Liquid ejection head

Abstract

To achieve both prevention of satellite droplets and a reduction in size in a first direction.SOLUTION: A head 1 includes: a pressure chamber 12P disposed along one plane; a nozzle 12N opened in a direction intersecting the one plane; and a connection flow passage 12D connecting the pressure chamber 12P and the nozzle 12D. The connection flow passage 12D includes: a first flow passage 21 extending parallel to the one plane; and a second flow passage 22 extending in a direction intersecting the one plane. The inertance of the first flow passage 21 is larger than the inertance of the second flow passage 22.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a droplet discharge head that discharges droplets from a nozzle.

Background Art

[0002] Patent Document 1 discloses that a connection flow path connecting a pressure chamber and a nozzle is composed of a plurality of portions having different flow path cross-sectional areas. The plurality of portions include a first portion adjacent to the pressure chamber and a second portion adjacent to the first portion and sandwiching the first portion between the second portion and the pressure chamber. The first portion has the smallest flow path cross-sectional area among the plurality of portions, and the flow path cross-sectional areas of the first portion, the second portion, and the pressure chamber satisfy predetermined conditions. Thereby, satellite droplets are suppressed and high-frequency driving is realized.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a result of intensive research, the inventors of the present application have found that providing a portion with a large inertia in the connection flow path is effective for preventing satellite droplets. Inertia is inversely proportional to the flow path cross-sectional area and proportional to the flow path length.

[0005] In Patent Document 1, the first portion extends in a direction (first direction) intersecting a plane in which the pressure chamber is disposed. In order to increase the inertia, there is a manufacturing upper limit to reducing the flow path cross-sectional area of the first portion, and it is conceivable to increase the flow path length of the first portion. However, in this case, the head becomes large in the first direction.

[0006] An object of the present invention is to provide a droplet discharge head capable of achieving both prevention of satellite droplets and miniaturization of the droplet discharge head in a first direction.

Means for Solving the Problems

[0007] The droplet discharge head according to the present invention includes a pressure chamber arranged along a plane, a nozzle opening in a direction intersecting the plane, and a connection flow path connecting the pressure chamber and the nozzle, the connection flow path including a first flow path extending parallel to the plane and a second flow path extending in a first direction intersecting the plane, and is characterized in that an inertia of the first flow path is larger than an inertia of the second flow path.

Effects of the Invention

[0008] The first flow path with a large inertia can cut high-order components of a pressure wave, and satellite droplets can be prevented. Further, the first flow path extends parallel to the plane in which the pressure chamber is arranged. Therefore, even if the flow path length of the first flow path is increased to increase the inertia of the first flow path, an increase in the size of the head in the first direction is suppressed. That is, it is possible to achieve both prevention of satellite droplets and miniaturization in the first direction.

Brief Description of the Drawings

[0009]

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Mode for Carrying Out the Invention

[0010] <First Embodiment> As shown in FIG. 1, the printer 100 has a head 1 according to the first embodiment of the present invention.

[0011] The printer 100 includes a housing 100A, a head unit 1X, a platen 3, a transport mechanism 4, and a control unit 5. The head unit 1X, the platen 3, the transport mechanism 4, and the control unit 5 are arranged inside the housing 100A. Further, the printer 100 further includes buttons arranged on the outer surface of the housing 100A.

[0012] The length of the head unit 1X in the paper width direction is longer than the length of the head unit 1X in the transport direction. The paper width direction is the direction along the width of the sheet 9 and is perpendicular to the vertical direction. The head unit 1X is fixed to the housing 100A. The type of the head unit 1X is a line type.

[0013] The head unit 1X includes four heads 1. The four heads 1 are arranged in a staggered pattern in the paper width direction. The length of the head 1 in the paper width direction is longer than the length of the head 1 in the transport direction.

[0014] The platen 3 is a plate along a plane perpendicular to the vertical direction and is arranged below the head unit 1X. The sheet 9 is supported on the upper surface of the platen 3.

[0015] The conveying mechanism 4 includes a pair of rollers 41 having two rollers, a pair of rollers 42 having two rollers, and a conveying motor 43 shown in FIG. 2. In the conveying direction, the head unit 1X and the platen 3 are arranged between the pair of rollers 41 and the pair of rollers 42. The conveying direction is orthogonal to the vertical direction and the paper width direction.

[0016] When the conveying motor 43 is driven under the control of the control unit 5, the rollers of the roller pairs 41 and 42 rotate. When the rollers of the roller pairs 41 and 42 rotate, the sheet 9 sandwiched between the rollers of the roller pairs 41 and 42 is conveyed in the conveying direction.

[0017] As shown in FIG. 2, the control unit 5 includes a CPU 51, a ROM 52, and a RAM 53.

[0018] Based on the data input from an external device, the CPU 51 executes various controls according to the programs and data stored in the ROM 52 and the RAM 53. The external device is, for example, a personal computer (PC). The CPU 51 corresponds to the "controller" of the present invention.

[0019] The ROM 52 stores programs and data for the CPU 51 to perform various controls. The RAM 53 temporarily stores the data used when the CPU 51 executes a program.

[0020] Next, the configuration of the head 1 will be described.

[0021] As shown in FIG. 5, the head 1 includes a flow path member 12, an actuator member 13, and a sealing member 15 disposed between the flow path member 12 and the actuator member 13.

[0022] The flow path member 12 has six plates 11A to 11F. The plates 11A to 11F are stacked in the vertical direction and adhered to each other. Holes forming the flow path are formed in the plates 11A to 11F. The flow path includes a common flow path 12A and a plurality of individual flow paths 12B.

[0023] As shown in FIG. 3, the common flow path 12A extends in the paper width direction. A supply port 121 is connected to one end of the common flow path 12A in the paper width direction. A return port 122 is connected to the other end of the common flow path 12A in the paper width direction. The supply port 121 and the return port 122 open on the upper surface of the flow path member 12. The upper surface of the flow path member 12 is the upper surface of the uppermost plate 11A among the six plates 11A to 11F. The supply port 121 and the return port 122 communicate with the ink tank via tubes. The common flow path 12A communicates with the ink tank via the supply port 121 and the return port 122 and also communicates with the plurality of individual flow paths 12B.

[0024] As shown in FIG. 3, the plurality of individual flow paths 12B are arranged in a staggered pattern in the paper width direction. Each of the plurality of individual flow paths 12B includes a pressure chamber 12P, a nozzle 12N, a connection flow path 12D connecting the pressure chamber 12P and the nozzle 12N, and a communication flow path 12E communicating the pressure chamber 12P and the common flow path 12A. The nozzles 12N are arranged in a staggered pattern in the paper width direction and form two nozzle rows R1 and R2. The nozzle row R1 is composed of a plurality of nozzles 12N arranged in the paper width direction. The nozzle row R2 is composed of a plurality of nozzles 12N arranged in the paper width direction.

[0025] As shown in FIG. 4, the pressure chamber 12P is arranged along a plane orthogonal to the vertical direction. The length of the pressure chamber 12P in the conveyance direction is longer than the length of the pressure chamber 12P in the paper width direction. The pressure chamber 12P has one end 12PX which is the downstream end in the conveyance direction and the other end 12PY which is the upstream end in the conveyance direction. The one end 12PX and the other end 12PY are arranged at the central portion of the pressure chamber 12P in the paper width direction.

[0026] In this embodiment, the plane in which the pressure chamber 12P is disposed is a plane orthogonal to the vertical direction, corresponding to the "one plane" of the present invention. The vertical direction is a direction intersecting the plane in which the pressure chamber 12P is disposed, corresponding to the "first direction" of the present invention. The direction along the conveyance direction, i.e., the left-right direction along the paper surface of FIG. 4, is a direction passing through one end 12PX and the other end 12PY of the pressure chamber 12P, corresponding to the "second direction" of the present invention. The paper width direction is a direction orthogonal to the conveyance direction and along the above-mentioned plane, corresponding to the "third direction" of the present invention.

[0027] As shown in FIG. 5, the pressure chamber 12P is constituted by a hole formed in the plate 11A and opens on the upper surface of the flow path member 12.

[0028] As shown in FIGS. 4 and 5, the connection flow path 12D connects the nozzle 12N and the other end 12PY of the pressure chamber 12P, and has a first flow path 21, a second flow path 22, and a vertical hole 26.

[0029] As shown in FIG. 5, the second flow path 22 is constituted by a hole formed in the plate 11E and extends in the vertical direction. The second flow path 22 has one end 22X in the vertical direction and the other end 22Y in the vertical direction. The other end 22Y of the second flow path 22 is connected to the nozzle 12N. The second flow path 22 and the nozzle 12N are columnar. The diameter of the second flow path 22 is larger than the diameter of the nozzle 12N.

