opposite to each other.

The supply reservoir29may include only the main portion29aor may additionally include other portions. In the illustrated example, the supply reservoir29includes a portion (reference symbol omitted) that extends from the main portion29adiagonally in the longitudinal direction of the head3to the supply port3b. Similarly, the collection reservoir31may include only the main portion31aor may additionally include other portions. In the illustrated example, the collection reservoir31includes a portion (reference symbol omitted) that extends diagonally in the longitudinal direction of the head3from the main portion31ato the collection port3c.

The cross-sectional shapes and dimensions of the supply reservoir29and the collection reservoir31(for example, of the main portions29aand31athereof) may be constant regardless of the position along the longitudinal directions of these flow paths or may vary with position. In the description of the embodiments, the former may be taken as an example. The cross-sectional shapes may be an appropriate shape such as a rectangular shape. The various dimensions of the supply reservoir29and the collection reservoir31may be set as appropriate in accordance with the specific technical field to which the ejecting device1is to be applied.

In the illustrated example, in addition to the two grooves serving as the supply reservoir29and the collection reservoir31, the second flow path member27has slits27a(FIGS.2A and2B) through which the signal transmission members23are inserted and a recess27b(FIGS.2B and3A) in which the actuator21is housed. The slits27a, for example, penetrate through the second flow path member27from the side where the first flow path member25is located to the opposite side and extend along the longitudinal direction of the head3. The recess27bhas a planar shape that is, for example, one size larger than the actuator21, and the planar shape is a rectangular shape having a longitudinal direction matching the longitudinal direction of the head3in the illustrated example.

The material and so forth of the second flow path member27may be chosen as appropriate. For example, the second flow path member27may be composed of a metal, a resin, a ceramic, or a combination of any of these materials.

(First Flow Path Member)

FIG.3Bis a planar see-through view of the head3. In this figure, the shape of the first flow path member25and the actuator21are illustrated.FIG.4is an enlarged view of a region IV inFIG.3B.

The flow path of the first flow path member25includes a plurality of supply manifolds33into which liquid is supplied from the supply reservoir29and a plurality of individual flow paths35into which liquid is supplied from the supply manifolds33. The individual flow paths35include nozzles (described later) that eject droplets from the ejection surface3a. The flow path of the first flow path member25also includes a plurality of collection manifolds37that collects liquid from the plurality of individual flow paths35and guides the collected liquid to the collection reservoir31.

Although not specifically illustrated, the first flow path member25may include other flow paths that are located in the directions D2 and D5 relative to the plurality of supply manifolds33, the plurality of individual flow paths35, and the plurality of collection manifolds37and that connect the supply reservoir29and the collection reservoir31to each other. Such flow paths contribute to, for example, making the temperature of the first flow path member25uniform.

(Manifolds)

The supply manifolds33include, for example, main portions33a(corresponding to the entirety of the supply manifolds33in the illustrated example) that extend in straight lines along the direction D4 from the side near the supply reservoir29to the side near the collection reservoir31. The direction D4 is inclined with respect to the lateral direction of the head3(direction D6). Similarly, the collection manifolds37include, for example, main portions37a(corresponding to the entirety of the collection manifolds37in the illustrated example) that extend in straight lines along the direction D1 from the side near the collection reservoir31to the side near the supply reservoir29. The direction D1 is inclined with respect to the lateral direction of the head3(direction D3). In the description of the embodiments, the shape, dimensions, and so forth of the supply manifolds33and the collection manifolds37may be described while focusing only on the main portions33aand37afor convenience.

One ends (the ends in the direction D1) of the supply manifolds33overlap the supply reservoir29in the planar see-through view. The one ends lead to the supply reservoir29via openings33bin a surface of the first flow path member25on the side where the second flow path member27is located. The other ends of the supply manifolds33(the ends in the direction D4) are dead ends. Therefore, the liquid in the supply reservoir29is supplied to the one ends of the supply manifolds33through the openings33band flows through the insides of the supply manifolds33in the direction from the one ends to the other ends of the supply manifolds33(direction D4).

One ends (the ends in the direction D4) of the collection manifolds37overlap the collection reservoir31in the planar see-through view. The one ends lead to the collection reservoir31via openings37bin a surface of the first flow path member25on the side where the second flow path member27is located. The other ends (ends in the direction D1) of the collection manifolds37are dead ends. Therefore, the liquid in the collection manifolds37flows in the direction from the other ends to the one ends (direction D4) and is collected in the collection reservoir31through the openings37b.

The supply manifolds33and the collection manifolds37have lengths that span the length, in the lateral directions (directions D3 and D6), of the region in which the plurality of nozzles is arranged (described later) (refer to the arrangement region of the actuator21). The ends of the supply manifolds33on the side near the collection reservoir31(the ends in the direction D4) are located, for example, nearer the supply reservoir29than the collection reservoir31. Similarly, the ends of the collection manifolds37on the side near the supply reservoir29(the ends in the direction D1) are located, for example, nearer the collection reservoir31than the supply reservoir29.

For example, in the plurality of supply manifolds33, the supply manifolds33have identical configurations to each other and are arranged at a constant pitch along the direction D2. In other words, the supply manifolds33extend parallel to each other and have the same length. The positions at which the supply manifolds33are connected to the supply reservoir29(openings33b) are arranged at a constant pitch along the supply reservoir29.

Similarly, in the plurality of collection manifolds37, for example, the collection manifolds37have identical configurations and are arranged at a constant pitch along the direction D2. In other words, the collection manifolds37extend parallel to each other and have the same length. The positions at which collection manifolds37are connected to the collection reservoir31(openings37b) are arranged at a constant pitch along the collection reservoir31.

The plurality of supply manifolds33and the plurality of collection manifolds37are, for example, arranged in an alternating manner at a constant pitch. The supply manifolds33and the collection manifolds37are adjacent to each other and extend parallel to each other. More specifically, the major portions of the supply manifolds33, except for the upstream parts thereof, and the major portions of the collection manifolds37, except for the downstream parts thereof, are adjacent to each other in the region where the plurality of nozzles is arranged.

The cross-sectional shapes and dimensions of the supply manifolds33and the collection manifolds37(for example, the main portions33aand37athereof) may be constant regardless of the position along the longitudinal directions of these flow paths or may vary with position. In the description of the embodiments, the former may be taken as an example. The cross-sectional shapes may be an appropriate shape such as a rectangular shape. The various dimensions of the supply manifolds33and the collection manifolds37may be set as appropriate in accordance with the specific technical field to which the ejecting device1is to be applied.

(Individual Flow Paths)

The individual flow paths35, for example, are roughly located between the supply manifolds33and the collection manifolds37, which are adjacent to each other, and are connected to both the supply manifolds33and the collection manifolds37. A plurality of individual flow paths35is provided for each set of manifolds (33and37). The individual flow paths35of the plurality of individual flow paths35connected to the same manifolds (33and37) are arranged along the manifolds (along the direction D1) at a certain pitch, for example, so as to form a single row of flow paths. The plurality of individual flow paths35is arranged in a matrix-like arrangement by arranging a plurality of rows of flow paths in the direction D2. Unlike in the illustrated example, two or more rows of individual flow paths35may be provided between adjacent supply and collection manifolds33and37.

Within a single flow path row, the individual flow paths35of the plurality of individual flow paths35basically have identical configurations. The configurations of the plurality of rows of flow paths are basically the same as or similar to each other. However, for example, the orientations of the individual flow paths35may be different between adjacent rows of flow paths (illustrated example). In addition, for example, within a single row of flow paths, the shapes and/or dimensions of the plurality of individual flow paths35may slightly vary from one another. Among the plurality of rows of flow path, the flow path rows located at the end in the direction D2 and at the end in the direction D5 may include so-called dummy individual flow paths that do not eject droplets.

The individual flow paths35include nozzles43that are open at the ejection surface3aand eject droplets. Rows composed of a plurality of nozzles43arranged in the direction D1 are referred to as nozzle rows. The direction in which the nozzles43are arranged within each nozzle row (direction D1) is inclined with respect to the direction of relative movement of the head3with respect to the object101(direction D3). The nozzles43belonging to the same nozzle row are located at different positions from each other in the direction D2 due to this inclination. In addition, the nozzle rows partially overlap each other in the direction D3. In these overlapping portions, the nozzles43of one nozzle row and the nozzles43of another nozzle row are located at different positions in the direction D2. When the plurality of nozzles43is projected in the direction D3, the nozzles43are lined up at substantially constant intervals in the direction D2.

This allows a plurality of dots to be formed on the surface of the object101, the dots being arrayed in the direction D2 at a pitch that is smaller than the distance between the nozzles43that are adjacent to each other in the head3. For example, thirty-two nozzles43are projected within the range of a virtual straight line R and the nozzles43are arrayed at intervals of 360 dpi within the range of the virtual straight line R. Thus, printing can be performed with a resolution of 360 dpi when the object101and the head3are moved relative to each other in a direction perpendicular to the virtual straight line R and droplets are ejected.

FIG.5is a perspective view of one individual flow path35.FIGS.6A and6Bare cross-sectional views of the first flow path member25and the actuator21.FIG.6Acorresponds to a line VIa-VIa inFIG.5.FIG.6Bcorresponds to a line VIb-VIb inFIG.5.

The individual flow path35includes, for example, supply flow paths39(first supply flow path39A and second supply flow path39B) connected to the corresponding supply manifold33, a pressure chamber41connected to the supply flow paths39, and a nozzle43connected to the pressure chamber41. As has already been described, the nozzle43opens at the ejection surface3aand leads to outside the first flow path member25. Liquid from the supply manifold33is supplied to the nozzle43via the supply flow paths39and the pressure chamber41. Then, when pressure is applied to the pressure chamber41by the actuator21, a droplet is ejected from the nozzle43. The individual flow path35also includes the collection flow path45connecting the pressure chamber41and the corresponding collection manifold37to each other. Liquid remaining in the pressure chamber41without being ejected is collected from the collection flow path45to the collection manifold37.

The pressure chamber41includes, for example, a pressure chamber body41ato which pressure is applied by the actuator21and a descender41bthat connects the pressure chamber body41ato the nozzle43.

The pressure chamber body41a, for example, is open to the pressurized surface25aof the first flow path member25and is blocked by the actuator21. Pressure is applied to the liquid inside the pressure chamber body41awhen the actuator21bends and deforms upward and/or downward. The descender41bextends from the lower surface of the pressure chamber body41atowards the ejection surface3a. The cross-sectional area of the descender41bis smaller than the area of a cross section of the pressure chamber body41aparallel to the pressurized surface25a.

The shape and dimensions of the pressure chamber body41amay be set as appropriate. In the illustrated example, the pressure chamber body41ahas a circular planar shape. Unlike in the illustrated example, the planar shape of the pressure chamber body41amay be a shape other than a circle, such as an ellipse or a rhombus, for example. The pressure chamber body41ahas a thin shape having a thickness that is smaller than the diameter in plan view. In the illustrated example, the shape and dimensions of a cross section of the pressure chamber body41aparallel to the pressurized surface25aare constant in the vertical direction. However, the shape and/or dimensions of the cross section of the pressure chamber body41amay be different at different positions in the vertical direction.

The shape and dimensions of the descender41bmay also be set as appropriate. In the illustrated example, the shape of the descender41bis a straight column. In the illustrated example, the cross-sectional shape is circular. Unlike in the illustrated example, the descender41bmay be inclined with respect to the vertical direction or may vary in diameter with respect to position in the vertical direction. The cross-sectional shape may be a shape other than a circular shape such as an elliptical shape.

The position at which the descender41bis connected to the pressure chamber body41ain plan view may also be chosen as appropriate. In the illustrated example, the descender41bis connected adjacent to the outer edge of the circular pressure chamber body41a. Unlike in the illustrated example, when the pressure chamber body41ahas an oval or diamond shape, for example, the descender41bmay be connected to an end of the pressure chamber body41ain the longitudinal direction.