[0030] As shown in FIG. 5, the first flow path 21 extends in the conveyance direction parallel to the plane in which the pressure chamber 12P is disposed. The first flow path 21 has one end 21X which is the upstream end in the conveyance direction and the other end 21Y which is the downstream end in the conveyance direction. One end 21X is connected to one end 22X of the second flow path 22. The other end 21Y is connected to the pressure chamber 12P via the vertical hole 26.

[0031] As shown in FIG. 5, the vertical hole 26 is formed in the plate 11B and extends downward from the other end 12PY of the pressure chamber 12P. The first flow path 21 is constituted by a hole formed in the plate 11C.

[0032] As shown in FIG. 4, the first flow path 21 has a decreasing flow path width from the upstream to the downstream in the conveyance direction. In the first flow path 21, the flow path width is the length in the paper width direction. The flow path width at the downstream end of the first flow path 21 in the conveyance direction is the same as the diameter of the vertical hole 26. The flow path cross-sectional area of the vertical hole 26 is smaller than the flow path cross-sectional area of one end 21X of the first flow path 21.

[0033] Here, the inertia of the first flow path 21 is larger than the inertia of the second flow path 22. In other words, the head 1 of the present embodiment is configured such that the first flow path 21 with a large inertia is provided in the connection flow path 12D, which is effective in preventing satellite droplets. The inertia of the flow path is calculated by dividing the density ρ [kg / m 2 of the ink in the flow path, the length L [m] of the flow path, by the cross-sectional area S [m 3 of the flow path, and is represented by ρL / S [kg / m 4 .

[0034] Note that the inertia of the first flow path 21 is 1.20×10 7 [kg / m 4 or more and is less than or equal to the inertia of the nozzle 12N.

[0035] As shown in FIGS. 4 and 5, the communication flow path 12E connects one end 12PX of the pressure chamber 12P and the common flow path 12A. The communication flow path 12E includes a vertical hole 24 communicating with one end 12PX of the pressure chamber 12P, a vertical hole 25 communicating with the common flow path 12A, and a third flow path 23 extending in the conveyance direction between the vertical hole 24 and the vertical hole 25.

[0036] As shown in FIG. 5, the vertical hole 24 is formed in the plate 11B and extends downward from one end 12PX of the pressure chamber 12P. The vertical hole 25 is formed in the plate 11D and extends upward from the common flow path 12A. The third flow path 23 is composed of a hole formed in the plate 11C.

[0037] The flow path width of the third flow path 23 is constant in the conveyance direction and is smaller than the diameter of the vertical hole 24 and the diameter of the vertical hole 25. In the third flow path 23, the flow path width is the length in the paper width direction.

[0038] As shown in FIG. 5, the nozzle 12N is composed of holes formed in the plate 11F and opens to the lower surface of the plate 11F. The lower surface of the plate 11F is the lower surface of the flow path member 12. The nozzle 12N opens downward, that is, in a direction intersecting the plane in which the pressure chamber 12P is arranged.

[0039] In the individual flow paths 12B, the vertical holes 24 to 26, the second flow path 22, and the nozzle 12N extend in the vertical direction.

[0040] The ink in the ink tank is supplied to the common flow path 12A through the supply port 121 and distributed from the common flow path 12A to a plurality of individual flow paths 12B by driving the pump 10 shown in FIG. 2 under the control of the control unit 5.

[0041] When the volume of the pressure chamber 12P decreases due to the drive of the piezoelectric element 13X described later, pressure is applied to the ink in the pressure chamber 12P. The ink to which pressure is applied is discharged as ink droplets from the nozzle 12N through the connection flow path 12D.

[0042] The ink that has been supplied to the common flow path 12A through the supply port 121 but not distributed to the individual flow paths 12B returns to the ink tank through the return port 122.

[0043] As shown in FIG. 5, the sealing member 15 is arranged on the upper surface of the flow path member 12 so as to cover the plurality of pressure chambers 12P. The sealing member 15 is made of a material with low ink permeability such as stainless steel.

[0044] As shown in FIG. 5, the actuator member 13 is fixed to the upper surface of the flow path member 12 through the sealing member 15. The actuator member 13 includes piezoelectric layers 13A and 13B, a plurality of individual electrodes 13C, and a common electrode 13D. The piezoelectric layers 13A and 13B and the common electrode 13D are arranged so as to cover the plurality of pressure chambers 12P. The individual electrodes 13C are provided for each pressure chamber 12P and are arranged so as to overlap the one pressure chamber 12P in the vertical direction.

[0045] In the actuator member 13, the portion overlapping the pressure chamber 12P in the vertical direction functions as a piezoelectric element 13X. The piezoelectric element 13X can be independently deformed according to the potential applied to the individual electrode 13C. The piezoelectric element 13X is a bulk piezoelectric element, not a thin film piezoelectric element. A thin film piezoelectric element is a so-called micro electro mechanical systems (MEMS), which is an extremely small device in which a plurality of piezoelectric elements are integrated by sequentially forming thin films such as an electrode film and a piezoelectric film on a substrate. A bulk piezoelectric element is a piezoelectric element in which a plurality of piezoelectric sheets obtained by firing are laminated.

[0046] The plurality of individual electrodes 13C and the common electrode 13D are electrically connected to the driver IC 14. The driver IC 14 maintains the potential of the common electrode 13D at the ground potential while changing the potential of the individual electrode 13C. The common electrode 13D functions as a common electrode that is common to the plurality of piezoelectric elements 13X.

[0047] The driver IC 14 generates a drive signal based on the control signal from the control unit 5 and supplies the drive signal to the individual electrode 13C. The drive signal changes the potential of the individual electrode 13C between a predetermined drive potential and the ground potential.

[0048] As described above, according to the present embodiment, the high-order components of the pressure wave can be cut by the first flow path 21 (see FIG. 5) having a large inertia, and satellite droplets can be prevented. Further, the first flow path 21 extends parallel to the plane in which the pressure chamber 12P is disposed. Therefore, even if the flow path length of the first flow path 21 is increased to increase the inertia of the first flow path 21, the head 1 does not increase in size in the vertical direction. The flow path length of the first flow path 21 is the direction along the conveyance direction in the present embodiment. Thus, according to the present embodiment, it is possible to achieve both prevention of satellite droplets and miniaturization in the vertical direction.

[0049] The first flow path 21 has the other end 21Y connected to the pressure chamber 12P (see Fig. 5). In this case, since the first flow path 21 with a large inductance is located closer to the pressure chamber 12P than the second flow path 22, higher-order components of the pressure wave can be efficiently cut, and satellite droplets can be more reliably prevented.

[0050] The inductance of the first flow path 21 is equal to or less than the inductance of the nozzle 12N (see Fig. 5). When the inductance of the first flow path 21 is larger than the inductance of the nozzle 12N, reflection of the pressure wave easily occurs in the first flow path 21 with a large inductance, and it is necessary to increase the driving voltage applied to the piezoelectric element 13X in order to propagate the pressure wave to the nozzle 12N. In this regard, in the head 1 according to the present embodiment, since the inductance of the first flow path 21 is equal to or less than the inductance of the nozzle 12N, reflection of the pressure wave hardly occurs in the first flow path 21, and the driving voltage applied to the piezoelectric element 13X can be lowered.

[0051] The head 1 includes plates 11B to 11E that constitute the connection flow path 12D (see Fig. 5). In this configuration, if a first portion with a locally small flow path cross-sectional area is provided as in Patent Document 1, the adhesive for adhering the plates 11B to 11E may enter the first portion, and the first portion may be blocked. On the other hand, in the present embodiment, since the first flow path 21 extends parallel to the plane in which the pressure chamber 12P is arranged, it is possible to increase the flow path length while making the flow path cross-sectional area such that it is not blocked by the adhesive. That is, blockage of the flow path by the adhesive can be prevented.

[0052] Both the first flow path 21 and the third flow path 23 are arranged on one of the plates 11B to 11E, i.e., the plate 11C (see FIG. 5). In this case, since the first flow path 21 and the third flow path 23 can be formed in the same process, variations in the dimensions of the first flow path 21 and the third flow path 23 can be suppressed, and the relationship between the inertances of the first flow path 21 and the third flow path 23 as described above can be established. On the other hand, when the first flow path 21 and the third flow path 23 are arranged on separate plates, the first flow path 21 and the third flow path 23 are formed in separate processes. In this case, due to the superposition of dimensional variations occurring in each process, the relationship between the inertances as described above may not hold.

[0053] The first flow path 21 and the third flow path 23 are arranged across the entire thickness of the plate 11C (see FIG. 5). In this case, compared with the case where the first flow path 21 and the third flow path 23 are arranged in a part of the thickness of the plate 11C by half-etching or the like, the vertical lengths of the first flow path 21 and the third flow path 23 can be made constant. Consequently, the sizes of the first flow path 21 and the third flow path 23 can be made as designed.