The nozzle43opens at a portion of the bottom surface of the descender41b. The nozzle43may, for example, open at the center of the bottom surface of the descender41bor may open at a position spaced away from the center of the bottom surface of the descender41b(example illustrated in the figures). The shape of a longitudinal section of the nozzle43is tapered, with the diameter decreasing toward the ejection surface3a. However, part or the entirety of the nozzle43may be reverse tapered. The shape of the cross section of the nozzle43is, for example, circular.

The supply flow paths39include, for example, the first supply flow path39A and the second supply flow path39B. Unlike in the illustrated example, the supply flow paths39may include only one out of the first supply flow path39A and the second supply flow path39B. The positions at which the supply flow paths39are connected to the supply manifold33and the pressure chamber41, and the shapes and dimensions of the supply flow paths39may be chosen as appropriate. In the illustrated example, the following is illustrated.

The first supply flow path39A connects the supply manifold33to the pressure chamber body41A. The first supply flow path39A extends upward from the upper surface of the supply manifold33, then extends in the direction D5, then extends in the direction D4, and then extends upward again so as to connect to the lower surface of the pressure chamber body41a. The cross-sectional shape and dimensions of the first supply flow path39A are generally constant across the majority (for example, 60% or more) of the length of the first supply flow path39A. The shape of the cross section across the majority of the length is rectangular.

The second supply flow path39B connects the supply manifold33to the descender41b. The second supply flow path39B extends from the lower surface of the supply manifold33in the direction D5 and then in the direction D1, and is connected to a side surface of the descender41b. The cross-sectional shape and dimensions of the second supply flow path39B are generally constant across the majority (for example, 60% or more) of the length of the second supply flow path39B. The shape of the cross section across the majority of the length is rectangular.

Only one collection flow path45is provided in a single individual flow path35, for example. Unlike in the illustrated example, two or more collection flow paths45may be provided. The position at which the collection flow path45is connected to the collection manifold37, the position at which the collection flow path45is connected to the pressure chamber41, and the shape and dimensions of collection flow path45may be chosen as appropriate. In the illustrated example, the following is illustrated.

The collection flow path45connects the collection manifold37to descender41b. The collection flow path45extends from a side surface of the collection manifold37in the direction D2 and then in the direction D4 before connecting to a side surface of the descender41b. The shape and dimensions of the cross section of the collection flow path45are generally constant across the majority (for example, 60% or more) of the length of the collection flow path45. The shape of the cross section across the majority of the length is rectangular.

As has already been described, individual flow paths35of a plurality of individual flow paths35connected to the same supply manifold33and the same collection manifold37are arranged at a constant pitch along the manifolds. Therefore, the positions at which the first supply flow paths39A are connected to the supply manifold33are aligned at a constant pitch along the supply manifold33. The same is true for the positions at which the second supply flow paths39B are connected to the supply manifold33and the positions at which the collection flow paths45are connected to the collection manifold37.

As illustrated inFIGS.6A and6B, the first flow path member25is formed by stacking a plurality of plates47A to47M. The various flow paths of the first flow path member25consist of holes or recesses formed in the plates47A to47M. The plurality of plates47A to47M may be formed of a metal or a resin, for example. In the example illustrated inFIG.6B, dampers (reference symbols omitted) are provided above and below the collection manifold37.

As has already been mentioned, the pressure chamber41is open at the pressurized surface25a. Unlike in the illustrated example, a plate may be provided in order to close the pressure chamber41. However, this case can be regarded as a question of whether a plate closing the pressure chamber41is regarded as being part of the first flow path member25or as being part of the actuator21. In the description of the present disclosure, such a plate will be considered as being part of the actuator21.

(Actuator)

As illustrated inFIG.2A, the actuator21is, for example, a roughly flat plate-shaped member, and is bonded to the pressurized surface25aof the first flow path member25(more precisely, the area indicated by the dotted line inFIG.2A). As illustrated inFIGS.6A and6B, the actuator21closes the opening at the top of the pressure chamber41. The actuator21basically extends across the region where all the pressure chambers41are arranged. The actuator21includes a displacement element49for each pressure chamber41.

The actuator21may have any of various known configurations and may be an application of a known configuration. In the illustrated example, the actuator21is a so-called unimorph piezoelectric actuator. A specific configuration is described below.

The actuator21includes a diaphragm51, a common electrode53, a piezoelectric layer55, and individual electrodes57, which are stacked in order from the side near the pressure chambers41. The diaphragm51, the common electrode53, and the piezoelectric layer55basically extend across the region where all the pressure chambers41are arranged. The individual electrodes57are provided for each of the pressure chambers41. The individual electrodes57, for example, have similar shapes to the planar shapes of the pressure chambers41in a planar see-through view, and also overlap the centers of the pressure chambers41.

The portions of the piezoelectric layer55sandwiched between the individual electrodes57and the common electrode53are polarized in the thickness direction. Therefore, when a voltage is applied between the individual electrodes57and the common electrode53, the piezoelectric layer55contracts or expands in directions along the surfaces. This contraction or expansion is restricted by the diaphragm51, and the displacement elements49bend towards the side near the pressure chambers41or towards the opposite side like a bimetal. As a result, pressure is applied to the liquid in the pressure chambers41.

The material and thickness of each layer of the actuator21may be chosen as appropriate. For example, the diaphragm51and the piezoelectric layer55may be, for example, composed of lead zirconate titanate (PZT)-based, NaNbO3-based, BaTiO3-based, (BiNa)NbO3-based, or BiNaNb5O15-based ceramic materials. The common electrode53and individual electrodes57may be composed of, for example, Ag—Pd-based or Au-based metallic materials.

The common electrode53, for example, is given a constant potential (reference potential). A drive signal is, for example, input to the individual electrodes57, as described previously. The method used to drive the displacement elements49(or waveform of the drive signal from another point of view) may be chosen as appropriate. For example, the driving method may be a so-called pull-hit method.