[0054] One end 12PX and the other end 12PY in the transport direction in the pressure chamber 12P are arranged at the central portion in the paper width direction in the pressure chamber 12P (see FIG. 4). When one end 12PX and the other end 12PY are arranged at one end and the other end in the paper width direction in the pressure chamber 12P, respectively, the propagation distance of the pressure wave in the pressure chamber 12P becomes long, and the natural frequency Fr becomes low. On the other hand, in the above configuration, the propagation distance becomes short, and the natural frequency Fr becomes high. Consequently, the driving frequency can be increased.

[0055] The inertia of the first flow path 21 is 1.20×10 7 [kg / m 4 or more. Thereby, higher-order components of the pressure wave can be cut, and satellite droplets can be prevented.

[0056] Next, the analysis conducted by the inventors of the present application will be described.

[0057] The inventors of the present application focused on the fact that the inertance of the third flow path 23 and the first flow path 21 affects the driving voltage applied to the piezoelectric element 13X and the natural frequency Fr of the individual flow path 12B, and analyzed to determine the relationship between the inertance of the third flow path 23 and the inertance of the first flow path 21 such that the driving voltage applied to the piezoelectric element 13X can be lowered at a high driving frequency.

[0058] The inertance of a flow path is ρL / S [kg / m 2 when the cross-sectional area of the flow path is S [m 3 , the length of the flow path is L [m], and the density of the ink in the flow path is ρ [kg / m 4 .

[0059] Figs. 6 to 8 show the results of the analysis conducted by the inventors of the present application.

[0060] It can be seen from Fig. 6 that there is a correlation between the inertance M1 of the third flow path 23, the inertance M2 of the first flow path 21, and the voltage ratio. The voltage ratio is the ratio when the viscosity of the ink in the flow path is 7 cps, the surface tension of the ink is 24 mN / m, the configuration other than the communication flow path 12E and the second flow path 22 in the individual flow path 12B is a predetermined configuration, and the driving voltage when the flying speed of the ink droplets ejected from the nozzle 12N is a predetermined speed (for example, 7 m / s) is set to "1".

[0061] In Fig. 6, the curve L1 is a line along the voltage ratio of 101%, and can be approximated by the formula "M2 = 3.23 × 10 -1 × M1 - 1.95 × 10 7 (where M1 is the inertance of the third flow path 23 [kg / m 4 , and M2 is the inertance of the first flow path 21 [kg / m 4 )". The driving voltage at the voltage ratio of 101% is, for example, 21 V.

[0062] The upper side of the curve L1 is a region where the voltage ratio exceeds 101%. In this region, as shown in Fig. 7A, the change in the vibration speed of the meniscus formed at the nozzle 12N is slow. Therefore, it is difficult to eject ink droplets from the nozzle 12N at a low driving voltage.

[0063] The curve L1 and the area below it are areas where the voltage ratio is 101% or less. In this area, as shown in FIG. 7B, a sharp change occurs in the vibration speed of the meniscus formed in the nozzle 12N. Therefore, even at a low driving voltage, it is easy to discharge ink droplets from the nozzle 12N.

[0064] Therefore, the head 1 of the present embodiment satisfies the following formula (1). That is, by being in the area of the curve L1 in FIG. 6 and the area below it, even when the driving voltage applied to the piezoelectric element 13X is low, a sharp change occurs in the vibration speed of the meniscus, and ink droplets can be discharged from the nozzle 12N. M2 ≦ 3.23×10 -1 ×M1 - 1.95×10 7 ··· Formula (1)

[0065] It can be seen from FIG. 8 that there is a correlation between the inertia M1 of the third flow path 23, the inertia M2 of the first flow path 21, and the natural frequency Fr.

[0066] In FIG. 8, the straight line L2 is a line along the natural frequency Fr = 155 kHz, and corresponds to the formula "M2 = -8.37×10 -1 ×M1 + 2.20×10 8 ".

[0067] The area above the straight line L2 is an area where the natural frequency Fr is less than 155 kHz. In this area, since the natural frequency Fr is too low, the driving frequency cannot be increased.

[0068] The straight line L2 and the area below it are areas where the natural frequency Fr is 155 kHz or more. In this area, since the natural frequency Fr is high, the driving frequency can be increased.

[0069] Therefore, the head 1 of the present embodiment further satisfies the following formula (2). That is, by being in the area of the straight line L2 in FIG. 8 and the area below it, the driving frequency can be increased. M2 ≦ -8.37×10 -1 ×M1 + 2.20×10 8···Formula (2)

[0070] In FIG. 8, the straight line L3 is a line along the natural frequency Fr = 170 kHz, and corresponds to the formula "M2 = -7.49 × M1 + 9.83 × 10 8 ".

[0071] Below the straight line L2 is a region where the natural frequency Fr exceeds 170 kHz. In this region, because the natural frequency Fr is too high, the driving voltage applied to the piezoelectric element 13X becomes high, and the heat generation amount of the piezoelectric element 13X tends to increase.

[0072] Above the straight line L3 is a region where the natural frequency Fr is less than 170 kHz. In this region, the natural frequency Fr is not too high, and the heat generation amount of the piezoelectric element 13X is unlikely to increase.

[0073] Therefore, the head 1 of the present embodiment further satisfies the following formula (3). That is, by being in the straight line L3 in FIG. 8 and the region above it, the heat generation amount of the piezoelectric element 13X is unlikely to increase. M2 ≧ -7.49 × M1 + 9.83 × 10 8 ···Formula (3)

[0074] As described above, according to the present embodiment, instead of excessively increasing the rigidity of the pressure chamber 12P, by satisfying the above formulas (1) and (2) with the configurations of the communication flow path 12E and the first flow path 21, the driving voltage applied to the piezoelectric element 13X can be lowered at a high driving frequency. Specifically, by satisfying formula (1), as is clear from the above analysis results (see FIGS. 6 and 7B), even if the driving voltage applied to the piezoelectric element 13X is low, a sharp change occurs in the vibration speed of the meniscus, and ink droplets can be ejected from the nozzle 12N. By satisfying formula (2), as is clear from the above analysis results (see FIG. 8), the natural frequency Fr is 155 kHz or more, and the driving frequency can be increased.

[0075] If the natural frequency Fr is too high, the driving voltage applied to the piezoelectric element 13X increases, and the amount of heat generated by the piezoelectric element 13X tends to increase. In this regard, the head 1 according to the present embodiment satisfies the above formula (3), and as is clear from the above analysis result (see FIG. 8), the natural frequency Fr is 170 kHz or less. Thereby, it is difficult for the amount of heat generated by the piezoelectric element 13X to increase.

[0076] Furthermore, the head 1 of the present embodiment satisfies the following formula (4). When M2 > M3, pressure wave reflection is likely to occur in the first flow path 21 with a large inertia, and in order to propagate the pressure wave to the nozzle 12N, it is necessary to increase the driving voltage applied to the piezoelectric element 13X. In this regard, the head 1 of the present embodiment satisfies the following formula (4), so that pressure wave reflection hardly occurs in the first flow path 21, and the driving voltage applied to the piezoelectric element 13X can be made more surely low. M2 ≤ M3 ··· Formula (4) (Here, M3 is the inertia of the nozzle 12N [kg / m 4 .)

[0077] The flow path cross-sectional area of the hole constituting the other end 21Y of the first flow path 21 is smaller than the flow path cross-sectional area of the one end 21X of the first flow path 21 (see FIG. 4). The other end 21Y of the first flow path 21 is a portion connected to the other end 12PY of the pressure chamber 12P. Since the inertia of this portion is large, the higher-order components of the pressure wave can be cut, and satellite droplets can be prevented. Satellite droplets are generated by the tail of the ink droplet separating from the main droplet of the ink droplet, and have a smaller volume than the main droplet.

[0078] Of the six plates 11A to 11F, both the third flow path 23 and the first flow path 21 are arranged on one plate 11C (see Fig. 5). In this case, since the third flow path 23 and the first flow path 21 can be formed in the same process, variations in the dimensions of the third flow path 23 and the first flow path 21 can be suppressed, and the above formulas (1) and (2) can be more reliably satisfied. On the other hand, when the third flow path 23 and the first flow path 21 are arranged on separate plates, the third flow path 23 and the first flow path 21 are formed in separate processes. In this case, due to the superposition of dimensional variations occurring in each process, the above formulas (1) and (2) may not hold.

[0079] The third flow path 23 and the first flow path 21 are arranged across the entire thickness of the plate 11C (see Fig. 5). In this case, compared with the case where the third flow path 23 and the first flow path 21 are arranged in a part of the thickness of the plate 11C by half-etching or the like, the vertical lengths of the third flow path 23 and the first flow path 21A can be made constant. As a result, the above formulas (1) and (2) can be more reliably satisfied.

[0080] One end 12PX and the other end 12PY in the conveyance direction in the pressure chamber 12P are arranged at the central part in the paper width direction in the pressure chamber 12P (see Fig. 4). When one end 12PX and the other end 12PY are arranged at one end and the other end in the paper width direction in the pressure chamber 12P, respectively, the propagation distance of the pressure wave in the pressure chamber 12P becomes long, and the natural frequency Fr becomes low. On the other hand, in the present embodiment, since one end 12PX and the other end 12PY are arranged at the central part in the paper width direction in the pressure chamber 12P, the propagation distance of the pressure wave in the pressure chamber 12P becomes short, and the natural frequency Fr becomes high. As a result, the driving frequency can be increased.

[0081] Furthermore, the head 1 of the present embodiment satisfies the following formula (5). Thereby, higher-order components of the pressure wave can be cut, and satellite droplets can be prevented. M2≧1.20×10 7 ···Formula (5)

[0082] Next, another analysis conducted by the inventors of the present application will be described.

[0083] An example of the drive signal is shown in FIG. 9.

[0084] The drive signal X shown in FIG. 9 includes three rectangular pulses within one ejection period (the time from time t0 to time t1) for forming one dot. The three pulses include a main pulse Pm, a pre-pulse Pp applied before the main pulse Pm, and a cancel pulse Pc applied after the main pulse Pm.

[0085] The main pulse Pm is for ejecting an ink droplet of a predetermined volume from the nozzle 12N. The pre-pulse Pp and the cancel pulse Pc are for preventing satellite droplets and have widths Tp and Tc smaller than the width Tm of the main pulse Pm. Satellite droplets are generated by the tail of the ink droplet separating from the main droplet of the ink droplet and have a smaller volume than the main droplet. The pre-pulse Pp cancels the pressure wave in the pressure chamber 12P generated in the ejection period before the current ejection period. The cancel pulse Pc cancels the pressure wave in the pressure chamber 12P generated by the application of the main pulse Pm in the current ejection period.

[0086] According to the width Tm of the main pulse Pm, the volume of the ink droplet ejected from the nozzle 12N changes, and gradation expression is realized. However, according to the width Tm, the flight speed of the ink droplet may also change. That is, variations may occur in the flight speed of the ink droplets in a plurality of waveforms with different widths Tm for gradation expression. When variations occur in the flight speed of the ink droplets, the image quality deteriorates.

[0087] As a result of intensive research, the inventors of the present application have found that the inertance of the third flow path 23 (communication flow path 12E) and the first flow path 21 affects the drive voltage applied to the piezoelectric element 13X, and that the drive voltage affects the vibration speed of the meniscus formed in the nozzle 12N. The inertance of the flow path is ρL / S [kg / m when the cross-sectional area of the flow path is S [m 2 , the length of the flow path is L [m], and the density of the ink in the flow path is ρ [kg / m 3 .4 It is represented by

[0088] Figures 10 to 12 show the results of the analysis conducted by the inventors of the present application.

[0089] From Figure 10, it can be seen that there is a correlation between the inertia M1 of the third flow path 23 (communication flow path 12E), the inertia M2 of the first flow path 21, and the voltage ratio. The voltage ratio is when the viscosity of the ink in the flow path is 7 cps, the surface tension of the ink is 24 mN / m, the configuration other than the communication flow path 12E and the first flow path 21 in the individual flow path 12B is a predetermined configuration, and the flying speed of the ink droplets ejected from the nozzle 12N is a predetermined speed (for example, 7 m / s). It is the ratio when the driving voltage is set to "1".

[0090] In Figure 10, the curves L1 and L2 are lines along the voltage ratio of 103%. Curve L1 can be approximated by the formula "M2 = 2.67×10 -16 ×M1 3 -7.84×10 -8 ×M1 2 +7.83×M1 - 2.31×10 8 ". Curve L2 can be approximated by the formula "M2 = -6.02×10 -10 ×M1 2 +4.88×10 -1 ×M1 - 2.66×10 7 ". Here, M1 is the inertia of the third flow path 23 [kg / m 4 , and M2 is the inertia of the first flow path 21 [kg / m 4 .

[0091] In the region above curve L1, the vibration speed of the meniscus changes as shown in Figure 11A. In the region below curve L2, the vibration speed of the meniscus changes as shown in Figure 11B. In these regions, a sharp change occurs in the vibration speed of the meniscus.

[0092] In the region sandwiched between curve L1 and curve L2, the vibration speed of the meniscus changes as shown in Figure 11C. In this region, the change in the vibration speed of the meniscus is slow.

[0093] Therefore, the head 1 of this embodiment satisfies the following formulas (6) and (7). That is, by being in the region sandwiched between the curve L1 and the curve L2 in FIG. 10, the change in the vibration speed of the meniscus is slow, and in a plurality of waveforms with different widths Tm for gradation expression, it is difficult for variations to occur in the flying speed of the ink droplets. M2 ≦ 2.67×10 -16 ×M1 3 -7.84×10 -8 ×M1 2 +7.83×M1 - 2.31×10 8 ··· Formula (6) M2 ≧ -6.02×10 -10 ×M1 2 +4.88×10 -1 ×M1 - 2.66×10 7 ··· Formula (7)

[0094] In the head 1 that satisfies the above formulas (6) and (7), when the width Tm is changed, the flying speed and the volume of the ink droplets change as shown in FIG. 12. From FIG. 12, it can be seen that when the width Tm is 2.0 to 3.5 μsec, the change in the flying speed is slow. Therefore, in this embodiment, the width Tm is set to 2.0 to 3.5 μsec.

[0095] Also, in order to drive the head 1 at a high driving frequency required by the inventors of the present application, it is desirable that the natural frequency Fr is 150 kHz or more.

[0096] As described above, according to this embodiment, since the natural frequency Fr is 150 kHz or more, the driving frequency can be increased, and thus high-speed recording can be realized. Furthermore, by satisfying formulas (6) and (7), as is clear from the above analysis results, it is difficult for variations to occur in the flying speed of the ink droplets in a plurality of waveforms for gradation expression.

[0097] Furthermore, the head 1 of the present embodiment satisfies the following formula (8). When M2 > M3, pressure wave reflection is likely to occur in the second flow path 22 with a large inertance, and in order to propagate the pressure wave to the nozzle 12N, it becomes necessary to increase the drive voltage applied to the piezoelectric element 13X. In this regard, by satisfying the following formula (8), the present embodiment makes it difficult for pressure wave reflection to occur in the second flow path 22, and can more reliably lower the drive voltage applied to the piezoelectric element 13X. M2 ≤ M3 ··· Formula (8) (Here, M3 is the inertance of the nozzle 12N [kg / m 4 .)

[0098] The flow path cross-sectional area of the hole constituting the other end 21Y of the first flow path 21 is smaller than the flow path cross-sectional area of one end 21X of the first flow path 21 (see FIG. 4). The other end 21Y of the first flow path 21 is a portion that connects to the other end 12PY of the pressure chamber 12P. By having a large inertance in this portion, higher-order components of the pressure wave can be cut, and satellite droplets can be prevented.

[0099] Both the third flow path 23 and the first flow path 21 are arranged on one of the six plates 11A to 11F, that is, on the plate 11C (see FIG. 5). In this case, by configuring the third flow path 23 and the first flow path 21 on the same plate 11C, manufacturing variations between the third flow path 23 and the first flow path 21 can be suppressed, and the above formulas (6) and (7) can be more reliably satisfied.

[0100] The third flow path 23 and the first flow path 21 are arranged over the entire thickness of the plate 11C (see FIG. 5). In this case, compared with the case where the third flow path 23 and the first flow path 21 are arranged in a part of the thickness of the plate 11C by half etching or the like, the vertical lengths of the third flow path 23 and the first flow path 21 can be made constant. As a result, the above formulas (6) and (7) can be more reliably satisfied.

[0101] One end 12PX and the other end 12PY in the conveyance direction in the pressure chamber 12P are arranged at the center in the paper width direction in the pressure chamber 12P (see FIG. 4). When one end 12PX and the other end 12PY are arranged at one end and the other end in the paper width direction in the pressure chamber 12P respectively, the propagation distance of the pressure wave in the pressure chamber 12P becomes long, and the natural frequency Fr becomes low. On the contrary, in the present embodiment, since one end 12PX and the other end 12PY are arranged at the center in the paper width direction in the pressure chamber 12P, the propagation distance of the pressure wave in the pressure chamber 12P becomes short, and the natural frequency Fr becomes high. As a result, the requirement that the natural frequency Fr is 150 kHz or more can be more reliably satisfied.

[0102] Furthermore, the present embodiment satisfies the following formula (9). Thereby, higher-order components of the pressure wave can be cut, and satellite droplets can be prevented. M2 ≧ 1.20×10 7 ··· Formula (9)

[0103] The width Tm of the main pulse Pm is 2.0 to 3.5 μsec. As is clear from the above analysis results (see FIG. 12), when the width Tm is 2.0 to 3.5 μsec, the effect that the flight speed of the ink droplets hardly varies in a plurality of waveforms for gradation expression can be more reliably obtained.