(Liquid)

FIG.7illustrates characteristics of a liquid used in the ejecting device1. In this figure, the horizontal axis represents shear rate D (1/s). The vertical axis represents viscosity η (Pa·s). EX1 and EX2 represent the characteristics of a first example and a second example of a liquid used in the ejecting device1.

As illustrated in this figure, the liquid used in the ejecting device1is a pseudoplastic fluid. For your information, a pseudoplastic fluid can be described as a non-Newtonian fluid having a viscosity that decreases with increasing shear rate. Shear rate is sometimes referred to as shear velocity, velocity gradient, or strain rate. Shear rate is calculated, for example, by simply dividing the difference in velocity between two positions separated from each other in a direction perpendicular to the flow direction by the distance between the two positions. Viscosity, for example, is conveniently calculated by dividing the shear stress by the shear rate. Shear stress is sometimes referred to as shearing stress. For the sake of simplification, shear stress is calculated by dividing the force required to shift, in the flow direction, two parallel surfaces (of the same area) that are separated from each other in a direction perpendicular to the flow direction by the area of one of the surfaces.

A pseudoplastic fluid can also be said to be a power law fluid where a power exponent p is less than 1 when a viscosity η is approximated using a power law as η=k×Dp-1. k is the viscosity coefficient and D is the shear rate. Since the viscosity η is a function of D, the viscosity η is sometimes referred to as apparent viscosity.

The liquid used in the ejecting device1may have or not have thixotropic properties where the viscosity decreases with increasing time under shear stress.

The specific constituents and/or composition of the pseudoplastic fluid may be various known ones or applications of known ones. For example, inks and paints are typically pseudoplastic fluids. The liquids of the first and second examples, whose properties are illustrated inFIG.7, are common paints (in other words, paints available on the market). The specific characteristics of the pseudoplastic fluids may also be chosen as appropriate. One example is as follows.

For example, the liquid may have a viscosity from 0.02 Pa·s to 0.4 Pa·s at a shear rate of 1000 s−1. In the paint of the first example, whose characteristics are illustrated inFIG.7, the viscosity is 0.3 Pa·s at a shear rate of 1000 s−1. In the paint of the second example, the viscosity is 0.1 Pa·s at a shear rate of 1000 s−1. The liquid may have a viscosity from 0.1 Pa·s to 0.3 Pa·s at a shear rate of 1000 s−1.

For example, the liquid may have a viscosity from 0.5 Pa·s to 50 Pa·s at a shear rate of 0.01 s−1. The paint of the first example, whose characteristics are illustrated inFIG.7, has a viscosity of 5 Pa·s at a shear rate of 0.01 s−1. The paint of the second example has a viscosity of 30 Pa·s at a shear rate of 0.01 s−1. The liquid may have a viscosity from 5 Pa·s to 30 Pa·s at a shear rate of 0.01 s−1.

For example, the liquid may have a viscosity coefficient k from 1.0 to 1.5 and a power exponent p from 0.35 to 0.65 when the viscosity is approximated using a power law. The paint of the first example has a viscosity coefficient k of 1.0 and a power exponent p of 0.65. The paint of the second example has a viscosity coefficient k of 1.5 and a power exponent p of 0.35. Approximation equations may be specified, for example, using a method of least squares.

(Average Viscosity)

Hereafter, the concept of average viscosity is introduced. Essentially, each minute region inside the flow path has a different value of viscosity. However, it is not necessarily appropriate to use the viscosity of each minute region to set the viscosity of the liquid in the flow path member19and additionally it may be difficult to calculate the viscosity of each minute region. Therefore, viscosities averaged over the respective parts of the flow path in the flow path member19are referred to as average viscosities. There is one value of average viscosity for each part within the flow path. For example, “the average viscosity of one supply manifold33” means the average viscosity of the entire one supply manifold33.

The average viscosity may be calculated, for example, as follows. First, the relationship between the shear rate D and the viscosity η of the liquid used in the ejecting device1is identified. Various known methods may be employed or known literature may be referenced in order to make this identification. Next, an approximation equation representing the identified relationship between the shear rate D and the viscosity η is obtained. The approximation equation may be, for example, appropriate equation such as a power law. The fitting method used may be a known method such as the method of least squares. Next, employing a circulation flow rate U (m3/s) as a boundary condition, fluid simulation is performed for each part of the flow path using the above approximation equation and a differential pressure ΔP (Pa) between the upstream end and the downstream end of each part is obtained. Then, an average viscosity μ (Pa·s) is calculated by substituting the circulation flow rate U, the differential pressure ΔP, and the dimensions of each part (m) into a prescribed equation.

An example of the equation used to calculate the average viscosity μ is given below.

The equation for a case where the shape of the flow path is cylindrical with the flow direction being the axial direction of the cylinder is as follows.
U=(πr4ΔP)/(8 μL)  (1)r is the radius of the cross section. L is the length of the flow path.

The equation for a case where the shape of the flow path is a prismatic (rectangular) cylinder with the flow direction being the axial direction of the cylinder is as follows.
U=(w3hΔP)/(4 μL)×(16/3−1024/π5×w/h×Σ(1/q5×tanh(qπh/2w))  (2)q=1, 3, 5, 7, 9 and 11, and Σ is the sum of six lots of (1/q5×tan h(qπh/2w)) when these six values are substituted as q. w is the flow path width. h is the flow path height. L is the flow path length.

In the reservoirs (29and31) and the manifolds (33and37), the flow rate U is different on the upstream side and the downstream side. In this case, for example, the highest flow rate, the lowest flow rate, or the average flow rate may be used. The average viscosity in the following description may be assumed to be calculated using any of the above flow rates. When comparing the average viscosities of the reservoirs (29and31) and the average viscosities of the manifolds (33and37), average viscosities calculated under the same conditions as each other may be compared. For example, average viscosities calculated using the highest flow rates (lowest average viscosities) may be compared to each other, average viscosities calculated using the lowest flow rates (highest average viscosities) may be compared to each other, or average viscosities calculated using the average flow rates (average viscosities) may be compared to each other. For example, the term average viscosity used in the following description may be taken as meaning an average viscosity calculated using the highest flow rate (lowest average viscosity). For example, the average viscosities of the supply reservoir29and the supply manifolds33may be taken as being calculated using the furthest upstream flow rates. The average viscosities of the collection reservoir31and collection manifolds37may be taken as being calculated using the furthest downstream flow rates.