[0104] Also, it is desirable to satisfy the following formulas (10) and (11). When M1 < 9.0×10 7 , it is difficult to suppress the residual vibration in the pressure chamber 12P. When M2 > 5.0×10 7 , it is difficult for the pressure wave to propagate to the nozzle 12N. By satisfying the following formulas (10) and (11), the above problems can be solved. M1 ≧ 9.0×10 7 ··· Formula (10) M2 ≦ 5.0×10 7 ··· Formula (11)

[0105] <Second Embodiment> As shown in FIG. 5, the flow path member 12 of the head 1 according to the first embodiment has six plates 11A to 11F. On the other hand, as shown in FIG. 13, the flow path member 212 of the head 201 according to the second embodiment has five plates 11A, 11C to 11F. That is, in the second embodiment, the plate 11B is omitted.

[0106] As a result, in the second embodiment, there are no vertical holes 24 and 26 (see FIG. 5), the third flow path 23 is directly connected to one end 12X of the pressure chamber 12P, and the first flow path 221 is directly connected to the other end 12PY of the pressure chamber 12P. The connection flow path 212D does not include the vertical hole 26 and includes the first flow path 221 and the second flow path 22. The communication flow path 212E does not include the vertical hole 24 and includes the third flow path 23 and the vertical hole 25.

[0107] Also, in the individual flow path 12B of the first embodiment, as shown in FIG. 4, the flow path width of the first flow path 21 becomes smaller from the upstream to the downstream in the conveyance direction. On the other hand, in the individual flow path 212B of the second embodiment, as shown in FIG. 14, the flow path width of the first flow path 221 is locally smaller between one end 221X and the other end 221Y of the first flow path 221A.

[0108] The portion where the flow path width is locally smaller is the constriction portion 221C. The flow path cross-sectional area of the constriction portion 221C is smaller than either the flow path cross-sectional area of one end 221X of the first flow path 221 or the flow path cross-sectional area of the other end 221Y of the first flow path 221.

[0109] As described above, according to the present embodiment, the other end 221Y of the first flow path 221 is connected to the pressure chamber 12P without passing through the vertical hole 26 (see FIG. 5) (see FIG. 13). In this case, by directly connecting the first flow path 221 having a large inertia to the pressure chamber 12P, higher-order components of the pressure wave can be cut more efficiently, and satellite droplets can be more reliably prevented.

[0110] Furthermore, according to the present embodiment, the constriction portion 221C having a large inertia can cut higher-order components of the pressure wave and prevent satellite droplets.

[0111] In addition, in the present embodiment, one end and the other end of the first flow path 221 and one end and the other end of the third flow path 223 are oval-shaped, not circular, in a plane orthogonal to the vertical direction.

[0112] <Third Embodiment> In the individual flow path 12B of the first embodiment, as shown in FIG. 4, the first flow path 21 and the third flow path 23 extend in the conveyance direction. On the other hand, in the individual flow path 312B of the third embodiment, as shown in FIG. 15, the first flow path 321 and the third flow path 323 extend in a direction inclined with respect to both the conveyance direction and the paper width direction.

[0113] According to the present embodiment, since the first flow path 321 and the third flow path 323 extend in the inclined direction, the size in the conveyance direction of the entire individual flow path 312B including the first flow path 321 and the third flow path 323 can be reduced.

[0114] In addition, in the present embodiment, similar to the second embodiment, one end and the other end of the first flow path 321 and one end and the other end of the third flow path 323 are oval-shaped, not circular, in a plane orthogonal to the vertical direction.

[0115] <Fourth Embodiment> As shown in FIG. 16, two supply ports 4111 and two return ports 4112 are open on the upper surface of the flow path member 412. The two supply ports 4111 are arranged at one end of the flow path member 412 in the paper width direction. The two return ports 4112 are arranged at the other end of the flow path member 412 in the paper width direction. The supply ports 4111 and the return ports 4112 communicate with the ink tank via tubes.

[0116] The flow path member 412 has two common flow paths 412A and a plurality of individual flow paths 412B.

[0117] The two common channels 412A are arranged in the conveying direction and each extends in the paper width direction. A supply port 4111 is connected to one end of the common channel 412A in the paper width direction. A return port 4112 is connected to the other end of the common channel 412A in the paper width direction. The common channel 412A communicates with the ink tank via the supply port 4111 and the return port 4112 and also communicates with a plurality of individual channels 412B.

[0118] As shown in FIG. 17, the individual channel 412B includes a nozzle 412N, a pressure chamber 412P, a first communication channel 412D, and a second communication channel 412E. One end of the first communication channel 412D communicates with the nozzle 412N and the other end communicates with the pressure chamber 412P. One end of the second communication channel 412E communicates with the common channel 412A and the other end communicates with the pressure chamber 412P. The first communication channel 412D communicates with one end of the pressure chamber 412P and the second communication channel 412E communicates with the other end of the pressure chamber 412P.

[0119] The channel member 412 includes eight plates 4121 to 4128. Note that the channel member 412 may be composed of eight or more or seven or less plates. Among the eight plates 4121 to 4128, a plurality of pressure chambers 412P are formed in the uppermost plate 4121 and a plurality of nozzles 412N are formed in the lowermost plate 4128.

[0120] A plurality of pressure chambers 412P open on the upper surface of the plate 4121 and a plurality of nozzles 412N open on the lower surface of the plate 4127. The opening of the nozzle 412N is circular, and the opening of the pressure chamber 412P is a substantially rectangular shape that is long in the conveying direction. That is, the width of the pressure chamber 412P in the paper width direction is shorter than the length in the conveying direction.

[0121] As shown in FIG. 17, the nozzle 412N has a tapered shape that narrows downward. The lower end of the nozzle 412N is an outlet 412N1 for ink droplets ejected from the nozzle 412N. The diameter of the outlet 412N1 of the nozzle 412N is smaller than the diameter of the upper end of the nozzle 412N, that is, the inlet 124N2 to the nozzle 412N. In the present embodiment, the side wall defining the nozzle 412N is inclined with respect to the vertical direction. The taper angle θ of the nozzle 412N is the angle on the acute angle side with respect to the vertical direction of the side wall defining the nozzle 412N.

[0122] As shown in FIG. 17, the first communication passage 412D has a first portion 412D1 and a second portion 412D2. The first portion 412D1 is connected to the upper end of the nozzle 412N and has a cylindrical shape. The first portion 412D1 constitutes one end of the first communication passage 412D connected to the nozzle 412N. The first portion 412D1 extends upward from the nozzle 412N (in the direction approaching the pressure chamber 12P) and is disposed at a position that does not overlap with the pressure chamber 412P in the upward direction. Further, the first portion 412D1 is formed by connecting the holes formed in each of the four plates 4124 to 4127, and has a diameter larger than the diameter of the inlet 412N2 of the nozzle 412N.

[0123] The second part 412D2 has a horizontal part 412D2A connected to the upper end of the first part 412D1 and a vertical part 412D2B connected to the pressure chamber 412P. The horizontal part 412D2A is a hole formed in the plate 4123 and extends along the conveyance direction from the upper end (the downstream end in the upward direction) of the first part 412D1. That is, the horizontal part 412D2A extends parallel to the upper surface of the flow path member 412 (one plane on which the pressure chamber 412P is disposed) from the upper end of the first part 412D1 toward the pressure chamber 412P. Further, as shown in FIGS. 16 and 17, the horizontal part 412D2A has a throttle part 412D2C that restricts the flow rate of the liquid. The throttle part 412D2C is formed in the central part of the horizontal part 412D2A in the conveyance direction, and its flow path width is smaller than the flow path width of the first part 412D1. The flow path width referred to here is the width in the paper width direction. Although the flow path widths at both ends of the horizontal part 412D2A in the conveyance direction in the present embodiment are larger than that of the throttle part 412D2C, the flow path width of the horizontal part 412D2A may be constant over the entire length.

[0124] As shown in FIG. 17, the vertical part 412D2B is a hole formed in the plate 4122 and extends upward toward the pressure chamber 412P from the end of the horizontal part 412D2A on the pressure chamber 412P side (the downstream end in the direction in which the horizontal part 412D2A extends from the first part 412D1). In this way, the second part 412D2 is formed by connecting the holes formed in the respective two plates 4122 and 4123 to each other.

[0125] As shown in FIG. 17, the second communication path 412E has a first part 412E1 and a second part 412E2. The first part 412E1 is a hole formed in the plate 4124 and is connected to the upper end of the common flow path 412A.

[0126] The second part 412E2 has a horizontal part 412E2A connected to the upper end of the first part 412E1 and a vertical part 412E2B connected to the pressure chamber 412P. The horizontal part 412E2A is a hole formed in the plate 4123 and extends from the upper end of the first part 412E1 along the conveyance direction toward the pressure chamber 412P. Also, as shown in FIGS. 16 and 17, the horizontal part 412E2A has a throttle part 412E2C for restricting the flow rate of the liquid. The throttle part 412E2C is formed in the central part in the conveyance direction, and its flow path width is smaller than the flow path width of the first part 412E1. Both end parts in the conveyance direction of the horizontal part 412E2A in the present embodiment have a larger flow path width than the throttle part 412E2C, but the flow path width of the horizontal part 412E2A may be constant over the entire length.