In the pressure chamber41, the pressure chamber body41a, or the descender41b, the direction of liquid flow is not always constant. The average viscosity in these parts in the following description is calculated with a direction of flow from above to below as the flow direction. For example, the average viscosity in the descender41bis calculated with the flow direction being a direction from the pressure chamber body41ato the nozzle43.

(Average Viscosity in Flow Path Member)

FIG.8illustrates an example of the relative relationships between different parts of the flow path of the flow path member19with respect to the average viscosities μ of the respective parts of the flow path of the flow path member19. In this figure, the vertical axis represents the plurality of parts of the flow path of the flow path member19. The horizontal axis represents the average viscosities μ of the individual parts.

In the figure, an average viscosity μ2 represents the average viscosity μ in one supply manifold33out of the plurality of supply manifolds33. For the other flow paths as well, the average viscosity μ in one flow path is illustrated. An average viscosity μ3 of the supply flow path39may be taken as being the average viscosity of either the first supply flow path39A or the second supply flow path39B.

In the liquid ejecting device1, the target flow rate for the circulation flow rate controlled by the flow rate setting unit13and the shape and dimensions of the flow path of the flow path member19are set so that the relationship between the average viscosities as illustrated in the figure is satisfied. For purposes of this disclosure, the concepts of “shape” and “dimensions” may both be expressed simply as “shape”. In other words, the flow path of the flow path member19has a flow path shape that satisfies the relationship illustrated inFIG.8when the circulation flow rate is equal to the target flow rate. In other words, the circulation flow rate is set to a value such that the relationship between the average viscosities illustrated inFIG.8is established for the shape and dimensions of the flow path of the flow path member19. For example, the circulation flow rate is set to a value such that the average viscosity of the liquid in the supply flow path39is less than or equal to half the average viscosity of the liquid in the supply manifold33for the shape and dimensions of the flow path of the flow path member19.

When the circulation flow rate is adjusted via open-loop control, there are large fluctuations in the circulation flow rate caused by the amounts of droplets ejected from the plurality of nozzles43. In this case, the relationship illustrated inFIG.8may be established, for example, for the circulation flow rate at a time when droplets are not being ejected from any of the nozzles43. In other words, the circulation flow rate at a time when droplets are not being ejected from any of the nozzles43in the product being implemented may be specified as the target flow rate of that product. This concept may also be applied to feedback control in which it takes more time for the circulation flow rate to become the target flow rate.

InFIG.8, the following relationships hold true for the average viscosities, for example

The average viscosity μ3 of the liquid in the supply flow path39(39A or39B) may be lower than the average viscosity μ2 of the liquid in the supply manifold33. More specifically, for example, the average viscosity μ3 may be less than or equal to ½, ⅓, or ⅕ the average viscosity μ2.

In this case, for example, the liquid can be smoothly supplied from the supply flow path39to the pressure chamber41because the average viscosity μ3 of the liquid in the supply flow path39is low. In addition, since the average viscosity μ2 is high in the supply manifold33, pressure waves are easily attenuated. As a result, the likelihood of pressure waves that have leaked from the pressure chamber41to the supply manifold33via the supply flow path39propagating to another pressure chamber41via another supply flow path39is reduced. In other words, so-called fluid crosstalk can be reduced.

A relationship the same as or similar to that described above may be established between the collection flow path45and the collection manifold37. That is, an average viscosity μ5 of the liquid in the collection flow path45may be lower than an average viscosity μ6 of the liquid in the collection manifold37. More precisely, for example, the average viscosity μ5 may be less than or equal to ½, ⅓, or ⅕ the average viscosity μ6. In this case, effects the same as or similar to those described above are achieved.

The average viscosity μ2 of the supply manifold33may be lower than an average viscosity μ1 of the supply reservoir29. More particularly, for example, the average viscosity μ2 may be less than or equal to ½, ⅓, or ¼ the average viscosity μ1.

In this case, for example, the low average viscosity μ2 of the liquid inside the supply manifold33enables the liquid to be supplied smoothly from the supply manifold33to the supply flow path39. In addition, the high viscosity inside the supply reservoir29makes it more likely for pressure waves to be attenuated, and consequently crosstalk caused by the propagation of pressure waves through the supply reservoir29can be reduced.

A relationship the same as or similar to that described above may be established between the collection manifold37and the collection reservoir31. That is, the average viscosity μ6 of the liquid in the collection manifold37may be lower than an average viscosity μ7 of the liquid in the collection reservoir31. More precisely, for example, the average viscosity μ6 may be less than or equal to ½, ⅓, or ⅕ the average viscosity μ7. In this case, effects the same as or similar to those described above are achieved.

An average viscosity μ4 of the descender41bmay be higher than the average viscosity μ5 of the collection flow path45. More specifically, for example, the average viscosity μ4 may be greater than or equal to 1.5 times the average viscosity μ5.

In this case, for example, the higher the viscosity, the greater the resistance to the movement of bubbles, and therefore the likelihood that a bubble that has entered the descender41bfrom the nozzle43can be collected from the collection flow path45is higher.

A relationship the same as or similar to that described above may be established between the descender41band the supply flow path39. That is, the average viscosity μ4 of the descender41bmay be higher than the average viscosity μ3 of the supply flow path39. More specifically, for example, the average viscosity μ4 may be greater than or equal to 1.5 times or 2 times the average viscosity μ3.

In this case, for example, the low average viscosity μ3 of the supply flow paths39enables the liquid to be smoothly supplied to the descender41b. As a result, for example, the likelihood of the liquid not being supplied to the descender41bin time due to continuous ejection of the liquid is reduced.

The average viscosity μ2 of the supply manifold33may be higher than the average viscosities (μ3, μ4, and μ5) of the individual flow path35(excluding the pressure chamber body41a). More particularly, for example, the average viscosity μ2 may be greater than or equal to 1.5 times any of the average viscosities μ3, μ4 and μ5.

In this case, for example, the liquid can be supplied smoothly to the nozzle43due to the low average viscosity μ of the individual flow path35. In addition, the high average viscosity μ of the supply manifold33causes leaking of pressure from the individual flow path35into the supply manifold33to be rapidly attenuated. Therefore, fluid crosstalk is unlikely to occur.

A relationship the same as or similar to that described above may be established between the collection manifold37and the individual flow path35. That is, the average viscosity μ6 of the liquid in the collection manifold37may be higher than the average viscosities (μ3, μ4, and μ5) of the individual flow path35. More precisely, for example, the average viscosity μ6 may be greater than or equal to 1.5 times any of the average viscosities μ3, μ4 and μ5. In this case, effects the same as or similar to those described above are achieved.

(Example of Values of Average Viscosities and so Forth)

There are countless combinations of liquid characteristics, circulation flow rates, flow path shapes and dimensions, and so forth with which the above relationship between average viscosities μ may be realized, and the combination may be chosen as appropriate in accordance with the specific technical field to which the ejecting device1is to be applied. An example of the values when a common paint is used, as described with reference toFIG.7, is described below.

The circulation flow rate may be, for example, from 50 ml/min to 300 ml/min. The pressure in the nozzles43when liquid is not being ejected may be ±2 kPa with respect to atmospheric pressure (around 100 kPa). The differential pressure between the supply port3band the collection port3cmay be from 40 kPa to 160 kPa.

The supply reservoir29and the collection reservoir31may each have a width w from 4 mm to 20 mm, a height h from 3 mm to 15 mm, and a length L from 200 mm and 800 mm. The supply manifolds33and the collection manifolds37may each have a width w from 0.2 mm to 2 mm, a height h from 0.5 mm to 6 mm, and a length L from 5 mm to 20 mm. The first supply flow paths39A may have a width w and a height h from 50 μm to 200 μm. The second supply flow paths39B may have a width w from 50 μm to 200 μm and a height h from 25 μm to 200 μm. The collection flow paths45may have a width w from 70 μm to 200 μm and a height h from 80 μm to 200 μm. The length L of the supply flow paths39and the collection flow paths45may be from 300 μm to 1500 μm. The descenders41bmay have a radius r from 50 μm to 250 μm and a length L from 0.5 mm to 2 mm. The nozzles43may have a radius r from 5 μm to 50 μm.

An example of estimation of the average viscosities μ under the above conditions is described below. The average viscosity μ in the descenders41bwas calculated using Equation (1) and the average viscosities μ of the other flow paths was calculated using Equation (2). The average viscosity μ in the supply reservoir29and the collection reservoir31is from 0.4 Pa·s to 2 Pa·s. The average viscosity μ in the supply manifold33and the collection manifold37is from 0.1 Pa·s to 0.4 Pa·s. The average viscosity μ in the supply flow paths39and the collection flow paths45is from 0.01 Pa·s to 0.1 Pa·s. The average viscosity μ in the descenders41bis from 0.05 Pa·s to 0.2 Pa·s.

(Fluid Resistance)

The fluid resistance (N−s/m5) in the flow path member19may be set as appropriate. For example, the fluid resistance may be set so that both Condition 1 and Condition 2 below are satisfied.
The sum of (1/2)×Rr×U(1+1/m) and (1/2)×Rm×(U/m)×(1+1/n) is smaller than 2σ/r.Condition 1:
Rr<1/10×Rm×(1/m)  Condition 2:
Rris the fluid resistance of the liquid in the supply reservoir29. Rmis the fluid resistance of the liquid in the supply manifolds33. m is the number of supply manifolds33connected to the supply reservoir29. n is the number of individual flow paths35(nozzles43) per supply manifold33. U is the flow rate (m3/s) of the liquid flowing into the supply reservoir29. σ is the surface tension (N/m) of the liquid. r is the radius (m) of each nozzle43.

Here, the supply manifolds33to which only dummy individual flow paths not capable of ejecting droplets are connected are ignored. It is also assumed that the same number of nozzles43are connected to each supply manifold33. It is also assumed that the pitch of the plurality of supply manifolds33, the distance from the upstream end of the supply reservoir29to the first supply manifold33, and the distance from the final supply manifold33to the downstream end of the supply reservoir29are equal to each other.

(1/2)×Rr×U(1+1/m) in Condition 1 corresponds to a pressure drop inside the supply reservoir29(pressure difference between upstream side and downstream side). Specifically, the pressure drop from the upstream end of the supply reservoir29to the first supply manifold33is calculated as U×Rr/m, and the pressure drop from the first supply manifold33to the second supply manifold is calculated as (U−U/m)×Rr/m. (1/2)×Rr×U(1+1/m) given above is then obtained from U×Rr/m+(U−U/m)×Rr/m+ . . . +U/m×Rr/m, which is the sum of the pressure drops from the upstream end to the downstream end.

(1/2)×Rm×(U/m)×(1+1/n) in Condition 1 corresponds to the pressure drop (pressure difference between the upstream end and the downstream end) in one supply manifold33. This equation is obtained in the same way or in a similar way to the pressure drop in the supply reservoir29described above. That is, in the equation for the supply reservoir29, a fluid resistance Rrof the supply reservoir29is replaced by a fluid resistance Rmof the supply manifolds33, a flow rate U into the supply reservoir29is replaced by a flow rate U/m of liquid into the supply manifolds33, and the number m of supply manifolds33is replaced by replaced by the number n of nozzles43.