[0127] As shown in FIG. 17, the vertical part 412E2B is a hole formed in the plate 4122 and extends upward from the end on the pressure chamber 412P side of the horizontal part 412E2A toward the pressure chamber 412P. Thus, the second part 412E2 is formed by connecting the holes formed in the respective two plates 4122 and 4123 to each other.

[0128] As shown in FIG. 16, the nozzles 412N are arranged in a staggered pattern in the paper width direction and constitute four nozzle rows R41 to R44. Each nozzle row R41 to R44 is composed of a plurality of nozzles 412N arranged in the paper width direction.

[0129] In each of the nozzle rows R41 to R44, the plurality of nozzles 412N are arranged at a pitch P of 300 dpi or more in the paper width direction. In the present embodiment, the recording resolution in each of the nozzle rows R41 to R44 is 300 dpi, and the pitch P is approximately 84 μm. The recording resolution is the resolution of the image recorded by the ink droplets ejected from the nozzles 412N.

[0130] Between two nozzle rows adjacent to each other in the conveying direction, the positions of the nozzles 412N in the paper width direction are shifted by half of the pitch P. As a result, when the recording resolution in each nozzle row R41 to R44 is 300 dpi, a recording resolution of 1200 dpi is achieved by the four nozzle rows R41 to R44. The head 1 of the present embodiment has a recording resolution of 1200 dpi × 1200 dpi in the paper width direction and the conveying direction.

[0131] The ink in the ink tank is supplied to the common flow path 412A through the supply port 4111 by driving the pump 10 shown in FIG. 2 under the control of the control unit 5, and is distributed from the common flow path 12A to a plurality of individual flow paths 412B.

[0132] In the individual flow path 412B, the ink in the pressure chamber 412P is discharged as ink droplets from the nozzle 412N through the first communication path 412D by the volume of the pressure chamber 412P decreasing and pressure being applied by driving a piezoelectric element 413X described later.

[0133] The ink supplied from the supply port 4111 moves in the common flow path 412A from one end in the paper width direction to the other end and reaches the return port 4112. The ink that has reached the return port 4112 is returned to the ink tank through a tube.

[0134] As shown in FIG. 17, the actuator member 13 is fixed to the upper surface of the flow path member 412. The actuator member 413 includes a metal diaphragm 413A, a piezoelectric layer 413B, and a plurality of individual electrodes 413C.

[0135] In the actuator member 413, the portion that vertically overlaps the pressure chamber 412P functions as a piezoelectric element 413X. The piezoelectric element 413X can be independently deformed according to the potential applied to the individual electrode 413C.

[0136] The piezoelectric element 413X is a thin-film piezoelectric element. A thin-film piezoelectric element is a so-called micro electro mechanical systems (MEMS). The piezoelectric element 413X is formed by successively depositing a thin film serving as a piezoelectric layer 413B and a thin film serving as an individual electrode 413C on the upper surface of a diaphragm 413A.

[0137] The diaphragm 413A is disposed on the upper surface of the flow path member 412 so as to cover a plurality of pressure chambers 412P. The piezoelectric layer 413B is disposed on the upper surface of the diaphragm 413A. The individual electrode 413C is disposed on the upper surface of the piezoelectric layer 413B so as to vertically overlap the pressure chamber 412P.

[0138] The diaphragm 413A and the plurality of individual electrodes 413C are electrically connected to a driver IC 414. The driver 4IC14 maintains the potential of the diaphragm 413A at the ground potential while changing the potential of the individual electrode 413C. The diaphragm 413A functions as a common electrode that is common to the plurality of piezoelectric elements 413X.

[0139] The driver 4IC14 generates a drive pulse signal based on a control signal from the control unit 45 and supplies the drive pulse signal to the individual electrode 413C. The drive pulse signal changes the potential of the individual electrode 413C between a predetermined drive potential and the ground potential. In this way, the piezoelectric element 413X is driven, and pressure is applied to the ink in the pressure chamber 412P, so that ink droplets are ejected from the nozzle 412N through the first communication path 412D.

[0140] Next, the analysis performed by the inventors of the present application will be described.

[0141] When the ink droplets ejected from the nozzle 412N are elongated along the ejection direction as shown in FIG. 18A, the ink droplets are likely to separate into the main droplet M and the satellite droplet S. Since the satellite droplet S is a minute droplet, it is likely to become a mist floating in the air. Further, when a plurality of satellite droplets S are generated from the ink droplet, the ink amount of the main droplet M decreases and becomes less than a predetermined amount. On the other hand, when the ink droplets ejected from the nozzle 412N have a shape close to a sphere as shown in FIG. 18B, the ink droplets are less likely to separate into the main droplet M and the satellite droplet S and are substantially composed of the main droplet M. For this reason, the ink amount of the ink droplet becomes a predetermined amount.

[0142] Therefore, the inventors of the present application analyzed the relationship between the meniscus flow velocity in the nozzle 412N when ejecting ink droplets from the nozzle and the shape of the ink droplets. As a result, it was found that the slower the meniscus flow velocity, the larger the radius of the ink droplets ejected from the nozzle 412N and the closer the shape of the ink droplets approaches a sphere. The meniscus flow velocity indicates the velocity when the meniscus swings in the ejection direction of the ink droplet by the pressure wave generated at the inlet 12N2 of the nozzle 412N (that is, one end of the first communication passage 412D) by driving the piezoelectric element 413X with a drive pulse signal. The meniscus flow velocity was obtained by performing image analysis on the change in the meniscus from the position where the meniscus was closest to the inlet 412N2 of the nozzle 412N to the position where it was closest to the outlet 412N1 when ejecting ink droplets from the nozzle 412N. More specifically, the meniscus flow velocity is obtained by dividing the number of changed pixels, which is the change from the number of pixels indicating the ink portion in the nozzle 412N where the meniscus was closest to the inlet 412N2 to the number of pixels indicating the ink portion in the nozzle 412N where the meniscus was closest to the outlet 412N1, by the time (μs) required for the above change in the meniscus.

[0143] When the piezoelectric element 413X is driven by a drive pulse signal, a pressure wave is generated between the pressure chamber 412P and the nozzle 412N. The shape of this pressure wave largely depends on the shape of the first communication passage 412D.

[0144] Therefore, the inventors of the present application analyzed the pressure waves generated at the inlet 412N2 of the nozzle 412N when driving the piezoelectric element 413X at driving frequencies of 150 kHz and 200 kHz in an analysis model in which the shape and size of the first connection passage 412D were variously changed, and obtained a plurality of frequency characteristics at the inlet 412N2 by Fast Fourier Transformation (FFT) analysis. Then, the frequency ratio of the secondary frequency to the primary frequency and the amplitude ratio of the secondary frequency to the amplitude of the primary frequency were obtained for the plurality of frequency characteristics at each driving frequency. The primary frequency in each frequency characteristic is almost determined by the pressure applied to the pressure chamber 412P and is equal to the driving frequency. The secondary frequency is the frequency at which the peak of the amplitude next to the primary frequency appears. The higher-order frequencies after the secondary frequency have amplitudes smaller than the amplitude at the secondary frequency and hardly affect the shape of the ejected ink droplets. Also, in the above analysis model, the meniscus flow rates were obtained when the driving frequencies were 150 kHz and 200 kHz. The analysis results are shown in FIGS. 19 and 20.

[0145] FIG. 19 shows the case where the driving frequency is 150 kHz, with the vertical axis representing the frequency ratio, the horizontal axis representing the amplitude ratio, and the corresponding meniscus flow rate shown in grayscale. FIG. 20 shows the case where the driving frequency is 200 kHz, with the vertical axis representing the frequency ratio, the horizontal axis representing the amplitude ratio, and the corresponding meniscus flow rate shown in grayscale. Note that the shapes of the pressure chamber 412P and the nozzle 412N in the above analysis model are both the same. The pulse width in the drive pulse signal when the drive frequency is 150 kHz is 3.1 μs, and the pulse width in the drive pulse signal when the drive frequency is 200 kHz is 2.5 μs.

[0146] When the meniscus flow rate becomes 1×10 15 (number of changing pixels / μs) or less, the ink droplets ejected from the nozzle 412N approach a spherical shape and the ink amount becomes a predetermined amount or more. The meniscus flow rate at the boundary where the ink amount becomes a predetermined amount or more is indicated by hatching in FIGS. 19 and 20.

[0147] When the shape of the first connection passage 412D is changed to bring the secondary frequency closer to the primary frequency, the amplitude of the secondary frequency decreases, and most of the amplitude ratio of the secondary frequency to the primary frequency becomes 0.5 or less. Also, when the amplitude ratio exceeds 0.5, it affects the amplitude of the primary frequency and the ink droplet volume decreases. Therefore, it is desirable that the amplitude ratio be 0.5 or less. This suppresses the influence on the amplitude of the primary frequency and the decrease in the ink droplet volume.