The sum of (1/2)×Rr×U(1+1/m) and (1/2)×Rm×(U/m)×(1+1/n) in Condition 1 roughly corresponds to the difference in pressure between the most upstream individual flow path35and the most downstream individual flow path35. The most upstream individual flow path35is the individual flow path35connected furthest upstream to the supply manifold33that is connected furthest upstream to the supply reservoir29. The most downstream individual flow path35is the individual flow path35connected furthest downstream to the supply manifold33that is connected to furthest downstream to the supply reservoir29. The pressure drops in the individual flow paths35are substantially identical among the plurality of individual flow paths35and therefore the above sum is equivalent to the pressure difference across all the nozzles43(the difference in pressure between the nozzle43having the highest pressure and the nozzle43having the lowest pressure).

In addition, when the above sum is smaller than 2σ/r, it is easy to maintain the meniscus under atmospheric pressure in all the nozzles43. As has already been described with respect to Condition 1, the supply manifolds33to which only dummy individual flow paths are connected and the dummy individual flow paths may be ignored. The number of individual flow paths35connected to the most upstream supply manifold33or the most downstream supply manifold33, and so forth, may be less than that for the other supply manifolds33. In this case, for example, the most upstream supply manifold33or the most downstream supply manifold33may be ignored, or alternatively, it may be assumed that the most upstream supply manifold33or the most downstream supply manifold33has the same number of individual flow paths35connected thereto as the other supply manifolds33.

Condition 2 represents the relationship between the fluid resistance Rrof the supply reservoir29and the fluid resistance Rmof the supply manifolds33. Since the flow rate of the fluid flowing into the supply manifolds33is 1/m of the flow rate of the fluid flowing into the supply reservoir29, the fluid resistance Rris compared to the fluid resistance Rmby multiplying the fluid resistance Rmby 1/m. Condition 2 being satisfied means that the fluid resistance Rrof the supply reservoir29is very small compared to the fluid resistance Rmof the supply manifolds33.

For example, in the technologies of the related art, Rris around ⅕ of Rm×(1/m). On the other hand, in this embodiment, Rrmay be greater than or equal to 1/40 of Rm×(1/m) and less than 1/10 of Rm×(1/m). Of course, in this embodiment, Rrmay be around ⅕ of Rm×(1/m), similarly to as in the technologies of the related art.

As a result of Condition 2 being satisfied, for example, the liquid readily flows from the supply reservoir29to the positions of the plurality of supply manifolds33and differences in flow rate between the plurality of supply manifolds33are reduced. Accordingly, the liquid can be stably supplied to all the supply manifolds33.

In addition to Conditions 1 and 2, the fluid resistance may be set so that Condition 3 below is satisfied.
Rm<1/10×Rn×(1/n)  Condition 3:
Rnis the fluid resistance in the nozzles43.

Condition 3 represents the relationship between the fluid resistance Rmof the supply manifolds33and the fluid resistance of the individual flow paths35. However, since the fluid resistance Rnof the nozzles43is much greater than the fluid resistance of the other parts of the individual flow paths35, the fluid resistance of the individual flow paths35is approximated by the fluid resistance Rnof the nozzles43. Since the flow rate of the liquid flowing into the individual flow paths35is 1/n of the flow rate of the liquid flowing into the supply manifolds33, the fluid resistance Rmis compared to the fluid resistance Rnby multiplying the fluid resistance Rnby 1/n.

Condition 3 being satisfied means that the fluid resistance Rmof the supply manifolds33is very small compared to the fluid resistance Rnof the nozzles43. For example, in technologies of the related art, Rmis approximately ⅙ of Rn×(1/n) Similarly to as in the technologies of the related art, Rmmay be around ⅙ of Rn×(1/n). For example, Rmmay be set to be from 1/10 to ¼ of Rn×(1/n).

As a result of Condition 3 being satisfied, for example, the liquid readily flows from the supply manifolds33to the positions of the plurality of individual flow paths35and differences in flow rate between the plurality of individual flow paths35are reduced. Accordingly, the liquid can be supplied stably to all the individual flow paths35.

The example of the dimensions and so forth of a flow path illustrated inFIG.8, serving as an example of the dimensions that realize the average viscosities, may be referred to as an example of dimensions and so forth of a flow path for which Conditions 1 to 3 are satisfied.

(Variation 1)

FIG.9is a schematic cross-sectional view of an individual flow path235according to a first variation.

A pressure chamber241of the individual flow path235includes a pressure chamber body241aand a descender241b, the same as or similar to the pressure chamber41of the embodiment. However, the descender241bhas a first portion241baand a second portion241bb, which have different cross-sectional areas from each other.

The first portion241bais connected to the nozzle43. The second portion241bbis connected to the pressure chamber body241a. In other words, the second portion241bbis a portion located nearer the pressure chamber body241athan the first portion241ba. The cross-sectional area of the second portion241bbis larger than that of the first portion241ba.

The average viscosities of the first portion241baand the second portion241bbare different from each other as a result of the first portion241baand the second portion241bbhaving different cross-sectional areas from each other, for example. For example, the average viscosity of the liquid in the second portion241bbis higher than the average viscosity of the liquid in the first portion241ba. In other words, the average viscosity in the descender241bincreases in a stepwise manner with increasing closeness to the pressure chamber body41afrom the nozzle43. The average viscosity may increase not only in one step but also in two or more steps. In other words, the descender may include a third portion and so on, in addition to the first and second portions.

When the average viscosity of the second portion241bb, which is located nearer the pressure chamber body241athan the first portion241ba, is higher than the average viscosity of the first portion241baas in the first variation, for example, bubbles that have entered the descender241bfrom the nozzle43have greater difficulty in moving towards the pressure chamber body241a. Consequently, the likelihood of bubbles remaining in the pressure chamber body241aand resulting in deterioration of the ejection characteristics is reduced.

In the case where at least one of two flow paths whose average viscosities are to be compared has a portion having a different shape, the average viscosities of the parts where the two flow paths contact each other may be compared with each other. For example, when comparing the average viscosity of the collection flow path45and the average viscosity of the descender241bin the individual flow path235of this first variation, the average viscosity of the second portion241bb, which is directly connected to the collection flow path45, may be used for the purpose of comparison rather than the average viscosity of the entire descender241b. This is because the average viscosity of the second portion241bbhas the greater effect on the flow between the collection flow path45and the descender241b.

(Variation 2)

FIG.10is a schematic cross-sectional view of the individual flow path335in an embodiment. The individual flow path335includes a nozzle343with a first shape, while the individual flow path235inFIG.9includes the nozzle343with a second shape. The first shape is different from the second shape, and is otherwise the same.

The nozzle343includes an inflow surface343aand a discharge surface343b. The inflow surface343ais perpendicular to the flow direction of the liquid. The nozzle343may have a reverse-tapered shape. Here, a cross-sectional area of the inflow surface343ais defined as S1, and a cross-sectional area of the discharge surface343bis defined as S2. Then, an equation of S1>S2 is satisfied. That is, S1 is larger than S2.

The liquid may have a high shear rate when passing through the discharge surface343bdue to small S2. The liquid passing through at the discharge surface343b, therefore, may have a low viscosity and is discharged efficiently from the nozzle343. In contrast, the liquid may have a low shear rate when passing through the inflow surface343adue to large S1. The liquid passing through the inflow surface343a, therefore, may have a high viscosity, and is hard to flow backward from the nozzle343to the pressure chamber body341awhen the liquid is drawn into the pressure chamber body341afrom the supply flow paths39A and/or39B. As a result, the individual flow paths335are less likely to be short of liquid supply.

The nozzle343has a reverse-tapered shape inFIG.10, but the shape is not limited to the reverse-tapered shape. For example, the flow path in the nozzle343may include a first flow path with a first diameter, and a second flow path with a second diameter that is different from the first diameter. The second path is closer to the discharge surface343bthan the first path. Therefore, the flow path in the nozzle343includes a step between the first path and the second path.

The pressure chamber341includes a pressure chamber body341aand a descender341b. S4 is larger than S3 where S3 is defined as a cross-sectional area of the individual flow path335at the inflow surface343athat is perpendicular to a flow direction of the liquid in the supply flow paths39A and39B or the recovery flow path45, and S4 is defined as a cross-sectional area of the individual flow path335at an outflow surface343cthat is perpendicular to the flow direction of the liquid at the descender341b(first site341ba) just above the nozzle343. Then, an equation of S4>S3 is satisfied. That is, S4 is larger than S3.

Having such a configuration, the liquid in the nozzle may not be dried out during a non-ejection state of the liquid in the individual flow passage335. More specifically, in the individual flow path335, the shear rate of the liquid flowing through the outflow surface343cis lowed while the viscosity of the liquid is high because S4 is large. Then, the liquid in the vicinity of the outflow surface343cof the first site341bais pulled by the liquid flowing into the first site341bafrom the supply passage39B. As a result, the liquid in the nozzle343can be forced to swing so that the nozzle343may not be dried out.

The individual flow paths335may satisfy S4>S3 if, for example, S4 is larger than S3 of the supply flow paths39A or39B, or if S4 is larger than the supply flow paths39A and39B. It may also be larger than S4 of the recovery channel45. Alternatively, S4 may be greater than S3 of the sum of the supply channels39A,39B and the recovery channel45.

S3>S1 is satisfied in the individual flow path335. The large S3 lowers the shear rate of the liquid flowing through the supply channels39A and39B, and the recovery channel45. This increases the viscosity of the liquid flowing through the supply channels39A and39B, and the recovery channel45, which tends to cause pressure damping in the supply channels39A and39B, and the recovery channel45. As a result, the pressure wave generated in the pressure chamber body341abecomes difficult to exit the individual flow path335through the supply channels39A and39B, and the recovery channel45. Therefore, the fluid crosstalk can be improved.

Similarly, S3>S2 may also be satisfied in the individual flow path335. The large S3 lowers the shear rate of the liquid flowing through the supply channels39A and39B, and the recovery channel45. This increases the viscosity of the liquid flowing through the supply channels39A and39B, and the recovery channel45, which tends to cause pressure damping in the supply channels39A and39B and the recovery channel45. As a result, the pressure wave generated in the pressure chamber body341abecomes difficult to exit the individual flow path335through the supply channels39A and39B and the recovery channel45. Therefore, the fluid crosstalk can be improved.

In some embodiments, cross-sectional areas S1, S2, S3 and S4 of the individual flow path335are as follows. S1 is from 0.001 to 0.01 mm2. S2 is 0.0001 to 0.01 mm2. S3 is from 0.001 to 0.5 mm2. S4 is from 0.01 to 1 mm2.

The technologies described in the present disclosure are not limited to the above embodiments and variations, and may be implemented in various forms.

For example, the liquid ejecting device is not restricted to being a piezoelectric-type liquid ejecting device that applies pressure to a liquid through means of a piezoelectric body. The liquid ejecting device may be a thermal-type liquid ejecting device that generates bubbles within the liquid by heating the liquid and applies pressure to the liquid accompanying the generation of these bubbles in order to eject droplets.

The flow paths may have various configurations other than those illustrated in the figures. For example, individual flow paths that are adjacent to each other may share common portions with each other. For example, portions of the collection flow paths on the side where the collection manifolds are located may be shared among the individual flow paths adjacent to each other.

The average viscosities may also be set in a different manner from that described in the embodiment. For example, the average viscosity μ3 of the supply flow path39may, in contrast to the embodiment, be larger than the average viscosity μ5 of the collection flow path45or may be 1.5 times higher. In this case, the liquid inside the descender41bwill be less likely to flow backwards (i.e., less likely to flow in the opposite direction from the circulation direction) during ejection of droplets. In addition, the liquid and/or bubbles are more likely to flow into the collection flow path.

REFERENCE SIGNS

1. . . liquid ejecting device,3. . . head,13. . . flow rate setting unit,19. . . flow path member,21. . . actuator,29. . . supply reservoir,31. . . collection reservoir,33. . . supply manifold,37. . . collection manifold,39. . . supply flow path,41. . . pressure chamber,43. . . nozzle,45. . . collection flow path.