[0148] In FIG. 19, when the amplitude ratio is 0.5 or less and the ink amount is a predetermined amount or more, the maximum range of the frequency ratio at which the meniscus flow rate is obtained is in the range of 2.0 to 3.2. The range of the frequency ratio narrows as the amplitude ratio decreases. More specifically, when the amplitude ratio is 0.3 or more and 0.5 or less, the range of the frequency ratio is 2.0 to 3.2. When the amplitude ratio is 0.2 or more and 0.3 or less, the range of the frequency ratio is 2.1 to 3.1. When the amplitude ratio is 0.1 or more and 0.2 or less, the range of the frequency ratio is 2.3 to 3.0.

[0149] Therefore, when the piezoelectric element 413X is driven at a driving frequency of 150 kHz, the flow path member 412 is configured to have a first connection passage 412D that satisfies the condition that the range of the frequency ratio at which the ink amount becomes a predetermined amount or more is within the range shown in FIG. 19.

[0150] In FIG. 20, when the amplitude ratio is 0.5 or less and the ink amount is a predetermined amount or more, the maximum range of the frequency ratio at which the meniscus flow rate is obtained is in the range of 2.0 to 3.3. By setting the driving frequency to 200 kHz, the upper limit of the frequency ratio increased slightly compared to when the driving frequency was 150 kHz, but the lower limit remained almost unchanged from when the driving frequency was 150 kHz.

[0151] Also, in FIG. 20 as well, similar to the case of FIG. 19, the range of the frequency ratio narrows as the amplitude ratio decreases. More specifically, when the amplitude ratio is 0.3 or more and 0.5 or less, the range of the frequency ratio is 2.0 to 3.3. When the amplitude ratio is 0.2 or more and 0.3 or less, the range of the frequency ratio is 2.1 to 3.2. When the amplitude ratio is 0.1 or more and 0.2 or less, the range of the frequency ratio is 2.3 to 3.1.

[0152] Therefore, when driving the piezoelectric element 413X at a driving frequency of 200 kHz, the flow path member 412 is configured to have the first communication path 412D that satisfies that the range of the frequency ratio, which is the boundary where the ink amount is equal to or more than the predetermined amount, is within the range shown in FIG. 20.

[0153] As described above, according to the head 1 of the present embodiment, by using the flow path member 412 configured such that the frequency ratio is within the range of 2.0 to 3.2 without performing complicated voltage control, it is possible to make the ink droplets ejected from the nozzle 412N have a shape close to a sphere. In this case, it is difficult for the ejected ink droplets to separate into main droplets and satellite droplets, and the generation of mist due to the satellite droplets can be suppressed.

[0154] When the driving frequency, that is, the primary frequency, is 150 kHz or more, it is preferable that the flow path member 412 satisfies being configured such that the frequency ratio is within the range of 2.0 to 3.2. By doing so, it is possible to suppress the generation of mist even when performing high-speed ejection with a short ejection interval for ejecting ink droplets from the nozzle 412N.

[0155] Also, when the driving frequency, i.e., the primary frequency, is 200 kHz or less, it is preferable that the flow path member 412 satisfies the condition of being configured such that the frequency ratio is within the range of 2.0 to 3.3. By doing so, it becomes possible to suppress the amount of ink droplets discharged from the nozzle 412N from becoming less than a predetermined amount. When the driving frequency exceeds 200 kHz, the pulse width in the driving pulse signal becomes less than 2.5 μs. As the pulse width decreases, the pressure applied to the ink in the pressure chamber 412P also decreases, and the amount of ink droplets discharged from the nozzle 12N becomes less than a predetermined amount.

[0156] Further, the amplitude of the secondary frequency satisfies being 0.5 times or less the amplitude of the primary frequency. Thereby, even when the flow path member 412 satisfies the condition of being configured such that the frequency ratio is within the range of 2.0 to 3.3, it becomes possible to maintain the amount of ink droplets discharged from the nozzle 412N at a predetermined amount. Furthermore, generation of mist can be effectively suppressed.

[0157] Also, the first communication path 412D has a throttle portion 412D2C. Thereby, in the frequency characteristics at the inlet 412N2 of the nozzle 412N, it becomes possible to significantly reduce the higher-order frequencies after the secondary frequency. Also, it becomes easier to make the secondary frequency closer to the primary frequency. For this reason, it is possible to easily realize the configuration of the flow path member 12 such that the frequency ratio is within the range of 2.0 to 3.2.

[0158] As a modification, the inventors of the present application changed the diameter of the outlet 412N1 of the nozzle 412N in the above-described analysis model in the embodiment within the range of 10 μm to 50 μm and performed the analysis in the same manner. Also in this analysis model, the results were almost the same as the analysis results shown in FIGS. 19 and 20. However, when the diameter of the outlet 412N1 is 14 μm or less, the amount of ink droplets discharged from the nozzle 412N itself becomes less than a predetermined amount. Therefore, it is desirable that the diameter of the outlet 412N1 be 14 μm or more. Thereby, it becomes possible to suppress the amount of ink droplets discharged from the nozzle 12N from becoming less than a predetermined amount.

[0159] Also, when the diameter of the outlet 412N1 exceeds 30 μm, the discharge speed of the ink droplets from the nozzle 412N becomes smaller than the predetermined speed. Therefore, it is desirable that the diameter of the outlet 412N1 be 30 μm or less. This makes it possible to suppress the discharge speed of the ink droplets discharged from the nozzle 412N from becoming smaller than the predetermined speed.

[0160] As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and various modifications are possible as long as they are within the scope described in the claims.

[0161] Although the first communication passage 412D in the above-described embodiment has the throttle portion 412D2C, it may not have the throttle portion 412D2C. That is, the flow path member 412 only needs to satisfy the condition that it is configured such that the frequency ratio is within the range of 2.0 to 3.2. Thereby, the same effect as described above can be obtained.

[0162] Also, the entire first communication passage 412D may overlap with the pressure chamber 412P along the vertical direction. In this case, the nozzle 412N may also overlap with the pressure chamber 412P along the vertical direction. This makes it possible to reduce the size of the flow path member 412.

[0163] Also, when the driving frequency is 200 kHz, the flow path member 412 only needs to satisfy the condition that it is configured such that the frequency ratio is within the range of 2.0 to 3.3. Thereby, the same effect as described above can be obtained.

[0164] When the set amount of the ink volume of the ink droplets discharged from the nozzle 412N is small, the diameter of the outlet 412N1 of the nozzle 412N may be less than 10 μm to 14 μm. When the set speed of the discharge speed of the ink droplets discharged from the nozzle 412N is slow, the diameter of the outlet 412N1 of the nozzle 412N may be 31 μm to 50 μm or less.

[0165] Further, although the above-described horizontal portion 412D2A had a throttle portion 412D2C with a narrow flow path width formed in the central portion in its extending direction (conveying direction), the flow path width may be smaller than the flow path width of the first portion 412D1 over the entire length.

[0166] In the above-described first to fourth embodiments, the electrodes constituting the piezoelectric element have a two-layer structure including individual electrodes and common electrodes, but may also have a three-layer structure. For example, the three-layer structure includes a driving electrode to which a high potential and a low potential are selectively applied, a high-potential electrode held at a high potential, and a low-potential electrode held at a low potential.

[0167] The piezoelectric element may be a thin film piezoelectric element.

[0168] The pressure chamber is not limited to being long in the second direction (conveying direction in FIG. 4). Further, the shape of the pressure chamber as viewed from a direction orthogonal to one plane thereof is not limited to a rectangular shape, and may be an elliptical shape, a circular shape, or the like.

[0169] The positional relationship in the first direction (vertical direction in FIG. 5) between the first flow path and the second flow path is not particularly limited. For example, the positional relationship in the vertical direction between the first flow path 21 and the second flow path 22 may be opposite to that of the above-described embodiment. In this case, the first flow path 21 may be connected to the nozzle 12N, and the second flow path 22 may be connected to the other end 12PY of the pressure chamber 12P. Further, for example, the first flow path 21 may be arranged between two second flow paths 22 in the vertical direction.

[0170] The type of the droplet discharge head of the present invention is not limited to a line type, and may be a serial type.

[0171] The object onto which droplets are discharged is not limited to paper. For example, the object onto which droplets are discharged may be cloth, a substrate, or plastic.

[0172] The droplets discharged from the nozzle are not limited to ink droplets. For example, the droplets may be droplets of a treatment liquid that aggregates or precipitates components in the ink.

[0173] The present invention is not limited to printers, but is also applicable to facsimile machines, copiers, and multifunction devices. Further, the present invention is also applicable to droplet ejection devices used for purposes other than image recording. For example, the present invention is applicable to a droplet ejection device that ejects a conductive liquid onto a substrate to form a conductive pattern.

Explanation of Signs

[0174] 1;201 Head (Droplet ejection head) 11B~11E Plates 12A Common flow path 12B;212B;312B Individual flow paths 12D;212D Connection flow paths 12P Pressure chamber 12PX One end 12PY The other end 12N Nozzle 21;221;321 First flow path 21X;221X One end 21Y;221Y The other end 221C Constriction 22 Second flow path 22X One end 22Y The other end 23;223;323 Third flow path 100 Printer

Claims

1. A pressure chamber arranged along a plane, a nozzle opening in a direction intersecting the plane, and a connecting flow path connecting the pressure chamber and the nozzle, the connecting flow path including a first flow path extending parallel to the plane and a second flow path extending in a first direction intersecting the plane. A droplet ejection head in which the inertia of the first flow path is greater than the inertia of the second flow path.

2. The second flow path has one end and the other end in the first direction, and the other end is connected to the nozzle. The droplet ejection head according to claim 1, wherein the first flow path has one end connected to the one end of the second flow path and the other end connected to the pressure chamber.

3. The droplet ejection head according to claim 2, wherein the other end of the first flow path is connected to the pressure chamber without passing through a flow path extending in a direction intersecting the plane.

4. The droplet ejection head according to claim 1, wherein the first flow path has a constricted portion, and the cross-sectional area of the flow path of the constricted portion is smaller than either the cross-sectional area of one end of the first flow path or the cross-sectional area of the other end of the first flow path.

5. The droplet ejection head according to claim 1, wherein the inertia of the first flow path is less than or equal to the inertia of the nozzle.

6. The droplet ejection head according to claim 1, further including a plurality of plates constituting the connecting flow path.

7. A plurality of individual flow paths respectively including the pressure chamber, the nozzle, and the connecting flow path, a common flow path communicating with the plurality of individual flow paths, and a third flow path included in each of the plurality of individual flow paths, the third flow path communicating one end of the pressure chamber, which is opposite to the other end to which the connecting flow path is connected, and the common flow path, and extending parallel to the plane. The droplet ejection head according to claim 6, wherein both the first flow path and the third flow path are arranged on one of the plurality of plates.

8. The droplet ejection head according to claim 7, wherein the first flow path and the third flow path are arranged over the entire thickness of the one plate.

9. The droplet ejection head according to claim 7, wherein the one end and the other end of the pressure chamber are arranged at the central portion of the pressure chamber in a third direction that is orthogonal to a second direction passing through the one end and the other end and along the plane.

10. The first flow path and the third flow path of claim 7 extend in a direction inclined with respect to two directions, namely, a second direction passing through the one end and the other end of the pressure chamber and a third direction orthogonal to the second direction and along the one plane.

11. The inertia of the first flow path is 1.20 × 10 7 [kg / m 4 , and the droplet discharge head according to claim 1, characterized in that it is as described above.

12. A flow path member having a plurality of individual flow paths each including the connection flow path and a common flow path communicating with the plurality of individual flow paths; A piezoelectric element fixed to the flow path member, Each of the plurality of individual flow paths, A pressure chamber disposed along one plane and having one end and the other end in a second direction along the one plane; A communication flow path that communicates the one end of the pressure chamber with the common flow path and has a third flow path extending parallel to the one plane; The nozzle; And the connection flow path, The connection flow path connects the nozzle and the other end of the pressure chamber, The piezoelectric element is configured to apply pressure to the liquid in the pressure chamber to eject droplets from the nozzle. The droplet ejection head according to claim 1, satisfying the following formulas (1) and (2). M2 ≤ 3.23×10- 1 ×M1 - 1.95×10 7 ... Equation (1) M2 ≤ -8.37×10 -1 ×M1 + 2.20×10 8 ... Equation (2) (Here, M1 is the inertia of the third flow path [kg / m 4 , and M2 is the inertia of the first flow path [kg / m 4 .)

13. The droplet ejection head according to claim 12, further satisfying the following formula (3). M2 ≥ -7.49 × M1 + 9.83 × 10 8 ... Equation (3)

14. The droplet ejection head according to claim 12, further satisfying the following formula (4). M2 ≦ M3... Formula (4) (Here, M3 is the inertia of the nozzle [kg / m 4 ).

15. The second flow path has one end and the other end in the first direction, and the other end is connected to the nozzle, The first flow path has one end connected to the one end of the second flow path and the other end connected to the other end of the pressure chamber, The other end of the first flow path is a hole extending in the first direction intersecting the one plane, The flow path cross-sectional area of the hole is smaller than the flow path cross-sectional area of the one end of the first flow path. The droplet ejection head according to claim 12.

16. The second flow path has one end and the other end in the first direction, and the other end is connected to the nozzle, The first flow path has one end connected to the one end of the second flow path and the other end connected to the other end of the pressure chamber, The first flow path has a constricted portion whose flow path cross-sectional area is smaller than either the flow path cross-sectional area of the one end of the first flow path or the flow path cross-sectional area of the other end of the first flow path. The droplet ejection head according to claim 12.

17. The droplet ejection head according to claim 12, further satisfying the following formula (5). M2 ≥ 1.20×10 7 ... Equation (5)

18. A flow path member having a plurality of individual flow paths each including the connection flow path and a common flow path communicating with the plurality of individual flow paths; A piezoelectric element fixed to the flow path member, Each of the plurality of individual flow paths A pressure chamber disposed along a plane and having one end and the other end in a second direction along the plane; A communication flow path that communicates the one end of the pressure chamber with the common flow path, the communication flow path having a third flow path extending parallel to the plane; The nozzle; The connection flow path, The connection flow path connects the nozzle and the other end of the pressure chamber, The piezoelectric element is configured to apply pressure to the liquid in the pressure chamber to discharge droplets from the nozzle, The natural frequency Fr of the individual flow path is 150 kHz or more, A droplet discharge head, characterized by satisfying the following formulas (6) and (7). M2 ≤ 2.67×10 -16 ×M1 3 −7.84×10 -8 ×M1 2 +7.83×M1 − 2.31×10 8 ・・・ Equation (6) M2 ≥ -6.02×10 -10 ×M1 2 +4.88×10 -1 ×M1 - 2.66×10 7 ・・・Equation (7) (Here, M1 is the inertia of the third flow path [kg / m 4 ], and M2 is the inertia of the first flow path [kg / m 4 ].)

19. The droplet discharge head according to claim 18, further characterized by satisfying the following formula (8). M2 ≦ M3... Formula (8) (Here, M3 is the inertia of the nozzle [kg / m 4 ).

20. The second flow path has one end and the other end in the first direction, and the other end is connected to the nozzle, The first flow path has one end connected to the one end of the second flow path and the other end connected to the other end of the pressure chamber, The other end of the first flow path is a hole extending in the first direction intersecting the plane, The flow path cross-sectional area of the hole is smaller than the flow path cross-sectional area of the one end of the first flow path. The droplet discharge head according to claim 18.

21. The second flow path has one end and the other end in the first direction, and the other end is connected to the nozzle, The first flow path has one end connected to the one end of the second flow path and the other end connected to the other end of the pressure chamber, The first flow path has a constricted portion with a flow path cross-sectional area smaller than both the flow path cross-sectional area of the one end of the first flow path and the flow path cross-sectional area of the other end of the first flow path. The droplet discharge head according to claim 18.

22. The droplet discharge head according to claim 18, further characterized by satisfying the following formula (9). M2 ≥ 1.20×10 7 ... Equation (9)

23. A controller for applying a drive signal to the piezoelectric element, The width of the pulse included in the drive signal for discharging droplets from the nozzle is 2.0 to 3.5 μsec. The droplet discharge head according to claim 18.

24. The droplet ejection head according to claim 1, wherein the flow path member is configured such that the ratio of the secondary frequency to the primary frequency of the driving frequency of the piezoelectric element at one end connected to the nozzle of the connection flow path is in the range of 2.0 to 3.

2.

25. The droplet ejection head according to claim 24, wherein the primary frequency is 150 kHz or more.

26. The droplet ejection head according to claim 25, wherein the primary frequency is 200 kHz or less.

27. The droplet ejection head according to any one of claims 24, wherein the diameter of the nozzle is 14 μm or more.

28. The droplet ejection head according to claim 27, wherein the diameter of the nozzle is 30 μm or less.

29. The droplet ejection head according to claim 24, wherein the amplitude of the secondary frequency is 0.5 times or less the amplitude of the primary frequency.

30. The connection flow path is a first portion constituting the one end of the connection flow path, extending in a direction approaching the pressure chamber from the nozzle and not overlapping the pressure chamber in the direction, a second portion extending parallel to a plane in which the pressure chamber is disposed from the downstream end of the first portion in the direction toward the pressure chamber, and having a flow path width smaller than the flow path width of the first portion. The droplet ejection head according to claim 24.

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